Age And Attribution Of Volcanic Rocks In The Dongxiang Volcanic Basin In The North Wuyi

Since Mesozoic,The North Wuyi area formed a series of Mesozoic volcanic basins and extensive volcano – intrusion on the basis of the paleozoic rift basin that included Dongxiang volcanic basin, Tianhuashan volcanic basin,Huanggangshan volcanic basin,Tongboshan volcanic basin and Xianxialing volcanic basin from west to east.The volcanic rock belt presented NNE is distributed along regional E-W-trending basement uplift,and is characterized by intensive explosive eruption and quiet overflowing.The predecessors have done a series of research on the volcano rocks in North Wuyi area but it is difficult to form a unified conclusion due to intensive structure andmagmatic activities since Mesozoic, the region formed the different sequence of orogeny and basining. Dongxiang volcanic basin is located in the west of the North Wuyi area which coveraged seriously and exposed less rocks.This article draw some recognizations through a series of field investigation,profile measurement,lab analysis and compared with the lithology of Ehuling Formation and Daguding Formation in area. It is almost certain:all the volcanic rocks of Dongxiang volcanic basin belong to Daguding Formation and the rock associations contains a large set of rhyolitic crystal tufflava, rhyolitic breccia tufflava at the bottom and a lot of andesite in the upper;which is consistent with rock associations of Daguding Formation in north Wuyi area.Major and trace elements coupled with REE distribution patterns of show that the tectonic background of Dongxiang volcanic basin belong to subduction-orogeny environment. The Izanagi plate dives to the Eurasian plate, causing shortening and thickening of the crust, thus compact rocks formed under the crust. Later on, the gravity instability result in delamination, as well as the thinning of lithosphere. The intruding mafic magmas heat the upper crust up, causing the upper crust melt and the resulting granitic magmas formed. Meantime, the assimilation and hybridization of mafic magmas with the upper crust result generated the andesitic magmas. The dating data of the andesite, trachy-andesite, and rhyolitic tuffolava indicate that the volcanic eruption is between 142 Ma and 134 Ma, and it belongs to Early Cretaceous according to the international geological time scale of TheUS geological science.. The eruption cycle can be subdivided into 3 volcanic eruption, corresponding time are 142 Ma, 137 Ma, and 134 Ma respectively. The geological sections of Caijiaqiao further validates that andesite can be the layer-marker between Daguding Formation and Ehuling Formation. Therefore, the age limitation of Daguding Formation and Ehuling Formation in areas needs further study.