Evolution of lithospheric mantle in the north of Nain‐Baft oceanic crust (Neo‐Tethyan ophiolite of Ashin,Central Iran)     

Nargess Shirdashtzadeh  Ghodrat Torabi  Tomoaki Morishita 《Island Arc》2020,29(1)

This study is focused on a plagioclase‐bearing spinel lherzolite from Chah Loqeh area in the Neo‐Tethyan Ashin ophiolite. It is exposed along the west of left‐lateral strike‐slip Dorouneh Fault in the northwest of Central‐East Iranian Microcontinent. Mineral chemistry (Mg#^olivine < ~ 90, Cr#^{clinopyroxene} < ~ 0.2, Cr#^spinel < ~ 0.5, Al₂O₃^{orthopyroxene} > ~ 2.5 wt%, Al₂O₃^{clinopyroxene} > ~ 4.5 wt%, Al₂O₃^spinel > ~ 41.5 wt%, Na₂O^{clinopyroxene} > ~ 0.11 wt%, and TiO₂^{clinopyroxene} > ~ 0.04 wt%) confirms Ashin lherzolite was originally a mid‐oceanic ridge peridotite with low degrees of partial melting at spinel‐peridotite facies in a lithospheric mantle level. However, some Ashin lherzolites record mantle upwelling and tectonic exhumation at plagioclase‐peridotite facies during oceanic extension and diapiric motion of mantle along Nain‐Baft suture zone. This mantle upwelling is evidenced by some modifications in the modal composition (i.e. subsolidus recrystallization of plagioclase and olivine between pyroxene and spinel) and mineral chemistry (e.g. increase in TiO₂ and Na₂O of clinopyroxene, and TiO₂ and Cr# of spinel and decrease in Mg# of olivine), as a consequence of decompression during a progressive upwelling of mantle. Previous geochronological and geochemical data and increasing the depth of subsolidus plagioclase formation at plagioclase‐peridotite facies from Nain ophiolite (~ 16 km) to Ashin ophiolite (~ 35 km) suggest a south to north closure for the Nain‐Baft oceanic crust in the northwest of Central‐East Iranian Microcontinent.  相似文献   

中下部地壳拆离断层带演化中的褶皱作用:以辽南变质核杂岩为例     

郑媛媛  张若愚  甘浩男  李弘珂  蒋浩  张雎易  刘俊来 《地学前缘》2019,26(2):58-71

作为变质核杂岩构造的重要组成部分,拆离断层带内广泛发育的褶皱构造与其寄主岩石一样记录了中下地壳拆离作用过程。选取辽南变质核杂岩金州拆离断层带内褶皱构造作为研究对象,基于叶理与褶皱构造关系分析,划分了褶皱期次与阶段性;通过形态组构分析、结晶学组构分析及石英古温度计等技术方法的应用,初步分析了拆离断层内褶皱的形成机制,为辽南地区拆离作用过程提供约束。根据褶皱形成与拆离作用的时间关系,将拆离带内褶皱分为拆离前褶皱、拆离同期褶皱和拆离后褶皱;拆离作用同期的褶皱按时间早晚分为早期(a1)阶段、中期(a2)阶段、晚期(a3)阶段。不同阶段褶皱的野外形态、叶理与褶皱关系等方面的差异,以及形态组构与结晶学组构的特征,为判断和恢复褶皱的形成机制提供了佐证,揭示出拆离断层带褶皱是在纵弯压扁和顺层流变的共同作用下递进剪切变形的产物。在拆离作用过程中, a1阶段和a2阶段褶皱以纵弯、压扁褶皱作用为主,a3阶段褶皱以弯滑作用为主。褶皱作用记录了拆离断层一定温度范围内(主要集中在380~500 ℃)的变形特征,拆离作用从早期到晚期的演化整体处于相对稳定的应变状态下。对金州拆离断层带而言,在区域NW-SE向伸展过程中,还伴随着NE-SW向微弱的收缩。  相似文献   

