Geochemical characteristics and zircon U-Pb age of gabbros in the Zhaqiaohe ophiolite mélange, and its limitation on the ocean ridge environment
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摘要:研究目的
扎巧合蛇绿岩处于中祁连和南祁连构造带的结合部位，带内蛇绿岩组分由蛇纹岩、蛇纹石化辉橄岩、辉长岩，辉绿岩、块层状蚀变玄武岩，少量枕状玄武岩、透镜状硅质岩等组成，为拉脊山蛇绿混杂岩带在青海省内的西延部分。
研究方法本文对扎巧合蛇绿岩中的辉长岩进行了年代学、岩石地球化学研究。
研究结果辉长岩以主化学成分SiO2、Na2O、K2O、（Fe2O3+FeO）及MgO等的特征判断，为拉斑系列的辉长岩。从其REE分布模式看，铕无异常或弱负异常，说明岩石在熔融过程中经历了斜长石的分离结晶作用，稀土配分曲线为一条近似平直曲线；微量元素具明显的Ta和Sr正异常特征，表明本区蛇绿岩中辉长岩具有与E-MORB类似的特征。LA-ICP-MS锆石UPb测年结果显示辉长岩结晶年龄为（524.0±2.5）Ma。
结论这些辉长岩起源于未发生大规模熔融的初始地幔，认为扎巧合蛇绿岩可能形成于古洋盆初始裂解阶段的洋脊环境。
创新点: 扎巧合蛇绿混杂岩带为拉脊山蛇绿混杂岩带在青海省内的西延部分，带内蚀变辉长岩的形成年龄为（524.0±2.5）Ma，为MOR型蛇绿岩，形成于古洋盆初始裂解阶段的洋脊环境。
Abstract:This paper is the result of geological survey engineering.
ObjectiveZhaqiaohe ophiolite is located at the junction of the Middle Qilian and South Qilian tectonic belt. The ophiolite in the belt is composed of serpentinite, serpentinized pyroxene peridotite, gabbro, diabase, block bedded altered basalt, a small amount of pillow basalt and lenticular silicite. It is the west extension of the Lachishan ophiolite melange belt in Qinghai Province.
MethodsIn this paper, the study on the chronology and petrogeochemistry of gabbro in Zhaqiaohe ophiolite has been carried out.
ResultsAccording to the characteristic judgment of the main chemical components of the gabbro, such as SiO2, Na2O, K2O, (Fe2O3 + FeO) and MgO, the gabbro is tholeiitic series, belonging to tholeiite. According to the REE distribution pattern, there is no Eu anomaly or weak negative anomaly, indicating that the rock experienced the separation and crystallization of plagioclase in the melting process, and the REE distribution curve is approximately flat; the trace elements have obvious Ta and Sr positive anomaly characteristics, indicating that gabbro in ophiolite in this area has similar characteristics with E-MORB. The results of LA-ICP-MS zircon U-Pb dating show that the gabbro crystallization age is (524.0±2.5) Ma.
ConclusionsIt is suggested that these gabbros originated from the initial slowness without large-scale melting. It is suggested that the Zhaqiaohe ophiolite may have formed in the oceanic ridge environment during the initial cracking stage of the paleo ocean basin.
