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Geological Society, London, Special Publications; 1995; v. 88; p. 473-492;
DOI: 10.1144/GSL.SP.1995.088.01.25
© 1995 Geological Society of London

Case Studies: Asia

Inversion-controlled uplift of an outer-arc ridge: Nias Island, offshore Sumatra

M. A. Samuel1, N. A. Harbury1, M. E. Jones1 & S. J. Matthews2

1 Research School of Geological and Geophysical Sciences, Birkbeck College and University College London, Gower Street, London WC1E 6BT, UK
2 BP Exploration, 4/5 Long Walk, Stockley Park, Middlesex UB11 1BP, UK

This study presents data from Nias Island which lies on an outerarc ridge 150 km to the west of mainland Sumatra. A new stratigraphy, geological map and cross-section of Nias have been produced from field data collected over all the island supplemented with aerial photography, LANDSAT and SAR (synthetic aperture radar) studies and these data form the basis for a new interpretation of the island. Where exposed the basement consists of ophiolitic rocks, originating from a variety of tectonic settings, and with a thin sedimentary cover. Three main sub-basins are identified on Nias. Late Paleogene-Neogene sedimentation in these basins was controlled primarily by major extensional faults though deposition within sub-basins was influenced by the presence of sub-basin transecting faults with significant vertical throws. Two phases of inversion are recognized: the first occurred during the Early Miocene, was limited to western regions and is identified by the presence of a localized unconformity and vitrinite and apatite fission track data. The second inversion initiated in Pliocene times and affected all the sub-basins on Nias. Latest Pliocene-Pleistocene rocks unconformably overlie the Miocene strata. Deformational styles within separate fault-bounded segments vary markedly; structural mapping demonstrates uplift and deformation has been largely controlled by reactivation of sub-basin extensional faults and oblique-slip movements on transecting faults. Diapiric melanges developed during inversion suggesting an intimate relationship between uplift and remobilization of overpressured mudrocks. This study concludes that the uplift of the sub-basins on Nias resulted from inversion of basin successions by reactivation of original major extensional faults rather than on thrust-slices developed in an accretionary prism. Nias does not form part of an accretionary complex; the accretionary prism has developed to the southwest of Nias.





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Geological Society, London, Special Publications, 2009; 318: 351 - 372.
[Abstract] [Full Text] [PDF]