内蒙西乌旗白音布拉格蛇绿岩地球化学特征   总被引：9，自引：5，他引：4  

李英杰  王金芳  李红阳  董培培  贺秋利  张红晨  宋鹏 《岩石学报》2013,29(8):2719-2730

内蒙古西乌旗白音布拉格蛇绿岩带是新发现的内蒙古西乌旗迪彦庙蛇绿岩带的北带,主要由蛇纹石化方辉橄榄岩、层状-块状辉长岩、斜长岩、枕状玄武岩、角斑岩-石英角斑岩及硅质岩等构造单元组成.白音布拉格蛇绿岩中的熔岩按照地球化学特征可以分为三组:第1组属于玻安岩系,以富Si(SiO2=52.71％、61.22％)、Mg(MgO=6.81％和10.88％)和贫Ti(TiO2 =0.49％、0.51％)、HREE及HFSE为特征;第2组具有低Ti(TiO2 =0.62％～0.78％)、高Mg(MgO =5.20％ ～11.30％)的特征,LREE弱亏损、类似N-MORB的稀土配分模式,但相对N-MORB,又具有富集LILE,亏损Nb、Ta等高场强元素的特征,类似岛弧拉斑玄武岩(IAT);第3组表现为:岩石具有高Ti(TiO2=1.86％、1.91％)、高Mg(MgO=5.25％和5.46％)及高P(P2O5=0.23％、0.27％),LREE和HREE分异较为明显((La/Yb)N=2.32、2.53)等特征,类似OIB.根据玻安岩与IAT的存在,推测白音布拉格蛇绿岩产于岛弧和弧前环境.  相似文献   

雅鲁藏布江缝合带西段东波蛇绿岩OIB型玄武岩的厘定及其形成环境   总被引：9，自引：8，他引：1  

刘飞  杨经绥  陈松永  梁凤华  牛晓露  李兆丽  连东洋 《岩石学报》2013,29(6):1909-1932

雅鲁藏布江缝合带(YZSZ)西段分为两支,南带蛇绿岩的成因对整个缝合带的性质和构造背景的探讨起到十分关键作用,但由于地区偏远、交通不便,研究程度一直十分薄弱.本文报道了南带的东波蛇绿岩中洋岛型玄武岩及有关沉积岩的发现和成因探讨.东波蛇绿岩主要由地幔橄榄岩(方辉橄榄岩、含单辉方辉橄榄岩和透镜状纯橄岩)和上覆火山-沉积岩组成,未见堆晶岩和枕状熔岩等典型洋壳端元.火山-沉积岩盖层为一套稳定的海相层序,主要由硅质灰岩、红色硅质岩等沉积岩和玄武岩和玄武火山碎屑岩组成.OIB型玄武岩的特征表现为低SiO2和MgO,高TiO2、P2O5和(K2O+Na2O),富集Nb、Ta,亏损Th、K、Pb、Sr.微量元素和Sr、Nd、Pb同位素数据显示,该玄武质源区来自石榴石尖晶石二辉橄榄岩2％ ～ 5％的部分熔融.成分研究显示,硅质岩形成于大陆边缘环境,为洋岛或海山和大陆边缘物质在生物作用下形成的.以上证据表明,东波火山-沉积岩层序具有典型海山特征,与世界上典型的地幔柱型蛇绿岩可对比,属于地幔柱热点活动的产物.因此,可以认为,地幔柱热点在与冈瓦纳大陆北缘岩石圈地幔相互作用过程中,不但促使YZSZ西段南带(达巴-休古嘎布)特提斯洋盆打开,还可能与YZSZ蛇绿岩中普遍包含金刚石等异常地幔矿物群有直接的动力学关系.  相似文献   

北阿尔金地区米兰红柳沟蛇绿岩的岩石学特征和SHRIMP定年   总被引：11，自引：23，他引：11  

杨经绥  史仁灯  吴才来  苏德辰  陈松永  王希斌 《岩石学报》2008,24(7)

