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Experimental modal metasomatism of a spinel lherzolite and the production of amphibole-bearing peridotite 总被引：6，自引：0，他引：6
Experiments have been done which simulate the modal metasomatism of spinel lherzolite by partial melts of the subducted slab. The experiments were designed so that the metasomatizing melts were generated during the experiments by partial melting of a slab analog (basaltic composition amphibolite). The melts are thought to be representative of hybridizing melts in that they are derived by high-pressure partial melting under conditions appropriate to a hot slab geotherm. During the experiments, the melts infiltrate into and metasomatize a model depleted peridotite. Chemical modifications to minerals in the peridotite are of the same nature and extent as those found in naturally metasomatized spinel lherzolites. Modal metasomatism produced pargasitic amphiboles in runs at 1.5 GPa and in all but the highest temperature run at 2.0 GPa. The amphiboles are indistinguishable from amphiboles found in amphibole-bearing peridotites from supra-subduction zone environments. Systematic variations in amphibole composition suggest that the melt infiltration process in the experiments involved continuous modification of the composition of the infiltrating melt as observed around inferred quenched melt (i.c., amphibolite or amphibolite/clinopyroxenite) veins in xenoliths and massif peridotites. The compositions of the initial and final mineral phases in the experiments and those of the metasomatizing melts are used to derive amphibole formation reactions at 1.5 and 2.0 GPa that are similar in form to those inferred in studies of natural amphibole-bearing peridotites. The metasomatism reactions show that the extent of amphibole formation in peridotite at 1.5 and 2.0 GPa will, in general, be limited by clinopyroxene and spinel abundance. 相似文献
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Amphiboles are the main mafic minerals in most metaluminous to peralkaline alkali-feldspar granites and syenites, and they usually preserve an important record of the compositional evolution of the melts from which they crystallize. In the alkaline association of the Serra da Graciosa A-type Granites and Syenites (southern Brazil), amphibole compositions span a large range, including calcic, sodic–calcic, and sodic amphiboles. Calcic amphiboles are typically observed in the metaluminous rocks, while sodic amphiboles are characteristic of the more strongly peralkaline rocks; sodic–calcic amphiboles are found in intermediate varieties. Compositional variations record the differentiation trends within two petrographic series of the alkaline association. The overall evolution of amphibole compositions is similar in both: they reveal a progressive increase in Na and Fe3+ with differentiation (increase in alkalinity of the magmas), a characteristic shared by undersaturated peralkaline (or agpaitic) differentiation trends. In detail, however, the evolutions of the amphibole compositions in the two series are distinct. In Alkaline series 1, the cores of the crystals form a continuum from calcic to sodic compositions, with the exception of a small compositional gap within the sodic–calcic amphiboles. The rims, however, show compositions that diverge from this main trend; this divergence results from increasing amounts of the oxy-amphibole component, and reflects more oxidizing conditions at the final stages of magmatic crystallization. In Alkaline series 2, these oxidation trends are much more subtle and a reverse trend is observed in the sodic amphiboles. Sodic–calcic amphiboles are in several cases replaced by intergrowths of post-magmatic sodic amphibole and Al-poor (“tetrasilicic”) biotite. 相似文献