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Keywords:
- ophiolite belt /
- gabbro /
- zircon U-Pb dating /
- E-MORB /
- Central Qilian /
- geological survey engineering /
- Zhaqiaohe /
- Qinghai Province
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图 1 扎巧合地区大地构造位置图（a）和地质简图（b）
1—全新世冲洪积；2—中三叠统切尔玛沟组；3—上二叠统忠什公组；4—上三叠统哈吉尔组；5—下—中二叠统草地沟组；6—下—中二叠统勒门沟组；7—上石炭统羊虎沟组；8—下石炭统臭牛沟组；9—下奥陶统吾力沟组；10—上寒武统六道沟组；11—青白口系五个山组；12—灰岩岩块/砾岩岩块；13—硅质岩岩块/凝灰岩岩块；14—玄武岩岩块；15—辉绿岩岩块；16—辉长岩岩块；17—千糜岩；18—整合/不整合界线；19—断层界线；20—层理/面理；21—剖面位置；22—采样位置及编号
Figure 1. Tectonic location map (a) and regional tectonic map of Zhaqiaohe area (b)
1-Holocene alluvium; 2-Middle Triassic Chermagou Formation; 3-Late Permian Zhongshigong Formation; 4-Late Triassic Hajir Formation; 5-Early and Middle Permian Caodigou Formation; 6-Early and Middle Permian Lemengou Formation; 7-Late Carboniferous Yanghugou Formation; 8-Early Carboniferous Chouniugou Formation; 9- Early Ordovician Wuligou Formation; 10-Late Cambrian Liudaogou Formation; 11-Qingbaikouji Wugeshan Formation; 12- Limestone blocks/conglomerate blocks; 13-Siliceous rock block/tuff rock block; 14-Basalt blocks; 15-Diabase blocks; 16-Gabbro rocks; 17-Phyllite; 18- Conformity/unconformity boundary; 19-Fault boundaries; 20-Bedding/foliation; 21-Profile position; 22-Sampling location and number
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图 2 扎巧合辉长岩野外露头及镜下照片
a—混杂岩产出特征；b—蚀变辉长岩露头；c—蚀变辉长岩显微照片；P1—斜长石；Cpx—单斜辉石；Hb—普通角闪石
Figure 2. Field and microscopic features of the Zhaqiaohe gabbro
a-Melange production characteristics; B-Altered gabbro outcrop; C-Altered gabbro micrograph; P1-Plagioclase; Cpx-Clinopyroxene; Hb-Hornblende
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图 3 扎巧合蚀变辉长岩TAS图解(a，据Middlemost，1994)和SiO2-FeOT/MgO图解(b，据Miyashiro and Shido, 1975)
Figure 3. TAS diagram (a, after Middlemost, 1994) and SiO2-FeOT/MgO diagram (b, after Miyashiro and Shido, 1975) of altered gabbro from Zhaqiaohe area
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图 4 扎巧合蚀变辉长岩的稀土元素配分模式(a)和原始地幔标准化蛛网图解(b)(标准化值据Sun and McDonough, 1989)
Figure 4. Chondrite normalized REE distribution patterns (a) and primitive mantle-normalized trace lements patterns (b) of the samples from Zhaqiaohe area (normalization values after Sun and McDonough, 1989)
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图 6 扎巧合辉长岩锆石U-Pb年龄谐和图（a）和加权年龄图（b）
Figure 6. Zircon U-Pb age harmonic diagram (a) and weighted diagram (b) of gabbros from Zhaqiaohe area
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图 7 扎巧合辉长岩Zr-Zr/Y图解（a, 据Pearce and Norry, 1979）和Hf/3-Th-Ta图解（b, 据Wood，1980）
MORB—洋中脊玄武岩；WPB—板内玄武岩；IAB—岛弧玄武岩；CAB—钙碱性玄武岩；N-MORB—正常洋中脊玄武岩；E-MORB+WPT—富集洋中脊和板内拉板玄武岩；IAT—岛弧拉斑玄武岩；WPAB—板内碱性玄武岩
Figure 7. Zr-Zr/Y diagram (a, after Pearce and Norry, 1979) and Hf/3-Th-Ta diagram (b, after Wood, 1980) of gabbros from Zhaqiaohe area
MORB-Mid-ocean ridge basalt; WPB-Intraplate basalt; IAB-Island arc basalt; CAB-Calc alkaline basalt; N-MORB-Normal mid-ocean ridge basalt; E-MORB+WPT-Enriched mid-ocean ridge and intraplate tholeiite; IAT-Island arc tholeiite; WPAB-Intraplate alkaline basalt
表 1 扎巧合蚀变辉长岩主量元素（%）、微量元素（10-6）分析结果
Table 1 Major element (%) and trace element (10-6) compositions of the samples from Zhaqiaohe area
下载: 导出CSV
表 2 扎巧合辉长岩U-Pb同位素参数特征
Table 2 U-Pb is otopeage determine dresult of the samples from Zhaqiaohe area
下载: 导出CSV
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Chen Xuanhua, Shao Zhaogang, Xiong Xiaosong, Gao Rui, Liu Xuejun, Wang Caifu, Li Bing, Wang Zengzhen, Zhang Yiping. 2019. Fault system, deep structure and tectonic evolution of the Qilian Orogenic Belt, Northwest China[J]. Geology in China, 46(5): 995-1020 (in Chinese with English abstract).
