| This thesis studies the well-developed Manketouebo Formation volcanic rocks of Keyihe area in the major ridge of the north section of Da Hinggan Moutains.Through the summarization of previous research data and field investigations in the field,the rock assemblage,distribution rules and geochemistry of Manketouebo Formation volcanic rocks will be described,and the nature of magma source,petrogenesis and tectonic settings will be discussed in this paper,which will provide new information to researches of the volcanism and tectonic evolution history in Late Jurassic to Early Cretaceous in northern Da Hinggan Moutains.Manketouebo Formation volcanic rocks,which are composed of rhyolite,rhyolite lava,tuff lava.The results of LA-ICP-MS ziron U-Pb dating are 137.1±5.1Ma and143.0±0.69Ma,revealing that Manketouebo Formation volcanic rocks are mainly formed in Early Cretaceous.The volcanic rocks contain high silica?SiO2=70.03%76.46%?and total alkali?K2O+Na2O=8.10%9.52%?concentrations,and low concentrations of CaO?0.03%0.95%?and MgO?0.07%0.67%?.the samples belong to high-K calc-alkaline peraluminous rock.The chondrite-normalized REE paterns indicate that the Mnaketouebo Formation volcanic rocks are enriched in light rare earth elements and almost all strong negative Eu anomaly.?REE=96×10-6231×10-6,the average value is 184×10-6,and the value of?La/Yb?N ranges from 8.27 to 21.11.they are enriched in large ion lithophile elements?LILEs;e.g.,Rb,Th,K?and depleted in high field strength elements?HFSEs;e.g.,Nb,Ti,P,Ta?.The study shows that the volcanic rocks in the Manketouebo formation are partially melted of the shallow crust.Through collation of past research data and comparison and analysis with the above data,it is concluded that Manketouebo Formation volcanic rocks were formed by the effect of the extensional environment caused by the closure of Mongolia-Okhotsk. |
PDF Full Text Request