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The kinematics and deformation pattern along the Altyn Tagh fault (ATF), one of the largest strike‐slip faults on Earth is of great significance for understanding the growth of the Tibetan Plateau. However, the initial rupture along the ATF remains debated given the limited constraints on the depositional age of associated Cenozoic syntectonic strata. Here we investigated the syntectonic Cenozoic strata in the Xorkol Basin, associated with the strike‐slip faulting along the ATF. New uranium‐lead analyses of the carbonate deposits in the Paleogene strata yield dates of 58.9 ± 1.29 Ma, representing the initial rupture of the ATF. This first documented radioisotopic age coincides with the ca. 60 Ma onset timing of India‐Asia collision, highlighting its far‐field effect at the northern edge of the Tibetan Plateau. We infer that the deformation of the entire Tibetan Plateau started synchronously with the India‐Asia collision. Plain Language Summary: Carbonate U‐Pb dating techniques applied to rocks associated with the Altyn Tagh fault, a major fault in North Tibet, reveal that the fault started slipping about 58.9 million years ago, coinciding with the time when India collided with Asia. This finding provides new constraints on when and where this fault formed and suggests that the northern Tibetan Plateau started deformation earlier than previously thought. This result emphasizes that the entire Tibetan Plateau deformed simultaneously in the early Cenozoic. Key Points: Calcite U‐Pb dating yields ca. 59 Ma age for carbonate strata in the East Xorkol BasinXorkol Basin was a pull‐apart basin during the Paleocene due to the left‐lateral strike‐slip faulting along the Altyn Tagh faultWidespread Paleocene‐Eocene tectonism in Northern Tibet highlights the far‐field effect of the India‐Asia collision [ABSTRACT FROM AUTHOR]

The Bilong Co oil shale is one of the most significant source rocks in the Mesozoic Qiangtang Basin (Northern Tibet); however, its absolute chronology remains controversial. In this study, in situ carbonate U–Pb isotope dating analysis was carried out for the first time. Detailed field geological investigations yielded some age-diagnostic ammonites, enabling a re-evaluation of the stratigraphic age of the Bilong Co oil shale. A total of 61 spots of U–Pb isotope dating from the middle part of the Bilong Co oil shale section suggests an average age of 181 ± 13 Ma. Elemental geochemistry and diagenetic analysis indicate that the proposed age represents the early deposition of the calcite, and the oil shale was deposited during the Early Jurassic time. This estimated age is further supported by the newly discovered ammonite assemblage of Hildoceratidae–Tiltoniceras sp. at the top part of the oil shale section, which confirms the deposition of the oil shale during the Toarcian age of the late Early Jurassic. Consequently, the Bilong Co oil shale can be assigned to the Quse Formation, which is attributed to the Lower Jurassic rather than the Middle Jurassic. The re-assessment of the stratigraphic age of the Bilong Co oil shale is of great significance for regional evaluation and exploration activities of hydrocarbon source rock layers in the Qiangtang Basin as well as for global stratigraphic correlation of the late Early Jurassic Toarcian oceanic anoxic event. [ABSTRACT FROM AUTHOR]

A large amount of distal skarn Pb–Zn deposits without any causative intrusions exposed have been discovered along the eastern Nyainqêntanglha metallogenic belt (NMB) in the Gangdese region, Tibet, China. As a typical distal skarn Pb–Zn deposit in the east of NMB, the Mengya'a deposit is adjacent to the Longmala Pb–Zn ± Cu ± Fe deposit. However, the linkage between these two deposits is not unclear due to the chaotic dating results. In situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS) U–Pb dating of reddish‐brown and yellow‐green garnet from Mengya'a yielded lower intersect ages of 53.6 ± 3.1 and 52.4 ± 4.4 Ma, respectively, indicating that Pb–Zn mineralization took place during the main collision stage of the India–Asia plates. The δDSMOW values of garnet, quartz and calcite vary from −148.4‰ to −140.4‰, −123.5‰ to −115.3‰ and −127.9‰ to −121.3‰, with the δ18OH2O values ranging from 5.8‰ to 6.6‰, 0.4‰ to 3.7‰ and 1.0‰ to 1.7‰, respectively. The δ13CV‐PDB and δ18OSMOW values of calcite range from −8.2‰ to −4.7‰ and 9.8‰ to 18.6‰, respectively. These C–H–O isotopic compositions of hydrothermal minerals indicate that the ore‐forming fluids were initially derived from the magmatic water with progressive input of meteoric water from the prograde stage to the retrograde stage. The 87Sr/86Sr(53 Ma) ratios of sphalerite (0.72321–0.73474) are consistent with those of Ando gneiss in the Lhasa‐Golmud area, indicating that the basement gneiss makes a great contribution for the source of ore‐forming materials. The newly obtained garnet U–Pb ages at Mengya'a are consistent with those of mineralization and causative intrusion in the Longmala Pb–Zn ± Fe ± Cu deposit, suggesting that the Mengya'a and Longmala deposits constitute an integrated distal skarn‐type system. This proposed hypothesis suggests that the Fe–Cu ± Pb ± Zn mineralization within the contact zone should focus on the locations beneath the identified Pb–Zn orebodies at Longmala and Pb‐21 orebody at Mengya'a. [ABSTRACT FROM AUTHOR]

