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Andean geology

On-line version ISSN 0718-7106

AndGeo vol.48 no.3 Santiago Sept. 2021

http://dx.doi.org/10.5027/andgeov48n3-3326 

Research Article

Geochronology of the Cordillera Real granitoids, the inner magmatic arc of Bolivia

Geocronología de los granitoides de la Cordillera Real, el arco magmático interno de Bolivia

Alvaro Rodrigo Iriarte1  2  * 

Umberto G. Cordani1 

Kei Sato1 

1Instituto de Geociências, Universidade de São Paulo - USP, Rua do Lago 562, CEP 05508-080, São Paulo, Brasil. arodrigoiriarte@gmail.com; ucordani@usp.br; kei@usp.br

2Universidad Mayor de San Andrés (UMSA), Campus Universitario Cota Cota, Calle 27, La Paz, Bolivia.

ABSTRACT

The Cordillera Real granitoids are a suite of Triassic and Oligocene plutons in the core of the Eastern Cordillera of the Central Andes of Bolivia. Their tectonic setting, chemical and ore compositions make them part of the so-called “Inner Magmatic Arc”, which differs from the current “Magmatic Arc” located immediately to the west. U-Pb SHRIMP data were obtained in order to constrain crystallization ages. The Triassic group yielded the following results: 239±2 Ma for the Huato granite, 231±1 Ma for the Illampu granodiorite, 221±3 Ma for the Huayna Potosí granite and 223±2 Ma for the Taquesi granodiorite. For the Oligocene group we obtained ages of 27 Ma for two samples of the Quimsa Cruz granite. Secondary processes related to regional thermal anomalies and magmatic melt-enrichment, reset the K-Ar and U-Pb isotopic systems, producing: a) younger ages by Ar loss and b) anomalous data plot in the Concordia diagram by reorganization of U-Pb isotopic ratios. As noted in previous studies, most zircon analysed from the Zongo/Kuticucho Triassic granite exhibited extremely high U enrichment, producing reverse discordia curves that obscure the true crystallization age. Relatively abundant zircon inheritance was found in these “cold” granitoids, with ages suggesting provenance from early Paleozoic metapelites that also contained recycled older sources. This relatively abundant xenocrystic inheritance probably records the influence of the subduction process acting during the Gondwanide orogeny (336-205 Ma) as an overall subduction arc environment, punctuated at its final stage with the imprint of a continental rifting (245-220 Ma).

Keywords Granitoids; U-Pb zircon age dating; Geochronology; SHRIMP; Central Andes

RESUMEN

Los granitoides de la cordillera Real de Bolivia son un conjunto de plutones triásicos y oligocenos, ubicados en el núcleo de la cordillera Oriental de los Andes Centrales. Las características estructurales, geoquímicas y de composición de menas asociadas, los agrupan dentro del llamado “arco magmático interno” que se distingue del “arco magmático” actual ubicado directamente hacia el oeste. Datos de U-Pb SHRIMP de estos granitoides fueron obtenidos para intentar definir sus edades de cristalización. El grupo de plutones del Triásico dio los siguientes resultados: 239±2 Ma para el granito Huato, 231±1 Ma para la granodiorita Illampu, 221±3 Ma para el granito Huayna Potosí y 223±2 Ma para la granodiorita Taquesi. Para el grupo de plutones del Oligoceno, obtuvimos edades de 27 Ma para dos muestras del granito Quimsa Cruz. Procesos secundarios relacionados con anomalías termales y enriquecimiento tardío de fluidos magmáticos resetearon los sistemas isotópicos K-Ar y U-Pb produciendo: a) edades más jóvenes debido a pérdida de Ar y b) anomalías en el diagrama Concordia debido a reorganización de las razones isotópicas de U-Pb. Como se ha indicado en estudios previos, la mayoría de los zircones analizados en el granito triásico Zongo/Kuticucho presentan un enriquecimiento de U extremadamente alto, que producen gráficos de discordia inversos, dificultando la determinación de su verdadera edad de cristalización. Una cantidad relativamente abundante de circones heredados fue encontrada en estos granitoides “fríos”, con edades que sugieren fuentes provenientes de las metapelitas del Paleozoico temprano, las cuales también retrabajaron fuentes más antiguas. Esta abundancia relativa de xenocristales heredados, probablemente registra la influencia de los procesos de subducción ocurridos durante la orogenia Gondwánica (336-205 Ma), mediante un ambiente regional de tipo arco magmático, caracterizado por un estadio final de rifting continental (245-220 Ma).

Palabras clave: Granitoides; Datación U-Pb en zircón; SHRIMP; Andes Centrales

1. Introduction

The Cordillera Real granitoids are located in the Eastern Cordillera of the Central Andes (Fig. 1). They are represented by eight syn-orogenic plutons, six of which are Triassic (∼220 Ma) and the other two are Oligocene (∼26 Ma) in age. The Triassic ones were emplaced along a rifted area that trends northwest towards SW Perú and coincides with the contemporaneous granitoids of the Carabaya Cordillera. This rift was widespread along the western border of the South American continent. The two Oligocene plutons were emplaced in a compressional regime, apparently related to subduction, coeval with uplifting of large plateaux (Altiplano and Puna), delamination of the lower crust and widespread mafic flows (Jiménez and López-Velásquez, 2008; Ramos, 2018). The country rocks for these anatectic granitoids are lower Paleozoic metapelites. Older basement crops out several hundred kilometers to the east (Rondonia-San Ignacio) and to the west (Arequipa-Antofalla). Along with these regional features, the chemical, mineral and ore compositions of this “inner magmatic arc” (Clark et al., 1990) are sharply different from the purely slab related magmatic arc of the Western Cordillera.

FIG. 1 Main morphostructural units of the Central Andes region, modified from Cordani et al., 2016. The rectangle shows the area included in figure 2

One of the enigmas about the generation of granitic rocks is the precise time span of their emplacement. It has been shown by high precision geochronology that many plutons of batholithic size have been assembled in several magmatic pulses that can last several million years (e.g., Tuolumne suite, Coleman et al., 2004; the Altiplano Puna Magmatic Body, De Silva and Gosnold, 2007). However, thermal modelling, geophysical and rheological constrains preclude longer times for large amounts of magma to remain melted within the crust (Lundstrom and Glazner, 2016). In this context more precise geochronology studies are needed to understand this enigma and ultimately the development of the continental crust.

Geochronological studies have shown that the age of the Real Cordillera granitic suite is not easy to determine. K-Ar age determinations are complicated due to thermal anomalies that reset this isotope system during tectonic events in the Oligocene (McBride et al., 1987; Farrar et al., 1988, 1990). Nevertheless this method defined a cooling age of the Real Cordillera granitoids at 211 Ma (Grant et al., 1979; Evernden et al., 1977; McBride et al., 1983, 1987). Previous U-Pb zircon age dating have shown a long time interval for the crystallization age of this granitic belt (Gillis et al., 2006). These authors found age ranges varying from 217 to 273 Ma indicating the necessity of better constraint on the emplacement age of the granitoids. Cordani et al. (2019) indicated the difficulty of obtaining reliable crystallization ages for the Huayna Potosí and Zongo plutons. Using new U-Pb zircon dates measured in the SHRIMP II laboratory of the University of São Paulo (USP), we set the following two objectives: a) to constrain the crystallization ages of the other granitic plutons of the Real Cordillera to put the crystallization age of this “inner magmatic arc” in a regional context within the Central Andes and b) to obtain additional robust geochronological data for the Huayna Potosí and Zongo plutons to understand better the evolution of their crystallization.

2. Regional framework and geological history

The Central Andes is an orogenic belt of 4,700 km length located at the middle part of the western border of the South American continent (Fig. 1). It is limited to the north and to the south by the Northern and Southern Andes respectively and differs from them by the lack of accreted Phanerozoic terrains or obducted oceanic crust (Ramos, 2009). It includes the Central Volcanic Zone (CVZ) that is the actual volcanic chain of Holocene to modern age.

To the west, older rocks correspond to the Arequipa-Antofalla basement located at the southern part of Perú and northern Chile. Following Loewy et al. (2004) it is divided in three domains: the northern domain, with Paleoproterozoic ages of about 2.0 Ga, the central domain represented by metavolcanic and migmatitic rocks of Mesoproterozoic age of 1.2 Ga and the southern domain with Phanerozoic granitoids that range in age from 467 to 434 Ma. At the eastern side of the Andean orogen another group of older rocks crops out and forms the western border of the Amazonian craton: the Rondonian-San Ignacio Province (1.56-1.3 Ga, Litherland et al., 1989; Bettencourt et al., 2010) that corresponds to a composite orogen of accreted oceanic and continental terrains.

Retro-arc pelites to metapelites associated with the Famatinian magmatic arc of late Neoproterozoic to middle and late Devonian age are represented in the study area as Ordovician, Silurian and Devonian formations (Ramos, 2018).

Magmatism went on from the early Paleozoic to practically nowadays, with intraplate and peraluminous magmatic compositions characterizing the Eastern Cordillera and “pure arc type”, calc-alkaline and subduction related magmatism characterizing the Western Cordillera. This sharp difference is also compositional, with mostly “I-type” granitoids bearing Cu-Mo mineralization located to the west and mostly “S-type” granitoids bearing Sn-W mineralization located to the east (Burnham, 1979; Romer and Kroner, 2016). These contrasting geotectonic environments, mineralogy, chemical composition of magmas and ores, are the basis over which we follow the distinction made by Clark et al. (1990) in regard to differentiate the “Western Cordillera magmatic arc” from the “Eastern Cordillera inner magmatic arc”. For these authors, the petrochemical assemblages are essential for the distinction between these two domains. The Main Arc, located under the Cordillera de la Costa and the entire Western Cordillera, is considered ultimately of mantle origin with several proportions of assimilated middle and upper crust, meanwhile the Inner Arc, restricted to the Eastern Cordillera of SE Perú and NW Bolivia, has been mainly formed by extensive anatexis of early Paleozoic metapelites.

3. Geological descriptions for the granitic plutons of the Cordillera Real

The felsic plutons of the Real Cordillera comprise granites, granodiorites, monzogranites and tonalites with minor quartz-diorites, aplites and pegmatites. The Huato, Illampu, Yani, Huayna Potosí, Zongo and Taquesi plutons are Triassic, whereas Illimani, Quimsa Cruz and Santa Vera Cruz are Oligocene (Fig. 2). Some bear two micas (Huato, Illampu, Huayna Potosí and Zongo) and are metaluminous to peraluminous in composition (Ávila, 1990; Jiménez and López-Velásquez, 2008; Cordani et al., 2019). They commonly bear 0.1-0.5 m rounded mafic enclaves of quartz-diorite. Aplites and pegmatites cut the granites and granodiorites. Near the contacts with the country rocks there are pegmatites 1-2 m thick, usually with greisen halos of Mo, Sn and W mineralization (Fabulosa and Chojlla mines). The country rocks consist of metapelites, hornfels, mica schists, sandstones and siltstones of the Silurian Catavi and Uncia and the Ordovician Amutara and Coroico formations. Hornfelses form the contact aureoles, although schists bearing mica, cordierite, sillimanite and garnet are present along the eastern edges of the Illampu, Yani and Zongo plutons (Bard et al., 1974). Concise description of the sampled granitoids follow: sample locations are shown in figure 2.

FIG. 2 Distribution of the plutons included in this work along the Cordillera Real and location of the analyzed samples. 

3.1. Huato granite

This pluton is located in the northern part of the Real Cordillera. It has an ellipsoidal shape with a dimension of 19x11 km. In the northern part of the pluton, towards its western border, the granite shows an equigranular texture of ca. 0.5 cm quartz, feldspar and biotite crystals. Muscovite appears in the assemblage towards the centre of the pluton. Feldspar shows alteration to sericite. The country rocks are hornfels and slates with millimetric veins of quartz and pyrite. A sample of the Huato granite (RIB-27) was taken in the north along the road from Charazani to Apolo.

3.2. Illampu batholith

The Illampu batholith is the largest of the Triassic granitoid bodies. It has an elongated shape with a length of 50 km and about 14 km width. Three units were distinguished: granodiorites and tonalites in the north, adamelites in the middle and granites to the south. Enclaves of quartz-diorites are common. Aplites and mineralized pegmatites are common towards the south. One sample of granodiorite (RIB-33) and one of quartz-diorite enclave (RIB-32) were taken from the northern unit. The granodiorite has quartz, feldspar, hornblende and biotite with clots of biotite and amphibole up to 5 cm long. The quartz-diorite enclave is rounded and quite mafic (abundant biotite, amphibole and iron oxides) with some crystals of subhedral quartz and feldspar. A further sample, of a two-mica granite (RIB-15) was taken in the southern part of the batholith (Fig. 2). The sample is quite felsic, exhibiting large euhedral crystals of feldspar (2-4 cm long), smaller quartz and biotite crystals and a lesser amount of muscovite. Sometimes it is possible to recognize garnet (up to 0.5 cm) in these granites.

3.3. Huayna Potosí granite

The Huayna Potosí pluton has an irregular, almost rectangular, shape with dimensions of 16x5 km. The rock is fresh and is generally two-mica granite with quartz, feldspar, biotite and muscovite, with lesser amounts of sericite and sometimes tourmaline. Aplites cutting the granite are widespread. It is also common to find rounded mafic enclaves 1 to10 cm long of quartz-diorite. Samples from the SW edge of this pluton are RIB-2, RIB-4, RIB-19 and RIB-22 (granites), and RIB-20 (granodiorite).

3.4. Zongo granite

The Zongo granite occurs to the northwest of the Huayna Potosí pluton. It also has an irregular shape and is cut by several systems of NW-striking faults. It is noticeably folded, showing oriented crystals 1 to 10 cm long of quartz, K-feldspar and two micas. In some outcrops the texture seems to vary gradually to coarsely pegmatitic. Towards the northern contact with the country rock, mica schists with porphyroblasts of cordierite up to 10 cm long define a metamorphic aureole. Two granitic facies were recognized in this pluton (McBride et al., 1987): the foliated Kuticucho located to the SW and the non-foliated and equigranular Sainani to the NE. Two samples from the foliated Kuticucho facies were taken for this study, samples RIB-5 and RIB-30.

