Arctic margin gravity highs: Deeper meaning for sediment depocenters?

Morphologic, gravity, and seismic reflection/refraction data from ca. 10,00 0 km of Arctic passive continental margins suggest that the numerous oval f ree-air gravity anomalies, their +50-150 mGal extrema typically located jus t landward of shelf breaks, are caused by combinations of rapidly deposited Plio-Pleistocene glacial marine sediment loads, older post-breakup sedimen ts, and perhaps causally related density anomalies (mascons) in the underly ing oceanic crust. Dispersed seismicity associated with some gravity highs may reflect ongoing brittle, flexural adjustment to the loads. Multi-channe l-seismic-controlled depocenter models for several prominent highs (includi ng the Hornsund gravity high re-examined here) suggest that sediments alone do not suffice to explain the gravity highs, unless depocenter seismic vel ocities have been significantly underestimated. A flexural backstripping mo del for the Hornsund anomaly only roughly replicates observed gravity. Subj acent 'mascons', if present below some depocenters, may be caused by (1) an omalous subsidence of initially formed dense/thin crust; (2) depocenter bla nketing of early-formed crust, mitigating hydrothermal fracturing and relat ed density reduction; or (3) metastable phase transitions, converting basal t/gabbro to denser phases (Neugebauer-Spohn hypothesis), while cracks close or fill under the increased pressures and temperatures.