Granitic magmatism, basement ages, and provenance indicators in the Malay Peninsula : insights from detrital zircon U-Pb and Hf-isotope data

The Malay Peninsula lies on two continental blocks, Sibumasu and East Malaya, which are intruded by granitoids in two provinces: the Main Range and Eastern. Previous models propose that Permian–Triassic granitoids are subduction-related and syn-to post-collisional. We present 752 U–Pb analyses that were carried out on zircons from river sands in the Malay Peninsula; of these, 243 grains were selected for Hf-isotope analyses. Our data suggest a more complex Sibumasu–East Malaya collision history. ¹⁷⁶Hf/¹⁷⁷Hfi ratios reveal that Permian–Triassic zircons were sourced from three magmatic suites: (a) Permian crustally-derived granitoids, (b) Early-Middle Triassic granitoids with mixed mantle–crust sources, and (c) Late Triassic crustally-derived granitoids. This suggests three Permian–Triassic episodes of magmatism in the Malay Peninsula, two of which occurred in the Eastern Province. Although the exact timing of the Sibumasu–East Malaya collision remains unresolved, current data suggest that it occurred before the Late Triassic, probably in Late Permian–Early Triassic. Our data also indicate that Sibumasu and East Malaya basements are chronologically heterogeneous, but predominantly of Proterozoic age. Some basement may be Neoarchaean but there is no evidence for basement older than 2.8 Ga. Finally, we show that Hf-isotope signatures of Triassic zircons can be used as provenance indicators.16 page(s

Detrital zircon U-Pb age and Hf-isotope perspective on sediment provenance and tectonic models in SE Asia

Detrital zircon U-Pb geochronology can make an extremely valuable contribution to provenance studies and paleogeographic reconstructions, but the technique cannot distinguish grains with similar ages derived from different sources. Hafnium isotope analysis of zircon crystals combined with U-Pb dating can help make such distinctions. Five Paleogene formations in West Java have U-Pb age populations of 80-50 Ma (Late Cretaceous-Paleogene), 145-74 Ma (Cretaceous), 298-202 Ma (Permian-Triassic), 653-480 Ma (mid-Neoproterozoic- latest Cambrian), and 1290- 723 Ma (late Mesoproterozoic-early Neoproterozoic). Hf-isotopes have been analyzed for 311 zircons from these formations. Differences in zircon U-Pb age and Hf-isotope populations refl ect changing sources with time. Late Cretaceous and Paleogene zircons are interpreted as having been derived from two temporally discrete volcanic arcs in Java and West Sulawesi, respectively. The Java arc was active before microcontinent collision, and the W Sulawesi arc developed later, on newly accreted crust at the SE Sundaland margin. The collision age is estimated to be ca. 80 Ma. U-Pb age and ¹⁷⁶Hf/¹⁷⁷Hfi characteristics allow a distinction to be made between Cretaceous granitic and volcanic arc sources. Zircons that are older than ca. 80 Ma have a continental Sundaland provenance. Mid-Cretaceous zircons in all upper Eocene and lower Oligocene formations were derived from granites of the Schwaner Mountains of SW Borneo. Permian-Triassic zircons were derived predominantly from granites in the SE Asian Tin Belt. ¹⁷⁶Hf/¹⁷⁷Hfi ratios permit distinction between Tin Belt granites in the Main Range and Eastern Provinces, and indicate that only the lower Oligocene Cijengkol Formation contains signifi cant input from the Main Range Province, suggesting a partial change in drainage pattern. Older zircon ages are more diffi cult to interpret but probably record contributions from allochthonous basement and sedimentary rocks that were deposited prior to rifting of continental blocks from Gondwana in the early Mesozoic.25 page(s

New insights into the geological evolution of Eastern Indonesia from recent research projects by the SE Asia Research Group

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