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本文对西藏丁青玻安岩类深成岩的辉石和新喀里多尼亚玻安岩的斜顽辉石进行了矿物学工作及高分辨电镜观察。丁青斜方辉石堆晶岩辉石的超微结构包括:单斜辉石的(100)双晶、斜方辉石a/4平移畴结构及斜方辉石—单斜辉石相转变。玻安岩斜顽辉石典型超微结构是(100)双晶。由矿物的碎裂、错动以及斜方辉石—单斜辉石相变中只出现偶数倍单斜辉石等表明:矿物结晶及成岩过程中曾受应力作用、后者可能与岩石所处的构造位置有关。由辉石成分计算的地质温度表明,丁青堆晶斜方辉石岩的辉石是在高温下晶出、岩石固结温度是1013～1111℃,当它们在～1000℃下稳定时,斜方辉石出溶了单斜辉石片晶。将玻安岩斜顽辉石加热至1100℃后淬冷及按120℃/h速度冷却均未得到纯的斜顽辉石,可能斜顽辉石是原顽火辉石在应力环境中高温淬冷所成。 相似文献
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西准噶尔白碱滩二辉橄榄岩中两种辉石的出溶结构及其地质意义 总被引：3，自引：11，他引：3
克拉玛依白碱滩尖晶石二辉橄榄岩主要由橄榄石、单斜辉石、斜方辉石和尖晶石组成,橄榄石和斜方辉石均发生程度不等的蛇纹石化。单斜辉石一般很新鲜。单斜辉石和斜方辉石均发育出溶结构,出溶条纹或者平直或者发生舒缓的弯曲变形(即便是在发生弯曲的情况下也是完全平行的)。透辉石-普通辉石出溶体一般呈针状(直径一般为1μm,长度>150μm),顽火辉石出溶条纹直径一般为1～3μm(长度>300μm)。斜方辉石主晶属于顽火辉石-易变辉石,单斜辉石主晶为透辉石(成分很均一)。地质温度压力估算表明,白碱滩二辉橄榄岩中辉石出溶结构发生的温度为700℃～1000℃、压力为2.0～2.7GPa,它们代表辉石出溶结构形成的最低PT条件。白碱滩二辉橄榄岩至少经历了三个演化阶段:原始辉石与尖晶石和橄榄石平衡共生(阶段Ⅰ,>94km);随着地幔上隆,原始辉石结构不稳定,分解并形成出溶结构(阶段Ⅱ,700℃～1000℃),斜方辉石开始分解的深度为94km,单斜辉石开始分解的深度为78km;之后,蛇绿岩经历的侵位事件导致辉石发生塑性变形(阶段Ⅲ)。蛇绿岩侵位之前,地幔岩曾发生了>50km的隆升,而且,在隆升过程中地幔岩没有发生明显部分熔融(地幔岩因此没有经历明显的岩浆抽提过程)。 相似文献
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石榴石辉石岩的单斜辉石中韭闪石和钛铁矿出溶结构及地质意义 总被引：10，自引：1，他引：10
本文首次报道了在苏鲁超高压变质带胡家岭地区石榴石辉石岩中发现的韭闪石出溶结构。该石榴石辉石岩是由石榴子石、单斜辉石以及镁铝尖晶石、钛铁矿和磁铁矿组成。在石榴子石巨斑晶中有单斜辉石包体，单斜辉石包体中又有石榴子石包体以及大量韭闪石出溶片晶和钛铁矿( 磁铁矿)出溶棒。单斜辉石中韭闪石出溶片晶呈平行条带状，其宽度在1～10μm之间。透射电子显微镜(TEM)观察韭闪石的(010)面平行于主晶透辉石的(010)面，且两者的界面在纳米尺度上是连续过渡的，证明韭闪石是出溶形成的。大量钛铁矿出溶棒的定向排列也显示出它们是自然出溶形成的。从单斜辉石出溶的矿物组合推测其原始单斜辉石成分中应富含H2O、Na和Ti，属高压型单斜辉石。该石榴石辉石岩经历了超高压变质作用后，在抬升减压过程中形成这些出溶结构。大量钛铁矿出溶棒均斜切韭闪石出溶片晶，表明该超高压岩石在减压过程中至少经历了两期以上导致温压明显变化的地质事件。 相似文献
