共查询到20条相似文献，搜索用时 93 毫秒
1.
和龙岩体赋存于新太古代夹皮沟-金城洞花岗绿岩带中，与围岩发生同变形变质，岩体具有典型的科马提岩冷凝结构分层和鬣刺结构、冷凝多面体节理，上述特征是作者1990年发现确认的，该科马提岩的矿物学特征；玻璃质脱玻形成铁皂石等矿物；斜方辉石和橄榄石鬣刺呈中空骸晶状，大部被滑石、铁白云石、绿泥石、磁铁矿等取代，但仍保留完好的长柱状假像；堆积带中侯榄石呈微细粒、鹇，仅发生网状蛇纹石化。岩石化学特征富MgO,CaO/Al2O3=1.04，用科马提岩分类图判别为超镁铁质科马提岩。 相似文献
2.
和龙岩体赋存于新太古代夹皮沟—金城洞花岗绿岩带中,与围岩发生同变形变质。岩体具有典型的科马提岩冷凝结构分层和鬣刺结构、冷凝多面体节理。上述特征是作者1990年发现确认的。该科马提岩的矿物学特征:玻璃质脱玻形成铁皂石等矿物;斜方辉石和橄榄石鬣刺呈中空骸晶状,大部被滑石、铁白云石、绿泥石、磁铁矿等取代,但仍保留完好的长柱状假像;堆积带中橄榄石呈微细粒、新鲜,仅发生网状蛇纹石化。岩石化学特征富MgO,CaO/Al_2O_3=1.04,用科马提岩分类图判别为超镁铁质科马提岩。 相似文献
3.
桂北中元古代的科马提岩 总被引：2，自引：0，他引：2
桂北四堡群的科马提岩,自下而上分为堆晶带、鬣剌带和冷凝带。它们分别由辉石质科马提岩、具鬣刺结构的玄武质科马提岩和淬碎熔岩组成。与国外太古代绿岩带科马提岩对比,岩石化学成分、分带性、特有的鬣刺结构及区域变质特征、含矿性等方面亟相似。但我国华南元古代科马提岩也有自己的特点,产于元古代古大陆边缘,化学成分为超镁铁—镁铁质,且以镁铁质为主。 相似文献
4.
山东蒙阴苏家沟科马提岩的特征及其意义 总被引：1，自引：0，他引：1
科马提岩作为太古代绿岩带的一个标志，一直受到广大地质工作者的重视，最近，在蒙阴县坦力家沟村发现的具典型鬣刺结构斜马提岩，进一步证实了鲁西地区是华北地台上乃至世界上最典型的太古代绿岩带之一，为鲁西地区太古代绿岩带及其矿产的研究提供了新的信息。苏家沟科马提岩呈透镜状残留体赋存于前寒武纪花岗质岩石中，主要由蛇纹石化橄榄科马提岩，透闪石岩、阳起透闪片岩，绿泥透闪片岩，黑云阳起片岩等组成，具典型的鬣刺结构和变余鬣刺结构，其岩石学，岩石化学及结构等特征与世界典型地区科马提岩极为相似，属橄榄科马提岩。 相似文献
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山东蒙阴苏家沟科马提岩的特征及其意义 总被引：1，自引：0，他引：1
科马提岩作为太古代绿岩带的一个标志,一直受到广大地质工作者的重视.最近,在蒙阴县坦埠镇苏家沟村发现的具典型鬣刺结构科马提岩,进一步证实了鲁西地区是华北地台上乃至世界上最典型的太古代绿岩带之一,为鲁西地区太古代绿岩带及其矿产的研究提供了新的信息.苏家沟科马提岩呈透镜状残留体赋存于前寒武纪花岗质岩石中,主要由蛇纹石化橄榄科马提岩、透闪石岩、阳起透闪片岩、绿泥透闪片岩、黑云阳起片岩等组成,具典型的鬣刺结构和变余鬣刺结构.其岩石学、岩石化学及结构等特征与世界典型地区科马提岩极为相似,属橄榄科马提岩. 相似文献
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大兴安岭吉峰地区中元古代科马提岩及成因类型 总被引：1，自引：0，他引：1
大兴安岭吉峰地区的橄榄质科马提岩具有良好的显微鬣刺结构,在橄榄石和辉石晶体间隙中充填有基质物质,说明其为火山岩.通过研究,对其初步划分了冷凝带和鬣刺带,它们构成一个不完整的冷凝单元.吉峰科马提岩在岩石化上表现了良好的科马提岩属性,与南非及西澳大利亚橄榄质科马提岩一致.岩石地球化学研究表明,科马提岩及与其伴生的玄武岩具有紧密的成因联系,它们的演化符合科马提岩-拉斑玄武岩的演化趋势,具良好的正相关特点.在主量元素、微量元素及REE特征上,本区科马提岩具有较好的II类科马提岩属性,与南非巴伯顿、印度、西格陵兰II类科马提岩极为相似.吉峰科马提岩的εNd（T）=+7.51,说明源于亏损地幔,并且以LREE轻度富集为特征,显示它们系亏损地幔经较小程度部分熔融产生的.吉峰拉马提岩的形成时代为中元古代,其形成环境可能是地壳拉伸减薄,上涌的科马提质岩浆在淬火快速冷却的条件下形成.这一岩石类型的发现为研究大兴安岭地区元古宙大地构造演化提供了一个新线索. 相似文献
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科马提岩(Komatiite),又叫鬣刺岩(Spinifex)。近年来,国内虽有较多报导,但均未提到该岩石的结构特征。我队四分队在小佳河公社幅和饶河县幅进行1∶20万区域地质调查时,经显微镜鉴定,发现了“科马提岩”的鬣刺结构。所见结构均属显微鬣刺结构。这一发现,为国内目前科马提岩的研究提供了重要资料。现将情况介绍如下: 相似文献
8.
蒙阴县苏家沟科马提岩 总被引：9，自引：1，他引：8
苏家沟科马提岩呈透镜状残留体赋存于早元古代二长花岗岩中,主要由蛇方石化橄榄科马提岩、透闪石岩、透闪片岩、阳起诱闪片岩、绿泥透闪片岩、黑云阳起片岩等组成,具典型的鬣刺结构及变余鬣刺结构。该科马提岩的岩石学、岩石化学及结构特征与民办典型地区科马提岩极为相似,属橄榄科马提岩。 相似文献
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桂北四堡群中科马提岩系及其成因类型 总被引：4，自引：0，他引：4
桂北四堡群中许多镁铁质—超镁铁质岩体,实际上是火山岩或次火山岩。有的还具有科马提岩岩流的结构分层,其堆积带上部橄榄石和辉石晶体间隙中充填有基质物质。这些基质中发育了典型的橄榄石鬣刺结构。科马提岩与其伴生玄武岩属具成因联系的同一演化系列。在微量元素及REE特征上,区内科马提岩具有较好的Ⅱ类科马提岩属性,它们系亏损地幔经较小程度部分熔融产生。 相似文献
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Komatiites II: Experimental and Theoretical Investigations of Post-emplacement Cooling and Crystallization 总被引：1，自引：2，他引：1
TURNER J. STEWART; HUPPERT HERBERT E.; SPARKS R. STEPHEN J. 《Journal of Petrology》1986,27(2):397-437
When komatiite lavas are emplaced on the sea floor most of theheat transfer occurs through the upper lava-seawater boundary.We have investigated the cooling and crystallization of komatiitesusing a series of analogue laboratory experiments with aqueoussolutions and by theoretical analysis. In komatiites the viscosityis sufficiently low that convection occurs in the interior ofthe flow and these motions, due both to thermal and compositionalvariations, have an important influence on the characteristicfeatures of komatiites such as the strong compositional andtextural layering. The experiments have been conducted with crystallizing aqueoussolutions which display the same overall dynamical processesas solidifying komatiites. The solutions used are simple eutecticsystems having the property that crystallization from a solutionwhich is substantially more concentrated than the eutectic compositionleaves behind residual fluid which is less dense than the originalfluid. This models the decrease in density of komatiite meltson cooling, due to the crystallization of olivine. Such solutionshave been cooled strongly through the metal roof of an otherwiseinsulated container, using a typical fluid depth of 80 mm. Dendriticcrystals grew down vertically from the roof and released lightfluid, depleted in solute, which rose to form a zone of stagnantfluid at the top of the container, while the tips of the crystalsextended just below the bottom of this light layer. A layerof solid eutectic, with a horizontal front, grew more slowlyand filled in the space between the vertically oriented crystals. The growth of the crystals and the eutectic layer were monitoredvisually, and in some experiments the temperatures at the topand in the fluid were recorded, until solidification throughoutthe layer was complete. The solid block was sampled, and themelted products analysed to give vertical concentration profiles.Both the texture and composition are strongly influenced bythe fluid conditions during crystal growth. The top concentrationis that of the original solution, rapidly quenched against theroof, and the mean concentration through the region influencedby the stable fluid layer is also close to the original. Atthe bottom the concentration is high, reflecting the in situgrowth of close-packed crystals, and there is a sharp decreasein concentration at an intermediate level, between the upperand lower crystal layers. The experiments and associated theory shed new light on theconsolidation of komatiites and the development of their characteristictextures and compositions. Since the lava is convecting withinthe interior, the early stages of cooling are characterizedby a rapid decrease in temperature. Initial cooling rates of1 to 100 °C h–1 are calculated. At this stage thecrust remains thin, but as the spinifex zone develops, convectionprogressively decreases in vigour and the cooling rate decreases.Spinifex texture is considered to form by constitutional supercoolingwhich is controlled by compositional convection. As the spinifextexture develops, the olivine dendrites form a layer of depletedfluid. The tips of the crystals extend beyond this differentiatedlayer into a convecting lower region and grow preferentiallyto produce the characteristic vertically oriented spinifex texture.The composition of spinifex zones is shown to be close, butnot identical, to the initial liquid composition. The compositionalprofiles of the solid products of the experiments are similarto those found in komatiites, with the most evolved rock compositionsbeing found just above the cumulate zone. The experiments alsosuggest an alternative explanation to crystal settling for thecumulate zone, in which growth of the spinifex zone by compositionalconvection concentrates crystals suspended within the turbulentlyconvecting lower layer. 相似文献