Coleman R G. 1977. Ophiolites: Ancient oceanic lithosphere?[J]. Mineralogical Magazine, 42(322): 308-308.
Feng Yimin, Cao Xuanduo, Zhang Erpeng, Hu Yunxu, Yang Junlu, Pan Xiaoping, Jia Qunzi, Li Wenming. 2002. Structural Orogenic Process and Dynamics of the West Qinling Orogenic Belt[M]. Xi'an: Xi'an Map Publishing House, 263(in Chinese with English abstract).
Feng Yimin, He Shiping. 1996. Geotectonics and Orogeny in Qilian Mountains[M]. Beijing: Geological Publishing House, 1-135(in Chinese with English abstract).
Fu Changlei, Yan Zhen, Guo Xiaoqin, Niu Manlan. 2014. Geochemistry and SHRIMP zircon U-Pb age of diabases in the Lajishankou ophiolitic melange, South Qilian terrane[J]. Actor Petrologica Sinica, 30(6): 1695-1706
Hou Qingye, Zhang Hongfei, Zhang Benren, Zhao Zhidan, Zhu Yunhai. 2005. Paleogeochronicity of the Laji Mountain in the middle Qilian orogenic belt and its attribution: Geochemical evidence from basic volcanic rocks[J]. Earth Science, 30(1): 61-70(in Chinese with English abstract).
Li Chunyu, Liu Yangwen, Zhu Baoqing, Feng Yimin, Wu Hanquan. 1978. Tectonic History of Qinling and Qilian Mountains[M]. Beijing: Geological Publishing House, 174-187(in Chinese with English abstract).
Li Jianfeng, Zhang Zhicheng, Han Baofu. 2010. Geochronolgy and geochemistry of Early Paleozoic plutons from Subei and Shibaocheng areas, the western segment of Central Qilian and their geological implications[J]. Acta Petrologica Sinica, 26(8): 2431-2344(in Chinese with English abstract).
Li Huaikun, Geng Jianzhen, Hao Shuang, Zhang Yongqing, Li Huiming. 2009. Determination of zircon U-Pb isotope ages by laser Ablation Multi-receiver Plasma Mass Spectrometer (LA-MC-ICPMS)[J]. Acta Mineralogica Sinica, 29(S1): 600-601 (in Chinese with English abstract).
Middlemost E A K. 1994. Naming materials in the magma/igneous rock system[J]. Earth-science Reviews, 37(3-4): 215-224. doi: 10.1016/0012-8252(94)90029-9
Miyashiro A, Shido F. 1975. Tholeiitic and calc-alkalic series in relation to the behaviors of titanium, vanadium, chromium, and nickel[J]. American Journal of Science, 275 (3): 265-277. doi: 10.2475/ajs.275.3.265
Nicolas A. 1989. Structures of Ophiolites and Dynamics of Oceanic Lithosphere[M]. Dordrecht: Kluwer. 1-367.
Pearce J A, Lippard S J, Roberts S. 1984. Characteristics and tectonic significance of super-subduction zone ophiolites[J]. Geological Society, London, Special Publications, 16(1): 74-94.
Qiu Jiaxiang, Zeng Guangce, Wang Siyuan, Zhu Yunhai. 1997. Early Paleozoic Marine Volcanic Rocks and Mineralization in Laji Mountain[M]. Wuhan: China University of Geosciences Press, 1-118(in Chinese with English abstract).
Sun S S, McDonough W F. 1989. Chemical and isotopic systematics of oceanic basalts: Implications for mantle composition and processes[J]. Geological Society, London, Special Publications, 42(1): 313-345 doi: 10.1144/GSL.SP.1989.042.01.19
Tseng C Y, Yang H J, Yang H Y, Liu D Y, Tsai C L, Wu H Q, Zuo G C. 2007. The Dongcaohe ophiolite from the North Qilian Mountains: A fossil oceanic crust of the Paleo-Qilian Ocean[J]. Chinese Science Bulletin, 52(7): 2390-2401
Wang Erqi, Zhang Qi, Burchfiel C B. 2000. Laji Mountain, Qinghai Province: A tectonic window of multi-stage uplift [J]. Chinese Journal of Geology, 35(4): 393-500(in Chinese with English abstract).
