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81.
82.
Amiya K. Samal Srinjoy Datta Jiten Pattnaik Deepak Kumar Rajesh K. Srivastava 《Chemie der Erde / Geochemistry》2022,82(1):125839
The presence of recycled crust in the lithospheric mantle of the Dharwar craton has been investigated using trace element geochemistry of olivine grains from an ENE-trending Paleoproterozoic picrite dyke (associated with the ca. 1.89–1.88 Ga Hampi dyke swarm) emplaced in the western Dharwar craton. Olivine grains are purely magmatic, formed as early phenocrysts in a fractionated basaltic melt. They exhibit enrichment in NiO contents (0.32–0.43 wt%) and depletion in Ca (1366–2105 ppm), Mn (1578–2663 ppm) and 100 1 Mn/Fe (1.28–1.48). Further, the compiled whole-rock geochemical data of the picrite dyke and associated dyke swarm illustrates relatively low CaO/MgO (0.55–1.78), intermediate FeO/MnO (47–54), negative to positive PX# (?0.34 to +1.86), and high values of FC3MS (0.24–0.90) and FCKANTMS (0.19–1.11). These chemical markers are not consistent with the derivation of the primary melt from a pure peridotite or a pyroxenite source; therefore, contribution from a mixed type of source having both peridotite and pyroxenite end members (pyroxene rich and olivine poor lithology) is suggested. The amount of pyroxenite and recycled crust varies from 46% to 86% and 14% to 44%, respectively. The Al-in-olivine based thermometer estimates the maximum crystallization temperature as 1407 °C, which is 137 °C higher than the average temperature of MORB and accordant with several well-established plume-induced large igneous provinces (LIPs) worldwide. Therefore, it is suggested that the studied picrite dyke is derived from a primary melt generated by plume-induced melting of a peridotite-pyroxenite mixed source. The ca. 1.89–1.88 Ga Hampi dyke swarm, being genetically linked with the studied dyke, could also be derived from this same source. Further, the recycled crust in the subcontinental lithospheric mantle of the western Dharwar craton may have generated the pyroxene rich mafic source during the Neoarchean convergence between eastern and western Dharwar craton. 相似文献
83.
《地学前缘(英文版)》2018,9(6):1945-1955
CO2 mineral sequestration (in ultrabasic or basaltic rocks) has been considered as a promising long-term and stable approach to reduce CO2 in the atmosphere and would counteract the effect of global warming. Meanwhile, clays are widely found in ultrabasic reservoirs. In our study, clays were observed in natural olivine samples, which were used for laboratory experiments in a supercritical CO2 system at 140 °C and 15 MPa. Initial olivine samples were crushed into two sizes which were large grains of ∼850–1000 μm and powder particles of ∼75–150 μm, with the durations of 400 and 1000 h for the powder and grains, respectively. The results showed amorphous silica was newly formed and this passivating layer could mitigate the water-rock interaction to some extent, but it would not play a long-term prohibited effect on secondary mineral carbonate formation as it is a Fe(III) free silica coating. More interestingly, the secondary carbonates were observed to form near the surface sites where locates more clays. Our findings provide insights into the reaction mechanisms of olivine-scCO2-water interaction process in natural ultrabasic rocks. 相似文献
84.
Evidence for stable grain boundary melt films in experimentally deformed olivine-orthopyroxene rocks
The microstructure of olivine-olivine grain boundaries has been studied in experimentally deformed (1200–1227 °C, 300 MPa)
partially molten olivine and olivine-orthopyroxene rocks. In-situ melting produced ∼1 vol% melt in all samples studied. Grain
boundary analyses were carried out using a number of transmission electron microscopy techniques. The grain boundary chemistry
in undeformed olivine-orthopyroxene starting material showed evidence for the presence of an intergranular phase along some,
but not all, of the olivine-olivine boundaries. In the deformed samples, ultrathin Si-rich, Al- and Ca-bearing amorphous films
have been observed along all investigated olivine-olivine grain boundaries. The chemistry of the grain boundaries, which is
considered to be indicative for the presence of a thin film, was measured with energy-dispersive X-ray spectroscopy (EDX)
and energy-filtering imaging. The amorphous nature of the films was confirmed with diffuse dark field imaging, Fresnel fringe
imaging, and high-resolution electron microscopy. The films range in thickness from 0.6 to 3.0 nm, and EDX analyses show that
the presence of Al and Ca is restricted to this ultrathin film along the grain boundaries. Because thin melt films have been
observed in all the samples, they are thought to be stable features of the melt microstructure in deformed partially molten
rocks. The transition from the occasional presence of films in the undeformed starting material to the general occurrence
of the films in deformed materials suggests that deformation promotes the formation and distribution of the films. Alternatively,
hot-pressing may be too short for films to develop along all grain boundaries. A difference in creep strength between the
studied samples could not be attributed to grain boundary melt films, as these have been found in all deformed samples. However,
a weakening effect of grain boundary melt films on olivine rheology could not be ruled out due to the lack of confirmed melt-film
free experiments.
Received: 13 April 1999 / Revised, accepted: 10 February 2000 相似文献
85.
Chusi?LiEmail author Zhanghua?Xu Sybrand?A.?de?Waal Edward?M.?Ripley Wolfgang?D.?Maier 《Mineralium Deposita》2004,39(2):159-172
The Jinchuan Ni–Cu sulfide deposit is hosted by an elongated, olivine-rich ultramafic body that is divided by subvertical strike-slip faults into three segments (central, eastern, and western). The central segment is characterized by concentric enrichments of cumulus olivine crystals and interstitial sulfides (pyrrhotite–pentlandite–chalcopyrite intergrowth), whereas the eastern and western segments are characterized by an increase of sulfides toward the lower contacts. In all segments sulfides are concentrated at the expense of intercumulus silicates. Olivine re-crystallization is found to be associated with actinolite alteration in some samples. The compositional variations of primary olivine from the sulfide-poor samples can be explained by a small degree of olivine crystallization (<5%) from a basaltic magma followed by local re-equilibration of the olivine with up to 30% trapped silicate liquid. In the sulfide-bearing samples the compositions of primary olivine record the results of olivine-sulfide Fe–Ni exchange that occurred after the trapped silicate liquid crystallized. Our olivine data indicate that Ni in the original sulfide liquids increased inward in the central segment and laterally away from the lower contact in the eastern segment. Variations in the compositions of sulfide liquids are thought to result from fractional segregation of immiscible sulfide liquid from a basaltic magma in a staging chamber instead of in situ differentiation. High concentrations of olivine crystals (mostly >50 modal%) and sulfide (averaging ~5 wt%) in the rocks are consistent with the interpretation that the Jinchuan deposit was formed by olivine- and sulfide-laden magma successively ascending through a conduit to a higher, now-eroded, level. Sulfide enrichment toward the center in the central segment and toward the lower contact in the eastern and western segments may have, in part, resulted from flow differentiation and gravitational settling during magma ascent, respectively.Editorial handling: P. Lightfoot 相似文献
86.
富铁橄榄石的高温变形实验研究 总被引:1,自引:3,他引:1
利用高精度Paterson气体介质变形装置对(Mg0.5,Fe0.5)2SiO4和(Mg0.7,Fe0.3)2SiO4橄榄石集合体进行了高温三轴压缩变形试验。首先用人工合成了纯铁橄榄石Fe2SiO4,然后用合成的纯铁橄榄石与天然圣卡罗橄榄石按一定比例混合烧结合成了含铁量分别为50%和30%的富铁橄榄石集合体Fo50和Fo70。三轴压缩蠕变变形试验在温度1223-1473 K和围压 300 MPa的条件下进行,差应力为10-300 MPa,应变率为10-7-10-4s-1,每个试件的最大变形量为20%.利用三维非线性方法对蠕变数据进行拟合,得出的流动律中,Fo50应力指数为4.1,活化能为499kJ/mol;Fo70应力指数为4.3,活化能为510kJ/ mol。将实验结果与Fo90圣卡罗橄榄石集合体的强度进行对比,发现含铁量的增加使橄榄石的强度明显下降,Fo50橄榄石集合体比Fo70的粘性低一个量级,Fo70比Fo90的粘性低一个量级。从而得到了含铁量对橄榄石的粘性(强度)影响的初步试验结果。 相似文献
87.
Romano Rinaldi G. D. Gatta G. Artioli K. S. Knight C. A. Geiger 《Physics and Chemistry of Minerals》2005,32(8-9):655-664
The thermal expansion, structural changes and the site partitioning of Co and Mg in synthetic CoMgSiO4 olivine have been studied by in situ time-of-flight neutron powder diffraction as a function of temperature, between 25 and
1,000°C. Thermal expansion of the unit cell dimensions and volume are linear within this temperature range and give no indications
of a phase transition, although the thermoelastic behaviour indicates a slight strain minimum around 700°C. Co2+ shows a strong preference for the M1 site throughout this temperature range with an oscillatory behaviour; it decreases slightly
at about 300°C, climbing up to nearly its original value at around 800°C and then decreasing by about 30% at 1,000°C. This
behaviour is in contrast with that of (Fe, Mg)2SiO4 olivine, in which the initial Fe2+ site preference for the M1 site switches to the M2 site beyond a cross-over temperature. The oscillatory site preference
in (CoMg)-olivine as a function of temperature is reflected in the M–O polyhedral volume changes and M–O bond lengths, as
well as, thermoelastic strain and atomic thermal displacement parameters. The imbalance between the increasing vibrational
and decreasing configurational entropy contributions, together with covalent bonding effects rather than crystal field contributions,
seem to drive the cation partitioning in (CoMg)-olivine. 相似文献
88.
The misorientation index: Development of a new method for calculating the strength of lattice-preferred orientation 总被引:5,自引:4,他引:5
Using orientation data from experimentally deformed olivine, we explore some practical problems with the J-index, a commonly applied measure of fabric strength. We show that the J-index is highly dependent on several factors, including the number of discrete data in the orientation distribution function (ODF), and arbitrary numerical parameters specified for its calculation. Because of this non-uniqueness, we conclude that the J-index is difficult to interpret and should only be applied with caution. As an alternative to the J-index, we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles. This “M-index” is shown to be insensitive to the parameters specified for its calculation. For typical deformed olivine samples, we show that 150 discrete data are adequate to quantify fabric strength using the M-index technique. The M-index correlates well with seismic anisotropy, particularly for materials of the same fabric type. Therefore, we conclude that the M-index technique is well-suited for the quantification of fabric strength and the comparison of like materials. 相似文献
89.
The empirical linear relation between volume and logarithm of bulk modulus of a material, discovered by Grover, Getting and
Kennedy is taken as the basis for our equation of state. Using the latest experimental information on the adiabatic bulk modulus,
the equation of state is applied to the three polymorphs of Mg2SiO4 to develop a consistent dataset of their thermodynamic properties in the temperature range of 200–2273 K and a pressure range
of 0.1 MPa–30 GPa. The results imply that the bulk sound velocity contrast (v
β−v
α)/v
α increases with temperature along the α–β phase boundary and reaches the value 8.9% at 13.5 GPa, a pressure equivalent to
410 km depth in the Earth. The bulk sound velocity contrast (v
γ−v
β)/v
β decreases with temperature along the β–γ phase boundary and becomes less than 0.7% at temperatures and pressures equivalent
to those associated with the 520-km seismic discontinuity in the Earth.
Received: 1 August 2000 / Accepted: 1 March 2001 相似文献
90.
The effects of deformation on the kinetics of the net-transfer reaction anorthite + forsterite → cpx + opx + spinel ± gt were
studied using static and shear deformation experiments. Experiments were performed on dry anorthite-olivine (An92–Fo93) samples at 900°C and pressures between 1,000 and 1,600 MPa in a Griggs apparatus. Deformed (‘non-hydrostatic’) and undeformed
(‘static’) samples are compared in terms of phase petrology, reaction rate and reaction mechanisms. Anorthite + olivine reactions
are diffusion-controlled as seen from reaction rim structures. In undeformed samples, delayed reaction onset and low reaction
rates demonstrate sluggish nucleation of reaction products and slow rates of diffusion at dry conditions, even at 700–900 MPa
confining pressure overstepping. The reaction rate is enhanced in deformed An–Fo samples. The higher rate is mainly attributed
to a combination of high stresses and viscous deformation processes of the reactants and products, which cause an increase
in the nucleation rate of products. The results imply that viscous deformation processes alone can be responsible for the
initiation and localisation of metamorphic reactions in dry rocks in the absence of fluid infiltration.
A. A. de Ronde was supported by the Swiss National Fond grants 2100-057092.99 and 2000-065041.01. 相似文献