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The west‐east contrast of magmatism in northern Tibet suggests that the lithospheric root has been removed in the west, following continental collision that led to lithospheric thickening and removal, but not in the east where paradoxically larger convergence occurred. Here we show a full‐wave Pn tomography model for the eastern Tibetan Plateau, which reveals a high‐velocity layer beneath the Moho extending to 150‐km depth. The anomalously high velocities and its northward dipping top surface suggest a very depleted and cold mantle consistent with an underthrusted Precambrian Lhasa lithosphere. A high‐velocity column connects this layer to another high‐velocity layer below 190‐km depth, representing early‐stage removal of the Tibetan mantle lithosphere and its interaction with the underthrusted Indian lithosphere. The west‐east contrast is thus attributed to different stages of lithospheric removal, which may be controlled by varying angles of Indian subduction from the west to the east. Plain Language Summary: The northern Tibetan Plateau can be divided into two parts: the western part with abundant young volcanic rock (<17 million years) and the eastern part where young volcanic rock is absent. Using compressional seismic waves that mainly travel in the upper mantle, we model the three‐dimensional wave speed structure of the upper mantle of the eastern Tibetan Plateau. Our model reveals that a very old and cold Tibetan mantle layer above 150‐km depth is experiencing foundering under eastern Tibet, and those foundered materials have downwelled onto the underlying Indian Plate below 190‐km depth. The mantle structure beneath the plateau east of ~93°E is different from that in the west where most of the Tibetan mantle lithosphere may have been removed already. This difference is consistent with the lateral contrast in recent volcanic activities and is presumably due to different styles of subduction of the Indian Plate between the west and the east. Key Points: The first full‐wave Pn model of the eastern Tibetan Plateau reveals early‐stage lithospheric founderingThe model shows a very depleted and cold underthrusted Lhasa lithosphere under the eastern Qiangtang TerraneThe west‐east contrast of magmatism in northern Tibet reflects different stages of lithospheric removal [ABSTRACT FROM AUTHOR]

[Display omitted] • The ore-forming biotite granite of the Longmala Pb–Zn–Fe–Cu deposit was emplaced at 54.6 ± 0.6 Ma. • The sulfur sources of the skarn Pb–Zn–(Ag), Pb–Zn–Fe–Cu and Fe–Cu deposits are mainly magmatic sulfur in the NGPB. • The ore-forming materials of Pb–Zn–(Ag) deposits originated from the S-type granites, whereas those of Pb–Zn–Fe–Cu and Fe–(Cu) deposits derived from the I-type granites. Many new skarn Pb–Zn–(Ag–Fe–Cu) deposits have been identified in the northern Gangdese polymetallic belt (NGPB). The NGPB comprises skarn deposits with different metal associations: Pb–Zn–(Ag), Pb–Zn–Fe–Cu, and Fe–Cu. The sources of ore-forming materials and whether intrusions contribute materials to these deposits, remain debated subjects. This study focused on zircon U–Pb dating and S–Pb isotopes of metal sulfides, ore-forming rocks, and wall rocks from the typical deposits in the three systems. Zircon U–Pb dating indicates that the biotite granite in the Longmala deposit was emplaced at 54.6 ± 0.6 Ma, which is consistent with its metallogenic age. The δ34S values of sulfides from the Pb–Zn–(Ag) deposits (Yaguila: −2.1‰ to + 6.0‰, Mengya'a: −0.8 ‰ to + 4.6 ‰) are similar to those from Pb–Zn–Fe–Cu deposits (Longmala: +1.6‰ to + 3.6‰, Lietinggang–Leqingla: −8.3 ‰ to + 2.0 ‰), suggesting a magmatic source of sulfur. The Pb isotopes of sulfides in Pb–Zn–(Ag) deposits (206Pb/204Pb = 18.4804–18.6935, 207Pb/204Pb = 15.6637–15.7331, and 208Pb/204Pb = 38. 0164–39.2612) are similar to those of the contemporaneous intrusions, as are those of Pb–Zn–Fe–Cu and Fe–Cu deposits, suggesting that the intrusions provided metals for the three systems. In comparison, the sulfides from the Pb–Zn–(Ag) deposits have higher 207Pb/204Pb values (15.6637 to 15.7331, mostly > 15.70) than the Fe–(Cu) deposits (15.6186 to 15.6848) and the Pb–Zn–Fe–Cu deposits (15.6163 to 15.7197), indicating that the metals of Pb–Zn–(Ag) deposits were derived from the upper-crust magma, whereas the metals of Fe–(Cu) and Pb–Zn–Fe–Cu deposits originated from the deep magma that required the involvement of mantle-derived components. Combined with previous research, we propose that the metals of Pb–Zn–(Ag) deposits originated from S-type granites, whereas those of Pb–Zn–Fe–Cu and Fe–(Cu) deposits were derived from I-type granites in the NGPB. [ABSTRACT FROM AUTHOR]

