Protolith origin and plate tectonic setting of metamorphic complexes in the Timor fold and thrust belt, Indonesia

Geologically, the arcuate double chain of islands and volcanoes forming the Banda arcs of eastern Indonesia is an emerging orogen created by the dynamic interaction and opposition of the Sunda, Philippine Sea and Australia plates. Additional complexity resulted from the sporadic breakup of Gondwana that fragmented the northern margin of the New Guinea-Australia (NGA) continent and caused crustal blocks to collide with SE Asia long before the Mio-Pliocene arc-continent collision in the Timor region. One consequence is that protoliths of two distinct metamorphic associations on Timor have mixed Gondwanan and SE Asian affinities. This article presents a re-grouping of the metamorphic rocks of Timor that identifies their provenance and the key tectonic events that affected them from the Jurassic to the present day. Four periods of metamorphism are recognised, where possible supported by published radiometric dating that reveals the timing of peak and cooling P-T conditions. Key conclusions are: [1] In the Cretaceous, a basement complex accreted to the Sundaland margin from Gondwana. [2] Oceanic crust and pelagic sediment of Jurassic to mid-Cretaceous age form a low-grade complex together with a Cretaceous to Paleocene cover sequence and were metamorphosed in the pre-collision Sunda forearc. [3] Eocene back-arc rifting led to unroofing of gabbro and peridotite, and separated the forearc from the Sundaland margin, causing a metamorphic overprint that peaked at 45 Ma. [4] The metamorphic Permo-Triassic Aileu Complex likely originated on Gondwana but includes Banda Sea upper plate peridotite that became attached during subduction and extrusion at the close of the Miocene.