Pumpellyite–actinolite facies of the Sanbagawa metamorphism     

S. BANNO 《Journal of Metamorphic Geology》1998,16(1):117-128

The pumpellyite–actinolite facies proposed by Hashimoto is defined by the common occurrence of the pumpellyite–actinolite assemblage in basic schists. It can help characterize the paragenesis of basic and intermediate bulk compositions, which are common constituents of various low-grade metamorphic areas. The dataset of mutually consistent thermodynamic properties of minerals gives a positive slope for the boundary between the pumpellyite–actinolite and prehnite–pumpellyite facies in P–T space. In the Sanbagawa belt in Japan, the mineral parageneses of hematite-bearing and -free basic schists, as well as pelitic schists have been well documented. The higher temperature limit of this facies is defined by the disappearance of the pumpellyite+epidote+actinolite+chlorite assemblage in hematite-free basic schists with X_Fe3+ of epidote around 0.20–0.25 and the appearance of epidote+actinolite+chlorite assemblage with X^Ep_Fe3+≤0.20. In hematite-bearing basic schists, there is a continuous change of paragenesis to higher grade, epidote–glaucophane or epidote–blueschist facies. In pelitic schists, the albite+lawsonite+chlorite assemblage does occur but only rarely, and its assemblage cannot be used to determine the regional thermal structure. The lower temperature equivalence of the pumpellyite–actinolite assemblage is not observed in the field. The Mikabu Greenstone complex and the northern margin of the Chichibu complex, which are located to the south of the Sanbagawa belt, are characterized by clinopyroxene+chlorite or lawsonite+actinolite assemblages, which are lower temperature assemblages than the pumpellyite+actinolite assemblage. These three metamorphic complexes belong to the same subduction-metamorphic complex. The pumpellyite–actinolite facies or subfacies can be useful to help reveal the field thermal structure of metamorphic complexes  相似文献   

Pumpellyites in two low grade metamorphic terranes North of Newcastle,NSW Australia     

R. Offler  C. K. Baker  J. Gamble 《Contributions to Mineralogy and Petrology》1981,76(2):171-176

Microprobe analyses of pumpellyites from rocks of variable chemistry formed under similar metamorphic conditions in two Palaeozoic, low grade metamorphic terranes show that they have an extreme range in composition (FeO^*=0.9–22.96) and that Fe²⁺Mg²⁺ and Fe³⁺Al³⁺ are the dominant substitutions. A less extreme variation in composition of pumpellyites has been noted in samples taken from a metamorphosed differentiated metadolerite. On an A1-Fe^*-Mg diagram, these pumpellyites extend through the fields of high pressure to low pressure terranes, indicating that pumpellyite compositions should be used with caution when determining metamorphic conditions.Bulk chemical composition of the host rock does not appear to be a controlling factor in determining pumpellyite compositions. Rather, intensity of alteration, particularly of opaque mineral phases, fluid chemistry and variation in oxidation potential are considered to be more important variables. Coexisting epidote and composition of the precursor mineral also appear to be important in some rocks.  相似文献   

Reactions Leading to the Disappearance of Pumpellyite in Low-grade Metamorphic Rocks of the Sanbagawa Metamorphic Belt in Central Shikoku, Japan   总被引：2，自引：0，他引：2  

NAKAJIMA  TAKASHI; BANNO  SHOHEI; SUZUKI  TAKASHI 《Journal of Petrology》1977,18(2):263-284

The major mineral assemblages of the metabasites of the Omoiji-Nagasawaarea in central Shikoku are hematite+epidote+chlorite+actinolite,riebeckitic actinolite+epidote+chlorite, epidote+chlorite+actinolite,and pumpellyite+epidote+chlorite+actinolite. The constituentminerals are often heterogeneous and assemblages in the fieldof a thin section sometimes do not obey the phase rule, butif grains apparently in non-equilibrium with others are excludedand domains of chemical equilibrium are appropriately chosenthe assemblages approximately obey the phase rule. The stability of hematite, pumpellyite, and epidote associatedwith chlorite and actinolite can be dealt with in terms of aternary system with appropriate excess phases. By fixing theFe²⁺/(Fe²⁺ +Mg) ratio of chlorite, it is dealt with in termsof stability relations in the system Ca₂Al₃Si₃O₁₂(OH)–Ca₂AlFe₂Si₃O₁₂(OH)with excess chlorite, actinolite, quartz, and controlled P_H2O.The maximum and minimum Fe³⁺ contents of epidote in this modelsystem are determined by hematite+epidote+chlorite+actinoliteand pumpellyite+epidote+chlorite+actinolite assemblages. Themaximum Fe³⁺ of the three phase assemblage epidote+chlorite+actinoliteis insensitive to temperature, but the minimum Fe³⁺ contentof epidote is sensitive to temperature and can be used to definethe metamorphic grade by a continuous quantity related to temperature.The phase relations expected for the model system are in goodagreement with the parageneses of the Sanbagawa terrain in centralShikoku and offer an explanation to the rule of Miyashiro &Seki (1958a) that the compositional range of epidote enlargeswith increasing temperature. The model also makes it possibleto estimate semi-quantitatively the temperature range in whichthe assemblage pumpellyite+epidote+chlorite+actinolite is stable.The possible maximum range is about 120 ?C, but the assemblageis stable in metabasite only for about 90 ?C. The higher temperaturelimit of the pumpellyite-actinolite facies defined by the disappearanceof pumpellyite in metabasite corresponds to the temperatureat which epidote with Fe³⁺/(Fe³⁺ +Al) = 0.10 0.15 coexistswith pumpellyite, actinolite, and chlorite. The compositions of epidotes in the metabasites of the Omoiji-Nagasawaarea cluster around Fe³⁺/(Fe³⁺ +Al) = 0.33. The grade of thisarea is close to the lower temperature stability limit of thepumpellyite+epidote+chlorite+actinolite assemblage.  相似文献   

