东北大学学报:自然科学版  2018, Vol. 39 Issue (10): 1438-1441  
0

引用本文 [复制中英文]

门业凯, 耿蓉蓉, 尤欣慰, 何强文. 山西袁家村组变沉积岩地球化学特征及构造意义[J]. 东北大学学报:自然科学版, 2018, 39(10): 1438-1441.
[复制中文]
MEN Ye-kai, GENG Rong-rong, YOU Xin-wei, HE Qiang-wen. Geochemical Features and Tectonic Significances of Yuanjiacun Formation Metasedimentary Rocks in Shanxi Province[J]. Journal of Northeastern University Nature Science, 2018, 39(10): 1438-1441. DOI: 10.12068/j.issn.1005-3026.2018.10.014.
[复制英文]

基金项目

国家重点研发计划项目(2016YFC0801603);中央高校基本科研业务费专项资金资助项目(N172303015);东北大学秦皇岛分校校内科研基金资助项目(XNB201720)

作者简介

门业凯(1986-),男,山东高密人,东北大学秦皇岛分校讲师,博士。

文章历史

收稿日期:2017-06-04
山西袁家村组变沉积岩地球化学特征及构造意义
门业凯1, 耿蓉蓉2, 尤欣慰3, 何强文3    
1. 东北大学秦皇岛分校 资源与材料学院, 河北 秦皇岛 066004;
2. 辽宁省冶金地质勘查局 地质勘查研究院, 辽宁 鞍山 114038;
3. 东北大学 资源与土木工程学院, 辽宁 沈阳 110819
摘要:早元古宙袁家村组岩层是吕梁地区主要的含矿地层.对岩层样品进行元素地球化学组分测试, 结果表明:主量元素以SiO2为主, 次为Al2O3, TFeO和K2O, SiO2的含量与其他主要氧化物负相关; LILE和HFSE明显富集; 稀土元素配分曲线具明显右倾的特征, 轻重稀土分馏明显, 轻稀土富集强烈; Ce异常极弱, Eu异常变化范围较大.袁家村组地层属副变质岩, 原岩以沉积岩为主, 沉积过程中风化作用较弱.物源性质以高成熟度的上地壳长英质沉积物为主, 沉积过程可能混入了少量含古老沉积物成分和安山质岛弧火成岩组分的岩石, 沉积构造环境为被动大陆边缘.
关键词袁家村组    元素地球化学    原岩恢复    物源属性    构造环境    
Geochemical Features and Tectonic Significances of Yuanjiacun Formation Metasedimentary Rocks in Shanxi Province
MEN Ye-kai1, GENG Rong-rong2, YOU Xin-wei3, HE Qiang-wen3    
1. School of Resources & Materials, Northeastern University at Qinhuangdao, Qinhuangdao 066004, China;
2. Geology Exploration Research Institute, Metallurgical Geology Exploration Bureau of Liaoning Province, Anshan 114038, China;
3. School of Resources & Civil Engineering, Northeastern University, Shenyang 110819, China
Corresponding author: MEN Ye-kai, E-mail: menyekai@163.com
Abstract: Early proterozoic Yuanjiacun Formation is the main ore bearing stratum in Lyuliang district. The elemental geochemical compositions of the samples were tested. Results showed that the major element is mainly SiO2, then is Al2O3, TFeO and K2O in sequence. SiO2 exhibits negative correlation with the other major oxides, and LILE and HFSE are significantly rich. The rare earth element distribution curves take on obvious right-divergent characteristics, with strong fractionations of light and heavy rare earth and rich light rare earth. The Ce anomalies are extremely weak, and the range of Eu anomalies is relatively large. The Yuanjiacun Formation is parametamorphite, and the original rock is dominated by sedimentary rock with weak weathering during the deposition process. The provenance attributem is dominated by high-mature upper crustal felsic sediments mixed by small amount of rocks containing ancient sedimentary components and andesitic arc igneous rock components in the sedimentary process. The tectonic environment is passive continental margin.
Key words: Yuanjiacun Formation    element geochemistry    protolith restoration    provenance attributem    tectonic environment    

