LA-ICP-MS zircon U-Pb dating of gneiss of Milan Group and mafic dyke swarms from Lapeiquan in northern Altun and its tectonic significance

Two stages of basic dykes(diabase-prophyrite and barkevite lamprophyre)were emplaced in Milan Group migmatic hornblende plagioclase gneiss on the northern side of Lapeiquan in northern Altun Mountains. This paper presents the zircon LA-ICP-MS U-Pb dating for these three types of rocks. The crystallizing age of migmatic hornblende plagioclase gneiss is 2007Ma±25Ma, which, together with structural thermal event of about 2.0Ga in northwest region, might suggest the probable relationship with the convergence of Columbia Supercontinent. There exists similar age structure between diabase-prophyrite and barkevite lamprophyre. These zircons of the old ages, which are respectively 1962-2093Ma and 1804-2038Ma, were captured from hornblende plagioclase gneiss; the youngest ages show that the emplacement of basic dykes occurred in 79-94Ma, suggesting a product of extension in the Late Cretaceous; and the Paleozoic ages(288-504Ma)imply that the rocks of northern Altun ophiolite belt were involved in the provenance for basic dykes.