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Petrogenesis and tectonic implications of Early Cretaceous andesitic–dacitic rocks, western Qinling (Central China): geochronological and geochemical constraints

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Feifei Zhang, Peter A. Cawood, Yunpeng Dong, Yuejun Wang

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Abstract

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.

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Original languageEnglish
Number of pages15
JournalGeoscience Frontiers
VolumeIn press
Early online date27 Nov 2018
DOIs
Publication statusE-pub ahead of print - 27 Nov 2018

    Research areas

  • Ar/Ar and zircon U–Pb geochronology, Sr–Nd isotopes, Early Cretaceous, AFC process, Continental lithospheric mantle, Western Qinling orogenic belt

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