Construction of oceanic crusts in ultraslow-spreading ridges are controlled by detachment faults, but the specific ways they are determined by detachments remain unclear. Abundant ophiolite massifs discovered along the Yarlung-Tsangpo Suture Zone, southern Tibet, are considered to represent ultraslow-spreading centers of the Cretaceous Neo-Tethys ocean. The presence of various mafic blocks within the ophiolitic mélange beneath the lithospheric mantle provides evidence of the entire processes involved in crustal generation. Therefore, in this study geochemical investigations on these mafic blocks from the southern Luqu (Xigaze) ophiolitic mélanges were conducted to shed new lights on the petrogenesis of mafic crust rocks in ultraslow-spreading settings. Geochronological results via zircon U–Pb dating gave evidence for their coeval formation to other Yarlung-Tsangpo ophiolitic crust rocks in the Early Cretaceous (ca. 120–130 Ma). Geochemistry and Sr–Nd–Hf isotopes document depleted and primitive characteristics, revealing that these mafic rocks were crystallized from residual melts experienced substantial fractional crystallization following along liquid lines of descent of H2O-poor magmas. However, amphiboles are pervasive throughout our samples, which is in contrast with expectations of clinopyroxene and plagioclase as dominant liquidus phases of anhydrous magma. Textures of replacement of clinopyroxene by magnesio-hornblende and their higher contents of trace elements and Eu negative anomalies support that the amphiboles crystallized during transition from dry magma to hydrous one, indicative of water additions to solidifying melts. Based on the tectonic settings of ultraslow-spreading centers, we proposed a model in which seawater-derived fluids induced through detachment faults could be responsible for the generation of ultraslow-spreading crust. [ABSTRACT FROM AUTHOR]

With the northward subduction and final closure of the Neo-Tethyan oceanic crust, the Indian and Eurasian plates finally collided together and underwent a strong collision orogenic event, resulting in large-scale crust–mantle magmatic interactions. In order to clarify the controversies about tectono-magmatic activities after the Indian–Eurasian continental collision, we report the newly dated Eocene Qiongduojiang gabbro explored in the Tethyan–Himalaya belt, southern Tibet. LA-ICP-MS zircon U-Pb dating shows that the crystallization age of the Qiongduojiang gabbro is 46.1 ± 1.7 Ma. The whole-rock major and trace elements, as well as Rb-Sr, Sm-Nd, and Pb isotopic data results, show that the Qiongduojiang gabbro is apparently depleted in Nd isotopes, is enriched in Pb isotopes, and has maintained a consistent 87Sr/86Sr(t) value. This paper argues that the E-MORB-like Qiongduojiang gabbro originated from asthenosphere upwelling caused by slab breakoff of the Neo-Tethyan oceanic plate. This event caused large-scale magmatic activities, a magmatic mixing process between ancient crust and deep mantle, and wild distribution of Eocene Gangdese plutons along the Yarlung–Tsangpo Suture Zone, and it rendered the subduction-modified Tibetan lithosphere fertile from the Gangdese porphyry Cu deposits. [ABSTRACT FROM AUTHOR]

Hydrothermal rutile (TiO2) is a widely distributed accessory mineral in hydrothermal veins or alteration assemblages of porphyry deposits and provides important information for further understanding hydrothermal fluid signatures. This study determines the geochemical composition and U-Pb dates of hydrothermal rutile from the Yulong porphyry Cu-Mo deposit in east Tibet, China. Three types of TiO2 polymorphs have been identified based on their Raman spectroscopic, textural, and chemical characteristics. (1) Brookite and anatase pseudomorphs after titanite in a fine-grained matrix, indicating low-temperature hydrothermal fluids destabilizing primary Ti-bearing minerals during argillic alteration (type-I). (2) Elongated and prismatic rutile present in hydrothermal veins or in clusters in accompanying alteration envelope characterized by weak zoning (type-II). And (3) rutile intergrown with sulfides in hydrothermal veins, characterized by well-developed patchy and sector zoning (type-III). In contrast to the type-I and type-II TiO2 polymorphs, tungsten is enriched in backscattered bright patches and sector zones in type-III rutile, which is due to the substitution of W6+ in the Ti4+ octahedral site. The mechanism of the enrichment of tungsten is efectively driven by the halogen-rich (F, Cl) aqueous fluids during hydrothermal mineralization. In situ U-Pb dating of the type-III rutile yields a lower intercept age of 41.8 ± 1.2 Ma, which brackets the timing of the Cu-Mo mineralization. The relationship between rutile textures and composition indicates that W-bearing rutile can serve as a recorder of hydrothermal processes in porphyry Cu deposits. [ABSTRACT FROM AUTHOR]

