甘肃北山炭山子东橄榄辉长岩年代学、地球化学特征及其地质意义  

Geochronology and geochemistry of Tanshanzidong olivine-gabbro in Beishan area,Gansu Province,and its geological significance

作　　者：余君鹏 王怀涛[2] 王玉玺[3] 孙新春 任文秀[2] 魏海峰[2] 王晓伟[2] YU Jun-peng;WANG Huai-tao;WANG Yu-xi;SUN Xin-chun;REN Wen-xiu;WEI Hai-feng;WANG Xiao-wei(Lanzhou University,Lanzhou 730000,China;Geological Survey of Gansu Province,Lanzhou 730000,China;Thirtl Institute of Geology and Mineral Kxploralion,Bureau of Geolog\r and Mineral Resources of Gansu Province,Lanzhou 730050,China)

机构地区：[1]兰州大学,甘肃兰州730000 [2]甘肃省地质调查院,甘肃兰州730000 [3]甘肃省地矿局第三地质勘查院,甘肃兰州730050

出　　处：《岩石矿物学杂志》2021年第2期202-216,共15页Acta Petrologica et Mineralogica

基　　金：2020年陇原青年创新创业人才项目(甘组通字[2020]9号);中国地质调查局项目(12120114014501)。

摘　　要：北山地区是中亚造山带的重要组成部分,位于北山地区大山头杂岩体西的炭山子东基性岩体是揭示中亚造山带南缘晚古生代构造演化的重要载体。炭山子东橄榄辉长岩LA-ICP-MS锆石U-Pb年龄为366.0±2.8 Ma,代表该岩体的形成年龄。岩石SiO2(47.83%~52.25%)、K_(2)O(0.12%~0.45%)、Na_(2)O(2.47%~3.19%)、MgO(5.30%~9.22%)具由拉斑系列向钙碱性系列演化的特点。岩石轻稀土元素(LREE)相对富集[(La/Yb)_(N)=1.57~4.12],具Eu正异常(δEu=1.15~1.41),富集大离子亲石元素(Rb、Ba、Sr、U、K),亏损高场强元素(Nb、Ta、Zr和Ti),Nb/La值为0.23~0.46,Hf/Th值为0.88~3.81,(^(87)Sr/^(86)Si)i值为0.7048~0.7049,εNd(t)值为+3.72~+4.30,指示其形成于活动大陆边缘弧环境。结合区域地质,认为炭山子东橄榄辉长岩是辉铜山-帐房山蛇绿岩所代表的弧后盆地在向北俯冲消减过程中,受俯冲流体交代的亏损岩石圈地幔发生部分熔融的产物,为中亚造山带晚泥盆世地壳垂向生长的直接证据。The Beishan area is an important part of the Central Asian Orogenic Belt.The Tanshanzidong basic complex located west of the Beishan Dashantou complex is an important carrier to reveal the late Paleozoic tectonic evolution on the southern margin of the Central Asian Orogenic Belt.This paper reports that the Tanshanzidong basic complex was emplaced with the zircon U-Pb age of 366.0±2.8 Ma.The rocks are characterized by SiO2(47.83%-52.25%),K_(2) O(0.12%~0.45%),Na_(2) O(2.47%~3.19%),MgO(5.30%~9.22%)and the evolution from tholeiitic series to calc-alkaline series.The rocks are enriched in LREE[(La/Yb)_(N)=1.57~4.12)]with positive Eu anomalies,depleted in Nb,Ta,Zr,Ti and enriched in Rb,Ba,Sr,U,K,with the data Nb/La=0.23~0.46,Hf/Th=0.88~3.81,(^(87)Sr/^(86)Sr)、(0.7048~0.7049)andεNd(t)(+3.72~+4.30),suggesting that they were formed in the arc environment of active continental margin.Based on regional geology,the authors hold that the Tanshanzidong basic complex was the product of partial melting of depleted lithospheric mantle,which was replaced by the subduction fluid during the subduction of the northward subduction of back-arc basin represented by Huitongshan-Zhangfangshan ophiolite.These results provide a direct indication for the vertical growth of the crust caused by the late Devonian crust in the Central Asian Orogenic Belt.

关 键 词：基性杂岩体 锆石U-PB年龄 SR-ND同位素 弧后盆地 北山 

分 类 号：P612[天文地球—矿床学] P597[天文地球—地质学]