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1.
大别山榴辉岩富流体退变质阶段的白色云母 总被引：1，自引：0，他引：1
大别山榴辉岩的退变质过程可分为贫流体、弱流体和富流体3个阶段。贫流体阶段的主要作用是榴辉岩造岩矿物的重结晶、同质多象转变和固溶体出溶;弱流体阶段有少量流体参与,并且其压力、温度较高,形成的白色云母主要为多硅白云母;富流体阶段在大量流体参与下,形成大量的低压含水矿物,其中包括多种白色云母。富流体阶段早期的白色云母主要为多硅白云母,其Si原子数介于6．5pfu和7．2pfu之间;晚期白色云母成分复杂,包括钠云母、白云母和珍珠云母。黑云母是退变质作用最晚期形成的云母。退变质云母具环带结构,其内带为钠云母,中带为白云母和珍珠云母的交生体,外带为黑云母。 相似文献
2.
桂北元宝山花岗岩岩体内发育一条长约25～30 km,宽约8～10 km,呈NNE向延伸的韧性剪切带,代表性的构造岩类型为长英质糜棱岩,其主要矿物都发生了不同程度的脆性–韧性变形。本文对韧性剪切带中代表性糜棱岩样品进行了细致的显微观察,同时利用电子探针技术对糜棱岩中不同产状的黑云母、白云母和绿泥石进行了详细的成分分析。在此基础上采用绿泥石成分地质温度计、白云母–绿泥石地质温度计、白云母/黑云母Ti温度计,结合多硅白云母Si压力计展开变质–变形温压研究,以期合理解译糜棱岩化过程中变形作用对云母类矿物中放射性成因氩(40Ar*)保存能力的影响以及这些云母矿物的40Ar/39Ar定年结果是代表冷却年龄还是变形年龄,为进一步探讨该地区在加里东期及其后的构造–热演化历史打下良好基础。显微镜下观察显示,糜棱岩中的云母类矿物主要以大颗粒残斑和细粒基质两种形式存在,其产状和粒径存在着较大的区别。电子探针成分分析结果显示,残斑云母与基质中新生或重结晶云母在化学成分上具有较大差异:与基质中的新生或重结晶白云母相比,残斑白... 相似文献
3.
大别山榴辉岩退变质多硅白云母及地压计可用性讨论 总被引：3，自引：0，他引：3
大别山榴辉岩中的多硅白云母可以分成三个世代；形成于榴辉岩相进变质阶段的原生Phel、榴辉岩相退变制裁晚阶段的Phe2和角闪岩相至绿片岩相退变质阶段的Phe3。电子探针测得，超高压下形成的Phel，其Si和Fe^2 Mg值出乎意料地低于低压下形成的Phe3，这与多硅白云母地压计的基本原理，即多硅白云i和Fe^2 Mg含量与其形成压力成正比这一原理产生了矛盾，产生这种矛盾的可能原因是，多硅白云母的成分除了取决于压力因素以外，还取决于主岩的铝-硅比值、Fe^2 Mg含量、氧逸度的变化、流体的存在等因素，因此，利用多硅白云母的硅含量来探讨退变质过程压力时必须加倍小心。 相似文献
4.
大别山榴辉岩退变质多硅白云母及地 总被引：4，自引：1，他引：4
大别山榴辉岩中的多硅白云母可以分成三个世代形成于榴辉岩相进变质阶段的原生Phe1、榴辉岩相退变质晚阶段的Phe2和角闪岩相至绿片岩相退变质阶段的Phe3.电子探针测得,超高压下形成的Phe1,其Si和Fe2++Mg值出乎意料地低于低压下形成的Phe3,这与多硅白云母地压计的基本原理,即多硅白云母的Si和Fe2++Mg含量与其形成压力成正比这一原理产生了矛盾.产生这种矛盾的可能原因是,多硅白云母的成分除了取决于压力因素以外,还取决于主岩的铝-硅比值、Fe2++Mg含量、氧逸度的变化、流体的存在等因素.因此,利用多硅白云母的硅含量来探讨退变质过程压力时必须加倍小心. 相似文献
5.