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肇东陨石低钙辉石超微结构的研究 总被引：1，自引：1，他引：1
在肇东陨石低钙辉石中观察到各种堆垛缺陷,包括斜方-单斜辉石相转变、畴结构、2.7nm长周期结构以及自然界极为罕见的奇数倍八面体层堆垛缺陷——1.35nm等。高分辨像所揭示的1.35nm的新特征是可以重复两次。文中提出1.35nm的结构是“A+B+A-”型。1.35nm片晶仅见于3,4型球粒陨石,因而它可作为由原顽火辉石淬冷形成的、末遭受后期热变质的典型结构。奇数倍0.9nm宽度单斜辉石片晶在吉林陨石(H5)、安龙陨石(H5)及东台陨石(LL6)中均有出现,它表明这些陨石的辉石都曾由原顽火辉石转变而成。 肇东陨石低钙辉石中相当频繁的相变以及高能量的奇数倍0.45nm层堆垛缺陷的存在,可能表明该陨石形成于退变质过程。 相似文献
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在球粒陨石群中顽火辉石球粒陨石具高度还原和独特的矿物学特征。顽火辉石球粒陨石几乎由纯的顽火辉石、金属(含有固溶体的硅)、硫化物及少量的斜长石、橄榄石和单斜辉石组成。硫化物矿物的组成相当复杂,普通球粒陨石(H、L及LL球粒陨石)的强亲石元素Ca、Cr、Ti、Mg、Mn、K在顽火辉石球粒陨石中呈硫化物相产出。最近我们在原有工作的 相似文献
9.
东南极格罗夫山主要由麻粒岩相高级变质岩和花岗岩类组成，其中变质岩以浅色和暗色含斜方辉石长英质片麻岩占主导地位，夹有少量镁铁质麻粒岩、变沉积岩和含方柱石钙硅酸盐岩。这些岩石一般都展示了平衡的矿物共生结构，但在镁铁质麻粒岩的单斜辉石中普遍发育斜方辉石(易变辉石)的出溶片晶。根据出溶辉石的重组分析获得麻粒岩相变质作用的峰期温度约为850℃，而浅色片麻岩中的石榴子石—斜方辉石—斜长石—石英组合给出的变质压力为0．61～0．67GPa。镁铁质麻粒岩中火成亚钙质普通辉石斑晶的保存表明格罗夫山地区可能只发育单一的泛非期高温麻粒岩相变质事件，岩石在高温变质之后经历了缓慢冷却过程，这主要归因于花岗质岩浆的板底垫托作用。 相似文献
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利用高分辨电子显微术研究了陨石和地幔岩中辉石的超微结构,观察并发现了多种畸变结构现象。清镇和吉林陨石顽火辉石中的斜顽辉石受冲击作用,SiO_3链发生弯曲甚至断裂并沿a轴方向错动36的距离,同时还有(100)扭转晶界形成,不同类型的SiO_3链相互转变形成了(001)90°和180°畴结构。单斜辉石中则有(100)层错和孪晶及其有关的缺陷。 相似文献
11.
P. P. K. Smith 《Contributions to Mineralogy and Petrology》1977,59(3):317-322
Ion-thinned samples of augite from four plutonic igneous rocks have been examined in the electron microscope at 100 kV. Lamellae less than 0.08 m thick were observed parallel to (010) in all four samples. Electron diffraction shows that the lamellae consist of clino-amphibole, space group I2/m, with crystallographic axes parallel to those of the augite. Analytical electron microscopy of the lamellae in one specimen shows that they are a hornblende. The amphibole lamellae have nucleated at the interface between the augite host and exsolution lamellae of orthopyroxene parallel to (100) of the augite. The interface between the amphibole lamellae and the augite is coherent.It is thought that the amphibole lamellae have formed by exsolution from the augite, implying the existence of finite solid solution between members of the pyroxene and amphibole groups of minerals. 相似文献
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A transmission electron microscope study of the microstructuresof olivine, augite and ortho-pyroxene in the Artfj?llet gabbroshows that the gabbro has been affected by two phases of deformation,exsolution and alteration. During the first phase, deformationand annealing of olivine led to the formation of elongated subgrains,with (100) subgrain boundaries consisting of regularly spacededge dislocations with [100] Burgers vectors. Localized strongerdeformation resulted in the development of mosaic subgrainswith (100) and (001) boundaries. Exsolution produced blebs and(100) lamellae of orthopyroxene in augite. Two types of blebsoccur, referred to as symplectitic augite and blebby augite.Symplectitic augite formed through discontinuous precipitation.The blebs in blebby augite are considered to have nucleatedat subgrain boundaries or dislocations in the augite. Blebs,melon pips and (100) lamellae of augite formed in orthopyroxene.These blebs and melon pips are thought to be due to nucleationat dislocations or to thickening of (100) lamellae at dislocations.Brown hornblende formed as blebs in augite and to a lesser extentorthopyroxene. This first event took place while the gabbrowas at a temperature of c. 900-1000 ?C and is thought to berelated to D2b, a regional flattening and thrusting event. Renewed exsolution in the pyroxenes occurred later, probablybefore the second subsolidus phase, -but its timing is poorlyconstrained. "100" lamellae of low-Ca clinopyroxene formed inaugite at an estimated temperature of c. 600 ?C. Thin (100)lamellae and Guinier-Preston zones were developed in orthopyroxene. During the second phase, deformation resulted mainly in cracks,along which hydrous fluids entered the gabbro, causing a variabledegree of metamorphism at a temperature of c. 500-550 ?C. Inolivine irregular dislocations of mixed edge-screw characterformed. Cr-spinel with an unknown phase, or magnetite with diopsideprecipitated in the olivine. Oxide minerals formed in the pyroxenesand brown hornblende: Cr-spinel in Cr-rich augite; rutile andilmenite in other augite, orthopyroxene and brown hornblende.The formation of these oxide minerals is thought to be due toexsolution of cations such as Ti and Cr, which these mineralsdo not tolerate in their structures at low temperatures, combinedwith oxidation in the case of magnetite in olivine. Alterationresulted in thin amphibole lamellae parallel to (010) in augite.This second subsolidus phase is correlated with the D3 regionaldeformation phase and the concomitant retrograde metamorphism. 相似文献
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Four different types of pyroxene found in a Beaver Bay ferrogabbro were analysed by microprobe. The crystallization sequence of pyroxene is augite-ferroaugite with exsolution lamellae of Ca-poor clinopyroxene → ferropigeonite with exsolution lamellae of augite → ferrohypersthene without exsolution lamellae+augite and ferroaugite without exsolution lamellae. The core of augite-ferroaugite with exsolution lamellae is cumulus pyroxene, whereas others, including the margin of augite-ferroaugite with lamellae, are interpreted to have crystallized from the intercumulus liquid. The sequence of crystallization of minerals from intercumulus liquid is different from that of minerals which have accumulated successively to the bottom and which were related to the fractionation of the whole layered series. The difference may be attributed to the different oxidation state of crystallization. 相似文献
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Exsolution lamellae of garnet in clinopyroxene and orthopyroxene porphyroclasts from garnet pyroxenites in the Moldanubian zone were studied to elucidate the pressure–temperature conditions of the exsolution process and to reconstruct the burial and exhumation path of ultramafic rocks in the Variscan orogen. The porphyroclasts occur in a fine-grained matrix with metamorphic fabrics, which consists of clinopyroxene and small amounts of garnet, orthopyroxene and amphibole. The clinopyroxene porphyroclasts contain garnet + orthopyroxene lamellae as well as ilmenite rods that have orientation parallel to (100) planes of the porphyroclasts. Orthopyroxene porphyroclasts host garnet and clinopyroxene lamellae, which show the same lattice preferred orientation. In both cases, lamellar orthopyroxene, clinopyroxene and garnet were partially replaced by secondary amphibole. Composition of exsolution phases and that of host pyroxene were reintegrated according to measured modal proportions and demonstrate that the primary pyroxene was enriched in Al and contained 8–11 mol.% Tschermak components. Conventional thermobarometry and thermodynamic modelling on the reintegrated pyroxene indicate that primary clinopyroxene and orthopyroxene megacrysts crystallized at 1300–1400 °C and 2.2–2.5 GPa. Unmixing and exsolution of garnet and a second pyroxene phase occurred in response to cooling and pressure increase before the peak pressure of 4.5–5.0 GPa was reached at ∼1100 °C. This scenario is consistent with a burial of hot upper-mantle ultramafics into a cold subcratonic environment and subsequent exhumation through 900 °C and 2.2–3.3 GPa, when the pyroxenites would have partially recrystallized during tectonic incorporation into eclogites and felsic granulites. 相似文献
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Symplectitic augite: evidence for discontinuous precipitation as an exsolution mechanism in Ca-rich clinopyroxene 总被引：2，自引：0，他引：2
Abstract Part of the augite in the Artfjället gabbro consists of symplectitic intergrowths between augite and blebs or lamellae of orthopyroxene. Mineral compositions are consistent with formation of these symplectites by exsolution of orthopyroxene from magmatic augite at a temperature of ca . 900–1000°C. The microstructures indicate that the exsolution mechanism is discontinuous precipitation, whereby the boundary of an augite grain sweeps through a neighbouring augite, leaving the symplectite in its wake. The formation of this symplectitic augite is catalysed by the presence of an intergranular water-rich fluid phase, which promotes grain boundary mobility. 相似文献
16.
A. C. Moore 《Australian Journal of Earth Sciences》2013,60(3):243-258
The orthopyroxenes of Gosse Pile, a layered ultramafic sequence within the Giles Complex of central Australia, show unusual exsolution features such as the development of ‘hour‐glass’ shapes by clinopyroxene lamellae, and also the exsolution of spinel and rutile. Both orthopyroxene and clinopyroxene have high R2O3 contents and their distribution coefficients for Mg and Fe are high (average KD = 0.88). Some, if not all, of these features are considered to indicate that the Gosse Pile rocks crystallized under high pressure. This interpretation also explains the predominance of orthopyroxene over olivine as an early cumulus phase. Estimated conditions during crystallization are 10–14 kilobars and between 1,200‐l,400°C. 相似文献
17.
V. I. FONAREV S. M. PILUGIN K. A. SAVKO M. A. NOVIKOVA 《Journal of Metamorphic Geology》2006,24(2):135-151
Archaean banded iron formation (BIF) of the Voronezh Crystalline Massif (VCM) contains coexisting clino‐ and orthopyroxenes with exsolution textures. The pyroxene in the VCM BIF is found in two generations, with only the first generation containing such textures. Clinopyroxene contains large (up to 5–10 μm) (0 0 1) orthopyroxene (Opx1L) lamellae in a host clinopyroxene (Cpx1H). This host Cpx, in turn, exsolves into thin (～1 μm) (1 0 0) lamellae of orthopyroxene (Opx2L) and clinopyroxene (Cpx2H). Orthopyroxene exhibits similar exsolution textures with large (up to 50 μm) (0 0 1) clinopyroxene (Cpx1L) lamellae developed in a host orthopyroxene (Opx1H). This clinopyroxene Cpx1L shows further exsolution of thin (1 0 0) Opx2LL lamellae and clinopyroxene (Cpx2LH). Point microprobe analysis, raster‐mode microprobe analysis, and microprobe element mapping of mineral grains with a large number of point analysis were used to determine the composition of the exsolution products and the primary chemistry of the coexisting clinopyroxene (CaO = 14.86–17.26 wt%) and pigeonite (CaO = 4.45–6.23 wt%). These pyroxenes crystallized during the peak of metamorphism, and application of the Lindsley geothermometer suggested that they formed at extremely high temperatures of about 1000 °C. Primary very dense CO2‐rich fluid inclusions (ρ = 1.152 g cm?3, Th = ?49.2 °C) were discovered for the first time in these BIF. With these data, the metamorphic pressure was estimated as 10–11 kbar (depth 36–40 km). Such ultrahigh temperature–high pressure (UHT–HP) conditions for the regional metamorphism of the Precambrian BIF have previously been reported only for Archaean meta‐ironstone from the Napier Complex (Enderby Land, Antarctica). They give an insight into the peak metamorphic conditions of the BIF of the VCM, their burial under thickened continental crust during this period of Earth evolution and suggest a more complicated multistage metamorphic and tectono‐thermal history for the region than has previously been postulated. 相似文献
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The exsolution phenomena of augite from Ferrogabbro 4430 of the Skaergaard Intrusion were examined in detail by single crystal X-ray diffraction and heating experiments to study the stepwise exsolution process. In the augite crystals, five different phases were detected: pigeonite (001), pigeonite (100), orthopyroxene (a), orthopyroxene (p) and a small amount of clinoamphibole. The two different pigeonites nearly share the corresponding (001) and (100) planes with the host. Orthopyroxene (a) and orthopyroxene (p) have (100) in common with the host and with exsolved pigeonite (001), respectively. Clinoamphibole was observed in the form of rather weak reflections in many crystals. It has (010) in common with the host.A large number of augite crystals exhibited a pigeonite (001) phase with curved, rotated reflections and diffuse streaks along the a* direction in (h0l) precession photographs. It appears that these streaks are related to orthopyroxene (p). Orthopyroxene (p) seems to be crystallized from pigeonite (001) by nucleation at (100) stacking fault planes (inverted pigeonite). Pigeonite (100) may be formed at growth ledges between augite host and exsolved orthopyroxene (a) at a later stage of exsolution to stabilize the boundaries.From the X-ray diffraction profiles and the results of the heating experiments, a possible exsolution sequence is suggested. Clinoamphibole appears to be a product of alteration at the latest stage of the exsolution process. It seems to be related to particular conditions of partial water pressure. 相似文献
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Lothar Schröpfer 《Physics and Chemistry of Minerals》1985,12(1):49-54
Diffuse streaks in diffraction patterns of synthetic pyroxene single crystals at elevated temperatures are used to determine which reactions are initiated and how they proceed. The samples investigated are a) a host orthopyroxene (Wo4En83Fs13) containing oriented pigeonite (Wo6En78Fs16) parallel to (100) and b) a pigeonite (Wo8En75Fs17). The maximum temperatures were 820° C and 1,015° C, respectively. No partial melting occurs at these temperatures, all reactions are in the subsolidus. In case a) augite is formed parallel to the (001) plane of pigeonite, but the augite is not exsolved by the pigeonite. This is proved by the absence of the obligatory streaks between corresponding reflections in highly resolved precession photographs. Instead, there are streaks from augite to the corresponding reflections of the host orthopyroxene. Example b) demonstrates that the temperature of the high-low transformation of pigeonite is very sensitive to the Ca content and clearly depends on the exsolution of augite. This augite is oriented parallel to (100) of pigeonite, not to (001). Both the high and the low pigeonite are present over a range of ～150° C, while the exsolution of augite continues. Simultaneously, orthopyroxene is also formed sharing (100) of pigeonite. There seems to be an indication that only low pigeonite inverts to orthopyroxene. 相似文献
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Monoclinic calcium-poor shear-transformation lamellae and calcium-rich exsolution lamellae occur parallel to (100) in orthopyroxene. The formation of both structures from an orthopyroxene host involves a shear on (100) parallel to [001], with additional cation exchange in the exsolution case. The shear transformation involves a macroscopic simple shear angle of 13.3° (shear strain of 0.236) and produces a specific a-axis orientation with respect to the sense of shear; we have found that this orientation dominates in exsolution lamellae in kinked orthopyroxene, where the sense of shear is known. In undeformed orthopyroxene, there is generally no preferred sense of orientation of the monoclinic a axes. We advance a specific model for exsolution involving nucleation and growth by shear transformation combined with cation exchange, thus circumventing the classical nucleation barrier and permitting exsolution at lower solute supersaturations. 相似文献