bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geothermobarometry in metasediments of the southern Grossvenediger area (Tauern Window, Austria)
Authors: DACHS E. 
Published: May 2007

Metasediments in the southern Grossvenediger area (Tauern Window, Austria) were studied along a cross‐section through rocks of increasing metamorphic grade from the margin of the Tauern Window in the south to the base of the Upper Schieferhülle, including the Eclogite Zone, in the north.In the southern part of the cross‐section there is no evidence for a pre‐late Alpine metamorphic history in the form of high‐pressure relics or pseudomorphs. Mineral assemblages are characterized by the stability of tremolite + calcite, biotite + calcite and biotite + chlorite + calcite. In the northern part a more complete Alpine metamorphic evolution is preserved. Primary high‐pressure assemblages are dolomite + quartz, tremolite + zoisite, zoisite + dolomite + quartz + phengite I and probably tremolite + dolomite + phengite I. Secondary, post‐kinematic assemblages [tremolite + calcite, talc + calcite, phengite II + chlorite + calcite (+ quartz), biotite + chlorite + calcite, biotite + zoisite + calcite] formed as a result of the dominant late Alpine metamorphic overprint. The occurrence of biotite + zoisite + calcite is confined to the northernmost area and defines a biotite–zoisite–calcite isograd. P–T estimates based on standard thermobarometric techniques and on stability relationships of tremolite + calcite + dolomite + quartz and zoisite give consistent results. P–T conditions of the main Tertiary metamorphic overprint were 525° C, P= 7.5 ± 1 kbar in the northern part of the cross‐section. The southern part was metamorphosed at lower temperatures of 430–470° C. The Si‐content of phengites from this area is almost as high as that of phengites from the Eclogite Zone (Simax= 3.4 pfu). Pressures > 10 kbar at 420° C are suggested by phengite barometry according to Massone & Schreyer (1987). In the absence of high‐pressure relics or pseudomorphs, these phengites, which lack late Alpine re‐equilibration, are the only record that rocks of the southern part probably also experienced an early non‐eclogitic high‐pressure metamorphism.
Aluminous reaction textures in orthoamphibole‐bearing rocks: the pressure–temperature evolution of the high‐grade Proterozoic of the Bamble sector, south Norway
Authors: VISSER D. , SENIOR A. 
Published: May 2007

Aluminous reaction textures in orthoamphibole‐bearing rocks from the Froland area, Bamble, south Norway, record the prograde pressure–temperature path of the high‐grade Kongsbergian Orogeny (c. 1600–1500 Ma) and the low–mid amphibolite facies overprint during the Sveconorwegian Orogeny (c. 1100–1000 Ma). The rocks contain anthophyllite/gedrite, garnet, cordierite, biotite, quartz, andalusite, kyanite, Cr‐rich staurolite, tourmaline, ilmenite, rutile and corundum in a variety of parageneses. The P–T path is deduced from petrographic observations, mineral chemistry and zoning, geothermometry and (N)FMASH equilibria. The results indicate the sequence of metamorphic stages outlined below. (a) An M1 phase characterized by the presence of strongly deformed andalusite, gedrite and tourmaline.(b) An M2 phase with the development of kyanite after andalusite and the growth of staurolite associated with strong Na–Al–Mg zoning in orthoamphibole, indicating an increase in pressure (4 8 kbar) and temperature (500° 650°C).(c) Pressure decrease at high P (6–7 kbar) and high T (600–700 °C) during M3a with the production of cordierite ° Corundum between kyanite, staurolite and orthoamphibole and cordierite growth between corundum and orthoamphibole.(d) Temperature increase to 740 ± 60 °C and 7 kbar; static growth of garnet (M3b) at the metamorphic climax (peak T). The heat supply necessary to explain the temperature increase between the M3a and M3b phases is correlated with synkinematic enderbitic–charnockitic and basic intrusions in the Arendal granulite facies terrain.(e) M3b metamorphic conditions were followed by an initial isobaric cooling path (early M4) and late‐stage pressure decrease (late M4). Early M4 conditions of 6–7 kbar and 550–600 °C, assuming PH2O < Ptotal are indicated by a retrograde talc–kyanite–quartz assemblage in late quartz–cordierite veins. Late M4 conditions of 3–4 kbar and 420–530 °C are inferred from a kyanite–andalusite–chlorite–quartz assemblage in vein‐cordierite. The M1–M3 stages are interpreted as being the result of the same metamorphic P–T path, which was caused by both tectonic and magmatic thickening. A prolonged crustal residence time is proposed for the Bamble sector before uplift during the later stages of M4 occurred.
The higher grade metamorphic zonation of the Sambagawa metamorphic belt in central Shikoku, Japan
Authors: HIGASHINO T. 
Published: May 2007

