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Marine Carbonate Component in the Mantle Beneath the Southeastern Tibetan Plateau: Evidence From Magnesium and Calcium Isotopes
Author(s) -
Liu Fang,
Li Xin,
Wang Guiqin,
Liu Yufei,
Zhu Hongli,
Kang Jinting,
Huang Fang,
Sun Weidong,
Xia Xiaoping,
Zhang Zhaofeng
Publication year - 2017
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2017jb014206
Subject(s) - geology , geochemistry , mantle (geology) , subduction , carbonate , incompatible element , adakite , isotope fractionation , oceanic crust , partial melting , fractionation , tectonics , paleontology , chemistry , organic chemistry
Tracing and identifying recycled carbonates is a key issue to reconstruct the deep carbon cycle. To better understand carbonate subduction and recycling beneath the southeastern Tibetan Plateau, high‐K cal‐alkaline volcanic rocks including trachy‐basalts and trachy‐andesites from Tengchong were studied using Mg and Ca isotopes. The low δ 26 Mg (−0.31 ± 0.03‰ to −0.38 ± 0.03‰) and δ 44/40 Ca (0.67 ± 0.07‰ to 0.80 ± 0.04‰) values of these volcanic rocks compared to those of the mantle (−0.25 ± 0.07‰ and 0.94 ± 0.05‰, respectively) indicate the incorporation of isotopically light materials into the mantle source, which may be carbonate‐bearing sediments with low δ 26 Mg and δ 44/40 Ca values. In addition, no correlations of δ 26 Mg and δ 44/40 Ca with either SiO 2 contents or trace element abundance ratios (e.g., Sm/Yb and Ba/Y) were observed, suggesting that limited Mg and Ca isotopic fractionation occurred during cal‐alkaline magmatic differentiation. A binary mixing model using Mg–Ca isotopes shows that 5–8% carbonates dominated primarily by dolostone were recycled back into the mantle. Since Tengchong volcanism is still active and probably related to ongoing plate tectonic movement, we propose that the recycled carbonates are derived from oceanic crust related to the ongoing subduction of the Indian plate.