bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluid‐rock interaction in some shear zones from the Pyrenees
Authors: McCAIG A. M. 
Published: May 2007

Abstract
Mylonites 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 investigated.
P‐T‐X (CO2) conditions in mafic and calc‐silicate hornfelses from Oberon, New South Wales, Australia
Authors: ANDREW A. S. 
Published: May 2007

Abstract
The 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 solid and fluid chemistries.
Phase equilibria in the hornblende‐bearing basic gneisses of the Uvete area, central Kenya
Authors: MIYAKE AKIRA 
Published: May 2007

Abstract
The 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 μH2O and 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 small enough for the fluid to migrate completely.
Two‐pyroxene thermometry of Precambrian granulites from Cape Riche, Albany‐Fraser Province, Western Australia
Authors: STEPHENSON N. C. N. 
Published: May 2007

AbstractCoexisting Ca‐poor and Ca‐rich pyroxenes in granulites at Cape Riche, in the Precambrian Albany‐Fraser Province, Western Australia, are dominantly chemically homogeneous within individual samples, suggesting a major episode of equilibration. However, occasional grains in a few samples contain exsolved domains interpreted as relics of an earlier, higher‐T assemblage. Pyroxene pairs in ten, presumably isothermal, samples from a restricted area are used to (i) assess the suitability of several versions of the two‐pyroxene thermometer for application to metamorphic rocks, and (ii) determine the thermal history of the Cape Riche pyroxenes.The various versions of the two‐pyroxene thermometer applied to the well‐equilibrated homogeneous pyroxene grains show poor to good precision and yield mean temperatures varying widely from 683° to 893°C, in the following order of increasing T: Lindsley (1983; opx version), 683°± 11°C; Kretz (1982;KDversion), 705°± 19°C; Ross & Huebner (1975), 709°± 30°C; Kretz (1982; solvus version), 735°± 24°C; Fonarev & Graphchikov (1982; opx version), <750°C; Lindsley (1983; cpx version), 784°± 40°C; Fonarev & Graphchikov (1982; cpx version), ~820°± 30°C; Wood & Banno (1973), 849°± 16°C; Powell (1978), 854°± 23°C; Wells (1977), 893°± 10°C. Independent T estimates, based on mafic assemblages and garnet‐biotite thermometry, suggest that the major episode of metamorphism occurred at 700‐800°C (P ~ 5 kbar). Therefore the Wells, Powell, Wood & Banno and Fonarev & Graphchikov (cpx) temperatures are almost certainly too high. In the absence of a more precise independent T estimate it is difficult to assess the relative merits of the results obtained from the remaining versions of the two‐pyroxene thermometer, none of which can be unequivocally demonstrated to be seriously in error, though the Lindsley (opx) T is probably too low. Other significant shortcomings evident in the results include the relatively poor precision obtained from the three methods based on purely graphical representation of the augite limb of the solvus (i.e., the Ross & Huebner, Fonarev & Graphchikov (cpx) and Lindsley (cpx) versions), and the apparent dependence of derived T on Mg/Fe2+ratio for the Powell, Wood & Banno and Lindsley (cpx) methods.For the bulk compositions of exsolved domains, the different versions of the two‐pyroxene thermometer yield mean temperatures 23° to 82°C (overall mean, 65°C) higher than for homogeneous grains in the same samples. These exsolved domains are interpreted as relics of a higher‐T (peak?) metamorphic assemblage, rather than an igneous precursor.
The pumpellyite‐actinolite and contiguous facies in part of the Phyllite‐Quartzite Series, central Northern Peloponnesus, Greece
Authors: BALTATZIS E. G. , KATAGAS C. G. 
Published: May 2007

AbstractVariations in assemblage and composition of the constituent minerals in basic and intermediate metavolcanics encountered in the Zarouchla Group of the Phyllite‐Quartzite Series are consistent with a progressive sequence, corresponding to temperature conditions estimated at 290‐380°C (minimum values) under a total pressure greater than 3°5kbar and possibly as high as 5 kbar. In the absence of more critical evidence, the parageneses recorded in the metavolcanic rocks are interpreted as belonging to a prograde facies series from the lawsonite‐albitechlorite facies through the pumpellyite‐actinolite facies to the greenschist facies. The present distribution of mineral assemblages does not show a simple increase of metamorphic grade in a given direction but is apparently related to the tectonic evolution of the metamorphic sequence.
Development of P‐T prograde and P‐retrograde, T‐prograde isogradic surfaces during blueschist to eclogite regional deformation/metamorphism in New Caledonia, as indicated by progressively developed porphyroblast microstructures
Authors: BELL T. H. , BROTHERS R. N. 
Published: May 2007

Abstract
The mid‐Tertiary blueschists, eclogites and eclogitic gneisses of northern New Caledonia are the products of four phases of regional metamorphism and deformation (D1–D4). Omphacite, lawsonite and Mn‐rich garnet isogradic surfaces were developed during the second deformation (D2) under prograde pressure and temperature conditions. Subsequent deformations (D3–D4) folded these D2 isogradic surfaces. However, within the P‐retrograde, T‐prograde metamorphic environment of the D4 phase, omphacite altered to albite and chlorite; as a result, a late‐stage sub‐horizontal isogradic surface developed for omphacite‐out where this mineral preserved as relics within syn‐D4 albite porphyroblasts. Other minerals that crystallized for the first time (epidote) or had rim additions (almandine phengite) during D4, also form nearly horizontal isogradic surfaces. Porphyroblastic garnet and albite contain inclusion trails, which allow their microstructural development and crystallization of the matrix to be traced from D2 to D4.Late syn‐D4 the temperature increased markedly in association with an extensive exothermic decarbonation, even though the rocks were in a state of pressure retrogression. This caused considerable neocrystallization, recrystallization and growth of mattix and porphyroblasts such that, although S2 foliation crenulated by D3 and D4 is readily observable, almost all signs of stored strain due to D3 and D4 have been removed, and the deeper schists and eclogitic gneisses superficially appear to have undergone a drastic annealing recrystallization, post‐dating deformation.
The greenschist metamorphism of Archaean synvolcanic stocks near Wawa, Ontario, Canada
Authors: STUDEMEISTER PAUL A. 
Published: May 2007

Abstract
Two Archaean synvolcanic stocks with contact aureoles occur in the Wawa greenstone belt near Wawa, Ontario, Canada. The Gutcher Lake and Jubilee stocks consist mainly of granitoid trondhjemite with feldspar laths mottled by white mica + calcite + epidote and rimmed by clear albite. Biotite is partly or wholly pseudomorphosed by chlorite + sphene; some epidote is partly altered to calcite + chlorite. The granitoid phase grades into a foliated phase of quartz + albite + white mica + calcite + chlorite near fracture zones traversing the stocks.The alteration of the Gutcher Lake stock along its foliated margin involved addition of K2O, H2O + CO2, MnO, plus Rb; loss of CaO plus Sr; and a shift in Fe+2/Fet from 0.66 to 0.81. The alteration of the Jubilee stock along the Darwin Shear involved addition of H2O + CO2; loss of Sr; and no significant shift in Fe+2/Fet. The greenschist alteration also modified the contact aureoles bordering both stocks.One interpretation is that regional metamorphism in the Archaean overprinted a greenschist assemblage on both stocks. The alteration was intense near fracture zones and sporadic remote from fractures. Lower integrated water to rock ratios along the Darwin Shear compared to the margin of the Gutcher Lake stock may explain the comparatively lower perturbation of the element abundances and redox state of iron.
Regression diagnostics and robust regression in geothermometer/geobarometer calibration: the garnet‐clinopyroxene geothermometer revisited
Authors: POWELL ROGER 
Published: May 2007

Abstract
The calibration of geothermometers and geobarometers should involve not only the determination of the parameters in the equation used, but also the uncertainties on, and the correlations between, these parameters. This necessitates the use of a technique such as least squares. Given the poor performance of least squares in the presence of outliers in the data, techniques for identifying outliers for exclusion—regression diagnostics, and techniques for handling data which include outliers—robust regression and jackknifing, are essential. These techniques are summarized and their importance is emphasized, and they are applied to the calibration of the garnet‐clinopyroxene Fe‐Mg exchange geothermometer.The experimental data of Raheim & Green (1974) and Ellis & Green (1979) are explored using regression diagnostics to discover outliers in the data. After exclusion of the two influential outliers found, a new geothermometer equation for garnet‐clinopyroxene Fe‐Mg exchange is derived using robust regression and based on all the data: thus, T(K) = 2790 + 10P+ 3140xca,g/1.735 + In KD where T is in Kelvin and P is in kbar. This equation, as might be hoped, is essentially identical to that of Ellis & Green (1979). Equations for calculating the uncertainty in a calculated temperature, contributed by uncertainties in the calibration, are also derived.
Effect of metamorphism and partial melting of host rocks on zircons
Authors: GUPTA L. N. , JOHANNES W. 
Published: May 2007

AbstractZircons have been studied from different layers of migmatites (from Arvika, western Sweden and Nelaug, southern Norway) and from a paragneiss (from Arvika) associated with one of the migmatites. The main purpose of the investigation is to establish whether or not information about zircons can help in the elucidation of the parentage and rock‐forming processes of migmatites.The elongation ratio of zircons from all layers is small and characteristic of sedimentary zircons. Further, the absence of characteristic colours and the growth trends of the zircons (indicated by the reduced major axes) observed in the various samples both support a sedimentary parentage for these rocks. The zircons of all layers exhibit secondary growth (overgrowth, outgrowth and multiple growth) due to metamorphism. Compared with the zircons from the paragneiss, those of the migmatite layers are more clouded and less rounded, some of them becoming opaque or even skeletal; this is especially true of the zircons from the leucosomes. These observations indicate an alteration of the original sedimentary zircons in the migmatite, especially in the leucosomes, in response to the migmatization process, previously interpreted as partial melting.
Metamorphic P–T Paths from pelitic schists and greenstones from the south‐west Tauern Window, Eastern Alps
Authors: SELVERSTONE JANE , SPEAR FRANK S. 
Published: May 2007

Abstract
Petrological data from intercalated pelitic schists and greenstones are used to construct a pressure–temperature path followed by the Upper Schieferhülle (USH) series during progressive metamorphism and uplift in the south‐west Tauern Window, Italy. Pseudomorphs of Al–epidote + Fe‐epidote + albite + oligoclase + chlorite after lawsonite and data on amphibole crystal chemistry indicate early metamorphism in the lawsonite‐albite‐chlorite subfacies of the blueschist facies at P± 7–8 kbar. Geothermometry and geobarometry yield conditions of final equilibration of the matrix assemblage of 475±25°C, 5–6 kbar; calculations with plagioclase and phengite inclusions in garnet indicate early garnet growth at pressures of ∼ 7.5 kbar. Garnet zoning patterns are complex and reversals in zoning can be correlated between samples. Thermodynamic modelling of these zoning profiles implies garnet growth in response to four distinct phases of tectonic activity. Fluid inclusion data from coexisting immiscible H2O–CO2–NaCl fluids constrain the uplift path to have passed through temperatures of 380 + 30°C at 1.3 + 0.2 kbar.There is no evidence for metamorphism of USH at pressures greater than ∼ 7.5 kbar in this area of the Tauern Window. This is in contrast to pressures of ± 10 kbar recorded in the Lower Schieferhülle only 2–3 km across strike. A history of differential uplift and thinning of the intervening section during metamorphism is necessary to reconcile the P–T data obtained from these adjacent tectonic units.
Garnet evolution in pre‐Variscan pelitic rocks from the Lake Emosson area, Aiguilles Rouges Massif, Western Alps
Authors: VON RAUMER JÜRGEN F. , SCHWANDER HANS W. 
Published: May 2007

Abstract
The chemical evolution of garnets from pelitic rocks of probable Palaeozoic age corresponds to a complex metamorphic evolution of the host rocks.Among the almandine‐rich garnets (Alm60–80), two main types of evolution can be distinguished. Early Mn‐rich garnets coexisting with kyanite may be replaced by plagioclase and then, during a late stage, by biotite and/or sillimanite. The second type of evolution corresponds to an overgrowth of Mn‐poor late‐stage garnet on older Mn‐rich garnets which corresponds to a thermal peak with sillimanite‐type of metamorphism. This new garnet may appear either as an overgrowth with a strong discontinuity, or as small, new euhedral garnet or as skeletal garnet.This chemical evolution of garnet corresponds to an early collisional stage of metamorphism (of high pressure type with high Mn values) of probable Ordovician age followed by uplift and a thermal peak (low Mn values) in Devonian times.
Porphyroblast nucleation, growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development
Authors: BELL T. H. , RUBENACH M. J. , FLEMING P. D. 
Published: May 2007

Abstract
In regional metamorphic rocks, the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain‐rate gradients across the boundaries between the partitioned zones. These generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer. Phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain, because of their uniquely layered crystal structure. However, most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients, and hence are susceptible to dissolution and solution transfer.As a consequence, zones of progressive shearing become zones of dissolution of most minerals, and of concentration of phyllosilicates and graphite. Exceptions are mylonites, where strain‐rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer. Porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing, as they would be dissolved by the effects of shearing strain on their boundaries. However, they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones, which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth. Zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation, this includes a build up of stored strain‐energy relative to zones of progressive shearing, in which dissolution is occuring.Porphyroblast growth is generally syndeformational, and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account.Porphyroblasts in a contact aureole do not grow statically either, as microfracturing, associated with emplacement, allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening.The criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning, reactivation of deforming foliations, and a general lack of rotation of porphyroblasts, with the spectacular exception of genuinely spiralling garnet porphyroblasts.
Incipient metamorphism in the Lower Palaeozoic marginal basin of Wales
Authors: ROBINSON D. , BEVINS R. E. 
Published: May 2007

Abstract
A diagenctic through anchizone to epizone transition is demonstrated in pelitic rocks of the Lower Palaeozoic marginal basin of Wales by examination of variations in phyllo‐silicate mineralogy, illite crystallinity and bo parameter of white micas. This transition represents a temperature range from ∼ 150°C to ∼ 400°C and the metamorphism is of a low‐pressure facies series type, with a geothermal gradient of ∼ 40°Ckm‐1. Variations in grade can be correlated largely with the original basin and shelf form, suggesting a depth‐related metamorphism. However, in areas closer to the site of Caledonian plate collision an increasingly syn‐tectonic metamorphic event is apparent.Correlation of pelite data with metabasite assemblages is variable, the most consistent relationship being between epizone crystallinity values andepidote‐actinolite (greenschist facies) assemblages. Diagenetic clay mineral assemblages are found associated with prehnite‐pumpellyite assemblages in metabasites and it is suggested that the latter represent non‐buffered, and therefore non‐diagnostic, assemblages.
P–T conditions for the eclogitic re‐equilibration of the metaophiolites from Val d'Ala di Lanzo (internal Piemontese zone, Western Alps)
Authors: SANDRONE R. , LEARDI L. , ROSSETTI P. , COMPAGNONI R. 
Published: May 2007

Abstract
A study has been made of the high‐pressure early‐Alpine re‐equilibration in the eclogites and metasedimentary cover of the Val d'Ala di Lanzo ophiolite. All of the main high‐pressure minerals have been analysed and their compositions used to determine re‐equilibration temperatures. The minimum conditions proposed (P= 1.3 GPa, T= 450–460°C) are also indicated by the presence of a jadeite+quartz‐bearing metagranite.The temperatures are compared with those reported for similar eclogites from the Voltri Group, the Aosta Valley and the Valais. Comparison of recalculated temperatures shows that the temperature (and probably the pressure) of the eclogitic re‐equilibration increased in the Aosta Valley and the Valais, in keeping with what has been observed in the internal Penninic basement of the Gran Paradiso and Monte Rosa crystalline massifs.