Abstract
Sections on SE Buru and Central Seram of continental Paleozoic metamorphics prograde north and demonstrate similar metamorphic histories following 40°C km −1 till medium grade. This is consistent with Buru and Seram forming one microplate. Mylonites in the northern part of the metamorphics of the Central Seram section indicate N300E dextral strike-slip. They mark, with sheared Triassic sediments exposed along their boundary, a zone along the length of the island, which is interpreted as an antithetic strike-slip expression of the Late Neogene 74° counterclockwise rotation. Thrusting (ultramafics over Paleozoic metamorphics over Mesozoic sediments) started during the early confrontation of the northward moving Buru-Seram microplate with the large westward moving Pacific and Irian Jaya plates. These also forced the Buru-Seram microplate into anticlockwise rotation, during which dextral strike-slip along former thrust planes became dominant. Resetting of radiometric systems of the mica schists took place in a 1.5-Ma period in the Early Pliocene, after obduction of hot mantle material and during the first part of rotation, which created an extensional regime, facilitating hypogene hydrothermal activity. With the creation of a second set of NW-SE dextral faults, allowing rotation beyond 45°, major shear zones were locked, thus inhibiting hydrothermal activity by which also the resetting of radiometric systems came to an end, 3 Ma ago. It is proposed that, since their obduction, the peridotites of Ambon and Seram have been rotated and migrated westward with the microplate. Radiometric data from mica schists indicate that 4.5 and 3 Ma ago these rocks were at temperatures of about 500 and 320°C, respectively. Assuming an ambient gradient of 100°C km −1, these data imply an average rate of uplift of 1.1 km Ma −1 since that time.
Published Version
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