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Geometrical problems and implications of large scale over-thrusting in the Banda Arc -Australian margin collision zone

1981; Geological Society of London; Volume: 9; Issue: 1 Linguagem: Inglês

10.1144/gsl.sp.1981.009.01.37

2041-4927

M. G. Audley‐Charles,

High-pressure geophysics and materials

Summary Inversion of stratigraphical sequences, the presence of high grade metamorphic rocks sitting on serpentinite rafts bounded by unmetamorphosed sedimentary rocks, and zones of imbrication have been cited as evidence of large scale overthrusting in the Outer Banda Arc. Earthquake data reveal a Benioff zone implying intermediate depth and deep focus underthrusting beneath the Banda Arc but there is a paucity of shallow focus shocks with underthrusting mechanisms. Multichannel seismic reflection surfeys between the Outer Banda Arc and the Australian-New Guinea shelf have been interpreted as showing imbrication in the north wall of the Timor Trough and the S wall of the Seram Trough. Quaternary steep angled block faulting post-dates and thus obscures much of the thrust faulting in the Banda Arc. Many geometrical problems arise in trying to interpret the structural history of this collision zone between Australia and the volcanic (Inner) Banda Arc. They include:- (1) the apparent absence of a subduction trench and accretionary arc-trench gap in the Banda Arc; (2) the location of the surface trace of the Benioff zone before collision; (3) the history of the Benioff zone after the Pliocene oceanic trench was destroyed; (4) the relationship of the developing fold and thrust belt to the pre-collision geometry of the Australia-New Guinea continental margin; (5) the apparent absence of the continental slope and rise in the northern Australia collision zone; (6) the relationship of the crystalline basement of the Outer Banda Arc to the cover rocks and (7) the tectonic significance of the apparent continuity of the stratigraphically and structurally very different Sunda and Banda Arcs. Continent-arc collision resulted from the convergence of Australia and the Banda volcanic arc. The associated deformation, represented by the folding and local imbrication of the Australian continental rise sediments of the Outer Banda Arcs with the emplacement of overthrust exotic sheets, was accomplished in 2 Ma. It appears to have been caused by the failure of the Benioff zone to accommodate the thick sediment prism of Australian proximal continental rise. Geometrical considerations suggest that, as a consequence, the Benioff zone and most of the approximately 200 km wide arc-trench gap were overridden by the Australian lithospheric plate during the continued plate convergence of the last 3 Ma. An important conclusion is that the Banda Arc fold and thrust belt developed in proximal continental rise deposits at the foot of the Australian continental slope