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921.
新疆巴里坤县苏吉山花岗岩体在构造上位于博格达造山带东段,岩性为铁浅闪石碱长花岗岩。全岩具有较高的
SiO2、K2O+Na2O、NK/A和较低的A/CNK含量;轻稀土相对富集、铕弱亏损;不同程度的富集大离子亲石元素和高场强元
素,亏损Cs、Sr、P、Ti;HFSE元素组合(Zr+Nb+Ce+Y) 介于451×10-6~674×10-6,锆石饱和温度范围841~883℃;以上特
征都表现为典型的A型花岗岩特征,判别图解进一步显示其为A2型花岗岩。造岩矿物角闪石属钙质普通角闪石,铁浅闪石
亚类,主量成分Al2O3介于2.9%~4.5%,Si/(Si+Ti+A1)为0.88~0.93,显示出壳源角闪石的特征。LA-ICP-MS 锆石U-Pb 年
龄为301.5±2.4 Ma,表明其形成时代为晚石炭世格舍尔阶。苏吉山A型花岗岩壳源角闪石特征指示其不同于A1亚型与地幔
热柱、裂谷有关的伸展机制,裂谷中晚期侵位表明其不同于A2亚型所代表的后造山环境。结合邻区花岗岩侵位时空特征,
苏吉山A型花岗岩应标志着一种裂谷作用减弱的局限伸展环境,也表明博格达裂谷作用受控于古亚洲洋沿卡拉麦里蛇绿岩
带的斜向俯冲作用。 相似文献
922.
LIU XiaoHan JU YiTai WEI LiJie & LI GuangWei Institute of Tibetan Plateau Research Chinese Academy of Sciences Beijing China Mineral Resource Institute of China Metallurgical Geology Bureau Beijing 《中国科学:地球科学(英文版)》2010,(1)
The new field investigations along the Yarlung Zangbo ophiolites zone show that these series underwent low green-schist metamorphism and were then fractured and occurred as slabs in tectonic melanges,without regional tectonic polarity.No large shear zone in north-south direction has been identified between ophiolite bodies and flysch layers on both side and a conformable contact relationship can be observed locally between them.A great mass of tectonic mélange has been substantiated as submarine olistolith ... 相似文献
923.
924.
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
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
925.
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
926.
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 IndusYarlungZangbo 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 themantlecrust 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 meltrock 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: meltrock interaction; REE; PGE; hydrous melt; mantle; ophiolite; Tibet 相似文献
927.
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
928.
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
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
929.
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
930.
An Early Aged Ophiolite in the Western Kunlun Mts., NW Tibetan Plateau and Its Tectonic Implications
XIAO Xuchang WANG Jun SU Li JI Wenhua SONG Shuguang Institute of Geology Chinese Academy of Geological Sciences Beijing Geological Lab Center China University of Geosciences 《《地质学报》英文版》2005,79(6):778-786
1 Introduction The Kuda ophiolite occurred in the western Kunlun Mountains, which lies about the intersection of longitude 77°10′ E and latitude 36°45′ N (Figs. 1, 2). The upper portion of the ophiolite mainly consists of a thick layer of basaltic pillow lavas, which was well exposed along the high way from Xinjiang Uygur Autonomous Region to the western Tibetan Plateau, and the middle-lower part, the mafic-ultramafic cumulates and upper mantle rocks occur at the top of the mountain n… 相似文献