Late Cretaceous lithospheric extension in SE China: Constraints from volcanic rocks in Hainan Island

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• Liang, Xinquan
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• Kröner, Alfred
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• Cai, Yongfeng
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• Shao, Tongbin
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• Wen, Shunv
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• Jiang, Ying
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• Fu, Jiangang
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• Wang, Ce
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• Dong, Chaoge

Abstract

Petrological, geochemical and in-situ zircon U-Pb dating and Hf-isotope analyses have been carried out on a suite of basalt-andesite-rhyolite volcanic rocks exposed in the Liuluocun area, Hainan Island, SE China. Zircon analyses show that these volcanic rocks crystallized in the Early Cretaceous (ca. 102 Ma). The basalts are characterized by low MgO contents and mg-numbers but high rare earth element, high field strength element and large ion lithophile element contents and Nb-Ta negative anomalies. They have relatively uniform Sr-Nd isotope compositions with ɛ_Nd(t) values of - 4.09 to - 3.63. The andesites show enrichment of high field strength element and rare earth element with negligible Eu anomalies. They have ɛ_Nd(t) values of - 2.35 to - 3.88 and ɛ_Hf(t) values of - 9.73 to - 1.13. The rhyolites have high K₂O and SiO₂ contents. They are characterized by prominent Eu, P and Ti negative anomalies and enrichment in large ion lithophile element, and show ɛ_Hf(t) values of - 7.51 to + 0.47 and ɛ_Nd(t) values of - 2.49 to - 2.69. Petrogenetic analysis indicates that the Liuluocun volcanic rocks were produced by incomplete reaction of the mantle wedge peridotite with felsic melts derived from partial melting of subducted sediment. All these characteristics, combined with geological observations, suggest that their formation was related to regional lithospheric extension in the South China Craton during the Early Cretaceous, which may have been caused by subduction of the Paleo-Pacific plate beneath the continental plate of China.