晓天—磨子潭断裂糜棱岩化过程的温压环境及其指示意义 总被引：1，自引：0，他引：1
晓天-磨子潭断裂带是大别造山带北部一条重要的断裂.探针分析表明,断裂带内糜棱岩中基质白云母每单位分子平均硅原子数大于3.3 p.f.u.,为典型的高压多硅白云母.利用Massonne多硅白云母压力计获得基质多硅白云母指示的平均压力值为1.0 GPa,由此计算断裂带变形深度为35 km左右.矿物变形记录的糜棱岩变形温度在600～700 ℃之间,对应的地温梯度为16.0～22.5 ℃/km.认为晓天-磨子潭断裂记录了高压-超高压岩石下地壳的折返事件,为同造山折返边界.糜棱岩中残斑白云母的探针分析结果与基质白云母相似,图解计算的压力与基质白云母相当,指示了变形的压力环境为残斑白云母生长的压力环境的极小值,推测糜棱岩原岩很可能经历了糜棱岩化之前的更高压力环境的变质作用. 相似文献
6.
拉萨地块松多榴辉岩主要矿物组合为石榴子石、绿辉石、角闪石、多硅白云母、绿帘石、金红石。石榴子石环带不明显,核部成分均一,从核部到边部,镁铝榴石和钙铝榴石含量降低,可能分别记录了榴辉岩峰期及退变质过程信息。绿辉石显示微弱的成分环带,硬玉含量从核部到边部略有升高,部分绿辉石边部发育韭闪石退变质边,反映了在减压过程中外来流体进入体系的过程。多硅白云母具有高的Si含量(3.5~3.6),其中石榴石包体中的多硅白云母相对基质中的白云母有更高的Si值。本文利用Thermocalc变质相平衡模拟软件,结合详细岩相学观察,在NCKMn FMASHTO体系下,模拟松多含多硅白云母榴辉岩的变质演化过程。其中,榴辉岩峰期矿物组合为g+o+law+phn+ru,石榴石核部最大镁铝榴石值和石榴子石包体中多硅白云母最大Si值确定的榴辉岩峰期温压条件约为620℃,32×105Pa,榴辉岩经历了近等温降压的退变质过程。相平衡模拟结果表明拉萨地块松多榴辉岩经历了超高压变质作用过程,并经历了相对快速的折返过程到中部地壳层次。 相似文献
7.
昌宁-孟连杂岩带澜沧岩群的岩石学、地球化学和变质演化及其对古特提斯构造演化的启示 总被引：3，自引：2，他引：1
云南三江地区昌宁-孟连杂岩带中的澜沧岩群内出露多种类型变沉积岩,主要包括含十字蓝晶石榴云母片岩、石榴云母片岩、硬绿泥石白云母片岩和绿泥蓝闪钠长片岩等。系统的岩相学观察、矿物化学和相平衡模拟研究结果表明,不同类型的变沉积岩保存了不同的变质演化历史。含十字蓝晶石榴云母片岩记录了自中温榴辉岩相降温降压至角闪岩相的退变质过程,峰期矿物组合为石榴子石+蓝晶石+多硅白云母+硬玉,变质温压条件为600～750℃和19～30kbar。通过石榴子石的X_(Prp)和X_(Grs),和多硅白云母的Si值限定石榴云母片岩的峰期矿物组合包括石榴子石+多硅白云母+绿辉石+硬柱石+钠云母,峰期温压条件为430～475℃和17～19.5kbar。硬绿泥石白云母片岩矿物组成包括硬绿泥石+多硅白云母+钠云母,然而峰期矿物组合则以多硅白云母+钠云母+纤柱石为特征,通过多硅白云母的Si值限定峰期温压条件约为300～330℃和17～19kbar。石榴云母片岩和硬绿泥石白云母片岩较为一致地记录了从峰期硬柱石蓝片岩相升温降压至绿帘石蓝片岩相的退变质过程。绿泥蓝闪钠长片岩主要通过变质反应和成因矿物学特征大致估算其温压条件约为430～520℃和9～11kbar。岩石地球化学性质研究结果表明,这些变沉积岩的平均化学成分与大陆岛弧、活动大陆边缘和上地壳沉积物成分较为接近,其原岩主要为一套成熟度较差的泥砂质岩类和少量的中基性火山岩。该泥砂质原岩的沉积物源以中酸性岩浆岩为主,存在不同程度古老沉积物的加入。构造判别图解表明,研究区样品主要形成于大陆岛弧或活动大陆边缘的构造背景。变质作用特征和原岩地球化学属性综合分析表明,昌宁-孟连杂岩带内大面积分布的澜沧岩群均发生不同程度的俯冲-消减过程,表现出多样的变质演化P-T轨迹的特征,表明澜沧岩群经历了多期/多阶段复杂的构造演化历史。 相似文献
8.
根据矿物成分及其结构演变,将大别山榴辉岩的退变质过程分为三个阶段:贫流体阶段、弱流体阶段和富流体阶段。贫流体阶段发生于榴辉岩相环境中,其主要作用是柯石英-石英和文石- 方解石等同质多象转变、石榴子石和绿辉石等的重结晶,以及绿辉石中硬玉和钠长石的固溶体出溶等。弱流体阶段发生于榴辉岩相退变质的晚期,含水矿物闪石、绿帘石和云母,以及钠长石等低压矿物大量形成之前,其标志是蓝晶石变斑晶和金红石脉的形成,以及浸染状金红石的富集成矿。富流体阶段始于低级角闪岩相退变质环境,并可能一直持续到近地表处。该阶段以出现大量含水和挥发份的矿物(如闪石、绿帘石、多硅白云母、钠云母、黑云母、磷灰石和碳酸盐等)为特征。围绕石榴子石和绿辉石的闪石次变边、闪 相似文献
9.
滇西南澜沧群多硅白云母的多型和化学成分特征及其意义 总被引：5，自引：0，他引：5
从理论、实验及实际观察的结果都表明，随着压力的增加白云母中绿鳞石的含量显著地增加，可以认为在多期变质作用过程中，尤其是在变质压力不同的多期变质作用下，形成的多硅白云母，其化学成分就会打上不同的烙印。７７个多硅白云母化学成分的统计结果表明，澜沧群低级变质岩中的多硅白云母有两种成因。在Ｎａ－Ｍｇ相关图上，反映了高压和中压变质特征，高压变质的多硅白云母约占７０％。这与用多硅白云母ｂ０值鉴别的高压和中压变质是相吻合的。多硅白云母的多型为３Ｔ和２Ｍ１型，以２Ｍ１型为主 相似文献
10.
大别山西段含蓝闪石-蓝晶石榴辉岩的相平衡研究 总被引：3，自引：2，他引：3
目前对于大别山西段超高压榴辉岩仍存在一些不清楚的问题和模糊的认识,如蓝闪石和蓝晶石组合的稳定范围,峰期温压条件和矿物组合,以及早期退变质过程的矿物演化和流体作用。本文对取自大别山西段新县高压-超高压榴辉岩单元内不同地点的超高压榴辉岩样品进行了详细的岩石学和矿物学研究,在此基础上使用相平衡定量分析方法的 PT 视剖面图对它们进行了正演模拟计算,结果表明:含蓝闪石和蓝晶石榴辉岩处于相对低温或低压的蓝闪石榴辉岩和相对高温高压的蓝晶石榴辉岩的过渡区,其稳定的温压范围大致为温度590～700℃,压力1.7～3.3GPa,而且压力大于2.5GPa 时温度范围很窄,为600～640℃。由石榴石边缘成分和 PT 视剖面图确定的榴辉岩峰期温压条件为压力2.85～2.95GPa 和温度625～630℃,峰期矿物组合为石榴石 绿辉石 蓝闪石 蓝晶石 硬柱石 柯石英±多硅白云母。峰期之后,榴辉岩经历了快速近等温降压(ITD)的早期高压退变质作用,这是一个非平衡过程,所发生的主要变化如下:柯石英→石英,硬柱石→黝帘石 蓝晶石,在相对富镁岩石中出现滑石,当水含量较高时可以出现钠云母,蓝闪石在原来基础上有一定量的生长,并且绿辉石和多硅白云母很可能只部分地发生了成分变化,而石榴石几乎未发生改变。这样形成了目前观察到的矿物组成为石榴石 绿辉石 蓝闪石 蓝晶石 黝帘石/绿帘石 石英±多硅白云母±钠云母±滑石,它代表了 UHP 榴辉岩在早期高压退变质阶段结束时所具有的矿物组成,这一阶段结束时的温压条件大致为2.0～2.2GPa 和600～630℃;早期高压退变质阶段是脱水过程,流体是内部缓冲的。 相似文献
11.
