Seafloor spreading, obduction and triple junction tectonics of the Mineoka Ophiolite, Central Japan     

Yujiro Ogawa  Akiko Takahashi 《Tectonophysics》2004,392(1-4):131

The Tertiary Mineoka ophiolite occurs in a fault zone at the intersection of the Honshu and Izu forearcs in central Japan and displays structural evidence for three major phases of deformation: normal and oblique-slip faults and hydrothermal veins formed during the seafloor spreading evolution of the ophiolite at a ridge-transform fault intersection. These structures may represent repeated changes in differential stress and pore-fluid pressures during their formation. The second series of deformation is characterized by oblique thrust faults with Riedel shears and no significant mineral veining, and is interpreted to have resulted from transpressional dextral faulting during the obduction of the ophiolite through oblique convergence and tectonic accretion. This deformation occurred at the NW corner of a TTT-type (trench–trench–trench) triple junction in the NW Pacific rim before the middle Miocene. The third series of deformation of the ophiolite is marked by contractional and oblique shear zones, Riedel shears, and thrust faults that crosscut and offset earlier structures, and that give the Mineoka fault zone its lenticular (phacoidal) fabric at all scales. This deformation phase was associated with the establishment and the southward migration of the TTT Boso triple junction and with the kinematics of oblique subduction and forearc sliver fault development. The composite Mineoka ophiolite hence displays rocks and structures that evolved during its complex geodynamic history involving seafloor spreading, tectonic accretion, and triple junction evolution in the NW Pacific Rim.  相似文献   

Hydrothermal alteration and tectonic evolution of an intermediate- to fast-spreading back-arc oceanic crust: Late Ordovician Solund-Stavfjord ophiolite, western Norway     

Hege  Fonneland-Jorgensen  Harald  Furnes  Karlis  Muehlenbachs  Yildirim  Dilek 《Island Arc》2005,14(4):517-541

Abstract The Solund‐Stavfjord ophiolite complex (SSOC) in western Norway represents a remnant of the Late Ordovician oceanic lithosphere, which developed in an intermediate‐ to fast‐spreading Caledonian back‐arc basin. The internal architecture and magmatic features of its crustal component suggest that the SSOC has a complex, multistage sea floor spreading history in a supra‐subduction zone environment. The youngest crustal section associated with the propagating rift tectonics consists of a relatively complete ophiolite pseudostratigraphy, including basaltic volcanic rocks, a transition zone between the sheeted dyke complex and the extrusive sequence, sheeted dykes, and high‐level isotropic gabbros. Large‐scale variations in major and trace element distributions indicate significant remobilization far beyond that which would result from magmatic processes, as a result of the hydrothermal alteration of crustal rocks. Whereas K₂O is strongly enriched in volcanic rocks of the extrusive sequence, Cu and Zn show the largest enrichment in the dyke complex near the dyke–volcanic transition zone or within this transition zone. The δ¹⁸O values of the whole‐rock samples show a general depletion structurally downwards in the ophiolite, with the largest and smallest variations observed in volcanic rocks and the transition zone, respectively. δ¹⁸O values of epidote–quartz mineral pairs indicate 260–290°C for volcanic rocks, 420°C for the transition zone, 280–345°C for the sheeted dyke complex and 290–475°C for the gabbros. The ⁸⁷Sr/⁸⁶Sr isotope ratios show the widest range and highest values in the extrusive rocks (0.70316–0.70495), and generally the lowest values and the narrowest range in the sheeted dyke complex (0.70338–0.70377). The minimum water/rock ratios calculated show the largest variations in volcanic rocks and gabbros (approximately 0–14), and generally the lowest values and range in the sheeted dyke complex (approximately 1–3). The δD values of epidote (?1 to ?12‰), together with the δ¹⁸O calculated for Ordovician seawater, are similar to those of present‐day seawater. Volcanic rocks experienced both cold and warm water circulation, resulting in the observed K₂O‐enrichment and the largest scatter in the δ¹⁸O values. As a result of metal leaching in the hot reaction zone above a magma chamber, Zn is strongly depleted in the gabbros but enriched in the sheeted dyke complex because of precipitation from upwelling of discharged hydrothermal fluids. The present study demonstrates that the near intact effect of ocean floor hydrothermal activity is preserved in the upper part of the SSOC crust, despite the influence of regional lower greenschist facies metamorphism.  相似文献   