Wang Jinrong, Zhang Xinhu, Zhang Xiang, Hui Xinwei, Zhang Benqi, Zhao Lei. 2021. Rock association, genesis and tectonic significance of Mustangshan structure in the western part of Middle Qilian[C]//Abstracts of the National Symposium on Petrology and Geodynamics, 466-468(in Chinese with English abstract).
Wood D A. 1980. The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary Volcanic Yrovince[J]. Earth and Planetary Science Letters, 50(1): 1-30. doi: 10.1016/0012-821X(80)90115-6
Xia Linqi, Xia Zuchun, Ren Youxiang, Peng Ligui, Zhang Cheng, Yang Jinghua, Wang Xingan, Li Zhipei, Han Song, Huang Zhongxiang. 1991. Marine Volcanic Kocks from Qilian and Qinling Mountains[M]. Wuhan: China University of Geosciences Press, 1-304 (in Chinese with English abstract)
Xiao Xuechang, Chen Guoming, Zhu Zhizhi. 1978. Geological tectonic significance of the ancient ophiolite belt in Qilian Mountains[J]. Acta Geologica Sinica, 52(4): 281-295 (in Chinese with English abstract).
Xiao W, Windley B F, Yong Y, Yan Z, Yuan C, Liu C, Li J. 2009. Early Paleozoic to Devonian multiple-accretionary model for the Qilian Shan, NW China[J]. Journal of Asian Earth Sciences, 35: 323-333. doi: 10.1016/j.jseaes.2008.10.001
Xu Zhiqin, Xu Huifen, Zhang Jianxin, Li Haibing, Zhu Zhizhi, Qu Jingchuan, Chen Daizhang, Chen Jinlu, Yang Kaichun. 1994. The proliferative terrane of Caledonian subduction complex in Nanshan of North Qilian Corridor and its dynamics[J]. Acta Geologica Sinica, 68 (1): 1-15 (in Chinese with English abstract).
Yan Zhen, Wang Zongqi, Li Jiliang, Xu Zhiqin, Deng Jinfu. 2012. Tectonic properties and accretionary orogeny of West Qinling wedge[J]. Acta Petrologica Sinica, 28(6): 1808-1828(in Chinese with English abstract)
Zhang Jianxin, Xu Zhiqin, Chen Wen, Xu Huifen. 1995. Discussion on the age of subduction-accretion complex/volcanic arc in the middle part of North Qilian [J]. Journal of Rock and Minerals, 16(2): 112-119 (in Chinese with English abstract)
Zhang Xueting, Yang Shengde. 2007. Qinghai Province Plate Tectonics Research 1/1 Million Qinghai Province Geotectonic Map Description [M]. Beijing: Geological Publishing House, 1-221 (in Chinese with English abstract).
Zhao Wenjin, Mechie J, Feng Mei, Shi Danian, Xue Guangqi, Shu Heping, Song Yang, Yang Hongwei, Liu Zhiwei. 2014. Orogeny in Qilian Mountains and the characteristic structure of the lithospheric mantle[J]. Geology in China, 41(5): 1411-1423(in Chinese with English abstract).
Zheng Ying, Chen Guangting, Zhang Xiaoyong, Song Taizhong, Liang Kunxian. 2017. Geochemical characteristics and chronological significance of Ordovician quartz diorite in Suli area, Middle Qilian [J]. Northwest Geology, 50(4): 588-597 (in Chinese with English abstract).
Zhong Mingjie. 1994. Discovery of Paleozoic in Laji Mountain, Qinghai Province[J]. Geological Review, 22(5): 347-347 (in Chinese with English abstract).
Zuo Guochao, Zhang Shuling, Cheng Jiansheng, Gong Yanxue, Wang Yanbin, Wu Hanquan. 1996. Division of ophiolite belt in Qilian area and its tectonic significance [C]//Proceedings of the Symposium on Ophiolite and Geodynamics, 129-134(in Chinese with English abstract).
