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Phantom recycled carbonates and mantle pyroxenites: insight from the low-δ26Mg intraplate basaltic province across central-eastern Asia
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  • Hongkun Dai,
  • Jianping Zheng,
  • Qing Xiong,
  • William L. Griffin,
  • jin-xiang huang,
  • Fang Huang,
  • Suzanne Yvette O'Reilly
Hongkun Dai
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences

Corresponding Author:[email protected]

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Jianping Zheng
China University of Geosciences (Wuhan)
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Qing Xiong
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences
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William L. Griffin
ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC, Macquarie University
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jin-xiang huang
CCFS, Macquarie University
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Fang Huang
Department of Earth and Space Sciences, University of Science and Technology of China
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Suzanne Yvette O'Reilly
Gemoc-Macquarie University
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Abstract

Mass recycling from subduction to magmatic extrusion shapes our habitable environment and Earth’s interior. Subducted igneous crust may form pyroxenites before participating magmatism, but the deep journey of associated carbonates remains unclear. Here we report new Mg-isotope data for ~89 to 81 Ma basaltic rocks in Langshan area, central Asia (δ26Mg = -0.391 to -0.513 ‰) with a synthesis for post-110 Ma basalts across eastern Asian continent. The merged low-δ26Mg basaltic province normally interpreted as derivations from carbonated sources paradoxically displays geochemical signatures (low Ca/Al and high K2O contents) resembling partial melts of uncarbonated sources. Negative correlations of δ26Mg vs TiO2 and FCKANTMS, the proxy of pyroxenitic melts, and adiabatic melting modeling suggest presence of Mg-isotopically light source pyroxenites transformed from decarbonated altered oceanic crust. This may explain ubiquitous pyroxenitic contributions in many low-δ26Mg basaltic suites and has significant implication for deep carbon cycling.