Estructura del Triásico de la región norte del Macizo Nordpatagónico (40°-41°S, 67°30'-69°45'O) Río Negro

Structure of the Triassic in the northern region of the Northpatagonian Massif. This paper describes the geometry, kinematic and geolo- gic relationships of the structures of the Los Menucos region, in the northern part of the Northpatagonian Massif that is characterized for the extensive outcrops of Late Triassic volcanic rocks accompanied by intrusive and sedimentary rocks. Their structure are characte- rized by large (>120 km) W-E dextral strike-slip faults that show evidence of kilometric displacements (> 7 km). Rocks associated with the Triassic volcanism as clastic sediments, andesitic flows, dacitic domes and extensional epithermal veins, show geometric and kinematic relationships with the faults. Younger rocks, including Cretaceous and Cenozoic sedimentary rocks and Tertiary flow basalts, are not deformed. Our interpretation of the relationships between faulting and volcanism, sedimentation and mineralization and the lack of the signifi- cant post-Triassic shearing, suggest that the age of the deformation was mainly Late Triassic, and some faults would be the shallow expres- sion of Paleozoic basement structures. In this framework it is possible to infer a rift morphology for the northern border of the basin. Faulting shows geometric and kinematic relationships that allow inferring a NNE-SSW to NE-SW regional oblique extension direction. It is consistent with the relationships between hydrothermal veins and faults, which suggest a specific type of the deformation regime at the time of vein formation (dextral transtension).