%0 Journal Article
%T Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin Metamorfismo de bajo grado de sucesiones cambro-ordov赤cicas en el cintur車n del Famatina, Andes Centrales de Argentina: Historia de enterramiento-exhumaci車n ligada a la evoluci車n del margen proto-andino de Gondwana
%A Gilda Collo
%A Margarita Do Campo
%A Fernando Nieto
%J Andean Geology
%D 2011
%I Servicio Nacional de Geolog赤a y Miner赤a (SERNAGEOMIN)
%X The metamorphic P-T conditions of low-grade units from the Famatina belt, Central Andes of Argentina, were estimated through petrography, X-ray diffraction, and electron microscopy. For the Middle-Upper Cambrian Negro Peinado Formation a tectono-metamorphic event associated with intense intrafoliar folding, with estimated temperatures between 290 and 400∼C (KIcis: 0.16-0.27A∼29, biotite blastesis and compositional homogeneity in dioctahedral micas) and intermediate pressure conditions (white mica b parameter: 9.010芍-9.035芍), was recognized. The Achavil Formation (Middle-Upper Cambrian) presents a main metamorphic event associated with temperatures between 200 and 290∼C (KIcis: 0.26-0.41A∼29) and intermediate- to low-pressure conditions (white mica b parameter values: 8.972芍-9.017芍). Some illitic substitution in dioctahedral micas also indicates lower metamorphic grade than the Negro Peinado Formation. For Upper Cambrian to Middle Ordovician sequences a burial metamorphic pattern, with a progressive decrease in metamorphic grade from Volcancito Formation to Cerro Morado Group (ca. 490-465 Ma; KIcis: 0.31-0.69A∼29) and absence of tendency changes linked to strati-graphic discontinuities was proposed. Mica and chlorite are the main phyllosilicates in the oldest units, while Ilt/ Sme (R3) mixed-layer is almost the only one in the youngest. White mica b parameter indicates intermediate- to low-pressure conditions for all these sequences. This burial metamorphic pattern presents a marked break as the youngest Ordovician unit (La Aguadita Formation, after ca. 452 Ma) records higher metamorphic conditions (IKcis: 0.28-0.19A∼29) than units from the Ordovician arc, with estimated temperatures between 270 and 330∼C and intermediate-pressure conditions. Our results indicate that basin contraction and inversion processes related to the Ordovician Ocloyic Orogeny involved at least two well-discriminated and not superposed metamorphic episodes in this region. Las condiciones P-T del metamorfismo de las unidades de bajo grado del cintur車n del Famatina, Andes Centrales de Argentina, fueron estimadas mediante petrograf赤a, difracci車n de rayos-X y microscop赤a electr車nica. La Formaci車n Negro Peinado (C芍mbrico Medio-Superior) fue afectada por un evento tectono-metam車rfico asociado con un plegamiento intrafoliar intenso, para el cual se estimaron temperaturas entre 290 y 400∼C (IKcis: 0,16-0,27 A∼29, bl芍stesis de biotita y homogeneidad composicional en micas diocta谷dricas) y presiones intermedias (par芍metro b de la mica blanca: 9,010 芍 y 9,035 芍). La Formaci車n Achavil (C芍mbric
%K Margen occidental de Gondwana
%K Orogenia Ocl車yica
%K Cintur車n de Famatina
%K Metamorfismo de bajo grado
%K Western Gondwana margin
%K Ocloyic orogeny
%K Famatina belt
%K Low-grade metamorphism
%U http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062011000200003