A source-depleted Early Jurassic granitic pluton from South China: Implication to the Mesozoic juvenile accretion of the South China crust

作者：Zhou, Zuo-Min^*; Ma, Chang-Qian^*; Wang, Lian-Xun^*; Chen, Shu-Guang; Xie, Cai-Fu; Li, Yong; Liu, Wei

来源：Lithos, 2018, 300: 278-290.

DOI：10.1016/j.lithos.2017.11.017

• Early Jurassic
• I-type granites
• Depleted isotopes
• SE China
• Nanling Region
• Juvenile crust

Source-depleted granites were rarely reported in South China. Hereby we identified such a granitic pluton, the Tiandong pluton, at Northeastern Guangdong province in Southeastern (SE) China. Whole-rock Sr-Nd and zircon Hf isotopes of the Tiandong granites both revealed obviously depleted source signatures, with initial isotopic values of initial Sr-57/Sr-86 = 0.7032-0.7040, epsilon(Nd)(t) = 1.1-1.5, and epsilon(Hf)(t) = 6-13, respectively. Zircon U-Pb dating implied the granite was intruded in Early Jurassic (188 Ma). The dominant minerals of the Tiandong granite consist of K-feldspar, plagioclase, quartz and biotite, with accessory mineral assemblage of apatite + zircon + magnetite. Based on the mineralogy and the depleted isotopic signature, the granites chemically show I-type affinity such as low Zr + Nb + Ce + Y (131.6 to 212.2),10(4) x Ga/Al (2.12-2.27), A/CNK values <1.1 (0.97-1.03), corundum molecule <1 (0-0.55) and extremely low P2O5 contents (0.05 wt). The one-stage and two-stage kdepleted mantle Nd model ages (T-DM = 0.89 to 0.84 Ga, T-2DM = 0.88 to 0.85 Ga) are consistent. T-DM(Hf) values of 0.31-0.63 Ga are also indistinguishable from T-2DM(Hf) values of 0.35-0.75 Ga. The Nd and Hf isotopic compositions confirm that the Tiandong granites are juvenile crustal accretion but decoupled Nd-Hf isotopic systems. The juvenile crust is likely to originate from a mixed source of the primary asthenospheric mantle and the subordinate EMII. Combined with early studies of adjacent rocks, we propose that the early Jurassic (-200-175 Ma) magmatism as evidenced by the Tiandong granites might be driven by upwelling of asthenosphere and subsequent underplating of mafic melts in an intra-plate extensional setting as a response to far-field stress during early stage subduction of the paleo-pacific plate.

• 出版日期2018-2
• 单位交通运输部天津水运工程科学研究所; 中国地质调查局武汉地质调查中心; 东华理工大学; 中国地质大学（北京）