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Geoscience ›› 2025, Vol. 39 ›› Issue (04): 947-963.DOI: 10.19657/j.geoscience.1000-8527.2025.023

• Ore Deposit and Petrology • Previous Articles     Next Articles

Zircon U-Pb Ages and Petrogenesis of Late Mesozoic Granitic Porphyries in the Northern Chaohu Area

WANG Ding(), CHEN Yuming, TAN Mingzhen, HU Zhixin, LI Zhensheng*(), LI Quanzhong   

  1. School of Resources and Environmental Engineering, Hefei University of Technology, Hefei, Anhui 230009, China
  • Online:2025-08-10 Published:2025-08-27
  • Contact: LI Zhensheng

Abstract:

Compared with the intense Late Mesozoic magmatism in the adjacent Middle-Lower Yangtze River Metallogenic Belt and Tanlu Fault Zone, intrusive rocks in the northern Chaohu (Chaobei) area are limited in distribution and development. In this study, zircon LA-ICP-MS dating and whole-rock elemental geochemical analyses are used to determine the formation age and petrogenesis of granitic porphyries in the Chaobei area, thereby providing new constraints on the regional tectonic evolution during the Late Mesozoic. The Chaobei granitic porphyries belong to strongly peraluminous, high-K calc-alkaline granites, consisting of 15%-30% phenocrysts (fine-grained feldspar, minor quartz, and biotite) and 70%-85% matrix (micrograined feldspar and quartz or biotite). Three crystallization ages of the Chaobei granitic porphyries were obtained in this study: (106.0±3.7) Ma, (103.9±4.4) Ma, and (97.1±4.6) Ma, corresponding to the Albian (Early Cretaceous) to Cenomanian (Late Cretaceous). These porphyries are coeval with or slightly younger than the highly fractionated A-type granites (108-103 Ma) in the Tanlu Fault Zone and adakitic rocks (109-100 Ma) in the Ningzhen area. The Chaobei granitic porphyries are relatively lowly fractionated S-type granites, formed by partial melting of the thickened Lower Yangtze Block lower crust under relatively high-temperature conditions, in a far-field back-arc weak extensional setting associated with the ortho-subduction of the Paleo-Pacific Plate. The decreased Sr/Y ratio of the Chaobei granitic porphyries, combined with the adakitic rocks in the Ningzhen area, provides robust evidence for lithospheric thinning of the Lower Yangtze Block during the Albian. Moreover, the A-type granites and bimodal volcanic rocks in the Tanlu Fault Zone clearly indicate that it is an intense lithospheric thinning zone.

Key words: strongly peraluminous granite, Paleo-Pacific plate, Cretaceous, zircon U-Pb age, northernChaohu

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