袁家村组沉积变质岩地层出露于山西省吕梁地区, 其内发育有袁家村铁矿、尖山铁矿等多个沉积变质型铁矿, 是国内重要的铁矿石产地.袁家村条带状铁建造(banded iron formation, BIF)形成于浅海相的海湾或泻湖环境中, 被认为可能是国内最接近Superior型的铁矿床[1-2].袁家村BIF的形成可能与全球大氧化事件关系密切[3].但前人的研究多集中在BIF的形成方面, 对袁家村组沉积变质岩的研究以地质特征为主, 在岩石地球化学方面的研究工作较少.

1 袁家村组变质沉积岩特征

袁家村组(图 1)底部为一层较稳定的石英岩, 顶部岩性逐渐变复杂, 沿走向发生较大相变.在簸箕山地区, 以BIF和绿片岩相地层为主, 夹有部分变石英岩和绢英片岩.在碾沟至孔家峪地区, BIF和绿片岩相地层变薄, 发育有较厚的绢英片岩和千枚岩.在孔家峪以南至尖山地区, 袁家村组地层以含碳质的石榴绢英片岩和变石英岩为主, 并发育大量的变斜长角闪岩、辉绿岩, BIF厚度增大.袁家村组含铁岩系按岩性组合由下而上, 自西向东包括3个相似的含铁岩段.

图 1 袁家村组地层分布图(据Hou等, 2014修改) Fig.1 Stratigraphic distribution map of Yuanjiacun Formation(modified from Hou et al, 2014) 1—第四系; 2—断层; 3—BIF; 4—吕梁群; 5—青杨沟组; 6—宁家湾组; 7—袁家村组; 8—裴家庄组; 9—近周峪组; 10—杜家沟组; 11—岚河群; 12—界河口群; 13—寒武-奥陶系; 14—铁矿山.
2 样品及分析结果

采集样品的岩性以碳质片岩、绢英片岩和变石英砂岩为主.主量元素采用X射线荧光融片法进行测定.微量和稀土元素含量采用电感耦合等离子体质谱法进行分析.

碳质片岩的主量元素以SiO2为主(均值69.8%),次为Al2O3(均值14.9%), TFeO(均值4.9%), K2O(均值3.0%), 其他氧化物的质量分数很低, 见表 1.LILE和HFSE明显富集, 见图 2.wr为岩样中微量元素的质量分数, wm为原始地幔中相应微量元素的质量分数.稀土元素经球粒陨石标准化具明显右倾的特征, 见图 3.ws为球粒陨石中相应微量元素的质量分数.wLREE/wHREE=4.8~12.3, 均值为9.8, (wLa/wYb)N=3.5~13.6, 均值为9.9, 轻重稀土分馏明显, 轻稀土富集强烈.Eu显示较小的负异常, δEu=0.6~0.9, 均值为0.8.Ce几乎无异常, δCe=1.0~1.1, 均值为1.0.

表 1 主量元素组成(质量分数) Table 1 Major element compositions
图 2 微量元素原始地幔标准化图(据Sun和McDonough, 1989) Fig.2 Diagram of primitive mantle-normalized trace elements(after Sun and McDonough, 1989)
图 3 球粒陨石标准化稀土元素配分图(据Sun和McDonough, 1989) Fig.3 Chondrite-normalized REE pattern(after Sun and McDonough, 1989)

绢英片岩主量元素以SiO2为主(均值73.6%),次为Al2O3(均值14.4%), TFeO(均值3.2%), K2O(均值4.1%).其他氧化物的质量分数很低.LILE和HFSE明显富集.稀土元素具明显右倾的特征.wLREE/wHREE =6.4~17.2, 均值为12.8, (wLa/wYb)N=5.6~36.7, 均值为19.6, 轻重稀土分馏明显, 轻稀土富集强烈.Eu显示较小的正异常, δEu=0.9~1.4, 均值为1.2.Ce几乎无异常, δCe=1.0~1.1, 均值为1.0.

