Abstract

The tectonic mechanism responsible for detachment of the Sibumasu terrane in the eastern Cimmerian continent from the Australian Gondwana margin remains poorly understood and debated. Our study on the late Paleozoic Woniusi basaltic province in the northern Sibumasu terrane may provide a new perspective on this problem, and further, on the rifting dynamics of eastern Gondwana’s northern margin. In this study, we revealed that the Woniusi basaltic province is spread over an area of ∼12,000 km2 with a thickness of ∼300–500 m for the eruptive phase. Direct zircon U-Pb dating of mafic dikes indicates that the Woniusi basaltic province was emplaced between the latest Carboniferous and late Early Permian (301 Ma to 282 Ma), synchronous with basaltic rocks from the Panjal Traps, Tethyan Himalaya (Bhote Kosi, Selong, Abor), Lhasa, and southern Qiangtang. Geochemically, the Woniusi basaltic rocks show subalkaline tholeiitic affinity and relatively homogeneous features of enriched light rare earth elements (LREEs) and large ion lithophile elements (LILEs) but depleted Nb and Ta patterns. They were most likely derived from an enriched subcontinental lithospheric mantle source and triggered by the mantle plume–induced rifting process. The Woniusi basaltic province, together with other coeval basaltic provinces from the Panjal Traps, Tethyan Himalaya, Lhasa, and southern Qiangtang, belongs to a fragmented large igneous province that may have had an original area of over 2 × 106 km2, which is comparable to that of the Ontong-Java, Deccan, or Siberian Traps. These Tethyan basaltic provinces share a common mantle plume centered in northern Greater India. It was this mantle plume that may have triggered the initial rifting of the eastern Cimmerian terranes (e.g., Sibumasu, southern Qiangtang) from both the northern Indian and Australian Gondwana margins, as well as the opening of Meso-Tethys Ocean. This study, moreover, sheds light on the paleopositions of the Lhasa and Tengchong terranes before their breakups.

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