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High-temperature contact metamorphism at the contact of an alpine-typeultramafic intrusion is described. Permian spilitic volcanicsand tuffs within a zone about 750 yards in width are convertedto amphibolites and pyroxene hornfelses. In the amphibolitesthe colour of the amphibole changes from green to brown-greenand finally to deep brown at the contact. Two-pyroxene hornfelsesare developed at the contact, together with wollastonite, grossular,and hydrogrossular. Chemical changes in the amphiboles acrossthe contact aureole are: increase in (Na+ K) and (Al(6) + Fe+3+Ti) approaching the contact, and progressive decrease in thewater content. Similar chemical changes are noted in a lensof country rock included within the main ultramafic intrusion. It is considered that original high-temperature-contact effectsare often obscured by later Ca-metasomatism during serpentinizationof the ultramafic rocks, or by later tectonic deformation ofthe rocks which may involve movement of the ultramafic mass,as a relatively cold solid intrusion, to higher levels. 相似文献
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铜官山岩体矿物学-矿物化学特征：岩浆结晶动力学意义 总被引：1，自引：0，他引：1
本文对皖南官山岩体开展详细地显微镜观察鉴定,利用电子探针和LA-ICP-MS技术对岩浆岩典型矿物斜长石、角闪石和榍石进行了主量和微量元素测定。显微镜鉴定表明,铜官山岩体中存在着大量的岩浆不平衡结构：如斜长石和角闪石嵌晶结构以及针状磷灰石等。这些现象的存在表明铜官山岩体在形成过程中曾发生过一次或多次岩浆混合作用。电子探针分析结果显示,斜长石的成分环带是震荡环带,而大尺度的震荡环带可能代表了大规模的岩浆混合作用;角闪石成分TiO2-Al2O3图解、CaO/NaO2-Al2O3/TiO2图解和Mg-(Fe2++Fe3+)- LiNaKCa角闪石成因矿物族三角图解指示铜官山岩体中角闪石很可能为壳-幔混合成因。LA-ICP-MS技术对主要造岩矿物的微量和稀土元素分析表明,角闪石很可能为幔源或壳幔混合源,斜长石可能为不同分异程度岩浆的混合形成。本研究比较明确地反映了铜官山岩体的形成过程中岩浆来源和结晶动力学过程,即壳幔源区的混合交代作用,与前人通过元素-同位素手段获得的信息比较吻合。 相似文献
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The Serra da Graciosa Granites and Syenites comprise five distinct plutons in the Brasiliano/Pan-African Graciosa A-type Province, southern Brazil. Six petrographic series can be identified in these plutons: (1) Alkaline series 1, composed of amphibole-bearing alkali feldspar syenites with varied mafic mineralogy and quartz contents, from alkali feldspar syenites with calcic amphibole, clinopyroxene, olivine and allanite to alkali feldspar quartz syenites with sodic–calcic amphibole and chevkinite–perrierite and to alkali feldspar granites with sodic amphibole; (2) Alkaline series 2, characterized by amphibole-bearing alkali feldspar granites, with limited modal variations but amphibole compositions also varying from calcic to sodic; (3) Alkaline series 3, of limited occurrence, which includes alkali feldspar syenites with olivine and clinopyroxene and no amphibole; (4) Aluminous series 1, of widespread occurrence, with various petrographic facies of biotite granites with amphibole; (5) Aluminous series 2, characterized by alkali feldspar granites with biotite and only minor amphibole; (6) Monzodiorites, typically with biotite, calcic amphibole and augitic clinopyroxene, partially mingled with granitic magmas. The mafic minerals present are, in general, Fe-rich with correspondingly low Mg and Al contents. In Alkaline series 1, amphiboles crystallized in progressively more oxidizing and alkaline conditions, while in Alkaline series 2, the initial conditions were somewhat more oxidizing and shifted to reducing in the final stages. In Aluminous series 1 and Aluminous series 2, amphiboles are calcic and comparatively homogeneous. The amphiboles in the monzodioritic rocks, while also homogeneous, are more Mg-rich and show compositions quite distinct from the calcic varieties in the other associations, and this is also the case for clinopyroxene. Mg# in biotite decreases from the monzodioritic rocks to Aluminous series 1 and further to Aluminous series 2. Contrasting evolution of the various associations suggests that several coeval magmatic series are present in the Serra da Graciosa granites. 相似文献
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In the Myanmar jadeitite area of Pharkan, amphibole felses occur between jadeitites and serpentinized dunites. These so-called amphibole fels boundary zones were studied optically and by electron microprobe, and found to include the six amphibole species magnesiokatophorite (Mg-kat), nyböite (Nyb), eckermannite (Eck), glaucophane (Gln), richterite (Rich) and winchite (Win). In most samples, the two main amphibole species Mg-kat and Eck coexist with amphiboles containing variable amounts of components of the remaining four species, as well as with the clinopyroxenes jadeite (Jd), omphacite (Omp) and kosmochlor (Ko). However, Mg-kat, Nyb and Eck are also present as separate phases as well as in zoned porphyroblasts with Mg-kat in the core, Nyb in the inner rims, and Eck in the outer rims. The analytical data on such zoned amphiboles reveal that the chemistry changes from core to inner rim by virtue of the substitution NaAlCa -1Mg -1 (glaucophane vector), and from the inner to the outer rim along MgSiAl -1Al -1 (tschermak vector). The overall substitution from core to outer rim is, therefore, along NaSiCa -1Al -1 (plagioclase vector). Based on the Si content, three groups can be distinguished within Eck: Eck coexisting with Nyb has low Si contents of <7.6 a.p.f.u., Eck rimming Nyb has higher Si contents of 7.6–8.0 a.p.f.u., and fine-grained Eck in the matrix has Si contents of 7.9–8.0 a.p.f.u. Plotting the amphibole analyses in a compositional volume with the axes (Na+K) in A, Na in M(4), and tetrahedral Si shows that three groups of amphibole compositions can be distinguished, one being subdivided into three subsets. Group A contains Rich and Mg-kat, B comprises of Win and Gln, whereas the subsets C can be defined as follows: C1: high-Na amphiboles with low tetrahedral Si; these are mainly amphiboles from the Eck field but overlap with the two fields of Gln and Win; C2: high-Na and low-Si Ecks overlapping to high-Si Nybs; this group is midway between Eck and Nyb end members; C3: high-Na Mg-kats. Textural observations indicate three stages of sodic and sodic–calcic amphibole growth: stage 1 are amphiboles of group A (Mg-kat+Rich), stage 2 are amphiboles of group C2 (Nyb+Eck with Si<7.6 a.p.f.u.), and stage 3 are amphiboles of groups C1 and B (Eck with Si>7.6 a.p.f.u., +Gln+Win). Based on the subdivision into the compositional groups A–C, the only hint to a miscibility gap is provided by the large gap in the (Na+K) content on the A site which may point to a possible solvus in the system Eck–Win. Overall, the amphiboles investigated here show discontinuities in their growth compositions, rather than miscibility gaps. Textural observations suggest amphibole formation during fluid infiltration in the contact zone between the jadeitite bodies and the surrounding peridotite under high-pressure conditions (>1.0 GPa) and rather low temperatures of about 250–370 °C. Based on compositional trends within the amphiboles as well as phase-equilibrium constraints between amphibole and coexisting pyroxene solid solutions, the chemical composition of zoned amphibole porphyroblasts indicates two growth episodes—increasing pressures from stage 1 to stage 2 lead to the formation of Nyb from Mg-kat, and subsequently decreasing pressures lead to the formation of stage 3 Eck from Rich. 相似文献
