Tectonothermal evolution and exhumation history of the Paleozoic Proto-Andean Gondwana margin crust: The Famatinian Belt in NW Argentina

DE LOS HOYOS C.; WILLNER, A.; LARROVERE, M.; ROSSI, J.N.; TOSELLI, A.J.; BASEI, M.A.

GONDWANA RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2011 vol. 20 p. 309 - 324

1342-937X

We studied the P–T–t evolution of a mid-crustal igneous-metamorphic segment of the Famatinian Belt in theeastern sector of the Sierra de Velasco during its exhumation to the upper crust. Thermobarometric andgeochronological methods combined with field observations permit us to distinguish three tectonic levels.The deepest Level I is represented by metasedimentary xenoliths and characterized by prograde isobaricheating at 20–25 km depth. Early/Middle Ordovician granites that contain xenoliths of Level I intruded in theshallower Level II. The latter is characterized by migmatization coeval with granitic intrusions and aretrograde isobaric cooling P–T path at 14–18 km depth. Level II was exhumed to the shallowest supracrustalLevel III, where it was intruded by cordierite-bearing granites during the Middle/Late Ordovician and its hostrockwas locally affected by high temperature–low pressure HT/LP metamorphism at 8–10 km depth. Level IIIwas eventually intruded by Early Carboniferous granites after long-term slow exhumation to 6–7 km depth.Early/Middle Ordovician exhumation of Level II to Level III (Exhumation Period I, 0.25–0.78 mm/yr) was fasterthan exhumation of Level III from the Middle/Late Ordovician to the Lower Carboniferous (Exhumation PeriodII, 0.01–0.09 mm/yr). Slow exhumation rates and the lack of regional evidence of tectonic exhumation suggestthat erosion was the main exhumation mechanism of the Famatinian Belt. Widespread slow exhumationassociated with crustal thickening under a HT regime suggests that the Famatinian Belt represents the middlecrust of an ancient Altiplano–Puna-like orogen. This thermally weakened over-thickened Famatinian crustwas slowly exhumed mainly by erosion during ~180 Myr.