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Minerals 2018, 8(8), 328; https://doi.org/10.3390/min8080328

Mesozoic High- and Low-SiO2 Adakites and A-Type Granites in the Lower Yangtze River Belt, Eastern China: Implications for Petrogenesis and Metallogeny

1
CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, 96 Jinzhai Road, Hefei 230026, China
2
MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, Xi’an Center of Geological Survey, CGS, Xi’an 710054, China
3
Center for Orogenic Belt Geology, Xi’an Center of Geological Survey, CGS, Xi’an 710054, China
4
School of Earth Science and Resource, China University of Geosciences, Beijing 100083, China
5
Department of Earth Sciences, University of Adelaide, Adelaide SA 5005, Australia
*
Authors to whom correspondence should be addressed.
Received: 8 June 2018 / Revised: 25 July 2018 / Accepted: 26 July 2018 / Published: 30 July 2018
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Abstract

The Lower Yangtze River Belt (LYRB) is one of the important magmatic and metallogenic belts in China and hosts abundant Mesozoic calc-alkaline magmatic rocks and economic mineral deposits. Anqing orefield in the southwestern of the LYRB received less attention during the last two decades. Here, we present an integrated study of whole-rock major and trace elements, zircon U-Pb dating and Lu-Hf isotopes on late Mesozoic adakites and A-type granites from the Anqing orefield. The adakites emplaced during 138–136 Ma and can be further subdivided into two types: high-SiO2 adakites (HSA) with SiO2 60 wt % from the Zongpu intrusion, and low-SiO2 adakites (LSA) 60 wt % from the Yueshan intrusion. The rocks display mid- to high-K calc-alkaline features and have consistent arc-like trace element characteristics with enrichment in LREE and LILE, and depletion in HREE and HFSE. The distinct zircon εHf(t) values for the LSA (from −27 to −20) and HSA (from −15 to −5) preclude a magma mixing model, yet suggest a subduction-related setting with partial melting of the subducted slab and overlying metasomatic mantle wedge. The A-type granites dated at 124 Ma from the Dalongshan intrusion characterized by LILE and LREE enrichment and slightly negative Eu anomalies, with lower MgO, CaO but higher K2O and Na2O contents. Their zircon εHf(t) values and geochemical features suggest that the parent magma was produced by the partial melting of Neoproterozoic crustal components, followed by variable degrees of fractional crystallization under a back-arc extensional setting, together with minor juvenile crust input. The adakites and A-type granites investigated in this study record a tectonic transition from compressive to extensional setting during 138–124 Ma. The transitional magmatic pulses are associated with distinct metallogenic signature with the adakites hosting copper deposits and the A-type granites linked to uranium mineralization. View Full-Text
Keywords: Adakite; A-type granite; Tectonic transition; Subduction; Lower Yangtze River Belt (LYRB) Adakite; A-type granite; Tectonic transition; Subduction; Lower Yangtze River Belt (LYRB)
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Liu, L.; Chu, G.; Li, Y.; Yang, X.; Santosh, M.; Hu, Q. Mesozoic High- and Low-SiO2 Adakites and A-Type Granites in the Lower Yangtze River Belt, Eastern China: Implications for Petrogenesis and Metallogeny. Minerals 2018, 8, 328.

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