LA-ICP-MS Zircon U-Pb Dating of Ganchankou Basite Diabase in Northern Qilian and Its Geological Significance

Located in Qilian orogenic belt, Ganchankou basite diabase emplaces in Tuolai terrain of Paleoproterozoic Era, and its lithology is dark grey diabase. In this paper, LA-ICP-MS zircon U-Pb dating method is adopted to date the diabase, and 293.0±1.8Ma is obtained which indicates that a stretch event happened in early Permian Epoch. This paper finds that the diabase belongs to tholeiite series, with the ratio of chemical A/CNK changing from 0.60 to 0.76, the value of A/NK varying from 2.40 to 4.35, the content of Al₂O₃ ranging from 11.60% to 18.36%, and the content of TiO₂ fluctuating between 0.66% and 2.85%. Meanwhile, trace elements such as K, Rb, Ba and Th have strong enrichment, but Hf and Zr are apparently depleted while Y and Yb are characterized by slight depletion. The study also shows that light rare earth elements after weak fractionation are enriched while the fractionation of heavy rare earth elements is not obvious in the diabase. At the same time there is a weak negative Eu anomaly. According to the regional tectonic background and the petrological and geochemical characteristics, it can be concluded that Ganchankou diabase dyke is formed by the post-tectonic crust thickening underplating of Qilian orogenic belt and the magma intermingling effect.