Zircon U-Pb dating, geochemical, and Sr-Nd isotopic characteristics of Duobagou trachyandesite from Dunhuang, NW China: Implications for crust-mantle interaction

摘要

Comprehensive petrological, zircon U-Pb dating, whole-rock geochemical, and Sr-Nd isotopic data are reported for the Duobagou volcanic rocks, intercalated with terrigenous clastic sequence, composing former Jurassic strata located at southeastern Dunhuang region, NW China. Duobagou volcanic interlayer is mainly composed of trachyandesite. LA-ICP-MS zircon dating yields a weighted mean Pb-206/U-238 age of 201.4 +/- 3.4 Ma, affirming the formation of Late Triassic. The trachyandesites are characterized by enrichment of LREE relative to HREE with negative Eu, Sr, and Ti anomalies. The epsilon(Nd)(t) values (-0.24-1.91) and (Sr-87/Sr-86)(i) (0.7037-0.7049) shows an affinity of OIB. The Duobagou trachyandesite and Lucaogou basalt were proposed to be produced via 1-5% and 10-20% partial melting of the spinel-garnet-bearing metasomatic enriched mantle and crystal fractionation coupled with slight extents of crustal contamination. Due to the delamination of thickened continental crust and asthenosphere upwelling, lower crustal material metasomatized and enriched the mantle source, leading to the eruption of trachyandesite. The Duobagou trachyandesite, Lucaogou sub-alkaline basalt and thick sedimentary strata revealed that the Dunhuang region remained in an extension setting accompanied by rifting from Late Triassic to Middle Jurassic.