新疆西准噶尔发现早泥盆世埃达克岩:大地构造及成矿意义  

Discovery of Early Devonian adakite in West Junggar,Xinjiang:Implications for geotectonics and Cu mineralization

作　　者：王金荣[1] 贾志磊[1] 李泰德 马锦龙[1] 赵磊[1] 何彦彬[1] 张伟 刘昆鑫[1] 

机构地区：[1]兰州大学地质科学与矿产资源学院甘肃省西部矿产资源重点实验室,兰州730000 [2]新疆有色地质矿产勘查局物探大队,乌鲁木齐830011

出　　处：《岩石学报》2013年第3期840-852,共13页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41173014);中国地质调查局地调项目(1212010880101)联合资助

摘　　要：新疆西准噶尔博什库尔-成吉斯(Boshchekul-Chingiz)岩浆弧南缘,额敏县东南约100km的阿克乔克含铜花岗闪长岩和花岗闪长斑岩,其锆石U-Pb年龄为410.5±2.9Ma,形成于泥盆世早期。岩石具有埃达克岩的地球化学特征,表现为高钾钙碱性-钙碱性,SiO2含量在61%～66%之间,具高Al(Al2O3=15.67%～16.87%)、Sr(475×10-6～879×10-6)及高Sr/Y比值(36～77),低Y(9.87×10-6～14.46×10-6)、Yb(0.96×10-6～1.49×10-6),富钠贫钾(Na2O=4.25%～5.58%,K2O=2.26%～3.27%,Na2O/K2O=1.40～2.47),MgO=1.51%～2.58%,Mg#=41～48,并显示富集强不相容元素(Ba、Rb、Sr、Th、U)和LREE,(La/Yb)N=6.0～10.2,强烈亏损高场强元素(Nb-Ta、Ti),Y/Yb=10,无Eu异常(Eu/Eu*≈1.0)和HREE呈平坦型的配分特点,以及与环太平洋新生代埃达克岩相当的Rb/Sr(0.04～0.07)和La/Ce(0.42～0.51)比值,但偏低的Nb/U比值可能与俯冲沉积物加入有关。阿克乔克花岗闪长岩及花岗闪长斑岩是早泥盆世早期库吉拜-和布克赛尔(Kujibai-Hebukesaier)及洪古勒楞蛇绿岩带所代表的古大洋向南俯冲的玄武质洋壳部分熔融的产物,源区残留相主要为角闪石+辉石+石榴石,源岩应为石榴角闪岩;阿克乔克早泥盆世埃达克岩及谢米斯台-赛尔山晚志留世-早泥盆世A-型花岗岩(422～405Ma,Chenetal.,2010)构造岩浆岩带可东延至扎河坝-阿尔曼太蛇绿岩带之北的岛弧带,构成一条贯穿东、西准噶尔北部的巨型构造带;阿克乔克埃达克岩伴有斑岩型Cu成矿作用,因此,在东、西准噶尔博什库尔-成吉斯-达拉特-巴依塔格巨型岩浆弧带有可能存在与埃达克岩有关的Cu-Au矿带。The accretionary orogenic belt of West Junggar, Xijiang, are accepted as the products of subduction, accretion, and tectonic assembly of the oceanic terranes due to the closure of paleo-Asian ocean in Paleozoic, in which the many ophiolitic melange zones, subduction-related plutons, volcanic-sedimentary rocks and arc igneous rocks, and post-collisional granitoids developed and studied well, but early Late-Paleozoic adakites are not definitely reported. The Akeqiaoke Cu-bearing granotoids,located about 100km southeast of Erming County, tectonically in the south margin of Boshchekul-Chingiz island arc of the West Junggar, formed in Early Devonian, and are 410. 5 ± 2.9Ma of LA-ICP-MS zircon U-Pb ages. They have geochemical features suggestive of the adakites from the circum-Pacific. The plutons exhibit high-K and calc-alkaline composition with SiO2 （61% - 66% ）, high A1 （A1203 = 15.67% - 16. 87% ）, Sr（475×10-6- 879 ×10-6 ）, Na （ Na2O = 4. 25% - 5.58% ） contents, and Sr/Y （ 36 - 77 ） and Na2O/K2O （ 1.40 2. 47 ） ratios, as well as MgO （ 1.51% - 2. 58 % ） and Mg# （41 - 48 ）, coupled with low Y （ 9.87×10^-6 14. 46×10-6 ） and Yb （0.96×10^-6 -1.49 ×10-6）. Furthermore, they display obviously rich in strongly incompatible elements （Ba, Rb, Sr, Th and U） and LREE with （La/Yb） N. Rb/Sr, La/Ce ratios of 6. 0 - 10. 2, 0.04 - 0. 07, 0. 42 - 0. 51, respectively, but depleted in HFSEs（ Nb- Ta and Ti）,HREE with Y/Yb ratio of 10, no Eu anomaly（Eu/Eu＊ ≈ 1.0）. However, compared with the modem adakites, they exhibit lower Cr, Ni contents and （La/Yb）N and Nb/U ratios, as well as flat HREE patterns, indicating these adakitic magmas were formed by relatively high degree of slab-melting, low reaction of the melt with mantle and input of subducted sedimentary components. The studied results show that the plutons of Early Devonian from Akeqiaoke were products -resulted from the slab melting of the southward subduction of paleo-ocean represented by the Kujibai-Hebukesaier

关 键 词：埃达克岩 板片熔融 巨型构造岩浆岩带 早泥盆世 Cu(Au)成矿 西准噶尔 

分 类 号：P588.122[天文地球—岩石学] P597.3[天文地球—地质学]