The higher grade metamorphic zonation of the Sambagawa (= Sanbagawa) belt is established for the first time for the whole area of central Shikoku. As discontinuous reactions to define the isograd are absent, the metamorphic grade is primarily determined by the Mg‐Fe partitioning between garnet and chlorite along representative traverses. However, for regional mapping, mineralogical features of the pelitic schists, such as using mineral assemblages of more than divariant equilibrium, the modal garnet to chlorite ratio, and the optical properties of chlorite, are employed as auxiliary criteria.The presence of the highest grade mineral zone in the middle of the structural level is confirmed, but its spatial distribution is far more complex than hitherto accepted. Thermal axes are now confirmed at three different structural levels. A model is presented in which the stacking of thrust sheets of different grade took place while metamorphic reactions were in progress. Thermal readjustment brought a continuous metamorphic temperature gradient across and within the thrust sheets. Tectonic blocks of metagabbro and ultramafic rock were emplaced synchronously with thinning and subsequently also re‐equilibrated. Local anomalies of metamorphic grade, represented by mixing of schists of different metamorphic grade, exist, but they are due to a later stage event.
Buffering in the assemblage staurolite‐aluminium silicate‐biotite‐garnet‐chlorite
Authors: GIARAMITA M. J. , DAY H. W. 
Published: May 2007

Abstract
The assemblage muscovite‐quartz‐staurolite‐aluminium silicate‐biotite‐garnet‐chlorite with H2O (SABGC assemblage) is invariant in the K2O‐FeO‐MgO‐Al2O3‐SiO2‐H2O (KFMASH) system. Such five‐phase AFM assemblages should be absent in nature, but reported occurrences from at least ten localities suggest that either the assemblage internally controls μH2O or non‐KFMASH components stabilize one or more of the phases.Least‐squares regression analysis of minerals from South Royalton and Gassetts, Vermont, USA, demonstrates that subsets of the minerals in single SABGC assemblages from both localities are related by balanced reactions involving water. These results are consistent with the interpretation that the subassemblages fixed μH2O at an arbitrary, specified pressure and temperature. Balanced dehydration reactions also may be written between minerals in the SABGC assemblages and four‐phase assemblages from the same outcrops interpreted to have equilibrated at the same pressures and temperatures as the five‐phase assemblages. These results suggest that different specimens from the same outcrops equilibrated at different values of μH2O, supporting the conclusion that μH2O was not controlled externally. We could not demonstrate internal control of fo2 using measured mineral compositions because oxygen balance occurred in all reactions derived by regression.Regression analysis of published mineral compositions from New Mexico failed to identify balanced reactions involving water or oxygen either among the phases in a single SABGC assemblage or between SABGC and nearby four‐phase assemblages. These results demonstrate that neither μH2O nor fo2 were fixed by the SABGC assemblages at these localities, and permit the interpretations that the assemblages were stabilized by the non‐KFMASH components Na or Ca and that μH2O and fo2 were controlled externally.
Fluid inclusion constraints on the uplift history of the metamorphosed massive sulphide deposits at Ducktown, Tennessee
Authors: HALL D. L. , BODNAR R. J. , CRAIG J. R. 
Published: May 2007

Abstract
Standard petrographic, microthermometric and Raman spectroscopic analyses of fluid inclusions from the metamorphosed massive sulphide deposits at Ducktown, Tennessee, indicate that fluids with a wide range of compositions in the C–O–H–N–S–salt system were involved in the syn‐ to post‐metamorphic history of these deposits. Primary fluid inclusions from peak metamorphic clinopyroxene contain low‐salinity, H2O–CH4 fluids and calcite, quartz and pyrrhotite daughter crystals. Many of these inclusions exhibit morphologies resembling those produced in laboratory experiments in which confining pressures significantly exceed the internal pressures of the inclusions. Secondary inclusions in metamorphic quartz from veins, pods, and host matrix record a complex uplift history involving a variety of fluids in the C–O–H–N–salt system. Early fluids were generated by local devolatilization reactions while later fluids were derived externally.Isochores calculated for secondary inclusions in addition to the chronology of trapping and morphological features of primary and secondary fluid inclusions suggest an uplift path which was concave toward the temperature axis over the P–T range 6–3 kbar and 550–225° C. Immiscible H2O–CH4–N2–NaCl fluids were trapped under lithostatic to hydrostatic pressure conditions at 3–0.5 kbar and 215 ± 20° C. Entrapment occurred during Alleghanian thrusting, and the fluids may have been derived by tectonically driven expulsion of pore fluids and thermal maturation of organic material in lower‐plate sedimentary rocks which are thought to underlie the deposits. Episodic fracturing and concomitant pressure decreases in upper‐plate rocks, which host the ore bodies, would have allowed these fluids to move upward and become immiscible. Post‐Alleghanian uplift appears to have been temperature‐convex.Uplift rates of 0.10–0.05 mm year−1 from middle Ordovician to middle Silurian – late Devonian, and 0.07–0.12 mm year−1 from middle Silurian – late Devonian to late Permian are suggested by our uplift path and available geochronological data.
Tectonometamorphic evolution of the Sebadani eclogitic metagabbro and the Sambagawa schists, central Shikoku, Japan: 40Ar/39Ar mineral age constraints
Authors: DALLMEYER R. D. , TAKASU A. 
Published: May 2007

