Abstract
South China is famous for the extensive magmatism and polymetallic mineralization that took place there in the Mesozoic. Shilu is a large porphyry–skarn Cu–Mo deposit in the Yangchun Basin, South China. The lithology of the Shilu intrusion is granodiorite and quartz diorite, both of which are high-K calc-alkaline series, with high Sr (>400 ppm) content along with low Y and Yb contents. Most of the samples have characteristics of adakite except for a few samples that have slightly higher Y and Yb contents, which may be plausibly explained by crustal contamination. Laser Ablation Inductively Coupled Plasma Mass Spectrometry zircon U–Pb dating revealed ages between 106.6 ± 1.3 and 103.9 ± 0.5 Ma, with multiple magmatic pulses. Molybdenite Re–Os isochron age of 102.2 ± 2.9 Ma (MSWD = 9.4) was determined, which is identical to the youngest zircon U–Pb age (103.9 ± 0.5 Ma) within error. The Shilu intrusion has high oxygen fugacity as indicated by high zircon Ce4+/Ce3+ and EuN/EuN* ratios. Considering the geochemical characteristics (high Sr, and low Y and Yb contents), high oxygen fugacity, and copper mineralization of the Shilu intrusion, it was most likely formed by partial melting of a subducted young oceanic slab. Whole-rock Sr–Nd isotope-, zircon Hf isotope-, and whole-rock trace element analyses show that Shilu adakitic magmas may have interacted with type II enriched mantle and/or crustal materials during ascent. South China was affected by the Pacific tectonic regime to the east and the Neo-Tethys tectonic regime to the south in the Cretaceous. Based on the Pacific Plate drifting and rotation history, it is hard to explain how the Pacific Plate would have subducted and melted, forming adakitic rocks in the Shilu region. Considering the tectonic history of Southeast Asia and the South China Sea, the Neo-Tethys trench should have been much closer to the South China Block in the Cretaceous, and thus have had a greater impact on the South China Block. Based on the subduction direction, time of subduction, and distance between the Neo-Tethys subduction zone and the Shilu deposit, subduction of the Neo-Tethys ridge is the best mechanism for explaining the Shilu adakitic rocks and Cu–Mo mineralization.
Highlights
In the Cretaceous, South China was surrounded by several continental terranes and oceanic plates, such as the North China Block to the north, the Songpan-Ganzi Block to theActa Geochim (2017) 36(2):132–150 west, the Indochina Block to the southwest, the Pacific Plate to the east, and the Neo-Tethys Plate to the south
South China is famous for the extensive magmatism and polymetallic mineralization that took place there in the Mesozoic
6 CAS Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Science, Beijing 100101, China (MSWD = 9.4) was determined, which is identical to the youngest zircon U–Pb age (103.9 ± 0.5 Ma) within error
Summary
In the Cretaceous, South China was surrounded by several continental terranes and oceanic plates, such as the North China Block to the north, the Songpan-Ganzi Block to theActa Geochim (2017) 36(2):132150 west, the Indochina Block to the southwest, the Pacific Plate to the east, and the Neo-Tethys Plate to the south. A variety of tectonic models have been proposed to explain these characteristics and the Mesozoic tectonic evolution of South China more generally (Gilder et al 1991, 1996; Li 2000; Zhou and Li 2000; Zhou et al 2006; Li et al 2007, 2012; Sun et al 2007a, 2012b; Ling et al 2009; Mao et al 2011; Wang et al 2011). It has been proposed that the Neo-Tethys Plate subducted beneath the South China Block in the Cretaceous (Sun et al 2016b; Sun 2016). In addition to the giant W, Sn, Sb, Nb, Ta, U, and rareearth element (REE) deposit belts, a number of copper deposits occur in South China as well. Copper deposits in the northeast part of the South China Block have been well-studied. The genesis and tectonic setting of copper deposits in the southern part of the South China Block remain obscure
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