Geology, Geochemistry and Tectonic Significance of Mafic-ultramafic Rocks of Mesoproterozoic Phulad Ophiolite Suite of South Delhi Fold Belt, NW Indian Shield     

M. Shamim Khan  T.E. Smith  M. Raza  J. Huang 《Gondwana Research》2005,8(4):553-566

A thick sequence of mafic-ultramafic rocks, occurs along a major shear zone (Phulad lineament), running across the length of Aravalli Mountain Range for about 300 kms. It has been suggested, that this sequence may represent a fragment of ophiolite or a rift related metavolcanic suite made up of basalts and fractionated ultramafics. The geological and tectonic significance of the complex is assessed using field relationships, petrography and geochemistry. Structurally, the lowest part of the complex comprises a discontinuous band of plastically deformed harzburgite (mantle component) followed by layered cumulus gabbroic rocks (crustal component). A complex of non-cumulus rocks comprising hornblende schists, gabbros, sheeted dykes and pillowed basalts structurally overlies layered gabbros. Huge bodies of diorite intrude volcanics.

Geochemical classification suggests that all non-cumulus mafic rocks are sub-alkaline basalts except one variety of dykes which shows mildly alkaline character. The sub-alkaline rocks are tholeiite to calc-alkaline with boninite affinity. Tectono-magmatic variation diagrams and MORB normalised patterns suggest a fore arc tectonic regime for the eruption of these rocks.

The mafic rocks of Phulad Ophiolite Suite are zoned across the strike in terms of their distribution from west to east. The hornblende schists and basalts are exposed at the westernmost margin followed by gabbros and dykes. The alkaline dyke occurs at the easternmost part. The rocks of Phulad suite are juxtaposed with shallow water sediments in the east followed by platformal sediments and then continental slope sediments in the further east indicating gradual thickening of the crust from west to east and an eastward subduction. The geochemical interpretation presented in this study, together with discussion of lithological association is used to decipher the tectonic evolution of the Mesoproterozoics of NW Indian shield.  相似文献   

Permo-Carboniferous Radiolarians from the Wupata＇erkan Group, Western South Tianshan, Xinjiang, China   总被引：1，自引：0，他引：1  

LIYuejun SUNLongde WUHaoruo ZHANGGuangya WANGGuolin HUANGZhibin 《《地质学报》英文版》2005,79(1):16-23

The Wupata‘erkan Group, also called Wupata‘erkan Formation, distributed in the South Tianshan, Xinjiang,China, mainly consists of gray and dark gray fine-grained clastic rocks, interlayered with volcanic rocks, carbonates and cherts. Some ultra-basic rocks (blocks) punctuate the formation. The formation was variously assigned to Silurian-Middle Devonian, Silurian-Lower Devonian, and pre-Devonian, mainly based on Atrypa bodini Mansuy, Hypothyridina parallelepipedia (Brour.) and Prismatophyllum hexagonum Yoh collected from the limestone interlayers, respectively.However, radiolarian fossils obtained from 24 chert specimens of the Wupata‘erkan Group, mainly include Albaillella sp.cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon, Albaillella sp. cf. A. indensis Won, Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto, Albaillella sp. and Latentifistulidae gen. et. sp.indet., are earliest Carboniferous and Late Permian. The earliest Carboniferous assemblage is characterized by Albaillella sp. cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon and Albaillella sp. cf. A. indensis Won, and the Late Permian assemblage by Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto. This new stratigraphic evidence indicates that the Wupata‘erkan Group is possibly composed of rocks with different ages from Silurian to Permian, and therefore, it is probably an ophiolite mrlange. The discovery of Late Permian Albaillella sp. cf. A. excelsa provides more reliable evidence supporting the existence of a Permian relic ancient oceanic basin in the western part of Xinjiang South Tianshan.  相似文献   

