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Polyphase white mica growth in low-grade metapelites from La Cebila Metamorphic Complex (Famatinian Belt, Argentina): evidence from microstructural and XRD investigations. (2011)

Verdecchia, Sebastian O. ; Collo, Gilda ; Baldo, Edgardo G.

Pontificia Universidad Catolica de Valparaíso

In: Andean Geology. 2011; 38(2): 268. Published 2011 Aug 09. doi: 10.5027/andgeov38n2-a02.

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Publication Date: 2011-08-09

Description: Two tectono-thermal metamorphic events, M1-D1 (S1, with associated white mica and chlorite: WM1-Chl1) and M2-D2 (S2, with development of WM2-Chl2), are established from polyphase white mica growth for low-grade units from the Ordovician metasedimentary successions of La Cebila Metamorphic Complex in the Famatinian belt (western-central Argentina). The thermobarometric characterization of the M1 main event was carried out by means of clay-mineral analysis and crystallo-chemical parameter measurements. Epizonal (temperatures between 300 and 400ºC) and low-pressure conditions are suggested for M1 event, based in Kübler index values ranging from 0.23 to 0.17 Δº2θ, white mica b parameter values between 9.004 and 9.022 Å (mean of 9.014 Å, n=16) and Si contents between 3.13-3.29 a.p.f.u. Temperatures of ~180-270ºC are estimated for the M2 event, with Kübler index values ranging from 0.31 to 0.46 Δº2θ. The M1-D1 event of La Cebila could be linked to highstrain heating tectono-metamorphic Ordovician regime recorded in others complexes from Famatinian foreland region of Sierras Pampeanas.

Print ISSN: 0718-7106

Electronic ISSN: 0717-618X

Topics: Geosciences

Published by Pontificia Universidad Catolica de Valparaíso

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Early Cambrian U-Pb zircon age and Hf-isotope data from the Guasayán pluton, Sierras Pampeanas, Argentina: implications for the northwestern boundary of the Pampean arc (2016)

Dahlquist, Juan A. ; Verdecchia, Sebastián O. ; Baldo, Edgardo G. ; [et al.]

Pontificia Universidad Catolica de Valparaíso

In: Andean Geology. 2016; 43(1): 137. Published 2016 Jan 08. doi: 10.5027/andgeov43n1-a08.

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Publication Date: 2016-01-08

Description: An Early Cambrian pluton, known as the Guasayán pluton, has been identified in the central area of Sierra de Guasayán, northwestern Argentina. A U-Pb zircon Concordia age of 533±4 Ma was obtained by LA-MC-ICP-MS and represents the first report of robustly dated Early Cambrian magmatism for the northwestern Sierras Pampeanas. The pluton was emplaced in low-grade metasedimentary rocks and its magmatic assemblage consists of K-feldspar (phenocrysts)+plagioclase+quartz+biotite, with zircon, apatite, ilmenite, magnetite and monazite as accessory minerals. Geochemically, the granitic rock is a metaluminous subalkaline felsic granodiorite with SiO2=69.24%, Na2O+K2O=7.08%, CaO=2.45%, Na2O/ K2O=0.71 and FeO/MgO=3.58%. Rare earth element patterns show moderate slope (LaN/YbN=8.05) with a slightly negative Eu anomalies (Eu/Eu*=0.76). We report the first in situ Hf isotopes data (εHft=-0.12 to -4.76) from crystallized zircons in the Early Cambrian granites of the Sierras Pampeanas, helping to constrain the magma source and enabling comparison with other Pampean granites. The Guasayán pluton might provide a link between Early Cambrian magmatism of the central Sierras Pampeanas and that of the Eastern Cordillera, contributing to define the western boundary of the Pampean paleo-arc.

Print ISSN: 0718-7106

Electronic ISSN: 0717-618X

Topics: Geosciences