Geophysical evidence for an extensive Pie de Palo Complex Mafic-Ultramafic belt, San Juan, Argentina

CHERNICOFF, C.J., VUJOVICH, G.I., VAN STAAL. C.R.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Año: 2009 p. 325 - 332

0895-9811

The recent completion of a high-resolution aeromagnetic survey over the Pie de Palo uplift of the western Sierras Pampeanas, has revealed an area of large magnetic anomalies associated with the Pie de Palo Complex. The Las Pirquitas thrust, which has transported and uplifted the Pie de Palo Complex, is recognized for at least 30 km in a roughly NE direction along the western boundary of the Pie de Palo Complex, beyond its limited outcrop. The type of sediments of the Caucete Group in the footwall of the Las Pirquitas thrust, which are regarded as the leading edge of the Precordillera terrane, are associated with much less pronounced magnetic anomalies. In addition, a conspicuous, NNE trending, broad magnetic high stands out in the survey, several Kms to the east of the main outcrops of the Pie de Palo Complex; this broad magnetic anomaly bisects the Pie de Palo basement block, and continues further south at least as far as 32°S the sounthern boundary of the latest aeromagnetic survey. This magnetic anomaly is interpreted to represent a structure corresponding to the Grenvillian Precordillera-Pie de Palo tectonic boundary zone, and would comprise the buried largest part of the mafic-ultramafic belt. The geophysical model of the magnetic data indicates that the boundary zone dips to the east, possibly suggesting the existence of a set of synthetic east dipping, west-verging thrusts, of which only one major structure (Las Pirquitas thrust) is exposed; the possibility of other slivers of upthrust boundary zone material can not be escluded. It is considered that the Pie de Palo Complex represents a small sliver upthrust from the unexposed boundary zone material (containing highly magnetic mafic-ultramafic rocks). The east-dipping,west verging structures associated with the Pie de Palo Complex are suggested to represent an Ordovician reactivation of a Grenvillian suture zone developed when the Precordillera basement and Pie de Palo terrane docked; this reactivation probably resulted fron the collision of the Cuyania terrane onto the western margin of Gondwana.