3.5. Taquesi granodiorite

The Taquesi granodiorite has a regular elliptical shape with dimensions of 15x9 km, with the longest axis following the NW trend of the cordillera. Granodiorites bearing quartz-diorite enclaves, along with tonalites, two-mica granites and aplites are characteristic of this pluton. Towards the SW rim the granodiorites have an equigranular texture made of crystals 1 to 2 cm long of quartz, feldspar, biotite and iron oxides. At its SW border, the country rock is a Silurian hornfels. Samples RIB-11 and RIB-12 from a granodiorite and a quartz-diorite enclave, respectively, were taken from this pluton.

3.6. Quimsa Cruz batholith

The Quimsa Cruz is an ellipsoidal batholith in the south of the Real Cordillera. It has a dimension of 35x13 km. Along with the Illimani pluton and the Cohoni volcanic and pyroclastic formation it forms the southern Oligocene band of the Real Cordillera belt. The Geological Service of Bolivia recognized two facies in this batholith: porphyritic granites and granodiorites to the north and equigranular granodiorites to the south (Geobol, 1968). Fractures affect this granite, filled by centimetric to metric scale vein mineralization of W-Sn and Fe-S, with a general E-W strike. K-Ar dating distinguishes this rock from the Triassic granites, yielding ages of 25 to 23 Ma (Evernden et al., 1977; McBride et al., 1983; Gillis et al., 2006). Two samples of fresh granite were taken: one to the west close to the Viloco mine (RIB-43) and other to the SE closer to the Pacuni mine (RIB-46).

4. Previous age dating

Early K-Ar geochronological studies on the age of the granitic magmatism of the Cordillera Real of Bolivia are summarized in table 1. Ages show wide ranges (e.g., 180-190 and 60-40 Ma), a characteristic observed also in the Carabaya granites (Kontak et al., 1990). This led to several studies (Kontak et al., 1990; McBride et al., 1987; Sandeman et al., 1995; Ramos, 2018) to define the Zongo-San Gabán regional thermal anomaly that opened the K-Ar isotopic system to Ar loss by heating associated with thrusting of the Andean orogeny.

TABLE 1 K-Ar PUBLISHED AGES FOR PLUTONS OF THE REAL CORDILLERA. 

Pluton Age (Ma) Mineral Author
Huato 218-225 M 4
Illampu 254 H 4
219-202 B 4
180 B 1
195 B 2
Huayna Potosí 211 B 3
205-218 M 4
Zongo 150-162 MU 3
Taquesi 199 B 3
195 B 2
211 B 4
Mina Chojlla 195-203 MU 4
Illimani 27-28 B 4
26 B 3
Quimsa Cruz 26 B 3
24 B 2
24-26 B 4
Santa Vera Cruz 23 B 2

Mineral abbreviations: M. micas, B. biotite, Mu. muscovite. Authors: 1. Evernden (1961) cited in Clark and Farrar (1973), 2. Cordani (1967) cited in Clark and Farrar (1973), 3.Evernden et al. (1977); 4.McBride et al., 1983.

McBride et al. (1987) defined systematic Ar loss in some profiles that cut the granites of the Zongo pluton. The apparent ages range from 210 to 39 Ma through a horizontal distance of 14 km and a vertical difference of almost 1.5 km. In the same study, a biotite yielded a well-defined Ar/Ar plateau of 39 Ma. They associated this descend in K-Ar ages with opening of the isotopic system (250-350 °K) due to regional Andean back-thrusting, with the biotite of 39 Ma recording this thermal event.

Farrar et al., 1990 were the first in study the Zongo granite using the U-Pb method in zircon and also described the K-Ar age decrease of the micas of this pluton. The age obtained for the Zongo/Kuticucho granite was 222.2+7.7/-9.1 and for the Zongo/Sainani granite was 225.1 Ma +4.1/-4.4, both recording an important inherited zircon component of Proterozoic age. Following the work of McBride et al. (1987), Farrar et al. (1988) defined the “cryptic tectonothermal zone” between the Carabaya and Real cordilleras at 39 Ma, calling it as the “Zongo-San Gabán Zone” (ZSGZ).

Gillis et al. (2006) studied the effects of the thermal anomaly associated to the uplift of the cordillera using Ar/Ar modelling in micas as well as fission track ages in apatites. They found a good 49Ar/30Ar age with a well-defined plateau for the Huayna Potosí pluton that yielded an age of 218±4 Ma. They also determined large intervals of U-Pb crystallization ages for the Triassic plutons (e.g., 249 to 218 Ma for the Huayna Potosí granite and 251 to 226 Ma for the Illampu batholith) and an age for the Oligocene Quimsa Cruz pluton at 26 Ma.

More recently U-Pb zircon dating for the Huayna Potosí and Zongo granites (Cordani et al., 2019) also yielded large ranges of zircon crystallization ages for the Huayna Potosí (240 to 220 Ma) along with anomalous U-rich zircons of the Zongo pluton, associating them with protracted pluton crystallization and a final event of U enrichment.

5. U-Pb SHRIMP zircon analyses

U-Pb dating was made in the Sensitive High Resolution Ion Microscope (SHRIMP IIe) of the Laboratory of the University of São Paulo, Brazil. Samples were crushed, milled and sieved. Then zircon crystals were concentrated from magnetic fractions using a Franz magnetic separator and then purified using bromoform and methylene iodide following standard laboratory steps. Then zircon mounts were prepared and cathode luminescence imaging (CL) was obtained with a FEI Quanta 250 Scanning Electron Microscope (SEM) and XMAX CL detector (Oxford Instruments) to reveal inner structures. SHRIMP analyses were run on single zircon crystals. U abundance and U/Pb ratios were calibrated against Z6266 and TEMORA II (416.78 Ma) standards. Pooled ages are weighted mean 206Pb/238U dates. Common Pb was corrected using the measured abundance of 204Pb. On tables 2A to 2O, errors on isotopic ratios are given as percentage and error on ages are reported as 1 sigma. The typical error component for the 206Pb/238U ratios was lower than 2%. Then isotopic ratios were reduced using the SQUID 2.5 software and Concordia diagrams were made using the software Isoplot 4 (Ludwig, 2009). Further technical and acquisition data processing are described in Williams (1998) and Sato et al. (2014).

TABLE 2 U/Pb ZIRCON SHRIMP ANALYSES. TABLE 2A. RIB-27 HUATO GRANITE. 

Spot Site Ch/h U (ppm) (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB27-9.1 rim osc, p 1,470 70 0.05 0.16 247 3 238 21 −4 25.6 1.2 0.05094 0.9 0.274 1.5 0.0391 1.2 0.8
RIB27-8.1 rim osc, p 1,087 65 0.06 0.25 238 3 230 57 −4 26.6 1.3 0.05075 2.5 0.263 2.8 0.0375 1.3 0.5
RIB27-3.1 rim osc, p 1,527 34 0.02 0.10 248 3 242 17 −3 25.5 1.2 0.05102 0.7 0.276 1.4 0.0392 1.2 0.9
RIB27-1.1 rim osc, p 2,003 936 0.47 4.40 254 4 249 135 −2 24.8 1.4 0.05118 5.9 0.284 6.0 0.0403 1.4 0.2
RIB27-10.1 core hb, p 477 282 0.59 0.28 610 7 609 24 −0 10.1 1.2 0.06016 1.1 0.823 1.6 0.0993 1.2 0.8
RIB27-7.1 rim osc, p 1,569 96 0.06 0.07 241 3 241 16 −0 26.3 1.2 0.05100 0.7 0.268 1.4 0.0381 1.2 0.9
RIB27-13.1 core hb, ov 235 22 0.09 0.19 790 9 793 23 +0 7.7 1.2 0.0656 1.1 1.18 1.6 0.130 1.2 0.7
RIB27-6.1 rim osc, p 1,124 189 0.17 0.17 241 3 242 24 +1 26.3 1.4 0.05103 1.0 0.268 1.7 0.0381 1.4 0.8
RIB27-14.1 core sz, p 461 159 0.35 0.96 235 2 239 99 +2 26.9 0.9 0.0510 4.3 0.26 4.4 0.037 0.9 0.2
RIB27-5.1 rim osc, p 1,579 95 0.06 0.33 244 3 250 28 +2 25.9 1.2 0.05119 1.2 0.273 1.7 0.0386 1.2 0.7
RIB27-12.1 core osc, p 521 52 0.10 1.17 213 4 218 129 +2 29.8 1.8 0.05049 5.6 0.234 5.8 0.0336 1.8 0.3
RIB27-2.1 rim osz, p 764 94 0.12 0.48 234 3 242 56 +3 27.0 1.4 0.05103 2.4 0.260 2.8 0.0370 1.4 0.5
RIB27-11.1 core hb, p 271 92 0.34 0.75 218 3 226 109 +4 29.1 1.3 0.05067 4.7 0.240 4.9 0.0344 1.3 0.3
RIB27-15.1 core hb, ov 135 18 0.13 3.38 299 5 314 427 +5 21.0 1.7 0.0527 18.8 0.35 18.8 0.048 1.7 0.1
RIB27-4.1 rim osc, p 535 106 0.20 0.39 231 3 246 55 +6 27.4 1.3 0.05111 2.4 0.257 2.7 0.0365 1.3 0.5

TABLE 2B RIB-32 ILLAMPU QUARTZDIORITE ENCLAVE. 

Spot Site Ch/h U (ppm) Th (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB32-2.1 rim osc, p 661 281 0.43 0.38 245 2 217 53 −13 25.8 1.0 0.0505 2.3 0.27 2.5 0.039 1.0 0.4
RIB32-9.1 rim osc, p 762 263 0.34 0.33 235 2 215 49 −9 27.0 0.9 0.0504 2.1 0.26 2.3 0.037 0.9 0.4
RIB32-11.1 core sz, p 685 482 0.70 0.47 232 2 214 43 −9 27.2 0.9 0.0504 1.9 0.26 2.1 0.037 0.9 0.4
RIB32-6.1 rim osc, fr 544 165 0.30 0.39 236 2 222 50 −6 26.8 1.0 0.0506 2.1 0.26 2.4 0.037 1.0 0.4
RIB32-4.1 rim osc, p 539 181 0.34 0.52 234 3 221 73 −6 27.1 1.2 0.0506 3.2 0.26 3.4 0.037 1.2 0.3
RIB32-1.1 rim osc, p 585 165 0.28 0.35 245 2 237 57 −4 25.8 1.0 0.0509 2.5 0.27 2.7 0.039 1.0 0.4
RIB32-3.1 rim osc, p 485 186 0.38 0.58 234 2 227 98 −3 27.1 1.0 0.0507 4.3 0.26 4.4 0.037 1.0 0.2
RIB32-12.1 rim osc, p 799 627 0.78 0.88 235 2 231 110 −2 26.9 0.9 0.0508 4.7 0.26 4.8 0.037 0.9 0.2
RIB32-13.1 core hb, ov 430 218 0.51 3.19 232 3 229 259 −1 27.3 1.1 0.0507 11.2 0.26 11.3 0.037 1.1 0.1
RIB32-14.1 core hb, rd 618 356 0.58 0.52 234 2 231 59 −1 27.1 0.9 0.0508 2.6 0.26 2.7 0.037 0.9 0.3
RIB32-8.1 rim osc, p 702 324 0.46 0.51 234 3 235 60 +0 27.0 1.1 0.0509 2.6 0.26 2.8 0.037 1.1 0.4
RIB32-15.1 core hb, p 634 521 0.82 0.91 232 2 238 71 +3 27.3 1.0 0.0509 3.1 0.26 3.2 0.037 1.0 0.3
RIB32-7.1 rim osc, p 599 186 0.31 0.53 236 2 244 71 +3 26.8 0.9 0.0511 3.1 0.26 3.2 0.037 0.9 0.3
RIB32-5.1 rim osc, p 381 154 0.41 1.29 234 2 243 137 +4 27.1 0.9 0.0511 5.9 0.26 6.0 0.037 0.9 0.2
RIB32-16.1 core hb, ov 604 295 0.49 0.53 235 2 249 69 +6 26.9 0.9 0.0512 3.0 0.26 3.1 0.037 0.9 0.3
RIB32-10.1 rim osc, p 635 186 0.29 0.41 241 2 258 44 +7 26.2 0.9 0.0514 1.9 0.27 2.1 0.038 0.9 0.4

TABLE 2C RIB-33 ILLAMPU GRANODIORITE. 

Spot Site Ch/h U (ppm) Th (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB33-1.1 core osz, p 785 274 0.35 0.11 232 2 221 25 −5 27.3 0.85 0.05056 1.1 0.256 1.4 0.0367 0.85 0.6
RIB33-7.1 rim sz, p 481 217 0.45 1.62 231 2 223 103 −4 27.4 0.93 0.05062 4.5 0.255 4.6 0.0365 0.93 0.2
RIB33-2.1 rim osc, p 616 179 0.29 0.19 230 2 222 32 −3 27.6 0.98 0.05059 1.4 0.253 1.7 0.0363 0.98 0.6
RIB33-4.1 rim osc, p 610 216 0.35 0.26 229 2 224 57 −3 27.6 0.80 0.05063 2.5 0.253 2.6 0.0362 0.80 0.3
RIB33-11.1 rim osc, p 644 195 0.30 0.30 230 2 227 40 −1 27.5 0.94 0.05070 1.7 0.254 2.0 0.0364 0.94 0.5
RIB33-5.1 rim osc, p 446 170 0.38 0.22 227 3 225 40 −1 27.9 1.13 0.05066 1.7 0.250 2.1 0.0358 1.13 0.5
RIB33-6.1 rim osc, p 672 221 0.33 0.25 232 2 236 36 +1 27.2 0.97 0.05089 1.5 0.258 1.8 0.0367 0.97 0.5
RIB33-10.1 rim osc, p 584 205 0.35 0.35 228 2 232 65 +2 27.7 0.81 0.05081 2.8 0.253 2.9 0.0360 0.81 0.3
RIB33-8.1 rim osc, p 712 276 0.39 0.20 233 2 238 30 +2 27.2 0.86 0.05094 1.3 0.259 1.6 0.0368 0.86 0.6
RIB33-9.1 core hb, p 376 275 0.73 0.63 231 2 255 87 +10 27.4 0.96 0.05131 3.8 0.258 3.9 0.0365 0.96 0.2
RIB33-3.1 rim osc, p 588 175 0.30 0.19 233 2 257 34 +10 27.2 0.88 0.05135 1.5 0.260 1.7 0.0367 0.88 0.5
RIB33-10.2 core hb, p 383 106 0.28 1.01 214 2 244 92 +12 29.6 1.07 0.05107 4.0 0.238 4.1 0.0337 1.07 0.3

TABLE 2D RIB-15 ILLAMPU GRANITE. 

