Constraining the timing and evolution of a long-lived tectonic boundary: An example from the early paleozoic, Argentina

RADICE, STEFANIA; SOLA, ALFONSO M.; MAFFINI, M. NATALIA; D'ERAMO, FERNANDO J.; WEINBERG, ROBERTO F.; PINOTTI, LUCIO P.; DEMARTIS, MANUEL; CONIGLIO, JORGE E.; BOFFADOSSI, M. ALEJANDRA; MURATORI, M. EUGENIA

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2021

0895-9811

The Guacha Corral shearzone (GCSZ) is one of the most prominent crustal-scale shear zones in the Eastern Sierras Pampeanas of Argentina, juxtaposing twodifferent metamorphic terranes: the eastern hanging wall,which was metamorphosed in the 550-510 Ma Pampean Orogen, andthe western footwall, metamorphosed in the 500-440 Ma Famatinian Orogen. In this study, the tectono-thermal evolution of thefootwall was constrained using U-Pb dating of zircon,monazite and apatite, and results were compared to the broader evolution of the shear zone. The main episode ofmigmatization was recorded in the footwall at ~475 Ma by zirconand monazite, indicating anatexis during the Famatinian Orogeny at amphibolitefacies conditions (~700 °C - Ti-in-zircon 25 thermometer). It was at this time that the major thrusting event was taking place dueto the docking of the Precordillera/Cuyania terrane to theproto-Andean margin. Anatexis in the footwall was followed by cooling reaching upper greenschist facies conditionsrecorded by apatite U/Pb ages at ~400 Ma. The cooling rates duringretrogression of footwall migmatites from ~690 °C to ~500 °C were at ~3-4 °C/Ma. The cooling processes after peakmetamorphism were temporally related to the waning of theFamatinian Orogeny during the early Devonian. After crossing apatite closure temperature, rocks entered greenschistfacies conditions and continued motion on the shear zone favored theinflux of fluids to retrogress the footwall. This late motion istemporally related to the collision of the Chilenia terrane to the proto- Andean margin at ~390 Ma, marking the start of the Chanic/AchalianOrogeny.