米兰红柳沟蛇绿岩是北阿尔金蛇绿岩带中发育和保留最好的蛇绿岩,主要由地幔橄榄岩、镁铁-超镁铁质堆晶杂岩、岩墙群和基性熔岩等组成.它们以规模不等的构造岩块产出,大者长十余km,宽近1km,组成一条近100km长的蛇绿混杂岩带.地幔橄榄岩以方辉橄榄岩为主,有少量纯橄岩,主要由橄榄石(Fo=91.2～92.7),斜方辉石(En=93-98)和少量单斜辉石(En=46)组成;副矿物尖晶石Cr#为43～69(平均55),Mg#为43～64(平均58),表现出深海橄榄岩(Abyssal peridotite)和俯冲带环境(SSZ)橄榄岩成分特点.深成堆晶岩主要由异剥橄榄岩-橄榄二辉石岩-(橄榄)辉石岩-辉长岩-斜长岩,该组合的堆晶岩通常被认为是SSZ构造背景的产物.席状岩墙群的岩石成分与熔岩一致,其TiO2(1%～1.5%)和低含量的K2O<0.3%和P2O5表明具有MORB型的岩石特征,并得到了不相容元素和LREE平坦型和亏损型的球粒陨石标准化模型等证据的支持.该地区另存在一套高Tj的洋岛型拉斑玄武岩.两类熔岩的存在,以及地幔橄榄岩和堆晶岩的不同特征,表明米兰红柳沟蛇绿岩组合可能来自不同构造背景.带中与洋壳俯冲有关的蓝片岩和榴辉岩组成的高压变质带的存在,以及与俯冲碰撞有关的不同类型花岗岩类的产出,表明米兰红柳沟蛇绿混杂岩带代表了一个复杂的板块缝合带.蛇绿岩中辉长岩的锆石SHRIMP年代为479±8Ma,这是获得的第一个北阿尔金蛇绿岩的锆石SHRIMP U-Pb同位素年龄,认为代表蛇绿岩的形成时代.因此,北阿尔金缝合带无论在年龄和特征等方面,均可以与阿尔金断裂带东部的北祁连缝合带对比,证实两个带曾经是一个带,被阿尔金断裂左旋错断了约400km.  相似文献   

西昆仑库地岩组及构造意义     

郭新成  郑玉壮  高军 《新疆地质》2013,(1):6-10

依莎克群由上、中、下3个断片构成,并非连续性沉积地层.区域上依莎克群上部碎屑岩段(晚泥盆—早石炭世)和下部基性火山岩段(震旦—寒武纪)地层年龄差别大,呈断层接触,依沙克群作为一个统一岩石地层单元已不合适.将依莎克群下部基性火山岩单独划分出来,命名为库地岩组.库地岩组火山岩属大洋拉斑玄武岩浆产物,成分特征接近洋中脊玄武岩,岩浆源于上地幔分熔,具蛇绿岩性质,时代为早青白口世至早寒武世.  相似文献   

科岗蛇绿岩地质特征及构造环境分析     

尹得功  高军  弓小平  韩琼 《新疆地质》2013,(3)

科岗蛇绿岩位于塔里木板块西南缘西昆仑中间地块与北侧西昆仑沟弧带分界线上。通过对科岗蛇绿岩带岩石组成、地质地球化学特征研究,肯定了新疆地质志对科岗蛇绿岩带“三位一体”蛇绿岩建造的认识,分别由下部变质橄榄岩相,中部堆晶岩相、浅色花岗岩相,上部块状辉长岩-辉绿岩相和火山岩及碎屑岩相组成。科岗蛇绿岩为造山带型,与洋中脊型蛇绿岩区别明显。其大地构造环境应为弧后盆地或破坏性大陆边缘小洋盆快速拉张环境产物。  相似文献   

Geochronology of the Dong Tso Ophiolite and the Tectonic Environment     

LI Jianfeng  XIA Bin  XIA Lianze  XU Lifeng  LIU Weiliang  CAI Zhourong  YANG Zhiqing 《《地质学报》英文版》2013,87(6):1603-1616