The Menderes Massif comprises an inner crystalline core with gneissic rocks and an outer surrounding schist belt with predominantly metasedimentary rocks. Both units have a complex metamorphic history including a late Alpine overprint. Temperatures inferred from oxygen isotope compositions of coexisting minerals increase from 420 to 600°C from the rim to the center. More positive '18O values in all minerals from the schist belt may reflect a higher abundance of sedimentary precursor material, whereas biotites and muscovites in core and rim are indistinguishable in hydrogen isotope composition. 'D values of muscovites range from -35 to -60, whereas 'D values of biotites range from -65 to -125, indicating normal values for muscovite but anomalously negative values for some biotites. For muscovite the trend can be interpreted in terms of increasing loss of water with rising metamorphic temperature. For biotite the 'D values decrease with increasing H2O content and decreasing Na2O+K2O content, which provides evidence for alteration processes or exchange of K and Na with water from interlayers of biotite forming hydro-biotite. The data suggest isotopic resetting of pre-Alpine characteristics during Alpine metamorphism. The hydrogen isotope composition of biotite was later disturbed, probably during extensional neotectonic movements in this region, as this allowed infiltration of and exchange with D-depleted meteoric water; however, the muscovites retained its Alpine characteristics. 相似文献
12.
Carl E. Jacobson 《Journal of Structural Geology》1984,6(5):563-570
The Pelona Schist, which forms the lower plate of the Vincent thrust in the San Gabriel Mountains of southern California, has undergone a complex history of folding. The youngest folds in the schist (style 2 folds) range in shape from open to tight and fold both compositional layering and schistosity. These are superposed upon isoclinal folds with axial-plane schistosity (style 1 folds) that, in turn, overprint older isoclinal folds (also called style 1 folds). Samples from the hinges of style 2 folds contain two generations of muscovite. Muscovites of the older generation are parallel to the folded (style 1) schistosity. The newer muscovites recrystallized during and/or after style 2 folding. Microprobe analysis indicates that the two generations of muscovite are very similar in composition, although the new muscovites tend to have slightly higher paragonite and celadonite contents than the old muscovites. From the gross similarity of the two groups of muscovite, it is concluded that the style 1 and style 2 folds were produced during a single progressive deformation. The slightly higher paragonite and celadonite contents of the new muscovites are thought to indicate that both pressure and temperature were increasing during the deformation. This is consistent with the deformation being due to underthrusting of the Pelona Schist beneath the upper plate of the Vincent thrust. 相似文献
13.
大别山北部榴辉岩的退变质特征及其地质意义 总被引：3，自引：2，他引：3
研究了大别山北部榴辉岩的变质岩岩石学。结果表明，该区榴辉岩相变质作用可分为早期(超高压)和晚期(高压)两个阶段，并在折返过程中形成了一系列特征性的退变质显微构造。其中，退变质结构主要包括：(1)由于压力降低而出溶形成的一些定向针状或叶片状矿物包裹体，如钠质单斜辉石中石英及石榴子石中的金红石、单斜辉石和磷灰石等；(2)冠状体或后成合晶，特别是石榴子石外围发育两期(“双层”)后成合晶；(3)反应边或退变边，如绿辉石的透辉石退变边、透辉石的角闪石退变边和金红石的钛铁矿退变边等。这些退变质结构为本区榴辉岩高级变质岩的快速折返过程和抬升历史提供了强有力的岩石学依据；石榴子石中针状矿物出溶体进一步证明研究区榴辉岩早期经历了超高压变质作用，峰期变质压力应大干4．0GPa，甚至可能达到5～7GPa或更高。 相似文献
14.
Two types of biotite isograd are defined in the low-grade metamorphism of the Wazuka area, a Ryoke metamorphic terrain in the Kii Peninsula, Japan. The first, BI1, is defined by the reaction of chlorite+K-feldspar= biotite+muscovite+quartz+H2O that took place in psammitic rocks, and the second, BI2, by the continuous reaction between muscovite, chlorite, biotite and quartz in pelitic rocks. The Fe/Mg ratios of the host rocks do not significantly affect the reactions. From the paragenesis of pelitic and psammitic metamorphic rocks, the following mineral zones were established for this low-pressure regional metamorphic terrain: chlorite, transitional, chlorite-biotite, biotite, and sillimanite. The celadonite content of muscovite solid solution in pelitic rocks decreases systematically with the grade of metamorphism from 38% in the chlorite zone to 11% in the biotite zone. Low pressure does not prohibit muscovite from showing the progressive change of composition, if only rocks with appropriate paragenesis are chosen. A qualitative phase diagram of the AKF system relevant to biotite formation suggests that the higher the pressure of metamorphism, the higher the celadonite content of muscovite at BI1, which is confirmed by comparing the muscovites from the Barrovian and Ryoke metamorphism. 相似文献
15.