Pumpellyite in low-grade metamorphic rocks from Ligurian and Lucanian Apennines,Maritime Alps and Calabria (Italy)     

Luciano Cortesogno  Gabriella Lucchetti  Piera Spadea 《Contributions to Mineralogy and Petrology》1984,85(1):14-24

In the Ligurian Apennines and the Brianzonese area of the Maritime Alps (Northern Italy), and in the Lucanian Apennines and Calabria (Southern Italy), pumpellyite formed during the Alpine metamorphism is widespread in terranes of Late Paleozoic to Miocene age, particularly in mafic ophiolites (Tethyan ophiolites of Jurassic-Early Cretaceous age).Pumpellyite developed under variable metamorphic conditions, which include zeolite, prehnite-pumpellyite, pumpellyite-actinolite, lawsonite-albite and blueschist facies. Pumpellyite from rocks belonging to all these facies was studied in 30 specimens of different chemistry, derived mostly from ophiolitic basalt and gabbro, but also from gneiss, amphibolite, and greywacke protoliths.Microprobe data give evidence of strong compositional variations of pumpellyite. The ranges are extreme for Al and Fe^tot (Al₂O₃=18.74–30.91; FeO_tot=0.46–12.71), to a lesser extent for Mg (MgO=0.58–4.00), with a reciprocal variation of Al and Fe^tot which suggests that most Fe is Fe³⁺.Pumpellyite compositions can be related with the metamorphic conditions, particularly an increase of the Al/Fe^tot ratio with increasing pressure, but larger compositional variation for each facies in the Al-Fe^tot-Mg diagram than those previously described was recognized. Particularly the compositions of pumpellyite from the pumpellyite-actinolite and blueschist fades assemblages extend towards higher Fe^tot contents. Moreover, pumpellyites of the lawsonite-albite facies rocks result to be more aluminous than in blueschist facies; such relations appear to be inconsistent with that expected by the effects of pressure on the Al content.As the rocks are generally incompletely re-equilibrated, their bulk chemistry is not an important factor of pumpellyite composition; in fact the correlations of Al, Fe^tot and Mg are low. The local environment of crystallization, more evidently the composition of the precursor minerals, seems to be a major controlling factor. The observed topologic relations indicate that either the nature of the precursor mineral, or the presence of relict phases have a great influence on the pumpellyite composition. The observed variations within individual specimens, as well as the interspecimen ones, can be explained by small-scale inhomogeneities and in some cases by differences in the activity of O₂.It can be therefore concluded that the composition of pumpellyite often reflects disequilibrium crystallization and cannot be generally used as an indicator of metamorphic conditions.  相似文献   

Polyphase and anticlockwise P-T evolution for Franciscan eclogites and blueschists from Jenner, California, USA   总被引：1，自引：0，他引：1  

E. J. KROGH  C. W. OH  J. C. LIOU 《Journal of Metamorphic Geology》1994,12(2):121-134

High-grade exotic blocks in the Franciscan Complex at Jenner, California, show evidence for polydeformation/metamorphism, with eight distinct stages. Two parallel sets of mineral assemblages [(E) eclogite, and (BS) laminated blueschist] representing different bulk chemistry were identified. Stage 1, recorded by parallel aligned inclusions (S1) of crossite + omphacite + epidote + ilmenite + titanite + quartz (E), and glaucophane + actinolite + epidote + titanite (BS) in the central parts of zoned garnets, represents the epidote blueschist facies. The onset of a second stage (stage 2) is represented by a weak crenulation of S1 and growth of garnet. This stage develops a well-defined S2 foliation of orientated barroisite + epidote + titanite (E), or subcalcic actinolite + epidote + titanite (BS) at c. 90d? to S1, with syntectonic growth of garnet, defining the (albite-)epidote-amphibolite facies. A third stage, with aligned inclusions of glaucophane + (subcalcic) actinolite + phengite parallel to S2 in the outermost rims of large garnet grains, is assigned to the transitional (albite-)epidote-amphibolite/(garnet-bearing) epidote blueschist facies. The fourth stage represents the peak metamorphism, and was identified by unorientated matrix minerals in the least retrograded samples. In this stage the mineral assemblages garnet + omphacite + glaucophane + phengite (E) and garnet + winchite + phengite + epidote (BS) both represent the eclogite facies. Stage 5 is represented by the retrogression of eclogite facies assemblages to the epidote blueschist facies assemblages crossite/glaucophane + garnet + omphacite + epidote + phengite (E), and glaucophane + actinolite + epidote + phengite (BS), with the development of an S5 foliation subparallel to S2. Stage 6 represents a crenulation of S5, with the development of a well-defined S6 crenulation cleavage wrapping around relics of the eclogite facies assemblages. This crenulation cleavage is further weakly crenulated during a D7 event. Post-D7 (stage 8) is recorded by the growth of lawsonite + chlorite ± actinolite replacing garnet, and by veins of lawsonite + pumpellyite + aragonite and phengite + apatite. The different, yet coeval, mineral parageneses observed in rock types (E) and (BS) are probably due to differences in bulk chemistry. The metamorphic evolution from stage 1 to stage 8 seems to have been broadly continuous, following an anticlockwise P-Tpath: (1) epidote blueschist (garnet-free) to (2) (albite-)epidote-amphibolite to (3) transitional epidote blueschist (garnet-bearing)/(albite-)epidote-amphibolite to (4) eclogite to (5) epidote blueschist (garnet-bearing) to (6-7) epidote blueschist (garnet-free) facies to (8) lawsonite + pumpellyite + aragonite-bearing assemblages. This anticlockwise P-T path may have resulted from a decreasing geothermal gradient with time in the Mesozoic subduction zone of California at early or pre-Franciscan metamorphism.  相似文献   

北祁连山硬柱石蓝片岩p-T条件相平衡计算及其岩石学意义   总被引：2，自引：0，他引：2  

王乾杰  张立飞  宋述光 《地学前缘》2007,14(1):157-171

北祁连硬柱石蓝片岩主要分布在甘肃省肃南县九个泉一带,是目前中国唯一报道的、确切地含有硬柱石的蓝片岩。文中在详细的岩石学和矿物学研究基础上,根据矿物共生组合的不同,将北祁连低温蓝片岩进一步划分为绿纤石蓝片岩、硬柱石蓝片岩和绿帘石蓝片岩。绿纤石蓝片岩的特征变质矿物组合为蓝闪石(>40%)+绿纤石(30%)+绿泥石(10%)+钠长石(8%)+石英(5%)+硬柱石(<3%)±方解石/文石(<1%)。硬柱石蓝片岩的矿物组合为蓝闪石(35%~40%)+硬柱石(35%~40%)+绿泥石(10%)+钠长石(10%)+石榴石(1%~2%)+黝帘石/斜黝帘石(<2%)+石英(<1%),副矿物有磷灰石和榍石,总含量小于2%。绿帘石蓝片岩的矿物组合为蓝闪石(30%~35%)+黝帘石/斜黝帘石/绿帘石(~30%)+绿泥石(15%)+钠长石(15%)+石榴石(2%)+石英(<2%),副矿物有金红石、磷灰石和磁铁矿,总含量小于2%。利用矿物内部一致性热力学数据和Domino/Theriak软件计算了这三种类型的蓝片岩形成的峰期温压条件,它们分别是绿纤石蓝片岩为320~350℃,0.75~0.85GPa;硬柱石蓝片岩为335~355℃,0.8~0.95GPa;绿帘石蓝片岩为345~375℃;0.75~0.85GPa。北祁连低温蓝片岩带由硬柱石蓝片岩相到绿帘石蓝片岩相的转化代表了俯冲变质过程中的递进变质过程。  相似文献   

Pumpellyite-bearing rocks in central Sweden and extent of host rock alteration as a control of pumpellyite composition     

J. O. Nyström 《Contributions to Mineralogy and Petrology》1983,83(1-2):159-168

Metamorphic assemblages and mineral compositions in basic to intermediate volcanic rocks of two Precambrian units (the sub-Jotnian and Jotnian) in the Dala region, central Sweden, reveal a history comprising two metamorphic episodes. The sub-Jotnian rocks were metamorphosed during a first episode: the metamorphic grade ranges from prehnite-pumpellyite facies (in a displaced block with sub-Jotnian (?) lava occurring in the border zone of a major impact structure), to pumpellyite-actinolite facies, and to greenschist facies in the lower part of the unit. The unconformably overlying Jotnian rocks were metamorphosed to prehnite-pumpellyite facies during a subsequent episode, which also left its imprint in the sub-Jotnian basement. Two other Jotnian sequences in central Sweden are in the same facies. There are systematic chemical differences in some of the secondary minerals. Sphenes contain more Al, and epidotes and pumpellyites are more Fe-rich in Jotnian (prehnite-pumpellyite facies) rocks compared with sub-Jotnian rocks of pumpellyite-actinolite facies. Most epidotes in Jotnian lavas are remarkably rich in Fe, with a replacement of Al by Fe³⁺ up to 1.5 atoms per formula unit (Ps₅₀). Compositions of epidote and pumpellyite in pervasively altered rocks vary sympathetically. Pumpellyite composition is partly controlled by the extent of alteration in its host rock. There is a trend for the compositional field of pumpellyite to shrink and shift away from the Al corner of the Al-Fe*-Mg triangle with increasing extent of host rock alteration. This trend is most evident in Jotnian rocks. Since the fields in the Al-Fe*-Mg triangle given in the literature as representative of pumpellyites from different metamorphic fades are partly based on analyses of samples containing relicts, these fields should be adjusted if future investigations show that the trend is of general validity.  相似文献   

P–T–X controls on phase stability and composition in LTMP metabasite rocks – a thermodynamic evaluation     

G. PHILLIPS  M. HAND  R. OFFLER 《Journal of Metamorphic Geology》2010,28(5):459-476

The stability of pumpellyite + actinolite or riebeckite + epidote + hematite (with chlorite, albite, titanite, quartz and H₂O in excess) mineral assemblages in LTMP metabasite rocks is strongly dependent on bulk composition. By using a thermodynamic approach (THERMOCALC), the importance of CaO and Fe₂O₃ bulk contents on the stability of these phases is illustrated using P–T and P–X phase diagrams. This approach allowed P–T conditions of ～4.0 kbar and ～260 °C to be calculated for the growth of pumpellyite + actinolite or riebeckite + epidote + hematite assemblages in rocks containing variable bulk CaO and Fe₂O₃ contents. These rocks form part of an accretionary wedge that developed along the east Australian margin during the Carboniferous–Triassic New England Orogen. P–T and P–X diagrams show that sodic amphibole, epidote and hematite will grow at these conditions in Fe₂O₃‐saturated (6.16 wt%) metabasic rocks, whereas actinolite and pumpellyite will be stable in CaO‐rich (10.30 wt%) rocks. With intermediate Fe₂O₃ (～3.50 wt%) and CaO (～8.30 wt%) contents, sodic amphibole, actinolite and epidote can coexist at these P–T conditions. For Fe₂O₃‐saturated rocks, compositional isopleths for sodic amphibole (Al³⁺ and Fe³⁺ on the M2 site), epidote (Fe³⁺/Fe³⁺ + Al³⁺) and chlorite (Fe²⁺/Fe²⁺ + Mg) were calculated to evaluate the efficiency of these cation exchanges as thermobarometers in LTMP metabasic rocks. Based on these calculations, it is shown that Al³⁺ in sodic amphibole and epidote is an excellent barometer in chlorite, albite, hematite, quartz and titanite buffered assemblages. The effectiveness of these barometers decreases with the breakdown of albite. In higher‐P stability fields where albite is absent, Fe²⁺‐Mg ratios in chlorite may be dependent on pressure. The Fe³⁺/Al and Fe²⁺/Mg ratios in epidote and chlorite are reliable thermometers in actinolite, epidote, chlorite, albite, quartz, hematite and titanite buffered assemblages.  相似文献   

SOME TRENDS IN THE STUDY OF CARBONATE SEDIMENTS IN THE FEDERAL REPUBLIC OF GERMANY     

《International Geology Review》2012,54(3):228-238

A stratigraphically coherent blueschist terrane near Aksu in northwestern China is unconformably overlain by unmetamorphosed sedimentary rocks of Sinian age (～600 to 800 Ma). The pre-Sinian metamorphic rocks, termed the Aksu Group, were derived from shales, sandstones, basaltic volcanic rocks, and minor cherty sediments. They have undergone multi-stage deformation and transitional blueschist/greenschist-facies metamorphism, and consist of strongly foliated chlorite-stilpnomelane-graphite schist, stilpnomelane-phengite psammitic schist, greenschist, blueschist, and minor quartzite, metachert, and meta-ironstone. Metamorphic minerals of basaltic blueschists include crossitic amphibole, epidote, chlorite, albite, quartz, and actinolite. Mineral parageneses and compositions of sodic amphibole suggest blueschist facies recrystallization at about 4 to 6 kbar and 300 to 400° C. Many thin diabasic dikes cut the Aksu Group; they are characterized by high alkali, TiO₂, and P₂O₅ contents and possess geochemical characteristics of within-plate basalts; some of these diabasic rocks contain sodic clinopyroxene and amphibole as primary phases and have minor pumpellyite, albite, epidote, chlorite, and calcite as the prehnite/pumpellyite-facies metamorphic assemblage. This prehnite/pumpellyite-facies overprint did not affect the host rocks of the blueschist-facies lithologies.

K-Ar and Rb-Sr ages of phengite and whole rocks from pelitic schists are ～690 to 728 Ma, and a ⁴⁰Ar/³⁹Ar age of crossite from the blueschist is 754 Ma. The basal conglomerate of the overlying Sinian to Eocambrian sedimentary succession contains clasts of both the blueschist and cross-cutting dike rocks, clearly demonstrating that conditions required for blueschist-facies metamorphism were attained and ceased at least 700 Ma. The northward-increasing metamorphic grade of the small blueschist terrane may reflect northward subduction of an accretionary complex beyond the northern edge of the Tarim craton. Abundant subparallel diabasic dikes indicate a subsequent period of Pre-Sinian rifting and diabasic intrusion along the northern margin of Tarim; a Sinian siliciclastic and carbonate sequence was deposited unconformably atop the Aksu Group and associated diabase dikes.  相似文献   

澜沧江杂岩带小黑江-上允地区蓝片岩的成因及变质演化     

王舫  刘福来  冀磊  刘平华  蔡佳  田忠华  刘利双 《岩石矿物学杂志》2016,35(5):804-820

通过对澜沧江杂岩带小黑江-上允地区蓝片岩的岩相学、地球化学、成因矿物学以及相平衡模拟的综合研究,阐述蓝片岩的原岩以及变质演化过程。地球化学分析结果显示,蓝片岩具有一致的稀土元素配分模式,具弱Eu正或负异常,稀土元素和微量元素特征与OIB相似,其原岩可能为OIB型玄武岩。详细矿物学研究表明,本区蓝片岩记录了俯冲峰期蓝片岩相变质和峰期后绿片岩相变质两个变质阶段,其矿物组合分别为蓝闪石+钠长石+多硅白云母+绿泥石+绿帘石和蓝闪石+钠长石±阳起石+绿泥石+绿帘石。通过Na_2O-Ca O-Fe O-MgO-Al_2O_3-SiO_2-H_2O-O体系相平衡计算,得到两个阶段的压力范围分别约为0.95 GPa和0.40 GPa。  相似文献   

Cold subduction of the Neotethys: the metamorphic record from finely banded lawsonite and epidote blueschists and associated metabasalts of the Nagaland Ophiolite Complex,India     

A. Ao  S. K. Bhowmik 《Journal of Metamorphic Geology》2014,32(8):829-860

In this study, we have deduced the thermal history of the subducting Neotethys from its eastern margin, using a suite of partially hydrated metabasalts from a segment of the Nagaland Ophiolite Complex (NOC), India. Located along the eastern extension of the Indus‐Tsangpo suture zone (ITSZ), the N–S‐trending NOC lies between the Indian and Burmese plates. The metabasalts, encased within a serpentinitic mélange, preserve a tectonically disturbed metamorphic sequence, which from west to east is greenschist (GS), pumpellyite–diopside (PD) and blueschist (BS) facies. Metabasalts in all the three metamorphic facies record prograde metamorphic overprints directly on primary igneous textures and igneous augite. In the BS facies unit, the metabasalts interbedded with marble show centimetre‐ to metre‐scale interlayering of lawsonite blueschist (LBS) and epidote blueschist (EBS). Prograde HP/LT metamorphism stabilized lawsonite + omphacite (X_Jd = 0.50–0.56 to 0.26–0.37) + jadeite (X_Jd = 0.67–0.79) + augite + ferroglaucophane + high‐Si phengite (Si = 3.6–3.65 atoms per formula unit, a.p.f.u.) + chlorite + titanite + quartz in LBS and lawsonite + glaucophane/ferroglaucophane ± epidote ± omphacite (X_Jd = 0.34) + chlorite + phengite (Si = 3.5 a.p.f.u.) + titanite + quartz in EBS at the metamorphic peak. Retrograde alteration, which was pervasive in the EBS, produced a sequence of mineral assemblages from omphacite and lawsonite‐absent, epidote + glaucophane/ferroglaucophane + chlorite + phengite + titanite + quartz through albite + chlorite + glaucophane to lawsonite + albite + high‐Si phengite (Si = 3.6–3.7 a.p.f.u.) + glaucophane + epidote + quartz. In the PD facies metabasalts, the peak mineral assemblage, pumpellyite + chlorite + titanite + phengitic white mica (Si = 3.4–3.5 a.p.f.u.) + diopside appeared in the basaltic groundmass from reacting titaniferous augite and low‐Si phengite, with prehnite additionally producing pumpellyite in early vein domains. In the GS facies metabasalts, incomplete hydration of augite produced albite + epidote + actinolite + chlorite + titanite + phengite + augite mineral assemblage. Based on calculated T–M(H₂O), T–M(O₂) (where M represents oxide mol.%) and P–T pseudosections, peak P–T conditions of LBS are estimated at ~11.5 kbar and ~340 °C, EBS at ~10 kbar, 325 °C and PD facies at ~6 kbar, 335 °C. Reconstructed metamorphic reaction pathways integrated with the results of P–T pseudosection modelling define a near‐complete, hairpin, clockwise P–T loop for the BS and a prograde P–T path with a steep dP/dT for the PD facies rocks. Apparent low thermal gradient of 8 °C km^?1 corresponding to a maximum burial depth of 40 km and the hairpin P–T trajectory together suggest a cold and mature stage of an intra‐oceanic subduction zone setting for the Nagaland blueschists. The metamorphic constraints established above when combined with petrological findings from the ophiolitic massifs along the whole ITSZ suggest that intra‐oceanic subduction systems within the Neotethys between India and the Lhasa terrane/the Karakoram microcontinent were also active towards east between Indian and Burmese plates.  相似文献   

Die Glaukophangesteine,ihre stofflichen Äquivalente und Uniwandlungsprodukte in Nordcalabrien (Süditalien)     

Dr. Christoph Hoffmann 《Contributions to Mineralogy and Petrology》1970,27(4):283-320

In the southern Apennin (= northern part of the region dealt with) and the Coasta Chain (= southern part) there are metabasalts wich are classified in the northern part as:

1. Glaucophane rocks of the albite-lawsonite-glaucophane-subfacies with the assemblage glaucophane + pumpellyite + lawsonite ±albite ±aragonite ±muscovite (7 rock analyses, 8 mineral analyses). These rocks are conceived as relics of an older burial metamorphism.
2. Rocks with pumpellyite and chlorite or also chlorite alone, that are interpreted as reaction rims between the metastable glaucophane rocks and the country rock (phyllites, quartzites). The assemblages pumpellyite + chlorite and chlorite alone are to be found (2 rock analyses and 2 mineral analyses).
3. Rocks with lawsonite and/or epidote belong to the same mineral facies as the country rock: a facies similar to the greenschist facies (called “lawsonite-albite-chlorite-subfacies”) which is characterized by the assemblages lawsonite + albite + chlorite ±calcite and also epidote ±lawsonite + albite + chlorite ± muscovite. These types are attributed to a younger dynamo-metamorphism (2 rock analyses).

In the southern part, the metabasalts can be found only as rocks with epidote and/or lawsonite, a metamorphism with more than one event cannot be proved petrologically (3 rock analyses). Equations of the observed mineral reactions are given. The transitions of one facies into another are represented in the pseudo-quaternary system Al₂O₃-CaO-Na₂O · Al₂O₃-2 Fe₂O₃ + FeO + MnO + MgO-(H₂O). The pressure-temperature conditions are estimated on the basis of published experimental data (300° C and 6–7 kb for the glaucophane rocks; 400° C and about 6 kb for the rocks with lawsonite and/or epidote) and are compared with geologic facts.  相似文献   

Mineralogy of New Caledonian metamorphic rocks     

Philippa M. Black 《Contributions to Mineralogy and Petrology》1973,38(3):221-235

A Cretaceous to low-Tertiary sequence of interbedded pelites, cherts, basic and acidic volcanics and calcareous lenses has been metamorphosed by an Oligocene event. A complete intergradational metamorphic sequence is exposed in the Ouégoa destrict. The following metamorphic zones have been recognised: — (1) lowest-grade rocks consisting of quartz-sericite phyllites and pumpellyite metabasalts (2) lawsonite zone, characterized by the association of lawsonite and albite (3) epidote zone, characterised by epidote-omphacite-sodic hornblendealmandine bearing metabasalts and epidote-albite-almandine-glaucophane bearing metasediments; calcareous metasediments may also carry omphacite. The epidote and lawsonite zones are separated by a narrow belt of transitional rocks. Garnets occur in metasediments throughout the lawsonite zone as rare tiny crystals (<0.03 mm diam.). Garnets first appear in metabasalts in lawsonite-epidote transitional rocks. Garnets are widespread and abundant in epidote-zone metasediments and metabasalts. 45 garnets from rocks representative of all lithologies and metamorphic grades have been analysed with an electron-probe microanalyser. The garnets were consistently zoned. Garnets in lawsonite and low-grade epidote zones show a “bell-type” zoning with cores enriched in Mn relative to Fe and rims enriched in Fe, Mg and frequently Ca. Garnets from high-grade epidote-zone metapelites and metabasalts show, in addition, a shallow oscillatory zoning with complimentary variations in Mn and Fe equivalent to 5 mole- % spessartine and almandine. The Fe-for-Mn substitutional zoning, believed to be caused by a diffusion/saturation effect similar to that of the Rayleigh fractional model (Hollister, 1966), appears to have had superimposed on it the effects of parent-rock chemistry and metamorphic grade which control in a complex manner the composition of the cores and the rims of garnets. Garnets from different rock types and metamorphic grade are compositionally distinct. Garnets from lawsonite-zone rocks, irrespective of parent-rock chemistry appear to be spessartine. Garnets from epidote-zone metaigneous rocks and most metasediments are almandine. Garnets from epidote-zone metasediments with bulk-rock compositions which are manganiferous, or have high oxidation ratios, or both, may be spessartine-rich. Garnets from metabasalts are consistently more pyropic in both core and rim compositions than garnets from pelitic metasediments; the pyrope content of cores and rims of garnets from equivalent rock types and mineral assemblages increases with increasing metamorphic grade. Cores of garnets from epidote-zone pelites are richer in grossular than garnets from lower-grade pelites. The reaction which brings almandine garnet into Ouégoa district blueschist assemblages simultaneously with the replacement of lawsonite by epidote involves components of chlorites and sodic amphiboles and can be represented by the following simplified equation: ferroglaucophane+Fe-rich chlorite+lawsonite → glaucophane+Mg-rich chlorite+epidote+almandine.  相似文献   

Calculated phase equilibria for MORB compositions: a reappraisal of the metamorphic evolution of lawsonite eclogite   总被引：3，自引：0，他引：3  

C. J. WEI  G. L. CLARKE 《Journal of Metamorphic Geology》2011,29(9):939-952

Pseudosections calculated with thermocalc predict that lawsonite‐bearing assemblages, including lawsonite eclogite, will be common for subducted oceanic crust that experiences cool, fluid‐saturated conditions. For glaucophane–lawsonite eclogite facies conditions (500–600 °C and 18–28 kbar), MORB compositions are predicted in the NCKMnFMASHO system to contain glaucophane, garnet, omphacite, lawsonite, phengite and quartz, with chlorite at lower temperature and talc at higher temperature. In these assemblages, the pyrope content in garnet is mostly controlled by variations in temperature, and grossular content is strongly controlled by pressure. The silica content in phengite increases linearly with pressure. As the P–T conditions for these given isopleths are only subtly affected by common variations in bulk‐rock compositions, the P–T pseudosections potentially present a robust geothermobarometric method for natural glaucophane‐bearing eclogites. Thermobarometric results recovered both by isopleth and conventional approaches indicate that most natural glaucophane–lawsonite eclogites (Type‐L) and glaucophane–epidote eclogites (Type‐E) record similar peak P–T conditions within the lawsonite stability field. Decompression from conditions appropriate for lawsonite stability should result in epidote‐bearing assemblages through dehydration reactions controlled by lawsonite + omphacite = glaucophane + epidote + H₂O. Lawsonite and omphacite breakdown will be accompanied by the release of a large amount of bound fluid, such that eclogite assemblages are variably recrystallized to glaucophane‐rich blueschist. Calculated pseudosections indicate that eclogite assemblages form most readily in Ca‐rich rocks and blueschist assemblages most readily in Ca‐poor rocks. This distinction in bulk‐rock composition can account for the co‐existence of low‐T eclogite and blueschist in high‐pressure terranes.  相似文献   

Phase equilibria among pumpellyite,lawsonite, epidote and associated minerals in low grade metamorphic rocks     

E. H. Brown 《Contributions to Mineralogy and Petrology》1977,64(2):123-136

Phase relations of pumpellyite, epidote, lawsonite, CaCO₃, paragonite, actinolite, crossite and iron oxide are analysed on an Al-Ca-Fe³⁺ diagram in which all minerals are projected from quartz, albite or Jadeite, chlorite and fluid. Fe²⁺ and Mg are treated as a single component because variation in Fe²⁺/Mg has little effect on the stability of phases on the diagram. Comparison of assemblages in the Franciscan, Shuksan, Sanbagawa, New Caledonia, Southern Italian, and Otago metamorphic terranes reveals several reactions, useful for construction of a petrogenetic grid:

1. lawsonite+crossite + paragonite = epidote+chlorite + albite + quartz + H₂O
2. lawsonite + crossite = pumpellyite + epidote + chlorite + albite+ quartz + H₂O
3. crossite + pumpellyite + quartz = epidote + actinolite + albite + chlorite + H₂O
4. crossite + epidote + quartz = actinolite + hematite + albite + chlorite + H₂O
5. calcite + epidote + chlorite + quartz = pumpellyite + actinolite + H₂O + CO₂
6. pumpellyite + chlorite + quartz = epidote + actinolite + H₂O

  相似文献   

Transition from the Zeolite to Prehnite-Pumpellyite Facies in the Karmutsen Metabasites, Vancouver Island, British Columbia   总被引：1，自引：0，他引：1  

CHO  MOONSUP; LIOU  J. G.; MARUYAMA  S. 《Journal of Petrology》1986,27(2):467-494

The upper Triassic Karmutsen metabasites from northeast VancouverIsland, B.C., are thermally metamorphosed by the intrusion ofthe Coast Range Batholith. The amygdaloidal metabasites developedin the outer portion of the contact aureole show a progressivemetamorphism from zeolite to prehnite-pumpellyite facies. Thesize of an equilibrium domain is extremely small for these metabasites,and the individual amygdule assemblages are assumed to be inequilibrium. Two major calcite-free assemblages (+chlorite+quartz)are characteristic: (i) laumontite+pumpellyite+epidote in thezeolite facies and (ii) prehnite+pumpellyite+epidote in theprehnite-pumpellyite facies. The assemblages and compositionsof Ca-Al silicates are chemographically and theoretically interpretedon the basis of the predicted P-T grid for the model basalticsystem, CaO-MgO-A1₂O₃-Fe₂O₃-SiO₂-H₂O. The results indicate:(1) local equilibrium has been approached in mineral assemblagesand compositions; (2) the X_Fe³⁺ values in the coexisting Ca-Alsilicates decrease from epidote, through pumpellyite to prehnite;(3) with increasing metamorphic grade, the Fe³⁺ contents ofepidotes in reaction assemblages decrease in the zeolite facies,then increase in the prehnite-pumpellyite facies rocks. Suchvariations in the assemblages and mineral compositions are controlledby a sequence of continuous and discontinuous reactions, andallow delineation of T-X_Fe³⁺ relations at constant pressure.The transition from the zeolite to prehnite-pumpellyite faciesof the Karmutsen metabasites is defined by a discontinuous reaction:0·18 laumontite+pumpellyite+0·15 quartz = 1·31prehnite+ 0·78 epidote+0·2 chlorite+ 1·72H₂O, where the X_Fe³⁺ values of prehnite, pumpellyite and epidoteare 0·03, 0·10 and 0·18, respectively.These values together with available thermodynamic data andour preliminary experimental data are used to calculate theP-T condition for the discontinuous reaction as P = 1·1±0·5 kb and T = 190±30°C. The effectsof pressure on the upper stability of the zeolite facies assemblagesare discussed utilizing T-X_Fe³⁺ diagrams. The stability of thelaumontite-bearing assemblages for the zeolite facies metamorphismof basaltic rocks may be defined by either continuous or discontinuousreactions depending on the imposed metamorphic field gradient.Hence, the zeolite and prehnite-pumpellyite facies transitionboundary is multivariant.  相似文献   

Petrology of Franciscan Metabasites Along the Jadeite-Glaucophane Type Facies Series, Cazadero, California   总被引：1，自引：0，他引：1  

MARUYAMA  S.; LIOU  J. G. 《Journal of Petrology》1988,29(1):1-37

The Cazadero blueschist allochthon lies within the Central MelangeBelt of the Franciscan assemblage in the northern Coast Rangeof California. Mineral compositions and assemblages of morethan 200 blueschists from Ward Creek were investigated. Theresults delineate lawsonite-, pumpellyite-, and epidote-zones.The lawsonite and pumpellyite zones are equivalent to the TypeII metabasites of Coleman & Lee (1963) and are characterizedby well-preserved igneous textures, relict augite, and pillowstructures, whereas epidote zone rocks are equivalent to theType III strongly deformed and schistose metabasites. Chlorite,phengite, aragonite, sphene, and minor quartz and albite areubiquitous. The lawsonite zone metabasites contain lawsonite ( < 3 wt.per cent Fe₂O₃), riebeckite-crossite, chlorite, and Ca-Na-pyroxene;some rocks have two distinct clinopyroxenes separated by a compositionalgap. The clinopyroxene of the lowest grade metabasites containsvery low X_jd. In pumpellyite zone metabasites, the most commonassemblages contain Pm + Cpx + Gl + Chl and some samples withhigher Al₂O₃ and/or Fe₂O₃ have Pm + Lw + Cpx + Chl, Actinolitejoins the above assemblage in the upper pumpellyite zone wherethe actinolite-glaucophane compositional gap is well defined.The epidote zone metabasites are characterized by the assemblagesEp + Cpx + two amphiboles + Chl, Lw + Pm + Act + Chl, and Ep+ Pm + two amphiboles + Chl depending on the Fe₂O₃ content ofthe rock. In the upper epidote zone, winchite appears, Fe-freelawsonite is stable, pumpellyite disappears and omphacite containsvery low Ac component. Therefore, the common assemblages areEp + winchite + Lw, and Lw + Omp + winchite. With further increasein metamorphic grade, epidote becomes Al-rich and lawsoniteis no longer stable. Hence Ep + winchite + omphacite ? garnetis characteristic. Mineral assemblages and paragenetic sequences delineate threediscontinuous reactions: (1) pumpellyite-in; (2) actinolite-in;and (3) epidote-in reactions. Using the temperatures estimatedby Taylor & Coleman (1968) and phase equilibria for Ca-Na-pyroxenes,the P–T positions of these reactions and the metamorphicgradient are located. All three metabasite zones occur withinthe aragonite stability field and are bounded by the maximumpressure curve of Ab = Jd + Qz and the maximum stabilities ofpumpellyite and lawsonite. The lawsonite zone appears to bestable at T below 200?C with a pressure range of 4–6?5kb; the pumpellyite zone between 200 and 290?C and the epidotezone above 290?C with pressure variation between 6?5 and 9 kb.The metamorphic field gradient appears to have a convex naturetowards higher pressure. A speculative model of underplatingseamounts is used to explain such feature.  相似文献   

Synthesis of Fe-pumpellyite and its stability relations with epidote     

PETER SCHIFFMAN  J. G. LIOU 《Journal of Metamorphic Geology》1983,1(2):91-101

Hydrothermal synthesis of Fe-pum-pellyites was conducted using high pressure cold-seal apparatus and solid oxygen buffering techniques at temperatures between 250°C and 550°C and 2.0–9.1 kbar P_fluid. Fe-pumpellyites were synthesized from partially crystalline gel mixtures of compositions: 4CaO - 2.1Al₂O₃_1.5FeO - 0.3MgO - 6SiO₂ (II) and 3CaO - 1.5 Al₂O₃ - 2.7FeO - 0.3MgO - 6SiO₂ (III) in the presence of excess H₂O at P_fluid of 5–9.1 Kbar, temperatures between 275°C and 325°C, and f_O2 defined by the QFM and HM buffers; for both of these compositions (II and III), the condensed synthetic run products included minor 7Å chlorite ± garnet ± Fe-oxide. The cell dimensions and aggregate refractive index (a= 19.13(2)Å, b= 5.940(4)Å, c= 8.847(5)Å, ±= 97.37(6)±, and n= 1.702(2)) of the pum-pellyite synthesized from the bulk composition II mix are compatible with those of natural pumpellyites containing similar total Fe contents. Attempts at synthesizing Fe-pumpellyites from a Mg-free bulk composition were not successful; these results are consistent with the total absence of natural Mg-free pumpellyites. The higher temperature, higher oxygen fugacity assemblages of the equivalent bulk compositions (II and III) consist of epidote ± minor amounts of chlorite, garnet, quartz, hematite, and magnetite. The results of these synthesis experiments accord with the mineral parageneses observed in low-grade metabasites which imply that Fe-pumpellyites are replaced by epidote with increasing temperature and/or f_O2 and that Fe³⁺ is preferentially partitioned into epidote with respect to coexisting pum-pellyite. In addition, these synthesis experiments indicate that Fe-bearing pumpellyites crystallize at and are stable to lower temperatures than more aluminous pumpellyites—a result also consistent with natural systems.  相似文献   

Prehnite-Pumpellyite to Greenschist Fades Transition in the Karmutsen Metabasites, Vancouver Island, B.C.     

CHO  MOONSUP; LIOU  J. G. 《Journal of Petrology》1987,28(3):417-443

Mineral paragenescs in the prehnite-pumpellyite to greenschistfades transition of the Karmutsen metabasites are markedly differentbetween amygdule and matrix, indicating that the size of equilibriumdomain is very small. Characteristic amygdule assemblages (+chlorite + quartz) vary from: (1) prehnite + pumpeUyite + epidote,prehnite + pumpellyite + calcite, and pumpellyite + epidote+ calcite for the prehnite-pumpellyite facies; through (2) calcite+ epidote + prehnite or pumpellyite for the transition zone;to (3) actinolite + epidote + calrite for the greenschist facies.Actinolite first appears in the matrix of the transition zone.Na-rich wairakites containing rare analcime inclusions coexistwith epidote or Al-rich pumpellyite in one prehnite-pumpellyitefacies sample. Phase relations and compositions of these wairakite-bearingassemblages further suggest that pumpellyite may have a compositionalgap between 0.10 and 0.15 X_Fe?. Although the facies boundaries are gradational due to the multi-varianceof the assemblages, several transition equilibria are establishedin the amygdule assemblages. At low X_co2, pumpellyite disappearsprior to prehnite by a discontinuous-type reaction, pumpellyite+ quartz + CO₂ = prehnite + epidote + calcite + chlorite + H₂O,whereas prehnite disappears by a continuous-type reaction, prehnite+ CO₂ = calcite + epidote + quartz-l-H₂O. On the other hand,at higher X_CO2 a prehnite-out reaction, prehnite + chlorite+ H₂O + CO₂ = calcite + pumpellyite + quartz, precedes a pumpellyiteoutreaction, pumpellyite + CO₂ = calcite + epidote + chlorite +quartz + H₂O. The first appearance of the greenschist faciesassemblages is defined at both low and high XCOj by a reaction,calcite + chlorite + quartz = epidote + actinolite+ H₂O + CO₂.Thus, these transition equilibria are highly dependent on bothX_Fe³⁺ + of Ca-Al silicates and X_H20 of the fluid phase. Phaseequilibria together with the compositional data of Ca-Al silicatesindicate that the prehnite-pumpellyite to greenschist faciestransition for the Karmutsen metabasites occurred at approximately1.7 kb and 300?C, and at very low X_co2, probably far less than0.1.  相似文献   

内蒙古头道桥地区蓝闪石片岩和相关变质岩石岩石学特征及其构造意义     

赵立敏  刘永江  滕加雨  李伟民 《吉林大学学报(地球科学版)》2018,48(2):534-544

内蒙古头道桥地区出露了一套经高压变质形成的岩石组合。本次研究通过岩相学和矿物化学分析,根据矿物组合的不同,识别出蓝片岩、绿片岩两种不同类型的岩石类型。其中,蓝片岩的矿物组合为角闪石（蓝闪石、蓝透闪石）+绿帘石+钠长石+绿泥石+石英+赤铁矿±多硅白云母±方解石±榍石;绿片岩的矿物组合为绿泥石+钠长石+石英±绿帘石±角闪石（阳起石、镁角闪石、蓝透闪石、冻蓝闪石等）±多硅白云母±赤铁矿。确定了蓝片岩的峰期变质级别为绿帘-蓝闪片岩相,峰期变质温度为400~600℃,压力为1.2~1.4 GPa。绿片岩的峰期变质级别为绿帘-角闪岩相。结合前人研究成果,认为蓝片岩和绿片岩的形成与额尔古纳地块和兴安地块的碰撞拼合有关。  相似文献