| Heihe area is located in the northeast of Heilongjiang Province,the junction of the Da Hinggan Mountains and Xiao Hinggan Mountains,and faces the city of Blagoveshchensk of Russia on the other side of Heilongjiang River.During the Mesozoic period,large-scale magmatic activities developed in Heihe area,a large amount of igneous rocks formed in this time.However,the exact age,rock assemblages,petrogenesis,magma source,tectonic setting of these igneous rocks are still disputed or unknown.Therefore,this paper had conducted detailed field geological survey and research of chronology,petrology,geochemistry and other research of these igneous rocks(including intrusive rocks,dike rocks and volcanic rocks)in Heihe area,and results are as below.1.The formation age of the Mesozoic intrusive rocks in Woniu Lake area were the end of Early Jurassic(175.3 ± 0.53 Ma and 177.25 ± 0.45Ma).The intrusive rocks ranged from neutral to acidic,and the rock assemblage was TTGG,belonged to the high-potassium-calcium-alkali series,quasi-aluminum-peraluminous rocks.The Peacock index was calcium-alkaline,and the elements such as Nb,Ta,La,and Ce are depleted,Pb and some other large-ion lithophilic elements were enriched,the distribution pattern of rare earth elements were right-inclined,with negative Eu anomaliy,Most of the diorite dike rocks were quasi-aluminum series rocks with high potassium and calcium alkali,Peacock index were alkali calcium and calcium alkaline.All of them are deficient in Nb,Ta,La,Ce,P,Ti elements,enriched in Rb,K,Pb elements,some other large-ion lithophile elements and Zr,Hf,Gd elements.The distribution pattern of rare earth elements was right-inclined,with weak negative Eu anomaly;2.Large-scale Mesozoic volcanic rocks were formed in the late Early Cretaceous(121.93 ± 0.42Ma).The rock assemblage was mainly composed of andesite-daciterhyolite and a small amount of basalt,andesite,trachyte.Most of them belonged to the high potassium calc-alkali series,and a few belonged to the calc-alkali series and the low potassium calc-alkali series,quasi-aluminum to aluminum series,the Peacock index was calcium-alkaline and alkaline-calcium,They were depleted in Nb,Ta,La,Ce,P,Ti elements,enriched in Rb,K,Pb,some other large-ion lithophile elements and Zr,Hf,Gd elements.The distribution pattern of rare earth elements was a relatively gentle right-inclined type,and the degree of differentiation of light rare earth elements were higher than that of heavy rare earth elements,with a weak negative Eu anomaly or no anomaly.3.The TTGG rocks of late Jurassic were mainly low-pressure TTG series,with more MgO,belonging to the MA series TTG.Combining their geochemical characteristics,it showed that these rocks were originated from the arc environment of ocean subduction.There was obvious magma mixing.It is speculated that the magmas mainly originated from the melting of the subducting oceanic crust(slab)(reaction with the overlying mantle wedge)and the local melting of the sub-crust of the Xing'an arc(crust-mantle interaction).The volcanic rocks were mainly composed of andesitedacite-rhyolite,including MA series and LMA series,combination of geochemical characteristics,indicating their magmas originated from the arc tectonic environment by ocean subduction.The source of magmas probably the melting of the subducted slab and react with the mantle wedge and partial melting of the crust beneath the Xing'an arc4.Based on the tectonic evolution,it is speculated that from Jurassic to Early Cretaceous in study area are related to the superposition of the southward subduction of the Mongolian-Okhotsk Ocean and the NW subduction of the Paleo Pacific,... |
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