Petrogenesis of high-Ti mafic dykes from Southern Qiangtang,Tibet: Implications for a ca. 290 Ma large igneous province related to the early Permian rifting of Gondwana |
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| Institution: | 1. College of Earth Science, Jilin University, Changchun 130061, China;2. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK;2. CASP, University of Cambridge, West Building, 181A, Huntingdon Road, Cambridge CB3 0DH, UK;3. NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK;4. Scottish Universities Environmental Research Centre, East Kilbride G75 0QF, UK;5. Department of Earth, Atmospheric, and Planetary Sciences, 77 Massachusetts Ave., Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA;6. Open University, Faculty of Science, Walton Hall, Milton Keynes MK7 6AA, UK;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;1. Nanjing Institute of Geology and Mineral Resources, Nanjing 210016, PR China;2. Department of Geology and Geography, Auburn University, Auburn, 36849-5305, USA;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, Guangdong 510640, China;2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China |
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| Abstract: | The presence and/or generation mechanism of a mantle plume associated with early Permian rifting on the northern margin of Gondwana are topics of debate. Here we report LA–ICP–MS U–Pb zircon ages, whole-rock geochemistry, and Sr–Nd isotope data for high-Ti mafic dykes from southern Qiangtang, Tibet, with the aim of assessing if a mantle plume formed in this region during the early Permian. Zircon U–Pb dating of diabase dykes yielded ages of 290.6 ± 3.5 Ma and 290.1 ± 1.5 Ma, indicating they were emplaced during the early Permian. Whole-rock geochemistry shows that these mafic dykes are alkaline (Nb/Y = 0.73–0.99), have high TiO2 (3.6%–4.8%), and have ocean-island basalt (OIB)-like trace element patterns with enrichments in Nb, Ta, and Ti. Whole-rock Sr–Nd isotope data show a relatively narrow range of εNd(t) (+ 2.29 to + 3.53), similar to basalts produced by a mantle plume (e.g., Emeishan continental flood basalts (ECFB)). Elemental and isotope data suggest that the dykes have undergone fractionation crystallization of mafic minerals and have experienced negligible crustal contamination. These mafic rocks show an affinity to OIB and may have been generated by partial melting of an OIB-type, garnet-bearing asthenospheric mantle source. On the basis of a similar emplacement age to the Panjal Traps basalts in the Himalayas, combined with a tectonic reconstruction of Gondwana in the early to middle Permian, our work suggests that the high-Ti mafic dykes in the Southern Qiangtang terrane and the coeval Panjal Traps basalts in the Himalayas together comprise a ca. 290 Ma large igneous province linked to a mantle plume, which probably played an active role in early Permian rifting on the northern margin of Gondwana and was related to circum-Pangea subduction. |
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