Las ofiolitas famatinianas (eopaleozoico) de la Precordillera

HALLER MJ; RAMOS VA

Buenos Aires

Congreso; IX Congreso Geológico Argentino; 1984

Based on new field evidences together with the geochemical analyses a reinterpretation of mafic and ultramafic rocks outcropping in the western Precordillera of San Juan and Mendoza and its southern extension in the foothills of the Cordillera Frontal of Mendoza is presented here. These rocks are considered as ophiolites taking in account their lithologic and structural features. An almost complete sequence represented by ultramafic rocks, gabbros, pillow basaltic lavas and lava flows, associated to turbiditic and pelagic sediments is recognized. The longitudinal development of the ophiolites along hundreds of kilometers allows defining a continental suture. The geochemical characteristics of the upper section of the ophiolites are typical of ocean floor tholeites, probably belonging to an anomalous oceanic ridge bearing a high Ti02 content. The close correlation of major and trace elements between the gabbros of Cortaderas and the basalts and associated rocks suggests their origin in a common tectonic environment. This environment is interpreted as composed by a set of oceanic ridges segmented by transform faults, obliquely subducted during the Early Paleozoic. The structural level presently exposed shows a higher structural relative uplift of the suture zone in the southern segment. The occurrence of these Famatinian ophiolites implies the existence of allochtonous blocks accreted from the west to the South American continent during Early Paleozoic times.