Abstract

Tectonostratigraphic reconstructions of Permo-Carboniferous to Quaternary rock formations in Sumatra and Timor indicate the existence of very similar geotectonic elements. In Sumatra, Laramic tectonic melanges are found along the entire length of the Bukit Barisan range covered laterally by olistostromes of Eocene to Lower Miocene age. These are in turn overlain by underformed Upper Miocene sediments. In Timor and Sumba almost the same situation occurs. Laramic tectonic melanges are found along the longitudinal axis of both islands, which are covered by olistostromes consisting of Eocene-Lower Miocene chaotic sediments. These are again in turn overlain by undeformed Upper Miocene to Quarternary deposits. On the islands of Rote (Roti), Sabu (Sawu) and Raijua within the Timor-Sumba island arcs, only olistostromes crop out. The tectonic melanges of these islands have apparently been covered by the olistostromes, and undeformed Upper Miocene-Quarternary deposits. () In both areas the Variscan orogeny is evidenced by high-grade metamorphics and ultramafic rock occurring as clasts within the Laramic melange complex and also as olistoliths in Eocene-early Miocene olistostromes.

Directions indicated by depositional structures within the Laramic melange are used to locate the Variscan source terrane, whereas the Laramic source terrane is deduced from olistoliths of the Eocene-early Miocene olistostromal complex. In western Indonesia the Variscan and Laramic source terranes are traced to the Sunda Platform, whereas in eastern Indonesia these terranes are located in the Irian Jaya Platform.

The Asian and Australian continents were separated by oceanic crust which was subducted, resulting in collision of the continents. On the margins of these colliding continents tectonic accretion took place and sediments were ponded between accretionary prisms of Eocene-early Miocene olistostromes and the overlyng late Miocene-Quarternary sediments.

Our detailed studies indicate the Sumba-Timor area belongs to the Australian Continent. However there are many questions about the tectonics of this area which need to be answered.