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1.
下扬子地区若干上地幔橄榄岩的显微构造研究 总被引：4，自引：1，他引：3
本文对下扬子区内２个玄武岩产地（江苏六合瓜埠山、安徽当涂釜山）的幔源包体进行研究,结果表明本区上地幔尖晶石二辉橄榄岩具原生粒状结构、碎斑结构、板状镶嵌等粒结构及部分熔融结构四种类型。在光学岩组图上显示出从原生粒状结构→碎斑结构→板状镶嵌等粒结构,其橄榄石光性方位优选性逐渐增强。变形橄榄石滑移轴为［１００］,滑移面以｛０ｋ１｝为主,（０１０）次之。高温高压人工变形实验证实,这种滑移系形成于高温低应变速率条件下。橄榄石位错类型多样,（１００）、（００１）位错壁分布广泛,位错壁间距显示对数正态分布特征．估算的本区上地幔高温蠕交流动差异应力为（１０．９～１１．５ＭＰａ）。上地幔流变速率、流动应力、等效粘滞度与深度关系指示本区新生代大地构造性质为大陆拉张带或大陆裂谷带。 相似文献
2.
也谈铙钹寨超镁铁岩体的成因和构造类型的归属问题 总被引：3，自引：2，他引：3
铙钹寨岩体是一个遭受角闪岩相一麻粒岩相变质作用改造的超镁铁岩体。由于其变质程度的不均一性，一部分仍保留着原地幔橄榄岩的基本特征（如粗粒，具三联点结构和熔融残余结构的方辉橄榄岩和纯橄岩）。另一部分则表现明显的重结现象，原地幔橄榄岩类的基本特征已部分或全部消失，形成以出现不同数量的新生矿物组合为特征的变橄榄岩类（以细粒变纯橄岩和似斑状角闪方辉橄榄岩为代表）。恢复其原岩，该岩体由纯橄岩（极少）、方辉橄榄岩（为主）和二辉橄榄岩组成。但在纯橄岩一方辉橄榄岩组合与二辉橄榄岩组合两者之间在成分上显示一个明显的间断。前者以贫Al（Al2O3含量〈1％）、Ca（CaO含量〈1％）、Ti（TiO，含量〈0．05％）和富Mg（Mg^#=92—93）为特征。其主要矿物Ol和Opx均属富镁橄榄石（Fo92-93）和顽火辉石（En92～93）。后者则相对富Al（Al2O3含量由3.36％～3．75％）、Ca（CaO含量由2．07％-3．15％）、Ti（TiO2 0．1％～0．12％）和相对低镁（Mg^#=89—90）为特征。其主要造岩矿物Ol和Opx属相对低Mg的镁橄榄石（F090）和顽火辉石（En89～90）。副矿物尖晶石具有多期熔融的复杂成因，但其成分区及趋势显示蛇绿岩地幔橄榄岩所常见的双频分布（bimodal distribution）特征。综合研究表明该两套地幔岩原岩组合代表了不同亏损程度和不同构造环境下多期熔融的地幔残余。以方辉橄榄岩（和少量纯橄岩）为代表，并伴有豆荚状铬铁矿化及其特征的瘤状矿石的产出背景，标志其遭受较高的部分熔融程度，可能代表产于洋内俯冲带之上（Supra—Subduetion zone）亲弧环境的上地幔残余，带有SSZ型蛇绿岩的某些印记。二辉橄榄岩可能代表来自MOR环境下，弱亏损的上地幔残余岩片。故该岩体超镁铁岩不具有大陆地幔橄榄岩的成因性质。 相似文献
3.
浙江新昌石榴石二辉橄榄岩包体的流变特征及其地质意义 总被引：6，自引：1，他引：6
浙江新昌的石榴石二辉橄榄岩包体以残斑结构为主，并有向粒状变晶结构过渡的趋势。橄榄石组构以［０１０］呈点极密型式，而［１００］和［００１］呈大圆环带为特征。橄榄石的位错亚构造以反映高温位错蠕变的位错壁、亚晶粒构造和滑动位错环为主要特征。利用新的地质温压计计算的平衡温度和压力分别为１１５０℃～１２１０℃和２．１～２．４ＧＰａ。利用显微构造应力计计算流动应力为２２～３０ＭＰａ，利用橄榄岩高温流变律计算的应变速率和等效粘滞度分别为１０－１４～１０－１３ｓ－１和１０１９～１０２０Ｐａ·ｓ，上述数据均已达到软流圈的数值。结合其流变特征认为该区的石榴石二辉橄榄岩代表软流圈的物质，其来源深度为６８～７８ｋｍ。它反映在新生代时期本区存在有软流圈的底辟，它可能控制了该区新生代大地构造的特征及地质演化。 相似文献
4.
