Petrogenesis and tectonic implications of Early Cretaceous andesitic–dacitic rocks, western Qinling (Central China) : geochronological and geochemical constraints
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40Ar/39Ar and zircon U–Pb geochronological and whole-rock geochemical analyses for the Laozanggou intermediate-acidic volcanic rocks from the western Qinling orogenic belt, Central China, constrain their petrogenesis and the nature of the Late Mesozoic lithospheric mantle. These volcanic rocks yield hornblende or whole-rock 40Ar/39Ar plateau ages of 128.3–129.7 Ma and zircon U–Pb age of 131.3 ± 1.3 Ma. They exhibit SiO2 of 56.86–66.86 wt.%, K2O of 0.99–2.46 wt.% and MgO of 1.03–4.47 wt.%, with Mg# of 42–56. They are characterized by arc-like geochemical signatures with significant enrichment in LILE and LREE and depletion in HFSE. All the samples have enriched Sr–Nd isotopic compositions with initial 87Sr/86Sr ratios ranging from 0.7112 to 0.7149 and ɛNd(t) values from −10.2 to −6.3. Such geochemical signatures suggest that these volcanic rocks were derived from enriched lithosphere-derived magma followed by the assimilation and fractional crystallization (AFC) process. The generation of the enriched lithospheric mantle is likely related to the modification of sediment-derived fluid in response to the Triassic subduction/collision event in Qinling orogenic belt. The early Cretaceous detachment of the lithospheric root provides a reasonable mechanism for understanding the petrogenesis of the Laozanggou volcanic sequence in the western Qinling orogenic belt.
Zhang , F , Cawood , P A , Dong , Y & Wang , Y 2019 , ' Petrogenesis and tectonic implications of Early Cretaceous andesitic–dacitic rocks, western Qinling (Central China) : geochronological and geochemical constraints ' , Geoscience Frontiers , vol. 10 , no. 4 , pp. 1507-1520 . https://doi.org/10.1016/j.gsf.2018.09.013
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DescriptionThis work is financially supported by National Natural Science Foundation of China (Grant Nos. 41421002, 41302176 and 41872236), National Basic Research Program of China (Grant No. 2014CB440901), and Foundation of Shaanxi Educational committee (14JK1760). P.A. Cawood acknowledges support from Australian Research Council (Grant FL160100168).
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