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The collision between India and Asia created the most significant orogenic system of the Cenozoic. Although numerous collision-related igneous rocks formed, many post-collisional rocks were emplaced but have received less attention. Recently, geophysical investigations and field observations have suggested significant lateral variations in crust-mantle structure beneath the collisional zone. However, there have been few attempts so far to reveal the possible relationship between the lateral variations in crust-mantle structure and the widely distributed post-collisional rocks. To reveal the possible linkage, we investigate the Pulu volcanic rocks in Western Kunlun, NW Tibet Plateau, through a combined analysis involving whole-rock geochemistry and Sr-Nd-Pb isotopes, and mineralogy. The similar profiles (e.g., Fo and An values) of olivine, pyroxene, and plagioclase phenocrysts, along with relatively consistent whole-rock isotopic compositions argue against mixing and significant crustal contamination. The sub-continental lithospheric mantle source (SCLM) was enriched by the input of sedimentary materials as indicated by Sr-Nd-Pb isotopic compositions (87Sr/86 Sr (t) < 0.708884, 143Nd/144Nd > 0.512344, and 204Pb/207Pb < 15.6831). The Pulu volcanic rocks in Western Kunlun display high Rb/Sr ratios (> 0.05) and low Ba/Rb ratios (〈23), indicating an amphibole-free phlogopite residual source at a depth of >70 km. In addition, high LREE/HREE (La N /Yb N > 49) and Nb/Ta ratios (> 20), and olivine geothermometer confirm a garnet-bearing mantle source at >970 °C under eclogite-facies conditions. In contrast to other post-collisional rocks formed under low pressure and widely variable temperatures associated with the delamination and thinning of SCLM in the eastern and southern Tibet Plateau, post-collisional rocks in Western Kunlun formed under the high pressure and a narrow range of temperature are attributed to lithospheric fractures at great depths before delamination. Such contrasting P-T conditions of the post-collisional rocks in Western Kunlun and eastern and southern Tibet Plateau record lateral variations in crust-mantle structures beneath the India-Asia collisional zone. • No magma mixing occurred in the post-collisional rocks in Western Kunlun. • Post-collisional rocks have high P-T conditions in Western Kunlun. • The P-T conditions reflect lateral variations in the crust-mantle structure. [ABSTRACT FROM AUTHOR]

During Carboniferous time, tremendous juvenile arc crust was formed in the southern Central Asian Orogenic Belt (CAOB), although its origin remains unclear. Herein, we presented zircon U-Pb-Hf and whole-rock geochemical and Sr-Nd isotopic data for a suite of volcanic and pyroclastic rocks from the Khan-Bogd area in southern Mongolia. These Carboniferous pyroclastic rocks generally have some early Paleozoic zircons, probably derived from the granitic and sedimentary rocks of the Lake Zone and the Gobi-Altai Zone to the north, indicative of a continental arc nature. In addition, they have a main zircon U-Pb age of ca. 370-330 Ma, positive Hf and Nd isotopes, and mafic-intermediate arc affinity, similar to the coeval arc magmatism. Moreover, the pyroclastic rocks of the northern area have more mafic and older volcanic components with depositional time (ca. 350-370 Ma; Visean and Bashkirian stages) earlier than that in the southern area (mainly ca. 350-315 Ma; Serpukhovian and Bashkirian stages). Combining a preexisting northward subduction supported by the available magnetotelluric data with a slab rollback model of the main oceanic basin of the Paleo-Asian Ocean (PAO) during Carboniferous and Triassic times, we infer that the Carboniferous arc magmatism was probably derived from a backarc ocean triggered by slab rollback. Thus, the juvenile arc volcanism of Mongolia, together with other areas (e.g., Junggar) in the southern CAOB, represented a significant lateral accretion that terminated after the Carboniferous due to a significant contraction of the PAO., (Copyright © 2022 Science China Press. Published by Elsevier B.V. All rights reserved.)