The wedge shaped Dong Tso ophiolitic block is distributed near the transition point from the western to the middle sub-belt of the Bangong-Nujiang suture zone.The ophiolite is characterized by well-developed cumulate rocks that are mainly composed of cumulate and massive gabbros.In the cumulate gabbros,the adcumulate amphiboles are distributed extensively around the plagioclase and residual pyroxene grains; hence,the rocks are named adcumulate amphibole-gabbro.In this study,the formation age of the ophiolite has been estimated to be 166 ± 4 million years （Ma） by the sensitive high-resolution ion microprobe （SHRIMP） Ⅱ U-Pb isotopic analysis of the zircons from the adcumulate amphibole-gabbro; the 40Ar/39Ar plateau age was estimated to be 148.19 ± 1.53 Ma,which should represent the emplacement time of the ophiolite,by isotopic dating of the pure amphibole mineral from the amphibole-schist.Two different suits of volcanic lavas have been recognized in this work.The purple colored pillow basalts have high TiO2 and P2O5 contents,and are rich in light rare earth elements （LREEs）,large-ion lithospheric elements （LILEs） and high-field-strength elements （HFSEs）,the characteristics that are the typical of the oceanic island basalt （OIB）.On the other hand,other massive basaltic andesites of celadon color are poor in MgO; rich in Fe2O3,LREEs,LILEs,and HFSEs; and especially characterized by negative Nb and Ta anomalies,the properties that establish the andesites as continental arc volcanic rocks.It is concluded that hotspots had developed in the old Dong Tso basin,the oceanic basin that had been developing from middle Jurassic （166 Ma） or even before and emplaced northward in late Jurassic （about 148 Ma）.  相似文献   

Cold subduction of the Neotethys: the metamorphic record from finely banded lawsonite and epidote blueschists and associated metabasalts of the Nagaland Ophiolite Complex,India     

A. Ao  S. K. Bhowmik 《Journal of Metamorphic Geology》2014,32(8):829-860

In this study, we have deduced the thermal history of the subducting Neotethys from its eastern margin, using a suite of partially hydrated metabasalts from a segment of the Nagaland Ophiolite Complex (NOC), India. Located along the eastern extension of the Indus‐Tsangpo suture zone (ITSZ), the N–S‐trending NOC lies between the Indian and Burmese plates. The metabasalts, encased within a serpentinitic mélange, preserve a tectonically disturbed metamorphic sequence, which from west to east is greenschist (GS), pumpellyite–diopside (PD) and blueschist (BS) facies. Metabasalts in all the three metamorphic facies record prograde metamorphic overprints directly on primary igneous textures and igneous augite. In the BS facies unit, the metabasalts interbedded with marble show centimetre‐ to metre‐scale interlayering of lawsonite blueschist (LBS) and epidote blueschist (EBS). Prograde HP/LT metamorphism stabilized lawsonite + omphacite (X_Jd = 0.50–0.56 to 0.26–0.37) + jadeite (X_Jd = 0.67–0.79) + augite + ferroglaucophane + high‐Si phengite (Si = 3.6–3.65 atoms per formula unit, a.p.f.u.) + chlorite + titanite + quartz in LBS and lawsonite + glaucophane/ferroglaucophane ± epidote ± omphacite (X_Jd = 0.34) + chlorite + phengite (Si = 3.5 a.p.f.u.) + titanite + quartz in EBS at the metamorphic peak. Retrograde alteration, which was pervasive in the EBS, produced a sequence of mineral assemblages from omphacite and lawsonite‐absent, epidote + glaucophane/ferroglaucophane + chlorite + phengite + titanite + quartz through albite + chlorite + glaucophane to lawsonite + albite + high‐Si phengite (Si = 3.6–3.7 a.p.f.u.) + glaucophane + epidote + quartz. In the PD facies metabasalts, the peak mineral assemblage, pumpellyite + chlorite + titanite + phengitic white mica (Si = 3.4–3.5 a.p.f.u.) + diopside appeared in the basaltic groundmass from reacting titaniferous augite and low‐Si phengite, with prehnite additionally producing pumpellyite in early vein domains. In the GS facies metabasalts, incomplete hydration of augite produced albite + epidote + actinolite + chlorite + titanite + phengite + augite mineral assemblage. Based on calculated T–M(H₂O), T–M(O₂) (where M represents oxide mol.%) and P–T pseudosections, peak P–T conditions of LBS are estimated at ~11.5 kbar and ~340 °C, EBS at ~10 kbar, 325 °C and PD facies at ~6 kbar, 335 °C. Reconstructed metamorphic reaction pathways integrated with the results of P–T pseudosection modelling define a near‐complete, hairpin, clockwise P–T loop for the BS and a prograde P–T path with a steep dP/dT for the PD facies rocks. Apparent low thermal gradient of 8 °C km^?1 corresponding to a maximum burial depth of 40 km and the hairpin P–T trajectory together suggest a cold and mature stage of an intra‐oceanic subduction zone setting for the Nagaland blueschists. The metamorphic constraints established above when combined with petrological findings from the ophiolitic massifs along the whole ITSZ suggest that intra‐oceanic subduction systems within the Neotethys between India and the Lhasa terrane/the Karakoram microcontinent were also active towards east between Indian and Burmese plates.  相似文献   

