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The Shyok Suture in western Himalaya preserves a record of the opening and closure of the Mesotethys Ocean between the Shyok ophiolite and Karakoram terrane prior to the India–Eurasia collision. The formation age of the Shyok ophiolite was unknown, which impeded correlation with similar rocks along the Shyok Suture in Pakistan and corresponding sutures in Tibet. We report the first zircon U–Pb ages of a newly documented suite, here named the Changmar Complex. The Changmar Complex gabbronorite and plagiogranite yielded SHRIMP U–Pb zircon Late Jurassic ages of 159.4 ± 0.9 Ma and 151.9 ± 1.5 Ma. Their highly positive initial εHf values (+14.9 to +16.9) indicate a juvenile mantle origin, without continental crust influence on the magma source. The Shyok ophiolite represents either: (1) a separate island arc that preceded formation of the Cretaceous–Eocene Ladakh Arc; or (2) the oldest magmatism and early stage of the Ladakh Arc. Intrusive and extrusive mafic rocks from the Shyok Suture analysed in this study have typical supra-subduction zone enrichment characteristics in their geochemistry and are classified as part of the volcanic-arc ophiolite. The U–Pb age and Hf isotopic signatures for the Shyok ophiolite are similar to the Late Jurassic Matum Das tonalite within the Kohistan Arc; we therefore suggest that they are part of the same intra-oceanic island-arc system that formed in the Mesotethys Ocean prior to Late Jurassic time.

The Gubaoquan eclogite occurs in the Paleozoic Beishan Orogen of NW China. Previously it has been interpreted as a fragment of subducted oceanic crust that was emplaced as a melange within continental rocks. Contrary to this, we demonstrate that the Gubaoquan eclogite protolith was a Neoproterozoic basic dyke/sill which intruded into Proterozoic continental rocks. The SHRIMP U Pb zircon dating of the metamorphic rims of the Gubaoquan eclogite yields an age 466 ± 27 Ma. Subdued heavy rare earth element abundances and lack of negative Eu anomalies of the metamorphic zircon domains confirm that this age represents eclogite facies metamorphism. The host augen orthogneiss has a U Pb zircon age of 920 ± 14 Ma, representing the timing of crystallization of the granitic protolith. A leucogranitic vein which intrudes the eclogite has a U Pb zircon age of 424 ± 8.6 Ma. This granitic vein marks the end of high-grade metamorphism in this area. The overcomplication of tectonic history of the Beishan Orogen is partially caused by inconsistent classifications and nomenclature of the same rock units and arbitrary subdivisions of Precambrian blocks as individual microcontinents. In an attempt to resolve this, we propose a simpler model that involves the partial subduction of the northern passive margin of the Dunhuang Block beneath the active continental margin developing on the Mazongshan-Hanshan Block to the north. Ocean closure and continental collision during the Late Ordovician resulted in continental thickening and eclogite facies metamorphism recorded by the mafic dykes/sills (now the Gubaoquan eclogite). In the light of the new data, the tectonothermal evolution of the Beishan Orogen is reviewed and integrated with the evolution of the Central Asian Orogenic Belt.

The Ladakh Arc was formed by subduction of Neotethyan oceanic lithosphere along the southern Eurasian margin before magmatic activity ceased upon the continental collision between India and Eurasia. The onset of arc magmatism is critical in terms of understanding when this subduction began. Termination of arc activity is associated with continental collision; thus, the youngest arc magmatism provides a maximum age for this collision. Intra-arc volcaniclastic sequences provide a stratigraphic record of arc magmatism, but also information on input from older basement rocks. We provide detailed U–Pb detrital zircon chronostratigraphy for the Khardung Formation, which represents the volcanic equivalent of the Ladakh Batholith. The lower section of the Khardung Formation is mafic to andesitic and has a maximum depositional age of c. 60 Ma and the oldest inherited zircon age population from this lowermost section is c. 69 Ma. A switch to felsic volcanism occurred soon after and continued until at least c. 52 Ma. The youngest portion of the sequence has been removed by erosion or faulting along the Miocene dextral Karakoram Fault. However, detrital zircon data from the post-collisional Indus Group indicate that magmatism within the Ladakh Arc continued until c. 41 Ma. A compilation of U–Pb zircon data for the Ladakh Batholith paired with our new data from the volcaniclastic sequence, reveal an inverse relationship between alternating pulses of volcanic and plutonic activity within the arc. We suggest, this magmatic pattern may relate to alternating episodes of extension (volcanism) and compression (plutonism) imposed on the arc.