Spot Site Ch/h U (ppm) Th (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB15-12.1 core sz, p 644 669 1.04 0.60 222 3 235 78 +5 28.5 1.2 0.0509 3.4 0.25 3.6 0.035 1.2 0.3
RIB15-10.1 core hb, p 196 53 0.27 1.83 223 3 223 286 −0 28.4 1.5 0.0506 12.4 0.25 12.4 0.035 1.5 0.1
RIB15-6.1 core hb, fr 1,114 819 0.73 0.55 225 2 226 56 +0 28.2 1.0 0.0507 2.4 0.25 2.6 0.036 1.0 0.4
RIB15-11.2 rim osc, p 5,014 20 0.00 0.32 225 3 235 32 +4 28.1 1.2 0.0509 1.4 0.25 1.8 0.036 1.2 0.6
RIB15-4.1 core sz, p 573 285 0.50 1.08 227 2 237 128 +4 27.9 1.1 0.0509 5.5 0.25 5.7 0.036 1.1 0.2
RIB15-9.2 rim hd, p 2,244 38 0.02 5.08 230 4 231 338 +0 27.6 1.9 0.0508 14.6 0.25 14.8 0.036 1.9 0.1
RIB15-1.1 core osc, p 699 58 0.08 1.90 230 3 233 179 +1 27.5 1.1 0.0508 7.8 0.25 7.8 0.036 1.1 0.1
RIB15-7.2 rim sz, p 1,962 43 0.02 0.40 231 2 237 36 +3 27.5 1.0 0.0509 1.6 0.26 1.9 0.036 1.0 0.5
RIB15-3.1 core sz, p 935 313 0.33 0.57 238 3 245 78 +3 26.6 1.2 0.0511 3.4 0.26 3.6 0.038 1.2 0.3
RIB15-2.1 rim osc, p 2,596 1062 0.41 0.23 240 2 238 23 −1 26.3 1.0 0.0509 1.0 0.27 1.4 0.038 1.0 0.7
RIB15-8.2 rim osc, p 2,282 462 0.20 0.20 241 3 236 28 −2 26.3 1.1 0.0509 1.2 0.27 1.6 0.038 1.1 0.7
RIB15-5.1 rim osc, p 2,633 85 0.03 0.08 242 3 230 18 −5 26.2 1.1 0.0508 0.8 0.27 1.3 0.038 1.1 0.8
RIB15-14.2 core hb, rd 1,929 25 0.01 0.29 242 5 229 39 −6 26.1 1.9 0.0507 1.7 0.27 2.6 0.038 1.9 0.7
RIB15-7.1 core hb, p 317 159 0.50 0.78 469 5 471 61 +1 13.3 1.1 0.0565 2.8 0.59 3.0 0.075 1.1 0.4
RIB15-13.1 core hb, p 395 553 1.40 0.40 579 6 583 34 +1 10.6 1.1 0.0594 1.6 0.77 1.9 0.094 1.1 0.6
RIB15-11.1 core hb, rd 76 40 0.52 1.97 610 8 645 185 +6 10.1 1.4 0.0612 8.6 0.84 8.7 0.099 1.4 0.2
RIB15-9.1 core osc, p 247 113 0.46 0.24 1091 11 1073 24 −2 5.4 1.1 0.0752 1.2 1.91 1.7 0.184 1.1 0.7
RIB15-8.1 core hb, ov 159 46 0.29 5.29 1217 13 1937 20 +41 4.8 1.2 0.1187 1.1 3.40 1.6 0.208 1.2 0.7
RIB15-14.1 rim osc, p 164 99 0.61 1.17 2046 21 2132 17 +5 2.7 1.2 0.1326 0.9 6.83 1.5 0.374 1.2 0.8

TABLE 2E RIB-2 HUAYNA POTOSÍ GRANITE. 

Spot Site Ch/h U (ppm) (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB2-9.1 core osc, p 1,334 88 0.07 -- 239 2 211 18 −14 26.5 1.0 0.0503 0.8 0.262 1.2 0.0378 1.0 0.8
RIB2-5.1 core hb, p 72 28 0.39 1.70 220 5 216 298 −2 28.8 2.4 0.0505 12.9 0.241 13.1 0.0347 2.4 0.2
RIB2-8.1 core osc, p 237 108 0.46 0.63 217 2 222 128 +3 29.3 1.1 0.0506 5.5 0.238 5.6 0.0342 1.1 0.2
RIB2-6.1 core osc, p 314 58 0.18 0.53 221 3 224 94 +1 28.7 1.2 0.0506 4.0 0.243 4.2 0.0348 1.2 0.3
RIB-2-22.1 core osc, p 507 64 0.13 0.26 236 3 229 46 −3 26.8 1.4 0.0507 2.0 0.261 2.4 0.037 1.4 0.6
RIB2-3.1 core osc, p 1,713 128 0.07 -- 246 3 235 15 −5 25.7 1.0 0.0509 0.6 0.273 1.2 0.0389 1.0 0.9
RIB-2-13.1 rim osc, p 576 460 0.80 0.08 227 3 236 29 +4 28.0 1.4 0.0509 1.2 0.251 1.9 0.036 1.4 0.8
RIB-2-15.1 rim hd, p 1,006 359 0.36 -- 244 4 238 20 −2 25.9 1.7 0.0509 0.9 0.271 1.9 0.039 1.7 0.9
RIB-2-17.1 rim hb, p 391 63 0.16 0.35 248 4 242 58 −3 25.5 1.7 0.0510 2.5 0.276 3.0 0.039 1.7 0.6
RIB-2-21.1 core osc, p 777 76 0.10 -- 247 3 242 21 −2 25.6 1.4 0.0510 0.9 0.275 1.7 0.039 1.4 0.8
RIB2-2.1 rim osc, p 999 80 0.08 -- 253 2 244 18 −4 25.0 1.0 0.0511 0.8 0.282 1.3 0.0400 1.0 0.8
RIB-2-24.1 rim osc, fr 1,950 77 0.04 0.03 257 4 248 14 −4 24.6 1.4 0.0512 0.6 0.287 1.5 0.041 1.4 0.9
RIB2-10.1 core osc, p 388 104 0.27 0.36 222 3 251 49 +12 28.5 1.3 0.0512 2.1 0.248 2.5 0.0351 1.3 0.5
RIB2-11.1 core osc, p 138 76 0.55 3.19 247 3 256 339 +3 25.6 1.3 0.0513 14.7 0.277 14.8 0.0391 1.3 0.1
RIB2-4.1 core osc, p 518 170 0.33 0.84 230 3 259 67 +11 27.5 1.3 0.0514 2.9 0.258 3.2 0.0363 1.3 0.4
RIB-2-16.1 core hb, p 931 147 0.16 0.25 312 6 300 46 −4 20.2 1.8 0.0523 2.0 0.358 2.7 0.050 1.8 0.7
RIB2-1.1 core hb, p 76 36 0.48 1.59 234 4 340 196 +32 27.0 1.9 0.0533 8.7 0.272 8.9 0.0370 1.9 0.2
RIB2-12.1 core osc, p 373 213 0.57 0.60 219 2 450 34 +52 28.9 1.0 0.0559 1.6 0.267 1.9 0.0346 1.0 0.5
RIB-2-18.1 rim osc, p 28,696 349 0.01 -- 577 13 474 24 −23 10.7 2.3 0.0565 1.1 0.730 2.5 0.094 2.3 0.9
RIB-2-19.1 rim osc, p 1,282 41 0.03 0.14 573 8 573 14 −0 10.8 1.4 0.0592 0.6 0.759 1.5 0.093 1.4 0.9
RIB-2-14.1 core hb, ov 175 78 0.44 0.63 509 7 599 44 +16 12.2 1.5 0.0599 2.0 0.678 2.5 0.082 1.5 0.6
RIB2-7.1 core hb, p 437 279 0.64 0.00 602 6 606 15 +1 10.2 1.0 0.0601 0.7 0.810 1.2 0.0978 1.0 0.8
RIB-2-23.1 core hb, p 636 39 0.06 0.48 801 13 881 12 +10 7.6 1.7 0.0684 0.6 1.248 1.8 0.132 1.7 0.9
RIB-2-20.1 core hb, ov 456 73 0.16 1.64 1186 22 1472 8 +21 5.0 2.1 0.0922 0.4 2.568 2.1 0.202 2.1 1.0

TABLE 2F RIB-4 HUAYNA POTOSÍ GRANITE. 

Spot Site Ch/h U (ppm) Th (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB4-10.1 core osc, p 319 52 0.16 0.39 215 3 226 57 +5 29.5 1.2 0.0507 2.5 0.237 2.8 0.0339 1.2 0.4
RIB-4-26.1 core hd, p 615 17 0.03 0.21 215 3 210 39 −3 29.4 1.6 0.0503 1.7 0.236 2.3 0.0340 1.6 0.7
RIB4-8.1 core hd, p 393 11 0.03 0.34 217 2 208 52 −5 29.2 1.0 0.0503 2.3 0.238 2.5 0.0343 1.0 0.4
RIB4-11.1 core osc, p 383 52 0.14 0.20 219 2 264 49 +17 28.9 1.0 0.0515 2.1 0.245 2.4 0.0345 1.0 0.4
RIB4-9.1 rim hb, p 729 162 0.22 0.25 221 2 217 40 −2 28.7 1.0 0.0505 1.7 0.242 2.0 0.0348 1.0 0.5
RIB4-1.1 core hd, p 783 31 0.04 0.28 223 2 216 42 −3 28.4 1.0 0.0505 1.8 0.245 2.1 0.0353 1.0 0.5
RIB4-2.1 core osc, p 457 66 0.14 0.18 228 2 224 68 −2 27.8 1.0 0.0506 2.9 0.251 3.1 0.0360 1.0 0.3
RIB-4-11.2 core osc, p 1,247 49 0.04 0.19 228 3 256 37 +11 27.7 1.5 0.0513 1.6 0.255 2.2 0.0361 1.5 0.7
RIB4-3.1 core hb, p 394 116 0.30 0.23 229 2 223 45 −3 27.6 1.0 0.0506 2.0 0.253 2.2 0.0362 1.0 0.5
RIB-4-14.1 core osc, p 514 199 0.39 0.13 238 4 235 33 −1 26.6 1.6 0.0509 1.4 0.264 2.2 0.0376 1.6 0.8
RIB-4-17.1 core osc, p 1,500 96 0.06 0.08 238 3 243 26 +2 26.6 1.4 0.0510 1.1 0.265 1.8 0.0377 1.4 0.8
RIB-4-12.1 core osc, p 181 71 0.39 1.01 240 4 290 108 +17 26.3 1.6 0.0521 4.7 0.273 5.0 0.0380 1.6 0.3
RIB-4-22.1 core osc, p 838 144 0.17 0.50 245 3 250 49 +2 25.8 1.4 0.0512 2.1 0.274 2.5 0.0388 1.4 0.6
RIB-4-16.1 core oscz, fr 224 60 0.27 1.21 247 4 240 126 −3 25.6 1.5 0.0510 5.5 0.275 5.7 0.0391 1.5 0.3
RIB-4-25.1 core osc, p 1,233 103 0.08 0.39 251 3 241 48 −4 25.2 1.4 0.0510 2.1 0.279 2.5 0.0397 1.4 0.6
RIB-4-18.1 rim osc, p 952 95 0.10 0.56 263 4 257 79 −2 24.0 1.4 0.0514 3.4 0.295 3.7 0.0417 1.4 0.4
RIB-4-13.1 core hb, p 426 130 0.30 0.32 265 4 264 54 −1 23.8 1.4 0.0515 2.4 0.298 2.8 0.0420 1.4 0.5
RIB-4-20.1 core hb, ov 194 26 0.13 1.19 275 4 386 121 +30 23.0 1.6 0.0544 5.4 0.326 5.6 0.0435 1.6 0.3
RIB-4-11.1 core osc, p 530 46 0.09 0.40 287 4 361 31 +21 21.9 1.4 0.0538 1.4 0.338 2.0 0.0456 1.4 0.7
RIB4-5.1 core hb, ov 500 20 0.04 0.62 385 9 458 33 +16 16.2 2.5 0.0561 1.5 0.477 2.9 0.0616 2.5 0.9
RIB-4-21.1 core hb, ov 279 134 0.48 0.55 468 7 579 30 +20 13.3 1.5 0.0593 1.4 0.616 2.0 0.0754 1.5 0.7
RIB-4-23.1 core osc, p 253 100 0.40 0.53 1364 18 1439 10 +6 4.2 1.5 0.0907 0.5 2.945 1.6 0.2356 1.5 0.9
RIB-4-24.1 core hb, ov 393 268 0.68 2.19 1655 21 1934 6 +16 3.4 1.4 0.1185 0.3 4.784 1.5 0.2927 1.4 1.0
RIB-4-19.1 core hb, ov 68 22 0.33 0.49 2026 29 2058 13 +2 2.7 1.7 0.1271 0.8 6.470 1.8 0.3692 1.7 0.9
RIB4-4.1 core osc, p 313 170 0.54 6.21 2070 18 2600 4 +24 2.6 1.0 0.1744 0.3 9.105 1.1 0.3787 1.0 1.0

TABLE 2G RIB-19 HUAYNA POTOSÍ GRANITE. 