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角闪岩作为中下地壳的重要物质组成,其岩石和矿物的变形行为及力学强度表现直接制约着中下地壳力学属性与状态,因此开展对其中重要组成矿物角闪石的变形行为和地震波各向异性研究,具有重要地质意义.以红河-哀牢山剪切带中出露的变形角闪岩中角闪石为研究对象,其中显微构造分析表明,变形角闪岩分别呈现出粗、中粒条带状糜棱岩和细粒条带状超糜棱岩.分别对这3种变形岩石中的角闪石矿物颗粒进行了EBSD晶格优选定向分析和地震波各向异性计算,结果表明3种变形角闪岩中的角闪石呈现出不同取向及典型晶质塑性变形特征,(100)[001]主要滑移系发育,同时发育不同程度的(010)[001]和(110)[001]次级滑移系.我们认为在剪切变形过程中,角闪石双晶滑移和解理面滑移共同作用致使角闪石细粒化.从粗粒到细粒条带状角闪石,随着角闪石颗粒粒度减小,角闪石中AV_p也有逐渐变小的趋势,表明角闪石变形行为、形态优选定向及晶格优选定向共同影响着地震波各向异性. 相似文献
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Lescano Leticia Marfil Silvina Maiza Pedro Sfragulla Jorge Bonalumi Aldo 《Environmental Earth Sciences》2013,70(4):1809-1821
Vermiculites with impurities of amphibole, a dry fine residue and calcined materials from three deposits in the province of Córdoba, Argentina, were studied. From a commercial perspective, amphiboles are considered as “asbestos”, a group of silicate minerals with strong and flexible fibres that are heat resistant and chemically inert, and thus well suited for heat insulation. These fibrous particles have provoked controversies about the toxicity impact on human health and the development of diseases such as mesothelioma, asbestosis or lung cancer. Their commercialization and exploitation are currently prohibited. The sampled minerals were identified with a petrographic microscope, chemical analyses, SEM and XRD. It was concluded that amphibole minerals are present in all the deposits studied and in every phase of plant production, but not all of them have asbestiform characteristics. 相似文献
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Amphibole-bearing gneiss fragments are common in the impact breccias of the Xiuyan crater, China. Three kinds of amphibole-bearing gneiss fragments with different shock-metamorphic levels have been identified. Shock-metamorphic features of amphiboles in these gneisses were investigated in situ by optical microscope, electron microprobe, Raman spectroscopy, and X-ray diffraction. Amphiboles in the weakly shocked gneiss (shock pressure less than 10 GPa) basically remain intact. Amphiboles in the moderately shocked gneiss (shock pressure range between 35 and 45 GPa) show strong deformation, reduced optical interference color, and partial loss of OH?. In the strongly shocked gneiss (shock pressure above 50 GPa), amphiboles are completely melted and dendritic pyroxenes crystallize from the melt. The formation of dendritic pyroxenes shows nearly complete loss of water in the amphibole melt at shock-induced high temperature above 1,500 °C. The occurrence of both diopside and pigeonite dendrites crystallized in the same amphibole melt shows inhomogenous melt composition and rapid cooling of the melt. 相似文献
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WANG Qiang ZHAO Zhenhua QIU Jiaxiang WANG Renjing XU Jifeng Guangzhou Institute of Geochemistry Chinese Academy of Sciences Guangzhou P.R.C China University of Geosciences Wuhan P.R.C 《Continental Dynamics》2001,(2)
l. IntroductionFluid, especially water is very important to thefOrmation of I--type and S-type granitic magmas,evel1 under high temperature (for example, l000 "C).Some researches suggest that dehydration melting ofhydrous minerals (muscovite, biotite and amphiboIe)under high temperature is the main mechanism ofdeep crustal anatexis (Clemens et al., l987, Skierlie,l993, WoIf et al., l995, Johannes, l996), and themain modeIs of the formation of granitic magmas inthe orogenic belt. Howevef, t… 相似文献
