Abstract
Subduction of the Paleo-Pacific Oceanic Plate is widely considered to have caused extensive Mesozoic magmatism, lithospheric deformation and mineralization in East Asia. However, it is still unclear when this subduction began. Here we report an Early Jurassic (~187Ma) mafic intrusive complex (including olivine norite, gabbro, and diorite) from the Tumen area in NE China. The olivine norite contains a mineral assemblage of olivine, pyroxene, Ca-plagioclase, and hornblende that crystallized in a water-saturated parental magma. The rocks in the complex show variable degrees of plagioclase and ferromagnesian mineral accumulation as reflected by positive Sr and Eu anomalies in primitive mantle-normalized incompatible element patterns. Mass-balance calculations indicate that the parental magma was calc-alkaline with arc-type trace element features (i.e., large ion incompatible and light rare earth element enrichment and Nb–Ta depletion). It also had Sr–Nd–Hf isotopic compositions (87Sr/86Sr(i)=0.7042 to 0.7044, εNd(t)=+2.5 to +3.5 and εHf(t)=+8.4 to +10.5) similar to those of modern arc basalts. The parental magma was likely derived from 5 to 20% melting of a mantle wedge metasomatized by an addition of 3–4% hydrous sediment melt from the subducting Paleo-Pacific Oceanic slab. The Tumen mafic intrusive complex, together with other contemporaneous mafic intrusions, I-type granitoids, and felsic lavas, constitutes an Early Jurassic N–S-trending arc magmatic belt that was formed by westward subduction of the Paleo-Pacific Ocean.
Published Version
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