Spot Site Ch/h U (ppm) (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB19-6.1 core hb, p 336 61 0.18 0.55 213 2 232 67 +8 29.78 0.84 0.05080 2.9 0.2352 3.0 0.03358 0.84 0.28
RIB19-2.2 core hb, p 143 67 0.47 1.98 214 2 232 253 +8 29.67 1.06 0.05080 11.0 0.2361 11.0 0.03370 1.06 0.10
RIB19-3.1 rim osc, p 265 94 0.36 0.62 215 2 214 148 −0 29.52 1.12 0.05042 6.4 0.2355 6.5 0.03387 1.12 0.17
RIB19-7.1 core osc, p 310 56 0.18 0.55 221 2 230 65 +4 28.62 0.84 0.05075 2.8 0.2445 2.9 0.03494 0.84 0.29
RIB19-10.2 core hb, p 331 36 0.11 0.19 222 2 219 48 −2 28.48 0.99 0.05052 2.1 0.2446 2.3 0.03511 0.99 0.43
RIB19-5.1 core hb, p 505 47 0.09 0.35 223 2 238 44 +6 28.35 0.99 0.05094 1.9 0.2478 2.1 0.03528 0.99 0.46
RIB19-16.1 core osc, p 532 47 0.09 1.47 224 3 251 113 +11 28.32 1.22 0.05121 4.9 0.2494 5.1 0.03531 1.22 0.24
RIB19-2.1 rim osc, p 407 57 0.14 0.52 224 2 221 52 −1 28.27 0.84 0.05057 2.3 0.2466 2.4 0.03537 0.84 0.35
RIB19-14.1 core hb, p 235 123 0.52 0.74 224 2 221 116 −2 28.24 1.01 0.05055 5.0 0.2468 5.1 0.03541 1.01 0.20
RIB19-9.1 core hb, ov 372 92 0.25 0.51 224 2 235 111 +5 28.22 0.83 0.05088 4.8 0.2486 4.9 0.03544 0.83 0.17
RIB19-11.1 core osc, p 466 265 0.57 0.38 225 2 226 45 +1 28.16 0.81 0.05068 1.9 0.2482 2.1 0.03552 0.81 0.39
RIB19-4.1 core hd, p 757 114 0.15 0.19 225 5 224 28 −1 28.12 2.04 0.05063 1.2 0.2482 2.4 0.03556 2.04 0.86
RIB19-18.1 rim osc, p 452 117 0.26 0.38 226 2 215 63 −5 28.04 0.95 0.05042 2.7 0.2479 2.9 0.03566 0.95 0.33
RIB19-17.1 core osc, p 229 45 0.20 5.26 226 3 225 368 −0 28.03 1.34 0.05066 15.9 0.2492 16.0 0.03567 1.34 0.08
RIB19-1.1 rim osc, p 396 46 0.12 0.29 229 2 235 42 +3 27.69 0.83 0.05087 1.8 0.2533 2.0 0.03612 0.83 0.41
RIB19-12.1 core osc, fr 709 85 0.12 0.17 229 2 231 29 +1 27.67 0.79 0.05079 1.3 0.2531 1.5 0.03615 0.79 0.53
RIB19-8.1 core hb, p 540 229 0.42 0.53 232 2 227 53 −2 27.34 0.93 0.05070 2.3 0.2557 2.5 0.03657 0.93 0.38
RIB19-13.1 core hb, p 247 91 0.37 0.82 232 2 227 104 −2 27.27 0.87 0.05069 4.5 0.2563 4.6 0.03667 0.87 0.19
RIB19-15.1 rim osc, p 899 244 0.27 0.14 235 2 224 23 −5 26.98 0.79 0.05064 1.0 0.2588 1.3 0.03707 0.79 0.62
RIB19-10.1 core hb, p 225 133 0.59 0.36 599 5 633 32 +6 10.26 0.89 0.06083 1.5 0.8173 1.7 0.09744 0.89 0.51

TABLE 2H RIB-20 HUAYNA POTOSÍ GRANITE. 

Spot Site Ch/h U (ppm) Th (ppm) Th/U % 206Pbc 206Pb238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB20-6.1 rim osc, p 0.73 415 68 0.16 227 3 219 88 −4 27.9 1.4 0.05051 3.8 0.249 4.0 0.0358 1.4 0.3
RIB20-7.1 rim osc, p 0.10 920 636 0.69 237 3 229 37 −3 26.7 1.3 0.05075 1.6 0.262 2.1 0.0374 1.3 0.6
RIB20-8.1 rim osc, p 1.15 294 55 0.19 220 3 216 138 −2 28.8 1.3 0.05045 5.9 0.242 6.1 0.0347 1.3 0.2
RIB20-6.2 core hd, p 10.35 1,574 163 0.10 254 5 251 335 −1 24.9 1.8 0.05122 14.6 0.284 14.7 0.0402 1.8 0.1
RIB20-5.1 rim hd, p 0.64 747 304 0.41 230 3 231 66 +0 27.5 1.4 0.05077 2.9 0.255 3.2 0.0364 1.4 0.4
RIB20-2.1 core osc, p 0.26 937 62 0.07 233 3 235 52 +1 27.1 1.2 0.05088 2.3 0.258 2.6 0.0368 1.2 0.5
RIB20-4.1 rim osc, p 0.63 578 54 0.09 237 3 239 83 +1 26.7 1.2 0.05097 3.6 0.263 3.8 0.0374 1.2 0.3
RIB20-10.1 rim osc, p 0.39 673 110 0.16 224 3 228 43 +2 28.3 1.4 0.05073 1.9 0.247 2.3 0.0354 1.4 0.6
RIB20-14.1 core hb, ov 0.62 504 56 0.11 236 2 241 66 +2 26.8 1.1 0.0510 2.9 0.26 3.0 0.037 1.1 0.4
RIB20-11.1 core hb, p 1.29 545 52 0.10 245 2 252 138 +3 25.8 1.0 0.0512 6.0 0.27 6.1 0.039 1.0 0.2
RIB20-3.1 rim osc, p 0.36 475 99 0.21 230 3 238 50 +3 27.5 1.5 0.05094 2.2 0.255 2.6 0.0363 1.5 0.6
RIB20-1.1 rim osc, fr 0.69 600 62 0.10 230 3 244 73 +6 27.5 1.5 0.05108 3.2 0.256 3.5 0.0364 1.5 0.4
RIB20-10.2 core hb, p 0.69 559 149 0.27 229 3 264 76 +13 27.6 1.3 0.05151 3.3 0.257 3.5 0.0362 1.3 0.4
RIB20-9.1 rim osc, p 0.53 580 57 0.10 228 3 267 78 +15 27.8 1.2 0.05159 3.4 0.256 3.6 0.0360 1.2 0.3
RIB20-1.2 rim osc, fr 0.83 258 30 0.12 210 3 260 96 +19 30.2 1.7 0.05142 4.2 0.235 4.5 0.0332 1.7 0.4
RIB20-12.1 core hb, p 1.08 298 72 0.24 221 3 327 124 +33 28.7 1.2 0.0529 5.5 0.25 5.6 0.035 1.2 0.2
RIB20-13.1 core osc, p 0.28 121 32 0.27 1413 18 2023 13 +34 4.1 1.4 0.1246 0.8 4.21 1.6 0.245 1.4 0.9
RIB20-9.2 rim hb, p 0.85 533 109 0.20 454 8 1600 29 +74 13.7 1.9 0.09869 1.6 0.993 2.4 0.0730 1.9 0.8

TABLE 2I RIB-22 HUAYNA POTOSÍ GRANITE. 

Spot Site Ch/h U (ppm) (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB22-2.2 rim osc, fr 2,461 40 0.02 0.10 275 3 243 18 −13 22.92 0.93 0.05105 0.8 0.3071 1.2 0.04362 0.93 0.76
RIB22-15.1 rim osc, p 985 100 0.10 0.24 242 2 230 36 −5 26.15 0.79 0.05076 1.6 0.2676 1.8 0.03824 0.79 0.45
RIB22-18.1 core hb, ov 518 87 0.17 0.23 222 2 217 57 −2 28.56 0.82 0.05047 2.5 0.2437 2.6 0.03502 0.82 0.32
RIB22-4.1 core hb, p 682 43 0.06 0.13 230 2 225 27 −2 27.54 0.91 0.05065 1.2 0.2536 1.5 0.03631 0.91 0.62
RIB22-7.1 rim osc, p 868 132 0.15 0.16 232 2 228 24 −2 27.33 0.84 0.05071 1.0 0.2558 1.3 0.03659 0.84 0.64
RIB22-8.1 core osc, p 307 53 0.17 0.40 222 2 221 80 −1 28.50 0.85 0.05056 3.5 0.2446 3.6 0.03509 0.85 0.24
RIB22-1.1 rim osc, p 820 67 0.08 0.16 232 2 230 26 −1 27.29 0.79 0.05077 1.1 0.2565 1.4 0.03664 0.79 0.58
RIB22-3.1 core hb, p 372 137 0.37 0.48 224 2 225 52 +0 28.25 0.97 0.05064 2.2 0.2472 2.4 0.03540 0.97 0.40
RIB22-6.1 core osc, p 310 102 0.33 0.47 225 2 226 58 +0 28.14 0.95 0.05067 2.5 0.2483 2.7 0.03553 0.95 0.36
RIB22-9.1 core osc, p 587 67 0.11 0.38 235 2 237 43 +1 26.97 0.82 0.05091 1.9 0.2603 2.0 0.03708 0.82 0.40
RIB22-14.1 core hb, p 434 43 0.10 0.33 227 2 231 47 +2 27.90 0.82 0.05079 2.1 0.2510 2.2 0.03584 0.82 0.37
RIB22-12.1 core hb, p 271 46 0.17 0.58 228 2 236 105 +4 27.82 1.01 0.05090 4.5 0.2523 4.6 0.03595 1.01 0.22
RIB22-10.1 core hb, p 688 293 0.43 0.22 227 2 236 52 +4 27.94 0.80 0.05090 2.2 0.2512 2.4 0.03579 0.80 0.34
RIB22-11.1 rim osc, p 748 208 0.28 0.26 229 3 240 33 +5 27.65 1.12 0.05099 1.4 0.2543 1.8 0.03616 1.12 0.62
RIB22-5.1 rim osc, p 401 123 0.31 0.41 238 3 252 53 +6 26.58 1.11 0.05125 2.3 0.2659 2.6 0.03763 1.11 0.43
RIB22-13.1 rim osz, p 114 45 0.40 1.77 219 2 240 242 +9 28.90 1.07 0.05097 10.5 0.2432 10.5 0.03461 1.07 0.10
RIB22-17.1 rim osc, fr 480 204 0.42 0.39 214 2 238 46 +10 29.66 0.82 0.05093 2.0 0.2367 2.1 0.03371 0.82 0.38
RIB22-16.2 rim osc, ov 290 73 0.25 0.23 759 6 878 21 +14 8.00 0.85 0.06832 1.0 1.1773 1.3 0.12497 0.85 0.64
RIB22-16.1 core osc, ov 301 84 0.28 0.14 733 7 865 28 +16 8.30 1.01 0.06789 1.3 1.1272 1.7 0.12042 1.01 0.60
RIB22-2.1 core hb, fr 154 94 0.61 0.48 500 8 786 42 +38 12.41 1.62 0.06537 2.0 0.7263 2.6 0.08058 1.62 0.63

TABLE 2J RIB-5 ZONGO/KUTICUCHO GRANITE. 