植物抗冻蛋白的研究进展及其应用   总被引：6，自引：0，他引：6  

吴建民  幸华  赵志光  安黎哲 《冰川冻土》2004,26(4):482-487

抗冻蛋白(antifreeze proteins,AFPs)是一类具有热滞效应和冰晶重结晶抑制效应的蛋白质,它们在受到低温环境胁迫时产生,能够使机体抵御冰冻环境.AFPs已经在多种冰冻耐受机体中发现,包括鱼类、昆虫、陆生节肢动物、细菌、真菌和植物,其中有关植物AFPs的研究起步较晚.综述了植物AFPs的发现,理化性质,组织及细胞定位,生理功能,作用机理,结构模型,及其在农业,医学,食品工业等方面的应用价值.  相似文献   

Direct physical evidence of dolomite recrystallization     

Stephen E. Kaczmarek  Duncan F. Sibley 《Sedimentology》2014,61(6):1862-1882

The possibility of recrystallization is a long‐standing barrier to deciphering the genetic origin of dolomites. There is often uncertainty regarding whether or not characteristics of ancient dolomites are primary or the consequence of later recrystallization unrelated to the original dolomitization event. Results from 65 new high‐temperature dolomite synthesis experiments (1 m , 1·0 Mg/Ca ratio solutions at 218°C) demonstrate dolomite recrystallization affecting stoichiometry, cation ordering and nanometre‐scale surface texture. The data support a model of dolomitization that proceeds by a series of four unique phases of replacement and recrystallization, which occur by various dissolution–precipitation reactions. During the first phase (induction period), no dolomite forms despite favourable conditions. The second phase (replacement period) occurs when Ca‐rich dolomite products, with a low degree of cation ordering, rapidly replace calcite reactants. During the replacement period, dolomite stoichiometry and the degree of cation ordering remain constant, and all dolomite crystal surfaces are covered by nanometre‐scale growth mounds. The third phase (primary recrystallization period), which occurs in the experiments between 97% and 100% dolomite, is characterized by a reduced replacement rate but concurrent increases in dolomite stoichiometry and cation ordering. The end of the primary recrystallization period is marked by dolomite crystal growth surfaces that are covered by flat, laterally extensive layers. The fourth phase of the reaction (secondary recrystallization period) occurs when all calcite is consumed and is characterized by stoichiometric dolomite with layers as well as a continued increase in the degree of cation ordering with time. Inferences of recrystallization, in natural dolomite, based on cation order or stoichiometry of dolomite, usually depend on assumptions about the precursor dolomite subjected to recrystallization. If it is assumed that the experimental evidence presented here is applicable to natural, low‐temperature dolomites, then the presence of mounds is direct evidence of a lack of recrystallization and the presence of layers is direct evidence of recrystallization.  相似文献   

几种花青染料的合成及分离     

李雅丽  孟燕 《地球科学与环境学报》1999,(Z1)

研究了Ｎ甲基对二甲胺基苯乙烯吡啶碘盐系列化合物的合成、分离方法,通过可见吸收、ＭＳ谱、ＨＮＭＲ 谱及氮素测定分析产物,证实了其结构和理论预期的一致性  相似文献   

Recrystallization of Magnesian Calcite Overgrowths on Calcite SeedsSuspended in Seawater     

Jane S. Tribble  Fred T. Mackenzie 《Aquatic Geochemistry》1998,4(3-4):337-360

The formation and subsequent reactions of magnesiancalcite overgrowths on calcite were investigated bymeans of closed system seeded precipitationexperiments. These experiments demonstrated that(1) thin overgrowths of magnesian calcite are precipitatedon calcite seeds suspended in seawater;(2) the solubilities of the coatings increase outward from theseed crystals as a linear function of the log ofrelative coating thickness;(3) during the period ofthese experiments (up to 5.5 months), the magnesiancalcite coatings continued to increase in thickness,but became less soluble in composition. Thestabilization reaction, referred to asrecrystallization, can be described by the followingequation:Cax Mg(1-x) CO3 + [z + y(x + z)]Ca2++ 2yHCO3- ]= (1 + y)Ca(x + z)Mg(1 - x -z)CO3 + [z + y(x + z - 1)]Mg2++ y CO2 + yH20;]4) recrystallization rate is dependent on solutionsaturation state, with a reaction order of 3.2 forartificial seawater and 4.0 for natural seawater; and(5) by the cessation of the closed system experiments,overgrowth compositions approached that of the stablecalcite (a few mol % MgCO3).Armoring of suspended carbonate particles in thesurface oceans with magnesian calcite overgrowthswould provide an effective barrier to release of theoceanic supersaturation with respect to calcite. Thicknesses of such coatings would be limited by therecrystallization rate of the magnesian calcite. Estimates based on the recrystallization ratesdetermined in this work indicate coatings on the orderof 0.02 µm in thickness could form on particles asthey sink through the mixed layer. According to thesecalculations, the total amount of carbon precipitatedannually in magnesian calcite overgrowths iscomparable to the riverine flux of dissolved carbon tothe oceans. Field observations of severalinvestigators indicate the likely presence ofmagnesian calcite coatings on planktonic particles,and provide evidence for possible recrystallization ofbiogenic magnesian particles in the marineenvironment.  相似文献   

The migration of fluid-filled grain boundaries in recrystallizing synthetic bischofite: first results of in-situ high-pressure, high-temperature deformation experiments in transmitted light   总被引：1，自引：1，他引：1  

O. SCHENK  J. L. URAI 《Journal of Metamorphic Geology》2005,23(8):695-709

The effect of fluids on recrystallization behaviour is well known; however, the detailed microscale distribution of fluid in grain boundaries and the influence of fluid on grain boundary migration are still unresolved. In this study, in‐situ deformation experiments in transmitted light microscopy were undertaken, as this allows continuous and direct observation of the whole range of processes involved in fluid‐assisted grain boundary migration. A new see‐through deformation apparatus was developed to enable the control of fluid pressure. Bischofite containing small amounts of aqueous fluid was deformed at temperatures between 50 and 90 °C, over a range of fluid pressure from 0.5 to 1 MPa, and strain rates of 5 × 10^?6 to 1 × 10^?4 s^?1. The rates of grain boundary migration were measured at different temperatures and strain rates. Detailed observations during and after the deformation illustrate the evolution of migrating fluid‐filled grain boundaries and show that the incorporation of fluids from inclusions as well as their pinch‐off is dependent on the grain boundary velocity, the thickness of the grain boundary and the size and shape of the inclusions. Direct evidence is presented for the contraction of the grain boundary fluids into isolated inclusions after equilibrium conditions are attained.  相似文献   

Plastic Deformation and Recrystallization of Garnet: A Mechanism to Facilitate Diffusion Creep   总被引：5，自引：0，他引：5  

STOREY  C. D.; PRIOR  D. J. 《Journal of Petrology》2005,46(12):2593-2613

Elongate and deformed garnets from Glenelg, NW Scotland, occurwithin a thin shear zone transecting an eclogite body that hasundergone partial retrogression to amphibolite facies at circa700°C. Optical microscopy, back-scattered electron imaging,electron probe microanalysis and electron back-scatter diffractionreveal garnet sub-structures that are developed as a functionof strain. Subgrains with low-angle misorientation boundariesoccur at low strain and garnet orientations are dispersed, aroundrational crystallographic axes, across these boundaries. Towardshigh-strain areas, boundary misorientations increase and thereis a loss of crystallographic control on misorientations, whichtend towards random. In high-strain areas, a polygonal garnetmicrostructure is developed. The garnet orientations are randomlydispersed around the original single-crystal orientation. Somegarnet grains are elongate and Ca-rich garnet occurs on thefaces of elongate grains oriented normal to the foliation. Commonly,the garnet grains are admixed with matrix minerals, and, wherein contact with other phases, garnet is well faceted. We suggestthat individual garnet porphyroclasts record an evolution fromlow-strain conditions, where dislocation creep and recoveryaccommodated deformation, through increasing strain, where dynamicrecrystallization occurred by subgrain rotation, to higheststrains, where recrystallized grains were able to deform bydiffusion creep assisted grain boundary sliding with associatedrotations. KEY WORDS: diffusion creep; EBSD; garnet; plastic deformation; recrystallization  相似文献   

