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<p>The North Sulawesi arc (NSUA) constitutes the northern arm of Sulawesi Island and is characterized by complex Cenozoic records of magmatism and tectonics. Zircon U-Pb geochrono-logical and Hf-O isotopic data, whole-rock major oxides, trace elemental, and Sr-Nd-Pb isotopic data of the high-silica granites from the NSUA document their petrogenesis and tectonic setting. Zircon elemental analysis of the granitic samples shows a juvenile oceanic crust origin and the U-Pb geochronology indicates their Oligocene ages between 30.4 and 27.3 Ma. The samples have high SiO<sub>2</sub> (75.05 wt.%–79.38 wt.%) and Na<sub>2</sub>O (4.48 wt.%–5.67 wt.%), low K<sub>2</sub>O (0.15 wt.%–1.34 wt.%) and MgO (0.07 wt.%–0.91 wt.%) contents, belonging to calc-alkaline I-type high-silica granites. They have enriched LREE and LILE, and depleted HREE and HFSE, showing significant Eu, Sr, Nb, and Ta negative anomalies. These high-silica granites have low (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>i</sub> ratios (0.704 412–0.704 592), positive <i>ε</i><sub>Nd</sub>(<i>t</i>) values (from +5.1 to +6.6), positive zircon <i>ε</i><sub>Hf</sub>(<i>t</i>) values (from +10.1 to +18.8), low zircon <i>δ</i><sup>18</sup>O values (4.20‰–5.02‰), and similar Pb isotope compositions to the Indian Ocean MORB. Such signatures suggest that these high-silica granites were derived by partial melting process of the juvenile arc crust in an intra-oceanic setting. The felsic magmatism in the NSUA was likely driven by mantle upwelling and decompression melting during the Oligocene, in response to slab roll-back linked with the convergence of the East Sulawesi ophiolitic crust or the microcontinental fragments.</p>

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Oligocene High-Silica Felsic Magmatism in Juvenile Intra-Oceanic Arc Crust, North Sulawesi Arc, Indonesia

  • 期刊论文

  • 发表日期：

    2025年6月17日

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  • Xianghong Lu,
  • Chengshi Gan,
  • Peter A. Cawood,
  • Xin Qian,
  • Yuejun Wang

摘要

The North Sulawesi arc (NSUA) constitutes the northern arm of Sulawesi Island and is characterized by complex Cenozoic records of magmatism and tectonics. Zircon U-Pb geochrono-logical and Hf-O isotopic data, whole-rock major oxides, trace elemental, and Sr-Nd-Pb isotopic data of the high-silica granites from the NSUA document their petrogenesis and tectonic setting. Zircon elemental analysis of the granitic samples shows a juvenile oceanic crust origin and the U-Pb geochronology indicates their Oligocene ages between 30.4 and 27.3 Ma. The samples have high SiO2 (75.05 wt.%–79.38 wt.%) and Na2O (4.48 wt.%–5.67 wt.%), low K2O (0.15 wt.%–1.34 wt.%) and MgO (0.07 wt.%–0.91 wt.%) contents, belonging to calc-alkaline I-type high-silica granites. They have enriched LREE and LILE, and depleted HREE and HFSE, showing significant Eu, Sr, Nb, and Ta negative anomalies. These high-silica granites have low (87Sr/86Sr)i ratios (0.704 412–0.704 592), positive εNd(t) values (from +5.1 to +6.6), positive zircon εHf(t) values (from +10.1 to +18.8), low zircon δ18O values (4.20‰–5.02‰), and similar Pb isotope compositions to the Indian Ocean MORB. Such signatures suggest that these high-silica granites were derived by partial melting process of the juvenile arc crust in an intra-oceanic setting. The felsic magmatism in the NSUA was likely driven by mantle upwelling and decompression melting during the Oligocene, in response to slab roll-back linked with the convergence of the East Sulawesi ophiolitic crust or the microcontinental fragments.