Study On Characteris Of The Volcanic Rocks From The Early Jurassic Erlanghe Formation In Dadingzi Area Of Heilongjiang Province

In this thesis,the volcanic rocks of the Erlanghe Formation of the Early Jurassic in the study Area were systematically studied by using the theories of petrology and geochemistry,and the characteristics of magmatic source of volcanic rocks were analyzed and discussed.Structural background of volcanic rocks formed in the Jurassic Erlanghe Formation.Achieve the following achievements and awareness:The content of SiO2 in the Erlanghe Formation is between 51.00%and 73.94%,which is intermediate-acid,acid volcanic rock.The content of Al2O3 is between 12.76%and 19.40%;the content of K2O is between 1.01%and 6.12;the content of Na2O is 2.46;Total Alkaline(Na2O+K2O)in the volcanic rocks is between 5.39%and 8.81%;Alkali rich(average Na2O+K2O=7.71);the Ritman index is between 1.64 and 2.65,belongs to calc-alkaline series.The consolidation index SI is between 2.20 and 17.95 with an average of 7.78,and the magma has a strong crystallization differentiation.The volcanic rocks in the study area are mainly arctic and rhyolite,which are mainly calc-alkaline rocks.The contents of FeO,MgO,TiO2,CaO,P2O5,Na2O and Al2O3 were significantly decreased with the increase of SiO2 content,which indicated that the differentiated crystallization existed in the process of magma evolution.(LILE)Rb,U,Nd,K are more enriched,and high field strength elements(HFSE)Nb,Ta,P,Ti and other strong losses.Reflecting the volcanic rocks in this area is formed in the extrusion structure,the magma may be contaminated by crustal material,and the continental shell material involved.The structural background discrimination shows that the volcanic rocks of the Erlanghe Formation have a tendency to over-tectonic environment,and the volcanic eruption products near the continental margin of the orogenic belt are closely related to the continental subduction of the Eurasian continent.Obviously,the magmatic source area has characteristics of the crustal source,and the magma is differentiated by crust..