秦岭晚中生代花岗岩时空分布、成因演变及构造意义  

Temporal-spatial variations,origin and their tectonic significance of the Late Mesozoic granites in the Qinling,Central China

作　　者：王晓霞[1] 王涛[2] 齐秋菊[3] 李舢[2] 

机构地区：[1]中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室,北京100037 [2]中国地质科学院地质研究所,北京100037 [3]中国地质大学,北京100083

出　　处：《岩石学报》2011年第6期1573-1593,共21页Acta Petrologica Sinica

基　　金：国家973项目(2009CBB25001);国家自然科学基金项目(40872054);地质调查项目(1212010012012;1212010811033和1212010611803);公益型行业专项课题(200911007);危机矿山接替资源找矿项目(20089949)联合资助

摘　　要：秦岭晚中生代花岗岩主要发育于秦岭北部的华北地块南缘和北秦岭,南秦岭仅有零星出露。本文报道了3个晚中生代大岩体的年代学和其中2个岩体的地球化学和同位素数据,并系统收集了发表的相关资料,对秦岭晚中生代花岗岩进行了初步总结。华北地块南缘蓝田花岗岩的锆石LA-ICPMSU-Pb年龄为133±1Ma,εNd(t)=-11.8～-18.3,锆石εHf(t)=-37.7～-5.7。北秦岭构造带中牧护关花岗岩的锆石LA-ICPMSU-Pb年龄为150±1Ma,εNd(t)=-7.6～-11.4,锆石εHf(t)=-7.3～-17.4;蟒岭花岗岩的锆石SHRIMPU-Pb年龄为149±2Ma。依据收集到的26个锆石U-Pb和3个黑云母Ar-Ar年代学资料,秦岭晚中生代花岗岩浆的演化可分为2个阶段:第一阶段为160～130Ma(晚侏罗世-早白垩世),以I-型花岗岩为主,主要发育于华北地块南缘和北秦岭,在南秦岭仅零星分布;第二阶段为120～100Ma(早白垩世中晚期),以I-A过渡型和A-型花岗岩为主,主要分布在华北地块南缘的东部和北秦岭,出露面积比第一阶段小。第一阶段(160～130Ma)花岗岩主要形成于古老地壳物质的部分熔融,并有年轻幔源组分的参与,形成于挤压向伸展转换的构造环境。第二阶段(120～100Ma)花岗岩的形成除了古老地壳物质的部分熔融外,有更多的年轻幔源组分加入,发育于陆内伸展环境。花岗岩的同位素特征显示,从华北地块南缘到南秦岭,底基物质中年轻组分有增加的趋势,花岗岩的物源受深部地壳物质组成特征的控制。Zircon U-Pb dating for three large granitoid batholiths,geochemical and Hf isotope analyses for two of them have been carried out in the different blocks of the Qinling.Zircon dating by LA-ICPMS for the Lantian granitoid in the southern margin of the North China Block gives an age of 133±1Ma.The granitoids show whole-rock εNd（t）=-11.8^-18.3,zircon εHf（t）=-37.7^-5.7.The Muhuguan and the Mangling granitoids in the North Qinling orogen yield zircon LA-ICPMS and SHRIMP age of 150±1Ma and 149±2Ma,respectively.The Muhuguan granitoids show whole-rock εNd（t）=-7.6^-11.4 and zircon εHf（t）=-7.3^-17.4.Combined with statistical analyses of 26 zircon ages and 3 Ar-Ar ages of granitoid plutons collected from the literature,the Late Mesozoic magmatism in the Qinling can be divided into two stages.The first-stage magmatism （160~130Ma） widely occurred in the southern margin of the North China Block,the North Qinling and occasionally in the South Qinling,and has features of I-type granitoids.The second-stage magmatism （120~100Ma） characterized by transition of I-to A-type and A-type granitoids took place in the North Qinling and the eastern part of the southern margin of the North China Block.The first-stage magmatism occurred in a transition from contractional to extensional settings,while the second-stage in the extension setting.The formation of the grantoids are interpreted as partial melting of old crust,mixed with juvenile mantle component.The second-stage granitoids contain more juvenile component than the first-stage.The isotope data of the granitoids show that juvenile compositions of the basement increas from the southern margin of the North China Block to the Shangdan suture.

关 键 词：锆石年代学 花岗岩组合 Nd Hf同位素 秦岭 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]