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Genesis and evolution mechanisms of granites provide clues regarding the development of architecture and composition of continental crust. Lithologically zoned granitoid complexes and mafic microgranular enclaves (MMEs) are common and enlightening in understanding of genesis and, particularly the dynamic evolution of granitoid magmas, as well as mantle–crust interaction. The Late Jurassic Xurucuo plutonic complex (XPC) in the South Lhasa is diverse in lithology, being composed of zoned monzogranite, granodiorite, quartz diorite, diorite, and MME. Here, zircon U Pb ages, oxygen and hafnium isotopes, and whole-rock and mineral geochemistries of the XPC were determined in order to reveal the genesis of the zoned pluton, and further, the dynamic processes of the crustal magmas. The XPC granitoids are high-K calc-alkaline and metaluminous to moderately peraluminous, I-type and arc-related magmatic rocks. These rocks were dated to be 159–154 Ma, with zircon δ18O values of 6.87–8.83‰ and negative eHf(t) values of −18.4 to −9.7. The concomitance of different lithologies and consistent O − Hf isotopic compositions suggest a prolonged cognate evolution of the magmas. The lithological and geochemical features of these granitoids indicate that they were generated from the reworking of crystal magma mush at shallow crustal levels aided by magma replenish, mixing and subsequent fractional crystallization. Combining our results with those of previous studies for the Late Jurassic magmatism in the Lhasa terrane, we propose an integrated model wherein mantle-derived magma intruded into crustal mush during the northward subduction of the Yarlung-Zangbo Neo-Tethyan oceanic lithosphere beneath the Lhasa terrane.

We report the occurrences of the remnants of a Meso-Tethyan oceanic plateau, encompassing an area of ~ 2 × 105 km2 in central Tibet. The plateau remnants include large volumes of pillow basalt formed largely by emergent to subaerial eruption, minor ultramafic intrusives and cumulates, exotic blocks of limestone, radiolarian chert, graywacke, and shale. Isotopic and paleontological dating suggest two major plateau eruptive events at 193–173 Ma and at 128–104 Ma, respectively. The basalts are characterized by enrichment of incompatible elements and a wide range of Sr–Nd isotope composition (initial eNd from –3.71 to + 7.9, initial 87Sr/86Sr from 0.703927 to 0.707618). The trace element and Sr–Nd isotopic data suggest that these basalts are of affinity with those from the Kerguelen and Tethyan plumes, indicative of a plume mantle upwelling origin with involvement of continental material. The wholesale obduction of the Meso-Tethyan oceanic plateau, along with the dismembered normal oceanic crustal fragments, over the Tibetan continental crust could have given rise to perhaps 2 km elevation of central Tibet during the Late Cretaceous.

Major and trace element, Sr–Nd–Pb and zircon U–Pb and Hf isotope data are presented for the newly discovered Abushan volcanic rocks in the southern Qiangtang Terrane, central Tibet. These results offer new insights into the evolution of the Tibetan plateau during Cretaceous. The Abushan volcanic rocks are composed mainly of andesites and trachy-andesites. Zircon U–Pb dating constrains the timing of emplacement as Late Cretaceous (79.9 ± 2.7–75.9 ± 0.49 Ma). Major element geochemistry shows that the Abushan volcanic rocks belong to high-K calc-alkaline series. All the andesites and trachy-andesites are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), and depleted in high field strength elements (HFSE) and heavy rare earth elements (HREE). The geochemical features and ages of the Abushan volcanic rocks relate them with post-collisional setting. Furthermore, the volcanic rocks display negative eNd(t) (− 3.1 to − 2.5), relatively constant 87Sr/86Sr ratios (0.70614–0.70735) and negative eHf(t) values (− 5.8 to − 2.1). The Sr–Nd–Pb and Hf isotope signature suggests that the andesites and trachy-andesites were derived from the anatexis of mafic lower crust by intrusion or underplating of mantle-derived basaltic magma. The petrogenesis of Abushan andesites provides robust evidence for the crustal thickening, delamination and early uplifting of central Tibet during Late Cretaceous.