Platinum-group element distribution in chromite ores from ophiolite complexes: implications for their exploration     

Maria Economou-Eliopoulos 《Ore Geology Reviews》1996,11(6):363-381

Compilation of some new data on ophiolites for Greece and Yugoslavia, and published data from previous studies, indicate that platinum-group element (PGE) and gold concentrations in chromite ores are generally low, ranging from less than 100 ppb to a few hundred ppb. However, samples from several ophiolite complexes exhibit an enrichment (of a few ppm) (a) only in Os, Ir and Ru,(b) only in Pt and/or Pd or (c) in all PGE. This enrichment (up to 10s ppm) is mainly related with chromitites hosted in supra-Moho dunites and dunites of the uppermost stratigraphic levels of the mantle sequence and it seems to be local, independent of the chromitite major element composition and the chromite potential of the ophiolite complexes. The contents of PGE combined with less chalcophile elements (Ni, Co, Cu), the ratios of incompatible/compatible elements, and PGE-patterns provide evidence for discrimination between chromitites derived from primitive magmas and those derived from partially fractionated magmas, although they have a similar major element composition. Thus, they can be used for a stratigraphic orientation in the mantle sequence, and therefore for exploration targets. Moreover, PGE data offer valuable information for the evaluation of the chromite potential in ophiolite complexes. The most promising ophiolites seem to be those which apart from the petrological and geochemical characteristics indicating extensive degree of partial melting in the mantle source contain only one chromite ore type (the other type being only in small proportion) of limited compositional variation, in both major elements and PGE, low ratios of , while PGE-enriched chromitites in the mantle sequence are only occasionally present. In contrast, ophiolites which contain both high-Cr and -Al chromitites, and where their chalcophile element data implies relatively extensive fractionation trend are not good exploration targets for chromite ores, although they are related with a SSZ environment.  相似文献   

对雅鲁藏布江结合带形成演化的再探讨     

张鑫全  张振利  王金贵  王硕  杨鑫朋  专少鹏  侯德华  张泽国  张立国  程洲 《中国地质》2020,47(4):944-970

通过1∶5万区域地质调查和收集相关资料的综合研究,本文对雅鲁藏布江结合带的形成演化作了进一步的探讨。雅鲁藏布江特提斯洋具有弧后扩张洋盆的性质,在早三叠世至中三叠世中期洋盆初步形成,中三叠世晚期至晚三叠世洋盆全面形成,从早侏罗世至晚白垩世洋盆逐步萎缩,到古新世至始新世关闭。南带的蛇绿岩主要为洋中脊扩张型(MORB型),形成于中三叠世晚期至晚三叠世。北带的蛇绿岩主要为与洋内俯冲相关的俯冲带上盘型(SSZ型),形成于早中侏罗世。带内侏罗纪至白垩纪其他岩浆岩主要为前弧玄武岩类(FAB型)。显示雅鲁藏布江特提斯洋从早侏罗世开始发生了洋内俯冲,并同步向北向冈底斯带之下主动俯冲消减和向南向喜马拉雅地块之下被动俯冲消减,持续发展到晚白垩世,在古新世至始新世俯冲碰撞消亡转化为结合带。  相似文献   

Integration of ASTER and landsat TM remote sensing data for chromite prospecting and lithological mapping in Neyriz ophiolite zone,south Iran          下载免费PDF全文

Alireza Eslami  Majid Ghaderi  Sankaran Rajendran  Amin Beiranvand Pour  Mazlan Hashim 《Resource Geology》2015,65(4):375-388

