摘要
稻城贡巴纳岩体位于义敦岛弧碰撞造山带的南东侧。采用LA-ICP-MS的方法研究了贡巴纳岩体,结果表明岩体锆石LA-ICP-MS U-Pb表面年龄为(226.7±2.8)Ma,是印支期岩浆活动的产物。岩性组合复杂,在岩相学特征上,呈浅灰-灰白色,暗色矿物含量低,并出现褐帘石等富铝矿物。岩石地球化学特征显示:高w(SiO2)=71.24%～73.86%,低MgO、FeOT、CaO,ALK=6.47%～6.86%,A/CNK=1.04～1.07,δ=1.36～1.57,AR=4.43～4.90,属于高钾钙碱性系列过铝质花岗岩。相对富集大离子亲石元素,贫化高场强元素;Rb/Sr=0.71～0.88,w(∑REE)=159.3×10-6～190×10-6,轻稀土元素相对富集,轻重稀土元素的分馏比值较高La/Yb=12.87～16.54,δEu=0.16～0.18,总体表现为右倾型,显示与Ⅰ型花岗岩的特征相似。根据花岗岩的R1-R2,Nb-Y构造环境判别图解及区域构造演化史研究,认为该岩体形成于同碰撞构造环境,其形成与义敦岛弧带俯冲碰撞造山活动有关,即三江古特提斯洋闭合事件对接时间为三叠纪。
The Gongbana granitic body is located in Daocheng County,Sichuan Province,tectonically suited in the southeast of Yidun island arc collision-orogenic belt.Zircon LA-ICP-MS U-Pb dating gave a weighted average apparent age of 226.7±2.8 Ma,representing the forming age of this granitoids resulted from Indo-Chinese magmatism.The lithological composition is complex and usually shows light grey-grey white color with low content of dark minerals.Some of the granitoid samples contain aluminous-rich minerals,such as allanite.The petrochemical and geochemical characters of the peraluminous granitoids show high-k calc-alkaline,with high w（SiO2）=71.24%-73.86%,low MgO,FeOT,CaO,ALK=6.47%-6.86%,A/CNK=1.04-1.07,δ=1.36-1.57,AR=4.43-4.90,relative LILE enrichment and HFSE depletion;Rb/Sr=0.71-0.88 and ∑REE=159.3×10-6-190×10-6,LREE was relatively rich,LREE and HREE fractionation ratio is higher La/Yb=12.87-16.54,δEu=0.16-0.18.The overall geochemical characteristics are similar to that of I-type granitoids.The discrimination diagrams of tectonic setting about R1-R2,Nb-Y and regional tectonic setting evolution study revealed that the rocks were formed in the syn-collisional tectonic environment.They were resulted from the collision orogenic activities of Yidun island arc,that is to say,the timing of closure event for the Sanjiang Palaeo-Tethys Ocean was Triassic.
出处
《地质科技情报》
CAS
CSCD
北大核心
2013年第4期55-63,共9页
Geological Science and Technology Information
基金
国家自然科学基金项目"青藏高原中部昆仑-巴颜喀拉-金沙江古特提斯构造岩浆演化及动力学"(1212011121270)