The tectonic transition from oceanic subduction to continental collision is a fundamental process during orogenesis, yet the nature of such transition and associated deep geodynamic processes for the Tibetan Plateau are still controversial. The long‐lived magmatism of the Gangdese Belt of southern Tibet provides an excellent opportunity to study the tectonic transition from subduction of the Neo‐Tethys oceanic lithosphere to the continental collision between Indian and Asian plates. We present zircon U–Pb–Hf isotopes, whole‐rock geochemistry, and Sr–Nd isotopes for the intrusions from Maizhokunggar, southern Lhasa Terrane. The zircon U–Pb dating indicates that two episodes of magmatism occurred in the Maizhokunggar region, ca. 70 Ma diorites and ca. 60 Ma granitoids. The ca. 70 Ma diorites are medium‐K calc‐alkaline and characterized by pronounced high‐field‐strength element depletion and light rare earth element enrichment, similar to arc‐type rocks. They have homogeneous (87Sr/86Sr)i ratios (0.70378–0.70424) and εNd(t) values (+2.6 to +3.4), and εHf(t) (+5.9 to +13.0) with relatively young depleted mantle model ages (307–762 Ma), suggesting that they were generated from the juvenile mafic lower crust induced by the underplating of basaltic magmas from depleted mantle wedge. The ca. 60 Ma granitoids, Kajiacun (KJC) granodiorites, and Qulongxue (QLX) and Bangdacun (BDC) monzogranites are high‐K series and metaluminous to weakly peraluminous. The KJC granodiorites with high Sr/Y ratios (25–43) are adakitic and were likely derived from partial melting of a thickened lower crust. The BDC monzogranites have more evolved Sr–Nd–Hf isotopes and older Nd–Hf model ages than the QLX monzogranites. These geochemical variations were mainly controlled by the fractionation crystallization with assimilation of ancient crustal materials. We propose that at ca. 70 Ma, the subduction of the Neo‐Tethys oceanic slab triggered the partial melting of the juvenile lower crust and formed the diorites with arc affinity, and then the initial collision (>60 Ma) between the Indian and Asian plates caused locally thickened lower crust, resulting in adakitic granodiorites. Our study sheds light on the lithospheric scale magma evolution from the deep mantle to the shallow crust during the critical geodynamic transition to collision, and early uplift. [ABSTRACT FROM AUTHOR]

The widely distributed Eocene mafic microgranular enclaves in the Lhasa Terrane of southern Tibet carry important information regarding crust–mantle interactions in collisional zones. Here, we report geochronological and geochemical data of granitoids and mafic enclaves from Quxu in the southern Lhasa Terrane. Zircon LA‐ICP‐MS U–Pb dating indicates that the Quxu granitoids and enclaves were synchronously emplaced at ca. 50 Ma. The granitoids are medium‐ to high‐K calc‐alkaline, metaluminous (A/CNK = 0.82–0.90) and have high Al2O3 (14.48–16.57 wt%) and low MgO (2.81–2.99 wt%). The mafic enclaves (SiO2 = 50.55–54.57 wt%) have 5.12–5.37 wt% MgO and an Mg# of 49–51, with weakly negative Eu anomalies (Eu/Eu* = 0.85–0.91). The Quxu granitoids and enclaves have similar zircon Hf isotopic compositions, with εHf(t) values ranging from +7.62 to +13.32. A comprehensive study of the data available for coeval rocks from the Gangdese Batholith indicates that the Quxu granitoids were derived from partial melting of the lower crust, while the parental magmas of the mafic enclaves were most likely derived from lithospheric mantle beneath southern Tibet. The Quxu granitoids are interpreted as the result of mixing between the lower crust‐derived melts and lithospheric mantle‐derived mafic melts, which are likely the magmatic response to the breakoff of the Neo‐Tethyan Oceanic slab at about 50 Ma. [ABSTRACT FROM AUTHOR]

The metamorphism of the Central Qilian Block in the northeastern Tibetan Plateau records a complete tectonic history of the Qilian Orogen. Here, results of structural measurements, geochronological data, and thermobarometry for metamorphic rocks in the Central Qilian Block were presented, which trace the tectonic evolution of the Qilian Orogen. New U–Pb dating of detrital zircon from one paragneiss shows a main age population between c. 1500 and c. 1250 Ma, with the youngest age of 1085 Ma. This unit was intruded by an orthogneiss which has a U–Pb weighted mean age of 920 ± 18 Ma. Together with c. 1200–1000 Ma ages from inherited zircon cores in amphibolites, these results indicate that the protoliths of the Huangyuan Group were formed during the Mesoproterozoic and Neoproterozoic. Rims of these zircons obtain tightly constrained and concordant ages ranging from c. 459 to c. 427 Ma, with a weighted mean age of c. 450 Ma. Phase equilibrium modelling and conventional thermobarometry jointly indicate high‐temperature/medium‐pressure HT–MP metamorphism along a clockwise pressure–temperature (P–T) path at c. 450 Ma, passing through prograde conditions of 7.8–8.0 kbar and 620–650°C to peak conditions of ~7 kbar and ~780–800°C. Together with documented widespread metamorphism, magmatism, and ductile shear belts, these new results reassert that the Central Qilian Block experienced a three‐stage tectono‐metamorphic evolution during the Early Palaeozoic and the HT–MP metamorphism of Huangyuan Group was developed by a continental collision geodynamic setting with coeval mafic and granitic magmatism. [ABSTRACT FROM AUTHOR]

Travertines formed of crystalline crust have been widely reported, but there has not been focus on their geochemical characteristics. We therefore carefully conducted a series of geochemical investigations and U-Th dating on a travertine mound mainly composed of crystalline crust from Sobcha (southwest China) to determine their geochemical features and geological implications. The Sobcha travertines dominantly consist of granular crystals and fan crystals and show δ13C from 3.4‰ to 4.9‰ V-PDB, δ18O from −26.7‰ to −23.7‰ V-PDB, and 87Sr/86Sr from 0.712458 to 0.712951. When normalized to PASS, the Sobcha travertines exhibit MREE enrichment relative to HREE and LREE, HREE enrichment relative to LREE, and positive Eu anomalies. The δ13C signatures and mother CO2 evaluation of the Sobcha travertines show that the Sobcha travertines were thermogene travertines largely receiving mother CO2 from (upper) mantle (i.e., magmatic CO2) or a mixture of soil-derived CO2 and CO2 related to carbonate decarbonation. The 87Sr/86Sr of the Sobcha travertines is out of the 87Sr/86Sr ranges of local deposits exposed at Sobcha and surrounding areas but is well matched with the mean 87Sr/86Sr of Nadi Kangri volcanic rocks which cropped out to the northeast of the studied travertines (over 20 km away). This might indicate the important role of the Nadi Kangri volcanic rocks in suppling Sr to the studied travertines, but more studies are required. The LREE depletion compared to MREE and HREE in the Sobcha travertines was interpreted to be caused by the difference in geochemical mobility between LREEs and HREEs during water–rock interaction at depth, while the MREE enrichment compared to HREE was considered to be most likely inherited from reservoir/aquifer rocks. The positive Eu anomalies of the Sobcha travertines may result from very high reservoir temperatures and/or preferential dissolution of Eu-rich minerals/rocks (especially plagioclase). The Sobcha travertine mounds displays no or very slight vertical variations in δ13C, 87Sr/86Sr, and REE patterns, indicating the compositional stability of mother CO2 and paleo-fluids. However, a significant vertical increase in δ18O was observed and was explained as the result of gradual water temperature decrease related to climate cooling, self-closure of the vents, or mound vertical growth. The findings in this study might help us better understand the deposition of crystalline crust in Ca2+-deficient hot spring systems. [ABSTRACT FROM AUTHOR]

Demingding is a promising porphyry Mo-dominated deposit recently discovered in the eastern Gangdese metallogenic belt in Tibet, China. We present zircon U-Pb-Lu-Hf isotopic studies, as well as geochemical data of the late monzogranites and the prior rhyolites from the Demingding porphyry deposit to uncover their origin and geodynamic mechanism. Zircon U–Pb dating yielded precise crystallization ages of 17.3 ± 0.6 Ma (MSWD = 2.5) and 186.5 ± 3.0 Ma (MSWD = 2.0) for monzogranite and rhyolite, respectively. The monzogranite is characterized by high-K calc-alkaline, adakitic affinities, and positive zircon εHf(t) values (+0.9∼+5.6, avg.+3.1) with TDM2 (0.73–1.04 Ga), while the rhyolite has εHf(t) values of (+2.1∼+7.3, avg.+5.2) and TDM2 of (0.76–1.09 Ga) similar to the monzogranite. Our results suggest that the Demingding porphyry Mo (Cu) deposit is related to magma generated from the Neo-Tethyan oceanic subduction. The subsequent monzogranite porphyry was likely formed by the remelting of previously subduction-modified arc lithosphere, triggered by continental collision crustal thickening in Miocene. The lower positive εHf(t) values of monzogranites suggest minor inputs from the Mo-rich ancient crust, suggesting that Mo favors the silicate melt. Such magmatic events and special metallogenesis typify intracontinental processes and porphyry copper deposits, which are normally confined to oceanic subduction and Cu-dominated style, thereby making the continental setting and Mo-dominated style of Demingding exceptional and possibly unique. [ABSTRACT FROM AUTHOR]

The Amdo microcontinent located within the Bangong–Nujiang Suture Zone (BNSZ) holds one of the important keys to understand the tectonic evolution of Central Tibet before the Qiangtang‐Lhasa terrane collision during the Mesozoic. Newly discovered eclogites were reported within the Amdo microcontinent in this study, and their metamorphic evolution is deciphered by petrographic observations, pseudosection modelling, geochemistry, and zircon U–Pb dating. The eclogites are characterized by peak metamorphic mineral assemblages of garnet, omphacite, rutile, and quartz, and underwent a four‐stage metamorphic evolution, including eclogite facies stage (M1) at ~20–24 kbar and 580–620°C, followed by HP granulite facies decompression stage (M2) at ~13–15 kbar and 750–780°C, subsequent MP–HT granulite facies heating stage (M3) at 8–10 kbar and >840°C, and final amphibolite facies retrogression (M4) at 5.3–6.0 kbar and 560–580°C. The eclogites exhibit rare earth element (REE) distribution patterns and trace element abundance similar to those of N‐MORB and arc‐related volcanics, which are inferred to have formed in a back‐arc Basin tectonic setting. Zircon U–Pb dating yields eclogite facies metamorphic age of 190 ± 1 Ma. The clockwise P–T–t paths and the oceanic protolith signature of retrograde eclogites suggest that part of the back‐arc Basin was subducted to the depths of ~80 km. The subsequent ultra‐high temperature metamorphic overprinting may be related to the upwelling of the asthenosphere. Tectonic erosion associated with the subduction of the Amdo microcontinent beneath the Tethys Ocean accounts for the deep subduction of the back‐arc Basin and the absence of arc magmatic rocks in the northern Amdo microcontinent. [ABSTRACT FROM AUTHOR]

[Display omitted] • First direct timing constraints on the Jiaoxi and Anglonggangri W mineralization. • Garnet-muscovite granite provided most Fe in Anglonggangri ore-forming metals. • Varied fluid component and redox state in wolframite and scheelite precipitation. • Highly-evolved granites play critical roles on the Fe-rich wolframite formation. Critical factors controlling Fe-enriched wolframite formation in the quartz vein-type wolframite deposit are in controversy. The Jiaoxi and Anglonggangri are typical examples of quartz vein-type wolframite mineralization found in western Lhasa terrane. The Jiaoxi wolframite comprise dominantly early hübnerite with late ferberite, whereas, the Anglonggangri wolframite are mainly ferberite. Wolframite U-Pb dating yields direct timing of 11.0 ± 0.2 Ma and 9.7 ± 0.2 Ma for Jiaoxi and Anglonggangri tungsten mineralization, respectively. Ages together with enrichment of Nb, Ta, Ti, and Sc and depletion of Sr and most Eu anomaly within Anglonggangri wolframite confirm that metals and fluids were mainly derived from the ore-forming garnet-muscovite granite. Iron and Mn mapping of garnet in the garnet-muscovite granite suggests this granite has changed from the early Mn-enriched to late Fe-rich affinity. Therefore, initial ore-forming fluids exsolved from garnet-muscovite granite have Fe-rich composition, that was significantly modified during tungsten mineralization. Positive trend between Mg and Fe/(Fe + Mn) of wolframite indicates biotite breakdown from country rock of biotite-muscovite granite to add Fe and Mg into fluid during greisenization. Meanwhile, decomposition of plagioclase and K-feldspar provided Ca, Sr, and Eu to form late scheelite. Enrichment of Sr with positive Eu anomaly and decline of REE, Nb, and Ta are typical features of the highly evolved and modified fluid. Positive and negative Eu anomalies within the same wolframite grains reveal the oxidized character and fluctuating composition of fluid during wolframite precipitation. By contrast, negative Eu anomaly and low Mo abundance of scheelite indicate the reducing fluid during scheelite crystallization. Identification of metal and fluid sources for Anglonggangri ferberite highlights the evolved granites play more crucial roles on ferberite formation than early hübnerite crystallization and Fe addition from country rocks during hydrothermal interaction. [ABSTRACT FROM AUTHOR]

The timing of the Lhasa–Qiangtang collision following the closure of the Bangong–Nujiang Tethys Ocean has not been well constrained. An integrated study of whole-rock geochemistry and zircon U–Pb–Hf isotopes was carried out for Early Cretaceous quartz diorite-porphyrites and granites from the Yilashan and Amdo areas, northern Tibet. LA–ICP–MS zircon U–Pb dating reveal that the Yilashan and Amdo granitoids were emplaced at ~121–110 Ma. These granitic rocks display selective enrichment of light rare earth elements, large ion lithophile elements (e.g., Rb, U) and Th, but depletion of Sr and high field strength elements (e.g., Nb, Ta, Ti) compared to its neighboring elements. These new data, combined with regional geological setting, show that these igneous rocks were formed under a geodynamic setting of the Lhasa and Qiangtang (–Amdo) collision with oceanic slab breakoff and asthenospheric upwelling. The BNTO had been closed at ~121–110 Ma in the study area. Yilashan-Amdo granitoids roughly yield high (87Sr/86Sr)i ratios and obvious negative εNd(t) and zircon εHf(t) values along with old Nd TDM and zircon Hf TDM2 ages. Together with their variable U–Pb ages, these features indicate a Precambrian "hidden" crustal source beneath the northern Lhasa and Amdo terranes. The YLSS S-type granophyres were derived from partial melting of Paleoproterozoic lower crustal metagraywackes, whereas the YLSZ quartz diorite–porphyrites and the Amdo I- and A-type granites were mainly derived from partial melting of Paleo–Mesoproterozoic lower crustal mafic rocks with a certain amount of addition of mantle-derived melts. Minor amounts of the materials originated from the Amdo orthogneisses may also be involved in the formation of the YLSZ quartz diorite–porphyrites and the Amdo I-type granites. In addition, the Yilashan ophiolite was intruded by the ~112–108 Ma granophyric and quartz diorite–porphyritic intrusions before its final emplacement into the surrounding strata. [ABSTRACT FROM AUTHOR]

Although a large number of Triassic magmatism were found in the Qiangtang terrane, central Tibet, the tectonic evolution of the Shuanghu Palaeo‐Tethys Ocean remains controversial. In this study, we present the zircon U–Pb age and major‐ and trace‐element data for the Late Triassic pluton from the Cairi area in the eastern Qiangtang terrane. Zircon U–Pb dating indicates that the samples were emplaced at ca. 230 Ma. The magmatism from the Cairi area primarily consists of granites (SiO2 = 67.28–77.74), with the characteristics of medium‐K calc‐alkaline, metaluminous, and peraluminous. The Cairi granites are enriched light rare earth elements ([La/Yb]N = 5.01–10.56), with obvious Eu anomaly (Eu/Eu* = 0.32–0.47). The Cairi granites are characterized by low 1,000 × Ga/Al (2.10–2.64), FeO*/MgO (3.41–5.03), Ce (57.95–114.36 ppm), Y (27.30–45.19 ppm), and negative correlation between P2O5 and SiO2. These geochemical features reveal that the Cairi granites are calc‐alkaline, I‐type granites. The four samples show relatively restricted (87Sr/86Sr)i ratios (0.70598–0.70724), 143Nd/144Nd ratios (0.51192–0.51196), and εNd(t) of −8.19 to −7.54. Based on the variations of Rb–Sr–Ba and Th–La–Nb and the zircon saturation of temperatures (806–868°C), we suggest that the primary magmas of the Cairi granites were generated through various degrees of mixing between sediments and mantle‐derived components. Petrological and geochemical characteristics, as well as regional geological characteristics indicate that the Cairi granites formed in a continental volcanic arc setting. Our results, in combination with the coeval granites and elcogite, indicate that the generation of Late Triassic (ca. 230 Ma) Cairi granites is related to ocean ridge subduction and subsequent development of a slab window. [ABSTRACT FROM AUTHOR]

The establishment of continental-scale drainage systems on Earth is largely controlled by topography related to plate boundary deformation and buoyant mantle. Drainage patterns of the great rivers in Asia are thought to be highly dynamic during the Cenozoic collision of India and Eurasia, but the drainage pattern and landscape evolution prior to the development of high topography in eastern Tibet remain largely unknown. Here we report the results of petro-stratigraphy, heavy-mineral analysis, and detrital zircon U-Pb dating from late Cretaceous–early Palaeogene sedimentary basin strata along the present-day eastern margin of the Tibetan Plateau. Similarities in the provenance signatures among basins indicate that a continental-scale fluvial system once drained southward into the Neo-Tethyan Ocean. These results challenge existing models of drainage networks that flowed toward the East Asian marginal seas and require revisions to inference of palaeo-topography during the Late Cretaceous. The presence of a continent-scale river may have provided a stable long-term base level which, in turn, facilitated the development of an extensive low-relief landscape that is preserved atop interfluves above the deeply incised canyons of eastern Tibet. This study provides evidence for a continental-scale river system that existed in eastern Tibet before the India-Asia collision. The river system developed an extensive low-relief landscape, which was uplifted and dissected during the late Cenozoic. [ABSTRACT FROM AUTHOR]

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[Display omitted] • The Mazhala Au-Sb deposit in South Tibet was constrained at ca. 35 Ma. • Mazhala apatite belongs to fluorapatite having F contents of 2–4%. • Mazhala apatite is rich in MREE but depleted in LREE- and HREE. • Mazhala apatite have δ18O values in the range of 16-19‰. • The Mazhala Au-Sb deposit was mainly precipitated from metamorphic water. Due to lack of suitable datable minerals, timing of the Mazhala Au-Sb deposit in South Tibet remains unresolved. Also, previous geochemical studies suggest an ambiguous conclusion on the source of ore-forming fluid, with diverse viewpoints of magmatic water, mixed magmatic–meteoric water or mixed metamorphic-meteoric water, respectively. In this study, hydrothermal apatite U-Pb dating constrains the Mazhala Au-Sb deposits to have formed at ca. 35 Ma, consistent with the timing of Eocene leucogranite intrusions in South Tibet. The Mazhala Au-Sb mineralization occurred during the main collision stage to late collision stage in Eocene to Oligocene, and predates the Cuonadong Sn mineralization in South Tibet which occurred during the crustal extension stage in Miocene. An EPMA analysis shows the apatite belongs to fluorapatite that have F contents in the dominant range of 2–4%. The Mazhala apatite displays an overall MREE enrichment and LREE- and HREE depletion distribution pattern with positive Eu anomalies, and have δ18O values dominantly in the range of 16-19‰ with a mean δ18O‰ value of 17.74 ± 0.15‰ (2σ), which suggest a relatively homogenous chemical composition for the ore forming fluids with a relatively stable temperature regime. In combination with previous temperature estimates, the ore forming fluids are inferred to have a dominant δ18O fluid value of 13-16‰, which overlap with metamorphic water. The combined age and geochemical data suggest Eocene leucogranite intrusion induced metamorphic fluid circulation within Paleozoic-Mesozoic metamorphic sedimentary rocks around the study area, which prompted precipitation of fluorapatite together with Au-Sb bearing pyrite and arsenopyrite in the Mazhala Au-Sb deposit. This study puts an emphasis on the contribution of metamorphic water as the dominant ore-forming fluid origin in the Mazhala Au-Sb deposit. In contrast, the close spatial and temporal association of the Cuonadong Sn polymetallic mineralization with the Miocene leucogranite intrusion-induced hydrothermal activity in the Cuonadong dome demonstrates that their genetic links, as was also evidenced by C-H-O-S-Pb isotope data that point to a dominant contritution of Miocene leucogranite to ore-forming fluid and materials for the Cuonadong Sn polymetallic ore deposits. As such, from a perspective of ore-forming model in South Tibet it be seen that during the main collision stage to late collision stage ore-forming fluid and materials were mainly derived from metamorphic water, whereas during the crustal extension stage, ore-forming fluid and materials were dominantly sourced from magmatic water. [ABSTRACT FROM AUTHOR]

[Display omitted] • The age of garnets (90–89 Ma) matched the age of Au-Cu mineralization (88.6 ± 0.6 Ma); • The Galale deposit is a typical Mg-skarn Au-Cu deposit; • The REE content of garnets was influenced by metasomatism and ore-forming fluids; • The high fO 2 of fluids in early stages is vital for Au-Cu enrichment. Compared to calcareous skarn Au-Cu deposits, magnesian skarn (Mg-skarn) Au-Cu deposits are scarce; hence the early evolution of the ore-fluids to late mineralization for the kinds of deposits has been inadequately investigated. Located at the southern margin of the Bangong-Nujiang metallogenic belt, the Galale Au-Cu deposit contains 32.59 tonnes of gold (average grade 2.04 g/t) and 105,600 tonnes of copper (average grade 0.66 %). The orebodies are hosted in an Mg-skarn with associated minerals, including olivine, pyroxene, garnet, and serpentine, which developed in the contact zone between the granodiorite and dolomite of the Jiega Formation. However, the genetic relationship between the Mg-skarn, granodioritic magma, and Au-Cu mineralization remains unclear. The contribution of early stage ore-forming fluids to late Au-Cu mineralization is still vague. In this study, we present the major and trace element compositions, and U–Pb isotope data for garnets obtained from the Galale deposit. We used the data to define the timing, nature, and evolution of early ore-forming fluid and described the genesis of the deposit. The color, at macro- and micro-scales, and chemical composition of the garnets can be used to divide them into two categories, namely early Al-rich Grt-I type garnets, and late stage Fe-rich Grt-II type garnets. In practice, Grt-I (And 29.5∼56.1 Gro 41.3∼68.0 Pra 1.6∼2.8) and Grt-II (And 96.7∼99.9 Gro 0∼2.7 Pra 0.1∼0.7) are grossular-andradite solid solution system garnets. Based on the chondrite-normalized REE patterns, Grt-I can be further divided into two sub-classes: Grt-I-1 domain in the core, enriched in HREEs and U, and Grt-I-2 material in the rim, relatively depleted in HREEs. Grt-II is enriched in LREEs and depleted in HREEs. Eu anomalies are slightly negative for the Grt-I-1 domain, weakly positive for the Grt-I-2 domain, and strongly negative for the Grt-II type garnets. The variations in texture and composition in garnets indicated that the formation of Grt-I garnets occurred during diffusive metasomatism in a relatively closed system, in a moderately oxidized ore-forming fluid setting. The formation of Grt-II occurred in a strongly oxidized setting during advective metasomatism in an open system. The enrichment of REE and U in Grt-I garnets was mainly controlled by a "menzerite" type substitution mechanism, partially explaining the strong positive correlation between Mg and REE concentrations. In the Grt-II type garnets, enrichment may also have been co-controlled by coupling substitution and adsorption. In situ U–Pb dating of garnet shows that Grt-I-1 and Grt-I-2 material has isotopic ages of 92 ± 2 Ma (2σ, MSWD = 0.85) and 91 ± 2 Ma (2σ, MSWD = 0.96), respectively. The results were consistent with the previous ages obtained from the granodiorite and Molybdenite using Re–Os isotopic dating within error. This indicates that magma, skarn alteration, and mineralization were spatially and temporally related. In addition, it indicates that the Galale deposit is a typical Mg-skarn Au-Cu deposit. In the earliest stages of deposit development, ore-forming fluids with a high oxygen fugacity (fO 2) have inherited their characteristics from the magma. The crystallization of many magnetites during the oxide stage has decreased oxygen fugacity in the metallogenetic system. This has resulted in a relatively low fO 2 fluid for Au-Cu precipitation. The study demonstrates that the ore-fluid fO 2 plays a vital role in metal migration, hence Au-Cu mineralization in Mg-skarn deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multi-stage intrusions from pre- to post-mineralization at Bairong are studied. • They formed at 14.1 to 11.6 Ma and derived from a cogenetic magma chamber in a post-collisional setting. • They are all oxidized and hydrous with comparable magmatic S contents, but have different Cl contents. • Fluid exsolution and buffering effect of magmatic anhydrite possibly result in S-Cl decoupling. • Oxidized and hydrous magma with effective fluid exsolution is the key factor for Bairong Cu-Mo mineralization. Volatiles are considered to play an important role in porphyry Cu mineralization, and high apatite S and Cl contents are often used to distinguish fertile magma systems from barren ones in the subduction zone. However, magmatic volatile evolution and its implications in post-collisional porphyry deposits remain enigmatic. To address this issue, we conducted zircon U-Pb dating and Hf isotope, and zircon and apatite chemical compositions of multi-stage magmatic rocks from the Bairong post-collisional porphyry Cu-Mo deposit in the Gangdese belt, Tibet. The magmatic rocks included pre-mineralized porphyritic monzogranite and biotite monzogranite, syn -mineralized monzogranite porphyry, and post-mineralized dacite porphyry that formed in 14.1–12.7 Ma, ca. 12.1 Ma, and 11.8–11.6 Ma, respectively. All these intrusions have depleted zircon Hf isotope (ε Hf (t) = 1.7–8.0, 3.7–9.0, 3.3–9.7 for pre-, syn-, and post-mineralized intrusions, respectively) together with the research results of contemporaneous magmatic rocks in the adjacent area, suggesting that the multi-stage intrusions at Bairong are derived from a cogenetic magma chamber in post-collisional extension setting. All the intrusions have similar zircon Ce N /Ce N *, Eu N /Eu N * ratios with average ΔFMQ values of 2.1 – 2.6, together with the high apatite Eu N /Eu N * ratios and low Ga concentrations, implying that their magmas are all oxidized. These intrusions have zircons (10,000 × Eu N /Eu N *) /Y all > 1 and Ce/Nd/Y mostly > 0.01, and obtain low average titanium-in-zircon temperatures of 659 to 714 °C, which indicate their magmas are hydrous. Apatite Cl contents decrease, combined with the drop of apatite X Cl /X OH and the surge of X F /X Cl ratios from pre- to syn -mineralized intrusions, possibly indicating that fluid exsolved from magma at the syn -mineralization stage. The apatite SO 3 contents in these different-stage intrusions, however, are almost unchanged. Combined with previous studies, the buffering effect of magmatic anhydrite maintains the stability of magma S content, which together with fluid exsolution leads to the S-Cl decoupling. Consequently, we conclude that the oxidized and hydrous magma with effective fluid exsolution is a critical control on the formation of Bairong porphyry Cu-Mo mineralization. Considering the wide variations of apatite Cl contents and the occurrences of S-Cl decoupling, simple application of high apatite SO 3 and Cl contents to distinguish the ore-forming and barren systems in the post-collisional porphyry system should be cautious. [ABSTRACT FROM AUTHOR]

