High-pressure/low-temperature metamorphism in the collision zone between the Chilenia and Cuyania microcontinents (Western Precordillera, Argentina)

BOEDO, FLORENCIA L.; MASSONNE, H.-J.; VUJOVICH, GRACIELA I.; WILLNER, ARNE P.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016 vol. 72 p. 227 - 240

0895-9811

In central-western Argentina, a Paleozoic belt including mafic-ultramafic bodies, marine metasedimentary rocks and high-pressure rocks occur along the western margin of the Precordillera and in the Frontal Cordillera. First pressure-temperature estimates are presented here for low-grade rocks of the southern sector of this belt based on two metasedimentary and one metabasaltic sample from the Peñasco Formation. Peak metamorphic conditions resulted within the range of 345-395°C and 7.0-9.3 kbar within the high pressure greenschist facies. The corresponding low metamorphic gradient of 13°C/km is comparable with subduction related geothermal gradients. Comparison between these results and data from other localities of the same collision zone (Guarguaraz and Colohuincul complexes) confirms a collision between Chilenia and the composite margin of South America and suggests a stronger crustal thickening in the south of the Paleozoic belt, causing exhumation of more deeply buried sequences. During the Early Paleozoic a long-lived marine sedimentation coupled with the intrusion of MORB-like basalts occurred along a stable margin before the collision event. This contrasts with the almost contemporaneous sedimentation registered during accretion in accretionary prism settings and additionally proves the development of a collision zone along western Precordillera and the eastern Frontal Cordillera as well as the existence of Chilenia as a separate microcontinent.