12.
The formation of platy olivine spinifex, the texture that characterizeskomatiite lavas, has long been enigmatic. A major problem isthat the dendritic morphology of the olivine resembles thatof crystals grown in laboratory experiments at high coolingrates (>50°C/h), but at the position where these texturesform, up to several meters below the komatiite flow top, thecooling rate cannot have been greater than 1–5°C/h.We performed experiments that demonstrate that the platy habitof spinifex olivine or pyroxene is a consequence of slow coolingof ultramafic magma in a thermal gradient (7–35°C/cm).The charges were cooled at rates between 2 and 1428°C/hand, even at the low cooling rates, the thermal gradient ledto constrained growth and the development of preferentiallyoriented dendritic crystals with morphologies like those innatural platy spinifex-textured lavas. Under these conditions,olivine starts to crystallize at temperatures well below theequilibrium liquidus temperature (37°C < –T<56°C) depending on the composition of the starting material.When the cooling rate is high, the thermal gradient has a negligibleeffect on the texture and the crystals have a random orientation,like that in the upper parts of komatiite flows. KEY WORDS: komatiite; spinifex; cooling rate; experimental petrology; thermal gradient 相似文献
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Mineral exploration of the Widgiemooltha-Norseman region of Western Australia has located massive and disseminated nickel sulphide mineralisation.This paper discusses the geological setting of the nickel sulphide mineralisation with reference to the stratigraphy, structure and metamorphism of the ultramafic sequence and spatially associated rocks. The amphibolite facies metamorphosed ultramafic rocks of the Widgiemooltha area are compared with greenschist metamorphosed ultramafic rocks at Eundynie, which exhibit excellently preserved pseudomorphs of primary igneous textures.Some 2000 ultramafic rock samples were analysed for 13 element/oxides and divided into four major mineralogically and texturally distinct groups. The data were analysed statistically by determination of means and standard deviations and multiple regression analyses.The data suggest differentiation of a magma at depth followed by a vast outpouring of lava to produce picritic-peridotitic rocks. The flows crystallised with upper spinifex zones and lower euhedral-olivine zones in varying proportions dependent on magma composition. The development of spinifex texture is compositionally controlled. This texture is not developed in rocks with MgO contents greater than 26% (± 2%).The comparison of the ultramafics of the Widgiemooltha and Eundynie areas indicates that talc-carbonate formation and serpentinization have modified primary igneous textures and geochemistries, resulting in the production of a diverse group of rock types. Such post-magmatic alteration processes in association with structural elements are considered important in the upgrading of nickel sulphide mineralisation. 相似文献
14.
Abstract: Several native sulfur specimens, collected from Shiretoko-Iwozan volcano, eastern Hokkaido, Japan, exhibit spinifex texture, which appears to resemble that often observed in komatiite. The spinifex texture is exhibited by yellow-colored elongated skeletal native sulfur crystals up to 5 cm long settled in medium gray-colored fine–grained clayey matrix. One surface of a specimen is coated by layers of micro pillow lava of native sulfur. Such specimens were rarely found as clasts or fragments around the 1936 No. 1 crater that erupted native sulfur flows, together with the most common monomineralic native sulfur fragments of native sulfur flows having pahoehoe surface and of native sulfur dikes. The elongated spinifex native sulfur crystals presently consist of aggregated polygrains of orthorhombic sulfur crystals formed through crystallo-graphic transition from the single crystal of monoclinic sulfur initially crystallized. The spinifex texture exhibited by elongated skeletal native sulfur crystals is a product of rapid cooling of sulfur melt. Many lithic fragments of altered country rocks are present in the specimens exhibiting native sulfur spinifex texture. This suggests that segregation of the sulfur melt from the mixture of lithic fragments and sulfur melt was incomplete because the mixture was chilled before the melt segregation. Elongated skeletal native sulfur crystals may have nucleated and crystallized directly from the molten sulfur liquid. Lithic fragments mixed in the melt are supposed to have acted as nuclei for the nucleation of the native sulfur crystals. On the other hand, the most of native sulfur flows consist of monomineralic massive native sulfur with very scarce lithic fragments. Such massive monomineralic native sulfur crystallized from the supercooled, solidified amorphous sulfur. Such supercooled amorphous state may have been attained due to the lack of nuclei because of the scarcity of lithic fragments. The unique structures exhibited by native sulfur lava flow, including pahoehoe surface and spinifex texture, are due to the characteristic physical property of molten sulfur liquid, that is, low viscosity. 相似文献
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Bélinda Godel Stephen J. Barnes Derya Gürer Peter Austin Marco L. Fiorentini 《Contributions to Mineralogy and Petrology》2013,165(1):173-189
High-resolution X-ray computed tomography has been carried out on a suite of komatiite samples representing a range of volcanic facies, chromite contents and degrees of alteration and metamorphism, to reveal the wide range of sizes, shapes and degrees of clustering that chromite grains display as a function of cooling history. Dendrites are spectacularly skeletal chromite grains formed during very rapid crystallization of supercooled melt in spinifex zones close to flow tops. At slower cooling rates in the interiors of thick flows, chromite forms predominantly euhedral grains. Large clusters (up to a dozen of grains) are characteristic of liquidus chromite, whereas fine dustings of mostly individual ~20-μm grains form by in situ crystallization from trapped intercumulus liquid. Chromite in coarse-grained olivine cumulates from komatiitic dunite bodies occurs in two forms: as clusters or chains of euhedral crystals, developing into “chicken-wire” texture where chromite is present in supra-cotectic proportions; and as strongly dendritic, semi-poikilitic grains. These dendritic grains are likely to have formed by rapid crescumulate growth from magma that was close to its liquidus temperature but supersaturated with chromite. In some cases, this process seems to have been favoured by nucleation of chromite on the margins of sulphide liquid blebs. This texture is a good evidence for the predominantly cumulus origin of oikocrysts and in situ origin of heteradcumulate textures. Our 3D textural analysis confirms that the morphology of chromite crystals is a distinctive indicator of crystallization environment even in highly altered rocks. 相似文献
16.
