METAMORPHISM AND DEFORMATION OF AN EARLY PERMIAN EXTENSIONAL BASIN SEQUENCE - THE MANNING GROUP, SOUTHERN NEW-ENGLAND OROGEN

The Manning Group is a deformed Early Permian extensional sedimentary basin sequence cropping out in the southern New England Orogen. Peak m etamorphism occurred during burial, with zeolite facies succeeded by p rehnite-pumpellyite facies assemblages at greater depth. Temperatures ranged from 160 to 260 degrees C according to vitrinite reflectance (R (0)) and chlorite geothermometric studies. Limited R(0)-depth data ind icate a geothermal gradient of similar to 24 degrees C/km, suggesting that similar to 10 km of Early Permian sedimentary rocks existed prior to erosion and that the Manning Group is similar to 4 km thick. Two d eformation events are recognised in the Manning Group. D-1 was caused by east-west compression and produced meridional folds and thrusting. East-west compression was also operative during D-2. At this time sigm a(3) changed from vertical to horizontal, which resulted in rotation o f the meridional structures into a southeast trend during sinistral mo vement on the Manning Fault System and the formation of cleavage in ad jacent high-strain zones. It is suggested that extension was accomplis hed by movement on a detachment fault.