Structure of West Timor (East Indonesia) along a north-south cross section

Abstract

A structural pattern of the central part of West Timor has been constructed along a North-South geological transect from Wini to Kolbano. Two main tectonic events have been distinguished : -thrusting of the allochton units over the Australian continental margin during the Oligocene. TTiis thrusting brought metamorphic, ophiolitic and volcano-sedimentary units of northern origin (allochton units) on top of the sedimentary formations which filled up the Australian passive margin (lower para-autochton units) ; -collision beetwen a northern island arc and the previous Timor fore-arc units at the end of the Early Pliocene (around 3 Ma). This collisional tectonic event reworked the Oligocene structures (lower para-autochton and allochton units) and the Mio-Pliocene volcano-sedimentary formations (upper para-autochton units) and thus is responsible of the present imbricated structures ; -alternating with the compressional periods, two tectonic extensio-nal periods have been evidenced. The first one is Late Oligocene or very Early Miocene, the second one is Upper Pliocene. From the South to the North, imbricated sheets include parts of the para-autochton or allochton units. The thrusts separating the imbricated structures in the para autochton are rooted in one main decollement level, namely the Triassic to Early Jurassic black shales. The matrix of tectonic melanges in the sole of the allochton nappes is essentially made of the Late Cretaceous to Early Paleocene red calcilutites. All the observations favour a "thin skin structure" above a "decollement zone" at least for the Northern allochthon and para autochthon blocks. A "horst and graben" structure below the "decollement zone" is proposed to explain the stratigraphie differences within the tectonics sheets.