Chronologic And Geochemical Studies Of The Muce Pluton In Xiong'er Mountain Area

The Trans-North China Orogen(TNCO)is one of the important orogenic belts in the North China Craton(NCC),which is of great significance to understand the formation of the NCC.The Xiong'er Mountain area is located on the southern edge of the central North China orogenic belt,and it is an important area for studying the collisional orogeny of the North China Plate and the Yangtze Plate.The Muce pluton is located in the middle part of the Xiong'er Mountain area,and it is distributed in an irregular rhombic shape near east-west.The exposed surface is about 9.8km².The rock mass is dominated by monzonite,which is mainly composed of biotite hornblende monzonite,monzonite granite and monzonite porphyry.The Muce pluton intrudes in the gneiss of Taihua Group formed in the Neo-Archean period,and was invaded by the Yanshanian granite formd later.This paper provides evidence for understanding the distribution range and evolution time of the TNCO.In this study,the Muce pluton is taken as the research object,and the formation age and tectonic evolution of Muce pluton is analyzed from the perspectives of petrology,petrography,geochemistry and chronology,and the main results are as follows.1.LA-ICP-MS zircon U-Pb dating shows that the ages of biotite hornblende monzonite of the Muce pluton are 2171±19Ma,2172±8Ma and 2186±7Ma,respectively;the age of monzonite granite is 2174±8Ma;and the monzonite porphyry is 1900±18Ma,which indicates that the Muce pluton intrusion located in the Paleoproterozoic.2.The geochemical characteristics show that Muce pluton belongs to alkaline quasi-aluminum high potassium basalt series.The biotite hornblendem onzonite and monzonite granite have the characteristics of A-type granite.The content of Si O₂,Al₂O₃,Fe₂O₃,Cr,Ni,and so on is close to the content of the lower crust.At the same time,the Nb/U ratio is also close to the lower crust,indicating that the magma originates from partial melting of the crust.The size of Mg^#(44.26)and the appearance of inclusions indicate that it is contaminated by mantle materials.The geochemical characteristics of the monzonite porphyry are similar to typical adakite magmatic rocks,and the values of Mg O,Ni and Cr are relatively low,indicating that the magma is derived from the partial melting of the thickened lower crust.3.Based on the study of the Muce pluton and the regional geological correlation,it is considered that the biotite hornblende monzonite and monzonite granite were formed in the rift environment;and the monzonitic porphyry was formed in the collision orogenic environment.It is suggested that the TNCO was formed in the Paleoproterozoic.