LA-ICP-MS zircon U-Pb dating and geochemical characteristics of the Mesozoic volcanic rocks from Longjiang basin in northern Da Hinggan Mountains and their geological implications

The Longjiang Formation in northern Da Hinggan Mountains is composed mainly of dacite and rhyolite with minor andesite. the LA-ICP-MS zircon U-Pb dating of these rocks yielded ages of 122.2~126.5Ma, corresponding to Early Cretaceous. These volcanic rocks are of high potassium calc-alkaline series possessing such geochemical characteristics as high ΣREE, remarkable (La/Yb)N values and negative Eu anomalies. In the spidergram, the rocks show pronounced enrichment of Rb, Ba, Th, U, K and depletion of Nb, Ta, P, Ti, much identical with the characteristics of the upper crust. Most of these rocks have typical adakitic characteristics, as shown by the data 300