摘要:

AbstractFluid inclusions in ore skarn minerals reflect the physiochemical nature of the solutions present during the skarn‐forming process. Because of the dense nature of skarn minerals and the dynamic processes operative during skarn genesis, sufficient primary fluid inclusions are usually present. Ore skarn solutions, as opposed to metamorphic skarn or ore vein solutions, have much higher CaCl2contents and usually very high formation temperatures (>500°C) and salinities (>40 wt % T.D.S.). Temperatures and salinities generally decrease away from the solution source, both in time and space. The gradients found at greater distances from the source in distal (far from contact) skarns tend to be less (e.g. 210–350°C) for a particular skarn stage to that in proximal (near contact) skarns (e.g. 400–650°C). This information is useful for delineating the parts of such a hydrothermal system. Temperatures also tend to decrease with time, which is reflected by the superimposition of various overprinting, retrograde mineral stages. In a few areas (e.g. Naica, Mexico) intermittent boiling of ore solutions occurs, periodically elevating both temperatures and salinities, but commonly boiling only occurs early in skarn genesis just after an early, commonly lower temperature, phase.Most fluid inclusions represent a mix of‘exhaust’or reacted solutions with minor unreacted or new (pre‐) ore solution components. Limited data on the distribution of elements present in fluid inclusions that do not normally take part in skarn genesis (Na, K and Cl) indicate that their proportions reflect the nature of the associated pluton. High KC1 contents are found in skarns adjacent to high K granitoids, whereas high NaCl contents are found in skarns adjacent to calcic granitoids.In many examples, daughter minerals present in minor proportions in opened fluid inclusion cavities reflect the metal characteristics of the ore solution. Small rare‐earth metal, tungsten, zinc and copper daughter(?) minerals have been identified. The temperature and (or) salinity data for skarns of different metal or geological type is not particularly useful to delineate whether a skarn locality is part of a more complex, as yet unexplored system. Solutions in Pb–Zn skarns tend to be lower‐temperature (150–400°C) and more dilute (<30 wt % T.D.S.) than in other skarn type

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1986.tb00358.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractA deerite‐bearing rock occurs at the boundary between quartzite and metabasites within the ‘schistes lustrés’of eastern Corsica. It contains the typomorphic assemblage pyroxene, blue amphibole, hematite and magnetite. Pyroxene shows homogeneous composition close to the aegirine end‐member and blue amphibole is zoned from crossite core to riebeckite rim. The bulk chemical analysis of the rock is remarkable by its very high iron content and the presence of an unusually large amount of Zn which is concentrated in both deerite and amphibole. Electron microprobe analyses of the Corsican deerite are compared with those published in the literature; as shown by deerite from the Fransciscan iron formation, the principal substitution for Fe2+is Mn whereas the amount of substitution for Fe3+is low. In the system SiO2‐FeO‐Fe2O3‐Al2O3‐Na2O‐MgO‐H2O the typomorphic paragenesis can be described by an univariant reaction interpreted as the result of a pressure decrease.P‐Tconditions of metamorphism, previously estimated to be 8 kbar and 300°C, are in good agreement with present knowledge of the deerite stability field. The occurrence of hematite and magnetite in equilibrium permits an estimation of the oxygen fugacity (logfo2= ‐29.41 bar). Oxidation conditions are higher than those previously mentioned in the literatur

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1986.tb00359.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe upper Jurassic Nikoro greenstone complex of eastern Hokkaido suffered high‐pressure intermediate type metamorphism. Characteristic minerals include lawsonite, aragonite, sodic pyroxene of the aegirinejadeite series, winchite. sodic amphibole of the glaucophane‐riebeckite series, pumpellyite, epidote and actinolite.High‐pressure metamorphism of the Nikoro greenstone complex is related to subduction of the Kula plate toward the Palaeo‐Okhotsk Land during Cretaceo

