Detrital record of late-stage silicic volcanism in the Emeishan large igneous province |
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| Institution: | 1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. Graduate University of Chinese Academy of Sciences, Beijing 100049, China;3. Berkeley Geochronology Center, Berkeley, CA 94709, USA;1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China;2. School of Earth, Atmosphere & Environment, Monash University, Melbourne, VIC 3800, Australia;3. College of Earth Sciences, Chengdu University of Technology, Chengdu 610059, China;4. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;1. Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Oslo, Norway;2. DougalEARTH ltd., Solihull, UK;3. Visiting Fellow, Earth, Environmental and Biological Sciences, Queensland University of Technology, Brisbane, Queensland, Australia;4. Department of Geography, Earth and Environmental Sciences (GEES), University of Hull, Hull HU6 7RX, UK;5. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK;6. Key Laboratory of Geobiology and Environmental Geology, China University of Geosciences, Wuhan 430074, PR China;7. Humboldt post-doc fellow, GeoZentrum Nordbayern, University of Erlangen-Nuremberg, Schlossgarten 5, 91054 Erlangen, Germany;8. NGU Geodynamics, Trondheim, Norway;9. School of Geosciences, University of Witwatersrand, Johannesburg, South Africa;1. State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, China;2. College of Geoscience and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing, 100083, China;3. School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia |
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| Abstract: | Silicic volcanic rocks generally constitute a minor, but key product to track the magmatic evolution in mafic rock dominated large igneous provinces (LIPs). However, for their generally late-stage nature of the silicic volcanic rocks they have a poor preservation potential due to extensive post-eruption erosion. We track the eroded volcanic rocks from the ～260 Ma Emeishan LIP by analyzing the provenance of the LIP-derived sedimentary rocks. Sandstones from a cored succession of the Late Permian Longtan Formation in the northern Youjiang Basin are rich in volcanic rock fragments, and associated mudstones have low Al2O3/TiO2 ratios. Detrital zircon grains from the Longtan Formation display typical unimodal U–Pb age spectra with a prominent peak at ca. 260 Ma. These detrital zircons show an overall geochemical affinity akin to those crystallized from within-plate/anorogenic magmas. Such petrological and geochemical characteristics are consistent with a dominant source from the Emeishan volcanic rocks. Through the sampled succession, zircon grains of ～260 Ma from the lower Longtan Formation generally display lower U/Yb (most < 0.5) and Th/Nb (most < 10) ratios and higher εHf(t) values (mostly in the range of +3 to +8) than those from the upper part. A similar sequential variation has also been observed in the Shaiwa Formation, which is an offshore time-equivalent unit to the Longtan Formation. These consistent temporal variations through the sedimentary successions in the Youjiang Basin are interpreted to reflect erosional unroofing of the Emeishan LIP during the Late Permian. These results, integrated with previous studies on the rhyolites and trachytes in Emeishan LIP, reveal a fractional crystallization dominated petrogenetic process with diminishing crustal assimilation for the late-stage silicic volcanism. |
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| Keywords: | Emeishan large igneous province Late permian Provenance Youjiang basin Detrital zircon |
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