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The Tonglvshan deposit is the largest Cu–Fe (Au) skarn deposit in the Edong district, which is located in the westernmost part of the Middle and Lower Yangtze River metallogenic belt, China. In this study, we performed a detailed in situ analysis of major and trace elements in amphiboles from the ore-related Tonglvshan quartz monzodiorite porphyry using electron microprobe (EMPA) analysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Two distinct populations of amphiboles, which can be distinguished by their aluminum content, are found in the quartz monzodiorite porphyry. The low-aluminum (Low-Al) amphiboles are subhedral or anhedral and formed at 46.3–73.5 MPa and 713–763 °C. In contrast, the high-aluminum (High-Al) amphiboles are euhedral and formed at 88–165 MPa and 778–854 °C. Some euhedral amphiboles are partially or completely replaced by Low-Al amphibole. The compositions of parental melts in equilibrium with the High-Al amphibole (Melt 1) and Low-Al amphibole (Melt 2) were computed by applying solid/liquid partition coefficients. This modeling shows that magma in equilibrium with High-Al amphibole (Melt 1) underwent 40% fractional crystallization of amphibole, plagioclase and apatite at a depth of ~5 km to evolve to magma in equilibrium with Low-Al amphibole (Melt 2). Copper enrichment occurred in the magma after undergoing fractional crystallization. The magma had a high oxygen fugacity, increasing from NNO + 1 (Melt 1) through NNO + 2 to HM (Melt 2), which could have prevented the loss of Cu (and possibly Au) to sulfide minerals during crystallization. Finally, the evolved magma intruded to shallower depths, where it presumably exsolved aqueous ore-forming fluids. Therefore, the large Cu–Fe–Au reserves of the Tonglvshan deposit can likely be attributed to a combination of controlling factors, including high oxygen fugacity, fractional crystallization, fluid exsolution, and a shallow emplacement depth. 相似文献
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Using the geologic setting of talc deposits as an indicator of amphibole asbestos content 总被引：1，自引：0，他引：1
This study examined commercial talc deposits in the U.S. and their amphibole-asbestos content. The study found that the talc-forming environment directly influenced the amphibole and amphibole-asbestos content of the talc deposit. Large talc districts in the U.S. have mined hydrothermal talcs that replaced dolostone. Hydrothermal talcs, created by siliceous fluids heated by magmas at depth, consistently lack amphiboles as accessory minerals. In contrast, mineable talc deposits that formed by contact or regional metamorphism consistently contain amphiboles, locally as asbestiform varieties. Examples of contact metamorphic deposits occur in Death Valley, California; these talc-tremolite deposits contain accessory amphibole-asbestos. Talc bodies formed by regional metamorphism always contain amphiboles, which display a variety of compositions and habits, including asbestiform. Some industrial mineral deposits are under scrutiny as potential sources of accessory asbestos minerals. Recognizing consistent relations between the talc-forming environment and amphibole-asbestos content may be used in prioritizing remediation or monitoring of abandoned and active talc mines. 相似文献
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Philippa M. Black 《Contributions to Mineralogy and Petrology》1973,39(1):55-64
