ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1984.tb00286.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1984.tb00287.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractAt Sulitjelma, Norway, there is a major inversion of metamorphic isograds beneath an inverted but undisrupted ophiolite. The flysch‐like Furulund schist in which the inverted isograds occur is also inverted and the early folds in it are downward facing. The isograds cut across the axial surfaces of early folds and across the schistosity. These relationships are explained as the consequence of metamorphism during the progressive development of a large overfold. The inverted limb of the overfold is regarded as a major, thick, gently‐dipping shear zone, separating the lower‐grade, lower part of the Caledonian allochthon below from the higher‐grade upper part of the allochthon above. The association between stratigraphical inversion, downward‐facing of syn‐schistosity folds and metamorphic inversion is explained by the progressive development of the shear zone. It is suggested that the presence of such shear zones is a common feature of orogenic belts formed by continenta

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1984.tb00288.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractA major system of steep Caledonian shear zones, of regional extent, has been identified in NE Scotland. The shear zones affect a wide range of lithologies, including Argyll and Southern Highland Group Dalradian, ‘Younger Basic’intrusives and their hornfelses, and also the earlier of the more acid intrusions. The observed fabrics and parageneses are consistent with low‐pressure amphibolite facies metamorphism. These shear zones represent a phase of movement which occurred in the 490‐465 Ma interval when ambient temperatures were still high, and it is concluded that this is the principal control on the metamorphic grade achieved within the shear zones, although local anomalies ma

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1984.tb00289.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe Hercynian granitic basement which forms the Tenda Massif in NE Corsica represents part of the leading edge of the European Plate during middle‐to‐late Cretaceous (Eoalpine) high P metamorphism. The metamorphism of this basement, induced by the overthrusting of a blueschist facies (schistes lustrés) nappe, was confined to a major ductile shear zone (c. 1000m thick) within which deformation increases upwards towards the overlying nappe. Metamorphism within the basement mostly records lower blueschist facies conditions (crossite + epidote) except near the base of the shear zone where the greenschist facies assemblage albite + actinolitic amphibole has developed instead of crossite. Study of the primary mafic phase breakdown reactions within hornblende granodiorite reveals the following metamorphic zonation. Zone 1: biotite to chlorite. Towards zone 2: biotite to phengite. Zone 2: Hornblende to actinolitic Ca‐amphibole + albite + sphene, and biotite to actinolitic Ca‐amphibole + albite + phengite + Ti‐ore + epidote. Zone 3: Hornblende to crossite + low Ti‐biotite + phengite + sphene, and biotite to crossite + low Ti‐biotite + phengite + Ti‐ore + sphene ± epidote. P‐T conditions at the base of the shear zone are estimated to have been 390‐490°C at 600‐900 M Pa (6‐9kbar) and the Corsican basement is therefore deduced to have been buried to 20‐30 km during metamorphism. This relatively shallow metamorphism contrasts with some other areas in the Western Alps where the Eoalpine event apparently buried the European continental crust to depths of 80 km or more. As there is no evidence for a long history of blueschist facies metamorphism prior to the involvement of the European continent, it is deduced that the Eoalpine blueschists were produced during the collision of the Insubric plate with Europe, rather than during Tethyan intraoceanic subduction. Coherent blueschist terrains such as the schistes lustres probably record buovant feature collision and obduction tectonics rather than any

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1984.tb00290.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThere are discrete masses of un‐deformed metabasite within the blueschist series of the island of Syros. Greece. Around the margins of these masses are zonal sequences through rocks showing intracrystalline deformation but without a geometric fabric, to rocks with discrete and anastomosing shear zones, and finally to penetratively foliated rocks with isolated relics of the original undeformed texture. Textural relics suggest that this spatial sequence is at least qualitatively also a temporal sequence.This progressive shear zone deformation took place concurrently with a glaucophane‐epidote to eclogite reaction. The reaction pathways in the rocks that underwent the shear zone deformation can be compared with those in rocks of a similar composition that suffered a longer deformation history and show no relics of an undeformed parent. Although the final assemblages are in both cases the same, the pathways are different. These differences are in part related to reactions promoted by the change from local to bulk equilibrium on the onset of deformation in the rocks. They are also related to the crystallization and later breakdown during the sequence of progressive equilibration of a metastable phase, in this case an impure glaucoph

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1984.tb00291.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractMylonites from shear zones cutting Hercynian gneisses in the central Pyrenees have been studied in thin section and using the electron microprobe. The shear zones contain retrogressive greenschist facies assemblages implying introduction of an aqueous fluid during deformation in the zones. Textural evidence suggests that fluid‐rock interaction occurred throughout the active life of the shear zones.Whole‐rock chemical changes during deformation are documented in a variety of mylonitic lithologies and retrogressed country rocks. The overall effect was to reduce chemical differences between lithologies. Activity diagrams show that this would be expected if a hydrous fluid was circulating between different lithologies during deformation. In most cases fluid/rock ratios were relatively small resulting in gradual chemical changes and repeated recrystallization. ‘Open‐system’behaviour with reduction in the number of phases is seen in some granite mylonites, suggesting focusing of fluid movement in parts of the shear zones. Continual fluid‐rock interaction may have led to reaction‐enhanced ductility in the shear zones over a long period of time. The source of fluid is uncertain, but may be related to underthrusting of material beneath the area

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1984.tb00292.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe Rockley Volcanics from near Oberon, New South Wales occur within the aureole of the Carboniferous Bathurst Batholith and have been contact metamorphosed at P ∼ 100 ± 50MPa (10.5kbar) and a maximum T ∼ 565°C in the presence of a C–O–H fluid. Prior to contact metamorphism the volcanics were regionally metamorphosed and altered with the extensive development of actinolite, chlorite, plagioclase, quartz and calcite. The contact metamorphosed equivalents of these rocks have been subdivided into: Ca‐poor (cordierite + gedrite), Mg‐rich (amphibole + olivine + spinel), mafic (amphibole + plagioclase) and Ca‐rich (amphibole + garnet + diopside; diopside + plagioclase; garnet + diopside + wollastonite) rocks.The chemistry of the minerals in the hornfelses was controlled by the bulk rock chemistry and fluid composition. Pargasites and hastingsites as well as an unusual phlogopite with blue green pleochroism, are found in Ca‐rich hornfelses. A comparison of the assemblages with experimentally derived equilibria suggests that the fluid phase associated with the Ca‐rich hornfelses was water‐rich (Xco2= 0.1 to 0.3) while that associated with the Mg‐rich hornfelses was enriched in CO2(Xco2>0.7). The different hornfels types have reacted to contact metamorphism independently in both their soli

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1984.tb00293.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe hornblende‐bearing basic gneisses in the Uvete area, central Kenya, were metamorphosed under a narrow range of P and T (6.5 ± 0.5kbar and 530 ± 40°C) of the staurolitekyanite zone in the Mozambique metamorphic belt. They show a wide variety of divariant and trivariant mineral assemblages consisting of hornblende, cumminatonite, gedrite, anthophyllite, chlorite, garnet, epidote, clinopyroxene, plagio‐clase and quartz. The bulk and mineral chemistries and the graphical representation of phase relations show that each mineral assemblage approaches chemical equilibrium and defines a unique composition volume in the A′(Al + Fe3+− (13/7)Na)‐F(Fe2+)‐M′(Mg)‐C′(Ca‐(3/7)Na) tetrahedron. The composition volumes are distributed quite regularly and do not overlap each other.The phase relations in the Uvete area are in contrast with those in the staurolite‐kyanite zone amphibolites in the Mt. Cube quadrangle, Vermont. The amphibolites there contain low‐variance mineral assemblages formed under different values of μH2Oand μCO2. These assemblages define overlapping composition volumes in the A′‐F′‐M′‐C’tetrahedron.The mineral assemblages in the Uvete area are interpreted as having formed in equilibrium with fluid at a high and nearly constant μH2O value. Such a fluid composition was externally controlled by the supply of H2O‐rich fluid expelled from the surrounding pelitic and psammitic rocks. The body size of the basic gneisses in the Uvete area (less than 400m in thickness) was sma

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1984.tb00294.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY