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1.
Progressive sequence of reactions of the Ryoke metamorphism in the Yanai district, southwest Japan: the formation of cordierite 总被引：2，自引：0，他引：2
T. IKEDA 《Journal of Metamorphic Geology》1998,16(1):39-52
The compositions of biotite and muscovite were examined in terms of the paragenesis and the metamorphic grade in low- to medium-grade pelitic rocks of the Ryoke metamorphism in the Yanai district, southwest Japan. The biotite and muscovite that coexist with K-feldspar have a higher K component in an A'KF diagram than those in rocks lacking K-feldspar. This fact reflects an increase in the K2 O content in muscovite, but in biotite it reflects an increase of not only the K2 O content but also of the octahedral vacancy.
At higher metamorphic grade beyond the cordierite isograd, where cordierite coexists with neither chlorite nor K-feldspar, the biotite shows an increase in illite, K Aliv □xii−1 Si−1, and Tschermak components, Alvi Aliv R+−1 Si−1, where □xii and R+ denote the interlayer vacancy and (Fe+Mg+Mn), respectively. A reaction to define the cordierite isograd is proposed by treating this chemical change as being responsible for the first appearance of cordierite, i.e. K,Al-poor biotite+phengitic muscovite=K,Al-rich biotite+cordierite+quartz+water .By treating this as a key reaction in medium-grade metamorphism, a set of reaction in a progressive metamorphism is established for the Ryoke metamorphism, a typical low-pressure type metamorphism. Some textures in one of the high-grade areas, the K-feldspar-cordierite zone, suggest that a further two prograde reactions have taken place, i.e. andalusite+biotite+quartz=cordierite+K-feldspar+water
and andalusite=sillimanite.quartz=cordierite+K-feldspar+water
This implies that this zone probably has a P–T path involving isobaric heating. 相似文献
At higher metamorphic grade beyond the cordierite isograd, where cordierite coexists with neither chlorite nor K-feldspar, the biotite shows an increase in illite, K Aliv □xii−1 Si−1, and Tschermak components, Alvi Aliv R+−1 Si−1, where □xii and R+ denote the interlayer vacancy and (Fe+Mg+Mn), respectively. A reaction to define the cordierite isograd is proposed by treating this chemical change as being responsible for the first appearance of cordierite, i.e. K,Al-poor biotite+phengitic muscovite=K,Al-rich biotite+cordierite+quartz+water .By treating this as a key reaction in medium-grade metamorphism, a set of reaction in a progressive metamorphism is established for the Ryoke metamorphism, a typical low-pressure type metamorphism. Some textures in one of the high-grade areas, the K-feldspar-cordierite zone, suggest that a further two prograde reactions have taken place, i.e. andalusite+biotite+quartz=cordierite+K-feldspar+water
and andalusite=sillimanite.quartz=cordierite+K-feldspar+water
This implies that this zone probably has a P–T path involving isobaric heating. 相似文献
2.
Disequilibrium in the Ross of Mull Contact Metamorphic Aureole, Scotland: a Consequence of Polymetamorphism 总被引：1，自引：0，他引：1
The Ross of Mull pluton consists of granites and granodioritesand intrudes sediments previously metamorphosed at amphibolitefacies. The high grade and coarse grain size of the protolithis responsible for a high degree of disequilibrium in many partsof the aureole and for some unusual textures. A band of metapelitecontained coarse garnet, biotite and kyanite prior to intrusion,and developed a sequence of textures towards the pluton. InZone I, garnet is rimmed by cordierite and new biotite. In ZoneII, coarse kyanite grains are partly replaced by andalusite,indicating incomplete reaction. Coronas of cordierite + muscovitearound kyanite are due to reaction with biotite. In the higher-gradeparts of this zone there is complete replacement of kyaniteand/or andalusite by muscovite and cordierite. Cordierite chemistryindicates that in Zone II the stable AFM assemblage (not attained)would have been cordierite + biotite + muscovite, without andalusite.The observed andalusite is therefore metastable. Garnet is unstablein Zone II, with regional garnets breaking down to cordierite,new biotite and plagioclase. In Zone III this breakdown is welladvanced, and this zone marks the appearance of fibrolite andK-feldspar in the groundmass as a result of muscovite breakdown.Zone IV shows garnet with cordierite, biotite, sillimanite,K-feldspar and quartz. Some garnets are armoured by cordieriteand are inferred to be relics. Others are euhedral with Mn-richcores. For these, the reaction biotite + sillimanite + quartz garnet + cordierite + K-feldspar + melt is inferred. Usinga petrogenetic grid based on the work of Pattison and Harte,pressure is estimated at 3·2 kbar, and temperature atthe Zone II–III boundary at 650°C and in Zone IV asat least 750°C. KEY WORDS: contact metamorphism; disequilibrium 相似文献
3.