5.
甘肃金川二矿区镁铁-超镁铁岩体中橄榄石具有明显的矿物定向排列特征。通过对岩体中二辉橄榄岩、斜长二辉橄榄岩及含二辉石橄榄岩的造岩矿物橄榄石进行组构特征研究,发现均表现出"A"型组构特征,Nm[001]表现为在面理上的点极密,表明其滑移方向为[001]。结合Ng[100]、Np[010]组构特征,其滑移面应为(100)和(010),反映低温组构滑移系为(100)[001]或(010)[001],表明二矿区岩体橄榄石形成于地壳浅部低压、低应力状态下。由于二矿区岩体为金川矿床第二期含矿岩浆上侵产物,结合岩体所受的构造应力场的变化特征,可初步认定二矿区岩体中橄榄石定向排列的现象为成矿期构造的反映,且橄榄石光轴发生了自西向东的旋转,这也与李区域组构特征的研究相一致。 相似文献
6.
北祁连山加里东期板块俯冲带的南缘的橄榄岩体,是时代为495～522 Ma的玉石沟蛇绿岩套底部地幔岩残片,主要由尖晶石相的方辉橄榄岩和纯橄岩组成,流动构造(包括叶理和线理)发育。强烈的构造重结晶作用使方辉橄榄岩呈典型的残斑结构,而纯橄岩则以粒状变晶结构为特征。橄榄石普遍发育平行(100)面的扭折带,根据扭折带测得橄榄石以(010)[100]高温滑移系为主。组构特征表明方辉橄榄岩的橄榄石Ng[010]沿与叶理面垂直的压应力方向优选方向,而纯橄岩则经历了强烈的旋转剪切流变。利用氧化缀饰法揭示出橄榄石的位错构造十分发育,包括高密度自由位错、倾斜壁、扭转壁(位错网格)、亚晶粒构造、位错弓弯和位错环等,表明岩石经历了在高温、高压、低应变速率状态下以位错蠕变和攀移多化为机制的 相似文献
7.
造山带环境中的东疆型镁铁—超镁铁杂岩 总被引：8，自引：5，他引：8
新疆东部黄山－镜儿泉一带产有大－中型铜镍矿床的镁铁－超镁铁岩体是中石炭统弧后盆地引张环境下的热侵位产物，主要岩石类型有橄榄岩、辉橄岩、橄辉岩、二辉岩、辉长苏长岩、苏长辉长岩、辉长岩、橄长岩、辉长岩和闪长岩等；其超镁铁岩相对富铁．不具变质组构，并具橄榄石＋斜方辉石＋单斜辉石＋角闪石±斜长石矿物组合；岩石化学以富硅、贫碱、贫铝、贫钙为特征，并具拉斑玄武岩系演化趋势。这些岩体是造山带杂岩体的一种新类型，可称为东疆型。 相似文献
8.
金川是世界第三大在采岩浆铜镍硫化物矿床,其成因备受中外地质学家的关注。金川岩体被一系列北东-东向左行平移断层自西向东依次划分为Ⅲ、Ⅰ、Ⅱ、Ⅳ等4个岩体。金川岩体主要由硫化物纯橄岩、二辉橄榄岩、橄榄辉石岩组成,边缘断续分布少量斜长石二辉橄榄岩和辉石岩。金川最大的1号矿体产于Ⅱ号岩体的中心,呈现出由中间硫化物纯橄岩向两侧浸染状的二辉橄榄岩和橄榄辉石岩过渡的对称式岩相分布。电子探针分析结果显示,金川Ⅱ号岩体橄榄石Fo值在79.7%～83.9%之间变化,w（Ni）为959×10-6～2060×10-6,大多低于从硫不饱和玄武岩浆中结晶出的橄榄石Ni含量。模拟计算表明金川岩体母岩浆为高MgO玄武岩浆(w（MgO）=10%～13%,w（FeO）=11.5%～12.5%)。橄榄石Ni含量偏低的原因是橄榄石结晶的同时发生了硫化物熔离,橄榄石与硫化物的质量比值约为40﹕1。硫化物纯橄岩和二辉橄榄岩中橄榄石的Ni含量及其与Fo值的相关性都存在显著的区别,暗示它们可能是从Ni含量不同的母岩浆中结晶出来的。同时,硫化物纯橄岩中橄榄岩经历了与硫化物熔体的Fe-Ni交换... 相似文献
9.
