• 标题：Post-collisional potassic rocks in Western Kunlun, NW Tibet Plateau: Insights into lateral variations in the crust-mantle structure beneath
• 关键词：Potassic rocks,Post-collisional,Crust-mantle structure,Western Kunlun,Tibet Plateau,India-Asia collision zone
• 作者：Peng Wang, Guochun Zhao, Yigui Han, Qian Liu, Ningchao Zhou, Jinlong Yao,Jianhua Li f, Yanguang Li

The collision between India and Asia created the most signifificant 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 fifield observations have suggested signifificant 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 profifiles (e.g., Fo and An values) of olivine, pyroxene, and plagioclase phenocrysts, along with relatively consistent whole-rock isotopic compositions argue against mixing and signifificant 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 (LaN/YbN > 49) and Nb/Ta ratios (> 20), and olivine geothermometer confifirm a garnetbearing 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.

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