Arctic margin gravity highs remain puzzling

Abstract

Many passive continental margins, particularly in the Arctic (Figures 1 and 2), are festooned by chains of elongate positive gravity anomalies overlying, in part, marginal oceanic crust. To this day, no simple unifying explanation has emerged to account for these highs. Variously modeled by mantle doming, crustal thinning, dense crust, basement rises, postbreakup sediment depocenters, and topographic effects, these anomalies epitomize nonuniqueness in geophysical inversion. It seems unlikely that all the highs share a common origin, but it seems even more unlikely that many disparate processes produce gravity anomalies so similar to each other.Upon consideration of several hypotheses, a phase change explanation seems the most plausible for Arctic margin gravity highs (AMGHs). The better studied highs are spatially correlated with sediment depocenters (Figure 2), which however by themselves account for only a fraction of the gravity anomalies (for example, Figure 3). Thus, a reason has to be found as to why dense or thinned oceanic crust (or dense mantle) is found underneath sediment loads. Essentially, the phase change explanation relies on the added lithostatic pressure under sediment piles to “densify” some of the buried oceanic crust, for example, by conversion to garnet granulite or even eclogite [Neugebauer and Spohn, 1981 ]. More well‐designed seismic experiments are needed, however, to delineate the velocity (and hence density) structure of the underlying crust to verify the depocentermascon association and test the phase change hypothesis and others discussed below.