共查询到20条相似文献，搜索用时 109 毫秒
1.
Manfred A. Lange Philippe Lambert Thomas J. Ahrens 《Geochimica et cosmochimica acta》1985,49(8):1715-1726
New infrared absorption spectra, thermo-gravimetric analyses and optical-and scanning electron microscopy of shock-recovered specimens of antigorite serpentine (Mg3Si2O5(OH)4) from the pressure range between 25 to 59 GPa are reported. The infrared spectra show systematic changes in absorption peaks related to structural and molecular surface absorbed water. H2O absorption peaks increase at the expense of OH peaks with increasing shock pressure. Changes in SiO bond vibrational modes with increasing shock pressure parallel those seen for other, non-hydrous minerals. Thermogravimetric analyses of shock-recovered samples determine the amount of shock-induced water loss. For samples shocked in vented assemblies, the data define a relation between shock-induced water loss versus shock pressure. Results for samples shocked in sealed assemblies demonstrate a dependence of water loss on shock pressure and target confinement. For the vented assembly samples, a linear relation between shock pressure and both the length of dehydration interval and the effective activation energy for releasing post-shock structural water in antigorite is found. Optical and scanning electron miscroscopy of shocked antigorite reveal a number of textures thought to be unique to shock loading of volatile-bearing minerals. Gas bubbles, which probably are the result of shock-released H2O appear to be injected into zones of partial melting. This process may produce the vesicular dark veins which are distributed throughout heavily shocked samples. The present observations suggest several criteria which may constrain possible shock histories of the hydrous matrix phases of carbonaceous condrites. A model is proposed for explaining hydrous alteration processes occurring on carbonaceous chondrite parent bodies in the course of their accretion. We speculate that shock loading of hydrous minerals would release and redistribute free water in the regoliths of carbonaceous chondrite parent bodies giving rise to the observed hydrous alterations. 相似文献
2.
3.
Dehydration temperatures of serpentine were measured in the pressure range between 1.0GPa and 5.0GPa by using the electrical conductivity metod simultaneously at high temperatures and high pressures.The results show that with increasing pressure th dehydration temperature of antigorite increases slightly below 2.0GPa ,but drops markedly above2.0GPa .This strongly suggests that high pressure would favor the dehydration of serpentine minerals and the water released thereby would be an important source of fluids involved in magmatism in a subduction zone and mantle metasomatism,Meanwhile,the greatly enhanced electric conductivity in the presence of water may be one of the reasons underlying the occurrence of a high-conductivity zone in the lower crust. 相似文献
4.
Youjun Zhang Toshimori Sekine Yin Yu Hongliang He Chuanmin Meng Fusheng Liu Mingjian Zhang 《Physics and Chemistry of Minerals》2014,41(5):313-322
Antigorite is one kind of hydrous serpentine that is present in meteorites and in the Earth mantle. In order to understand its dynamic behaviors, metastability and decomposition, shock experiments on antigorite have been conducted using a two-stage gas gun, and wave profiles of particle velocities have been measured to obtain the Hugoniot up to ~130 GPa and sound velocity at high pressures. The results show three regions of low-pressure phase below ~43 GPa and its metastable extension above a pressure of ~43 GPa for short durations of shock and high-pressure phase(s) above a pressure of ~43 GPa for long durations of shock. The dynamic behaviors of antigorite depend on not only the pressure but also the compression duration. Metastable extension state indicates that antigorite may survive beyond the stability depending on the shock conditions. Shock temperatures for antigorite are calculated along the Hugoniot. The pressure–density, sound velocity–pressure and shock temperature–pressure plots demonstrate that the decomposition reaction of antigorite into high-pressure phase(s) is accompanied by a volume expansion, sound velocity increase and temperature decrease, relative to the metastable extension phase above ~43 GPa. The decomposition should be sluggish and needs enough reaction time to complete and to overcome the activation energy. As a result of the high metastability of antigorite and possible decomposition assemblages, the hydrous serpentine (antigorite) may play a crucial role for the origin of water during the Earth accretion. 相似文献
5.
广西陆川蛇纹石玉的岩相结构及成矿机理 总被引：3，自引：2，他引：1
应用外束质子激发X射线荧光光谱法、X射线衍射、激光拉曼光谱、扫描电子显微镜等无损分析技术,对广西陆川蛇纹石玉的成分、物相和结构进行分析。X射线衍射结果显示样品的衍射峰主要位于0.724、0.456、0.362、0.248、0.153和0.150 nm处,表明陆川蛇纹石玉主要矿物成分是蛇纹石,同时伴生方解石矿物与蛇纹石形成穿插交织结构。成矿机理分析表明,陆川蛇纹石玉是由白云质大理岩热液交代作用形成的,和广东的信宜玉均属于富镁碳酸盐型蛇纹石。拉曼光谱显示叶蛇纹石的特征峰位于229、376、457、686和1046 cm-1处,纤蛇纹石的特征峰位于228、345、386、624、690和1102 cm-1处,通过激光拉曼光谱可以快速区分陆川蛇纹石玉中纤蛇纹石和叶蛇纹石两种不同结构的蛇纹石亚种。 相似文献
6.
Annette K. Kleppe Andrew P. Jephcoat Joseph R. Smyth 《Physics and Chemistry of Minerals》2006,32(10):700-709
Raman spectra of monoclinic Fo90 hydrous wadsleyite with 2.4 wt% H2O have been measured in a diamond-anvil cell with helium as a pressure-transmitting medium to 58.4 GPa at room temperature. The most intense, characteristic wadsleyite modes, the Si–O–Si symmetric stretch at 721 cm−1 and the symmetric stretch of the SiO3 unit at 918 cm−1, shift continuously to 58.4 GPa showing no evidence of a first order change in the crystal structure despite compression well beyond the stability field of wadsleyite in terms of pressure. The pressure dependence of these two modes is nearly identical for Fo90 hydrous and Fo100 anhydrous wadsleyite. A striking feature in the high-pressure Raman spectra of Fo90 hydrous wadsleyite is the appearance of new Raman modes above 9 GPa in the mid-frequency range (300–650 cm−1 at 1-bar and shifted to 500–850 cm−1 at 58.4 GPa) accompanied by a significant growth in their intensities under further compression. In the OH stretching frequency range Fo90 hydrous wadsleyite exhibits a larger number of modes than the Mg end-member phase. The higher number of modes may be due to either additional protonation sites or simply that we observe a different subset of all possible OH modes for each sample. The high-pressure behaviour of the OH stretching modes of Fo90 and Fo100 hydrous wadsleyite is consistent: OH stretching modes with frequencies <3,530 cm−1 decrease with increasing pressure whereas the higher-frequency OH modes show a close to constant pressure dependence to at least 13.2 GPa. The approximately constant pressure dependence of the OH modes above 3,530 cm−1 is consistent with protons being located at the O1···O edges around M3. 相似文献
7.
Serpentines are hydrous phyllosilicates which form by hydration of Mg–Fe minerals. The reasons for the occurrence of the structural varieties lizardite and chrysotile, with respect to the variety antigorite, stable at high pressure, are not yet fully elucidated, and their relative stability fields are not quantitatively defined. In order to increase the database of thermodynamic properties of serpentines, the P–V Equations of State (EoS) of lizardite and chrysotile were determined at ambient temperature up to 10 GPa, by in situ synchrotron X-ray diffraction in a diamond-anvil cell. Neither amorphization nor hysteresis was observed during compression and decompression, and no phase transition was resolved in lizardite. In chrysotile, a reversible change in compression mechanism, possibly due to an unresolved phase transition, occurs above 5 GPa. Both varieties exhibit strong anisotropic compression, with the c axis three times more compressible than the others. Fits to ambient temperature Birch–Murnaghan EoS gave for lizardite V 0=180.92(3) Å3, K 0 = 71.0(19) GPa and K′ 0=3.2(6), and for chrysotile up to 5 GPa, V 0 = 730.57(31) Å3 and K 0 = 62.8(24) GPa (K′ 0 fixed to 4). Compared to the structural variety antigorite is stable at high pressure (HP) (Hilairet et al. 2006), the c axis is more compressible in these varieties, whereas the a and b axes are less compressible. These differences are attributed to the less anisotropic distribution of stiff covalent bonds in the corrugated structure of antigorite. The three varieties have almost identical bulk compressibility curves. Thus the compressibility has negligible influence on the relative stability fields of the serpentine varieties. They are dominated by first-order thermodynamic properties, which stabilizes antigorite at high temperature with respect to lizardite, and by out-of-equilibrium phenomena for metastable chrysotile (Evans 2004). 相似文献
8.
The Zermatt‐Saas serpentinite complex is an integral member of the Penninic ophiolites of the Central Alps and represents the mantle part of the oceanic lithosphere of the Tethys. Metamorphic textures of the serpentinite preserve the complex mineralogical evolution from primary abyssal peridotite through ocean‐floor hydration, subduction‐related high‐pressure overprint, meso‐Alpine greenschist facies metamorphism, and late‐stage hydrothermal alteration. The early ocean floor hydration of the spinel harzburgites is still visible in relic pseudomorphic bastite and locally preserved mesh textures. The primary serpentine minerals were completely replaced by antigorite. The stable assemblage in subduction‐related mylonitic serpentinites is antigorite–olivine–magnetite ± diopside. The mid‐Tertiary greenschist facies overprint is characterized by minor antigorite recrystallization. Textural and mineral composition data of this study prove that the hydrated mineral assemblages remained stable during high‐pressure metamorphism of up to 2.5 GPa and 650 °C. The Zermatt‐Saas serpentinites thus provide a well documented example for the lack of dehydration of a mantle fragment during subduction to 75 km depth. 相似文献
9.
Economic important minerals and ore deposits are common in hydrothermal altered serpentinized zone. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite sensor is capable of discrimination of such hydrothermal mineralized zone and detection of hydrothermal altered minerals. In the present study, the hydrothermal altered serpentinized harzburgites of Wadi Hibi area of Northern Oman Mountains have been discriminated by using ASTER VNIR–SWIR spectral bands by image processing methods and the occurrences of Ni-magnesioferrite–magnetite–awaruite in the rocks are studied. The color composite RGB image developed using ASTER spectral bands 8, 4 and 1, mapped well the occurrence of weathered peridotites by pale green to dark blue in colors and discriminated the hydrothermally altered serpentinized rocks by pale brown to dark blue colors due to the strong absorption of OH and Mg–OH molecules that occurred in the serpentine minerals of the rocks in the study area. The ASTER band ratios 4/7, 4/1, and 2/3 × 4/3 RGB images studied are capable of discrimination of hydrothermal mineralized areas more clear by pale blue to purple colors due to the strong absorption of such hydroxyl bearing serpentine minerals. The studied image processing methods are evaluated by applying to the region of Wadi Sarami situated in the Semail ophiolite (Oman). In addition to that, the occurrence of serpentine minerals namely, lizardite and antigorite in the hydrothermally altered serpentinized region are detected qualitatively and quantitatively using Spectral Angle Mapper (SAM) supervised classification image processing method and studied.The interpreted images are verified in the field and checked for the occurrences of minerals including Ni-magnesioferrite, magnetite, pentlandite and awaruite and are confirmed through laboratory studies. Petrographic study of serpentinized harzburgites shows that the rocks consist predominantly of antigorite and lizardite serpentines, olivine and have the opaque minerals assemblage of Ni-magnesioferrite + magnetite + awaruite + pentlandite developed during serpentinization of the rock. The occurrences of such minerals are confirmed by XRD, electron microprobe analyses and spectral measurements in the laboratory.ASTER sensor proved its capability in discriminating the hydrothermal altered serpentinized zone and detecting the mineral occurrences and thus the study recommends the technique to the exploration geologists, scientists and mining geologists for mapping of such rocks and minerals in the similar arid region. 相似文献
10.
High pressure and temperature reactions of a mixture of forsterite and hydrogen molecules have been carried out using a laser
heated diamond anvil cell at 9.8–13.2 GPa and ~1,000 K. In situ X-ray diffraction measurements showed no sign of decomposition
or phase transitions of the forsterite under these experimental conditions, indicating that the olivine structure was maintained
throughout all runs. However, a substantial expansion of the unit cell volume of the forsterite was observed for samples down
to ~3 GPa upon quenching to ambient pressure at room temperature. The Raman spectroscopy measurements under pressure showed
significant shifts of the Raman peaks of the Si–O vibration modes for forsterite and of the intramolecular vibration mode
for H2 molecules toward a lower frequency after heating. Additionally, no OH vibration modes were observed by Raman and FT-IR spectroscopic
measurements. These lines of evidence show that the observed volume expansion in forsterite is not explained by the incorporation
of hydrogen atoms as hydroxyl, but suggest the presence of hydrogen as molecules in the forsterite structure under these high
pressure and temperature conditions. 相似文献
11.
Maria Rosa Scicchitano Michael J. Spicuzza Eric T. Ellison David Tuschel Alexis S. Templeton John W. Valley 《Geostandards and Geoanalytical Research》2021,45(1):161-187
The ability to constrain the petrogenesis of multiple serpentine generations recorded at the microscale is crucial for estimating the extent and conditions of modern versus fossil serpentinisation in ophiolites. To address matrix bias effects during oxygen isotope analysis by SIMS, we present the first investigation analysing antigorite in the compositional range Mg# = 77.5–99.5 mole %, using a CAMECA IMS‐1280 secondary ion mass spectrometer. Spot‐to‐spot homogeneity is ≤ 0.5‰ (2s) for the new antigorite reference materials. The relative bias between antigorite reference materials with different Mg/Fe ratios is described by a second‐order polynomial, and a maximum difference in bias of ~ 1.8‰ was measured for Mg# ~ 78 to 100. We observed a bias up to ~ 1.0‰ between lizardite and antigorite attributed to their different crystal structures. Orientation effects up to ~ 1‰ were observed in chrysotile. The new analytical protocol allowed the identification of oxygen isotope zoning up to ~ 7‰ in serpentine minerals from two serpentinites recovered from an area of active serpentinisation in the Samail ophiolite. Thus, in situ analysis is capable of resolving isotopic heterogeneity that may directly reflect changes in the physical and chemical conditions of multiple serpentinisation events in the Samail ophiolite. 相似文献
12.
Raman spectra of diopside were collected from atmospheric pressure to 71 GPa. The pressure dependences of 22 modes were determined.
Changes occurred in the spectra at three different pressures. First, at approximately 10 GPa, the two Raman modes at 356 and
875 cm−1 disappeared, while the mode at 324 cm−1 split into two modes, diverging at this pressure with significantly different pressure shifts; second, at approximately 15
GPa, a small (1 to 2 cm−1) drop in several of the frequencies was observed accompanied by changes in the pressure dependency of some of the modes;
and third, above 55 GPa, the modes characteristic of chains of tetrahedrally coordinated silicon disappeared, while those
for octahedrally coordinated silicon appeared. The first change at 10 GPa appears to be a C2/c to C2/c transition involving a change in the Ca coordination. The third change above 55 GPa appears to be a change in the silicon
coordination. At 15 GPa, it is suggested that a change in compressional mechanism takes place.
Received: 14 November 2000 / Accepted: 9 January 2002 相似文献
13.
David C. Palmer Russell J. Hemley Charles T. Prewitt 《Physics and Chemistry of Minerals》1994,21(8):481-488
The pressure dependence of the cristobalite Raman spectrum has been investigated to 22 GPa at room temperature, using single-crystal Raman spectroscopy with a diamond-anvil cell. We observe a rapid, first-order phase transition on increasing pressure, consistent with the cristobalite I?II transition revealed in previous x-ray diffraction experiments. The phase transition has been bracketed at 1.2±0.1 GPa on increasing pressure and 0.2±0.1 GPa on decreasing pressure. The pressure shifts II) of 11 Raman bands in the high-pressure phase (cristobalite have been measured. Evidence for an unusual hybridization of modes at 490–500 cm?1 is found. Changes in the Raman spectra also reveal an additional phase transition to a new phase at P ≈ 11 GPa, which remains to be fully characterized. 相似文献
14.
《Comptes Rendus Geoscience》2019,351(4):303-311
This paper presents the first seismic measurements of serpentinite of Bou Azzer ophiolite, central Anti-Atlas of Morocco, including seismic velocities and anisotropy. Two serpentinite samples collected from the Ait Ahmane fault zone were analyzed in order to define the mineralogical and seismic features of the natural serpentinite of the Bou Azzer ophiolite. The mineralogical features were investigated using microscopic observation and Raman spectroscopy, while the seismic features were performed using an Electron Backscatter Diffraction (EBSD) instrument. Microscopy and spectroscopy analyses confirmed that the investigated serpentinite suffers from a variable degree of serpentinization, and the antigorite is the dominant variety of serpentine minerals in the study area. The crystal preferred orientation (CPO) results show that the axis [001] of the antigorite deformation is aligned subnormal to the foliation, while the axis [010] is mostly aligned subparallel to the lineation. The seismic anisotropy results are depending on serpentine amount in the rock samples. The sample with a low serpentine amount (30%) shows lowest P- and S-wave anisotropy (Vp = 7.2% and AVs = 6.55%), while the sample with a high amount of serpentine (85%) presents highest P-wave and S-wave anisotropy (Vp = 8.6% and AVs = 11.06%). Consequently, the results indicate that seismic anisotropy increases when increasing the antigorite amount. 相似文献
15.
Shin-Ichi Machida Hisako Hirai Taro Kawamura Yoshitaka Yamamoto Takehiko Yagi 《Physics and Chemistry of Minerals》2007,34(1):31-35
High-pressure Raman studies of methane hydrate were performed using a diamond anvil cell in the pressure range of 0.1–86 GPa
at room temperature. Raman spectra of the methane molecules revealed that new softened intramolecular vibration mode of ν
1 appeared at 17 GPa and that the splitting of vibration mode of ν
3 occurred at 15 GPa. The appearance of these two modes indicates that an intermolecular attractive interaction increases between
the methane molecules and the host water molecules and between the neighboring methane molecules. These interactions might
result in the exceptional stability of a high-pressure structure, a filled ice Ih structure (FIIhS) for methane hydrate, up
to 40 GPa. At 40 GPa, a clear change in the slope of the Raman shift versus pressure occurred, and above 40 GPa the Raman
shift of the vibration modes increased monotonously up to 86 GPa. A previous XRD study showed that the FIIhS transformed into
another new high-pressure structure at 40 GPa. The change in the Raman spectra at 40 GPa may be induced by the transition
of the structure. 相似文献
16.