浙西南八都杂岩早中生代泥质麻粒岩变质作用及构造意义 总被引：1，自引：0，他引：1
遂昌-大柘泥质麻粒岩出露于华夏地块东北部的浙西南八都杂岩中,该岩石保留了典型的减压反应结构.但其变质演化特点、变质作用时代及构造意义目前尚不明确.通过系统的岩相学、矿物化学和同位素年代学分析,结果表明遂昌-大柘泥质麻粒岩记录了4个阶段的变质矿物组合,其中早期进变质阶段M1的矿物组合为石榴石+黑云母+石英;压力峰期变质阶段M2的矿物组合为石榴石+铝绿泥石+金红石+蓝晶石+刚玉+黑云母+石英±十字石,该矿物组合可能预示着岩石曾经历了超高压变质作用过程;峰期变质阶段M3的矿物组合为石榴石+黑云母+夕线石+石英±钾长石±斜长石±钛铁矿;峰后近等温降压M4-1阶段的矿物组合为石榴石+黑云母+夕线石+堇青石+石英+钛铁矿±尖晶石±斜长石±钾长石;M4-2阶段的矿物组合为石榴石+堇青石+夕线石+斜长石+黑云母+石英±钾长石.相平衡模拟结合传统地质温压计限定其峰期变质阶段的温压条件为T=780~810 ℃、P=8.0~9.2 kbar;峰期后近等温降压的M4-1阶段的温压条件为T=780~860 ℃和P=5.7~6.0 kbar,M4-2阶段的温压条件为T=~700 ℃和P=~4.4 kbar,具有典型的顺时针近等温减压型P-T轨迹特征.LA-ICP-MS U-Pb定年结果表明其麻粒岩相变质作用时代为233.5~238.9 Ma.变质作用历史说明浙西南地体可能卷入了古特提斯洋域内印支-华南-华北板块之间的俯冲-碰撞过程,并经历了早中生代的麻粒岩相变质作用后快速折返至地表. 相似文献
4.
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
5.
M. SHIBA 《Journal of Metamorphic Geology》1988,6(3):273-296
Abstract The Hidaka metamorphic terrane in the Meguro-Shoya area, Hokkaido, Japan is divided into four progressive metamorphic zones: A—biotite zone; B—cordierite zone; C—cordierite–K-feldspar zone; and, D—sillimanite–K-feldspar zone of the andalusite–sillimanite facies series type of metamorphism. The metamorphic grade ranges from the higher temperature part of the greenschist facies (zone A) through the amphibolite facies (zones B and C) to the lower temperature part of the granulite facies (zone D). The zone boundaries intersect the bedding planes at high angles. P–T conditions estimated are 450–550°C and 2 kbar for zone A, 550–600°C and 2–2.5 kbar for zone B, 600–650°C and 2.5–3 kbar for zone C and 650–750°C and 3–4 kbar for zone D. The metapelites of zone D were partially melted.
At the later stage of the regional metamorphism which is early Oligocene to early Miocene in age, cordierite tonalite and biotite tonalite intrusives associated with segments of the highest grade rocks (zone D) were emplaced into the lower temperature part of the regional metamorphic rocks, giving rise to a contact metamorphic aureole. The thermally metamorphosed terrain (zone C') belongs to the amphibolite facies and its P–T conditions are estimated to have been 550–700°C and 2 kbar.
The P–T–t paths of the Hidaka metamorphism show a thickening–heating–uplifting process. The metamorphism is inferred to have taken place beneath an active island arc accompanied by partial melting of the crust. 相似文献
At the later stage of the regional metamorphism which is early Oligocene to early Miocene in age, cordierite tonalite and biotite tonalite intrusives associated with segments of the highest grade rocks (zone D) were emplaced into the lower temperature part of the regional metamorphic rocks, giving rise to a contact metamorphic aureole. The thermally metamorphosed terrain (zone C') belongs to the amphibolite facies and its P–T conditions are estimated to have been 550–700°C and 2 kbar.
The P–T–t paths of the Hidaka metamorphism show a thickening–heating–uplifting process. The metamorphism is inferred to have taken place beneath an active island arc accompanied by partial melting of the crust. 相似文献
6.
浙西南遂昌-大柘地区八都岩群在印支期变质事件影响下发生变质变形,通过详细野外调查和岩相学研究,可将其划分为3期变质变形序列：S1变形期,NW向片麻理记录的残留紧闭褶皱,共生矿物组合为石榴子石变斑晶及其内部定向分布的包裹体矿物,石榴子石+黑云母+石英（泥质）和石榴子石+角闪石+斜长石+石英（长英质）;S2变形期,区域性宽缓褶皱及NE向缓倾透入性片麻理,共生矿物组合为石榴子石变斑晶及定向分布的基质矿物,矽线石+石榴子石+黑云母+石英+斜长石±钾长石（泥质）和石榴子石+钾长石+斜长石+黑云母+石英（长英质）;S3变形期,NE向陡倾透入性片麻理及韧脆性断裂大部分被花岗斑岩脉填充,共生矿物组合为石榴子石变斑晶及其周围退变矿物,石榴子石+矽线石+堇青石+斜长石+黑云母+石英±钾长石（泥质）和角闪石+斜长石+黑云母+钛铁矿（长英质）。结合前人研究成果,八都岩群印支期变质事件峰期变质程度达到麻粒岩相,显示顺时针近等温降压（ITD）型的p-T演化轨迹,S1-S3变质变形反映出从俯冲碰撞到快速折返冷却的演化过程,伴随S3同期侵位的花岗斑岩锆石U-Pb定年结果,将该演化过程完成时间约束在229.7 Ma,可能是浙西南地区对印支期古特提斯洋域内印支-华南-华北板块之间俯冲-碰撞过程的响应。 相似文献
7.
