东天山东段四顶黑山一带早泥盆世岛弧花岗岩年龄、特征及构造意义  

Age, Characteristics and Tectonic Significances of the Early Devonian Island Arc Granites from Sidingheishan,the Eastern Segment of the East Tianshan Orogen

作　　者：施文翔[1] 廖群安[2] 李奇祥[2] 张家新 张旺生[2] 

机构地区：[1]新疆维吾尔自治区地质矿产勘查开发局第一区域地质调查大队,新疆乌鲁木齐830011 [2]中国地质大学(武汉)地球科学学院,湖北武汉430074 [3]新疆有色集团704队,新疆哈密839000

出　　处：《新疆地质》2015年第1期21-26,共6页Xinjiang Geology

基　　金：中国地质调查局国土资源大调查项目(1212010911055)资助

摘　　要：对出露在东天山东段四顶黑山一带的早泥盆世花岗岩进行锆石LA-ICP-MS U-Pb定年,结果为（414.0±3.5）Ma,属早泥盆世。其岩石组合为石英闪长岩、英云闪长岩、花岗闪长岩、二长花岗岩,暗色矿物以角闪石为主,岩石Si O2变化范围较大（54.35%~75.18%）、低K2O/Na2O,高Mg O、Fe Ot、Ca O,A/CNK为0.73~1.11,δ为1.36~2.83,为准铝-偏铝质中低钾钙碱性系列,稀土元素具轻稀元素土较富集、重稀土元素较为平坦的右倾型分布模式,微量元素显示出富集大离子亲石元素、亏损高场强元素的特征,具明显的Nb,Ta负异常,总体具岛弧I型花岗岩特征,在构造环境判别图中均位于岛弧花岗岩区。值得注意的是,低硅端元样品具高Mg O、Mg#、Cr和Ni的特征,与高镁闪长岩特征相近;其余多数样品具高Sr,低Yb,Y,高Sr/Y的埃达克岩特征。高镁闪长质岩石和埃达克质岩石的共生,反映岩浆可能来自俯冲板片熔融的产物,源区可能为俯冲板片变质形成的榴闪岩或榴辉岩。该套花岗岩的厘定不仅证实东天山东段早泥盆世时期为岛弧构造环境,也限定了围岩大南湖组时代应早于早泥盆世早期。A suit of Early Devonian I-type granites is discovered in northern of the Sidingheishan,eastern segment of the East Tianshan orogen.Fifteen zircon grains from a biotite-hornblende tanolite sample were dated using LA-ICP-MS U-Pb method.They yielded a weighted average206Pb/238 U age of（414.0±3.5）Ma,which represented the emplacement age of the granites.The I- type granitoid suites include quartz- diorite,granodiotite, tonalite,and monzogranite.they have large- scale variational values of Si O2（59.46% ~75.18%）,low K2O/Na2 O ratio, high Mg O、Fe Ot and Ca O contents, A/CNK ratios is0.73~1.11,δis 1.36~2.83, indicating that the granites belong to intermediate- low- potassic calc- alkaline series rock.The Early Devonian granites show a slope right chondrite-normalized REE pattern with LREE enrichment and smooth HREE.In addition,they are characterized by enrichment of LILEs（large ion field lithophile elements） and depletion of HFSEs（high field siderophile elements）,as well as remarkable Nb and Ta depletion.These petrochemical and geochemical characteristics indicate that the I-type granites were formed in an island arc tectonic environment. It is worth noting that, samples of low silicon components have high Mg O, Mg#,Cr and Ni content,similar to magnesia diorite.While most of the other componetnts have high Sr, low Yb,Y,and high Sr/Y ratio,that similar to adakite.Intergrowth with magnesia dioritic rocks and adakitic rocks, reflecting that the magma maybe formed from the melting of subducted slabs. The source of the Early Devonian granite may be garnet amphibolite or eclogite formation from metamorphic of subducting plate.The determining of the early Devonian granites not only confirmed the island arc tectonic environment in the eastern East Tianshan during the period of the early Devonian, but also limited the age of the wall rock stratum,the age of which should not be late than early Devonian.

关 键 词：东天山 四顶黑山 早泥盆世 岛弧 花岗岩 

分 类 号：P588.121[天文地球—岩石学]