西藏罗布莎豆荚状铬铁矿床深部找矿突破与成因模式讨论   总被引：2，自引：1，他引：1       下载免费PDF全文

章奇志  巴登珠  熊发挥  杨经绥 《中国地质》2017,44(2):224-241

中国铬铁矿资源的瓶颈状态已持续多年。最近,在西藏罗布莎蛇绿岩地幔橄榄岩的深部勘探发现200万t致密块状铬铁矿床,这是中国近50年来铬铁矿找矿的重大突破,对今后继续寻找同类型的铬铁矿床具有重要指导意义。蛇绿岩地幔橄榄岩中产出的豆荚状铬铁矿床是工业需求铬的重要来源。研究豆荚状铬铁矿的成矿作用和矿体围岩地幔橄榄岩地质特征,建立铬铁矿的成矿模型和找矿标志,是开展寻找同类型矿床的重要保证。随着近些年在豆荚状铬铁矿及围岩地幔橄榄岩中金刚石等深部矿物的不断发现和深入研究,人们对蛇绿岩型铬铁矿的物质来源和形成过程,有了新的认识,提出了铬铁矿的深部成因模式。研究认为深部成因铬铁矿床主要经历了4个阶段:(1)早期俯冲到地幔过渡带(410~660 km)的陆壳和洋壳物质被脱水和肢解,过渡带产生的热和流体促成了地幔的熔融和Cr的释放和汇聚;(2)铬铁矿浆在地幔柱驱动下,运移到过渡带顶部冷凝固结,并有强还原的流体进入,后者携带了深部形成的金刚石、斯石英等高压矿物,进入"塑性—半塑性地幔橄榄岩"中;(3)随着物质向上移动,深度降低,早期超高压相矿物发生相变,如斯石英转变成柯石英,高压相的铬铁矿中出溶成柯石英和单斜辉石;(4)在侵位过程和俯冲带环境下,含水熔体与方辉橄榄岩反应形成了不含超高压矿物的规模相对较小的浸染状铬铁矿及纯橄岩岩壳。进一步研究表明,同处雅鲁藏布江缝合带西段的几个大型地幔橄榄岩岩体与罗布莎岩体可以对比,经历了相同的构造背景和豆荚状铬铁矿的成矿作用,存在较大的找矿空间。  相似文献   

西藏永珠——果芒错蛇绿岩的地球化学特征及其构造意义   总被引：8，自引：1，他引：7  

叶培盛  吴珍汉  胡道功  江万  杨欣德 《现代地质》2005,19(4):508-514

永珠-果芒错蛇绿岩位于西藏永珠藏布-纳木错蛇绿岩带西段,主要由变质橄榄岩、辉长辉绿岩及玄武岩等组成。变质橄榄岩以富Mg,贫Ti、∑REE为特征。辉绿岩和玄武岩的主量元素、微量元素分析显示其含有洋脊拉斑玄武岩和岛弧拉斑玄武岩的双重成分特征,其中高场强元素（Nb、Ta、Zr、Hf等）亏损,大离子亲石元素（Rb、Sr、Ba等）相对富集,具有岛弧玄武岩的特点;在球粒陨石标准化稀土元素配分模式图上显示稀土元素特征为LREE亏损的平坦型,无负Eu异常,与洋中脊玄武岩的特征类似。通过与典型地区作对比和应用构造环境判别图解,推断永珠-果芒错蛇绿岩形成于弧后盆地的构造环境。  相似文献   

The genesis of the carbonatized and silicified ultramafics known as listvenites: a case study from the Mihalıççık region (Eskişehir), NW Turkey     

Mehmet Akbulut   zkan Pi&#x;ki&#x;n  Ali&#x; &#x;hsan Karayi&#x;i&#x;t 《Geological Journal》2006,41(5):557-580

The Mihalıççık region (Eskişehir) in NW Turkey includes an ophiolitic assemblage with a serpentinite‐matrix mélange. The serpentinites of this mélange host silica‐carbonate metasomatites which were previously named as listvenites. Our mineralogical and geochemical studies revealed that these alteration assemblages represent members of the listvenitic series, mainly the carbonate rocks, silica‐carbonate rocks and birbirites, rather than true listvenites (sensu stricto). Tectonic activity and lithology are principal factors that control the formation of these assemblages. Carbonatization and silicification of the serpentinite host‐rock is generated by CO₂, SiO₂‐rich H₂O hydrothermal fluid which includes As, Ba, Sb and Sr. Low precious metal (Au, Ag) contents of the alteration assemblages indicate lack of these metals in the fluid. Primary assemblages of the alteration are carbonate rocks that are followed by silica‐carbonate rocks and birbirites, respectively. Petrographic studies and chemical analyses suggested an alkaline and moderate to high temperature (350–400°C) fluid with low oxygen and sulphur fugacity for the carbonatization of the serpentinites. The low temperature phases observed in the subsequent silicification indicated that the fluid cooled during progressive alteration. The increasing Fe‐oxide content and sulphur phases also suggested increasing oxygen and sulphur fugacity during this secondary process and silica‐carbonate rock formation. The occurrence of birbirites is considered as a result of reactivation of tectonic features. These rocks are classified in two sub‐groups; the Group 1 birbirites show analogous rare earth element (REE) trends with the serpentinite host‐rock, and the Group 2 birbirites simulate the REE trends of the nearby tectonic granitoid slices. The unorthodox REE trend of Group 2 birbirites is interpreted to have resulted from a mobilization process triggered by the weathering solutions rather than being products of enrichment by the higher temperature hydrothermal activity. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