Spot Site Ch/h U (ppm) (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB5-3.1 core osc, p 1,157 522 0.45 0.01 220 2 212 20 −4 28.8 1.0 0.0504 0.8 0.241 1.3 0.0348 1.0 0.8
RIB5-1.1 core osc, ov 522 36 0.07 0.05 228 3 223 35 −2 27.8 1.2 0.0506 1.5 0.251 1.9 0.0360 1.2 0.6
RIB-5-21.1 rim hd, p 5,470 68 0.01 0.24 234 4 175 78 −34 27.1 1.6 0.04957 3.4 0.252 3.7 0.0369 1.6 0.4
RIB-5-1.2 rim osc, ov 483 36 0.07 -- 239 3 233 27 −3 26.5 1.4 0.0508 1.2 0.26 1.8 0.038 1.4 0.8
RIB-5-9.2 rim hd, ov 10,540 46 0.00 0.11 243 4 188 59 −29 26.1 1.5 0.04986 2.6 0.264 3.0 0.0384 1.5 0.5
RIB-5-1.2 rim osc, ov 6,475 17 0.00 0.20 252 4 187 83 −35 25.1 1.7 0.04983 3.6 0.273 3.9 0.0398 1.7 0.4
RIB-5-20.1 rim hd, fr 12,104 77 0.01 -- 259 4 238 29 −9 24.4 1.6 0.05095 1.3 0.288 2.0 0.0410 1.6 0.8
RIB-5-19.1 rim hd, p 8,295 39 0.00 -- 263 4 172 35 −54 24.0 1.5 0.04951 1.5 0.284 2.2 0.0416 1.5 0.7
RIB-5-16.1 rim hd, p 10,295 44 0.00 -- 269 4 166 45 −63 23.5 1.5 0.04938 1.9 0.290 2.5 0.0426 1.5 0.6
RIB-5-17.1 rim hd, p 14,104 75 0.01 -- 271 4 213 34 −28 23.3 1.6 0.05039 1.5 0.298 2.1 0.0429 1.6 0.7
RIB-5-14.1 core hd, fr 11,368 152 0.01 0.31 276 4 243 56 −14 22.9 1.6 0.05105 2.4 0.308 2.9 0.0437 1.6 0.5
RIB-5-18.1 core hb, p 12,238 69 0.01 -- 286 4 186 35 −55 22.0 1.6 0.04980 1.5 0.312 2.2 0.0454 1.6 0.7
RIB-5-13.1 core hd, fr 8,274 2,055 0.25 -- 287 5 268 30 −7 22.0 1.7 0.05160 1.3 0.323 2.2 0.0455 1.7 0.8
RIB-5-28.1 core hb, ov 2057 40 0.02 0.35 287 4 388 14 +27 22.0 1.3 0.0544 0.6 0.34 1.5 0.046 1.3 0.9
RIB-5-10.2 rim hd, p 14,647 128 0.01 -- 291 4 185 55 −59 21.6 1.5 0.04978 2.4 0.317 2.8 0.0462 1.5 0.5
RIB5-8.1 core hb, ov 197 50 0.25 1.34 326 4 462 87 +30 19.3 1.1 0.0562 3.9 0.402 4.1 0.0519 1.1 0.3
RIB-5-15.1 rim hd, fr 36,691 182 0.00 -- 331 5 212 17 −58 19.0 1.5 0.05037 0.7 0.366 1.7 0.0527 1.5 0.9
RIB-5-18.2 rim hd, p 1,958 298 0.15 0.21 335 5 349 15 +4 18.8 1.4 0.0535 0.7 0.39 1.5 0.053 1.4 0.9
RIB5-12.1 rim hd, p 15,652 78 0.00 -- 348 5 314 26 −11 18.0 1.5 0.0527 1.1 0.403 1.8 0.0554 1.5 0.8
RIB5-11.2 rim hd, p 8,353 40 0.00 -- 359 11 273 16 −32 17.5 3.1 0.0517 0.7 0.408 3.2 0.0572 3.1 1.0
RIB-5-25.1 core hb, fr 705 162 0.23 0.33 395 5 443 32 +11 15.8 1.4 0.0558 1.4 0.49 2.0 0.063 1.4 0.7
RIB-5-22.1 core hb, ov 1,306 62 0.05 1.45 415 5 659 44 +38 15.0 1.4 0.0616 2.0 0.57 2.5 0.067 1.4 0.6
RIB5-6.2 rim hd, fr 16,273 95 0.01 -- 457 17 182 14 −157 13.6 3.8 0.0497 0.6 0.504 3.9 0.0735 3.8 1.0
RIB-5-26.1 core hb, ov 759 171 0.23 0.21 479 6 534 24 +11 13.0 1.4 0.0581 1.1 0.62 1.8 0.077 1.4 0.8
RIB5-2.1 core hd, ov 2,261 20 0.01 -- 537 5 502 17 −7 11.5 1.0 0.0573 0.8 0.686 1.2 0.0869 1.0 0.8
RIB5-6.1 core hb, ov 296 104 0.35 0.27 557 6 542 31 −3 11.1 1.0 0.0583 1.4 0.725 1.7 0.0902 1.0 0.6
RIB5-10.1 core osc, ov 662 243 0.37 0.23 579 6 573 20 −1 10.6 1.1 0.0592 0.9 0.767 1.4 0.0940 1.1 0.8
RIB-5-27.1 core hd, fr 312 59 0.19 3.44 607 9 1286 27 +55 10.1 1.6 0.0837 1.4 1.14 2.1 0.099 1.6 0.8
RIB5-4.1 core hb, p 421 125 0.30 3.72 869 32 1579 71 +48 6.9 4.0 0.0976 3.8 1.942 5.5 0.1443 4.0 0.7
RIB5-5.1 core hb, ov 792 38 0.05 5.10 987 9 1840 7 +50 6.0 1.0 0.1125 0.4 2.566 1.1 0.1654 1.0 0.9
RIB5-7.1 core hb, ov 227 136 0.60 0.09 1020 10 986 18 −4 5.8 1.1 0.0720 0.9 1.701 1.4 0.1713 1.1 0.8
RIB5-11.1 core hb, p 161 55 0.34 0.44 1148 12 1149 24 +0 5.1 1.1 0.0781 1.2 2.099 1.6 0.1950 1.1 0.7
RIB-5-23.1 core hb, ov 291 258 0.89 1.32 1503 19 1675 21 +12 3.8 1.4 0.1028 1.1 3.72 1.8 0.263 1.4 0.8
RIB5-9.1 rim hd, ov 151 93 0.62 0.27 1638 16 1661 12 +2 3.5 1.1 0.1020 0.6 4.070 1.3 0.2893 1.1 0.9
RIB-5-24.1 core hb, ov 106 57 0.53 -- 1824 24 1802 22 −1 3.1 1.5 0.1101 1.2 4.97 2.0 0.327 1.5 0.8
RIB-5-1.3 rim hd,ov 6,475 17 0.00 0.2 252 4 187 83 −35 25.1 1.7 0.04983 3.6 0.273 3.9 0.0398 1.7 0.4
RIB-5-12.1 rim hd, p 15,652 78 0.00 -- 348 5 314 26 −11 18 1.5 0.0527 1.1 0.403 1.8 0.0554 1.5 0.8

TABLE 2K RIB-30 ZONGO/KUTICUCHO GRANITE. 

Spot Site Ch/h U (ppm) Th (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB30-15.1 rim hd, fr 16,246 69 0.004 0.10 226 5 220 62 −3 28.0 2.39 0.05053 2.7 0.248 3.6 0.0357 2.39 0.7
RIB30-12.1 rim hd, ov 19,962 102 0.005 0.00 226 4 261 53 +14 28.0 1.65 0.05145 2.3 0.253 2.8 0.0357 1.65 0.6
RIB30-11.1 rim hd, p 15,325 108 0.007 -- 229 2 214 65 −7 27.6 0.81 0.05041 2.8 0.252 2.9 0.0362 0.81 0.3
RIB30-14.1 rim hd, fr 18,210 62 0.003 0.08 231 2 286 50 +20 27.4 0.80 0.05201 2.2 0.261 2.3 0.0365 0.80 0.3
RIB30-9.1 rim hd, fr 15,565 2624 0.169 1.16 236 2 300 108 +22 26.8 0.84 0.05234 4.7 0.269 4.8 0.0373 0.84 0.2
RIB30-4.1 rim hd, fr 14,259 67 0.005 -- 244 2 229 43 −6 26.0 0.79 0.05075 1.9 0.270 2.0 0.0385 0.79 0.4
RIB30-10.1 rim hd, p 18,372 60 0.003 -- 252 3 209 41 −21 25.1 1.26 0.05030 1.8 0.276 2.2 0.0399 1.26 0.6
RIB30-5.1 rim hd, p 17,042 65 0.004 0.10 259 4 226 60 −15 24.4 1.42 0.05068 2.6 0.287 3.0 0.0410 1.42 0.5
RIB30-7.1 rim hd, p 18,524 155 0.008 -- 263 2 263 76 +0 24.0 0.79 0.05150 3.3 0.295 3.4 0.0416 0.79 0.2
RIB30-8.1 rim hd, p 1,8333 444 0.024 0.42 298 3 224 47 −34 21.1 0.86 0.05064 2.1 0.331 2.2 0.0474 0.86 0.4
RIB30-2.1 core osc, p 15,654 213 0.014 -- 301 2 283 35 −6 20.9 0.82 0.05194 1.6 0.342 1.8 0.0477 0.82 0.5
RIB30-13.1 rim hd, fr 15,917 98 0.006 -- 303 3 216 58 −41 20.8 0.92 0.05045 2.5 0.335 2.7 0.0481 0.92 0.3
RIB30-6.1 rim hd, p 17,698 104 0.006 0.38 306 3 205 52 −50 20.5 0.89 0.05022 2.2 0.337 2.4 0.0487 0.89 0.4
RIB30-3.1 core sz, fr 829 139 0.167 0.63 216 3 100 285 −117 29.3 1.21 0.04802 12.1 0.226 12.1 0.0341 1.21 0.1
RIB30-17.1 rim osc, fr 425 269 0.634 1.05 236 3 236 98 +0 26.8 1.4 0.05089 4.3 0.262 4.5 0.0373 1.4 0.3
RIB30-1.1 core osc, fr 1,888 162 0.086 -- 237 2 281 73 +16 26.7 0.88 0.05191 3.2 0.268 3.3 0.0375 0.88 0.3
RIB30-18.1 rim hb, p 454 122 0.269 0.28 241 3 246 44 +2 26.2 1.3 0.05111 1.9 0.269 2.3 0.0381 1.3 0.6
RIB30-19.1 core sz, fr 860 61 0.071 0.46 262 3 272 59 +4 24.1 1.3 0.05170 2.6 0.296 2.9 0.0415 1.3 0.5
RIB30-20.1 core sz, p 1,694 113 0.067 0.03 266 3 252 20 −6 23.7 1.2 0.05124 0.9 0.298 1.5 0.0421 1.2 0.8
RIB30-2.2 rim hd, p 1,990 188 0.095 0.83 291 4 292 164 +1 21.7 1.41 0.05216 7.2 0.332 7.3 0.0461 1.41 0.2
RIB30-16.1 core hb, p 488 185 0.380 0.34 507 6 529 27 +4 12.2 1.2 0.05797 1.2 0.654 1.7 0.0818 1.2 0.7
RIB30-22.1 core hb, p 201 46 0.228 0.50 974 13 1167 34 +18 6.1 1.4 0.07878 1.7 1.771 2.2 0.1631 1.4 0.6
RIB30-21.1 core hb, fr 191 63 0.330 0.56 1228 17 1291 42 +5 4.8 1.5 0.08392 2.2 2.429 2.7 0.2099 1.5 0.6
RIB30-24.1 core hb, p 89 70 0.790 4.01 1451 27 1425 111 −2 4.0 2.1 0.08995 5.8 3.131 6.2 0.2525 2.1 0.3
RIB30-23.1 core hb, fr 119 47 0.400 0.40 1661 25 1993 14 +19 3.4 1.7 0.12251 0.8 4.966 1.9 0.2940 1.7 0.9
RIB30-25.1 core hb, p 594 307 0.517 0.14 2323 33 2603 10 +13 2.3 1.7 0.17473 0.6 10.451 1.8 0.4338 1.7 0.9

TABLE 2L RIB-11 TAQUESI GRANODIORITE. 

Spot Site Ch/h U (ppm) Th (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB11-9.1 core hb, p 247 45 0.18 0.36 218 2 230 67 +6 29.1 1.1 0.0508 2.9 0.240 3.1 0.0343 1.1 0.3
RIB11-8.1 core osc, p 248 195 0.79 0.58 219 2 212 84 −3 28.9 1.1 0.0504 3.6 0.240 3.8 0.0346 1.1 0.3
RIB11-5.1 core hb, p 217 166 0.77 0.60 219 3 252 81 +13 28.9 1.3 0.0512 3.5 0.244 3.7 0.0346 1.3 0.3
RIB11-12.1 core sz, p 179 248 1.38 5.00 220 3 271 340 +19 28.8 1.3 0.0517 14.8 0.247 14.9 0.0347 1.3 0.1
RIB11-2.1 core osz, p 449 34 0.08 0.13 221 2 257 53 +14 28.7 1.0 0.0514 2.3 0.247 2.5 0.0348 1.0 0.4
RIB11-6.1 core osc, p 336 199 0.59 -- 221 3 209 305 −6 28.6 1.2 0.0503 13.2 0.242 13.2 0.0349 1.2 0.1
RIB11-7.1 core osc, p 378 193 0.51 0.81 221 2 244 109 +9 28.6 1.0 0.0511 4.7 0.246 4.8 0.0349 1.0 0.2
RIB11-10.1 core osc, p 512 335 0.65 0.08 221 2 219 33 −1 28.6 1.0 0.0505 1.4 0.243 1.7 0.0350 1.0 0.6
RIB11-3.1 core sz, p 514 163 0.32 0.28 228 2 285 34 +20 27.8 1.0 0.0520 1.5 0.258 1.8 0.0360 1.0 0.6
RIB11-4.1 core osc, p 813 80 0.10 0.03 228 2 218 25 −5 27.7 1.0 0.0505 1.1 0.251 1.5 0.0361 1.0 0.7
RIB11-1.1 core sz, p 1,441 144 0.10 0.04 230 2 236 15 +3 27.6 1.0 0.0509 0.7 0.255 1.2 0.0363 1.0 0.8
RIB11-11.1 core sz, p 226 142 0.63 0.30 573 15 582 34 +2 10.8 2.7 0.0594 1.6 0.761 3.1 0.0929 2.7 0.9

TABLE 2M RIB-12 TAQUESI QUARTZDIORITE (ENCLAVE). 

Spot Site Ch/h U (ppm) Th (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB12-13.1 rim sz, p 282 123 0.44 0.54 213 2 227 75 +7 29.8 1.19 0.05071 3.2 0.235 3.4 0.0336 1.19 0.3
RIB12-9.1 rim osz, p 186 100 0.54 1.28 216 2 234 162 +8 29.3 0.97 0.05086 7.0 0.239 7.1 0.0341 0.97 0.1
RIB12-11.2 core osc, p 1,631 206 0.13 0.14 221 2 229 27 +4 28.7 0.87 0.05075 1.2 0.244 1.5 0.0348 0.87 0.6
RIB12-7.1 rim osc, p 785 197 0.25 0.21 225 2 222 48 −1 28.1 0.80 0.05059 2.1 0.248 2.2 0.0356 0.80 0.4
RIB12-3.1 rim sz, p 512 427 0.83 0.43 226 2 231 68 +3 28.1 1.07 0.05079 3.0 0.250 3.1 0.0356 1.07 0.3
RIB12-14.1 rim osc, p 821 190 0.23 0.15 226 2 207 27 −9 28.1 0.79 0.05027 1.2 0.247 1.4 0.0356 0.79 0.6
RIB12-4.1 rim osc, p 1,037 135 0.13 0.05 226 2 226 19 −0 28.0 0.78 0.05067 0.8 0.250 1.1 0.0357 0.78 0.7
RIB12-10.1 rim osc, p 898 109 0.12 0.33 226 2 203 33 −12 28.0 1.03 0.05017 1.4 0.247 1.7 0.0358 1.03 0.6
RIB12-5.1 rim osc, p 550 313 0.57 0.43 227 2 236 45 +4 28.0 0.91 0.05090 2.0 0.251 2.2 0.0358 0.91 0.4
RIB12-12.1 rim osc, p 1,483 189 0.13 0.02 228 2 220 15 −4 27.8 0.89 0.05055 0.6 0.251 1.1 0.0360 0.89 0.8
RIB12-6.1 rim osc, p 563 43 0.08 0.25 230 2 235 36 +2 27.5 0.80 0.05087 1.6 0.255 1.8 0.0363 0.80 0.5
RIB12-15.1 rim osc, p 1,897 250 0.13 -- 231 2 234 14 +1 27.4 0.98 0.05084 0.6 0.256 1.2 0.0365 0.98 0.8
RIB12-8.1 rim osc, p 1,333 538 0.40 0.04 233 2 222 16 −5 27.1 0.87 0.05060 0.7 0.257 1.1 0.0368 0.87 0.8
RIB12-2.1 rim osc, p 1,687 211 0.13 0.09 234 2 206 16 −14 27.1 0.77 0.05023 0.7 0.256 1.0 0.0369 0.77 0.7
RIB12-1.1 rim osc, p 1,332 48 0.04 0.12 236 2 196 29 −21 26.9 0.78 0.05002 1.3 0.257 1.5 0.0372 0.78 0.5
RIB12-11.1 core hb, ov 211 121 0.57 0.62 530 8 698 44 +25 11.7 1.61 0.06271 2.0 0.740 2.6 0.0856 1.61 0.6

TABLE 2N RIB-43 QUIMSA CRUZ GRANITE. 

