西北蘇門答臘碎屑鋯石鈾鉛定年與鉿同位素研究

Abstract

In NW Sumatra, Tertiary sedimentary basins that occur in forearc and backarc settings with respect to the present-day subduction system were deposited in three major terranes, namely, the Woyla Nappe, the East Sumatra block, and the West Sumatra block. NW Sumatra represents the product of complex accretion/collision/subduction histories among these three terranes, which have originated from the eastern margin of Gondwanaland. To better understand the complex histories, we present a detrital zircon study in NW Sumatra that, together with our unpublished work on major magmatic rocks in the area, allow us to reach the following conclusions: (1) Detrital zircons from 14 samples (river sand or sandstone) in the forearc basin reveal seven age peaks at ~1050 Ma (n=74), ~550 Ma (n=65), ~214 Ma (n=138), ~131 Ma (n=14), ~100 Ma (n=65), ~52 Ma (n=238) and 17-0 Ma (n=303), respectively; (2) Detrital zircons from nine samples in the backarc basin show similar age populations; (3) The Late Triassic zircons, with εHf(T) values of -18 to 0, are sourced mainly from the Indosinian granitoids that are widespread in the East Sumatra block; (4) The less abundant Early Cretaceous zircons, with εHf(T) values of -5 to 0, are most likely from the West Sumatra block; (5) The Late Cretaceous zircons, with εHf(T) values of +11 to +16, are from the Woyla Nappe due probably to the Woyla accretion; (6) The Eocene and younger zircons, with εHf(T) values of +6 to +17, are from the initial stage and modern arc magmatic rocks related to the Indian Ocean plate subduction.