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1986.tb00360.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe magnitudes of plastic strains of 104 metacherts were determined from the deformed shape of initially spherical radiolarians in the Sambagawa high‐Ptype metamorphic belt of Western Shikoku, Japan. The strain magnitude increases with increasing metamorphic temperature from several per cent to 250%. The a2/a3ratio of strain ellipsoids in the higher metamorphic grades decreases with increasing metamorphic grade while the a1/a2ratio increases rapidly. The long axis of the strain ellipsoid for every grade is nearly parallel to the length of the metamorphic belt, suggesting that the flow direction of the synmetamorphic deformation was uniform along the belt. A map of strain zones within the Sambagawa high‐Ptype metamorphic belt reveals that the metamorphic belt underwent a progressive bulk inhomogeneous shear deformation and that the high‐grade zones represent a deep‐seated boundary shear zone on the accretionary wedge between a subducting oceanic plate and the immobile rigid continenta

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1986.tb00361.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractReactivation of early foliations accounts for much of the progressive strain at more advanced stages of deformation. Its role has generally been insufficiently emphasized because evidence is best preserved where porphyroblasts which contain inclusion trails are present. Reactivation occurs when progressive shearing, operating in a synthetic anastomosing fashion parallel to the axial planes of folds, changes to a combination of coarse‐ and finescale zones of progressive shearing, some of which operate antithetically relative to the bulk shear on a fold limb. Reactivation of earlier foliations occurs in these latter zones.Reactivation decrenulates pre‐existing or just‐formed crenulations, generating shearing along the decrenulated or rotated pre‐existing foliation planes. Partitioning of deformation within these foliation planes, such that phyllosilicates and/or graphite take up progressive shearing strain and other minerals accommodate progressive shortening strain, causes dissolution of these other minerals. This results in concentration of the phyllosilicates in a similar, but more penetrative manner to the formation of a differentiated crenulation cleavage, except that the foliation can form or intensify on a fold limb at a considerable angle to the axial plane of synchronous macroscopic folds.Reactivation can generate bedding‐parallel schistosity in multideformed and metamorphosed terrains without associated folds. Heterogeneous reactivation of bedding generates rootless intrafolial folds with sigmoidal axial planes from formerly through‐going structures. Reactivation causes rotation or ‘refraction’of axial‐plane foliations (forming in the same deformation event causing reactivation) in those beds or zones in which an earlier foliation has been reactivated, and results in destruction of the originally axial‐plane foliation at high strains. Reactivation also provides a simple explanation for the apparently ‘wrong sense’, but normally observed ‘rotation’of garnet porphyroblasts, whereby the external foliation has undergone rotation due to antithetic shear on the reactivated foliation. Alternatively, the rotation of the external foliation can be due to its reactivation in a subsequent deformation event.Porphyroblasts with inclusion trails commonly preserve evidence of reactivation of earlier foliations and therefore can be used to identify the presence of a deformation that has not been recognized by normal geometric methods, because of penetrative reactivation. Reactivation often reverses the asymmetry between pre‐existing foliations and bedding on one limb of a later fold, leading to problems in the geometric analysis of an area when the location of early fold hinges is essential. The stretching lineation in a reactivated foliation can be radically reoriented, potentially causing major errors in determining movement directions in mylonitic schistosities in folded thrusts.Geometric relationships which result from reactivation of foliations around porphyroblasts can be used to aid determination of the timing of the growth of porphyroblasts relative to deformation events. Other aspects of reactivation, however, can lead to complications in timing of porphyroblast growth if the presence of this phenomenon is not recognized; for example, D2‐grown porphyroblasts may be dissolved against reactivated S1and he

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1986.tb00362.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractIn the Kamuikotan zone, jadeite occurs in pelitic rocks, in metaplagiogranites, in veins in amphibolites and mafic sedimentary rocks, and in jadeite‐albite rocks. In the first and second types, jadeite is associated with quartz, and is often in direct contact with it. However, such rock‐types never occur as part of the coherent metamorphic sequence, but are found only as exotic blocks enclosed in serpentinite. Thus, jadeite + quartz‐bearing assemblages are not regarded as representative of the Kamuikotan metamorphism. Lawsonite and aragonite, however, commonly do occur in the Kamuikotan metamorphic rocks, and this metamorphism belongs to a subfacies of the lawsonite‐albite facies, in which aragonite is stable. The serpentinite matrix which carried jadeite + quartz‐bearing pelites and metaplagiogranites into the metamorphic sequence is interpreted as a tectonic rather than a sedimentar

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1986.tb00363.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1986.tb00364.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1986.tb00365.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY