ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1990.tb00470.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

METPET is a package of three interactive microcomputer (IBM PC or compatible) programs. FILEMAN is a utility program to create, edit and print ‘composition files’, i.e. files containing the records of chemical compositions of minerals or rocks, expressed in terms ofprimarychemical components. PROJECT recalculates selected compositions in terms of new (secondary) components. It then projects these compositions onto a subspace defined by two, three or more of the secondary components, first giving a plot on the screen and then, if requested by the user, on a selected graphic device. REACT calculates a possible set of independent reactions between a set of phases, whether pure compounds or solutions. Any linear combination of the independent reactions can be calculated on requ

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1990.tb00471.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Low‐pressure metamorphic facies (i.e. highT/Pratios) are widespread in a wide range of tectonic settings. Explanations offered for the occurrence of these facies include extensional and/or magmatic models. However, these fail to explain that the low‐Pfacies metamorphism is commonly coeval with a phase of pervasive crustal thickening, withT/Pratios increasing during, or slightly lagging behind, the thickening. We propose an alternative explanation based on the approximate synchroneity of crustal thickening and erosion (thinning) of the mantle lithosph

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1990.tb00472.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Metamorphic mineral assemblages and textures from Early Palaeozoic continental margin rocks in north‐western Newfoundland indicate that different structural levels have contrasting metamorphic histories. Rocks of the East Pond Metamorphic Suite, which represent the older, structurally lower level of the margin, experienced an early high‐pressure–low‐temperature stage of metamorphism (10–12 kbar minimum, 450–500°C) which produced eclogite in mafic dykes and phengite–garnet assemblages in pelites. This was overprinted by higher temperature–lower pressure amphibolite facies metamorphism (700–750°C, 7–9 kbar minimum) which produced complex symplectic textures in rocks of all compositions. Rocks of the Fleur de Lys Supergroup, which were deposited in the stratigraphically higher levels of the rifted margin, reached pressures of 7–8.5 kbar at about 450°C during the early stages of metamorphism, overprinted by assemblages which indicate maximum temperatures of 550–600°C at about 6.5 kbar. The metamorphic history of both units is interpreted to be the result of thermal relaxation following initial burial of a continental margin by overriding thrust sheets. Since there is no evidence that maximum pressures or temperatures within the Fleur de Lys Supergroup were ever as high as those reached in the East Pond Metamorphic Suite, these rocks may have followed parallel, ‘nested’P–T–tpaths, with the more deeply buried East Pond Metamorphic Suite subjected to greater thermal relaxation effects. Quantitative modelling ofP–T–tpaths is not possible with the present data, owing to both large uncertainties inP–Te

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1990.tb00473.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Eclogites in the Tromsø area, northern Norway, are intimately associated with meta‐supracrustals within the Uppermost Allochthon of the Scandinavian Caledonides (the Tromsø Nappe Complex). The whole sequence, which includes pelitic to semipelitic schists and gneisses, marbles and calc‐silicate rocks, quartzofeldspathic gneisses, metabasites and ultramafites, has undergone three main deformational/metamorphic events (D1/M1, D2/M2and D3/M3). Detailed structural, microtextural and mineral chemical studies have made it possible to construct separate P–T paths for these three events.Chemically zonedlate syn‐ to post‐D1garnets with inclusions of Bt, Pl and Qtz in Ky‐bearing metapelites indicate a prograde evolution from 636°C, 12.48 kbar toc.720°C, 14–15 kbar. This latter result is in agreement with Grt–Cpx geothermometry and Grt–Cpx–Pl–Qtz geobarometry on eclogites and trondhjemitic to dioritic gneisses. Maximum pressures atc.675°C probably reached 17–18 kbar based on Cpx–Pl–Qtz inclusions in eclogitic garnets, and Grt–Ky–Pl–Qtz and Jd–Ab–Qtz in trondhjemitic gneisses.Post‐D1/pre‐D2decompressional breakdown of the high‐Passemblages indicates a substantial drop in pressure at this stage. Inclusions and chemical zoning insyn‐ to post‐D2garnets from metapelites record a second episode of prograde metamorphism, from 552°C, 7.95 kbar, passing through a maximum pressure of 10.64 kbar at 644°C, with final equilibration atc.665°C, 9–10 kbar. The corresponding apparently co‐facial paragenesis Grt + Cpx + Pl + Qtz in metabasites yieldsc.635°C, 8–10 kbar. In the metapelitespost‐D3, Grt in apparent equilibrium with Bt, Phe and Pl yieldc.630°C, 9 kbar. The D1/M1and D2/M2episodes are exclusively recorded in the Tromsø Nappe Complex and must thus pre‐date the emplacement of this allochthonous unit on top of the underlying Lyngen Nappe, while the D3/M3episode is common for the two units.A previously published Sm–Nd mineral isochron (Grt–Cpx–Am) on a partly retrograded and recrystallized ecologite of 598 ± 107 Ma represents either the timing of formation of the eclogites or the post‐eclogite/pre‐D2decompression stage, while a Rb–Sr whole rock isochron of an apparently post‐D1/pre‐D2granite of 433 ± 11 Ma is consistent with a K–Ar age of post‐D1/pre‐D2amphiboles from a retrograded eclogite of 437 ±

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1990.tb00474.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

In the Proterozoic Mary Kathleen Fold Belt, northern Australia, infiltration of large volumes of externally derived fluid occurred synchronously with regional amphibolite‐facies metamorphism and deformation. This paper develops a model of structurally controlled fluid migration by comparing the distribution of fossil fluid pathways with the inferred stress and strain patterns during the deformation. Intense fluid flow was localized within strong, relatively brittle meta‐intrusive bodies, and in discrete, veined, brecciated and altered zones around their margins. In metasediments folded in a ductile manner outside these areas, fluid infiltration was negligible. The direct correlation between structural styles and the magnitude of veining and metasomatism suggests control of permeability enhancement, and hence fluid flow, by deformation. Finite difference modelling of a strong body in a weaker matrix has been used to evaluate the variation of stresses during the deformation, from which it is clear that stress and strain heterogeneities have systematically influenced the development and maintenance of metamorphic fluid pathways. Particular regions in which mean stress may be significantly lower than the average lithostatic pressures include the ‘strain shadow’zones adjacent to the strong bodies, other dilatant zones around the bodies, and the bodies themselves. This geometry is favourable not only for localized brittle deformation under amphilobite facies conditions, but also for focused fluid flow in the low mean stress regions, as evidenced by the abundance of veins. Fluid access through these metamorphic aquifers occurred during tensile failure episodes, with particularly large dilations and decimetre‐scale veining in areas of strain incompatibility. It appears likely that fluid circulated many times through the Fold Belt, with flow concentrated in the metamorphic aquifers. A model is developed that explains both the structurally focused fluid flow and the postulated multi‐pass recirculation by dilatancy pumping, the ‘pump engines’comprising the low me

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1990.tb00475.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Analysis of the precision of the illite ‘crystallinity’technique shows that machine errors are<5%, while intra‐ and inter‐sample errors are variable but are up to 12% and 14%, respectively (1σ). Consideration of this error analysis shows that the isocryst approach, which involves close contouring (e.g. 0.03 Δ2°) of illite ‘crystallinity’data, has a very low degree of confidence (0.8) it is necessary that contours should be at intervals of 0.1 ΔΘ2°, which is equivalent to subdivision of the anchizone into upper and lower units. Where previous interpretations have relied upon an isocryst method of contouring at less than 0.1 ΔΘ2° the conclusions must be regarded as unsubstantiated.Centrifuge separation of clay fractions (based on a Stokes’law application) gives separations in which a significant, but variable, percentage of grains have long axes greater than the size calculated. For the typical<2‐μm fraction utilized, some 20% of grains lie in the 2–4‐μm range, although the proportion is not believed to have a significant effect upon ‘crystallinity’values. The formula is applicable for grain‐sizes down to 0.5 μm. Illite ‘crystallinity’values on samples prepared by an ultrasonic disaggregation method show a small increase on those prepared by ball mill crushing. The differences are minimal at the epi/anchizone level but increase to some 10% at the anchizone/diagenetic level. The effect on grade determinations is again thought to be minimal and indicates that concern over unsuitability of the ultr

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1990.tb00476.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

An Early Palaeozoic (Ordovician ?) metamudstone sequence near Wojcieszow, Kaczawa Mts, Western Sudetes, Poland, contains numerous metabasite sills, up to 50 m thick. These subvolcanic rocks are of within‐plate alkali basalt type. Primary igneous phases in the metabasites, clinopyroxene (salite) and kaersutite, are veined and partly replaced by complex metamorphic mineral assemblages. Particularly, the kaersutite is corroded and rimmed by zoned sodic, sodic–calcic and calcic amphiboles. The matrix is composed of actinolite, pycnochlorite, albite (An ≤ 0.5%), epidote (Ps 27–33), titanite, calcite, opaques and, occasionally, biotite, phengite and stilpnomelane.The sodic amphiboles are glaucophane to crossite in composition with NaBfrom 1.9 to 1.6. They are rimmed successively by sodic–calcic and calcic amphiboles with compositions ranging from magnesioferri‐winchite to actinolite. No compositions between NaB= 0.92 and NaB= 1.56 have been ascertained.The textures may be interpreted as representing a greenschist facies overprint on an earlier blueschist (or blueschist–greenschist transitional) assemblage. The presence of glaucophane and no traces of a jadeitic pyroxene + quartz association indicate pressures between 6 and 12 kbar during the high‐pressure episode. Temperature is difficult to assess in this metamorphic event. The replacement of glaucophane by actinolite + chlorite + albite, with associated epidote, allows restriction of the upper pressure limit of the greenschist recrystallization to<8 kbar, between 350 and 450°C. The mineral assemblage representing the greenschist episode suggests theP–Tconditions of the high‐pressure part of the chlorite or lower biotite zone. The latest metamorphic recrystallization, under the greenschist facies, may have taken

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1990.tb00477.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The amphibolite facies Puolankajärvi Formation (PjF) occupies the western margin of the Early Proterozoic Kainuu Schist Belt (KSB) of northern Finland. The lower and middle parts of the PjF consist of turbiditic psammites and pelites and tempestitic semipelites. This report concentrates on the pelitic lithologies which include quartz–two‐mica–plagioclase schists with variable amounts of garnet, staurolite, andalusite and biotite porphyroblasts as well as sillimanite and cordierite segregations.The KSB forms a major north–south‐trending synclinorium between two Archaean blocks. It contains both autochthonous and allochthonous units and is cut by faults and shear zones. The PjF lies on the western side of the KSB and is probably allochthonous. The formation has undergone six major deformation phases (D1, D2, D3a, D3b, D4and D5). During D3a‐D5the maximum principal stress (σ1) changed in a clockwise direction from south‐west to north‐east. Between D2and D3the intermediate principal stress (σ2) changed from horizontal to vertical and the interval between D2and D3marks a transition from thrust to strike‐slip tectonics.Relict structures in the porphyroblasts indicate the following mineral growth–deformation evolution in the PjF. (1) Throughout the PjF there was a successive crystallization of garnet (syn‐D1), poryphyroblastic biotite (inter‐D3/4) and staurolite (inter‐D3/4) during the pre‐D4stage. (2) A syn‐D4‐inter‐D4/5crystallization of kyanite, sillimanite (fibrolite), porphyroblastic tourmaline, magnetite, rutile, cordierite and muscovite–biotite–plagioclase pseudomorphs after staurolite was most localized at and near D4shear zones. (3) A syn‐ to post‐D5generation of andalusite, ilmenohematite and sheet silicates after staurolite and after cordierite occurred near D5faults.The evolution outlined here permits the relative dating of the PjF parageneses, which is used in the second part of the study (Tuisku&Laajoki, 1990), and, together with the knowledge of the pressure–temperature conditions during various growth events, makes it possible to compile pres

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1990.tb00478.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The paragenetic relationships between sillimanite, andalusite, kyanite, chlorite, cordierite, biotite, garnet and staurolite in the Early Proterozoic Puolankajärvi Formation (PjF), together with mineral compositions, are used to construct a partial petrogenetic grid for metapelites with significant Mn content (MnO = 0.1–0.5%) by adding a six‐phase invariant point over the garnet‐absent invariant point for Mn‐free AMF‐phases.The grid and textural relations of the PjF are used to construct part of theP–T–deformation path for the PjF. Relatively short deformation pulses and associated flow of oxidizing fluid along shear zones were responsible for the paragenetic and compositional changes during cooling and decompression at 600–500°C and 6.0–2.5 kbar. Oxidation led to decreased Fe2+and further stressed the importance of Mn (increased Mn/divalent cations).A tectonothermal evolution of the Kainuu Schist Belt is presented which includes crustal thinning and steepening of a previously established thermal gradient. This was followed by thrusting and folding of the isotherms into a thermal antiform on the weste

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1990.tb00479.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY