bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluid flow and mass transport at the Valentine wollastonite deposit, Adirondack Mountains, New York State
Authors: GERDES M. L. , VALLEY J. W. 
Published: May 2007

ABSTRACTThe Valentine wollastonite skarn in the north‐west Adirondack Mountains, New York, is a seven million ton deposit which resulted from channellized infiltration of H2O‐rich, silica‐bearing fluids. The wollastonite formed by reaction of these fluids with non‐siliceous calcite marble. The skarn formed at the contact of the syenitic Diana Complex and was subsequently overprinted by Grenville‐age granulite facies metamorphism and retrograde hydrothermal alteration during uplift. Calcite marbles adjacent to the deposit have generally high δ18O values (c. 21‰), typical of Grenville marbles which have not exchanged extensively with externally derived fluids. Carbon isotopic fractiona‐tions between coexisting calcite and graphite in the marbles indicate equilibration at 675d̀ C, consistent with the conditions of regional metamorphism. Oxygen isotopic ratios from wollastonite skarn are lower than in the marbles and show a 14‰ variation (‐1‰ to 13‰). Some isotopic heterogeneity is preserved from skarn formation, and some represents localized exchange with low‐δ18O retrograde fluids. Detailed millimetre‐ to centimetre‐scale isotopic profiles taken across skarn/marble contacts reveal steep δ18O gradients in the skarn, with values increasing towards the marble. The gradients reflect isotopic evolution of the fluid as it reacted with high δ18O calcite to form wollastonite. Calcite in the marble preserves high δ18O values to within <5 mm of the skarn contact. The preservation of high δ18O values in marbles at skarn contacts and the disequilibrium fractionation between wollastonite skarn and calcite marble across these contacts indicate that the marbles were not infiltrated with significant quantities of the fluid. Thus, the marbles were relatively impermeable during both the skarn formation and retrograde alteration. Skarn formation may have been episodic and fluid flow was either chaotic or dominantly parallel to lithological contacts. Although these steep isotope gradients resemble fluid infiltration fronts, they actually represent the sides of the major flow system. Because chromatographic infiltration models of mass transport require the assumption of pervasive fluid flow through a permeable rock, such models are not applicable to this hydrothermal system and, by extension, to many other metamorphic systems where low‐permeability rocks restrict fluid migration pathways. Minimum time‐integrated fluid fluxes have been calculated at the Valentine deposit using oxygen isotopic mass balance, reaction progress of fluid buffering reactions, and silica mass balance. All three approaches show that large volumes of fluid were necessary to produce the skarn, but silica mass balance calculations yield the largest minimum flux and are hence the most realistic.
Contact metamorphism around the Stawell granite, Victoria, Australia
Authors: XU G. , POWELL R. , WILSON C. J. L. , WILL T. M. 
Published: May 2007

ABSTRACTThe contact metamorphosed metapelitic and metapsammitic rocks surrounding the Stawell granite, western Victoria, Australia, are divided into three zones: the low‐grade zone, the medium‐grade zone and the high‐grade zone. Detailed petrological study shows consistency of element distributions, implying that equilibrium was widely attained in the rocks, although equilibrium volumes are generally small (millimetre scale) and considerable mineral chemical variations exist between adjacent domains. The metamorphic mineral assemblages are generally of high variance (KFMASH variance ≤ 2). Consequently, the chemical evolution of assemblages is controlled largely by bulk composition and metamorphic temperature, the former factor being more important in most rocks. The chemographic relations of mineral assemblages in low‐ and medium‐ to high‐grade zones are presented in compatibility diagrams projected from biotite, quartz and H2O, and biotite, K‐feldspar and H2O, respectively. These compatibility diagrams have the advantage of showing both quartz‐bearing and quartz‐absent assemblages. The metamorphic reactions are modelled successfully by a calculated petrogenetic grid that combines both KFASH and KMASH equilibria. Based on petrographic observations and with constraints from the calculated petrogenetic grid, the following KFMASH reactions, in the order of increasing metamorphic grade, are responsible for producing the various mineral assemblages in the Stawell rocks:chl + mu + q = bi + cd + V,chl + q + cd = g + V,mu + bi + q = ksp + cd + V,mu + q = ksp + and + cd + V (or KASH mu + q = ksp + and + V),mu + cd = ksp + and + bi + V,mu + bi + and = ksp + sp + V,and + bi = ksp + sp + cd + V,mu + bi = ksp + cor + sp + V,mu = ksp + cor + and + sp + V (or KASH mu = ksp + cor + V),bi + cd + q = g + ksp + V.The combined KFASH and KMASH grid provides constraints on reaction coefficients in the above sequence of reactions and on temperature and pressure of metamorphism.
Timing of metamorphism in the Tauern Window, Eastern Alps: Rb‐Sr ages and fabric formation
Authors: INGER S. , CLIFF R. A. 
Published: May 2007