点苍山变质杂岩新生代变质-变形演化及其区域构造内涵 总被引：3，自引：2，他引：1
点苍山变质杂岩体是哀牢山-红河韧性剪切带四个变质杂岩体之一,遭受了多期多阶段变质-变形作用改造。本文重点针对点苍山杂岩的新生代变质-变形作用,尤其是以富铝质高级变质岩即夕线石榴黑云片麻岩和侵位于其中的糜棱岩化细晶花岗质岩石开展了深入研究。对夕线石榴黑云片麻岩的显微构造分析与矿物共生组合研究,确定了高角闪岩相和低角闪岩相变质矿物共生组合,分别为:石榴石(Grt)+夕线石(Sil)+钾长石(Kfs)+黑云母(Bi)+斜长石(Pl)±石英(Q)和夕线石(Sil)+白云母(Ms)+黑云母(Bi)+石英(Q)。对其中的变质锆石进行SHRIMP U-Pb测试,获得了新生代三个阶段的变质作用年龄,即54.2±1.7Ma、31.5±1.5Ma和27.5±1.2Ma.本文还深入研究了侵位于高级变质岩中的一个花岗岩质糜棱岩的宏观与显微构造特点,其LA-ICP-MS年龄为24.4±0.89Ma,代表着同剪切就位花岗质岩浆侵位和结晶年龄。夕线石榴黑云片麻岩中变质锆石从2150～27Ma多期多阶段表观年龄的发育,表明点苍山变质杂岩体具有复杂的构造演化史。点苍山杂岩的多阶段新生代构造-热演化归咎于印度-欧亚板块会聚与碰撞作用(约54Ma)、造山后伸展作用(大约40～30Ma)和沿着哀牢山-红河剪切带大规模左行走滑变形作用(约27～21Ma)。 相似文献
8.
Low-pressure granulite facies metasedimentary gneisses exposed in MacRobertson Land, east Antarctica, include hercynitic spinel-bearing metapelitic gneisses. Peak metamorphic mineral assemblages include spinel + rutile + ilmenite + sillimanite + garnet, spinel + ilmenite + sillimanite + garnet + cordierite, ortho-pyroxene + magnetite + ilmenite + garnet, spinel + cordierite + biotite + ilmenite and orthopyroxene + cordierite + biotite, each with quartz, K-feldspar and melt. The presence of garnet + biotite- and cordierite + orthopyroxene-bearing assemblages implies crossing tie-lines in AFM projection for the K2 O-FeO-MgO-Al2 O3 -SiO2 -H2 O (KFMASH) system. This apparent contradiction, and the presence of spinel, rutile and ilmenite in the assemblages, is acounted for by using the KFMASH-TiO2 -O2 system, i.e. AFM + TiO2 + Fe2 O3 . We derive a petrogenetic grid for this system, applicable to low-pressure granulite facies metamorphic conditions. Retrograde assemblages are interpreted from corona textures on hercynitic spinel and Fe-Ti oxides. The relative positions of the peak and retrograde metamorphic assemblages on the petrogenetic grid suggest that corona development occurred during essentially isobaric cooling. 相似文献
9.
Eugene J. L. Dietvorst 《Contributions to Mineralogy and Petrology》1981,75(4):327-337
The formation of ferroan gahnite by breakdown of zinc-bearing biotite has been studied in metapelitic gneisses from the Kemiö region in southwestern Finland. Spinel compositions range from herc50 gahn40spin10 to herc15gahn82spin3; biotite contains up to 0.24 wt.% ZnO. Individual spinel grains show a gradual compositional zoning owing to increasing zinc contents towards the grain margins.Chemical and textural evidence indicate that spinel has been formed by breakdown of zinc-bearing biotite. During prograde metamorphism ferroan gahnite formed according to the reaction: biotite+sillimanite +quartz=cordierite+spinel+fluid, and during retrogressive metamorphism ferroan gahnite was formed by chloritization of biotite. It is proposed that the zinc-saturation limit of biotite depends on the metamorphic conditions. Decrease of this limit during retrogression to values below the zinc content of biotite initiated release of zinc and formation of ferroan gahnite. The activity of the Fe and Mg end members of retrogressively formed spinel are fixed by the coexisting biotite. 相似文献
10.
M. J. RUBENACH 《Journal of Metamorphic Geology》1992,10(3):333-346
In the Hazeldene area, situated in the Mount Isa Inlier, Queensland, the metamorphic grade changes from chlorite zone, through biotite and cordierite zones, to sillimanite/K-feldspar zone.
Microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation (S2), was replaced by biotite, andalusite and sillimanite at the metamorphic peak late in S2, and in turn by kyanite + chlorite adjacent to localized small post-D2 shear zones. Although the anticlockwise P–T–t path is well defined, the precise P–T conditions are uncertain because of problems with experimental and thermodynamic data. The best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600° C at 4 kbar.
The metamorphism has been dated at 1544 Ma, and was synchronous with a major crustal shortening event. Because proposed extensional events occurred more than 60 Ma earlier, their contribution to the peak metamorphic thermal perturbation would have been insignificant. The syn-metamorphic Mica Creek Pegmatites, the abundance of high heat-producing elements in the nearby pre-D2 Sybella Granite, and advective heat by fluids which caused considerable metasomatism in the Hazeldene area, may have each contributed to the thermal budget. However, the metamorphic thermal gradient may be 80°C km-1 or higher, strongly suggesting a local magmatic control. As none are known in the area, such syn-metamorphic plutons would have to lie beneath the exposed high-grade rocks. 相似文献
Microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation (S2), was replaced by biotite, andalusite and sillimanite at the metamorphic peak late in S2, and in turn by kyanite + chlorite adjacent to localized small post-D2 shear zones. Although the anticlockwise P–T–t path is well defined, the precise P–T conditions are uncertain because of problems with experimental and thermodynamic data. The best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600° C at 4 kbar.
The metamorphism has been dated at 1544 Ma, and was synchronous with a major crustal shortening event. Because proposed extensional events occurred more than 60 Ma earlier, their contribution to the peak metamorphic thermal perturbation would have been insignificant. The syn-metamorphic Mica Creek Pegmatites, the abundance of high heat-producing elements in the nearby pre-D2 Sybella Granite, and advective heat by fluids which caused considerable metasomatism in the Hazeldene area, may have each contributed to the thermal budget. However, the metamorphic thermal gradient may be 80°C km
11.
R. A. Jamieson 《Contributions to Mineralogy and Petrology》1984,86(4):309-320
The Kelly's Mountain gneiss complex of Cape Breton Island, Nova Scotia, is a migmatitic paragneiss dominated by biotite- and cordierite-bearing assemblages. Metamorphic grade throughout the complex is in the upper amphibolite facies, with garnet absent and only retrograde muscovite present. In the high grade core of the complex the reaction biotite+andalusite+quartz=cordierite+K-feldspar+sillimanite+ilmenite+H2O is preserved. The pelitic migmatites contain cordierite- and K-feldspar-rich leucosomes and biotite-rich melanosomes. Minor clinopyroxene-bearing amphibolite in the complex does not show migmatitic textures. The migmatites are interpreted as in situ peraluminous partial melts on the basis of phase relations and textural criteria. Retrograde metamorphism under conditions of high fluid pressure locally produced muscovite after K-feldspar and muscovite+green biotite+chlorite after cordierite in paragneiss, and sphene after ilmenite in amphibolite. Peak metamorphic conditions of 1–3.5 kb and 580–700° C are estimated. The high geothermal gradient inferred from these conditions was probably caused by the intrusion of diorites associated with the gneiss complex. The Kelly's Mountain complex represents a rare example of migmatites formed in the low-pressure facies series, and illustrates some of the reactions involving melting in high grade pelitic rocks. 相似文献
12.
Abstract The central sector of Mühlig-Hofmannfjellet (3°E/71°S) in western Dronning Maud Land (East Antarctic shield) is dominated by large intrusive bodies of predominantly orthopyroxene-bearing quartz syenites (charnockites). Metasedimentary rocks are rare; however, two distinct areas with banded gneiss–marble–quartzite sequences of sedimentary origin were found during the Norwegian Antarctic Research Expedition NARE 1989/90. Cordierite-bearing metapelitic gneisses from two different localities contain the characteristic mineral assemblage: cordierite + garnet + biotite + K-feldspar + plagioclase + quartz ± sillimanite ± spinel. Thermobarometry indicates equilibration conditions of about 650°C and 4 kbar. Associated orthopyroxene–garnet granulites, on the other hand, revealed pressures of about 8 kbar and temperatures of 750°C. The earlier granulite facies metamorphism is not well preserved in the cordierite gneisses as a result of excess K-feldspar combined with interaction with an H2 O-rich fluid phase, probably released by the cooling intrusives. These two features allowed the original high-grade K-feldspar + garnet assemblages to recrystallize as cordierite–biotite–sillimanite gneisses, completely re-equilibrating them. Phase relationships indicate that the younger metamorphic event occurred in the presence of a fluid phase that varied in composition between the lithologies. 相似文献
13.
In a prograde amphibolite-granulite transition zone in the Namaqualand Metamorphic Complex, metapelites show an interbanding of the amphibolite facies association biotite+sillimanite+quartz with the granulite facies association garnet+cordierite+K-feldspar. Relict graded bedding shows that compositional banding is of sedimentary origin. The garnet-cordierite-K-feldspar gneisses contain quartzofeldspathic segregations surrounding garnets, and have more Fe-rich bulk compositions than the biotite-sillimanite schists.The contrasting asemblages could have formed at the same pressure and temperature provided that a(H2O) was systematically lower in the garnet-cordierite-K-feldspar layers. The a(H2O) reduction resulted from the production of silicate melt by a vapour-absent continuous Fe-Mg reaction such as biotite+sillimanite+quartz=garnet+K-feldspar+liquid which affects Fe-rich compositions before vapour-absent melting occurs in more Mg-rich rocks. The segregations represent the solid and liquid products of the reaction.Such processes imply local control of a(H2O), and indicate that this granulite transition did not result from a regional influx of metasomatising fluids. 相似文献
14.
YOUNG EDWARD D.; ANDERSON J. LAWFORD; CLARKE H. STEVE; THOMAS WARREN M. 《Journal of Petrology》1989,30(1):39-60
Proterozoic migmatitic paragneisses exposed in the McCulloughRange, southern Nevada, consist of cordierite+almanditic garnet+biotite+sillimanite+plagioclase+K-feldspar+quartz+ilmenite+hercynite.This assemblage is indicative of a low-pressure fades seriesat hornblende-granulite grade. Textures record a single metamorphicevent involving crystallization of cordierite at the expenseof biotite and sillimanite. Thermobarometry utilizing cation exchange between garnet, biotite,cordierite, hercynite, and plagioclase yields a preferred temperaturerange of 590–750?C and a pressure range of 3–4 kb.Equilibrium among biotite, sillimanite, quartz, garnet, andK-feldspar records aH2O between 0?03 and 0?26. The low aH2Otogetherwith low fO2 (QFM) and optical properties of cordierite indicatemetamorphism under fluid-absent conditions. Preserved mineralcompositions are not consistent with equilibrium with a meltphase. Earlier limited partial melting was apparently extensiveenough to cause desiccation of the pelitic assemblage. The relatively low pressures attending high-grade metamorphismof the McCullough Range paragneisses allies this terrane withbiotite-cordierite-garnet granulites in other orogenic belts.aosure pressures and temperatures require a transient apparentthermal gradient ofat least 50?C/km during part of this Proterozoicevent in the southern Cordillera.
*Present address: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90024-1567 相似文献
15.
大陆碰撞过程中的巴罗式变质作用及原地深熔作用:以南阿尔金为例 总被引：1，自引：1，他引：0
南阿尔金吐拉地区所出露的变质泥质岩和变质基性岩普遍经历了中压麻粒岩相变质作用,其中变泥质岩以出现石榴子石+夕线石+长石+黑云母+石英为特征,而基性麻粒岩则以石榴子石+单斜辉石+紫苏辉石+斜长石+石英为特征,具有典型中压相系的麻粒岩相变质作用矿物组合,即显示"巴罗式"变质作用特征。野外宏观特征显示这套变泥质岩普遍经历了原地深熔作用,并局部发生混合岩化作用。岩相学观察结果显示泥质片麻岩保留了关键的深熔作用显微结构证据:(1)石榴子石内部发育有钾长石、石英和斜长石组成的矿物集合体,可能代表了早期熔体的假象;(2)黑云母颗粒边界发育尖锐的、不规则的微斜长石,而且黑云母边界溶蚀明显,形成锯齿状不规则的边界,指示深熔作用可能与黑云母的分解密切相关,即黑云母可能为深熔作用的主要反应相;(3)石英、斜长石或石榴子石颗粒边界发育圆珠状不规则的钾长石,而且颗粒边界或三联点中尖锐状钾长石与周围矿物的形成较小的二面角,有些甚至相互连通呈网络状,这也与它们继承了熔体结构特征一致;(4)不规则钾长石(或微斜长石)分布在石榴子石和夕线石附近,指示石榴子石和夕线石可能为深熔作用的残留相。锆石U-Pb定年结果显示麻粒岩相变质作用和相关深熔作用时代基本一致,主要发生在~450Ma。因此,吐拉地区的中压麻粒岩相变质作用和深熔作用明显要晚于南阿尔金地区榴辉岩和高压麻粒岩的峰期变质时代40~50Myr,而是与榴辉岩折返过程中麻粒岩相叠加变质作用的时代较为接近。但南阿尔金~450Ma的变质作用、深熔作用和岩浆作用是否为独立的构造热事件抑或深俯冲板片折返阶段的产物,这还需要今后进一步的工作验证。 相似文献
16.
