Volume 38: January - December 1997

Issue 1: January 1997

Abstract

High-pressure ( 2000 MPa) kyanite- and glaucophane-bearing pelitic schist and eclogite from Cordillera de la Costa Belt, Venezuela

VB. Sisson, IE. Ertan and HGA. Lallemant Department of Geology and Geophysics, Rice University, MS-126, Houston, TX 77005-1892, USA and Corresponding author Email: Jinnys@rice.edu
ABSTRACT
In the Cretaceous melange of the Cordillera de la Costa belt, north-central Venezuela, there are knockers of eclogite, and pelitic glaucophane schist. These occur in a metamorphic melange matrix that locally consists of marble, serpentinite, amphiobolite, actinolite schist, feldspathic shcist and gneiss, graphitic schist, chloritoid schist, and garnet-bearing mica schist. The protoliths for these various rock types exhibit a wide age range (Cambrian to Early Cretaceous?). Recently discovered knockers of pelitic glaucophane schist contain Mg-glaucophane + paragonite + kyanite + garnet + talc + graphite + rutile + quartz. The coexistence of kyanite and Mg-glaucophane suggests minimum P 2000 MPa at T >600^oC. Eclogite knockers from the same outcrop contain garnet and clinopyroxene which yield 500^oC for cores, 700^oC for rims, and P >= 1200 MPa. The assemblage garnet-biotite-phengite-albite within schists of the melange matrix of this locality indicates metamorphic conditions of T = 450-520^oC at P = 1800 MPa. Because all lithologies in this outcrop record high-P conditions, this metamorphic melange formed before or during peak metamorphism in a mid-Cretaceous subduction zone.

Keywords: geothermobarometry; high-P pelitic schist; eclogite; Puerto Cabello, Venezuela.

Pages: 65 - 83

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