Crustal structure of the outer Banda arc: New free-air gravity evidence

Abstract

Marine gravity data from the Banda arc in the vicinity of western Timor and the central Savu Sea, integrated with geophysical and geological information, support the postulated subduction of Australian continental crust beneath the Timor trough and the island of Timor. Gravity analysis also indicates the presence of a mass deficit in the upper mantle or crust beneath the entire Savu Sea. This mass deficit is interpreted to be related to a combination of 1. (1) subducted, lighter continental crust, 2. (2) downward flexing of the upper crustal plate in the forearc area, and 3. (3) possibly anomalous, low-density upper mantle below the Savu Sea. The North Sumba ridge, a bathymetric and structural high dividing the Savu Sea, is underlain by high-density material possibly related to an older volcanic arc located between the present-day volcanic arc and Timor. The crust beneath the northern Savu basin appears nearly oceanic in character but thickens beneath the modern volcanic arc. Finally, our analysis suggests thickening of crust beneath Timor forming a root in relation to the Savu Sea crust to the north.