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Metamorphic complexes in Buru and Seram, Northern Banda Arc

1989; Elsevier BV; Volume: 24; Issue: 2-3 Linguagem: Inglês

10.1016/0077-7579(89)90160-9

1873-1406

K. Linthout, H. Helmers, Jan Sopaheluwakan, E.Surya Nila,

earthquake and tectonic studies

The Palaeozoic Wahlua complex of Southeast Buru and the Tehoru complex of Central Seram are chiefly composed of graphitic phyllites/schists and arkosic quartzites with minor intercalations of marble and amphibolite. The complexes show similar polyphase deformation and pre-Triassic metamorphic history as reflected in their simple (Barrovian-style) PT-loops. Both complexes may very well have originated in the same pre-Triassic metamorphic belt. Mylonite structures in the northern part of the Tehoru complex indicate right-lateral, N300E directed movements, and are explained as strike-slip along a transcurrent fault separating a southern metamorphic block from a northern essentially Triassic and younger non-metamorphic block. These movements in their turn are caused by the anticlockwise rotation of Seram since late-Triassic times. In Kaibobo, phyllonites and amphibolites adjacent to the ultramafic net-veined complex reveal temperatures of metamorphism of up to 740°C; these are explained as superimposed upside-down metamorphism caused by an over-riding late-Miocene to early-Pliocene ultramafic sheet. Suprisingly young K/Ar ages of 4 to 5 Ma of biotites and muscovites from Wahlua and Tehoru complex are explained by re-heating of the pre-Triassic mica blasts due to overthrusting by hot mantle slabs, now largely eroded away. An average uplift rate of about 0.1 cm·a−1 during the last 4–5 Ma is calculated for Southeast Buru and Central Seram. Thrusting of metamorphics over non-metamorphics in 'median' Seram and of the ultramafic sheet in Southwest Seram may be also related to the anticlockwise rotation of Seram.