A scanning electron microscope study of the effects of dynamic recrystallization on lattice preferred orientation in olivine     

Kyung-Ho Lee  Zhenting Jiang  Shun-ichiro Karato   《Tectonophysics》2002,351(4)

Effects of dynamic recrystallization on lattice preferred orientation (LPO) in olivine were investigated through the combination of two SEM-based techniques, electron backscattered diffraction (EBSD) technique for crystallographic orientation measurement and backscattered electron imaging (BEI) for dislocation observation. Samples are experimentally deformed olivine aggregates in simple shear geometry. In the sample deformed at T=1473 K and high stresses (480 MPa), only incipient dynamic recrystallization is observed along grain-boundaries. Orientations of these small recrystallized grains are more random than that of relict grains, suggesting an important role of grain-boundary sliding at this stage of recrystallization. In the sample deformed at T=1573 K and low stress (160 MPa), dynamic recrystallization is nearly complete and the LPO is characterized by two [100] peaks. One peak is located at the orientation subparallel to the shear direction and is dominated by grains with high Schmid factor. The other occurs at high angles to the shear direction and is due to the contribution from grains with low Schmid factor. Grains with high Schmid factor tend to have higher dislocation densities than those with low Schmid factor. Based on these observations, we identify two mechanisms by which dynamic recrystallization affects LPO: (1) enhancement of grain-boundary sliding due to grain-size reduction, leading to the modification of LPO caused by the relaxation of constraint for deformation; (2) grain-boundary migration by which grains with lower dislocation densities grow at the expense of grains with higher dislocation densities. Based on the deformation mechanism maps and stress versus recrystallized grain-size relation, we suggest that the first mechanism always plays an important role whereas the second mechanism has an important effect only under limited conditions.  相似文献   

The eastern Tonale fault zone: a ‘natural laboratory’ for crystal plastic deformation of quartz over a temperature range from 250 to 700 °C     

Michael Stipp  Holger Stünitz  Rene Heilbronner  Stefan M. Schmid 《Journal of Structural Geology》2002,24(12)

Near the eastern end of the Tonale fault zone, a segment of the Periadriatic fault system in the Italian Alps, the Adamello intrusion produced a syn-kinematic contact aureole. A temperature gradient from 250 to 700 °C was determined across the Tonale fault zone using critical syn-kinematic mineral assemblages from the metasedimentary host rocks surrounding deformed quartz veins. Deformed quartz veins sampled along this temperature gradient display a transition from cataclasites to mylonites (frictional–viscous transition) at 280±30 °C. Within the mylonites, zones characterized by different dynamic recrystallization mechanisms were defined: Bulging recrystallization (BLG) was dominant between 280 and 400 °C, subgrain rotation recrystallization (SGR) in the 400–500 °C interval, and the transition to dominant grain boundary migration recrystallization (GBM) occurred at 500 °C. The microstructures associated with the three recrystallization mechanisms and the transitions between them can be correlated with experimentally derived dislocation creep regimes. Bulk texture X-ray goniometry and computer-automated analysis of preferred [c]-axis orientations of porphyroclasts and recrystallized grains are used to quantify textural differences that correspond to the observed microstructural changes. Within the BLG- and SGR zones, porphyroclasts show predominantly single [c]-axis maxima. At the transition from the SGR- to the GBM zone, the texture of recrystallized grains indicates a change from [c]-axis girdles, diagnostic of multiple slip systems, to a single maximum in Y. Within the GBM zone, above 630±30 °C, the textures also include submaxima, which are indicative of combined basal a- and prism [c] slip.  相似文献