RELATIONSHIP BETWEEN NEO-ACADIAN MID-CRUSTAL TRANSPRESSION AND EXTRUSION IN THE NEW ENGLAND APPALACHIANS WITH FORELAND BASIN DEVELOPMENT: COMPARISON OF NEW MONAZITE EPMA GEOCHRONOLOGY WITH THE SEDIMENTARY RECORD

It has been established that the Neo-Acadian and Alleghanian orogenies imparted significant effects on the tectonic development of the Northern Appalachians, including the mid-crustal Bronson Hill (BHZ) and Central Maine zones (BHZ) of southern and central New England. New monazite geochronology corroborates previous studies and shows that the preponderance of deformation across the CMZ and BHZ in Massachusetts occurred continuously throughout the Carboniferous. Syntectonic monazite growth occurred from ~355 to ~320 Ma in upper amphibolite and granulite pelitic gneisses that characterize dextral transpression in the CMZ. This followed intrusion of diorites, tonalites, granites, and pegmatites from ~365 to ~355 Ma. The style and timing of deformation extended west of the CMZ into the Greenwich syncline and Monson Gneiss of the BHZ. West of the Monson Gneiss, deformation is characterized by a regional sinistral shear system and monazite ages show a temporal overlap with dextral transpression to the east, with the bulk of ages ranging from ~325 Ma to ~275 Ma. This is consistent with dextral transpression, extrusion, and north-directed lateral escape of a segment of the middle crust in the Carboniferous, and are attributed to a period of oblique convergence between Laurentia and Avalonia/Meguma in the Mississippian. The geographic location between the northern edge of the New York Promontory and Quebec Embayment provided a mechanism for lateral escape of the crustal block and the lateral variation of the style of dextral transpression. Published geochronology also suggests that mid-crustal deformation was focused in this area of New England. Carboniferous dextral convergence has also been documented by foreland basin sediments. The pattern of deposition of earliest Tournaisian Sunbury and Riddlesburg black shales indicate an identical scenario, with intense loading near the New York Promontory, which continued for almost ~45 million years. Basin development was identical, within error, to the onset of plutonism and dextral transpression recorded in the middle crust.