The high-pressure metamorphic belt （HPMB） of eclogite-blueschist in Central Qiangtang （羌塘） lies in the Longmu Co （龙木错）-Shuanghu （双湖） suture zone. To the west, the HPMB extends 500 km from Hongjishan （红脊山） to Caiduochaka （才多茶卡）, east of Shuanghu; to the east it extends to Baqing （巴青） and Jitang （吉塘） in Qamdo （昌都）, and then bends southward to Yunnan （云南） Province. Including the Lancangjiang （澜沧江） blueschist belt, the entire HPMB is about 2 000 km long. In Central Qiangtang, the belt is mainly composed of blueschist and eclogite, whereas in West Yunnan it contains only blueschist. The Baqing-Jitang segment is dominated by garnet phengite schist. 40Ar-39Ar dating of glaucophane and phengite from the blueschists yielded plateau ages ranging from 223 to 215 Ma, whereas SHRIMP U-Pb dating of zircon from the eclogites gives metamorphic ages of 243-217 Ma. The calculated metamorphic conditions for the blueschists are 410-460 ℃ and 0.67-0.75 GPa, and for the eclogites, 〈500℃ and 1.56-2.35 GPa. The metamorphic ages suggest that the Longmu Co-Shuanghu suture closed in the Late Triassic. The region south of the Longmu Co-Shuanghu- Lancang suture consists of the pan-African basement overlain by Condwana sedimentary and metasedimentary rocks, whereas the region north of the suture is dominated by the Jinning （晋宁） basement and Yangtze sedimentary and metasedimentary rocks. The Qiangtang HPMB marks the closure of the paleo-Tethys Ocean.
U-Pb zircon age, geochemical, and Sr-Nd-Pb isotopic data of mafic dykes from eastern Shandong Province, eastern China is reported herein. Laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） U-Pb zircon analyses of two samples from the investigated mafic dykes yield consistent ages ranging from 121.9 Ma ± 0.47 Ma to 122.9 Ma ± 0.61 Ma. The mafic dykes are characterized by high （87Sr/86Sr） i ranging from 0.7087 to 0.7089, low εNd（t） values ranging from -16.9 to -17.8, 206Pb/204Pb = 17.15 to 17.17, 207Pb/204Pb = 15.45 to 15.47, and 208Pb/204Pb = 37.59 to 37.68. Results from the current study suggest that the mafic dykes are derived from partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from foundered lower crustal eclogite. The mafic dykes may have been generated through subsequent insignificant crystal fractionation and very minor crustal contamination during magma ascent. Combined with previous studies, the current findings provide new evidence that the intense lithospheric thinning beneath the eastern Shandong Province of eastern China occurred at ~120 Ma, and that this condition was caused by the removal of the lower lithosphere （mantle and lower crust）.
LIU ShenHU RuizhongFENG CaixiaGAO ShanFENG GuangyingLAI ShaocongQI YouqiangIan M. COULSONYANG YuhongYANG ChaoguiTANG Liang
