Geochemical and zircon U–Pb study of the Huangmeijian A-type granite: implications for geological evolution of the Lower Yangtze River belt

Abstract

The Early Cretaceous Huangmeijian Pluton is an A-type granite located on the northern bank of the Lower Yangtze River in Anhui Province, east-central China. It intruded the SE edge of the Early Cretaceous Luzong volcanic basin. The moderate- to coarse-grained granite is mainly composed of alkali feldspar, plagioclase, and quartz and has a typical A-type geochemical signature. LA-ICP-MS zircon dating yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 127.1 ± 1.4 Ma, similar to other A-type granites in the Lower Yangtze River belt, indicating an Early Cretaceous extensional environment. Temperatures calculated using the Ti-in-zircon thermometer suggest that the magma formed under high-temperature conditions (720–880°C). The low calculated Ce(IV)/Ce(III) ratio based on zircon rare earth element patterns indicates low oxygen fugacity for this A-type magma. Previous studies suggested that eastern China was an active plate margin related to the Early Cretaceous subduction of the Pacific and Izanagi plates. The ridge between these two plates probably passed under the Lower Yangtze River belt, forming A-type granites and adakites. The Huangmeijian Pluton is roughly the same age within error but is marginally older than the Baijuhuajian A-type granite in the eastern part of the Lower Yangtze River belt. A-type granite genesis in the Lower Yangtze River belt only lasted for 2–3 million years and slightly predates the transition from regional extension to compression. All these can be plausibly interpreted by the ridge subduction model, that is, A-type granites formed because of mantle upwelling through the slab window during subduction of the ridge separating the Pacific and Izanagi plates.

Keywords:

• A-type granitic intrusion
• geochemistry
• LA-ICP-MS zircon dating
• Huangmeijian Pluton
• Luzong volcanic basin
• east-central China

Acknowledgements

The contribution is supported by the Key Research project of the Chinese Academy of Sciences (KZCX1-YW-15), Ministry of Science and Technology of China (2006CB403505), and the Natural Science Foundation of China (No. 40525010). We thank Ying Liu (Guangzhou Institute of Geochemistry, Chinese Academy of Sciences) for assistance in fieldwork and analysis of XRF and ICP-MS. Constructive review comments from Zhaochong Zhang and Taofa Zhou are sincerely thanked. Contribution No. IS-1203 from GIGCAS.