The Research Of Volcanic Rocks Of Paleoproterozoic Nansizhang Formation In The Area Of Ceyu-Linchen Of The Heibei Province

The study area is located in the northwest of QiShanHu practice base in Lincheng County,Hebei Province.It has a large amount of volcanic rocks developed during the Paleoproterozoic and formed a intracontinental rifting eruption environment.It consists of volcanic agglomerates,Breccia,tuff and volcanic lava,and controlled by the intraplate structure,volcanic rocks are mainly distributed in the Gan Taohe Group watershed.The lithologic metamorphism of the Nansizhang Formation volcanic rocks in the Gantaohe Group of Lincheng County has been metamorphosed into amphibole schist,chloritized amphibole schist and epidote.However,the lava pillow structure can be seen and the stomatal structure is generally developed.The volcanic rocks in the Nansizhang Formation are generally subjected to green-shale petrochemical and chloritization alteration.The metamorphic deformation is relatively low in the Lincheng area,and the volcanic structure can be observed more easily.The developed stomatal and almond structure has been Chlorite,quartz,calcite and other minerals.From the geochemical characteristics,the rock has high aluminum oxide,high magnesium oxide characteristics,light and heavy rare earth elements of the more obvious for the right.The metamorphic volcanic rocks of the Nansizhang Formation in the Paleoproterozoic Gantaohe Formation in the study area have the same lithology,contact relationship,structure,geochemical characteristics and isotopic age as the metasomatic basic volcanic rocks of the Qingshicun Formation of the Hutuo Group in the Area of Wutai Mountain,and therefore can be compared.The volcanic eruption intensity is periodically changed in the study area.The volcanic eruption rhythm layer can be clearly distinguished by field observation and local rhythmic histogram.Based on the previous volcanic cycle division scheme and the volcanic rock characteristics in this area,The results show that the volcanic rocks of the Nansizhang Formation in the Paleoproterozoic Gantaohe Formation are divided into six eruptive cycles.The crustal evolution of the North China craton is well represented in the study area,mainly as the metamorphism of lateral crustal growth and the magmatic effect of vertical growth.