High-Pressure (~2000 MPa) Kyanite- and Glaucophane-bearing Pelitic Schist and Eclogite from Cordillera de la Costa Belt, Venezuela |
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Authors: | Sisson Virginia B; Ertan Inci Evren; Lallemant Hans G Ave |
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Affiliation: | Department of Geology and Geophysics, Rice University MS-126, Houston, TX 77005-1892, USA |
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Abstract: | Cretaceous melange of the Cordillera de la Costa belt, north–centralVenezuela, there are knockers of eclogite, barroisite-bearingeclogite, and pelitic glaucophane schist. These occur in a metamorphicmelange matrix that locally consists of marble, serpentinite,amphibolite, actinolite schist, feldspathic schist and gneiss,graphitic schist, chloritoid schist, and garnet-bearing micaschist. The protoliths for these various rock types exhibita wide age range (Cambrian to Early Cretaceous?). Recently discoveredknockers of pelitic glaucophane schist contain Mg-glaucophane+ paragonite + kyanite + garnet + talc + graphite + rutile +quartz. The coexistence of kyanite and Mg-glaucophane suggestsminimum P 2000 MPa at T > 600°C. Eclogite knockers fromthe same outcrop contain garnet and clinopyroxene which yield500°C for cores, 700°C for rims, and P 1200 MPa. Theassemblage garnet–biotite–phengite–albitewithin schists of the melange matrix of this locality indicatesmetamorphic conditions of T = 450–520°C at P = 1800MPa. Because all lithologies in this outcrop record high-P conditions,this metamorphic melange formed before or during peak metamorphismin a mid-Cretaceous subduction zone. KEY WORDS: geothermobarometry; high-P pelitic schist; eclogite; Puerto Cabello; Venezuela |
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