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Garnet amphibolite is one of the common metabasic rocks exposed in collisional orogenic belt, the metamorphic evolution of which is associated closely with orogenic processes. The Yaganbuyang garnet amphibolites occur as blocks hosted by massive granitic gneiss, and consist mainly of hornblende, garnet, clinopyroxene, plagioclase, biotite, quartz with minor rutile/ilmenite and phengitic muscovite. These garnet amphibolites were interpreted to have experienced decompression-dominated evolution that can be divided into three generations (M1, M2, M3), based on the petrographic observations and phase equilibria modeling calculated by THERMOCALC. The assemblage of the first generation (M1) is inferred to possibly be dominated by garnet + omphacite + rutile + phengite + quartz, which is modeled to be roughly stable at P > 25 kbar and T > 800 °C. The second generation (M2) is characterized by the local symplectites of clinopyroxene + plagioclase produced from omphacite, indicating a near-isothermal decompression from ∼23.8 kbar/875 °C to ∼10 kbar/852 °C. The third generation (M3) is marked by the kelyphitic rims of plagioclase + hornblende around garnet and of hornblende + ilmenite around clinopyroxene, involving the late-stage retrogression from ∼9.8 kbar/848 °C to ∼5.8 kbar/645 °C. Zircon U-Pb dating yielded one group metamorphic age of c. 500 Ma that is interpreted to represent the timing of the peak eclogite-facies metamorphism. A combination of petrography observation, phase modeling results and geochronology data suggests that the Yaganbuyang garnet amphibolites have once undergone eclogite-facies metamorphism by continental subduction rather than crustal thickening. Therefore, the Yaganbuyang area is an eastward extension part of the South Altyn HP-UHP metamorphic belt. [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]