Abstract

Reconnaissance field traverses in Seram have led to major revisions in the stratigraphy, structure, tectonic history and geological maps. The island is composed of 4 principal stratigraphical-structural elements: (1) metamorphic continental of uncertain structural status and palaeogeographical affinity, (2) an entirely marine early Triassic-Miocene imbricate succession regarded as para-autochthonous, (3) an allochthon composed of several different thrust sheets, including metamorphic rocks, Triassic limestone and a late Miocene olistostrome, (4) a Plio-Pleistocene post-orogenic autochthon. The apparently over-thrust slices of metamorphic basement complex can be interpreted as derived from either the Asian or Australian craton. The Australian shelf, slope and rise sediments, possibly including some oceanic sediment, are regarded as para-autochthonous. Remarkably close correlation is demonstrated between the stratigraphical breaks reported from the Mesozoic-Cenozoic succession of the NW Australian shelf, from Misool, and the para-autochthonous rocks of Seram and Timor. This emphasizes the presence of the Australian craton underlying these 3 islands. Close correlation is also found between the allochthonous rocks of Seram and Timor. Some of these thrust sheets are interpreted as having been derived from the Asian continental margin. The ultrabasic rocks of SW Seram and Ambon seem to form the highest thrust sheets. The main period of orogenesis, involving over-thrusting, olistostrome emplacement and imbrication of the underlying Australian cover-rock sequences occurred in the late Miocene-early Pliocene (N.18). The structural position of the volcanic rocks of Ambon is uncertain. A tentative interpretation is that they are in situ, having been extruded from deep-seated fractures that penetrate the 'Asian' thrust sheets and the underlying Australian continental basement.

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