The chemistry and phase relations of calcic and sodic amphiboles in the Ouégoa blueschists are investigated. The first appearance of sodic amphiboles is controlled by bulkrock chemistry. Sodic amphibole appears first in weakly-metamorphosed pumpellyite metabasalts prior to the crystallization of lawsonite but does not crystallize in pelitic schists until the middle of the lawsonite zone; sodic amphibole continues as an apparently stable phase in rocks of all bulk compositions into, and throughout, the highest-grade rocks in the district. Calcic amphibole is widespread in metabasalts of the lawsonite and epidote zones and also occurs in metasediments of appropriate composition. Coexisting pairs of calcic and sodic amphiboles are common in metabasalts but they have also been found in some metasediments. A grunerite-riebeckite pair is described.Electron-probe analyses of 120 amphiboles from representative rock-types are presented in graphical form. Sodic amphiboles show an increased Mg/(Mg+Fe) ratio with increasing metamorphic grade. Sodic amphiboles in pelitic schists are ferroglaucophane in the lawsonite zone and crossite and glaucophane in the epidote zone. Sodic amphiboles in metabasalts are iron-rich crossites in weakly-metamorphosed rocks and more-magnesian crossites and glaucophanes in the lawsonite and epidote zones. The abrupt increase in Mg/(Mg+Fe) ratio in sodic amphiboles at the epidote isograd is attributed to the crystallization of epidote and almandine which take the place of lawsonite and spessartine of the lawsonite zone. Calcic amphiboles are fibrous actinolites in the lawsonite zone and grade with increasing Al and Na/Ca ratio into prismatic blue-green hornblendes (barroisites) in the upper epidote zone. In calcic amphiboles, increasing metamorphic grade effects the coupled substitution of (Na+Al) for (Ca+Mg) and a small increases in Fe/Mg ratio; octahedrally and tetrahedrally coordinated Al increases in an approximately 11 ratio. Both the calcic and the sodic amphiboles show an increase in A-site occupancy with increasing metamorphic grade. In two-amphibole assemblages Ti, Mn and K are concentrated in the calcic amphibole.The textural and chemical relations between coexisting calcic and sodic amphiboles are discussed. If the calcic and sodic amphiboles are an equilibrium pair then the data collected from the Ouégoa amphiboles gives a picture of a very asymmetric solvus in the system glaucophane-actinolite-hornblende, i.e. steep-sided to glaucophane and with a gentle slope to the calcic amphibole field; there is no indication of any termination of the solvus under the pressure-temperature conditions of crystallization of the Ouégoa schists. 相似文献
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河北武安坦岭多斑斜长斑岩中基质矿物特征及其研究意义 总被引：2，自引：0，他引：2
河北武安坦岭斜长斑岩具有多斑斑状结构,基质为显微晶质结构。岩相学观察表明,斜长石斑晶有一个宽广的核部和一个宽度可变的条纹长石反应边,个别核部包含有角闪石、黑云母等矿物。基质矿物主要由蓝透闪石、条纹长石(An0Ab8.4Or91.5～An0.1Ab57.3Or42.6)、石英、钾长石(An0.3Ab5.9Or93.7～An0.3Ab4.7Or95.2)、钠长石(An0.2Ab98.3Or1.5～An0.1Ab99.2Or0.7)、磁铁矿、赤铁矿、钛铁矿、磷灰石、榍石和锆石等11种矿物组成。角闪石温压计计算结果得出,基质角闪石核部的结晶压力高于边部,核部为34.05 MPa,对应的结晶温度为660.35℃,结晶深度为1.29km;边部的结晶压力为24.32MPa,结晶温度为598.32℃,结晶深度为0.92km;而斜长石斑晶中的角闪石形成时压力为159.51～178.19MPa,温度为817.68～819.79℃,对应的形成深度为6.03～6.73km。基质角闪石在Al2O3-TiO2图上落在壳源区,而斑晶中的角闪石和黑云母都落在壳幔混合区。斜长石、条纹长石、磁铁矿和磷灰石的微量和稀土元素测试数据显示,其都具有相对富集LILE、亏损HFSE的特点,暗示了基质矿物的形成有流体参与。ICT三维扫描结果显示,斜长斑岩基质中的孔隙体积含量约为3.428%,铁质体积含量为4.371%,且铁氧化物和孔隙具弱连通性。通过讨论分析,笔者得出:(1)坦岭斜长斑岩中斜长石斑晶具有明显的交代结构,且晶体本身没有明显熔蚀现象,这些特征表明大量的斜长石斑晶快速上升,即"冻结岩浆房"的活化机制与流体密切相关;(2)斜长斑岩中基质矿物有十一种,且矿物类型复杂,不符合平衡系统矿物相律,应属于流体晶矿物组合;(3)坦岭斜长斑岩的基质"岩浆"可能是一种富Fe、K、P、Si、Na等元素的熔体-流体流;(4)多斑斜长斑岩的形成经历了(1)深度6～7km的深部岩浆房形成斜长石堆晶→(2)富Fe、K、P、Si、Na等元素的熔体-流体流加入深部岩浆房,冻结岩浆房活化→(3)由于流体超压,含大量斜长石斑晶的熔体-流体在地壳浅部(0.9～1.2km)呈小岩株状或岩脉状就位。多斑斜长斑岩为深部找矿提供了有力的线索。 相似文献
17.
高温高压实验作为地球科学研究的重要方向之一,通过模拟地球深部的温度和压力条件,了解地球深部物质的物理化学性质、地球内部结构和动力学演化。角闪石属于双链硅酸盐矿物,为地幔岩石圈的重要组成,广泛分布在海洋地壳、俯冲板块、变质岩和火成岩中。作为俯冲带的重要含水矿物,角闪石的广泛分布和高温高压下的脱水对于理解俯冲带水含量以及水迁移具有重要作用,同时在俯冲带的地震活动、高电导率异常、地震波速异常和岩浆活动中扮演重要角色。在过去的近百年时间里,国内外学者对角闪石高温高压物理化学性质进行了大量的研究。角闪石具有非常复杂的元素组成和结构特征,由此也导致了不同角闪石物理化学性质存在显著不同,包括脱水与脱羟基反应中元素迁移的差异、角闪石形成与分解过程中碱性元素(K+Na)和H2O含量对热稳定的影响、不同空间群结构下的高压结构相变、原位条件下不同结晶方向的电导率异常、不同结晶学优选方位(CPO)下的波速异常等。已有的研究对于角闪石的物理化学性质以及其在俯冲带中发挥的作用有了比较清楚的认识,但仍然有许多问题需要进一步研究,如角闪石的高压脱水动力学、热物性和变形机制等。 相似文献
18.
