New geochronological and isotope data for the Las Chacras ? Potrerillos and Renca batholiths: A contribution to the Middle-Upper Devonian magmatism in the pre-Andean foreland (Sierras Pampeanas, Argentina), SW Gondwana

ALASINO, PABLO H.; MORENO, JUAN A.; DAHLQUIST, JUAN A.; BASEI, MIGUEL A.S.; MORALES CÁMERA, MATÍAS M.; MACCHIOLI GRANDE, MARCOS; GALINDO, CARMEN

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2019 vol. 93 p. 348 - 363

0895-9811

The Las Chacras-Potrerillos together with the Renca batholith (Sierras de San Luis) are the largest Devonian igneousbodies in the Sierras Pampeanas after the Achala batholith (Sierra de Córdoba), all emplaced in the Devonian forelandregion. The Achala batholith has U-Pb ages (SHRIMP or LA-MC-ICP-MS, ranging from 366 to 379 Ma), whilecomparable ages for the Las Chacras-Potrerillos batholith remain absent (a single U-Pb conventional zircon age isavailable for this batholith), and one weighted mean age (U-Pb SHRIMP zircon) is available for Renca batholith. U-Pbzircon LA-MC-ICP-MS data sets from a monzogranite sample of the biotite-amphibole porphyritic granite unit(CHA-101), the largest granitic unit of the Las Chacras-Potrerillos batholith, yielded three ages: 377 ± 3, 384 ± 2, and393 ± 3 Ma. These ages (outside error limits), suggest the existence of a long-lived magmatic plumbing system, ofaround 15 Ma, with intrusion of younger batches into older crystal mushes. This interpretation leads us to assume along period of heating in the source through the earliest Middle - early Upper Devonian ranging from 377 to 393 Ma.Based on previous studies of ascent and emplacement of granitic magmas, we propose that the majority of the zirconages measured could be inherited from a deeper level of the magmatic system (i.e., antecrysts) and only some couldbe assigned to in-situ crystallization during the emplacement in middle-upper crust. Additionally, U-Pb zircon SHRIMPdata sets from a monzogranite sample of the biotite-amphibole porphyritic granite unit (REN-103), the largest graniticunit of the Renca batholith, yielded two ages: 353 ± 4 Ma and 393 ± 3 Ma. The older age is equal to that obtained forthe CHA-101 sample and confirms that the magmatism started in the earliest Middle Devonian. The younger age iscomparable to previous ages determined in micas crystallized in intragranitic pegmatites as well as cooling ages frombiotite hosted in granites of the Las Chacras-Potrerillos batholith, strongly suggesting a long-lasting cooling history ofca. 24 or 40 Ma (according to the crystallization age assumed, 377 or 393 Ma) or a reheating effect at around 350 Maas was suggested in previous works. Recent Carboniferous crystallization ages determined in granites of the SierrasPampeanas produced similar values (i.e., close to 350 Ma), and suggest a longer time of magmatic activity embracingthe Middle-Late Devonian ? Early Carboniferous (~ 40 Ma), in the Devonian foreland (present-day Eastern SierrasPampeanas). Nd and Sr isotopes data from CHA-101 and REN-103 samples (εNdt and 87Sr/86Srt ranging from -3.0to -1.1 and from 0.706861 to 0.707275, respectively), are consistent with previous data reported for the studied graniticunits and suggest a continental source with probable participation of subcontinental lithospheric mantle. TDM values(1.2 and 1.4 Ga) support the idea of an older Gondwana lithosphere source for the studied monzogranites