Geochemical Characteristics And Geological Significance Of The Mesozoic Lavas From The Yiiehuii

The study area is located in the Greater Khingan Range Yilehuli MountainMesozoic volcanic belt north eastern, which is an important part of the giantcontinental-margin volcanic belts of the eastern Asia continent. Tectonically, the studyarea located in the southern continental margin of the Siberian plate, northeast ofXingmeng orogenic belt, and southern of North China Block. Jixianggou Formation ofNeoproterozoic-lower Cambrian are the most ancient crystalline basement in the studyarea. After Neoproterozoic, it experienced a very complex crustal accretiontransformation history. Since Paleozoic it has been affected by the evolution,development and closing of the Paleo-Asian Ocean. The subduction of Izanagi platetoward Paleo-Asian plate had led to intense Mesozoic tectonic-magmatic activities.They together formed quite spectacular Greater Khingan Range Mesozoic volcanicbelt.Based on the identification of the spatial and temporal distribution, as well aseruption cycles of the Mesozoic volcanic rocks, the stratigraphic sequence and thedivision of the volcanic facies and assemblages has been determined. Based on systemsresearch of the petrography and geochemistry of these volcanic rocks, and combinedwith new geophysical data and regional tectonic setting, the formation ages of thevolcanic rocks, magmatic origin and evolution mechanism have been discussed.According to these studies, we have made major achievements and understandingsas followes:(1) Re-determine the stratigraphic sequence of volcanic rocks, from bottom to topare divided into the Upper Jurassic Manketouebo Formation, Manitu Formation,Baiyingaolao Formation and the Lower Cretaceous Guanghua Formation;(2) Based onzircon U-Pb dating, the formation of the group of volcanic rocks have been determined:the Manketouebo Formation formed at157.8±2.3Ma, the Manitu Formation formed at154±2Ma, the Guanghua Formation formed at124±1.1Ma;(3) Mesozoic volcanicrocks in this area are mainly a shoshonite-latite-trachy dacite-trachyte-rhyolite rockassemblages, and are alkali-rich and mainly belong to high potassium calc-alkalineseries; They are strongly enriched in large ion lithophile elements such as K, Rb, Sr,Ba, Cs, and depleted in compatible elements such as Cr, Co, Ni, and high strength fieldelements including Nb, P, Ti; LREE are strongly enriched, and show no or weaknegative Eu anomalies;(4) The volcanic rocks have the affinity of the activecontinental margin and were related to the subduction of the Paleo-Asian plate (Izanagiplate) toward the Northeast Asia continent.