ABSTRACTThe Peripheral Schieferhülle of the Tauern Window of the Eastern Alps represents post‐Hercynian Penninic cover sequences and preserves a record of metamorphism in the Alpine orogeny, without the inherited remnants of Hercynian events that are retained in basement rocks. The temperature‐time‐deformation history of rocks at the lower levels of these cover sequences have been investigated by geochronological and petrographic study of units whose P‐T evolution and structural setting are already well understood.The Eclogite Zone of the central Tauern formed from protoliths with Penninic cover affinities, and suffered early Alpine eclogite facies metamorphism before tectonic interposition between basement and cover. It then shared a common metamorphic history with these units, experiencing blueschist facies and subsequent greenschist facies conditions in the Alpine orogeny. The greenschist facies phase, associated with penetrative deformation in the cover and the influx of aqueous fluids, reset Sr isotopes in metasediments throughout the eclogite zone and cover schists, recording deformation and peak metamorphism at 28‐30 Ma.The Peripheral Schieferhülle of the south‐east Tauern Window yields Rb‐Sr white mica ages which can be tied to the structural evolution of the metamorphic pile. Early prograde fabrics pre‐date 31 Ma, and were reworked by the formation of the large north‐east vergent Sonnblick fold structure at 28 Ma. Peak metamorphism post‐dated this deformation, but by contrast to the equivalent levels in the central Tauern, peak metamorphic conditions did not lead to widespread homogenization of the Sr isotopes. Localized deformation continued into the cooling path until at least 23 Ma, partially or wholly resetting Sr white mica ages in some samples.These isotopic ages may be integrated with structural data in regional tectonic models, and may constrain changes in the style of crustal deformation and plate interaction. However, such interpretations must accommodate the demonstrable variation in thermal histories over small distances.
Reaction textures and fluid behaviour in very high pressure calc‐silicate rocks of the Münchberg gneiss complex, Bavaria, Germany
Authors: KLEMD R. , MATTHES S. , SCHÜSSLER U. 
Published: May 2007

ABSTRACTCalc‐silicate rocks occur as elliptical bands and boudins intimately interlayered with eclogites and high‐pressure gneisses in the Münchberg gneiss complex of NE Bavaria. Core assemblages of the boudins consist of grossular‐rich garnet, diopside, quartz, zoisite, clinozoisite, calcite, rutile and titanite. The polygonal granoblastic texture commonly displays mineral relics and reaction textures such as post kinematic grossular‐rich garnet coronas. Reactions between these mineral phases have been modelled in the CaO‐Al2O3‐SiO2‐CO2‐H2O system with an internally consistent thermodynamic data base. High‐pressure metamorphism in the calc‐silicate rocks has been estimated at a minimum pressure of 31 kbar at a temperature of 630d̀ C with XH2, O ≥ 0.03. Small volumes of a CO2‐N2‐rich fluid whose composition was buffered on a local scale were present at peak‐metamorphic conditions. The P‐T conditions for the onset of the amphibolite facies overprint are about 10 kbar at the same temperature. XCo2 of the H2O‐rich fluid phase is regarded to have been <0.03 during amphibolite facies conditions. These P‐T estimates are interpreted as representing different stages of recrystallization during isothermal decompression. The presence of multiple generations of mineral phases and the preservation of very high‐pressure relics in single thin sections preclude pervasive post‐peak metamorphic fluid flow as a cause of a re‐equilibration within the calc‐silicates. The preservation of eclogite facies, very high‐pressure relics as well as amphibolite facies reactions textures in the presence of a fluid phase is in agreement with fast, tectonically driven unroofing of these rocks.
Evidence for pre‐regional metamorphic fluid infiltration of the Lower Calcsilicate Unit, Reynolds Range Group (central Australia)
Authors: BUICK I. S. , CARTWRIGHT I. , HAND M. , POWELL R. 
Published: May 2007

ABSTRACTGrandite garnet‐rich calcsilicate rocks from the Lower Calcsilicate Unit of the regionally metamorphosed Reynolds Range Group (central Australia) crop out along a strike‐parallel section in which a transition zone from M22 amphibolite to granulite facies rocks is exposed. Across this transition the grandite‐rich layers do not show systematic changes in mineral assemblages, compositions and modes, or stable isotope compositions. These layers are deformed by F22 folds that are associated with the peak of regional low‐pressure/high‐temperature metamorphism. Therefore, the grandite‐rich layers appear to pre‐date regional metamorphism and to have acted as closed chemical systems during prograde M22 metamorphism.Mineral assemblages in the grandite‐rich layers are consistent with their formation through the infiltration of oxidized, water‐rich fluids (Xco2 < 0.1–0.3; log fo2 ‐16 to ‐14). The stable isotope values of calcite (Δ13C=‐4.2 to ‐0.8%0 PDB; Δ18O = 10.5–14.0%0 V‐SMOW) and bulk‐silicate fractions (Δ18O = 6.1 to 10.8%) of the grandite‐rich layers are most consistent with the infiltrating fluid being from a magmatic source. It is most likely that fluid infiltration occurred during the pre‐M22 contact metamorphism (M21) that affected much of the Reynolds Range Group. The preservation of these assemblages is probably due to their high variance and little pervasive fluid‐rock interaction having occurred during M22.The clinopyroxene‐ and feldspar‐rich calcsilicate rocks that host the grandite‐rich layers contain poikiloblastic grandite garnet that formed during prograde M22 metamorphism. Thin marbles that locally occur with the grandite‐rich layers contain a third garnet generation that is post‐ or late M22. This grossular‐rich garnet occurs in coronas around calcite, plagioclase, clinopyroxene, wollastonite and scapolite. These coronas are consistent with cooling and/or compression. However, because the marble assemblages are themselves overprinted by M21 grandite‐rich layers the development of coronal garnet does not reflect a continuous P‐T‐t path. Rather, it more probably reflects the partial re‐equilibration of M21 contact metamorphic assemblages to post‐M22 conditions.
Qualitative thermobarometry of inverted metamorphism in the Pelona and Rand Schists, southern California, using calciferous amphibole in mafic schist
Authors: JACOBSON C. E. 
Published: May 2007

Abstract
The Rand and Pelona Schists consist of eugeoclinal rock types overlain by continental basement along the Vincent‐Chocolate Mountains (VCM) faults. Both schists display inverted metamorphic zonation, defined in part by a systematic variation in composition of calcic to sodic‐calcic amphibole in mafic schist structurally upward. The compositional progressions include increase of total A1, A1IV and Ti, but decrease in the ratios of Na/(Na + Ca) to A1/(A1 + Si), and NaM4 to (A1VI+ Fe3++ Ti). These variations imply that structurally high rocks belong to a lower‐pressure metamorphic fades series than those at depth. This result is consistent with previous views that the inverted metamorphic zonations represent intact structural sequences.Amphibole composition is dependent not only on structural position (i.e. P‐T), but also upon bulk‐rock composition. The important controls are whole‐rock Mg/(Mg + Fe2++ Mn) and Fe3+/Fe2+. The greatest impact of these factors, however, is on the absolute values of Na and Al, rather than their ratio. Thus, interpretation of facies series is not seriously hindered by compositional variability.Sodic amphibole in epidote blueschists from the Rand Schist is extensively replaced by sodic‐calcic amphibole. Sodic‐calcic amphibole in the Rand Schist and Pelona Schist is, itself, rimmed by actinolitic amphibole. Similar blueschist to greenschist transitions in other metamorphic terranes are typically attributed to exhumation. In the Rand and Pelona Schists, the sequence probably formed during burial.
Pre‐Middle Jurassic accretionary metamorphism in the southern Klamath Mountains of northern California, USA
Authors: GOODGE J. W. 
Published: May 2007

