SHRIMP U-Pb zircon dating of Neoarchean metagabbro dikes on the southwestern margin of the Tarim plate and its significance

Abstract：Several metagabbro dikes are found on the southwestern margin of the Tarim plate. They are characterized by lower total REE contents, enrichment in LREE and LILE and depletion in HREE and HFSE. SHRIMP U-Pb zircon dating shows that: the 207Pb/206Pb weighted mean age for six spots is 2 675±12 Ma (MSWD=0.20); the discordia upper and lower intercept ages for nine spots are 2 671±13 Ma and 287±16 Ma (MSWD=0.91) respectively. The weighted mean age of 2 675 or the discordia upper intercept age of 2 671 represents the crystallization age of metagabbro, and the lower intercept age of 287±16 Ma represents the metamorphism age of metagabbro. The discovery of the Neoarchean metagabbro dikes on the southwestern margin of the Tarim plate proves the existence of an Archean old continental nucleus on the southwestern margin of Tarim, provides the record of magmatic activity of the breakup of the Neoarchean old continental nucleus in the North China craton and furnishes important information for the stratigraphic division and correlation in this region and tectonic evolution of the old continental nucleus in the early stage.