Spot Site Ch/h U (ppm) Th (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB43-15.1 rim osc, eq 509 228 0.45 2.95 25.9 0.4 87.4 464 +71 248.8 1.6 0.0478 19.6 0.03 19.6 0.004 1.6 0.1
RIB43-12.1 core osc, p 950 171 0.18 2.74 26.4 0.5 48.8 426 +46 244.1 1.9 0.0470 17.8 0.03 17.9 0.004 1.9 0.1
RIB43-7.1 core osc, p 739 263 0.36 2.04 26.5 0.4 25.5 415 −4 243.2 1.4 0.0465 17.3 0.03 17.4 0.004 1.4 0.1
RIB43-1.1 rim osc, p 468 280 0.60 3.82 26.5 0.6 47.2 595 +44 242.7 2.2 0.0470 24.9 0.03 25.0 0.004 2.2 0.1
RIB43-9.1 rim osc, p 734 300 0.41 4.10 26.6 0.5 59.8 631 +56 241.9 1.7 0.0472 26.5 0.03 26.5 0.004 1.7 0.1
RIB43-5.1 rim osc, p 704 200 0.28 2.85 26.6 0.5 49.2 403 +46 241.7 2.0 0.0470 16.9 0.03 17.0 0.004 2.0 0.1
RIB43-2.1 rim osc, p 467 162 0.35 5.92 26.7 0.5 −20 837 +234 241.0 1.8 0.0457 34.6 0.03 34.6 0.004 1.8 0.1
RIB43-13.1 rim osc, p 627 185 0.30 3.55 26.7 0.5 4.8 475 −453 241.0 1.7 0.0461 19.7 0.03 19.8 0.004 1.7 0.1
RIB43-10.1 rim osc, p 504 201 0.40 3.09 27.0 0.5 67.1 498 +60 238.2 1.9 0.0474 20.9 0.03 21.0 0.004 1.9 0.1
RIB43-8.1 core osc, p 932 326 0.35 1.88 27.5 0.4 48.0 256 +43 233.5 1.5 0.0470 10.7 0.03 10.8 0.004 1.5 0.1
RIB43-6.2 rim osc, p 752 174 0.23 1.65 27.7 0.4 64.2 215 +57 232.2 1.5 0.0473 9.0 0.03 9.2 0.004 1.5 0.2
RIB43-11.1 rim osc, p 1,001 273 0.27 3.00 27.8 0.4 57.5 324 +52 231.1 1.4 0.0472 13.6 0.03 13.7 0.004 1.4 0.1
RIB43-3.1 rim osc, p 1,105 301 0.27 1.55 28.0 0.3 45.4 256 +38 229.9 1.2 0.0469 10.7 0.03 10.8 0.004 1.2 0.1
RIB43-4.1 rim osc, p 1,386 270 0.20 1.23 33.7 0.4 51.7 206 +35 190.7 1.1 0.0470 8.6 0.03 8.7 0.005 1.1 0.1
RIB43-14.1 rim osc, p 740 176 0.24 0.55 324 3 907 29 +66 19.4 0.9 0.0693 1.4 0.49 1.7 0.052 0.9 0.5
RIB43-6.1 core osc, p 257 95 0.37 0.31 600 5 606 33 +1 10.3 0.9 0.0601 1.5 0.81 1.8 0.097 0.9 0.5

TABLE 2O RIB-46 QUIMSA CRUZ GRANITE. 

Spot Site Ch/h U (ppm) (ppm) Th/U % 206Pbc 206Pb/238U age (Ma) ±1σ (Ma) 207Pb/206Pb age (Ma) ±1σ (Ma) % Disc 238U/206Pb* ±% 207Pb*/206Pb* ±% 207Pb*/235U ±% 206Pb*/238U ±% Err corr
RIB46-3.1 rim osc, p 931 170 0.18 2.36 25.9 0.4 49.4 317 +48 248.0 1.69 0.04700 13.3 0.026 13.4 0.0040 1.69 0.1
RIB46-8.2 core hb, p 347 135 0.39 10.76 26.5 1.0 138 1487 +81 242.7 3.62 0.04880 63.3 0.028 63.4 0.0041 3.62 0.1
RIB46-8.1 rim osc, p 834 188 0.23 2.66 26.5 0.3 40.7 437 +35 242.4 1.11 0.04683 18.3 0.027 18.3 0.0041 1.11 0.1
RIB46-6.1 rim osc, p 834 230 0.28 1.19 26.6 0.5 78.5 211 +66 242.1 1.71 0.04758 8.9 0.027 9.0 0.0041 1.71 0.2
RIB46-13.1 rim osc, p 734 278 0.38 3.81 26.7 0.4 75.9 534 +65 241.1 1.65 0.04753 22.5 0.027 22.6 0.0041 1.65 0.1
RIB46-5.1 rim osc, p 1,068 204 0.19 1.48 26.7 0.3 49.7 228 +46 240.5 1.10 0.04701 9.6 0.027 9.6 0.0042 1.10 0.1
RIB46-12.1 rim osc, p 944 197 0.21 0.98 26.8 0.3 28.8 156 +7 239.8 1.22 0.04660 6.5 0.027 6.6 0.0042 1.22 0.2
RIB46-11.1 rim osc, p 552 122 0.22 2.40 26.8 0.4 25.7 423 −4 239.8 1.34 0.04654 17.6 0.027 17.7 0.0042 1.34 0.1
RIB46-4.1 rim osc, p 719 220 0.31 1.88 26.9 0.6 74.8 432 +64 239.5 2.35 0.04751 18.2 0.027 18.3 0.0042 2.35 0.1
RIB46-11.2 rim osc, p 899 173 0.19 1.03 26.9 0.3 58.2 207 +54 239.3 1.14 0.04718 8.7 0.027 8.8 0.0042 1.14 0.1
RIB46-7.1 rim osc, p 679 265 0.39 1.57 27.0 0.3 77.8 257 +65 238.6 1.10 0.04757 10.8 0.027 10.9 0.0042 1.10 0.1
RIB46-9.1 rim osc, p 1,220 143 0.12 1.03 27.2 0.3 11.9 276 −128 236.3 1.15 0.04627 11.5 0.027 11.5 0.0042 1.15 0.1
RIB46-2.2 rim osc, p 1,544 143 0.09 1.36 27.3 0.3 38.8 149 +30 235.5 1.13 0.04680 6.2 0.027 6.3 0.0042 1.13 0.2
RIB46-1.1 rim osc, p 1,352 386 0.29 1.37 28.0 0.3 43.7 150 +36 229.7 1.19 0.04689 6.3 0.028 6.4 0.0044 1.19 0.2
RIB46-10.2 rim osc, p 1,465 147 0.10 2.06 29.8 0.5 58.9 255 +49 215.6 1.53 0.04719 10.7 0.030 10.8 0.0046 1.53 0.1
RIB46-10.1 core osc, p 367 211 0.57 0.07 1608 12 1707 7 +7 3.5 0.82 0.10461 0.4 4.087 0.9 0.2833 0.82 0.9
RIB46-2.1 core sz, p 121 102 0.84 0.40 1648 28 1645 30 −0 3.4 1.93 0.10114 1.6 4.063 2.5 0.2913 1.93 0.8

Ch/ corresponds to textural zircon characteristics (osc oscillatory zoning, hb homogeneous bright, hd homogeneous dark and sz sector zoning). /h corresponds to habit (p prismatic, ov oval and fr fragment). % 206Pbc is percentage of measured common 206Pb. ±1sigma reported error in ages. % Disc is percentage of discordance. Following Faure and Mensing (2005), isotopic ratios correspond as follows: 238U/206pb=1eλ1t1 ; 207pb/206pb=1137.88(eλ21eλ11 , 207pb/235U=eλ2t1 and 206Pb*/238U = eλ1t -1. “t” is the age, λ1 is the decay constant of 238U and equals to 1.55125 * 10−10 y−1 and λ2 is the decay constant of 235U and equals to 9.8485 * 10−10 y−1 (Steiger and Jäger, 1977). Sp1ot sites chosen to calculate Concordia ages are shown as bold text.

5.1. U-Pb zircon ages

The location of the collected samples is displayed in figure 2. Analytical results are shown in tables 2A to 2O and U-Pb Concordia curves are shown in figures 4 to 20. For the calculation of Concordia ages, we selected U-Pb ages younger than 300 Ma and discordances of less than 10%. Discordant spots with large error were also excluded. Selected spots for individual Concordia age calculation are displayed on the figure captions (Figs. 6 to 16) and in bold on tables 2A to 2O. CL images of the representative analysed zircon crystals are shown in figure 3. A summary of Concordia ages, MSWD values and associated errors at 1 and 2 sigma and 95% confidence is presented in table 3.

TABLE 3 SUMMARY OF CONCORDIA AGES CALCULATED FOR THE STUDIED PLUNTONS FROM THE CORDILERA REAL. 

Sample Age (Ma) ±1 sigma (MA) ±2 sigma (Ma) ±95% confidence (Ma) MSWD
RIB-2 220.7 1.3 2.7 1.1
RIB-2 247.6 1.2 2.4 3.6 1.9
RIB-4 222.9 0.96 1.9 3.2 2.3
RIB-4 243.9 1.6 3.1 3.1 1.18
RIB-11 222.9 0.87 1.7 2.7 2
RIB-12 227.8 0.65 1.3 1.03
RIB-15 226.9 1 2 0.78
RIB-15 240.3 1.2 2.5 0.19
RIB-19 213.6 1.2 2.4 0.09
RIB-19 226 0.57 1.1 1.4 1.4
RIB-20 230.7 0.94 1.9 2.7 1.9
RIB-22 226.9 0.61 1.2 1.6 1.6
RIB-22 238.3 1.2 2.4 3.7 1.5
RIB-27 239.5 0.96 1.9 2.8 0.39
RIB-32 234.2 0.65 1.3 0.2
RIB-33 230.7 0.63 1.3 0.46
RIB-43 27 0.12 0.24 0.29 1.3
RIB-46 27 0.1 0.2 0.8

MSWD: values and errors at 1, 2 sigma and 95% confidence as calculated by the Isoplot 4.0 of Ludwig (2009).

FIG. 3 Cathodoluminescence images of zircons from the analyzed samples with spot sites and 238U/204Pb ages. 

FIG. 4 Concordia diagram with entire dataset of sample RIB-2 (Huayna Potosí granite, see table 2E) with histogram of Concordia ages in the inset. Spot sites with large errors or discordance >10% were excluded from Concordia age calculation and are shown as grey ellipses. Magmatism is recorded continuously by means of zircon ages from nearly 250 to 220 Ma. This large interval of ages does not allow Isoplot software to calculate a single Concordia age. Two groups can be distinguished at around 240 and near 220 Ma, respectively. 

FIG. 5 Concordia diagram with entire dataset of sample RIB-4 (Huayna Potosí granite, see table 2F) with histograms of Concordia ages in the inset. Spot sites with large errors or discordance >10% were excluded from Concordia age calculation and are shown as grey ellipses. Magmatism is recorded continuously by means of zircon ages from nearly 290 to 215 Ma. This large interval of ages does not allow Isoplot software to calculate a single Concordia age. Two groups can be distinguished at 220 and 240 Ma with spots at around 270 Ma considered as “early antecrysts”. 

FIG. 6 Concordia diagrams for sample RIB-2 (Huayna Potosí granite) displaying two calculated Concordia ages. For the younger age (A), four spot sites were chosen (8.1, 6.1, 10.1, and 13.1) displayed as bold text in table 2E. For the older age shown below (B), seven spots were chosen (22.1, 15.1, 3.1, 21.1, 17.1, 2.1 and 24.1) displayed also as bold text on table 2E. Grey ellipses were excluded from the age calculation and the light blue ellipses correspond to the calculated Concordia ages. 

FIG. 7 Concordia diagrams for sample RIB-4 (Huayna Potosí granite) displaying two Concordia ages. For the younger age (A), six spot sites were chosen (26.1, 8.1, 9.1, 1.1, 2.1 and 3.1) displayed as bold text in table 2F. For the older age shown below (B), five spots were chosen (14.1, 17.1, 22.1, 16.1 and 25.1) displayed also as bold text in table 2F. Grey ellipses were excluded from the age calculation and the light blue ellipses correspond to the calculated Concordia ages. 

FIG. 8 Concordia diagram for sample RIB-19 (Huayna Potosí granite). Thirteen zircon spot sites were chosen for the Concordia age calculation (7.1, 10.2, 5.1, 2.1, 14.1, 9.1, 11.1, 4.1, 18.1, 1.1, 12.1, 8.1 and 13.1), displayed as bold text in table 2G. Three spots (6.1, 2.2 and 3.1) define a younger age of 214 Ma, however they were rejected due their large error ellipses (in grey). Light blue ellipse corresponds to the calculated Concordia age. 

FIG. 9 Concordia diagram for sample RIB-20 (Huayna Potosí granodiorite). Ten zircon spot sites were chosen for the Concordia age calculation (8.1, 10.1, 6.1, 3.1, 1.1, 5.1, 2.1, 14.1, 4.1 and 7.1), displayed as bold text in table 2H. Grey ellipses were excluded from the age calculation and the light blue ellipse corresponds to the calculated Concordia age. 

