Calcite and quartz microstructural geothermometry of low-grade metasedimentary rocks, Northern Range, Trinidad

The Northern Range of Trinidad is a mountainous exposure of deformed metase dimentary rocks with Mesozoic depositional ages and Tertiary metamorphic ag es located in the Caribbean-South American plate boundary zone. These rocks lack precise mineralogical indicators of metamorphic grade. Using temperat ure-sensitive quartz and calcite microstructures, and fission track data, w e identify, describe, quantify, and map a nearly continuous spectrum of rel atively low (>150 degreesC) To relatively high (250-400 degreesC) deformati on temperatures from east to west across the range. Average estimated rock exhumation rates also increase systematically along this trend. The analysi s illuminates a sharp, east-west-trending. major thermal discontinuity (i.e . a fault) along the southern boundary of the range. Kinematic analysis of faults and shear bands adjacent to this boundary and modeling indicate that the fault probably dips southward at 80-85 degrees and accommodated normal dip-slip at rates that decreased from west to east. Earlier experimental s tudies at high strain rates illustrated a strong strain rate dependency for quartz microstructural transitions. Our work indicates a possible strong t emperature control for quartz microstructural transitions at natural strain rates. (C) 2001 Elsevier Science Ltd. All rights reserved.