SHRIMP dating of the Permo-Carboniferous Jinshajiang ophiolite, southwestern China: Geochronological constraints for the evolution of Paleo-Tethys   总被引：9，自引：0，他引：9  

Ping Jian  Dunyi Liu  Xiaomeng Sun 《Journal of Asian Earth Sciences》2008,32(5-6):371

SHRIMP U–Pb zircon dating of gabbro, anorthosite, trondhjemite and granodiorite from the Jinshajiang ophiolitic mélange of southwestern China provides geochronological constraints on the evolution of Paleo-Tethys. The ophiolitic mélange is exposed for about 130 km along the Jinshajiang River where numerous blocks of serpentinite, ultramafic cumulate, gabbro, sheeted dikes, pillow lavas and radiolarian chert are set in a greenschist matrix. A cumulate gabbro-anorthosite association and an amphibole gabbro have ages of 338 ± 6 Ma, 329 ± 7 Ma and 320 ± 10 Ma, respectively, which constrain the time of formation of oceanic crust. An ophiolitic isotropic gabbro dated at 282–285 Ma has the same age as a trondhjemite vein (285 ± 6 Ma) cutting the gabbro. These ages probably reflect a late phase of sea-floor spreading above an intra-oceanic subduction zone. At the southern end of the Jinshajiang belt, a granitoid batholith (268 ± 6 Ma), a gabbro massif (264 ± 4 Ma), and a granodiorite (adakite) intrusion (263 ± 6 Ma) in the ophiolitic mélange constitute a Permian intra-oceanic plutonic arc complex. A trondhjemite dike intruded serpentinite in the mélange at 238 ± 10 Ma and postdates the arc evolution of the Jinshajiang segment of Paleo-Tethys.  相似文献   

The Grenvillian Songshugou ophiolite in the Qinling Mountains, Central China: Implications for the tectonic evolution of the Qinling orogenic belt   总被引：6，自引：0，他引：6  

Yun-Peng Dong  Mei-Fu Zhou  Guo-Wei Zhang  Ding-Wu Zhou  Liang Liu  Qi Zhang 《Journal of Asian Earth Sciences》2008,32(5-6):325

The Qinling Mountains in Central China mark a gigantic composite orogenic belt with a complex tectonic evolution involving multiple phases of rifting and convergence. This belt separates the North China and South China Blocks and consists of the South and North Qinling terranes separated by the Shangdan suture. The suture is marked by the Grenvillian Songshugou ophiolite along the southern margin of the North Qinling terrane, which is key to understanding the Proterozoic tectonic evolution of the belt. The ophiolite consists of highly metamorphosed ultramafic and mafic rocks. Three groups of meta-basalts are present: group 1 rocks are LREE depleted and have a MORB compositional affinity. Their low Ta/Yb ratios (<0.1) are consistent with high degrees of partial melting of a depleted asthenospheric mantle. Rocks of group 2 have higher TiO₂ (1.63–2.08 wt%) and Ta/Yb ratios (>0.12), and display slight enrichment of LREE, suggesting that the original magmas were derived from a depleted mantle source mixed with some enriched material. Samples from group 3 are enriched in LREE and other incompatible elements (Ti, Zr, Ta, Nb), suggesting derivation from an enriched mantle source, possibly a plume. All the basalts have high εNd(t) (+4.2 to +6.9), variable εSr(t) and high ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios for given ²⁰⁶Pb/²⁰⁴Pb ratios. These characteristics are compatible with formation at a mid-ocean ridge system above an anomalous Dupal mantle region. The mafic rocks have a Sm–Nd whole-rock isochron age of 1030 ± 46 Ma.The Songshugou ophiolite was emplaced onto the southern margin of the North Qinling terrane, an active continental margin from the Meso-Proterozoic to Neo-Proterozoic.  相似文献   