Abstract
High‐P/T metamorphic parageneses are preserved within two late Palaeozoic to early Mesozoic assemblages of the southern Klamath Mountains that show contrasting structural styles and mineral parageneses reflecting formation in different parts of a subduction‐zone regime. Blueschist facies tectonites of the Stuart Fork terrane represent a coherent subduction complex formed at relatively deep crustal levels, whereas the chaotic metasedimentary mélange of the eastern Hayfork terrane contains a diverse range of metamorphic parageneses reflecting complex structural mixing of metamorphic components at shallower levels. The convergent‐margin‐type accretionary metamorphism evident in both terranes pre‐dates Middle Jurassic low‐P/T metamorphism resulting from regional tectonic contraction and magmatism.The epidote‐ to lawsonite‐zone Stuart Fork blueschists (and eclogites locally) formed at pressures of about 6‐11 kbar and temperatures of 250‐400° C. Deformed matrix material of the eastern Hayfork mélange formed at similar temperatures but lower pressures, on the order of 3‐6 kbar. The mélange contains a diverse assemblage of tectonic blocks that formed under a range of P‐T conditions, including those of the blueschist, pumpellyite‐actinolite, greenschist and upper greenschist to amphibolite facies.The succession of mineral parageneses and inferred P‐T conditions of the eastern Hayfork blocks reflect those of igneous protolith formation, structural mixing, subduction‐zone metamorphism, olistolith transport, and tectonic and erosional denudation. Although temporal relations are not well constrained, the evolution of these terranes is consistent with formation within a single convergent‐margin system.
High‐pressure micro‐inclusions and development of an inverted metamorphic gradient in the Santiago Schists (Ordenes Complex, NW Iberian Massif, Spain): evidence of subduction and syncollisional decompression
Authors: ARENAS R. , PASCUAL F. J. RUBIO , GARCIA F. DIAZ , CATALAN J. R. MARTINEZ 
Published: May 2007

Abstract
The Santiago Schists are located in the Basal Unit of the Ordenes Complex, one of the allochthonous complexes outcropping in the inner part of the Hercynian Belt in the north‐west of the Iberian Peninsula. Their tectonothermal evolution is characterized by the development of an eo‐Hercynian metamorphic episode (c. 374 Ma) of high‐P, low‐ to intermediate‐T. The mineral assemblage of the high‐P episode is preserved as a very thin Si= S1 foliation included in albite porphyroblasts, being composed of: albite + garnet‐I + white mica‐1 + chlorite‐1 + epidote + quartz + rutile ± ilmenite. The equilibrium conditions for this mineral assemblage have been estimated by means of different thermobarometers at 495 ± 10 °C and 14.7 ± 0.7 kbar (probably minimum pressure). The later evolution (syn‐D2) of the schists defines a decompressive and slightly prograde P‐T path which reached its thermal peak at c. 525 ± 10 °C and 7 kbar. Decompression of the unit occurred contemporaneously with an inversion of the metamorphic gradient, so that the zones of garnet‐II, biotite (with an upper subzone with chloritoid) and staurolite developed from bottom to top of the formation.The estimated P‐T path for the Santiago Schists suggests that the Basal Unit, probably a fragment of the Gondwana continental margin, was uplifted immediately after its subduction at the beginning of the Hercynian Orogeny. It also suggests that the greater part of the unroofing history of the unit took place in a context of ductile extension, probably related to the continued subduction of the Gondwana continental margin and the contemporaneous development of compensatory extension above it. The inverted metamorphic gradient seems related to conductive heat transferred from a zone of the mantle wedge above the subducted continental margin, when it came into contact with the upper parts of the schists along a detachment, probably of extensional character.The general metamorphic evolution of the Santiago Schists, with the development of high‐P assemblages with garnet prior to decompressive and prograde parageneses with biotite, is unusual in the context of the European Hercynian Belt, and shows a close similarity to the tectonothermal evolution of several high‐P, low‐ to intermediate‐T circum‐Pacific belts.
A multi‐stage pressure—temperature record in the Chilka Lake granulites: the epitome of the metamorphic evolution of Eastern Ghats, India?
Authors: SEN S. K. , BHATTACHARYA S. , ACHARYYA A. 
Published: May 2007

