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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.
Highlights
The Lower Yangtze River Belt (LYRB) in China has been the focus of several geological, geochemical and geochronological studies in relation to the voluminous magmatism and associated metallogeny [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
Previous studies have proposed diverse models on the genesis of these rocks such as: (1) mixing of melts from enriched mantle and lower continental crust (LCC) [11,13]; (2) partial melting of subducted slab or ridge subduction followed by crustal assimilation [6,7,9,12]
We present an integrated study of whole-rock major and trace elements, zircon U-Pb dating and Lu-Hf isotopes on the adakites and A-type granites
Summary
The Lower Yangtze River Belt (LYRB) in China has been the focus of several geological, geochemical and geochronological studies in relation to the voluminous magmatism and associated metallogeny [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. (1) mixing of melts from enriched mantle and lower continental crust (LCC) [11,13]; (2) partial melting of subducted slab or ridge subduction followed by crustal assimilation [6,7,9,12] The former model envisages an extensional setting for the calc-alkaline magmatic rocks, whereas the latter proposes a compressional setting. The late Mesozoic adakite and A-type granite intrusions in this area provide a window to explore magma evolution, tectonic setting and the relation with metallogeny. With this objective, we present an integrated study of whole-rock major and trace elements, zircon U-Pb dating and Lu-Hf isotopes on the adakites and A-type granites
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