Chromite deposits in Iran are located in the ophiolite complexes, which have mostly podiform types and irregular in their settings. Exploration for podiform chromite deposits associated with ophiolite complexes has been a challenge for the prospectors due to tectonic disturbance and their distribution patterns. Most of Iranian ophiolitic zones are located in mountainous and inaccessible regions. Remote sensing approach could be applicable tool for choromite prospecting in Iranian ophiolitic zones with intensely rugged topography, where systematic sampling and conventional geological mapping are limited. In this study, Landsat Thematic Mapper (TM) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data were used for chromite prospecting and lithological mapping in the Neyriz ophiolitic zone in the south of Iran. Image transformation techniques, namely decorrelation stretch, band ratio and principal component analysis (PCA) were applied to Landsat TM and ASTER data sets for lithological mapping at regional scale. The RGB decorrelated image of Landsat TM spectral bands 7, 5, and 4, and the principal components PC1, PC2 and PC3 image of ASTER SWIR spectral bands efficiently showed the occurrence of major lithological units in the study area at regional scale. The band ratios of 5/3, 5/1, 7/5 applied on ASTER VNIR‐SWIR bands were very useful for discriminating most of rock units in the study area and delineation of the transition zone and mantle harzburgite in the Neyriz ophiolitic complex. Spectral Angle Mapper (SAM) technique was implemented to ASTER VNIR‐SWIR spectral bands for detecting minerals of rock units and especially delineation of the transition zone and mantle harzburgite as potential zones with high chromite mineralization in the Neyriz ophiolitic complex. The integration of information extracted from the image processing algorithms used in this study mapped most of lithological units of the Neyriz ophiolitic complex and identified potential areas of high chromite mineralization (transition zone and mantle harzburgite) for chromite prospecting targets in the future. Furthermore, image processing results were verified by comprehensive fieldwork and laboratory analysis in the study area. Accordingly, result of this investigation indicate that the integration of information extracted from the image processing algorithms using Landsat TM and ASTER data sets could be broadly applicable tool for chromite prospecting and lithological mapping in mountainous and inaccessible regions such Iranian ophiolitic zones.  相似文献   

西准噶尔蛇绿岩:古大洋俯冲增生过程的记录     

杨高学  朱钊  刘晓宇  李海  佟丽莉 《地质学报》2023,97(6):2054-2066

蛇绿岩记录了大洋岩石圈形成、演化、消亡的全过程,是刻画区域板块构造和洋 陆格局演化的关键证据。本文通过系统梳理前人相关研究,总结西准噶尔蛇绿岩最新研究成果,探讨大陆地壳增生方式、恢复古大洋演化历史,从而对西准噶尔构造体制转化提供新制约。西准噶尔地区发育多条震旦纪—石炭纪被构造肢解的蛇绿岩带,具有典型的岩块 基质结构,绝大多数蛇绿岩包括正常洋壳组分和海山/大洋高原残片,其中基性岩具有MORB和OIB的地球化学特征。基于前人研究,本文认为在西准噶尔古大洋发育过程中,发育不同时代与地幔柱有关的海山/大洋高原,同时存在增生型和侵蚀型两类汇聚板块边界。另外,大洋高原增生不仅是大陆地壳增生的有效途径之一,还可能诱发俯冲极性反转和传递。而在大洋高原形成初期,还可能存在地幔柱诱发俯冲起始机制。  相似文献   

Discovery and significance of the Misimiao ophiolite in Xi U jimqin Banner,Inner MongoliaSCIEI北大核心CSCD     