Geochemical and isotopic constraints on the age and origin of the Nidar Ophiolitic Complex, Ladakh, India: Implications for the Neo-Tethyan subduction along the Indus suture zone     

T. Ahmad  T. Tanaka  H.K. Sachan  Y. Asahara  R. Islam  P.P. Khanna 《Tectonophysics》2008,451(1-4):206-224

The Nidar ophiolite complex is exposed within the Indus suture zone in eastern Ladakh, India. The suture zone is considered to represent remnant Neo-Tethyan Ocean that closed via subduction as the Indian plate moved northward with respect to the Asian plate. The two plates ultimately collided during the Middle Eocene. The Nidar ophiolite complex comprises a sequence of ultra-mafic rocks at the base, gabbroic rocks in the middle and volcano-sedimentary assemblage on the top. Earlier studies considered the Nidar ophiolite complex to represent an oceanic floor sequence based on lithological assemblage. However, present study, based on new mineral and whole rock geochemical and isotopic data (on bulk rocks and mineral separates) indicate their generation and emplacement in an intra-oceanic subduction environment. The plutonic and volcanic rocks have nearly flat to slightly depleted rare earth element (REE) patterns. The gabbroic rocks, in particular, show strong positive Sr and Eu anomalies in their REE and spidergram patterns, probably indicating plagioclase accumulation. Depletion in high field strength elements (HFSE) in the spidergram patterns may be related to stabilization of phases retaining the HFSE in the subducting slab and / or fractional crystallization of titano-magnetite phases. The high radiogenic Nd- and low radiogenic Sr-isotopic ratios for these rocks exclude any influence of continental material in their genesis, implying an intra-oceanic environment.

Nine point mineral–whole rock Sm–Nd isochron corresponds to an age of 140 ± 32 Ma with an initial ¹⁴³Nd/¹⁴⁴Nd of 0.513835 ± 0.000053 (E_Nd t = + 7.4). This age is consistent with the precise Early Cretaceous age of Hauterivian (132 ± 2 to 127 ± 1.6 Ma) to Aptian (121 ± 1.4 to 112 ±1.1 Ma) for the overlying volcano-sedimentary (radiolarian bearing chert) sequences based on well-preserved radiolarian fossils (Kojima, S., Ahmad, T., Tanaka, T., Bagati, T.N., Mishra, M., Kumar, R. Islam, R., Khanna, P.P., 2001. Early Cretaceous radiolarians from the Indus suture zone, Ladakh, northern India. In: News of Osaka Micropaleontologists (NOM), Spec. Vol., 12, 257–270.) and cooling ages of 110–130 Ma based on ³⁹Ar/⁴⁰Ar for Nidar–Spontang ophiolitic rocks (Mahéo, G., Berttrand, H., Guillot, S., Villa, I. M., Keller, F., Capiez, P., 2004. The South Ladakh Ophiolites (NW Himalaya, India): an intra-oceanic tholeiitic arc origin with implications for the closure of the Neo-Tethys. Chem. Geol., 203, 273–303.). As these gabbroic and volcanic rocks are interpreted to be arc related, the new Sm–Nd age data may indicate that intra-ocean subduction in the Neo-Tethyan ocean may have started much before  140 ± 32 Ma as this date is interpreted as the age of crystallization of the arc magma. Present and published age data on the arc magmatic rocks from the Indus suture zone may collectively indicate episodic magmatism with increasing maturity of the arc from more basic (during ~ 140 ± 32 Ma) when the arc was immature through intermediate (andesitic/granodioritic) at ~ 100 Ma to more felsic (rhyolitic/dioritic) magmatism at ~ 50–45 Ma, when the Indian and the Asian plates collided.  相似文献