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

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 ?_Nd(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.