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Petrogenesis and tectonic implications of A-type granites in the Dabie orogenic belt, China: geochronological and geochemical constraints

LING CHEN^*,, CHANG-QIAN MA^*,,, ZHEN-BING SHE^*,, ROGER MASON^*, JIN-YANG ZHANG, and CHAO ZHANG^*,

^* Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China
Faculty of Mineral Resources, China University of Geosciences, Wuhan 430074, China

Author for correspondence: cqma{at}cug.edu.cn

The Dabie orogenic belt is characterized by the presence of large volumes of intrusive and volcanic rocks that formed in Late Mesozoic times. Most of the intrusive bodies are I-type granites but it is still unclear whether there are contemporary A-type granites. Here, we report the first unambiguous discovery of A-type granite from Baiyashan in the North Dabie tectonic belt. The crystallization age of the body has been fixed as 120.4 ± 1.2 Ma using U–Pb analysis of zircons by LA-ICPMS. The Baiyashan granite is enriched in Si, K, Na, Rb and REE, has elevated FeO^tot/(FeO^tot + MgO) and Ga/Al ratios, and is depleted in Mg, Ca, Mn, Ba, Sr, P and Ti. The REE composition shows highly fractionated patterns with (La/Yb)_N = 6.95–16.68 and Eu*/Eu = 0.33–0.59. Its crystallization age, field relationships, petrographic and geochemical data show beyond doubt that the Baiyashan granite is an Early Cretaceous A-type granite. Sr–Nd isotope systematics are characterized by a high I_Sr of 0.708–0.714 and a low _Nd of –7.5 to –19.4, with T_DM2 = 1.5–2.5 Ga, and these data indicate that the magmas were dominantly sourced from partial melting of middle to lower crustal intermediate-felsic igneous rocks and mingling with mafic to intermediate magmas, during rift-related magmatism associated with subduction of the Palaeo-Pacific Plate beneath Eastern China in Early Cretaceous times.

Key Words: A-type granites • petrogenesis • Late Mesozoic • Dabie orogenic belt