FIG. 10 Concordia diagram for sample RIB-22 (Huayna Potosí granite). Eleven zircon spot sites were chosen for the Concordia age calculation (18.1, 8.1, 3.1, 6.1, 10.1, 14.1, 12.1, 11.1, 4.1, 7.1 and 1.1). Three spots (9.1, 5.1 and 15.1) defined an older age of 238 Ma. These chosen spots are displayed as bold text in table 2I. Grey ellipses were excluded from the age calculation and the light blue ellipse corresponds to the calculated Concordia age. 

FIG. 11 Concordia diagram for samples RIB-5 (top) and RIB-30 (bottom) of Zongo/Kuticucho granite. Both samples from the same granite, display a reverse Discordia line above the Concordia curve. This feature might be related to damage in the zircon crystal lattice (Kusiak et al., 2013). Fifteen spots were chosen for the RIB-5 (1.3, 12.1, 11.2, 6.2, 21.1, 9.2, 20.1, 19.1, 16.1, 17.1, 14.1, 13.1, 18.1, 10.2 and 15.1), meanwhile 13 were chosen for the RIB-30 (15.1, 12.1, 11.1, 14.1, 9.1, 4.1, 10.1, 5.1, 7.1, 8.1, 2.1, 13.1 and 6.1). These chosen spots are displayed as bold text in tables 2J and 2K, respectively. 

FIG. 12 Concordia diagram for sample RIB-11 (Taquesi granodiorite). Seven zircon spot sites were chosen for the Concordia age calculation (9.1, 8.1, 6.1, 7.1, 10.1, 4.1 and 1.1), displayed as bold text in table 2L. Grey ellipses were excluded from the age calculation and the light blue ellipse corresponds to the calculated Concordia ages. 

FIG. 13 Concordia diagram for sample RIB-12 (Taquesi quartzdiorite enclave). Nine zircon spot sites were chosen for the Concordia age calculation (7.1, 3.1, 14.1, 4.1, 5.1, 12.1, 6.1, 15.1 and 8.1), displayed as bold text on table 2M. Grey ellipses were excluded from the age calculation and the light blue ellipse corresponds to the calculated Concordia age. 

FIG. 14 Concordia diagram for sample RIB-27 (Huato granite). Nine zircon spot sites were chosen for the Concordia age calculation (4.1, 2.1, 14.1, 8.1, 7.1, 6.1, 5.1, 9.1 and 3.1), displayed as bold text on table 2A. Two spots (12.1 and 11.1) define a younger age of 216 Ma, however they were rejected due their large error ellipses. Grey ellipses were excluded from the age calculation and the light blue ellipse corresponds to the calculated Concordia age. 

FIG. 15 Concordia diagram for sample RIB-33 (Illampu granodiorite). Eleven zircon spot sites were chosen for the Concordia age calculation (5.1, 10.1, 4.1, 2.1, 11.1, 9.1, 7.1, 1.1, 6.1, 3.1 and 8.1), displayed as bold text on table 2C. Grey ellipses were excluded from the age calculation and the light blue ellipse corresponds to the calculated Concordia age. 

FIG. 16 Concordia diagram for sample RIB-32 (Illampu quartzdiorite enclave). Twelve zircon spot sites were chosen for the Concordia age calculation (15.1, 11.1, 5.1, 14.1, 3.1, 4.1, 8.1, 9.1, 16.1, 12.1, 6.1 and 7.1), displayed as bold text on table 2B. Grey ellipses were excluded from the age calculation and the light blue ellipse corresponds to the calculated Concordia age. 

FIG. 17 Concordia diagram with entire dataset for sample RIB-15 (Illampu granite, see table 2D) with histograms of Concordia ages in the inset. As it was observed on the samples of the Huayna Potosí, magmatism is recorded continuously by means of zircon ages from nearly 240 to 220 Ma. This large age interval does not allow Isoplot software to calculate a single Concordia age. Two groups can be distinguished at 240 and near 220 Ma. 

FIG. 18 Concordia diagrams for sample RIB-15 (Illampu granite) displaying two calculated Concordia ages. For the younger age shown on top (A), Six spot sites were chosen (12.1, 6.1, 11.2, 4.1, 1.1 and 7.2) displayed as bold text on table 2D. For the older age shown below (B), 5 spots were chosen (3.1, 2.1, 8.2, 5.1 and 14.2) displayed also as bold text on table 2D. Grey ellipses were excluded from the age calculation and the light blue ellipses correspond to the calculated Concordia ages. 

FIG. 19 Concordia diagram for sample RIB-43 (Quimsa Cruz granite). Thirteen zircon spot sites were chosen for the Concordia age calculation (15.1, 12.1, 7.1, 1.1, 9.1, 5.1, 2.1, 13.1, 10.1, 8.1, 6.2, 11.1 and 3.1), displayed as bold text on table 2N. Grey ellipses were excluded from the age calculation and the light blue ellipse corresponds to the calculated Concordia age. 

FIG. 20 Concordia diagram for sample RIB-46 (Quimsa Cruz granite). Fourteen zircon spot sites were chosen for the Concordia age calculation (3.1, 8.2, 8.1, 6.1, 13.1, 5.1, 12.1, 11.1, 4.1, 11.2, 7.1, 9.1, 2.2 and 1.1), displayed as bold text on table 2O. Grey ellipses were excluded from the age calculation and the light blue ellipse corresponds to the calculated Concordia age. 

The Huayna Potosí samples (RIB-2 and RIB-4), belonging to the same pluton, and studied previously by Cordani et al. (2019), are a good example of a sample of Cordillera Real granitoids displaying a composite range of ages (Figs. 4 and 5). In the case of RIB-2, the U-Pb zircon ages range from 217 to 257 Ma. This wide range of ages does not allow a single crystallization age to be obtained (e.g., Isoplot software cannot calculate Concordia age, Fig. 4). When displaying the Concordia ages in a histogram plot, peaks are observed at 220 and 240 Ma (histogram in inset of figure 4, see also Cordani et al., 2019). The CL image shows prismatic zircon crystals always with oscillatory zoning and some with dark rims (Fig. 3). Xenocrystal inheritance ages related to detrital zircon ranges from 312 to 1,186 Ma. Given this wide range, concordant spots were selected to calculate Concordia ages (Fig. 6). In the case of the younger population of sample RIB-2, a Concordia age of 221±3 Ma (2σ) was obtained. For the older population, a Concordia age of 248±4 Ma (95% confidence) was also obtained.

For sample RIB-4, the U-Pb zircon ages range from 215 to 265 Ma. This sample also shows a wide range of ages in the histogram inset of figure 5. It can be seen in the CL images (Fig. 3) that zircons present dark U-rich rims, some almost completely dark with small bright U-poor cores (e.g., RIB4-17.1 and RIB4-25.1). Presumed xenocrysts yielded ages of 362, 468, 1364, 1655, 2026 and 2070 Ma. Given also the wide range of ages, two populations were separated to obtain concordant ages (Fig. 7). For the younger population a Concordia age of 223±3 Ma (95% confidence) was obtained. For the older population a Concordia age of 244±3 Ma (95% confidence) was calculated. Rejected spot were 10.1 for having large error and 18.1 and 13.1 (with U/Pb of 263 and 265 Ma, respectively) that we considered as “early antecrysts”.

Sample RIB-19 presented U-Pb zircon ages ranging from 213 to 235 Ma. The CL image shows prismatic crystals with oscillatory zones some with dark rims and an appearance similar to sample RIB-2. An inherited core of 600 Ma rimmed by a younger edge of 222 Ma was measured in spots RIB19-10.1 and RIB19-10.2 respectively. For the calculation of the Concordia age (Fig. 8) the selected spots yielded a Concordia age of 226±1 Ma (2σ). Spots 6.1, 2.2 and 3.1 that defined a younger Concordia age of 214 Ma were rejected for having large analytical error.

Sample RIB-20 presented U-Pb zircon ages ranging from 216 to 251 Ma. CL image shows prismatic crystals with oscillatory zoning some with darker rims and domains (Fig. 3). Two xenocrystal zircon grains yielded discordant ages of 454 and 1413 Ma. For the age calculation (Fig. 9) the selected spots yielded a Concordia age of 231±3 Ma (95% confidence).

Sample RIB-22 presented U-Pb zircon ages ranging from 214 to 242 Ma. Three xenocrystal zircon grains yielded ages of 500, 733 and 759 Ma. For the age calculation (Fig. 10) the selected spots yielded a Concordia age of 227±2 Ma (95% confidence). We also obtained an older Concordia age of 238±2 Ma using spots 9.1, 5.1 and 15.1. Then this sample also shows the bimodal distribution of samples RIB-2 and RIB-4.

For the Kuticucho facies of the Zongo pluton, two granitic samples were dated, both presenting clear deformation shown by the orientation of quartz, K-feldspar, biotite and muscovite. One of them (RIB-5) was already considered by Cordani et al. (2019). For this sample, the U-Pb zircon ages range from 220 to 291 Ma. CL images for dated zircons are presented in figure 3, having dark rims surrounding relictic bright cores. The low Th/U ratios probably yielded a reverse Discordia line forced through the origin (Fig. 11), with a poor constrained lower intercept at 222±25 Ma. Inheritances are abundant especially as bright cores that yielded ages of 333, 1020, 1503, 1638 and 1,824 Ma (Fig. 3). For sample RIB-30, the U-Pb zircon ages range from 216 to 298 Ma also generating a reverse Discordia with a poor constrained lower intercept at 240±28 Ma. This sample displays crystals with dark domains, some of them completely dark, similar to sample RIB-5. This dark rims on zircons, reflecting high U also yielded a reverse discordance as the sample RIB-5 (Fig. 11). However, some of the crystals do not have these dark domains and show instead a normal oscillatory zoning (spots RIB30-3.1, RIB30-17.1 and RIB30-18.1 and RIB30-19.1). Xenocrystic zircons yielded 1,451 and 2,323 Ma.

For the Taquesi pluton, two samples were analysed. One of these is a typical granodiorite (RIB-11) and the other is a mafic enclave (RIB-12) extracted from the same rock. For the RIB-11 sample, the U-Pb zircon ages range from 218 to 230 Ma. Only one zircon xenocryst was found, with an age of 573 Ma. For the calculated age (Fig. 12) selected spots yielded a Concordia age of 223±3 Ma (95% confidence). On the RIB-12 mafic enclave, the U-Pb zircon ages range from 213 to 233 Ma. As seen in sample RIB-11, the CL images of zircon crystals show prismatic habits, with oscillatory zoning, some of them showing dark rims and domains. The only xenocryst analyzed yielded an age of 530 Ma. For the age calculation (Fig. 13) the selected spots yielded a Concordia age of 228±1 Ma (2σ).

For the RIB-27 sample of the Huato granite, the U-Pb zircon ages range from 213 to 249 Ma. Some of the zircon crystals measured have low Th/U ratios (lower than 0.1). Some dark domains are also present in the CL images. Two xenocrystal zircons (spots RIB27-11.1 and RIB27-13.1) reported ages of 610 Ma and 790 Ma. For the age calculation (Fig. 14) selected spots yielded a Concordia age of 239±3 Ma (95% confidence). Spots 1.1, 11.1, 12.1 were rejected for because of their large error.

For the Illampu batholith three samples were analysed. One is a typical granodiorite (RIB-33) of the northern part, the other is a mafic enclave (RIB-32) hosted by this granodiorite and the third sample (RIB-15) comes from a two mica granite located to the southern part of the batholith. For the RIB-33 granodiorite the U-Pb zircon ages range from 227 to 233 Ma. In the CL image (Fig. 3), all zircons have prismatic habit with well-developed oscillatory zoning. Th/U ratios are generally magmatic (Table 2C). No inheritance was measured in this sample. For the calculated age (Fig. 15), selected spots yielded a Concordia age of 231±1 Ma (2σ). For the RIB-32 enclave, the U-Pb zircon ages range from 232 to 236 Ma. The CL images show some zircon crystals with oscillatory zoning but also with massive or irregular core suggesting for the cores a xenocrystic or antecrystic origin (see for instance Corfu et al., 2003). For the calculated age (Fig. 16), the selected spots yielded a Concordia age of 234±1 Ma (2σ). For the RIB-15 granite, the U-Pb zircon ages range from 222 to 242 Ma. As in the case of the two-mica granites of the Huayna Potosí pluton, it also shows a wide range of Concordia ages (histogram inset in Fig. 17), suggesting also a protracted age interval for these granites. The CL image displays prismatic zircon crystals with oscillatory zoning, some with dark rims as it was observed in the zircons from the Huayna Potosí granite. Xenocrystal zircon yielded ages of 471, 583, 645, 1073, 1937 and 2132 Ma. For the age calculations, as we did on samples RIB-2 and RIB-4 two groups were differentiated (Fig. 18). Selected spots yielded a younger Concordia age of 227±2 Ma (2σ). A second group of selected spots yielded an older Concordia age of 240±2 Ma (2σ).

Finally, two samples (RIB-43 and RIB-46) were dated from the Quimsa Cruz granite. Sample RIB-43 presented U-Pb zircon ages ranging from 26 to 28 Ma. Zircon CL images show prismatic zircons with well-developed oscillatory zoning (Fig. 3). Xenocrystal zircon grains have ages of 34, 324 and 600 Ma. Spots used to calculate the age (Fig. 18) yielded a Concordia age of 27±0.2 Ma (2σ). Spot 4.1 with U-Pb age of 33.7 Ma was considered a xenocrystal. Sample RIB-46 presented U-Pb ages ranging from 26 to 30 Ma. Its CL image shows prismatic zircons with well-developed oscillatory zoning similar to sample RIB-43. Xenocrystal zircons have ages of 1608 and 1655 Ma. Spots used to the calculate age (Fig. 19) yielded a Concordia age of 27±0.2 Ma (2σ). This younger Oligocene pulse of felsic magmatism yielded good analytical quality results, possibly related to the good looking appearance of its prismatic oscillatory zoned zircons, almost without dark domains (Fig. 3).

