北山地区芨芨台子蛇绿岩地球化学特征及形成环境  

Geochemical Characteristics and Tectonic Setting of the Jijitaizi Ophiolite in Beishan area

作　　者：武磊 翟新伟 王二腾 王赟 郭志昂 宋高瑞 王金荣 杜君 WU Lei;ZHAI Xinwei;WANG Erteng;WANG Yun;GUO Zhi’ang;SONG Gaorui;WANG Jinrong;DU Jun(School of Earth Sciences,Lanzhou University,Lanzhou 730000,Gansu,China;Key laboratory of Mineral Resources in Western China,Lanzhou 730000,Gansu,China;People's Government of Caijia Town,Jiangjin District,Chongqing 400000,China)

机构地区：[1]兰州大学地质科学与矿产资源学院,甘肃兰州730000 [2]甘肃省西部矿产资源重点实验室,甘肃兰州730000 [3]重庆市江津区蔡家镇人民政府,重庆400000

出　　处：《西北地质》2025年第1期27-42,共16页Northwestern Geology

基　　金：第二次青藏高原综合科学考察研究(2019QZKK0901);中国地质调查局项目“中国北方(天山-北山-阴山以北)中段石炭纪—二叠纪构造演化研究”(121201011000161111-01)联合资助。

摘　　要：甘肃北山地区芨芨台子蛇绿岩是芨芨台子–小黄山蛇绿岩带重要组成部分,位于公婆泉单元和明水–旱山微陆块之间的北山造山带中部,主要由超基性岩、辉长岩和玄武岩组成。为揭示芨芨台子蛇绿岩带的形成环境,开展辉长岩、玄武岩岩石学及地球化学研究。辉长岩、玄武岩MgO为6.04%~6.73%、6.21%~9.66%,Mg^(#)为32.33~37.03、27.58~46.27,SI固结指数27.66~31.55、24.96~42.20,Al_(2)O_(3)为15.82%~16.79%、13.38%~15.38%,Na_(2)O高于K_(2)O含量(Na_(2)O/K_(2)O=9.75~17.15、1.95~23.26),Na_(2)O+K_(2)O分别为4.48%~4.90%和3.37%~4.68%,P_(2)O_(5)分别为0.07%~0.09%和0.16%~0.27%,均具富集LREE和LILE,亏损HREE和HFSE,Eu无明显异常(δEu=0.98~1.09、0.88~1.06);(^(87)Sr/^(86)Sr)i为0.703700~0.704768,(^(143)Nd/^(144)Nd)i为0.512234~0.512361,ε_(Nd)(t)为+4.18~+6.66。这些特征指示芨芨台子蛇绿岩带属于SSZ型蛇绿岩带,玄武岩与辉长岩来源于亏损地幔部分熔融,并经历了一定程度的结晶分异及地壳混染作用。结合区域地质背景,芨芨台子蛇绿岩形成于弧后盆地,为红柳河–牛圈子–洗肠井洋盆北向俯冲引起弧后扩张所致。The Jijitaizi ophiolite belt in the middle of the Beishan orogenic belt,between the Mingshui-Hanshan microcontinental block and the Gongpoquan unit is an important part of the Jijitaizi-Xiaohuangshan ophiolite belt,composed of ultrabasic rocks,gabbro and basalt.To reveal the tectonic setting of Jijitaizi ophiolite belt,gabbro and basalt are selected for petrological and geochemical studies.MgO of gabbro and basalt is 6.04%~6.73%and 6.21%~9.66%,Mg^(#)values are 32.33~37.03,27.58~46.27,respectively,SI consolidation index is 27.66~31.55 and 24.96~42.20,Al_(2)O_(3) is 15.82%~16.79%and 13.38%~15.38%,Na_(2)O higher than K_(2)O content(Na_(2)O/K_(2)O=9.75~17.15,1.95~23.26),Na_(2)O+K_(2)O is 4.48%~4.90%and 3.3%~4.68%,P_(2)O_(5) is 0.07%~0.09%and 0.16%~0.27%.Both of gabbro and basalt enrichment of LILEs and LREE,depletion of HREE and HFSEs and Eu have no obvious anomalies(δEu=0.98~1.09、0.88~1.06).(^(87)Sr/^(86)Sr)i is 0.703700~0.704768,(^(143)Nd/^(144)Nd)i is 0.512234~0.512361,ε_(Nd)(t)is+4.18~+6.66.These characteristics indi-cate Jijitaizi ophiolite belt belong to SSZ type ophiolite belt,basalt and gabbro originated from partial melting of the depleted mantle and experienced crystallization differentiation and crustal contamination.Combined with geological background,it can be concluded that the Jijitaizi ophiolite may form in a back-arc basin,resaulting from northward subduction of the Hongliuhe-Niujuanzi-Xichangjing ocean basin.

关 键 词：北山地区 芨芨台子蛇绿岩 SSZ型蛇绿岩 弧后扩张 

分 类 号：P584[天文地球—岩石学]