The application of a gravimetric forward modelling of the lithospheric structure for an estimate of the average density of the upper asthenosphere

Abstract

The average density of 3300 kg m −3 is often attributed for the asthenosphere. In this study, we inspect this value by estimating the average value of the (upper)asthenosphere based on applying the gravimetric forward modelling of major known lithospheric density structures. The LITHO1.0 global seismic model of the lithospheric density structure is used for this purpose, while considering that the lithosphere-asthenosphere boundary (LAB)is rheological, conventionally taken at the 1300 °C isotherm, above which the mantle behaves in a rigid fashion and below which it behaves in a ductile fashion. According to our result, the average density of the upper asthenosphere is roughly 3400 kg m −3 . This density value closely agrees with the corresponding average value 3371 kg m −3 computed based on an empirical density model provided in the Preliminary Reference Earth Model (PREM), while using the LITHO1.0 LAB depth data. We also demonstrate that the sub-lithospheric mantle gravity map exhibits mainly a thermal signature. The most prominent features in this gravity map are mid-oceanic spearing ridges marked by gravity lows, while oceanic subductions in the West Pacific are characterized by the most pronounced gravity highs.