Microestructuras en xenolitos de basaltos postplateau. Meseta de Somún Curá. Provincia de Río Negro

CERREDO, M. E.,; REMESAL, M.

Asociaciòn Geológica Argentina Serie D

Asociación Geologica Argentina

Lugar: Buenos Aires; Año: 2001 vol. 5 p. 65 - 68

0328-2767

ABSTRACT. Microstructnres in xenoliths of postplateau basalts. Meseta de Somun Curd. Rio Negro Province. The Somiin Cura basaltic plateau occurs in the northern extra-Andean Patagonia. The Tertiary volcanism of Somun Cura consists of extensive Oligocene olivine plateau basalts, the major part of the plateau is covered by younger alkali basalts, typically rich in xenoliths and xenocryslals. These post-plateau basalts enclose small (cm-scale), generally rounded xenoliths which may be grouped in two main suites: 1) an acid group, composed of quartz-feldspar assemblages, which displays brittle-ductile deformation features and 2) a basic group of fairly uniform gabbroic composition. These show a span of microstructu.es which vary from mainly brittle to ductile in character. The xenoliths of acid lithologies invariably show microstructures related to the battle-ductile regime, with microcracking/ frictional sliding and minor evidences of incipient recovery. The gabbroic xenoliths display similar modal compositions (gahbros/noritcs) and a span of deformation features. These vary from virtually undeformed to partially recrystallizcd, oriented fabrics. Therefore, the present meseta crust, as imaged by the xenoliths brought by the Post-plateau Basalts in route to the surface, would be composed of both felsic and mafic lithologies. The former might have undergone widespread brittle deformation, whereas the mafic units have been affected by heterogeneous, not pervasive, deformation likely in the form of discrete medium-T shear zones.