The stripe-like distributed Mesozoic granites developed in the East Kunlun Orogenic Belt (EKOB) is a gigantic granitic magma belt, which has inseparable relationship with the evolution of lithospheric dynamics in the area. This study carried out comprehensive analyses on petrography, petro-geochemistry, and LA-ICP-MS zircon U-Pb chronology for the Cocoe A'Long quartz diorite pluton in the Hongshuichuan area in the south margin of the eastern EKOB. Our results show that three groups of zircon concord ages: ① the first group is older than 402Ma, representing the age of xenocryst; ② the second one is about (243.9±3.0) Ma (MSWD=0.94), marked perhaps the age of underplating of the basaltic magma in the area; and ③ (218.3±1.4) Ma (MSWD=0.52) for the last one, giving the crystallized age of the plutons. Geochemical analysis shows that the pluton is rich in Sr, low in Y and Yb, a high ratio of Sr/Y, and strong differentiation between HREE and LREE, and no distinct Eu anomaly, and this presents the lithological feature of adakitic rock. Additionally, low Nb and Ta, and high Cr and Ni, and high Mg# and Nb/Ta ratio show that the mantle peridotite underwent metasomatism in rutile existing phase through partial melting. Some conclusions can be drawn on the data overall that the Cocoe A'Long pluton was firstly derived from a thickened lower crust that formed by the early basaltic magma of subduction and fell into asthenosphere as eclogite facies triggered by lithosphere delamination under the condition of HP(high pressure) and dehydration later than, after that the melt undergone chemical reaction with lithospheric mantle and contaminated by crust in order while ascending. All of these phenomenon indicates an event of lithospheric crust delamination that happened at 218 Ma in Late Triassic in EKOB.