中天山白石泉镁铁-超镁铁质岩体岩石学与矿物学研究 总被引：16，自引：0，他引：16
白石泉地区镁铁一超镁铁质岩体处于塔里木板块前缘活动带与中天山地块接合部位，是中天山地块华力西中期岩浆活动的产物。主要岩石类型有辉石橄榄岩（斜方辉石橄榄岩、斜长二辉橄榄岩）、橄榄辉石岩、橄长岩、辉长岩及角闪辉长岩等，主要造岩矿物为橄榄石、斜方辉石、单斜辉石、角闪石、斜长石及黑云母。橄榄石均为贵橄榄石，其Fo值（78-85）位于含铜镍硫化物矿橄榄石的Fo值范围之内；辉石主要有顽火辉石、古铜辉石、紫苏辉石、透辉石等；斜长石的环带构造较为发育；角闪石的FeO含量随着岩浆的演化逐渐增加。它们与造山带环境中的东疆型镁铁一超镁铁杂岩中的造岩矿物具有相同的特征。这些特征表明了白石泉地区的镁铁一超镁铁质岩体的原始岩浆为高镁的拉斑玄武质岩浆。 相似文献
10.
平南幔源包体中橄榄石的显微构造研究及其意义 总被引：1，自引：0，他引：1
平南玄武岩中的尖晶石二辉橄榄岩包体的平衡温度为930~980℃, 平衡深度为59~74km, 包体中橄榄石的扭折带滑移系多为(010) [100], 但也有(001) [100]的滑移系类型; 斜方辉石的滑移系为(100) [001], 它们均为高温低应变速率下的滑移系, 说明该区的上地幔主要是在高温低应变速率条件下经历了塑性变形作用.橄榄石位错组态多样, 有自由位错、位错壁、位错弓弯、缠结、{110}滑移带, 反映了上地幔的塑性变形特征.根据位错壁的大小估算, 上地幔差异流动应力为24.5~42.1MPa, 流动速率为2.93×10-17~8.36×10-16s-1, 有效粘度为1.72×1023~2.80×1024 Pa·s, 特征与中国东部新生代上地幔较为一致, 反映同处于拉张环境. 相似文献
11.
随着深部构造研究的不断深入,岩石流变作用日益受到人们重视,普遍认为塑性流变是地壳深部构造形成的主要机制。超基性岩的流变作用目前已成为研究上地幔流变、岩石圈板块动力学和热对流,甚至震源机制的重要内容。 本文拟通过对构成雅鲁藏布江蛇绿岩套底部的藏南超基性岩的研究,重点划分塑性流变的结构类型,探讨不同结构类型中橄榄石的组构特征及实际存在的滑动系,用不同方法计算超基性岩形成和侵位过程中的流动应力值,并认为由于橄榄石塑性流变而获得的晶格方位排列是造成地震波速度不连续性的主因,岩石的塑性流动有可能是深部能量释放和诱发 相似文献
12.