L. D. Minnigh 《Journal of Structural Geology》1979,1(4):275-282
A detailed meso- and microscopic structural investigation of a laminated manganiferous meta-chert from the Western Italian Alps has resulted in the recognition of five deformation phases. During the third phase large subhorizontal shear movements took place, resulting in reorientation of pre-existing structures and sheath-fold formation. This was accompanied by a decrease in pressure, reflected by the zoning of blue-amphiboles and by microboudinage and the formation of stretching cracks in minerals. The orientation of amphiboles, together with some evidence from quartz c-axis fabrics suggest that the deformation took place by simple shear. During the late stages of sheath-fold formation the deformation became non-rotational. 相似文献
19.
Peter Mazzone Dion C. Stewart John M. Hughes 《Contributions to Mineralogy and Petrology》1987,97(2):292-296
Several petrologic experiments have demonstrated that in igneous and metamorphic reactions amphibole minerals can break down by a subsolidus dehydration reaction, but evidence for the reaction in natural rocks has been lacking. Evidence for the breakdown of an edenite-pargasite amphibole by a subsolidus dehydration reaction has now been found in an andesite flow from Garner Mountain, southern Cascase Range. The andesite contains one modal percent of crystal clots formed of crystallites of opx, cpx, plag, K-spar, opaque and quartz. The crystal clots retain the original amphibole morphology and intra-clot pyroxenes are aligned with crystallographic c parallel to c in the amphibole precursor; these conditions would not be duplicated by a melting reaction.Microprobe analyses of the bulk clot and the intra-clot minerals suggest the solid-state reaction: 100 amph+10 SiO2=>55 cpx+33 plag+22 opx+ 1 opq+1 ksparPyroxene thermometry of the andesite groundmass pyroxenes and the intra-clot pyroxenes demonstrates that the amphibole dehydration reaction occurred in the xenocrystic amphiboles as a result of heating by the near-solidus andesite magma. 相似文献
20.
A corundum-bearing mafic rock in the Horoman Peridotite Complex, Japan, was derived from upper mantle conditions to lower crustal conditions with surrounding peridotites. The amphiboles found in the rock are classified into 3 types: (1) as interstitial and/or poikilitic grains (Green amphibole), (2) as a constituent mineral of symplectitic mineral aggregates with aluminous spinel at grain boundary between olivine and plagioclase (Symplectite amphibole) and (3) as film-shaped thin grains, usually less than 10 μm in width, at grain boundary between olivine and clinopyroxene (Film-shaped amphibole). The Film-shaped amphibole is rarely associated with orthopyroxene extremely low in Al2O3, Cr2O3 and CaO (Low-Al OPX). These minerals were formed by infiltration of SiO2- and volatile-rich fluids along grain boundaries after the rock was recrystallized at olivine-plagioclase stability conditions, i.e. the late stage of the exhumation of the Horoman Complex.
Chondrite-normalized rare earth element patterns and primitive mantle-normalized trace-element patterns of the Green amphibole and clinopyroxene are characterized by LREE-depleted patterns with Eu positive and negative anomalies of Zr and Hf. These geochemical characteristics of the constituent minerals were inherited from original whole-rock compositions through a reaction involving both pre-existing clinopyroxene and plagioclase. We propose that the fluids were originally rich in a SiO2 component but depleted in trace-elements. Dehydration of the surrounding metamorphic rocks in the Hidaka metamorphic belt, probably related to intrusion of hot peridotite body into the Hidaka crust, is a plausible origin for the fluids. 相似文献