粤南长蛇山分异Ⅰ型花岗岩的年代学、地球化学特征及其构造意义  

Petrogenesis and Its Geological Implications of the Changsheshan Fractionated Ⅰ-type Granites in the Coastal Area,Southern Guangdong

作　　者：孟德磊 贾小辉[2,3] 谢国刚[2] 吴俊[2] 卜建军[2] 曾海良 Meng Delei;Jia Xiaohui;Xie Guogang;Wu Jun;Bu Jianjun;Zeng Hailiang(No.912 Geological Surveying Party,Jiangxi Bureau of Geology and Mineral Exploration and Development,Yingtan Jiangxi 335001,China;Wuhan Center of Geological Survey,China Geological Survey,Wuhan 430223,China;Research Center for Petrogenesis and Mineralization of Granitoid Rocks,China Geological Survey,Wuhan 430223,China)

机构地区：[1]江西省地质矿产勘查开发局九一二大队,江西鹰潭335001 [2]中国地质调查局武汉地质调查中心,武汉430223 [3]中国地质调查局花岗岩成岩成矿研究中心,武汉430223

出　　处：《地质科技情报》2019年第4期193-204,共12页Geological Science and Technology Information

基　　金：中国地质调查局特殊地区地质填图工程项目“珠三角阳江-珠海地区海岸带1∶5万填图试点”(DD20160064-01);国家自然科学基金项目(41302046)

摘　　要：在年代学、岩石学、地球化学和Sr-Nd-Hf同位素组成等研究的基础上,探讨了广东南部长蛇山花岗岩的岩石成因及其对区域晚中生代构造背景的指示意义。LA-ICP-MS锆石U-Pb测年结果显示,长蛇山花岗岩形成于中侏罗世晚期(163 Ma)。花岗岩具有富硅、富碱更富钾,贫磷,准铝-弱过铝质(A/CNK=0.98~1.11),富集大离子亲石元素(如Rb、Th、U、Pb),亏损高场强元素(如Nb、Zr、Ti)及Ba、Sr等特征。P2O5与SiO2表现为负相关关系,Y与Rb表现正相关关系,总体表现出高钾钙碱性分异Ⅰ型花岗岩特征,与同期次"南岭系列"花岗岩相似。长蛇山花岗岩具有相对低的(87Sr/86Sr)i值(0.705 54~0.709 40)和高的εNd(t)值(-4.6^-0.4),相应的Nd同位素两阶段模式年龄为0.99~1.33 Ga,锆石原位Hf同位素组成变化大(εHf(t)=-7.9^+4.5,tDM2=0.99~1.81 Ga)。元素及同位素结果表明,长蛇山花岗岩可能源自中元古代古老地壳物质的部分熔融,形成过程中遭受了显著的幔源物质混染,并经历了长石、磷灰石和富钛矿物相等的分异结晶。长蛇山分异Ⅰ型花岗岩可能与"南岭系列"花岗岩具有相同的构造背景,形成于古太平洋板块俯冲作用下的弧后伸展环境。LA-ICP-MS U-Pb zircon dating for the Changsheshan granite is(163.4±3.0)Ma and(163.2±0.6)Ma respectively,indicating that the granite was generated in the late Middle Jurassic.The granites are enriched in silicon,alkali and potassium and depleted in phosphorus,and exhibit metaluminous to weakly peraluminous,with A/CNK ratios of 0.98-1.11.They are also enriched in large ion lithophile elements,such as Rb,Th,U and Pb,and depleted in high field strength elements,such as Nb,Zr,Ti,Ba and Sr.They have relatively low 104×Ga/Al ratios and(Zr+Nb+Ce+Y)contents.In addition,P2O5 contents decrease with increasing SiO2 contents,and Y contents decrease with increasing Rb contents.All these characteristics suggest that the Changsheshan granites are high-K calc-alkaline and highly fractionatedⅠ-type granites,similar to the"Nanling-series"granites.The Changsheshan granites have relatively low initial(87Sr/86Sr)ratios(0.705 54-0.709 40)and highεNd(t)values(-4.6 to-0.4),together with highly variableεHf(t)values(-7.9 to+4.5)and tDM2 model age(0.99-1.81 Ga)for the zircons.Combining with geochemical and isotopic compositions,we suggest that the Changsheshan granitic magmas were likely generated by partial melting of the Mesoproterozoic metamorphic basement,involved by small mantle-derived magmas,and that the subsequent extensive fractional crystallization of minerals(feldspar,apatite and Ti-bearing phase)produced the granites.The Changsheshan granites emplaced in the backarc extensional environment are related to subduction of the Paleo-Pacific plate,with the same tectonic settings as those of the"Nanling-series"granites.

关 键 词：分异I型花岗岩 锆石U-PB定年 SR-ND-HF同位素 岩石成因 弧后伸展作用 

分 类 号：P588.121[天文地球—岩石学]