The Sanbagawa belt is one of the famous subduction‐related high‐pressure (HP) metamorphic belts in the world. However, spatial distributions of eclogite units in the belt have not yet satisfactorily established, except within the Besshi region, central Shikoku, southwest Japan because most eclogitic rocks were affected by lower pressure overprinting during exhumation. In order to better determine the areal distribution of the eclogite units and their metamorphic features, inclusion petrography of garnet porphyroblasts using a combination of electron probe microanalyser and Raman spectroscopy was applied to pelitic and mafic schists from the Asemi‐gawa region, central Shikoku. All pelitic schist samples are highly retrogressed, and include no index HP minerals such as jadeite, omphacite, paragonite, or glaucophane in the matrix. Garnet porphyroblasts in pelitic schists occur as subhedral or anhedral crystals, and show compositional zoning with irregular‐shaped inner segments and overgrown outer segments, the boundary of which is marked by discontinuous changes in spessartine. This feature suggests that a resorption process of the inner segment occurred prior to the formation of the outer segment, indicating discontinuous crystallization between the two segments. The inner segment of some composite‐zoned garnet grains displays Mn oscillations, implying infiltration of metamorphic fluid during the initial exhumation stage. Evidence for an early eclogite facies event was determined from mineral inclusions (e.g., jadeite, paragonite, glaucophane) in the garnet inner segments. Mafic schists include no index HP minerals in the matrix as with pelitic schists. Garnet grains in mafic schists show simple normal zoning, recording no discontinuous growth during crystal formation. There are no index HP mineral inclusions in the garnet, and thus no evidence suggesting eclogite facies conditions. Quartz inclusions in garnet of the pelitic and mafic schists show residual pressure values (?ω1) of >8.5 cm?1 and <8.5 cm?1 respectively. The combination of Raman geobarometry and conventional thermodynamic calculations gives peak P–T conditions of 1.6–2.1 GPa at 460–520°C for the pelitic schists. The ?ω1 values of quartz inclusions in mafic schists are converted to a metamorphic pressure of 1.2–1.4 GPa at 466–549°C based on Raman geothermometry results. These results indicate that a pressure gap definitely exists between the mafic schists and the almost adjacent pelitic schists, which have experienced a different metamorphic history. Furthermore, the peak P–T values of the Asemi‐gawa eclogite unit are compatible with those of Sanbagawa eclogite unit in the Besshi region of central Shikoku, suggesting that these eclogite units share a similar P–T trajectory. The Asemi‐gawa eclogite unit exists in a limited area and is composed of mostly pelitic schists. We infer that these abundant pelitic schists played a key role in buoyancy‐driven exhumation by reducing bulk rock density and strength. 相似文献
17.
The effect of chrysotile nanotubes on the serpentine-fluid Li-isotopic fractionation 总被引：1，自引：0，他引：1
Bernd Wunder Fabien Deschamps Anke Watenphul Stéphane Guillot Anette Meixner Rolf L. Romer Richard Wirth 《Contributions to Mineralogy and Petrology》2010,159(6):781-790
We determined the lithium isotope fractionation between synthetic Li-bearing serpentine phases lizardite, chrysotile, antigorite,
and aqueous fluid in the P,T range 0.2–4.0 GPa, 200–500°C. For experiments in the systems lizardite-fluid and antigorite-fluid, 7Li preferentially partitioned into the fluid and Δ7Li values followed the T-dependent fractionation of Li-bearing mica-fluid (Wunder et al. 2007). By contrast, for chrysotile-fluid experiments, 7Li weakly partitioned into chrysotile. This contrasting behavior might be due to different Li environments in the three serpentine
varieties: in lizardite and antigorite lithium is sixfold coordinated, whereas in chrysotile lithium is incorporated in two
ways, octahedrally and as Li-bearing water cluster filling the nanotube cores. Low-temperature IR spectroscopic measurements
of chrysotile showed significant amounts of water, whose freezing point was suppressed due to the Li contents and the confined
geometry of the fluid within the tubes. The small inverse Li-isotopic fractionation for chrysotile-fluid results from intra-crystalline
Li isotope fractionation of octahedral Li[6] with preference to 6Li and lithium within the channels (Li[Ch]) of chrysotile, favoring 7Li. The nanotubes of chrysotile possibly serve as important carrier of Li and perhaps also of other fluid-mobile elements
in serpentinized oceanic crust. This might explain higher Li abundances for low-T chrysotile-bearing serpentinites relative to high-T serpentinites. Isotopically heavy Li-bearing fluids of chrysotile nanotubes could be released at relatively shallow depths
during subduction, prior to complete chrysotile reactions to form antigorite. During further subduction, fluids produced during
breakdown of serpentine phases will be depleted in 7Li. This behavior might explain some of the Li-isotopic heterogeneities observed for serpentinized peridotites. 相似文献
18.
