Geophysical Evidence for Terrane Boundaries in South-Central Argentina

Abstract

The geological interpretation of high-resolution aeromagnetic data over the La Pampa province, in central Argentina, in addition to lower resolution magnetic information from the region of the Neuquén and Colorado basins, leads to the definition of the precise boundaries of the Chilenia, Cuyania, Pampia and Patagonia terranes, as well as that of the Río de la Plata Craton, within the study region. The high-resolution aeromagnetic survey data are compared and studied in conjunction with all the available geological information, to produce a map of the solid geology of this region, which is largely covered by Quaternary sediments. A number of structures of different magnitudes, as well as their relative chronology, are also recognized, i.e., regional faults, sub-regional faults, fractures and shear zones, as well as the most conspicuous magnetic fabric of the basement that reflects its main planar structures. Three different basements are distinguished on the basis of their contrasting magnetic character, and are interpreted to represent the Cuyania and Pampia terranes and the Río de la Plata Craton, separated from each other by large-scale discontinuities. In the western part of the study region an additional major discontinuity separates the Chilenia and Cuyania terranes. In the southernmost area studied, WNW-trending structures are predominant, particularly a major NNE-vergent thrust that indicates the truncation of the Cuyania-Pampia suture and is regarded to be related to the possible collision of the Patagonia terrane. An E–W – trending magnetic and gravity anomaly traversing the full extra-Andean Argentine territory, located immediately to the south of 39°S, represents a major structure. The activation of this structure during the Mesozoic gave rise to the Huincul Ridge and marks the interruption of the distinct N-S structures of the Chilenia, Cuyania and Pampia terranes, as well as those of the Río de la Plata Craton, to the north. This E–W represents the suture zone of the Patagonia terrane.