ANOMALOUS, LONG-LIVED UPLIFT ON THE 'PASSIVE' MARGIN OF EASTERN NORTH AMERICA: EVIDENCE FOR MAGMATIC UNDERPLATING, CRUSTAL INTRUSION, AND/OR LITHOSPHERIC DRIPS

On many ‘passive’ margins, a significant episode of uplift and erosion, not predicted by simple lithospheric stretching, develops during the transition from rifting to drifting. To better understand the cause(s) of this anomalous uplift and erosion, we have analyzed and synthesized new and previously published geologic and geophysical data (seismic, field, core, wireline, and vitrinite-reflectance) from onshore and offshore rift basins in the central segment of the Eastern North American (ENAM) rift system (i.e., the Newark, Connecticut Valley, and New York Bight basins) and the northern end of the post-rift Baltimore Canyon trough. Our research shows that a broad, long-lived arch, parallel to the syn-rift and pre-rift crustal fabric, not the continent-ocean boundary, developed on the ENAM margin during and after the rift-drift transition. Restorations suggest that rift basins in the study area were deep, broad, and likely interconnected by latest Triassic time. Arching began during the extrusive and intrusive igneous activity associated with the Central Atlantic Magmatic Province (CAMP, ~201 Ma) in latest Triassic/earliest Jurassic time. As arching began, extension rates increased significantly with increased activity on the rift-basin border faults and the development of new intrabasin normal faults. Arching and erosion continued after rifting and breakup throughout Jurassic time. As a result, the rift basins in the study area underwent significant exhumation, particularly along the axis of the arch between the extant Newark and Connecticut Valley basins where exhumation exceeded 5 km. The eroded material likely contributed to infilling of the adjacent, subsiding post-rift Baltimore Canyon trough, which contains up to 13 km of sedimentary rock, 9 km of which is Jurassic. The characteristics of the arch (i.e. parallelism with syn-rift/pre-rift crustal fabric, not the continent-ocean boundary; coeval onset with CAMP; significant and prolonged exhumation far from the site of breakup) suggest that crustal intrusion/magmatic underplating associated with CAMP and/or the formation of ‘drips’ of dense lower crust and lithospheric mantle developed directly beneath the ENAM rift basins during the rift-drift transition.