变石英砂岩的主量元素以SiO2为主(91.2%), 次为Al2O3(4.3%).其他氧化物的质量分数很低.LILE和HFSE明显富集.稀土元素具明显右倾的特征.wLREE/wHREE =17.5, (wLa/wYb)N=21.4, 轻重稀土分馏明显, 轻稀土富集强烈.Eu显示负异常, δEu=0.7.Ce几乎无异常, δCe=1.0.

霍邱群吴集组含铁岩系位于华北板块南缘霍邱地区, 是一套岩性与袁家村组地层较为类似的火山-沉积岩系[4].其地球化学特征与袁家村组地层相比, 二者具有较为一致的元素地球化学特征,暗示其成因可能较为接近.

3 讨论 3.1 原岩恢复

主量元素、过渡族元素、高场强元素和稀土元素在变质作用过程中含量保持不变[5].因此, 这些元素经常被用来约束变质岩的原岩.在DF变质岩判别式中, 袁家村组变质岩的DF值为-3.30~-8.51, 均值为-4.69, 表明原岩应为沉积岩.

3.2 风化沉积特征

沉积再循环过程将导致Th, U元素的分馏[6-7].风化和再沉积循环作用的持续进行, 造成了沉积岩中的wTh/wU逐渐增大, 因此可根据wTh/wU特征反推风化和再沉积过程的发展程度.袁家村组沉积变质岩样品的wTh/wU=2.8~6.1, 平均值为4.3, 与上地壳平均值(3.8)相差不大, 可能代表了该岩层在沉积成岩过程中遭受了较弱的风化作用, 沉积演化过程相对简单, 见图 4.

图 4 wTh/wu-wTh图解(据McLennan et al, 1993) Fig.4 wTh/wu-wTh diagrams(modified after McLennan et al, 1993) `
3.3 物源特征分析

Cr, Zr, Th, Sc在沉积过程中的分异效应较小, wCr/wZrwTh/wSc能够指示源区镁铁质和长英质组分的相对量的大小.袁家村组沉积变质岩的样品总体显示较低的wCr/wZr(wCr/wZr=0.20~0.60, 平均值0.33), 较高的wTh/wSc(wTh/wSc=0.53~2.10, 平均值1.18), 暗示了源区的镁铁质组分较少, 沉积物主要来源于长英质源区.

稀土元素可对沉积物的性质提供重要的约束[8].wLa/wTh-wHf物源属性判别图解(图 5)表明了其源区属性可能以上地壳长英质沉积岩为主, 原岩沉积过程中有少量含古老沉积物和安山质岛弧岩浆岩化学组分的岩石加入.

图 5 wLa/wTh- wHf图解(据Floyd和Leveridge, 1987) Fig.5 wLa/wTh- wHfdiagrams(after Floyd and Leveridge, 1987)
3.4 大地构造环境分析

大洋中脊构造环境中形成的沉积岩δCe均值为0.3, 大洋盆地构造环境形成的沉积岩δCe均值为0.55, 大陆边缘构造环境中形成的沉积岩δCe=0.76~1.54[9].袁家村组地层δCe处于大陆边缘构造环境中形成的沉积岩δCe值范围内, 可能表明了袁家村组变质沉积岩形成的构造环境为大陆边缘.wTi/wZr-wLa/wSc构造环境判别图解(图 6)进一步表明了袁家村组地层可能沉积于被动大陆边缘构造环境.