Phase Petrology and Mineral Chemistry of Coexisting Amphiboles from Telemark, Norway 总被引：1，自引：1，他引：1
Electron microprobe analyses of coexisting amphiboles, garnet,and cordierite in specimens collected from a single outcropprovide the basis for phase diagrams thought to be representativeof fixed external conditions in the sillimanite zone. A projectionthrough the compositions of quartz and plagioclase is employedto characterize the mineral facies and to facilitate comparisonswith other metamorphic terrains. Limiting recalculations whichbracket the possible range of Fe+3 contents in calcic amphiboleanalyses by electron probe permit an additional projection throughthe composition of magnetite, a ubiquitous phase. From thesedata the apparent non-ideality exhibited by various combinationsof coexisting cumming-tonite, anthophyllite, gedrite, and calcicamphibole is explained by intracrystalline cation ordering. 相似文献
17.
Metapelitic granulites from Jetty Peninsula,east Antarctica: formation during a single event or by polymetamorphism? 总被引：5，自引：0，他引：5
M. HAND I. SCRIMGEOUR R. POWELL K. STÜWE C. J. L. WILSON 《Journal of Metamorphic Geology》1994,12(4):557-573
Granulite facies metasedimentary gneiss exposed on Jetty Peninsula, east Antarctica, contains assemblages involving garnet-sillimanite-biotite-cordierite-spinel-ilmenite-rutile and garnet-orthopyroxene-cordierite-biotite, as well as quartz and K-feldspar. Peak assemblages involve garnet + sillimanite + ilmenite (±rutile) and garnet + orthopyroxene. P-T calculations suggest formation conditions of approximately 800d? C at 7-7.5 kbar. Cooling from peak conditions is suggested by biotite + garnet (±sillimanite) overprinting some peak assemblages. A subsequent increase in temperature is inferred from the formation of cordierite + garnet + biotite + ilmenite, garnet + sillimanite + cordierite + ilmenite and cordierite + orthopyroxene assemblages during D2. In slightly zincian bulk compositions, hercynitic spinel + cordierite + sillimanite constitutes the peak D2 assemblage. Average pressure calculations indicate peak pressures of 5.9 ±0.4 kbar at 700d? C for the cordierite-bearing D2 assemblages. Available radiometric data suggest that peak metamorphism occurred at c. 1000 Ma and D2 occurred after 940 ± 20 Ma. The following two possibilities exist for the metamorphic evolution. (1) The formation of the lower pressure cordierite-bearing assemblages is associated with a separate metamorphic event (M2), unrelated to the peak assemblage (M1), and the lower pressure assemblages have no relevance in terms of a single tectonothermal event. (2) The cordierite-bearing assemblages formed during a progression from peak conditions. In this case, the lower pressure assemblages reflect a broadly decompressional metamorphic evolution, during which temperatures fluctuated. Comparison with P-T paths from granulites of similar age in adjacent areas suggests that the second possibility should be preferred. The cooling interval between peak conditions and the development of cordierite-bearing coronas and symplectites suggests affinities with isobarically cooled granulites of similar age immediately to the west, and the low-P/high-T post-peak conditions are similar to the later stages of decompressional paths recognized in much of east Antarctica. 相似文献
18.
S. BABA 《Journal of Metamorphic Geology》1998,16(6):819-841
The Leverburgh Belt and South Harris Igneous Complex in South Harris (northwest Scotland) experienced high-pressure granulite facies metamorphism during the Palaeoproterozoic. The metamorphic history has been determined from the following mineral textures and compositions observed in samples of pelitic, quartzofeldspathic and mafic gneisses, especially in pelitic gneisses from the Leverburgh Belt: (1) some coarse-grained garnet in the pelitic gneiss includes biotite and quartz in the inner core, sillimanite in the outer core, and is overgrown by kyanite at the rims; (2) garnet in the pelitic gneiss shows a progressive increase in grossular content from outer core to rims; (3) the AlVI/AlIV ratio of clinopyroxene from mafic gneiss increases from core to rim; (4) retrograde reaction coronas of cordierite and hercynite+cordierite are formed between garnet and kyanite, and orthopyroxene+cordierite and orthopyroxene+plagioclase reaction coronas develop between garnet and quartz; (5) a P–T path is deduced from inclusion assemblages in garnet and from staurolite breakdown reactions to produce garnet+sillimanite and garnet+sillimanite+hercynite with increasing temperature; and (6) in sheared and foliated rocks, hydrous minerals such as biotite, muscovite and hornblende form a foliation, modifying pre-existing textures. The inferred metamorphic history of the Leverburgh Belt is divided into four stages, as follows: (M1) prograde metamorphism with increasing temperature; (M2) prograde metamorphism with increasing pressure; (M3) retrograde decompressional metamorphism with decreasing pressure and temperature; and (M4) retrograde metamorphism accompanied by shearing. Peak P–T conditions of the M2 stage are 800±30 °C, 13–14 kbar. Pressure increasing from M1 to M2 suggests thrusting of continental crust over the South Harris belt during continent–continent collision. The inferred P–T path and tectonic history of the South Harris belt are different from those of the Lewisian of the mainland. 相似文献
19.