东帕米尔及邻区古生界基性火山岩地球化学特征与构造属性   总被引：1，自引：0，他引：1  

丁道桂  刘伟新  王道轩  孙世群 《新疆地质》2003,21(1):96-102

西昆仑山库地、乌依塔格地区的超铁镁质岩及基性火山岩的岩石化学、微量元素、稀土元素特征表明：在震旦－早古生代时期塔里木板块南部的被动陆缘上存在一个扩张规模有限的边缘海洋盆;而在喀喇昆仑山南带的明铁盖地区下二叠统的深海相的硅质岩、纹泥岩、滑塌堆积物及基性火山岩岩石化学、微量、稀元素特征表明,是属于塔里木板块南部活动大陆边缘上的弧后盆地,陆壳的增生是以软碰撞的方式实现的。  相似文献   

金沙江蛇绿岩带蛇纹岩中异剥钙榴岩的成因及意义   总被引：1，自引：1，他引：0  

魏君奇  陈开旭 《矿物岩石》2003,23(4):70-73

金沙江蛇绿岩带绒角蛇绿岩由超镁铁岩与异剥辉长岩岩脉组成,在蛇绿岩就位过程中,异剥辉长岩岩脉碎裂为不规则的岩块包裹于超镁铁岩中,形成超镁铁岩中的构造包体。经过交代蚀变作用,超镁铁岩形成蛇纹岩,异剥辉长岩形成异剥钙榴岩。异剥钙榴岩的形成是超镁铁岩蛇纹石化和异剥辉长岩中斜长石钙铝榴石化循环作用的结果,并与对蛇绿岩起过作用的构造运动有关系,是变形作用伴随交代作用的产物。绒角蛇绿岩中的异剥钙榴岩的发现,说明金沙江蛇绿岩带不存在榴辉岩,其变质相属葡萄石一绿泥石低温低压相．也说明金沙江蛇绿岩带是洋壳残片“冷侵入”的产物。  相似文献   

P-T paths from high temperature shear zones beneath ophiolites     

R. A. JAMIESON 《Journal of Metamorphic Geology》1986,4(1):3-22

Abstract Mctamorphic rocks of the St Anthony Complex of north-western Newfoundland are best interpreted in terms of a high-temperature shear zone formed between down-going continental margin rocks and overriding oceanic lithosphere in a subduction zone. High-grade rocks, immediately beneath the oceanic lithosphere peridotite, display retrograde meta-morphism in high-strain zones, whereas lower grade rocks, near the base of the metamorphic complex, display prograde metamorphism in high-strain zones. Mylonite zones in meta-basitcs at all levels in the complex contain the assemblage epidote-hornblende-albite-sodic oligoclase. These observations suggest that the 'inverted metamorphic gradient'within the St Anthony Complex results from the fortuitous preservation of residual metamorphic assemblages from different crustal levels within an epidote amphibolite facies shear zone. The degree of re-equilibration is strongly dependent on the degree of strain, and is best achieved in synmetamorphic mylonite zones. This interpretation of the St Anthony Complex can be extended to other sub-ophiolite metamorphic sheets, which show very similar relationships. It is proposed that most metamorphic sheets beneath ophiolites are high temperature shear zones, the P-T paths of which preserve records of burial and exhumation in subduction zones.  相似文献   

REE and PGE Geochemical Constraints on the Formation of Dunites in the Luobusa Ophiolite, Southern Tibet   总被引：19，自引：0，他引：19  

ZHOU  MEI-FU; ROBINSON  PAUL T.; MALPAS  JOHN; EDWARDS  STEPHEN J.; QI  LIANG 《Journal of Petrology》2005,46(3):615-639