5.2. Zircon inheritance and saturation temperature

From the zircon CL images shown in figure 3, all studied granitic plutons present a significant amount of inherited zircon grains that record U-Pb ages older than 250 Ma. Tables 2A to 2O, show the existence of xenocrystal grains with ages from 330 to 2300 Ma. This is not dissimilar to other zircon age distributions found in Ordovician pelites from other localities of the Eastern Cordillera (e.g.,Bahlburg et al., 2011). However, some Proterozoic grains (found in the Zongo/Kuticucho granite) are distinctive of the Cordillera Real. Considering that the country rocks for the studied granitoids are metapelites of Ordovician and Silurian formations, which may also have recycled older sources, it is noticeable that some zircon ages range from 300 to 400 Ma. The zircon grains that yield these ages have low Th/U ratios, and probably reflect some degree of U enrichment. A few of the grains record ages older than 2.2 Ga, and this age was also found nearby in the Amutara and Coroico (Ordovician) formations (Reimann et al., 2010).

The zircon saturation temperature model of Watson and Harrison (1983) provides a good way to estimate temperatures and compositions at which magmas saturate in Zr and therefore crystallize zircon. Granites with high amount of inheritance have been termed as “cold granites” by Miller et al. (2003) that described them as melts that do not reach temperatures sufficient to dissolve xenocrystal zircon, therefore showing high population of inheritance and less newly formed zircon autocrysts. These inherited xenocrysts saturate the melts in Zr at their sources; therefore, the temperatures obtained for this method are the upper limits for magmatic temperatures. Following the study of Miller et al. (2003), the assumed maximum temperature for cold granites is 766 °C. Table 4 displays the “M values”, associated to the whole rock composition and the Zr saturation temperatures calculated for the Huayna Potosí and Illampu plutons, using the software GCDkit 5.0. It is shown in Table 4 and in figure 21, which displays a histogram of zircon saturation temperatures and a diagram of these temperatures versus SiO2. The mean calculated Zr saturation temperatures are 735 °C for granites, 76 °C for granodiorites and 774 °C for quartz-diorites.

TABLE 4 ZIRCON SATURATION TEMPERATURES AND M VALUES OF THE HUAYNA POTOSÍ AND ILLAMPU PLUTONS, BASED ON WATSON AND HARRISON (1983). 

Sample Pluton Rock M SiO2 Temp. Zr. sat. °C
OL-COA Illampu Quartz-diorite 2.27 57.8 760
O-2 Illampu Quartz-diorite 1.51 58.2 801
S-12-X Illampu Quartz-diorite 1.75 58.3 768
S-15 Illampu Quartz-diorite 1.70 59.8 772
XE 1A Huayna Potosí Quartz-diorite 2.46 60.3 739
RIB-53 Huayna Potosí Quartz-diorite 1.50 62.6 810
Geometric mean of Zr saturation temperatures (°C) quartz-diorites 774.4
RIB-20 Huayna Potosí Granodiorite 1.25 66.0 740
O-7A Illampu Granodiorite 1.69 66.5 752
O-1 Illampu Granodiorite 1.60 67.2 766
S-3 Illampu Granodiorite 1.59 68.1 787
O-3 Illampu Granodiorite 2.26 68.2 715
OL-Oc Illampu Granodiorite 1.26 68.4 786
S-22 Illampu Granodiorite 1.58 68.6 786
Geometric mean of Zr saturation temperatures (°C) granodiorites 761.1
RIB-22 Huayna Potosí Granite 1.13 70.64 742
RIB-19 Huayna Potosí Granite 1.24 71.78 738
RIB-56 Huayna Potosí Granite 1.14 73.30 790
RIB-55 Huayna Potosí Granite 1.12 73.76 749
GRS 1 Huayna Potosí Granite 1.70 73.93 724
RIB-5 Huayna Potosí Granite 1.09 73.95 734
RIB-30 Huayna Potosí Granite 1.06 74.07 678
RIB-2 Huayna Potosí Granite 1.13 74.71 728
RIB-4 Huayna Potosí Granite 1.12 74.95 726
S-19-Apl Illampu Aplite 1.47 78.55 750
Geometric mean of Zr saturation temperatures (°C) granites 735.4

Whole rock data was taken from unpublished compiled data. M values correspond to the ratio of (Na+K+2Ca)(AlSi) , SiO2 in wt%.

FIG. 21 Zircon saturation temperatures. Top: Histogram of Zr saturation temperatures. Bottom: Temperatures (°C) versus SiO2 (wt%) diagram. Unpublished whole rock dataset for granitoids from the Cordillera Real. 

The quartzdiorite enclaves of the Illampu and Taquesi granodiorites both yielded slightly older ages than their hosts. This can be explained by the zircon saturation temperatures discussed above, where higher temperatures are needed for mafic magmas to saturate in Zr (Siégel et al., 2018). Therefore, it is possible that the enclaves simply did not crystallize zircon and probably host antecrystal zircons from older pulses.

6. Discussion

6.1. Magmatic pulses

The main goal of this paper is to obtain a better knowledge of the crystallization age of the Cordillera Real granitoids. However, as it can be seen in the Concordia diagrams of figures 4 to 20, it is not an easy task to obtain a single Concordia age to constrain the crystallization of these plutons.

At the larger regional scale we should consider the longevity of granitoid formation in continental arcs. Magmatism above subduction zones (melts, mushes, etc.) is episodic in space and time, at scales ranging from entire arcs to simple volcanoes. To study the temporal histories of magmatic arcs, several hundred (or more) U-Pb zircon measurements may be needed.

A large number of ages recording the periodicity of large arc-related magmatic systems has been documented along the western coast of the American continent (Paterson and Ducea, 2015). Time intervals for Mesozoic magmatic and bedrocks average 60-70 Ma, while for Cenozoic rocks the average is 20-30 Ma. For the case of the well studied and purely slab-related Sierra Nevada Batholith, a period of 72 Ma during the Triassic was found. In this context, relatively short time intervals of high magma addition rates are termed “flare-ups”. A well documented flare-up has been studied by De Silva and Gosnold (2007) in the Central Andes, known as the Altiplano Puna Volcanic Complex (APVC), which lasted 10 Ma and implies the construction of a batholith over that interval of time. These magmatic pulses and their protracted character is also supported by geochronological, geophysical, field and thermodynamic evidence, implying that plutons of batholithic size accumulate in several pulses over protracted time intervals (Glazner et al., 2004). Following their model, a “regular” magma chamber of 5 km thick and 20 km wide, at 900 °C and a normal gradient of 20 °C/km will be completely crystallized in less than 1 Ma.

In our case, we have a long-lasting subduction system during the Gondwanide orogeny that started at 336 to 285 Ma (early stage) and ended at 230 to 205 Ma (late stage, Ramos, 2018). The wide range of observed zircon ages from 200 to 280 Ma for these cool magmas suggests the presence of antecrysts produced in earlier flare-up pulses of a protracted magmatic arc (Paterson and Ducea, 2015). From the previous Concordia plots (Figs. 4 to 18), we believe that our plutons may record a final crystallization episode, in which pre-existing zircon crystals formed during former magmatic pulses are present. These zircon antecrysts may not have been reabsorbed due to the low temperature of these “cool magmas” (section 5.2), although their CL images (Fig. 3) show that they are indistinguishable from the new zircon crystals, formed during the final crystallization episode.

In order to visualize better this magmatic pulses, the Concordia ages obtained in our study (Figs. 4 to 20), were used to elaborate the figure 22 that displays histogram plots and respective kernel density curves, calculated using the software R (R Core Team, 2020)1. For the case of the Huato pluton, the 11 Concordia ages of sample RIB-27 were used. For the case of the Illampu pluton samples RIB-32, RIB-33 and RIB-15 were combined (n=34). For the Taquesi pluton, we combined samples RIB-11 and RIB-12 (n=16). For the case of the Huayna Potosí pluton, samples RIB-2, RIB-4, RIB-19, RIB-20 and RIB-22 were combined (n=59). The few zircon ages that range from 260 to 280 were considered as early Gondwanide zircons and ages older than 400 Ma were rejected as we considered them as xenocrysts derived from the country rocks. Although subtle, two predominant peaks seem to appear on the populations of these four plutons.

FIG. 22 Histogram plots of Concordia ages of the Huato, Taquesi, Illampu and Huayna Potosí plutons showing number of samples (n) and in red the kernel density curves. In each case, the age distribution seems to display two peaks near 220 and between 230 to 240 Ma, maybe related to climatic flare-ups. Overall, the age pattern shows a protracted magmatism of about 60 Ma. 

In figure 23, two histograms display all measured Triassic and Oligocene Concordia ages. For the case of the Quimsa Cruz pluton, the two samples (RIB-43 and RIB-46) were combined, n=29. The age range suggests a main magmatic pulse from 28 to 25 Ma, with an early “antecrystic” population at 29-30 Ma. In the case of the Triassic ages, a protracted range of 60 Ma is displayed, possibly characterized by two pulses at 220 and 235 Ma.

FIG. 23 Probability density plot of Concordia ages of the Triassic and Oligocene (Quimsa Cruz) plutons from the Cordillera Real showing number of samples (n) and in red the kernel density curves. 

Although it is tempting to constrain these two peaks of Concordia ages at 220 and 235 Ma for the whole Cordillera Real Triassic magmatism, as proposed by Cordani et al. (2019), we remain cautious and rather suggest a long time interval, probably biased by the existence of antecrysts formed in preceding pulses. This overall interval of 60 Ma falls within the range studied by Paterson and Ducea (2015) for arc-related Mesozoic magmatism: the age range recorded in the zircon antecrysts of the Cordillera Real plutons corresponds to magmatic pulses that were precursors of the final magmatic episode at 220 Ma.

6.2. Xenocrystic population

As mentioned in Section 5.2, tables 2A to 2O include xenocrystal zircons with ages older than 300 Ma. Ages between 300 to 400 Ma could correspond to late Paleozoic magmatic rocks belonging to the Gondwanide orogeny. Some older ages are probably related to the early Paleozoic Famatinian arc and the largest peaks can be assigned to a late Neoproterozoic (Brasiliano) cycle. Even older sources are represented, sometimes by single zircon grains, with ages spanning the Proterozoic eon up to 2500 Ma.

Locally, the geodynamical environment in which the Triassic Real Cordillera granitoids were formed corresponds to a continental rift linked to the breakup of Pangea (Jiménez and López Velásquez, 2008; Sempere et al., 2002; Ramos, 2018). The volcano-sedimentary Mitu Group in SE Perú is representative of this environment and the younger detrital zircon population from these sequences yields a U-Pb age of around 255 Ma (Spikings et al., 2016). The probable “antecryst age” of about 250 Ma recorded in many of the zircon crystals of the Huayna Potosí pluton can be considered coeval with the initiation of the Mitu Rift. If the younger crystallization age of 222 Ma is considered as the end of both plutonism and the rifting stage, then it can be said that the duration of this local extensional regime was probably about 30 Ma. This interval seems to be reasonable for this type of environment and even falls within the shorter category when compared to longer time estimates (e.g., 55 Ma for the Norwegian-Greenland Sea Rift, Ziegler and Cloetingh, 2004).

6.3. The end of the magmatism. Rapid cooling and secondary processes

If we take in consideration the Ar-Ar age obtained by Gillis et al., 2006, for the Huayna Potosí pluton (which was not affected by the thermal anomaly of the ZSGZ), with a well-defined plateau at 218±3 Ma, it is the same, within experimental error, with our statistically optimal U-Pb age of 221±3 Ma for the RIB-2 sample. Therefore, these two isotopic systems may have been closed at almost the same time, with fast cooling after this last magmatic pulse. Probably it means that the regional Sn-W mineralization may also have been contemporaneous with the crystallization and cooling of this pluton.

The final enrichment in fluids, bearing highly incompatible elements at the final stage of the pluton consolidation could be associated with the U anomalies, sometimes bringing excess U and Pb to the zircons of the Cordillera Real granitoids. Probable remobilization of U and Pb associated to damage of the zircon crystal lattice and a potential matrix-related calibration bias during secondary ion mass spectrometry (SIMS) analysis (Kusiak et al., 2013) produced the reverse discordias of figure 11.

Conclusions

The granitic plutons of the Cordillera Real fall within the “inner magmatic arc”, in a regional context of the Central Andes and holding an intraplate imprint reflected in the geotectonic and temporal environment. We have also contributed to the understanding of the generation of these plutons, indicating a possible time span for their emplacement and evolution.

All plutons of the Cordillera Real yielded U-Pb zircon ages showing the succession of magmatic events in time. It seems that all record a final crystallization episode with a similar Late Triassic age, preceded by magmatic pulses whose age is recorded by antecrysts. The Huayna-Potosí is the pluton with the most data and accounts for a protracted magmatic system history of about 60 Ma. One sample yielded an 40Ar-39Ar age of 218±3 Ma, which can be considered as a cooling age of the pluton. The overlap of the younger zircon population of sample RIB-2 (221±3) and the mentioned 40Ar-39Ar age indicates a rapid cooling interval for the granite.

The zircon saturation method yielded “low” average temperatures suggesting that the Real Cordillera plutons correspond to cold and consequently inheritance-rich granitoids. These cold granites recorded important xenocrystal and antecrystal inheritance, reflecting important geological events of magmatic crystallization from Precambrian to Phanerozoic times. U-Pb zircon geochronological studies of the antecrysts included in the plutons of the Cordillera Real could be of great help in deciphering the history and duration of the magmatic pulses, which would be very important to understanding the origin and development of the continental crust. The studied plutons also record the influence of the Gondwanide orogeny (336-205 Ma) as an overall subduction arc environment, punctuated in its final stage by continental rifting (245-220 Ma) related to the Mitu Rift.

Enrichment of residual melts in incompatible elements, probably related to the W-Sn mineralization stage, as well as posterior damage of the zircon crystal lattice could be the cause of reverse Discordia recorded by the Zongo/Kuticucho granite.

1R Core Team 2020. R.A. Language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/.

Acknowledgments

We would like to thank to the technical staff of the Centro de Pesquisas Geocronológicas (CPGeo), the professors of the Instituto de Geociências of the University of São Paulo and the professors of the Universidad Mayor de San Andrés for their help, dedication and technical support during the realization of the present paper. Special thanks to W. Vivallo and R.J. Pankhurst who kindly and thoroughly reviewed our paper.

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Received: February 07, 2020; Accepted: December 10, 2020; pub: May 31, 2021

* Corresponding author: arodrigoiriarte@gmail.com

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