Abstract
In the eastern North China Craton (NCC), Mesozoic tectonics was dominated by the Paleo-Pacific subduction rollback and the Tanlu crustal-scale fault movement. The regional transtension had generated extensive adakitic magmatism, some Cu-Au ore-forming but others not. To establish the geodynamic setting and any metallogenic link for the adakites from the southeastern NCC margin, we analyzed the ore-barren adakitic rocks from underground mines in the Huaibei-Linhuan coalfield (where surface igneous outcrops are scarce), and compared their ages and geochemistry with other mineralized and ore-barren adakites across Eastern China. Zircon U-Pb dating reveals two magmatic episodes in the Huaibei-Linhuan coalfield: 1) early-Early Cretaceous (ca. 130–129 Ma) (quartz-)diorite and granodiorite, and 2) late-Early Cretaceous (ca. 115.8 and 105.8 Ma) microgabbro and dolerite. Whole-rock geochemistry indicates that the (quartz-)diorite and granodiorite are high-Mg adakitic, featured by low K2O/Na2O (avg. 0.33), high Sr/La (avg. 44.3), and lack of correlation between SiO2 (fractionation index) and Sr/Y (avg. 56.55) and MREE/HREE (avg. 1.09), resembling typical adakites derived from oceanic-slab partial melting. Geochronological correlation with the regional tectonic events suggests that the slab-melting may have been caused by the Paleo-Pacific subduction rollback. Further extension and crustal thinning in the late-Early Cretaceous along the southern Tanlu fault may have formed the gabbro-dolerite in the coalfield. Geochemical comparison suggests that parental magma of the Huaibei-Linhuan adakites may have had similar water content [similar zircon 10,000*(Eu/Eu*)/Y and Eu/Eu* ratios] to typical porphyry Cu-Au ore-forming magmas, yet the former may have been considerably more reduced (lower zircon Ce/Nd and whole-rock V/Sc ratios). We considered that the assimilation of Carboniferous-Permian coal seams in the area may have further lowered the magma fO2 and thus its potential to form Cu-Au mineralization.
Highlights
The Mesozoic eastern North China craton (NCC) is tectonically complex due to the co-influence of a number of tectonic events, including the North China-South China collision, the Paleo-Pacific subduction and rollback, the gradual NCC decratonization, together with the ∼500-km sinistral movement of the regional Tanlu fault zone and the accompanied pull-apart basin formation (e.g., Li et al, 2012, 2017; Hong et al, 2020; Zhang et al, 2020; Sun et al, 2021; Ye et al, 2021)
The Huaibei-Linhuandioritegranodiorite are of similar age than the Tongguanshan Cu-Au ore-forming adakites (∼136.7 Ma; Tongling orefield), and the ore-barren high-Mg adakitic plutons at Fangjiangzhuang (∼129.1 Ma) and Qiaotouji (∼131.7 Ma) in the MLYRB (Liu S.-A. et al, 2010; Jiang et al, 2020). This suggests that the emplacement of the Huaibei-Linhuandiorite and granodiorite was part of the extensive Early Cretaceousadakitic magmatism, which extended from the along the eastern MLYRB northward along the Tanlu fault
1) Petrography, zircon U-Pb dating and whole-rock geochemistry suggests that the Huaibei-Linhuan intrusive rocks fall into two types, early-Early Cretaceous high-Mg adakiticdiorite and granodiorite, and late-Early Cretaceous calc-alkaline microgabbro and dolerite
Summary
The Mesozoic eastern North China craton (NCC) is tectonically complex due to the co-influence of a number of tectonic events, including the North China-South China collision, the Paleo-Pacific subduction and rollback, the gradual NCC decratonization, together with the ∼500-km sinistral movement of the regional Tanlu fault zone and the accompanied pull-apart basin formation (e.g., Li et al, 2012, 2017; Hong et al, 2020; Zhang et al, 2020; Sun et al, 2021; Ye et al, 2021). The complex tectonic interactions resulted in the formation of important Cu-Au mineralization across the region, notably the world-class Jiaodong-Liaodong orogenic gold province (e.g., Goldfarb and Santosh, 2014; Zhang Z. et al, 2019; Liu et al, 2019, 2020; Li J. et al, 2020; Deng et al, 2020), and the Cu-Au-Fe polymetallic Middle-Lower Yangtze River Metallogenic Belt (MLYRB) (e.g., Pirajno and Zhou, 2015; Zhou et al, 2015; Zhang Y. et al, 2019; Lü et al, 2021) Many of these deposits are closely related in space-time to adakitic magmatism, yet many adakitic units in the region are ore-barren (e.g., Liu S.-A. et al, 2010; Li C. et al, 2020; Jiang et al, 2020). Through zircon U-Pb dating and whole-rock geochemical analyses, and by comparing geochemically with the coeval Cu-Au mineralized/barren adakites across Eastern China (esp. in the MLYRB and along/ near the southern Tanlu fault), we discuss why some adakites are ore-forming and some are not
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