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The Altun orogenic belt is situated along the northern boundary of the Tibetan Plateau. In this study, we present an analysis of the ore deposit, mineral composition, and carbon isotope signatures of the Tugeman graphite deposit within the Altun orogenic belt. The graphite in the Tugeman graphite deposit occurs within graphite-bearing schists and marble. Graphite enrichment is observed in the ductile shear zone. The carbon isotope values of graphite range between −18.90‰ and −10.03‰ (with an average value of −12.70‰). These values differ significantly from those observed in organic matter and marine carbonates, suggesting the occurrence of a mixing process involving reduced carbon fluid derived from biological organic material during regional metamorphism as well as a potential influx of oxidized carbon fluid from external sources. In addition, the metamorphic temperature of Tugeman graphite calculated from Raman spectroscopy is between 494 °C and 570 °C, which indicates that the disordered material is transformed from greenschist-amphibolite facies metamorphism to moderate-crystalline graphite. Combining the geological and carbon isotope characteristics of the Tugeman graphite deposit, we argue that the Tugeman graphite deposit is a regional metamorphic graphite deposit of biogenic origin, and during the late stage of metamorphism, it underwent interaction with fluids. [ABSTRACT FROM AUTHOR]

We discovered that biotite granite is associated with biotite–oligoclase–microcline pegmatite and gneisses biotite granite is associated with two–mica microcline–albite pegmatite in Tugman area. A combined study of the field investigation, petrography, geochronology, and major-trace element of granite and pegmatite was performed in this study. The results indicate that pegmatites can be formed during both highly fractionated and less-evolved stages of granite formation, but only highly differentiated granites are favorable for the Li and/or Be mineralization; The Tugeman granites formed during the late Cambrian–Middle Ordovician (500–440 Ma) and can be divided into three groups related to the northward subduction of the Central Altun Ocean crust at 520–490 Ma, the closure of the Central Altun Ocean at 490–480 Ma, and post-collisional extension inducing by slab break-off and delamination at 480–440 Ma. [Display omitted] • Tugeman granites formed during the 500–440 Ma. • Granitic pegmatite can be formed at different stages of crystal fractionation. • Tugeman granitoids were derived from a Proterozoic crustal source. The Altun Orogenic Belt (AOB) is located on the northern margin of the Tibetan Plateau. We report the petrography, zircon U-Pb ages, Hf isotopic compositions, and whole-rock geochemistry of the Tugeman pegmatitic and granitic rocks from the AOB to constrain their petrogenesis and tectonic setting. Zircon U-Pb dating of the pegmatitic and granitic rocks yielded ages of 500–440 Ma, which we interpret as the emplacement ages of the granites and formation age of pegmatite. The granites are weakly peraluminous to peraluminous (A/CNK = 1.01–1.26), and they have high SiO 2 (63.9–74.2 wt%) and Al 2 O 3 (13.7–17.6 wt%) and low CaO (0.72–3.80 wt%) and P 2 O 5 (0.06–0.44 wt%) contents. They show marked depletion in HREEs, enrichment in LREEs, and pronounced negative Eu anomalies, and they are enriched in Th, U, K, Pb, Nd, and Sm and depleted in Ba, Nb, Ce, Sr, P, and Ti. Zircon ε Hf (t) values vary from − 12.0 to + 3.3, with two-stage Hf model ages of 2.2–1.2 Ga, implying that the granites were derived mainly from ancient crust with a minor contribution from juvenile crust. Weakly peraluminous pegmatitic rocks have geochemistry characters of SiO 2 (74.4–79.9 wt%) and Al 2 O 3 (12.3–14.9 wt%) and low CaO (0.08–0.69 wt%) and P 2 O 5 (0.05–0.33 wt%), depletion in HREEs, enrichment in LREEs, depletion in Ba, La, Ce and Ti, enriched in U, K, Pb and P. Granitic pegmatite can be formed at different stages of crystallization differentiation of granitic magma, but the pegmatite associated with highly differentiated granites is favorable to the Li and/or Be mineralization, while the pegmatite associated with low differentiated granites (such as biotite granites) is unfavorable to the Li and/or Be mineralization. Based on our findings, we propose that the Tugeman granitic magmas originated from partial melting of crustal metagreywacke and metabasalt. Furthermore, we suggest that the early Paleozoic magmatism in the Central Altun Block (CAB) can be categorized into three groups, which correspond to different tectonic events. These events include the northward subduction of the Central Altun Ocean (CAO) beneath the CAB around 520 Ma, the closure of CAO at 490–480 Ma, and post-collisional extension at 480–440 Ma induced by slab breakoff and delamination of the subducted CAO. [ABSTRACT FROM AUTHOR]

