Whole-rock geochemistry of the Hili Manu peridotite, East Timor: implications for the origin of Timor ophiolites

Abstract

The Hili Manu peridotite occupies a key position at the outer limit of continental crust on the north coast of East Timor. Most models for the tectonic evolution of the Outer Banda Arc interpret peridotite bodies on Timor, such as Hili Manu, as fragments of young oceanic lithosphere from the Banda Arc (upper plate). However, recent workers have used major-element geochemistry to argue that the peridotite bodies on Timor were derived from the Australian subcontinental lithosphere. Our major, trace and isotopic geochemical study of the Hili Manu peridotite body supports a supra-subduction origin from either a forearc or backarc position for the Hili Manu peridotite. In particular, the wide range in Nd and Sr isotopic compositions, overlapping that of arc volcanics from the Sunda-Banda Island arc, and highly fractionated Nb/Ta values indicate a supra-subduction setting. As there is no evidence for subduction beneath the rifted Australian continental margin, it is unlikely that the Hili Manu peridotite is Australian subcontinental lithosphere. This result, along with the clear supra-subduction setting of the Ocuzzi peridotite and associated volcanics in West Timor, gives support to the interpretation that the Miocene collision between the Banda Arc and the Australian continental margin has produced widespread Cordilleran-style ophiolites on Timor.