图 6 构造环境判别图解(据Bhatia和Crook, 1986) Fig.6 Tectonic environment discrimination diagrams (after Bhatia and Crook, 1986)

华北板块的东部陆块与西部陆块在1.85 Ga最终碰撞形成了统一的华北克拉通[10].袁家村组变质岩地层发育在中央造山带西缘的中部.根据本文的研究成果, 结合前人测年和构造演化的研究, 东部和西部陆块在早元古宙碰撞过程中, 西缘为被动大陆边缘, 洋壳与陆壳保持相对稳定.稳定的陆缘构造环境为Fe, Si沉积及Fe的成矿创造了有利条件.

4 结论

1) 原岩恢复结果显示, 袁家村组地层属副变质岩, 原岩以沉积岩为主.

2) wTh/wU特征显示, 袁家村组地层沉积过程中风化作用较弱, 沉积演化过程较简单.

3) 沉积物源区物质以成熟度较高的上地壳长英质沉积物为主, 沉积过程可能混入了少量含古老沉积物成分和安山质岛弧火成岩组分的岩石.

4) 稀土元素特征和构造环境判别图解显示, 袁家村组地层可能形成于被动大陆边缘构造环境中.

参考文献
[1]
张连昌, 翟明国, 万渝生, 等. 华北克拉通前寒武纪BIF铁矿研究:进展与问题[J]. 岩石学报, 2012, 28(11): 3431–3445.
( Zhang Lian-chang, Zhai Ming-guo, Wan Yu-sheng, et al. Study of the Precambrian BIF-iron deposits in the North China Craton:progresses and questions[J]. Acta Petrologica Sinica, 2012, 28(11): 3431–3445. )
[2]
Hou K, Li Y, Gao J, et al. Geochemistry and Si-O-Fe isotope constraints on the origin of banded iron formations of the Yuanjiacun Formation, Lyuliang group, Shanxi, China[J]. Ore Geology Reviews, 2014, 57(3): 288–298.
[3]
Wang C, Konhauser K O, Zhang L. Depositional environment of the paleoproterozoic Yuanjiacun banded iron formation in Shanxi Province, China[J]. Economic Geology, 2015, 110(6): 1515–1536. DOI:10.2113/econgeo.110.6.1515
[4]
Liu L, Yang X. Temporal, environmental and tectonic significance of the Huoqiu BIF, southeastern North China Craton geochemical and geochronological constraints[J]. Precambrian Research, 2015, 261(6): 217–233.
[5]
Alirezaei S, Cameron E M. Mass balance during gabbro-amphibolite transition, Bamble Sector, Norway:implications for petrogenesis and tectonic setting of the gabbros[J]. Lithos, 2002, 60(1/2): 21–45.
[6]
Wronkeiwicz D J, Condie K C. Geochemistry and provenance of sediments from the Pongola Surpergroup, South Africa:evidence for a 3.0Ga old continental Craton[J]. Geochimica et Cosmochimica Acta, 1989, 53(7): 1537–1549. DOI:10.1016/0016-7037(89)90236-6
[7]
Mclennan S M, Taylor S R. Sedimentary rocks and crustal evolution:tectonic setting and secular trends[J]. Journal of Geology, 1991, 99(1): 1–21. DOI:10.1086/629470
[8]
Nancen W B, Taylor S R. Rare earth element patterns and crustal evolution Ⅰ:Australian post-archean sedimentary rocks[J]. Geochimica et Cosmochimica Acta, 1976, 40(12): 1539–1551. DOI:10.1016/0016-7037(76)90093-4
[9]
Murray R W, Buchholtz T B M R, Jones D L, et al. Rare earth elements as indicators of different marine depositional environments in chert and shale[J]. Geology, 1990, 18(3): 268–271. DOI:10.1130/0091-7613(1990)018<0268:REEAIO>2.3.CO;2
[10]
赵国春. 华北克拉通基底主要构造单元变质作用演化及其若干问题讨论[J]. 岩石学报, 2009, 25(8): 1772–1792.
( Zhao Guo-chun. Metamorphic evolution of major tectonic units in the basement of the North China Craton:key issues and discussion[J]. Acta Petrologica Sinica, 2009, 25(8): 1772–1792. )