Caroline Bollinger Paul Raterron Olivier Castelnau Fabrice Detrez Sébastien Merkel 《Physics and Chemistry of Minerals》2016,43(6):409-417
We report results from axisymmetric deformation experiments carried out on forsterite aggregates in the deformation-DIA apparatus, at upper mantle pressures and temperatures (3.1–8.1 GPa, 1373–1673 K). We quantified the resulting lattice preferred orientations (LPO) and compare experimental observations with results from micromechanical modeling (viscoplastic second-order self-consistent model—SO). Up to 6 GPa (~185-km depth in the Earth), we observe a marked LPO consistent with a dominant slip in the (010) plane with one observation of a dominant [100] direction, suggesting that [100](010) slip system was strongly activated. At higher pressures (deeper depth), the LPO becomes less marked and more complex with no evidence of a dominant slip system, which we attribute to the activation of several concurrent slip systems. These results are consistent with the pressure-induced transition in the dominant slip system previously reported for olivine and forsterite. They are also consistent with the decrease in the seismic anisotropy amplitude observed in the Earth’s mantle at depth greater than ~200 km. 相似文献
13.
M. A. G. M. Manthilake N. Miyajima F. Heidelbach V. Soustelle D. J. Frost 《Contributions to Mineralogy and Petrology》2013,165(3):495-505
The effect of alumina and water solubility on the development of fabric in orthopyroxene in response to simple shear deformation has been investigated at a pressure of 1.5 GPa and a temperature of 1,100 °C using the D-DIA apparatus. The microstructure observations at these conditions indicate that dislocation glide is the dominant deformation mechanism. In MgSiO3 enstatite and hydrous aluminous enstatite, partial dislocations bounding the stacking faults in [001] glide parallel to the (100) (or) the (100) [001] slip system. Electron backscattered diffraction analysis of anhydrous aluminous enstatite, however, indicates operation of the (010) [001] slip system, and microstructure analysis indicates dislocation movement involving [001] on both (100) and {210} planes. The strong covalent bonding induced by the occupation of M1 and T2 sites by Al could have restricted the glide on (100), activating slip on {210}. The resulting seismic anisotropies (~2 %) in orthopyroxene are weaker compared to olivine (~9.5 %), and reduced anisotropy can be expected if orthopyroxene coexists with olivine. Weak anisotropy observed in stable cratonic regions can be explained by the relatively high abundance of orthopyroxene in these rocks. 相似文献
14.
We have used a first-principle approach based on the calculation of generalised stacking faults (GSF) to study the influence
of pressure on the mechanical properties of forsterite. Six cases corresponding to [100] glide over (010), (021) and (001),
and [001] glide over (100), (010) and (110) have been considered. The relaxed energy barriers associated with plastic shear
have been calculated by constraining the Si atoms to move perpendicular to the fault plane and allowing Mg and O atoms to
move in every direction. These conditions, which preserve dilations as a relaxation process, introduce Si–O tetrahedral tilting
as an additional relaxation mechanism. Relaxed GSF show little plastic anisotropy of [100] glide over different planes and
confirms that [001] glide is intrinsically easier than [100] glide. The GSF are affected by the application of a 10 GPa confining
pressure with a different response for each slip system that cannot be explained by sole elastic effect. In particular, [100](010)
is found to harden significantly under pressure compared to [001](010). Our results give the first theoretical framework to
understand the pressure-induced change of dominant slip systems observed by Couvy et al. (in Eur J Mineral 16(6):877–889,
2004) and P. Raterron et al. (in GRL, submitted). It appears necessary to account for the influence of pressure on the mechanical
properties of silicates in the context of the deep Earth. 相似文献
15.
Cordierite — (Mg,Fe)2Al4Si5O18 — occurs as porphyroclasts within metapelitic and metavolcanic rocks from the Kemiö-Orijärvi belt, SW Finland. After crystallisation the cordierites have been deformed at temperatures between 550–825° C and pressures of 3–5 kbar. Optical microscopy reveals the following deformation-induced microstructures: a bimodal size distribution between host, 0.3 to 4.0 mm, and recrystallised (new) grains, 0.1 to 0.5 mm; the intracrystalline defect-structures of host grains yield undulatory extinction, subgrains and some twinning. Recrystallised grains are optically strain free. Grain and subgrain boundaries are generally straight and parallel to crystallographic low-index planes. Orientation distribution diagrams for host and recrystallised grains yield similar fabric diagrams, i.e. [010] perpendicular to foliation -S-, [001] and [100] parallel to S and [001] parallel to lineation -L-. The fabric diagrams indicate that [001] (010) is the dominant slip system. Transmission electron microscopy reveals straight free dislocations, glide and climb loops, minor {130} and {110} microtwins, isolated nodal points and dislocation walls. Contrast analyses yield Burgers vector b = [001] being dominant and b = [100] subordinate. Climb loops consist of 〈c〉-dislocations that are dissociated in (001) planes, glide loops are defined by [100] [010] and [001] (100). The cordierite microstructures have been interpreted to be generated by dislocation creep. The dominant recrystallisation mechanism is thought to be subgrain rotation subsequently followed by minor grain or twin-band boundary migration. 相似文献
16.
