Bangong Co—Nujiang River (Bangong Lake—Nujiang River) suture is one of the largest sutures in the Qinghai—Xizang (Tibet) Plateau and it is situated between the Qiangtang terrance and the Lhasa terrance.With its complex tectonic settings,there are existed many disputes on the Bangong Co—Nujiang River suture,especially in Gaize area,which are mainly about two basic and key issues,which restrict our researches on the geological settings and the evolution of the Xizang. They are the polarity of subduction and the timing of opening.Based on the petrology，geochemistry and chronology of the Gelegear gabbro in Gaize area，we focus on its formation age，petrogenesis，tectonic settings and the evolution process of the subduction to closing.The gabbro sample separation and target preparation of zircons was carried out at the Lab Test Center of the Hebei Institute’s Regional Geology & Mineral Survey. The samples were processed by contaminant free crushing. The zircon grains were obtained by selection under a binocular eyepiece after magnetic and electrical separation. Representative zircon grains were then selected for target preparation, and transmission and reflected light photography was used to investigate the zircons by cathode luminescence. Zircon UPb dating was performed by LAICPMS at the Mineral Resource Institute of the Chinese Academy of Geological Sciences，with a Newwave UP 213 laser ablation system and the FinniganNeptune; U, Th, Pb, and other elements had an integration time of 20s.Data processing was performed using Isoplot 3.0 software and the data was with a high concordance degree was eliminated.The major elements testing is in School of Geosciences and InfoPhysics，Central South University.It used powder direct compression with instrument of ZSX Primus II Xray fluorescene. Spectrometer with analytical precision less than 1%.Trace elements testing is completed in Institute of Tibetan Plateau Research Chinese Academy of Sciences with instrument of X series ICPMS.The testing samples are preprocessed by using acid dissolution.The LAICPMS dating indicates that the babbro was emplanced at 122.9±1.6Ma.The babbro is formed in the Early Cretaceous.Geochemical data show that the Gabbro consists high content of Al2O3（15.39%～16.83%），low content of TiO2（0.78%～0.92%），P2O5（0.09%~0.17%），（Na2O+K2O= 3.93%~4.41%）.The REE content is between 63.37×10-6 and 73.76×10-6，average 68.84×10-6，with (La／Yb)N ratio of 2.43～3.09 and δEu of 0.89～1.03.REE diagram shows rightward incline and week negative Eu abnormity.The gabbro is remarkably characterized by enrich LREE and depleted HREE.The LILE such as Rb，Ba，Th，U is enriched，while HFSE such as Nb，Ta，P，Ti is depleted.The ratios of Nb/Ta and Zr/Hf are sharp beneath that of primitive mantle.The geochemical characteristics and tectonic discriminations show that the parental magma of gabbro derived probably from the mantle influenced by the subduction.The parental magma is developed by the upper crustal assimilation contamination during the magma evolution and experience a certain extent of separation and crystallization as well.The Gelegear gabbro formes in an island arc environment related to northward subduction of the Bangong—Nujiang and indicates that during 122.9±1.6Ma，Bangong—Nujiang oceanic basin continues its northward subduction in research area.Combined with regional data，this study concludes that the closure time of Bangong Co—Nujiang River ocean basin was between 110Ma and 85Ma in the Gaize area.