The Luobusa ophiolite, Southern Tibet, lies in the Indus–YarlungZangbo suture zone that separates Eurasia to the north fromthe Indian continent to the south. The ophiolite contains awell-preserved mantle sequence consisting of harzburgite, clinopyroxene(cpx)-bearing harzburgite and dunite. The harzburgite containsabundant pods of chromitite, most of which have dunite envelopes,and the cpx-bearing harzburgites host numerous dunite dykes.Dunite also exists as a massive unit similar to those of themantle–crust transition zones in other ophiolites. Allof the dunites in the ophiolite have a similar mineralogy, comprisingmainly olivine with minor orthopyroxene and chromite and tracesof clinopyroxene. They also display similar chemical compositions,including U-shaped chondrite-normalized REE patterns. Mantle-normalizedPGE patterns show variable negative Pt anomalies. Detailed analysisof a chromite-bearing dunite dyke, which grades into the hostcpx-bearing harzburgite, indicates that LREE and Ir decrease,whereas HREE, Pd and Pt increase away from the dunite. Thesefeatures are consistent with formation of the dunite dykes byinteraction of MORB peridotites with boninitic melts from whichthe chromitites were formed. Because the transition-zone dunitesare mineralogically and chemically identical to those formedby such melt–rock reaction, we infer that they are ofsimilar origin. The Luobusa ultramafic rocks originally formedas MORB-source upper mantle, which was subsequently trappedas part of a mantle wedge above a subduction zone. Hydrous meltsgenerated under the influence of the subducted slab at depthmigrated upward and reacted with the cpx-bearing harzburgitesto form the dunite dykes. The modified melts ponded in smallpockets higher in the section, where they produced podiformchromitites with dunite envelopes. At the top of the mantlesection, pervasive reaction between melts and harzburgite producedthe transition-zone dunites. KEY WORDS: melt–rock interaction; REE; PGE; hydrous melt; mantle; ophiolite; Tibet  相似文献   

新疆木纳布拉克蛇绿岩地球化学特征及形成构造背景分析     

邓瑞林  马铁球  柏道远 《沉积与特提斯地质》2005,25(3):94-100

木纳布拉克蛇绿岩是新疆境内最大的蛇绿混杂岩带,由超镁铁质岩、镁铁质岩、浅色分异物和变玄武岩组成,形成时代为中元古代晚蓟县世,侵位时代为新元古代早青白口世,可能代表了阿尔金山地区中元古代的板块俯冲带.蛇绿岩可能形成于孤后或孤间有限洋盆小扩张脊;最后侵位到深海沉积物中,形成了造山带中的蛇绿岩.  相似文献   

蛇绿岩地幔岩中自由SiO2的发现及其地质意义   总被引：1，自引：0，他引：1  

方青松任玉峰  杨经绥白文吉 戎合颜秉刚  施倪承李国武 马喆生 《岩石矿物学杂志》2005,24(5):385-392

自由SiO_2系指石英及其同质多型物(polymorphs)柯石英、斯石英等。石英广泛分布于地壳中的各种岩石中,柯石英和斯石英只存在于超高压岩石和陨石坑中。由于石英和非饱和SiO_2的橄榄石不能共生,因此在地幔橄榄岩和超镁铁岩中不存在原生石英。最近笔者在西藏罗布莎蛇绿岩的地幔岩(方辉橄榄岩)的豆荚状铬铁矿中发现了自由SiO_2和柯石英相。根据高温高压相平衡实验资料,橄榄石、辉石这样的硅酸盐矿物在地幔深部的压力条件下可以分解成简单氧化物,如FeO(方铁矿)、MgO(方镁石)以及SiO_2(斯石英)等。由此推测,西藏蛇绿岩地幔岩中自由SiO_2可能是来自于下地幔的矿物,是地幔柱作用将其搬运到上地幔浅部。  相似文献   

西天山那拉提构造带及邻区几个构造问题的讨论     

杨志华  王宏君  邓亚婷  倪新源  何建喜  李兵  胡志军  宋俊峰  周晓飞  李红兵 《陕西地质》2005,23(2):31-43

西天山-伊宁地区以独特的结构特征和关键的大地构造部位，历来成为中外地质学家所关注、研究的重要地区，而那拉提构造带及邻区又在西天山-伊宁地区占有举足轻重的地位。由于客观条件的制约，那拉提构造带及西天山造山带在基础地质的许多方面存在不少问题，直接影响到对天山造山带和伊犁盆地的正确认识。笔者根据近十年来在那拉提带及邻区进行10个1：5万区调填图和收集到的其它资料，对该区几个重要层位的时代、大哈拉军山火山岩系的形成背景、蛇绿岩和蓝闪片岩的产出特征以及该区的结构、构造单元划分和发展演化的动力学机制进行了充分的讨论，其中的许多认识和看法将对该区的进一步研究产生积极的推动作用。  相似文献