17.
藏南变质橄榄岩的橄榄石组构可划分为三个主要类型:[100]、[010]和[001]组构。橄榄石[100]组构反映洋壳下部—上地幔上部的高温粘性流变和高温塑性流变,橄榄石[010]和[001]组构基本上是构造侵位阶段陆壳中低温塑性流变结果。变质橄榄岩中橄榄石组构转化具有明显的规律性,在岩体变形过程中,总的显示由高温的[100]组构逐渐转化为低温的[001]、[010]组构。高温塑性流变组构影响和制约低温塑性流变组构的发育,叠加变形有利于橄榄石[100]极密的加强和[100]组构向[010]、[001]组构的转化。 相似文献
18.
We have studied the plastic deformation of Mg2SiO4 wadsleyite polycrystals. Wadsleyite was synthesized from a forsterite powder in a multianvil apparatus. It was then recovered
and placed in a second multianvil assembly designed to induce plastic deformation by compression between two hard alumina
pistons. After the deformation experiment, the microstructures are characterized by transmission electron microscopy (TEM)
and large-angle convergent beam electron diffraction (LACBED). Deformation experiments have been carried out at 15–19 GPa
and at temperatures ranging from room temperature to 1800–2000 °C. Five different dislocation types have been identified by
LACBED: [100], 1/2〈111〉, [010], 〈101〉 and [001]. The [001] dislocations result from dislocation reactions and not from activation
of a slip system. The [010] dislocations are activated under high stresses at the beginning of the experiments and further
relax by decomposition into 1/2〈111〉 dislocations or by dissociation into four 1/4[010] partial dislocations. The following
slip systems have been identified: 1/2〈111〉{101}, [100](010), [100](001), [100]{011}, [100]{021}, [010](001), [010]{101} and
〈101〉(010).
Received: 15 July 2002 / Accepted: 14 February 2003
Acknowledgements High-pressure experiments were performed at the Bayerisches Geoinstitut under the EU IHP – Access to Research Infrastructures
Programme (Contract no. HPRI-1999-CT-00004 to D.C. Rubie). P.C. has benefited from a Congé thématique pour recherche from
the University of Lille, and would like to thank warmly all the people in Bayreuth who contributed to this work by daily assistance
and discussions: Nathalie Bolfan-Casanova, Daniel Frost, Jed L. Mosenfelder and Brent Poe. The quality of the preparation
of the TEM specimens by H. Schultze is greatly appreciated. 相似文献
19.
岩石磁化率椭球体的三个轴与应变椭球体的三个轴方向相平行,并具有一定的共构关系.变形岩石的磁组构参数P、T、F、L以及磁化率椭球体主张量方向等可以用来定量地表征岩石变形的性状及期次.本文通过实测和计算27个样品的磁组构参数,研究了博白-合浦断裂带的变形性状与期次,结果表明:博白-合浦断裂带大致经历了三期构造变形作用,不同时期具不同性质的构造变形.变形性状分别表现为韧性、韧-脆性及脆性变形,应变行为分别表现为平面、非平面和线性应变. 相似文献
20.
磁组构成分析是利用岩石磁化率各向异性研究构造变形特征及其应力作用方式和方向的方法,研究表明,中甲地区岩石各向异性度Ｐ值比较小,反映本区总体变形较弱,但变质石英砂岩相对变形较强。变质石英砂岩磁面理发育,磁线理较弱,显示压扁变形,变形主压应力方向是ＮＷ－ＳＥ向。火山（碎屑）岩具有明显的磁线理,反映流纹构造特征;最大磁化率轴方向屡示本区火山岩流体构造为ＮＷ－ＳＥ向。矿化蚀变岩和矿石的磁各向异性度Ｐ值明显 相似文献