Transition of UHP eclogites to gneissic rocks of low-amphibolite facies during exhumation: evidence from the Dabie terrane, central China 总被引：11，自引：0，他引：11
The Shuanghe ultrahigh-pressure (UHP) slab in the Dabie Mountains consists of layered coesite-bearing eclogite, jadeite quartzite, marble and biotite gneiss, and is fault bounded against hosting orthogneiss. Representative assemblages of eclogite are Grt+Omp+Coe+Rt±Ky±Phn±Mgs; it formed at P>27 kbar and 680–720±50 °C. During exhumation, these UHP rocks experienced multistage retrograde metamorphism. Coesite was overprinted by quartz aggregates, phengite by biotite±muscovite and rutile by titanite. Garnet was successively replaced by a thin rim of Amp, Amp+Pl, and Amp+Ep±Bt+Pl (minor). Omphacite and kyanite were replaced by Amp+Pl±Cpx (or ±Bt) and by Zo+Pl+Ms±Mrg±Bt, respectively. Secondary calcite occurs as irregular pockets in some layers. An outcrop near the UHP slab border is composed of 20 thin, concordant layers of foliated eclogites, amphibolite and gneissic rocks of variable bulk composition. These layers exhibit mineral assemblages and textures transitional from less altered through extensively retrograded eclogite to gneissic rock of low-amphibolite facies through hydration, metasomatism and recrystallization. Retrograde metamorphism has caused oxygen and hydrogen isotope disequilibria between some of the minerals, but the fluid for retrograde reactions was internally buffered in the stable isotope compositions. Retrograde metamorphism of variable extent may be attributed to selective infiltration of retrograde fluids of CO2-rich and low-salinity aqueous, intensity of deformation and mineral resistance to alteration. The fluid phase for retrogression may have occurred either as discontinuous flow along grain boundaries in completely retrograded eclogites, and/or as isolated pockets in extensive or less altered eclogite layers. 相似文献
16.
The mineralogy of the Moine schists of the Ardnamurchan areahas been studied, using twenty-two analyses of muscovites, eighteenof biotites, seven of garnets (including five partial analyses),and one analysis of an epidote. The muscovites range in composition from phengite-ferrimuscovitein the biotite grade of metamorphism to nearly pure muscovite(sensu stricto) in the staurolite grade. The amounts of aluminiumin octahedral and tetrahedral co-ordination in the muscovitesincrease as the grade of metamorphism increases. In the associatedbiotites the amount of octahedral aluminium shows only slightvariations which are not related to the grade of metamorphism,but the amount of tetrahedral aluminium increases with increasein the grade of metamorphism. Muscovites and biotites from epidote-bearingrocks contain smaller amounts of tetrahedral aluminium thanmicas from rocks without epidote at the same grade of metamorphism.The amounts of tetrahedral aluminium in micas from rocks ofsimilar composition can probably be used as an index of thegrade of metamorphism. Magnesium and ferrous iron show a consistent distribution relationbetween coexisting muscovites and biotites. The value of thedistribution coefficient for these cations between the two micasis about 2.5 to 3.0, with magnesium preferentially concentratedin the muscovite. The value of the distribution coefficientdoes not vary appreciably within the medium grades of regionalmetamorphism. There is also a consistent pattern of distributionof magnesium, ferrous, and ferric iron between the two micas,but ferric iron is relatively concentrated in muscovite in rocksthat contain epidote without garnet; it is possible that thebiotites in these rocks attain a maximum possible content ofFe3+ at about 10 per cent of the total Mg+Fe2++Fe3+ content.The consistent distribution of magnesium and iron between coexistingmicas suggests that it can be used as an index of the attainmentof chemical equilibrium with respect to these two elements inmetamorphic rocks. All but one of the analysed micas have deficiencies in the occupancyof the large cation site; there appears to be a consistent relationshipin the extent of the large cation deficiency between the twocoexisting micas, wjth the biotites having a greater deficiencythan the muscovites. Sodium is relatively concentrated in themuscovites but does not show a consistent distribution relationshipbetween the coexisting micas. The analysed garnets are almandine-spessartines with appreciablesolid solution towards grossularite. The garnets that containthe largest amounts of grossularite are those from the epidote-bearingrocks. In the rocks without epidote the garnets show a poorcorrelation of decreasing calcium content with increasing gradeof metamorphism. 相似文献
17.