Martin Okrusch 《Contributions to Mineralogy and Petrology》1969,22(1):32-72
Zusammenfassung Bereits vor der Intrusion des Leuchtenberger Granits waren seine Rahmen-gesteine unter den Bedingungen der Amphibolit-Fazies regionalmetamorph eingeformt worden, wobei sich folgende Paragenesen bildeten: Muscovit + Biotit + Granat ± Sillimanit ± Staurolith (+ Quarz + Plagioklas) Muscovit + Biotit ± Kalifeldspat (+ Quarz + Plagioklas).Die Kontaktmetamorphose führt in den äußeren Bereichen der Aureole zur Paragenese Muscovit + Andalusit + Cordierit + Biotit (+ Quarz + Plagioklas), die der Hornblende-Hornfels-Fazies entspricht.In der inneren Kontaktzone werden die p-t-Bedingungen einer höhergradierten Hornfelsfazies erreicht, die sich in der Paragenese ± Kalifeldspat + Sillimanit + Cordierit ± Almandin + Biotit (+ Quarz + Plagioklas) dokumentiert.Die zonale Anordnung der Mineral-Paragenesen im Kontakthof läßt sich durch quantitative Verbreitungskarten anschaulich machen (150 Modalanalysen aus 59 Fundpunkten). Phasenbeziehungen und Mineralreaktionen werden anhand von AKF- und AFM-Diagrammen diskutiert, für deren Aufstellung 19 Mineralanalysen neu ausgeführt wurden.Durch den Vergleich mit derzeit verfügbaren experimentellen Unterlagen lassen sich die p-t-Bedingungen im Steinacher Kontakthof abschätzen. Danach ist ein Druckbereich von 1,5–3 kbar am wahrscheinlichsten. Mit der Bildung der höchst-gradierten Hornfelse waren 550° C sicher überschritten, während nach dem Jaeger-Modell 700° C als alleroberste Temperaturgrenze anzusehen ist. In der innersten Kontaktzone muß man mit geringen O2-Partialdrucken rechnen.
Prof. S. Matthes (Würzburg) möchte ich für das lebhafte, fördernde Interesse an dieser Arbeit sowie für die Überlassung von Proben und von Geräten der DFG meinen herz-lichen Dank aussprechen. Wesentlichen Anteil am Gelingen dieser Untersuchung hat auch Prof. B. W. Evans, dem ich für die freundschaftliche Aufnahme in Berkeley, für die ständige Bereitschaft zur Diskussion und für wertvolle Anregungen zu großem Dank verpflichtet bin. Weiter danke ich Prof. W. Schreyer (Bochum) und Prof. F. J. Turner (Berkeley) für die kritische Durchsicht des Manuskripts sowie Mr. L. K. Burns (Berkeley), Dr. A. Peters und Dr. P. Richter (Würzburg) für wichtige Hinweise bei der Analytik. Die Untersuchungen an der Mikrosonde in Berkeley wurden durch ein Stipendium der Deutschen Forschungs-gemeinschaft ermöglicht; das Gerät stand durch die Unterstützung der National Science Foundation (grant GA 500) zur Verfügung. Beiden Organisationen sei für ihre Hilfe gedankt.
