Data for: The Cumbres Calchaquíes Range (NW-Argentina). Provenance, tectonic setting and metamorphic evolution of a Neoproterozoic sedimentary basin

Published: 30-03-2019| Version 1 | DOI: 10.17632/m6yz2thr47.1
Contributors:
jose pablo lopez,
LAURA BELLOS,
Christina Günter,
UWE ALTENBERGER

Description

The Cumbres Calchaquíes form a part of the Famatinian metamorphic basement of the Eastern Sierras Pampeanas. The sedimentary protoliths of the metamorphic sequence were deposited in a marine basin along the western margin of Gondwana during the Neoproterozoic. New petrologic, geochemical and thermobarometric informations give inside into the evolution of the sedimentary basin, its sediment source area, its later metamorphic overprint and the its relation to the other parts of the basin. The studied series is composed of banded schists and gneisses and rare calcsilcate-felses and migmatites reworked by mid- to deep-crustal metamorphic and structural processes. The bulk rock composition displays former shale, wacke, marl (later calcsilicate-fels) as well as litharenitic protoliths. The metamorphosed clastic sediments have a major and trace element composition pointing unequivocally to an upper continental granitoid-dominated crustal source area with low sediment recycling. The acidity grade of the previous sediments suggests relatively low maturity. Therefore, the Cumbres Calchaquíes records a sedimentary sequence of turbidity currents with shifting of the depositional environments to lower water depth, as indicated by quartz- and carbonate-rich sediments. The overall data consistently suggest that the geodynamic environment was a basin controlled by a continental magmatic arc as the most probable scenario. for the deposition of the sedimentary precursors of the studied units. Whereas the sedimentary protoliths of the metamorphic basement of the Sierra de Ancasti and Sierra de Aconquija, located ca 100-300km to the South are interpreted as originating from a probably evolving back-arc basin, the source area of the Cumbres Calchaquíes sediments is a pronounced felsic magmatic continental arc with no significant influx of debris of basic rocks. The later, Famatinian, metamorphic evolution shows typical prograde Barrow-type metamorphism culminating in partial melting of the metasediments. Conventional and internally-consistent thermobarometric calculations (pseudosections) reveal prograde metamorphic evolution reaching peak conditions of up to 700°C and 0.7 GPa. This points to a slightly increased geothermal gradient of ca 33°C, suggesting a period of crustal thinning, as known from back-arc basins or to additional heat supply by voluminous intrusions nearby.

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