LiuYican LiShuguang XuShutong ChenGuanbao 《中国地质大学学报(英文版)》2004,15(4):349-354
The ultrahigh-pressure eclogites from the northern Dabie Mountains in central China occurred as tectonic lens or blocks within granitic gneisses or meta-peridotites. Petrologic studies suggest that the studied eclogites experienced strongly retrogressive metamorphism and produced a series of characteristic retrogressive microstructures. The retrograde structures mainly include: (1) oriented needle mineral exsolution, e. g. , quartz needles in Na-clinopyroxene and rotile, clinopyroxene and apatite exsolution in garnet formed under decreasing pressure conditions during exhumation; (2) symplectite, especially, two generations of symplectites developed outside the garnet grains, which are called ““double symplectite““ here; (3) compositional zoning of minerals such as garnet and clinopyroxene; (4) minerals with a reaction rim or retrograde rim, e.g. , omphacite with a diopside rim, diopside with an amphibole rim and rutile with a rim of ilmenite. These retrograde textures, especially mineral zoning and symplectite, provide important petrologic evidence for the exhumation process and uplift of high-grade metamorphic rocks such as eclogite in the northern Dabie Mountains, indicating a rapid exhumation process. 相似文献
18.
柴北缘锡铁山一带榴辉岩的岩石学特征及其退变PT轨迹 总被引：1，自引：1，他引：0
柴北缘锡铁山地区榴辉岩以透镜体的形式存在于花岗质片麻岩和副变质片麻岩中.根据矿物组合的不同,可以分为多硅白云母榴辉岩和角闪石榴辉岩.在多硅白云母榴辉岩中首次发现了柯石英假象.利用榴辉岩中Grt-Cpx-Phn矿物温压计.结合绿辉石中存在柯石英假象包体的现象,得到锡铁山榴辉岩的峰期温压条件为751～791℃,2.71～3.17GPa,证明了锡铁山地区与柴北缘其他地块一样,也经历了超高压变质作用.通过PT视剖面图计算了榴辉岩退变的PT轨迹具有2个阶段演化特征：即先等温降压,然后再降温降压的PT轨迹.详细的岩石学研究探讨了榴辉岩在退变过程中,各矿物的成分和结构的改变过程.石榴石在等温降压过程中成分变化不大,而在角闪石出现后,其边部镁铝榴石含量明显降低,进而形成了韭闪石+斜长石的冠状体.绿辉石在水饱和状态下经过贫硬玉化改造,而后形成了Di+Ab+Amp的后生合晶.多硅白云母分解形成白云母+黑云母及少量石英及钾长石的组合.角闪石随着温压条件的降低由钠钙质闪石逐渐向钙质闪石转化. 相似文献
19.
出露于桐柏造山带松扒-龟梅断裂带南侧的龟山杂岩经历了两阶段变质及多期变形作用,但其变质变形时代及其与秦岭造山带中产于相同构造部位的武关杂岩的构造关系尚缺乏深入研究.为此,对取自于龟山杂岩中的4件变质沉积岩和2件变质火山岩样品中的白云母进行了40Ar/39Ar同位素定年.结果表明,白云母的40Ar/39Ar坪年龄从306.7±1.7 Ma（保存最好的白云母斑晶）延续到279.2±2.6 Ma（经历后期变形改造的白云母）.结合前期锆石U-Pb定年结果推测龟山杂岩的两阶段变质及主期逆冲推覆变形均发生在石炭纪,并在二叠纪遭受到左行走滑剪切作用的改造.龟山杂岩与武关杂岩具有类似的岩石组成和变质变形演化历史,二者共同构成一条>500 km的晚古生代中级变质带,是华北-华南陆块最终碰撞之前大洋俯冲-增生的产物. 相似文献
20.
Compositional variation of muscovite as a function of metamorphic grade and assemblage in metapelites from N.W. Maine 总被引：1，自引：0，他引：1
C. V. Guidotti 《Contributions to Mineralogy and Petrology》1973,42(1):33-42
Chemical data are presented for 49 muscovites from high and low Al specimens collected form N.W. Maine at metamorphic grades ranging from the upper staurolite to the upper sillimanite zone. Data also are presented for two muscovite from St. Paul Island, two muscovites+three paragonites from Gassetts, Vermont, and one muscovite from an adamellite in N. W. Maine.These data given further information on the effects of P, T, and bulk composition on muscovite composition. Specifically, temperature clearly influences the Na/Na+K ratio of muscovite in limiting assemblages but may not have much effect on the phengite content. Increase in pressure clearly does cause an increase in phengite content. Bulk composition (assemblage) has a very great effect on both Na/Na+K ratio and phengite content so that attempts to use either of these factors to monitor metamorphic grade should generally be done in the context of a limiting assemblage. 相似文献