Sarah-Jane Barnes M. P. Gorton A. J. Naldrett 《Contributions to Mineralogy and Petrology》1983,83(3-4):293-308
A petrological and geochemical study of an olivine and of a clinipyroxene spinifex textured flow, from Alexo, indicates that the initial liquid in both flows probably came from the same mantle melting event and that the source was incompatible element depleted. The starting liquid of the clinopyroxene flow had experienced more olivine fractionation (10%) prior to its emplacement at Alexo, than the initial liquid of the olivine spinifex flow. The development of each of the textural and compositional zones in the flows can be modelled by means of crystal fractionation. In the case of the clinopyroxene flow the B-zone is formed by the fractionation of olivine, low-Ca pyroxene and chromite. An unusual feature of the Alexo clinopyroxene flow is presence of a peridotitic komatiite above the pyroxene cumulate layer, where a basaltic komatiite would usually be present. The presence of the peridotitic komatiite suggests an influx of new magma and hence a dynamic model for the flow. The composition of the clinopyroxene spinifex zone represents a mixture of clinopyroxene plus liquid, rather than simply a frozen liquid. This could happen if the clinopyroxene needles grew stalactitelike from the chilled upper surface of the flow into a flowing basaltic liquid. In the olivine spinifex flow the zones can be modelled as frozen liquids in the A2-zone, as initial liquid which has fractionated 30% olivine in the A3-zone and as liquid plus 50% olivine in the B-zone. But, if the clinopyroxene spinifex developed by stalactite growth of clinopyroxene needles into the a flowing liquid, the possibility that the olivine spinifex represent fractionated liquid plus stalactite olivines arises. 相似文献
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Sabah Yilmaz ahin 《Chemie der Erde / Geochemistry》2008,68(1):81-92
Rocks of the Late Cretaceous Tamdere Quartz Monzonite, constituting a part of the Eastern Pontide plutonism, include mafic microgranular enclaves (MMEs) ranging from spheroidal to ellipsoidal in shape, and from a few centimeters to decimeters in size. The MMEs are composed of diorite, monzodiorite and quartz diorite, whereas the felsic host rocks comprise mainly quartz monzonite, granodiorite and rarely monzogranite on the basis of both mineralogical and chemical compositions. The common texture of felsic host rocks is equigranular. MMEs are characterized by a microgranular texture and also reveal some special types of microscopic textures, e.g. antirapakivi, poikilitic K-feldspar, small lath-shaped plagioclase in large plagioclase, blade-shaped biotite, acicular apatite, spike zones in plagioclase and spongy-cellular plagioclase textures.
The distribution of major, trace and RE elements apparently reflect exchange between the MMEs and the felsic host rocks mainly due to thermal, mechanical and chemical interactions between coeval felsic host magma and mafic magma. The most evident major element transfer from felsic host magma to mafic magma blob is that of alkalis such as Na and K. LILEs such as Rb, Sr, Ba and some HFSEs such as Nb, Y, Zr and Th have been migrated from felsic host magma to MMEs. Apart from these major and trace elements, the other element transfer from felsic host magma to mafic one concerns REE contents. Such a transfer of REEs has evidently increased the LREE contents of MMEs. Enrichments in alkalis, LILEs, HFSEs and REEs could have been achieved by diffusional processes during the solidification of magma sources. The felsic and mafic magma sources behave as Newtonian and visco-plastic materials. In such an interaction, small MMEs behave as a closed system due to immediate rapid cooling, whereas the bigger MMEs suffer greater diffusion from the Newtonian felsic host magma due to slow cooling. 相似文献
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矿物的结构和成分可用来反演岩浆演化过程。为探讨酸性岩浆房内岩浆演化过程,以浙江拔茅火山主体英安岩中的斜长石为例,对其开展了矿物学、地球化学研究。结果显示,斜长石普遍具有核-幔-边结构,暗示其在喷发前处于开放性岩浆房内,并经历了复杂的岩浆过程。对代表性斜长石的电子探针成分及背散射图像分析表明,斜长石核部、幔部及边部分别具有不同的成因,反映了英安岩岩浆从深部聚集并在浅部岩浆房内周期性补给的过程。岩浆的这种周期性补给过程抑制了结晶分异作用对熔体成分的改变,全岩地球化学特征主要反映其源区特征及熔融过程。 相似文献
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