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The history of crustal thickening is critical for comprehending the evolution process of the Tibetan plateau. The genetic relationship and spatiotemporal distribution of adakitic rocks with high Sr/Y, (La/Yb) N ratios may impose fundamental constraints on specific geodynamic and crustal thickening processes. The Songka intrusive suite consists of adakitic rocks with high-Mg adakite (monzonites), low-Mg adakitic rocks (quartz monzonites), and gabbroic-diorites. Their geochemical characteristics, petrogenesis, and geodynamic implication is discussed in this paper. Songka high-Mg adakites formed when subducting Neo-Tethyan oceanic slab melts were assimilated by mantle peridotite at elevated temperatures (average Ti-in-zircon temperatures of sample SK1319 are 830 °C). Low-Mg adakitic rocks exhibit markedly different geochemical characteristics than those formed in the juvenile thickened lower crust. The least-squares mass balance and trace element simulations indicate that Songka low-Mg adakitic samples were formed at a degree of 60–65% fractional crystallization of melts resembling Songka high-Mg adakites. Songka gabbroic diorites are formed in the metasomatic mantle wedge. The genetic relationship between these rocks indicates that the crust of the southern Tibet did not appear to thicken obviously during the early stage of late Cretaceous (100–90 Ma). The intensive emplacement of late Cretaceous high-Mg adakites (Mg# > 50) and mafic rocks (SiO 2 < 52%) in the southern Lhasa terrane around 95–90 Ma, together with the slow convergence velocity of the Indian-Asian continent, can be explained by the response of rapid crustal thickening and Neo-Tethyan slab rollback at 95–90 Ma. • High-Mg adakitic rocks were formed from partial melting of Neo-Tethyan slab. • Coeval low-Mg adakitic rocks were produced by fractional crystallization. • Rapid crustal growth and Neo-Tethyan slab rollback occurred at 95–90 Ma. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ~91 Ma Chemen intrusion represents a magmatic product of the Late Cretaceous Gangdese magmatic 'flare-up' event. • The Chemen intrusion was derived from partial melting of Neo-Tethys oceanic crust during ridge subduction. • Compositions of zircon and apatite indicate that the Chemen intrusion has a high mineralization potential. • The mineralization potentials of some other Late Cretaceous intrusions may be limited due to low magma oxygen fugacities. Large-scale Late Cretaceous magmatic intrusions have been recognized in the southern Gangdese magmatic belt, although their genesis and mineralization potential remain controversial. In this paper, we present new zircon U-Pb ages, whole-rock compositions, and major- and trace element compositions of zircon and apatite from the Chemen granodioritic intrusion. When integrated with compiled literature data for other Late Cretaceous igneous rocks in the southern Gangdese belt, our new dataset provides new insight into their genesis and mineralization potential. The Chemen intrusion obtains a zircon U–Pb age of ~91 Ma, similar to the age of Late Cretaceous magmatic intrusions across the entire southern Gangdese belt. Both the Chemen and other Late Cretaceous intrusions have geochemical characteristics that resemble those of adakites. When considered alongside the coeval formation of mafic intrusive rocks, high-temperature adakitic charnockites, and thickening of continental crust in the region, ridge subduction is considered most likely to be responsible for this 'flare-up' event. The Ce4+/Ce3+ ratios in zircon and SO 3 contents of apatite from the Chemen granodiorites both indicate a high oxygen fugacity during crystallization. Further, trace elements in Chemen apatite indicate that the Chemen intrusion has a great mineralization potential; however, no mineralization has been found in some of the Late Cretaceous intrusions in the southern Gangdese belt. Compiled data show that these barren Late Cretaceous intrusions generally formed from magmas with a low oxygen fugacity. Thus, we speculate that the low oxygen fugacity of some Late Cretaceous intrusions may limit the extent to which mineralization may occur. [ABSTRACT FROM AUTHOR]