[Display omitted] • Here we characterize the geology and mineralization of the Sangri porphyry-skarn Cu-Mo deposit. • Zircon and garnet U-Pb, molybdenite Re-Os and K-feldspar Ar-Ar geochronology link magmatism, mineralization and alteration. • The Multi-isotopic dating could help to construct the defined time-framework of porphyry system. Obtaining a precise time framework has been a key but difficult problem for the study of metallogenic porphyry systems. This is more complicated when there are several stages of intrusion emplacement, different alterations, and mineralization events. To solve this problem, the Sangri porphyry-skarn Cu-Mo deposit in the Bangongco-Nujiang metallogenic belt, Tibet, was used as a study site for multiple isotopic dating studies. Zircon U-Pb dating of different intrusions shows that the magmatism of intermediate-felsic intrusions dates from 83.2 ± 0.8 Ma to 81.7 ± 0.7 Ma. Garnet U-Pb dating places the skarn as being formed in 83.2 ± 2.3 Ma. Re-Os dating of molybdenite in quartz-molybdenite vein and Ar-Ar dating of K-feldspar indicate ore-forming and alteration periods of 82.6 ± 0.6 Ma and 80.3 ± 1.8 Ma, respectively. The Sangri deposit is a product of magmatic-hydrothermal mineralization between 84 and 80 Ma in the Late Cretaceous. The mineralization of the Sangri deposit and precise geochronology data indicate that there was a Late Cretaceous metallogenic event in the Central Bangongco-Nujiang metallogenic belt, which provides a new clue for regional exploration and metallogeny. Finally, multi-element isotopic dating is shown to be an important method for constructing the time framework of porphyry systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nianzha is an ophiolite-hosted large orogenic type gold deposit in Southern Tibet. • Two different types (magmatic and hydrothermal) of apatite were identified in the Nianzha. • U-Pb dating of hydrothermal apatite revealed an Eocene gold mineralization event (ca. 44 Ma) in Nianzha. • Hydrothermal apatite U-Pb chronometer is effective in constraining the age of orogenic-type gold mineralization. Mineralization age dating is essential for understanding orogenic-type gold metallogeny, but suitable minerals for dating are not always available. Apatite can incorporate considerable amount of U and Th, making it a potential U-Pb geochronometer to study hydrothermal alteration and mineralization processes. The newly-discovered Nianzha is a large orogenic Au deposit (∼25 t @ 3.08 g/t Au) and located in the contact fault zone between ultramafic rocks and diorite in the Renbu tectonic mélange of southern Tibet. Two different types of apatite were identified in the Nianzha gold deposit: type I magmatic apatite hosted in diorite and syenite, and intergrown with other magmatic minerals; type II hydrothermal apatite hosted in mineralized diorite. These apatite grains are coarse euhedral granular and closely associated with auriferous sulfides (e.g., pyrite, chalcopyrite, galena). Type I apatite is F- and SO 3 -rich, whereas type II apatite is distinct from type I apatite by its significantly higher Cl, Mn, rare earth elements (REE), U, Th, and As contents, indicative of a hydrothermal origin. Thus, formation age of type II apatite reflects the timing of gold mineralization. Two type I magmatic apatite samples yielded similar discordia U-Pb ages of 80.35 ± 1.56 Ma (MSWD = 1.3; n = 86) and 79.53 ± 1.27 Ma (MSWD = 0.91; n = 72), respectively, whilst type II hydrothermal apatite yielded a discordia age of 44.60 ± 1.45 Ma (MSWD = 1.2; n = 64). The gold mineralization age is consistent with that of nearby orogenic gold deposits (e.g., Mayum, Bangbu, Zhemulang, and Juqu) in the region. Therefore, we suggest that hydrothermal apatite U-Pb dating can effectively constrain the timing of orogenic Au mineralization events. [ABSTRACT FROM AUTHOR]