李英杰  王金芳  董培培  李红阳  张夏炜  王帅 《岩石学报》2023,(5):1305-1321

内蒙古西乌旗新发现的米斯庙蛇绿岩,位于中亚造山带东段迪彦庙SSZ型蛇绿岩带的西延米斯庙一带。大比例尺填图结果显示,米斯庙蛇绿岩呈NEE向展布,宽约5km,长约20km,蛇绿岩各单元出露较齐全,岩性主要为蛇纹石化方辉橄榄岩、暗色均质辉长岩、浅色均质辉长岩、斜长岩、枕状前弧玄武岩(fore-arc basalt,FAB)、枕状过渡熔岩和泥质硅质岩,局部见斜长花岗岩侵入于玄武岩之中,其岩性组合和岩石序列可与代表洋内初始俯冲的迪彦庙前弧蛇绿岩相对比。该米斯庙蛇绿岩岩石序列中辉长岩锆石U-Pb年龄为336.5±3Ma,与东部迪彦庙蛇绿岩的辉长岩同期。米斯庙FAB主要发育无斑结构和少斑结构,基质为球颗结构,枕状构造;枕状过渡熔岩,发育斑状结构,比FAB具有更多的斜长石斑晶。米斯庙FAB地球化学成分与大洋中脊形成的强亏损玄武岩相似,但与N-MORB相比,高场强元素(HFSE)Nb和Ta等含量略低于N-MORB,与弧拉斑玄武岩相似;与米斯庙FAB相比,米斯庙枕状过渡熔岩的地球化学特征是更加亏损Ti、HREE和HFSE,指示大洋板片的渐进性俯冲,类似于IBM前弧的演化。米斯庙蛇绿岩与迪彦庙前弧蛇绿岩均发育类似于马里亚纳前弧的FAB序列,两者延伸长度可达40km,表明在古亚洲洋东段早石炭世沿迪彦庙-米斯庙一带发育洋内初始俯冲,记录了早石炭世古亚洲洋东部洋内初始俯冲事件。  相似文献   

Mantle property of Hegenshan ophiolite in Inner Mongolia: Constrains from element geochemistry and Re-Os isotopes of harzburgiteSCIEI北大核心CSCD     

王智慧  杨振宁  王志伟  韩雪 《岩石学报》2023,(5):1322-1338

贺根山蛇绿岩带是中亚造山带东部出露面积最大的晚古生代蛇绿岩带,然而研究者对它是大洋岩石圈的残余还是陆内岩石圈地幔伸展的产物仍存在较大争议,主要归因于一直缺少橄榄岩Re-Os同位素的有效制约。基于此,本文对贺根山蛇绿岩中方辉橄榄岩进行了系统的岩石学、地球化学和Re-Os同位素研究。方辉橄榄岩主要由橄榄石、斜方辉石、粗粒的铬尖晶石和少量单斜辉石组成。贺根山方辉橄榄岩具有难熔地球化学特征,显示出高的MgO(45.1%~48.1%)含量,低的CaO(0.09%~0.26%)和Al 2O 3(0.58%~0.90%)含量及Tb/Yb比值,低于原始上地幔的^(187)Os/^(188)Os(0.1236~0.1263)同位素组成;橄榄石具有较高的Fo值(91.0~91.7)和NiO含量(0.26%~0.48%),而且单斜辉石具有低的重稀土含量,暗示了贺根山方辉橄榄岩是尖晶石相陆下岩石圈地幔高程度(20%~30%)部分熔融的难熔残余。另外,方辉橄榄岩相对富集LREE和大离子亲石元素,亏损高场强元素(例如Nb、Ta),且单斜辉石具有高Ti/Eu值和低的La/Yb,揭示了地幔源区受到硅酸盐熔体交代作用的改造。另一方面,方辉橄榄岩显示出相对年轻的Re亏损模式年龄,t RD为454~825Ma,表明贺根山地区岩石圈地幔形成的时代应该在0.8Ga之前,而后经历过多期熔体抽离和交代,与区域上大规模地壳增生时代吻合,可能是罗迪尼亚超大陆裂解的响应。结合蛇绿岩中大量深源矿物(金刚石等)和捕获锆石的存在、南北两侧一致的地质记录,本文认为贺根山方辉橄榄岩可能是陆内伸展环境下深部地幔物质上涌减压熔融的产物。  相似文献