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The Jurassic magmatic and volcanic rocks are widespread along the west central Lhasa subterrane. However, the petrogenesis of these rocks is poorly understood because of lacking high-quality geochronology and geochemical data. Here, we present new zircon U-Pb age and Hf isotopic data, whole-rock geochemical and Sr-Nd-Pb isotopic data for the Songduole and Qiangnong plutons in Geji area. LA-ICP-MS dating of zircon yield crystallization ages of 172.1 ± 1.9 and 155.9 ± 1.2 Ma for the Songduole and Qiangnong plutons, respectively. Geochemically, Songduole and Qiangnong granodiorite are characterized by high MgO (2.63-3.49 wt%), high Mg# (49-50), and low TiO2 (0.48-0.57 wt%). Besides, all rocks show metaluminous, calc-alkaline signatures, with strong depletion of Nb, Ta, and Ti, enrichment of large-ion lithophile (e.g. Rb, Th, K), and a negative correlation between SiO2 and P2O5. All these features are indicative of arc-related I-type magmatism. Five samples from the Songduole granodiorite have whole rock (87Sr/86Sr)i of 0.71207-0.71257, εNd(t) values of −15.1 to −13.9, zircon εHf(t) values of −17.4 to −10.5, (206Pb/204Pb)t ratios of 18.402-18.854, (207Pb/204Pb)t ratios of 15.660-15.736, and (208Pb/204Pb)t ratios of 38.436-39.208. Samples from the Qiangnong granodiorite have (87Sr/86Sr)i of 0.71230-0.71252, εNd(t) values of −15.1 to −14.2, zircon εHf(t) values of −12.6 to −6.4, (206Pb/204Pb)t ratios of 18.688-18.766, (207Pb/204Pb)t ratios of 15.696-15.717, and (208Pb/204Pb)t ratios of 38.546-39.083. These geochemical signatures indicate that the two plutons most likely originated from partial melting of the ancient Lhasa lower crust with obvious inputs of mantle-derived melts. Combined with regional geology, our results indicate that the Jurassic magmatism in the west central Lhasa subterrane most likely resulted from the southward subduction of the Bangong Ocean lithosphere beneath the central Lhasa terrane. [ABSTRACT FROM AUTHOR]

This article reports new zircon laser ablation-multicollector-inductively coupled plasma-mass spectrometry U-Pb and Hf isotope, whole-rock major and trace element, and Sr-Nd isotope data for mineralized and barren intrusions associated with the Duolong porphyry-epithermal copper-(gold) deposit (DPCD, a mining camp containing several individual deposits) in the western Qiangtang Terrane (QT), central Tibet. These data are used to further our understanding of the geological evolution of this region. The mineralized and barren DPCD intrusions are typical I-type granitoids that were synchronously emplaced at ca. 112.6-125.9 Ma. These igneous rocks show arc affinities that are characterized by enrichments in the light rare earth elements (LaN/YbN = 4.08-15.23) and the light ion lithophile elements (Rb, Th, U, K, and Pb), and depletions in the high field strength elements (Nb, Ta, and Ti). They have 87Sr/86Sr(i) values of 0.7046-0.7079, Nd(t) values of -6.0 to +1.1, and two-stage Nd model ages of ca. 823-1410 Ma. Zircons from these intrusive rocks have variable but generally positive εHf(t) values (-2.7 to +13.7) and relatively young zircon Hf crustal model ages of 335-1351 Ma. Combining these data with geochemical data reported in recent studies, we infer that the mineralized and barren DPCD intrusions formed in a continental marginal arc setting and likely originated from a common parental magma that was result of magma mixing of juvenile crust-derived basaltic melts and old lower crust-derived melts. The formation of the DPCD intrusions indicates that the Bangongco-Nujiang oceanic lithosphere was still undergoing northward subduction beneath the western QT at ca. 112.6-125.9 Ma, suggesting in turn that the oceanic basin have not closed completely during the Early Cretaceous. These new data also indicate that the processes that occur during the subduction of oceanic crust in continental marginal arc settings produce and preserve juvenile crustal material, leading to net continental crust vertical growth and thickening. [ABSTRACT FROM AUTHOR]