Faja Intrusiva La Majada, sierra de Ancasti, Catamarca: Caracterización petrológica-estructural

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Abstract

La Faja Intrusiva La Majada se extiende con rumbo NNO-SSE a lo largo de 40 km aproximadamente, en el sector centro - sur de la sierra de Ancasti, SE de la provincia de Catamarca. Está constituida por un basamento metamórfico compuesto por esquistos y gneises bandeados cuyas paragénesis minerales corresponden a un metamorfismo de mediano a alto grado. Están deformados según dos episodios D1 y D2. En este tramo de la sierra, donde la deformación D2 es más intensa, se produce un importante magmatismo, representado por la intrusión de una secuencia ígnea sintectónica cuya composición varía de gabros y dioritas, tonalitas, granodioritas y monzogranitos. Su emplazamiento se produjo en el pico del metamorfismo M2, junto con el desarrollo de procesos de fusión del cual resultaron distintos tipos de migmatitas. También se reconoce la intrusión de granitos, leucogranitos y pegmatitas, que se emplazan en una etapa sin a tardío tectónica. El estrecho vínculo entre mayor deformación y metamorfismo, con desarrollo de migmatitas y mayores volúmenes de emplazamientos de plutonitas sugiere que el magmatismo, metamorfismo y deformación estarían estrechamente vinculados temporalmente y ligados a una zona de cizalla profunda de edad paleozoica inferior.

Translated abstract

La Majada area occur within a NNW-SSE trending along 40 kilometers in the SE Catamarca province. Is formed by schists and gneisses where the first schistosity (D1) is tightly folded and transposed by a second deformation (D2), which is coeval with the peak metamorphism (M2) and magmatism. Synkinematic granitoids emplacements are two different suites of igneous rocks : a) a magmatic sequence, consisting of small gabbro - diorite bodies and tonalite, granodiorite and monzogranite plutons; and b) granites, leucogranites and pegmatites. The relations between folds and crenulation cleavage in the metamorphic rocks and deformational fabrics in the granitoids and migmatites provide good evidence for the penecontemporaneity of deformational processes, magmatism and migmatization.

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Most cited references 23

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Melt segregation and magma flow in migmatites: implications for the generation of granite magmas

E. SAWYER (1996)

To form a granite pluton, the felsic melt produced by partial melting of the middle and lower continental crust must separate from its source and residuum. This can happen in three ways: (1) simple melt segregation, where only the melt fraction moves; (2) magma mobility, in which all the melt and residuum move together; and (3) magma mobility with melt segregation, in which the melt and residuum move together as a magma, but become separated during flow. The first mechanism applies to metatexite migmatites and the other two to diatexite migmatites, but the primary driving forces for each are deviatoric stresses related to regional-scale deformation. Neither of the first two mechanisms generates parental granite magmas. In the first mechanism segregation is so effective that the resulting magmas are too depleted in FeO T , MgO, Rb, Zr, Th and the REEs, and in the second no segregation occurs. Only the third mechanism produces magmas with compositions comparable with parental granites, and occurs at a large enough scale in the highest grade parts of migmatite terranes, to be considered representative of the segregation processes occurring in the source regions of granites.