A restraining bend in a young collisional margin: Mount Mundo Perdido, East Timor

Abstract

Mount Mundo Perdido, a 1750 m-high, steep-sided massif situated in the Viqueque district of East Timor, comprises approximately 30 km² of complexly juxtaposed rocks deriving from both sides of the collisional plate boundary between the Australian Plate and the Banda Arc. Lithologies include Triassic–Jurassic interior-rift basin deposits, Cretaceous–Oligocene pelagites of Australian passive margin origin, neritic Oligocene–Miocene limestones and volcanics of Asiatic affinity, and Pliocene–Pleistocene synorogenic deposits. Detailed structural mapping shows Mount Mundo Perdido to be dominated by recent, high angle, oblique-slip and strike-slip faults that have been active into the Pleistocene and control the present-day topography. The fault architecture and stratigraphic distribution in the study area are comparable to pop-up structures developed at restraining bends, in this case within an east–west oriented zone of sinistral strike-slip. Our observations, supported by comparisons to scaled sandbox models and to similar pop-up structures developed in strike-slip systems elsewhere in the world, suggest that plate boundary-parallel strike-slip deformation is an integral part of the kinematics within the collisional zone between the Australian and Eurasian/Pacific plates in the Timor region.

KEY WORDS:

• Mount Mundo Perdido
• Timor
• collision
• strike-slip
• restraining bend
• high-angle faults
• biostratigraphy.

ACKNOWLEDGEMENTS

We thank Eni Australia Ltd for supporting our research in Timor Leste and making this project possible, with special thanks to Tony Heynen and Jose Sabino at Eni Timor Leste for their assistance in Dili. Thank you Norberta da Costa, Director, and all the staff at the National Directorate of Geology and Mineral Resources in the Secretariate for Energy and Natural Resources (SERN) for your continuing support. We thank the Viqueque District Administrator, Ossu Sub-District Administrator, and Sucu Chiefs of Liaruca, Builale and Ossu de Cima for facilitating our fieldwork at Mundo Perdido. Thanks to Eujay McCartian for logistical help during the 2009 field season. We thank Matt Dixon for assistance with palynological determinations, and Mary Gee for assistance with the igneous material. Many thanks to Gilsel Borges, now Geoscientist at Eni Timor Leste; without your assistance and expertise in geological mapping this project would not have been possible. We are very grateful to everyone who assisted in the field, including Januario de Carvalho, Manuel Hornai Gonsalves and Andy Montiero. Finally, we thank the Montiero family, who opened up their home to us while in Ossu with unreserved generosity and hospitality.