北秦岭蟒岭花岗岩体岩浆演化及源区:来自矿物学和Sr-Nd-Hf同位素证据

Magmatic Evolution and Origin of Mangling Granitic Pluton in North Qinling,China:Evidence from Mineralogy and Sr-Nd-Hf Isotopes

蟒岭花岗岩体位于北秦岭构造带黑沟—栾川断裂和乔端—瓦穴子断裂之间,是由3期岩浆侵入形成的岩浆杂岩体,其岩石类型从早到晚依次为含辉石黑云母闪长岩、二长花岗岩和黑云母正长花岗岩。在详细的野外调查和岩相学观察基础上,对蟒岭花岗岩体中的前两期岩石进行了系统的矿物学和Sr-Nd-Hf同位素研究。结果表明:蟒岭花岗岩体以I型花岗岩为主,从早到晚(含辉石黑云母闪长岩→二长花岗岩→黑云母正长花岗岩),其岩石成因类型具有从I型向I-A过渡型花岗岩变化的趋势;含辉石黑云母闪长岩和二长花岗岩中黑云母形成于较高氧逸度环境,其结晶温度分别为675℃~740℃和550℃~675℃;蟒岭花岗岩体是古老地壳物质部分熔融形成的长英质岩浆与可能起源于幔源的基性岩浆混合而成的产物。

Mangling granitic pluton is located between Heigou-Luanchuan fault and Qiaoduan-Waxuezi fault in North Qinling.It is a magmatic complex formed by 3 stages of magmatic intrusion,including pyroxene-bearing biotite diorites,monzogranites and biotite syenogranite from early stage to late stage.Based on detailed field survey and petrographic observation,the mineralogy and Sr-Nd-Hf isotopes of the first two rocks in Mangling granitic pluton were systematically studied.The results show that Mangling granite pluton is mainly I type granite;from early stage to late stage(pyroxene-bearing biotite diorites→monzogranites→biotite syenogranites),the petrogenetic type of granite has a tendency of changing from I type to I-A transitional type;the biotites from the first two rocks are formed in high oxygen fugacity,and their crystallization temperatures are 675℃-740℃and 550℃-675℃,respectively;Mangling granite pluton is a mixture of felsic magma formed by partial melting of ancient crust and mafic magma possibly derived from mantle.