Abstract
Metapelitic and charnockitic granulites exposed around Chilka Lake in the northern sector of the Eastern Ghats, India, preserve a multi‐stage P—T record. A high‐T decompression from above 10 kbar to 8 kbar around 1100°C has been determined from Mg‐rich metapelites (XMg>0.60) with quartz‐cordierite‐orthopyroxene‐sillimanite and cordierite—orthopyroxene—sapphirine—spinel assemblages. Between this and a second decompression to 6.0 kbar, isobaric cooling from 830 to 670°C at 8 kbar is evident. These changes are registered by the rim compositions of orthopyroxene and garnet in charnockites and metapelites with an orthopyroxene—quartz—garnet—plagioclase—cordierite assemblage, and are further supported by the garnet + quartz ± orthopyroxene + cordierite and biotite‐producing reactions in sapphirine‐bearing metapelites. Another indication of isobaric cooling from 800 to 650°C at 6.0 kbar is evident from rim compositions of orthopyroxene and garnet in patchy charnockites. Two sets of P—T values are obtained from metapelites with a quartz—plagioclase—garnet—sillimanite—cordierite assemblage: garnet and plagioclase cores yield 6.2 kbar, 700°C and the rims 5 kbar, 650°C, suggesting a third decompression.The earliest deformation (F1) structures are preserved in the larger charnockite bodies and the metapelites which retain the high P—T record. The effects of post‐crystalline F2 deformation are observed in garnet megacrysts formed during or prior to F1 in some metapelites. Fold styles indicate a compressional regime during F1 and an extensional regime during F2. These lines of evidence and two phases of cooling at different pressures point to a discontinuity after the first cooling, and imply reworking.Two segments of the present P—T path replicate parts of the P—T paths suggested for four other granulite terranes in the Eastern Ghats, and the sense of all the paths is the same. This, plus the signature of three phases of deformation identified in the Eastern Ghats, suggests that the Chilka Lake granulites could epitomize the metamorphic evolution of the Eastern Ghats.
Experimental study of phase relations involving osumilite in the system K2O‐FeO‐MgO‐Al2O3‐SiO2‐H2O at high pressure and temperature
Authors: AUDIBERT N. , BERTRAND P. , HENSEN B. J. 
Published: May 2007

AbstractPhase relations and mineral chemistry for garnet (Grt), orthopyroxene (Opx), sapphirine (Spr), water‐undersaturated cordierite (Crd), osumilite (Osu), sillimanite (Sil), K‐feldspar (Kfs), quartz (Qtz) and a water‐undersaturated liquid (Liq) have been determined experimentally in the system KFMASH (K2O‐FeO‐MgO‐Al2O3‐SiO2‐H2O) under low PH2Oand fO2conditions. Four compositions have been studied with 100 [Mg/(Mg + Fe)] ranging from 65.6 to 89.7. Based on our experimental data, a P‐T grid is derived for the KFMASH system in the presence of quartz, orthopyroxene and liquid. Osumilite has been found in various mineral assemblages from 950 to 1100°C and 7.5 to 11 kbar. In the temperature range 1000‐1100°C, the pair Os‐Grt is stable over a pressure range of about 3kbar. The divariant reaction Os + Opx = Grt + Kfs + Qtz runs to the right with increasing pressure. Because osumilite is the most magnesian phase it is restricted to Mg‐rich compositions at high pressure. The reaction defining the upper pressure stability limit of Os‐Grt is located around 11 kbar with a nearly flat dP/dT slope over the temperature range 950–100°C. Over the entire temperature range investigated osumilite is not stable beyond 12 kbar. The data imply a restricted pressure range between 11 and 12 kbar for the stability of the assemblage Os‐Opx‐Sil‐Kfs‐Qtz. At 1050°C and above, osumilite occurs in various mineral assemblages together with the high‐T pair Spr‐Qtz.When coexisting with garnet, orthopyroxene or sapphirine, osumilite is always the most magnesian phase. At 1050 and 1100°C, liquid is invariably the most Fe‐rich phase in the run product.Our data support a theoretical P‐T grid for the KFMAS system in which osumilite is stable outside the field of the high‐T assemblage Spr‐Qtz. Moreover, our grid indicates that Os‐Opx‐Sil‐Kfs‐Qtz has a more restricted pressure and compositional stability domain than Os‐Grt, in agreement with natural occurrences. Osumilite is stable over a large pressure range, such that in Mg‐rich rocks, and at high temperature, it can occur at any depth in normal thickness continental crust.
Experimental diffusion of hydrogen into synthetic fluid inclusions in quartz
Authors: HALL D. L. , STERNER S. M. 
Published: May 2007

Abstract
Quartz‐hosted, synthetic CO2‐H2O fluid inclusions behave as open systems with respect to diffusional transfer of hydrogen during laboratory‐simulated metamorphic re‐equilibration at 650, 750 and 825°C and 1.5 kbar total pressure with fO2 defined by the C‐CH4 buffer. Microthermometry and Raman spectroscopy show that the initial CO2‐H2O inclusions become CO2‐CH4‐H2‐H2Oinclusions after diffusive influx of hydrogen from the reducing confining medium. Measurable changes are observed in inclusion compositions after only 15 days of re‐equilibration, implying significant hydrogen mobility at still lower temperatures over geological time spans. Results of synthetic inclusion re‐equilibrium experiments have profound implications for the interpretation of natural fluid‐inclusion data; failure to account for potential hydrogen migration in inclusions from high‐temperature geological environments may lead to erroneous estimates of P‐T, and/or the compositions of metamorphic fluids.