Origin of Early Cretaceous Guandian adakitic pluton in central eastern China: partial melting of delaminated lower continental crust triggered by ridge subduction

ABSTRACT

Early Cretaceous adakite or adakitic plutons are widely distributed in central eastern China, e.g. lower Yangtze river belt (LYRB), the south Tan–Lu fault (STLF), and the Dabie orogen. Their genesis, however, remains controversial. In this contribution, we present detailed geochemical and geochronological study on the Guandian pluton in central Anhui Province, eastern China, which has been formerly regarded as a part of the north belt in the LYRB and lately classified in the STLF. Namely, it is located near the boundary between ridge subduction related slab melting and partial melting of lower continental crust (LCC). The Guandian pluton consists of quartz monzonite and is metaluminous and high-K calc-alkaline according to the chemical composition. The samples show high SiO₂ (59.15–62.32%), Al₂O₃ (14.51–15.39%), Sr (892–1184 ppm), Sr/Y (56.74–86.32), and low Y (12.65–18.05 ppm), similar to typical geochemical features of adakite. The Guandian adakitic rocks also exhibit high K₂O (2.88–3.86%), MgO (3.89–5.24%), and Mg# (55–60), negative anomalies of high field strength elements (e.g. Nb, Ta, and Ti), and positive anomalies of Ba, Pb, and Sr. LA-ICP-MS zircon U–Pb dating yielded a weighted average age of 129.2 ± 0.7 Ma. Calculations of zircon Ce⁴⁺/Ce³⁺ (6.97–145) and (Eu/Eu*)_N (0.23–0.42) on the basis of in situ zircon trace element analysis indicate that the magma had a lower oxygen fugacity relative to the ore-bearing adakites in the LYRB and Dexing, which is consistent with the fact of ore-barren in the research area. In combination with previous research, we propose that Guandian adakitic pluton was formed by partial melting of delaminated LCC triggered by Early Cretaceous ridge subduction of the Pacific and Izanagi plates. During ridge subduction, physical erosion destructed the thickened LCC and resulted in delamination, while thermal erosion facilitated partial melting of the delaminated LCC.

KEYWORDS:

• Adakitic pluton
• Early Cretaceous
• lower Yangtze river belt (LYRB)
• southTan–Lu fault (STLF)
• ridge subduction
• delamination
• lower continental crust (LCC)
• oxygen fugacity

Acknowledgements

We would like to thank Editor-in-Chief Professor Robert J. Stern and Guest Editor Professor Xiao-Yong Yang for handling and comments, and Dr. Sheng-Ao Liu and the other anonymous reviewer for constructive comments on the manuscript. This study was supported by National Key R&D Program of China: [Grant Number 2016YFC0600408], Natural Science Foundation of China: [Grant Numbers 41421062, 41103006 and 41402064], Guangdong Natural Science Funds: [Grant Numbers 2014A030306032 and 2015TQ01Z611], and Youth Innovation Promotion Association: [Grant Number CAS (2016315)]. This is contribution No. IS-2451 from GIGCAS.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Key R&D Program of China: [Grant Number 2016YFC0600408], Natural Science Foundation of China: [Grant Numbers 41421062, 41103006 and 41402064], Guangdong Natural Science Funds: [Grant Numbers 2014A030306032 and 2015TQ01Z611], and Youth Innovation Promotion Association: [CAS (2016315)].