Tectonic significance of multiple motions on terrane-bounding faults in the northern Appalachians

Abstract

Faults bounding three tectonostratigraphic terranes in southeastern New England have been studied to determine their role in the accretion of northern Appalachian terranes. Different fault segments have experienced different motion histories. The earliest documented motion occurred on the Bloody Bluff fault and consisted of deep-seated sinistral faulting active sometime during Middle Silurian-Early Devonian time. Comparison with stratigraphic, paleomagnetic, and paleontologic data suggests that this episode of motion was associated with accretion of northern Appalachian terranes. Alleghanian (Permian) reactivation of some fault segments (Lake Char, Honey Hill, Willimantic, and Clinton-Newbury) removed any evidence of earlier motion, although xenoliths of mylonite in a Silurian-aged gabbro suggest that these fault segments were a southward continuation of the Bloody Bluff fault. Late Paleozoic reactivation resulted in low-angle normal motion with the hanging wall moving toward the northwest. Motion began when the area was at upper greenschist- to lower amphibolitefacies conditions and continued during uplift and cooling to temperatures below the brittle-ductile transition temperature of quartz. The tectonic environment of these normal motions was most likely associated with a releasing bend in a major, pan-Appalachian Alleghanian-aged dextral fault system.