Crust-mantle interaction is essential to the evolution of continental crust, but its type and mechanism remain controversial in continental collision zones. Post-collisional ultrapotassic and adakitic rocks in southern Tibet can provide important constraints on this issue. Here, we newly identify the Miocene ultrapotassic enclaves hosted within the coeval Renduo adakitic granitoids (17–16 Ma), an excellent target to decipher the origin of two types of magmatism and their genetic relationship. The petrographic observations, together with elemental and isotopic features, argue for a magma mixing process. In addition, the ultrapotassic enclaves are not only enriched in incompatible trace elements and radiogenic isotopes, but also characterized by Nd Hf isotopic decoupling and sub-chondritic Hf/Sm ratios, indicating that their lithospheric mantle source was metasomatized by previous Neo-Tethyan oceanic components rather than by Indian continental materials. The adakitic host granitoids have relatively low MgO and compatible trace element contents, as well as low but variable whole-rock ε Nd (t) and zircon ε Hf (t) values. This suggests that they were generated by partial melting of thickened ancient lower crust, with varying degrees of involvement of ultrapotassic melts and asthenosphere-derived juvenile components. In combination with previously published results, we propose that relative to the metasomatism of subcontinental lithospheric mantle by subducted Indian crustal materials, the interaction between mantle-derived melts and overlying Lhasa continental crust was much more significant during the collisional orogeny, and played an important role in the crustal growth and reworking of southern Tibet; besides, the extensive post-collisional magmatism was likely triggered by the tearing of subducted Indian slab. [Display omitted] • Miocene ultrapotassic enclaves are hosted in coeval Renduo adakitic granitoids. • Enriched mantle source of ultrapotassic enclaves was metasomatized by Neo-Tethyan subduction processes. • Host adakitic rocks were originated from thickened ancient lower crust with involvement of mantle-derived materials. • Extensive interaction exists between mantle-derived melts and overlying continental crust in collisional orogens. [ABSTRACT FROM AUTHOR]

• The deposit is the first greisen-type W deposit recognized in the Lhasa terrane. • Crust-dominated granitic magmas are critical to W mineralization. • High degrees of fractional crystallization of the magmas is very important. • This study helps to understand the regional W mineralization potential. The Jiagang W-Mo deposit is the first greisen-type tungsten deposit recognized in the Lhasa terrane, and thus it has important genetic implications for understanding the regional tungsten mineralization potential. Greisen-type orebodies dominate in the deposit. Ores characterized by veinlets and dissemination are located in intensively altered monzogranite and contact zones between the monzogranites and sedimentary rocks. The minor quartz vein-type orebodies occuring as large quartz veins mainly precipitated in the sedimentary rocks. Intrusions associated with the Jiagang deposit are monzogranites, which can be subdivided into medium-grained monzogranite (MMG), porphyritic monzogranite (PMG), and fine-grained monzogranite (FMG). The zircon U-Pb ages of the PMG and MMG are 18.2 ± 0.2 Ma and 18.6 ± 0.1 Ma, respectively. These ages are consistent with the muscovite 40Ar-39Ar plateau ages (18.7 ± 0.2 Ma, 18.5 ± 0.2 Ma) and the molybdenite Re-Os isochron age (19.0 ± 0.3 Ma) within errors, indicating that the Jiagang W-Mo mineralization took place during the post-collisional stage of the Indo-Asian continental collision. The mineralization is temporally, spatially and genetically associated with the monzogranitic intrusions. The FMGs have the lowest SiO 2 contents (70.8–71.5 wt%), lowest differentiation index (DI = 85.7–86.3) and least obviously negative Eu anomalies (Eu/Eu* = 0.22–0.42). The PMGs and MMGs have higher SiO 2 contents (72.6–76.3 wt%), higher differentiation index (DI = 89.3–92.7) and more negative Eu anomalies (Eu/Eu* = 0.11–0.24). Almost all of the rocks are strongly peraluminous (A/CNK = 1.02–1.29), enriched in LILEs and depleted in HFSEs. Concentrations of K 2 O, CaO, FeOT and TiO 2 of the three types of monzogranites show negative correlations with SiO 2 , while P 2 O 5 exhibits the opposite trend. Values of Nb/Ta decrease with SiO 2 contents, and those of (La/Yb) N increase with La contents. Whole rock ε Nd (t) of the FMGs range from −11.3 to −11.1 with two-stage Nd isotopic model ages (T DM2) of 1741–1797 Ma, which are similar to those of the PMGs and MMGs (ε Nd (t) = −10.9– −10.6; T DM2 = 1709–1816 Ma). Zircon ε Hf (t) values of the PMG and MMG range from −13.8 to −5.3 with two-stage Hf isotopic model ages of 1439–1979 Ma. These data suggest that the ore-forming monzogranites are strongly peraluminous S-type granites, which should be derived from anatexis of the Proterozoic metagreywackes underneath the central Lhasa subterrane. The PMG and MMG are highly fractionated through various degrees of fractional crystallization of plagioclase, K-feldspar, biotite, monazite and allanite from the parental melts represented by the FMG. Zircon trace elements suggest that oxygen fugacity of the ore-forming magmas is relatively low and decreased as the magmas evolved, which is favorable to remove substantial tungsten from melts into the tungsten-mineralizing hydrothermal fluids. A high degree of fractional crystallization of the crustally-derived magmas with relatively low magmatic oxidation state are the critical factors determining the generation of the tungsten mineralization in the Jiagang deposit. Combined with the existing breakthroughs in prospecting exploration, we propose that the central Lhasa subterrane has great metallogenic potential in W-(Mo) mineralization associated with the Indo-Asian continental collision. [ABSTRACT FROM AUTHOR]