陈宣华, 邵兆刚, 熊小松, 高锐, 刘雪军, 王财富, 李冰, 王增振, 张义平. 2019. 祁连造山带断裂构造体系、深部结构与构造演化[J]. 中国地质, 46(5): 995-1020. doi: 10.12029/gc20190504 冯益民, 曹宣铎, 张二朋, 胡云绪, 杨军禄, 潘晓萍, 贾群子, 李文明. 2002. 西秦岭造山带结构造山过程及动力学[M]. 西安: 西安地图出版社, 263. 冯益民, 何世平. 1996. 祁连山大地构造与造山作用[M]. 北京: 地质出版社, 1-135. 付长垒, 闰臻, 郭现轻, 牛漫兰. 2014. 拉脊山口蛇绿混杂岩中辉绿岩的地球化学特征及SHRIMP锆石U-Pb年龄[J]. 岩石学报, 30(6): 1695-1706. 侯青叶, 张宏飞, 张本仁, 赵志丹, 朱云海. 2005. 祁连造山带中部拉脊山古地慢特征及其归属: 来自基性火山岩的地球化学证据[J]. 地球科学, 30(1): 61-70. 李春昱, 刘仰文, 朱宝清, 冯益民, 吴汉泉. 1978. 秦岭及祁连山构造发展史[M]. 北京: 地质出版社, 174-187. 李建锋, 张志诚, 韩宝福. 2010. 中祁连西段肃北、石包城地区早古生代花岗岩年代学、地球化学特征及其地质义[J]. 岩石学报, 26(8): 2431-2444. 李怀坤, 耿建珍, 郝爽, 张永清, 李惠民. 2009. 用激光烧蚀多接收器等离子体质谱仪(LA-MC-ICPMS)测定锆石U-Pb同位素年龄的研究[J]. 矿物学报, 29(增刊): 600-601. 丘家骧, 曾广策, 王思源, 朱云海. 1997. 拉脊山早古生代海相火山岩与成矿[M]. 武汉: 中国地质大学出版社, 1-118. 王二七, 张旗, Burchfiel C B. 2000. 青海拉鸡山: 一个多阶段抬升的构造窗[J]. 地质科学, 35(4): 393-500. 王金荣, 张新虎, 张翔, 翟新伟, 张本旗, 赵磊. 2012. 中祁连西段野马南山构造岩石组合、成因及其构造意义[C]//全国岩石学与地球动力学研讨会论文摘要集, 466-468. 夏林圻, 夏祖春, 任有祥, 彭礼贵, 张诚, 杨静华, 王兴安, 李智佩, 韩松, 黄忠祥. 1991. 祁连、秦岭山系海相火山岩[M]. 武汉: 中国地质大学出版社, 1-304. 肖序常, 陈国铭, 朱志直. 1978. 祁连山古蛇绿岩带的地质构造意义[J]. 地质学报, 52(4): 281-295. 许志琴, 徐惠芬, 张建新, 李海兵, 朱志直, 曲景川, 陈代璋, 陈金禄, 杨开春. 1994. 北祁连走廊南山加里东俯冲杂岩增生地体及其动力学[J]. 地质学报, 68(1): 1-15. 闫臻, 王宗起, 李继亮, 许志琴, 邓晋福. 2012. 西秦岭楔的构造属性及其增生造山过程[J]. 岩石学报, 28(6): 1808-1828. 张建新, 许志琴, 陈文, 徐惠芬. 1995. 北祁连中段俯冲-增生杂岩/火山弧的时代探讨[J]. 岩石矿物杂志, 16(2): 112-119. 张雪亭, 杨生德. 2007. 青海省板块构造研究1/100万青海省大地构造图说明书[M]. 北京: 地质出版社, 1-221. 赵文津, Mechie J, 冯梅, 史大年, 薛光琪, 宿和平, 宋洋, 杨宏伟, 刘志伟. 2014. 祁连山造山作用与岩石圈地幔的特型结构构造[J]. 中国地质, 41(5): 1411-1423. http://geochina.cgs.gov.cn/cn/article/id/20140501 郑英, 陈光庭, 张小永, 宋泰忠, 梁坤先. 2017. 中祁连苏里地区奥陶纪石英闪长岩地球化学特征及年代学意义[J]. 西北地质, 50(4): 588-597. 钟明杰. 1994. 青海拉脊山下古生界的发现[J]. 地质论评, 22(5): 347-347. 左国朝, 张淑玲, 程建生, 巩彦学, 王彦斌, 吴汉泉. 1996. 祁连地区蛇绿岩带划分及其构造意义[C]//蛇绿岩与地球动力学研讨会论文集, 129-134.
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