中祁连东段什川杂岩基的岩石化学特征及年代学研究  

Geochemical characters and LA-ICPMS zircon U-Pb dating constraints on the petrogenesis and tectonic setting of the Shichuan intrusion,east segment of the Central Qilian,NW China.

作　　者：陈隽璐[1,2] 徐学义[1] 曾佐勋[2] 肖林[3] 王洪亮[1] 王宗起[4] 肖绍文 

机构地区：[1]中国地质调查局西安地质矿产研究所,西安710054 [2]中国地质大学地球科学学院,武汉430074 [3]甘肃省地质调查院,兰州730050 [4]中国地质科学院地质研究所,北京100037 [5]广西壮族自治区地球物理勘察院,柳州545005

出　　处：《岩石学报》2008年第4期841-854,共14页Acta Petrologica Sinica

基　　金：国家科技支撑计划项目(2006BAB01A11);自然科学基金(40773044);中国地质调查局国土资源大调查研究项目(1212010610319、1212010611807)联合资助。

摘　　要：祁连造山带被托菜南山-了高山构造带及宗务隆山-贵得构造带分为北祁连、中祁连及南祁连构造带。什川岩基位于中祁连构造带东部,由闪长岩、斜长花岗岩、二长花岗岩组成;对二长花岗岩进行U-Pb单颗粒锆石微区LA-ICP-MS同位素测定,获得444.6Ma及414.3Ma两组加权平均年龄,前者代表岩石的形成年龄,后者代表构造热事件年龄。二长花岗岩主量元素W(SiO_2)=68.66%～80.77%,w(K_2O)/w(Na_2O)>1和A/CNK介于0.95～1.21间,总体为钾质钙碱性过铝质花岗岩。岩石富集LILE元素(K、Th、Rb、Ba等),亏损HFSE元素(Ta、Nb、Y等);稀土元素总量较高(∑REE多介于109.05×10^(-6)～322.66×10^(-6)),轻重稀土强烈分馏(∑LREE/∑HREE介于7.92～31.68),稀土元素分配模式为轻稀土富集型,具中等-强Eu负异常(δEu=0.26～0.58)。岩石矿物组合及岩石地球化学特征共同表明,什川岩基为中上地壳泥砂质岩石部分熔融而成,形成温度较低,为加厚地壳拆沉熔融成因。这为祁连造山带构造演化及其深部动力学机制研究提供了新的资料。The Qilian Orogen is divided into the Northern, Central and Southern Qilian by the Tuolainanshan-Liaogaoshan tectonic melange and The Zong Wulongshan-Guide tectonic mrlange on northern and southern sides of the Central Qilian, respectively. The Shichuan intrusion is located in the Central Qilian and is composed of diofites, granodiorites, plagiogranites and monzogranites. These monzogranites, which are the focus of this study, yielded two LA-ICP-MS U-Pb zircon weighted ^206Pb/^238U ages of 444.6 and 414.3 Ma. The former is interpreted as its emplacement age, whereas the later is attributable to the imprinting age of late tectonothermal event. The modal compositions of these monzogranite samples mainly correspond to two-mica （muscovite-biotite） monzogranite belonging to the granitoids generated by crustal fusion. Compositionally, these rocks have SiO2 ranging from 68.66% to 80. 77% , K2O/Na2O more than 1, and molar A/CNK = 0.95 ～ 1.21, indicating that they are typically characterized as peralumious （S-type） granitoid. They also show general trends of decreasing contents of some major oxides （ Al2O3, Fe2O3 , CaO, P2O5 and TiO2 ） with increasing SiO2 but K2O amounts not. These monzogranites are depleted in HFSE, such as Ta, Nb and Y, such as enriched in IDLE, such as K, Th, Rb and Ba, and light rare earth elements （ LREE）, with total REE contents ranging from 109.05 to 322.66 ppm and ∑ LREE/ ∑ HREE ratios of 7.92 - 31.68. The Chondrite-normalized REE patterns of these monzogranites exhibit enrichment in LREE and depletion in HREE with moderate-pronounced negative Eu anomalies （Eu/Eu^ ＊ = 0. 26 ～0.58）. The petrological and geochemical characteristics, emplacement age as well as the previous Nd and Sr isotopic data, integrated with regional geodynamics, indicate that these mozongranites could represent typical S-type granite suite due to varying degree of partial fusion of sedimentary protoliths （ mud- sandstones） under low temperature, and form in a syn-to postcollisional orogenic se

关 键 词：U—Pb锆石LA—ICPMS定年 什川岩体 同碰撞 中祁连 

分 类 号：P597.3[天文地球—地球化学]