Adrian J. Williams 《Tectonophysics》1979,58(1-2)
At Glenrock, near the southern end of the Peel Fault System, two fault zones are delineated by mélanges in which serpentinite is the main rock type.Protogranular and mylonitic textures are present in relicts of the parent peridotite and in blocks of massive pseudomorphic serpentinite that are surrounded by schistose serpentinite. In schistose serpentinite, the earliest foliation (S1) is defined, microscopically, by the parallel alignment of platy and fibrous serpentine minerals (lizardite and chrysotile) and by trains of magnetite and flattened serpentine pseudomorphs after olivine and pyroxene. It is considered that the schistosity formed perpendicular to the direction of maximum shortening, under conditions in which lizardite and chrysotile were ductile, but antigorite was not, by breakdown of pre-existing serpentine minerals and new growth of lizardite and chrysotile.Post-s1 foliations (S2andS3) superficially resemble crenulation cleavages in the field but, microscopically, show evidence of shear displacement and are referred to as microshear sets. They probably originated in the ductile-brittle transitional field of serpentine behaviour (Raleigh and Paterson, 1965). 相似文献
19.
The studied serpentinites occur as isolated masses, imbricate slices of variable thicknesses and as small blocks or lenses incorporated in the sedimentary matrix of the mélange. They are thrusted over the associated island arc calc-alkaline metavolcanics and replaced by talc-carbonates along shear zones. Lack of thermal effect of the serpentinites upon the enveloping country rocks, as well as their association with thrust faults indicates their tectonic emplacement as solid bodies. Petrographically, they are composed essentially of antigorite, chrysotile and lizardite with subordinate amounts of carbonates, chromite, magnetite, magnesite, talc, tremolite and chlorite. Chrysotile occurs as cross-fiber veinlets traversing the antigorite matrix, which indicate a late crystallization under static conditions. The predominance of antigorite over other serpentine minerals indicates that the serpentinites have undergone prograde metamorphism or the parent ultramafic rocks were serpentinized under higher pressure. The parent rocks of the studied serpentinites are mainly harzburgite and less commonly dunite and wehrlite due to the prevalence of mesh and bastite textures. The serpentinites have suffered regional metamorphism up to the greenschist facies, which occurred during the collisional stage or back-arc basin closure, followed by thrusting over a continental margin. The microprobe analyses of the serpentine minerals show wide variation in SiO2, MgO, Al2O3, FeO and Cr2O3 due to different generations of serpentinization. The clinopyroxene relicts, from the partly serpentinized peridotite, are augite and similar to clinopyroxene in mantle-derived peridotites. The chromitite lenses associated with the serpentinites show common textures and structures typical of magmatic crystallization and podiform chromitites. The present data suggest that the serpentinites and associated chromitite lenses represent an ophiolitic mantle sequence from a supra-subduction zone, which were thrust over the continental margins during the collisional stage of back-arc basin. 相似文献
20.
采用Fourier变换红外吸收光谱和X射线粉晶衍射技术对四川石棉县蛇纹石猫眼进行了研究。红外吸收光谱结果表明:四川蛇纹石猫眼可分为纤蛇纹石和叶蛇纹石两种类型,两者在(960-1100)cm-1和(3600-3690)cm-1的范围内由Si-O伸缩振动的E1类振动和OH伸缩振动表现出的红外谱带分裂强度及谱带特征存在明显的差异。在(960- 1100)cm-1间:纤蛇蚊石的红外光谱分裂成三个明显的谱带,而叶蛇纹石在此区间只有两条谱带。在570cm-1附近的红外谱带以肩状出现;OH伸缩振动区:纤蛇蚊石出现两条红外谱带,而叶蛇蚊石只出现一条红外谱带。X射线粉晶衍射结果表明:叶蛇蚊石具有d202=0．2522nm(I/I0=19)和d203=0．2430nm(I／I0=18)的特征谱线,而纤蛇纹石则具有d202、006=0．2446nm(I／I0=29)的特征谱线,d020>0．245nm近0．249 nm的特征谱线缺失。 相似文献