The Early Paleozoic Tiefosi syn-collisional granite in the northern Dabie Orogen:Geochronological and geochemical constraints  

作　　者：ZHANG JinYang MA ChangQian SHE ZhenBing ZHANG XiangGuo ZHOU HongSheng 

机构地区：[1]Faculty of Earth Sciences,China University of Geosciences,Wuhan 430074,China [2]State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074,China [3]Key Laboratory of Continental Dynamics,Northwest University,Xi’an 710069,China [4]Department of City&Environmental Science,Xinyang Normal University,Xinyang 464000,China

出　　处：《Science China Earth Sciences》2007年第6期847-856,共10页中国科学（地球科学英文版）

基　　金：the National Natural Science Foundation of China (GrantNo.40334037);the Fund for Creative Research Groups (Grant No.40521001)

摘　　要：The Tiefosi granitic pluton is located 5 km northwest of Xinyang City, northern Dabie Orogen, and was emplaced in the Proterozoic Qinling Group. SHRIMP zircon U-Pb dating suggests its crystallization at 436 ± 11 Ma. It is composed of monzogranite and syenogranite containing some amounts of muscovite and few mafic minerals. The rocks are characterized by high and restricted SiO2 content, low FeO, Fe2O3 and MgO contents, high K2O/Na2O ratio, and display high-K calc-alkaline and peraluminous (ACNK>1.1) characteristics. They are generally enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE). They can be divided into three groups in light of rare earth elements (REE) and trace elements. Group I is moderate in ΣREE and characterized by the absence of Eu anomaly, high (La/Yb)N ratio, and moderate Rb/Sr and Rb/Ba ratios. Group II has moderately negative Eu anomaly, low (La/Yb)N ratio and high ΣREE contents, Rb/Sr and Rb/Ba ratios. Group III displays positive Eu anomaly, moderate (La/Yb)N ratio, and low ΣREE, Rb/Sr and Rb/Ba ratios. The calculated ? Nd(440Ma) values of the rocks vary from ?8.8 to ?9.9 and Nd depleted mantle model ages are about 2.0 Ga, which resemble those of the paragneisses from the Qinling Group. The results indicate that the Tiefosi granite is crust-derived, syn-collisional S-type granite. Generation of Group I was related to low degree melting of the Qinling Group, while Group II was formed by fractionational crystallization of plagioclase from Group I magmas, and Group III resulted possibly from magma mingling with plagioclase cumulates. The Tiefosi granite was formed within crustal level related to the collision between the North China and South China blocks in the Early Paleozoic time.The Tiefosi granitic pluton is located 5 km northwest of Xinyang City,northern Dabie Orogen,and was emplaced in the Proterozoic Qinling Group. SHRIMP zircon U-Pb dating suggests its crystallization at 436 ± 11 Ma. It is composed of monzogranite and syenogranite containing some amounts of muscovite and few mafic minerals. The rocks are characterized by high and restricted SiO2 content,low FeO,Fe2O3 and MgO contents,high K2O/Na2O ratio,and display high-K calc-alkaline and peraluminous (ACNK>1.1) characteristics. They are generally enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE). They can be divided into three groups in light of rare earth elements (REE) and trace elements. Group I is moderate in ΣREE and characterized by the absence of Eu anom-aly,high (La/Yb)N ratio,and moderate Rb/Sr and Rb/Ba ratios. Group Ⅱ has moderately negative Eu anomaly,low (La/Yb)N ratio and high ΣREE contents,Rb/Sr and Rb/Ba ratios. Group Ⅲ displays positive Eu anomaly,moderate (La/Yb)N ratio,and low ΣREE,Rb/Sr and Rb/Ba ratios. The calculated εNd(440Ma) values of the rocks vary from 8.8 to 9.9 and Nd depleted mantle model ages are about 2.0 Ga,which resemble those of the paragneisses from the Qinling Group. The results indicate that the Tiefosi granite is crust-derived,syn-collisional S-type granite. Generation of Group I was related to low degree melting of the Qinling Group,while Group Ⅱ was formed by fractionational crystallization of plagioclase from Group I magmas,and Group Ⅲ resulted possibly from magma mingling with plagioclase cumulates. The Tiefosi granite was formed within crustal level related to the collision between the North China and South China blocks in the Early Paleozoic time.

关 键 词：zircon SHRIMP dating Paleozoic syn-collisional GRANITE DABIE OROGEN 

分 类 号：P588.1[天文地球—岩石学]