Textlich gekürzte, aber um neue Untersuchungsergebnisse erweiterte Fassung einer Habilitationsschrift, angenommen im Januar 1968 von der Naturwissenschaftlichen Fakultät der Universität Würzburg. 相似文献
The gneiss-hornfelses of Steinach, Oberpfalz (Bavaria)
The southern margin of the Leuchtenberg granite massive is surrounded by a thermal aureole in which banded gneisses and mica schists have been transformed into hornfelses containing andalusite, sillimanite, cordierite, and almandine.Before the intrusion of the granite, the country rocks had undergone regional metamorphism to give mineral assemblages typical of the amphibolite facies: Muscovite + biotite ± K-feldspar + quartz + plagioclase in the banded gneisses and muscovite + biotite + garnet ± sillimanite ± staurolite + quartz + plagioclase in the mica schists.In the outer zone of the aureole, contact metamorphism produced the assemblage: Muscovite + andalusite + cordierite + biotite + quartz + plagioclase, corresponding to the hornblende-hornfels facies.In the inner zone of the aureole, increasing temperatures yielded the high grade assemblages: K-feldspar + sillimanite + cordierite ± almandine + biotite + quartz + plagioclase sillimanite + cordierite ± almandine + biotite + quartz + plagioclase.The zonal arrangement of the mineral assemblages within the Steinach aureole is shown in quantitative distribution maps of andalusite, contact-metamorphic sillimanite, cordierite, and contact-metamorphic garnet respectively, based on 150 modal analyses (from 59 points, Fig. 1). Andalusite (Fig. 10) reaches its maximum at about 200–400 m from the granite border and, toward it, is more and more substituted by sillimanite (Fig. 11). On the other hand, contact metamorphic sillimanite goes to the outer zone of the aureole almost as far as andalusite. This means that the sillimanite isograd passed across the andalusite zone during the contact metamorphism. Cordierite (Fig. 12) shows a constant increase from the margin to the innermost zone of the aureole, as does contact metamorphic garnet (Fig. 13). Phase relations and mineral reactions are discussed in terms of AKP- and APM-diagrams (Figs. 14, 15, 17, 18) based on 19 new mineral analyses (Tables 5–9).With respect to the experimental data so far available, possible P-T-conditions within the Steinach aureole have been discussed. The transition from the low to the high grade assemblages took place very near to the cross-over point of the andalusite/sillimanite equilibrium curve and the breakdown curve of muscovite + quartz in the P-T-diagram (Figs. 16, 19).This gives a minimum H2O-pressure of 1 kbar. In the innermost contact zone, temperatures must have exceeded 550° C, which is in good agreement with recent oxygen-isotope data as well as with Jaeger's model. As is shown by the ore mineral assemblages, studied in polished sections (Table 10), the oxygen activity in the high grade hornfelses was low.
Prof. S. Matthes (Würzburg) möchte ich für das lebhafte, fördernde Interesse an dieser Arbeit sowie für die Überlassung von Proben und von Geräten der DFG meinen herz-lichen Dank aussprechen. Wesentlichen Anteil am Gelingen dieser Untersuchung hat auch Prof. B. W. Evans, dem ich für die freundschaftliche Aufnahme in Berkeley, für die ständige Bereitschaft zur Diskussion und für wertvolle Anregungen zu großem Dank verpflichtet bin. Weiter danke ich Prof. W. Schreyer (Bochum) und Prof. F. J. Turner (Berkeley) für die kritische Durchsicht des Manuskripts sowie Mr. L. K. Burns (Berkeley), Dr. A. Peters und Dr. P. Richter (Würzburg) für wichtige Hinweise bei der Analytik. Die Untersuchungen an der Mikrosonde in Berkeley wurden durch ein Stipendium der Deutschen Forschungs-gemeinschaft ermöglicht; das Gerät stand durch die Unterstützung der National Science Foundation (grant GA 500) zur Verfügung. Beiden Organisationen sei für ihre Hilfe gedankt.
Textlich gekürzte, aber um neue Untersuchungsergebnisse erweiterte Fassung einer Habilitationsschrift, angenommen im Januar 1968 von der Naturwissenschaftlichen Fakultät der Universität Würzburg. 相似文献
20.
Cordierite gneisses of southern Kerala,India: petrology,fluid inclusions and implications for crustal uplift history 总被引：2，自引：0，他引：2
M. Santosh 《Contributions to Mineralogy and Petrology》1987,96(3):343-356
The cordierite-bearing gneisses occurring as elongate patches in an 8- to 10-km-wide zone along the Achankovil fault-lineament at the northern margin of the southern Kerala crustal segment represent an important lithological unit in the Archaean granulite terrane of south India. The textural relationships in these rocks are consistent with the following main reactions: (1) garnet+quartz=cordierite+hypersthene; (2) garnet+sillimanite+quartz=cordierite; (3) hypersthene+sillimanite+quartz=cordierite; (4) sillimanite+spinel=cordierite+corundum; and (5) biotite+quartz+sillimanite=cordierite+K-feldspar. Many of the mineral associations and reaction textures, including the remarkable preservation of symplectites, are indicative of partial replacement of high-pressure assemblages by cordierite-bearing lower-pressure ones during an event of rapid decompression. Temperature estimates from coexisting mineral phases show 710° (garnet-biotite), 791° (garnet-cordierite) and 788° C (garnet-orthopyroxene). Pressure estimates from mineral assemblages range from 5.4 to 7 kb. Detailed fluid inclusion studies in quartz associated with cordierite show high-density CO2 (0.80–0.95 g/cm3) as the dominant fluid phase, with traces of probable CH4 (?) in the sillimanite-bearing rocks. The isochore for the higher-density fluid inclusions defines a pressure of 5.5 kb. The fracture-bound CO2 and CO2-H2O (±CH4?) inclusions indicate simultaneous entrapment at 400° C and 1.7 kb in the cordierite-hypersthene assemblage and 340° C and 1.2 kb in the cordierite-sillimanite assemblage. The P-T path delineated from combined solid and fluid data corresponds to the piezothermic array of the gneisses and is characterized by T-convex nature, indicative of rapid and virtually isothermal crustal uplift, probably aided by extensional tectonics. 相似文献