Xenolith Constraints on Northern Appalachian Lithosphere -A Pilot Study

University Of Maryland, College Park, College Park MD

Investigators

Abstract

EAR-0106586 Minarik The northwestern Appalachians in New York, Vermont and Quebec experienced a complex geologic history. Mesoproterozoic collisional tectonics are recorded in rocks exposed in the Adirondack Mountains and as erosional windows in the Appalachians of New England. Subsequent rifting and development of an oceanic basin was followed by episodic Paleozoic convergence and accretion to the eastern edge of North America, forming the Appalachian chain. This was followed by Triassic-Jurassic extension and rifting resulting in the modern North Atlantic basin. Current knowledge of the lower continental crust and continental lithospheric mantle in this area is derived primarily from geophysical methods and studies of tectonically exhumed high pressure units. Upper-crustal and lower-mantle xenoliths in Cretaceous Monteregian dikes offer a unique glimpse into the northwestern Appalachian lithosphere. This study aims to determine the thermal, tectonic and geochemical evolution of rocks represented by these xenoliths. Petrography and geothermobarometry of the xenoliths will constrain the P-T history of the assemblages sampled by the dikes. Sm-Nd and Re-Os isotopic systematics of the crustal and mantle xenoliths will give the age of formation and of isolation from the convecting upper mantle. These constraints on the nature of the deep crust and lithospheric mantle will be applied to unravel questions about the evolution of the lithospheric mantle and lower crust during Appalachian deformation and accretion. The proposed Sm-Nd and Re-Os isotopic measurements represent a first for xenoliths from this area.