[Display omitted] • Grenville-age terrane is identified in the Qilian orogen. • The Precambrian basement of the Qilian orogen is divided into four distinct mega-sequences. • ∼475 Ma metamorphism was related to the subduction of the Proto-Tethys Ocean. The Qilian orogen at the northeastern margin of the Tibetan Plateau records a complete history from continental breakup to oceanic basin evolution and back to continental collision during the Neoproterozoic to Paleozoic interval. The Qilian Ocean, as a branch of the Proto-Tethys Ocean, was connected to the Iapetus Ocean but is lesser known than its two more famous counterparts. This paper presents zircon U-Pb and biotite-muscovite 40Ar/39Ar isotope data from the Yemananshan Complex in the western Central Qilian belt to assess the age and provenance of late Mesoproterozoic-early Paleozoic successions in the Qilian orogen. The results indicate the Central Qilian belt is characterized by Late Mesoproterozoic-early Neoproterozoic orogenesis with magmatism from 1200 Ma to 900 Ma and clastic metasedimentary rocks deposited between 1050 and 920 Ma. Statistical analysis of detrital zircon data and auxiliary temporal information from the Qilian orogen affirms the notion that sedimentation occurred in four distinct megasequences: (1) 1950–1850 Ma, the oldest known strata, (2) 1250–920 Ma, during Grenvillian-Sveconorwegian orogenesis, (3) 840–760 Ma, the disintegration of Rodinia, and (4) 650–550 Ma, which is typical of the orogenic belts that sutured the Gondwana continental blocks. Metamorphic zircon and 40Ar/39Ar isotope data indicate early Paleozoic metamorphism at ca. 475 Ma, which overlaps with magmatic activity associated with arc-back-arc basin development in the Central Qilian belt, which was associated with subduction of the Proto-Tethys in eastern Gondwana. [ABSTRACT FROM AUTHOR]

• The early Neoproterozoic granitoids in the Qaidam block show typical S-type properties, generating via partial melting of Mesoproterozoic metasedimentary rocks. • These granitoids were formed under high-temperature and low-pressure conditions in a late syn- to post-collision setting. • Qaidam block was located at the core of the Rodinia supercontinent, adjacent to Laurentia, Baltica and Amazonia during the Neoproterozoic. Neoproterozoic granitoids are widely distributed in the Altyn Tagh, and provide indispensable information on the pre-Cenozoic tectonics and evolutionary history at the northeastern margin of Tibetan Plateau. In this study, zircon U-Pb geochronological results show that the granitoids were emplaced during the interval between 997 Ma and 901 Ma. Petrological studies reveal that these granitoids have high Al 2 O 3 and K 2 O, low CaO and Na 2 O contents with Al-rich minerals, such as muscovite, which show typical S-type properties. These Neoproterozoic granitoids contain abundant inherited cores of Mesoproterozoic age with ε Hf (t) values between 9.43 to 4.60. We interpret this to indicate magma generation via partial melting of Mesoproterozoic metasedimentary rocks. Based on a comparison to similar Neoproterozoic magmatic and metamorphic events described in the East Kunlun and North Qaidam, we suggest that the Altyn Tagh, East Kunlun and North Qaidam were part of the same terrane (Qadiam block) during the early Neoproterozoic. Petrogenetic data when combined with other geological and tectonic information suggest a late syn- to post-collisional setting rather than a syn -collisional setting. The Qaidam block was probably located adjacent to Laurentia, Baltica and Amazonia, during Neoproterozoic time. [ABSTRACT FROM AUTHOR]

Felsic igneous rocks in the Songxi area are a key part of the Qiangtang Terrane and India–Asia collision zone, and can constrain the evolution of the Tibetan Plateau. This paper presents new geochronological, geochemical, and isotopic data for Early Cretaceous granodiorites (119 Ma), leucogranites (111 Ma), and monzogranites (107–102 Ma) from the Songxi area in the western Qiangtang Terrane. The granodiorites are characterized by enriched Sr–Nd–Pb–Hf isotopic compositions (87Sr/86Sr i = 0.70721–0.70925, ε Nd (t) = −7.6 to −5.6, 206Pb/204Pb i = 18.907–18.964, 207Pb/204Pb i = 15.782–15.825, and ε Hf (t) = −24.0 to −2.0) and are adakitic with low Mg# values (39–44) and high K 2 O contents (2.6–3.9 wt%). The leucogranites have low Sr concentrations (80–100 ppm), high Rb/Sr (2.83–3.53) and low CaO/Na 2 O (0.19–0.22) ratios, high initial 87Sr/86Sr ratios (0.71653–0.71721), and low ε Nd (t) (−12.4 to −11.8) and ε Hf (t) (−18.8 to −6.8) values. The monzogranites are I-type granitoids and have enriched Sr–Nd–Pb–Hf isotopic compositions (87Sr/86Sr i = 0.70956–0.70966, ε Nd (t) = −8.5 to −8.3, 206Pb/204Pb i = 18.740–18.749, 207Pb/204Pb i = 15.759–15.778, and ε Hf (t) = −16.9 to −1.4). Our data suggest that these three types of granitoids were likely generated by partial melting of a thickened lower crust, metapelite-dominated source by fluid-absent muscovite melting, and normal lower crust, respectively. Integration of our new and existing data allows us to conclude that the Songxi granitoids formed in a continental margin arc setting. This further suggests that some sediment-derived leucogranites form in a continental arc setting, and are unrelated to continental collision. Tectonic compression and crustal thickening of the western Tibetan Plateau during the Early Cretaceous occurred when the Bangong–Nujiang oceanic lithosphere was subducted northward at a low angle beneath the western Qiangtang Terrane before ca. 119 Ma. [Display omitted] • The Songxi adakitic granodiorites were derived from thickened lower crust • Some sediment-derived leucogranites can be formed in continental arc setting • The Cretaceous crustal thickening of the western Tibetan Plateau began at ca. 119 Ma [ABSTRACT FROM AUTHOR]