Abstract
The Sambagawa metamorphic belt exposed in central Shikoku records a high‐P–T metamorphic event. It is represented by the Oboke nappe and structurally overlying, internally imbricated, Besshi nappe complex. These major structural units are in ductile thrust contact. A melange is developed along a ductile internal tectonic contact within the Besshi nappe complex. Tectonic emplacement of a high‐T enclave (Sebadani eclogite) in the melange zone resulted in the development of a contact metamorphic aureole within the host Sambagawa rocks. 36Ar/40Ar versus 39Ar/40Ar isotope correlation ages recorded by hornblende from the Sambagawa basic schists which surround the Sebadani enclave are 83.4 ± 0.3 Ma (within contact aureole) and 83.6 ± 0.5 Ma (outside aureole). 40Ar/39Ar plateau ages recorded by muscovite from the same samples are 87.9 ± 0.3 and 89.3 ± 0.4 Ma. Amphibole from the amphibolite within the Sebadani enclave records isotope correlation ages of 93.7 ± 1.1 and 96.5 ± 0.7 Ma (massive interior) and 84.6 ± 1.2 Ma (marginal shear zone). Amphibole within the massive amphibolite is significantly higher in XMg than that within the host Sambagawa basic schists. The older ages recorded by amphibole within the Sebadani enclave are interpreted to date cooling through somewhat higher closure temperatures than which characterize the more Fe‐rich amphibole in surrounding schists. The younger amphibole age recorded within the marginal shear zone probably indicates that crystallization of amphibole continued until cooling through the relatively lower amphibole closure temperatures.These results, together with the previously published 40Ar/39Ar ages of the Sambagawa schists, suggest: (i) metamorphic culmination occurred in the Besshi nappe complex at c. 100–90 Ma; (ii) at c. 95 Ma the Besshi nappe complex was internally imbricated and tectonic enclaves were emplaced; (iii) at c. 85 Ma, the composite Besshi nappe was rapidly exhumed and tectonically emplaced over the Oboke nappe (which attained peak metamorphic conditions at c. 75 Ma); (iv) the Besshi and Oboke nappe complexes were further exhumed as a coherent tectonic unit and unconformably overlain by the Eocene Kuma Group at c. 50 Ma.
Shear sense
Authors: BELL T. H. , JOHNSON S. E. 
Published: May 2007

Investigation of microstructural relationships in major movement zones in metamorphic rocks, where the sense of displacement is known from regional geological relationships, indicates numerous problems with current concepts of shear‐sense criteria and their application. The direction of apparent shearing commonly conflicts from one criterion to another (e.g. from the symmetry of quartz c‐axis orientation diagrams to the asymmetry of extensional crenulation cleavages). This implies that interpretations of shear sense along foliations from some mesoscale and microscale criteria have been erroneous.A new approach to interpreting shear sense, involving the use of strain fields, resolves conflicts in mesoscopic and microscopic criteria and provides a method for determining coherent shear‐sense histories extending back before the last shearing event for ‘any foliated metamorphic rock’. It also provides a powerful tool for determining the structural/metamorphic path that a rock has followed within an orogen. For determination of the shear sense on the last foliation developed in a rock, this approach uses geometries developed around competent heterogeneities such as quartz pebbles, pegmatite pods, veins, porphyroclasts, porphyroblasts and breccia clasts. A shear‐sense history is derived by applying this approach to earlier foliations preserved within the heterogeneities and their strain shadows.
P–T evolution of the Teslin suture zone and Cassiar tectonites, Yukon, Canada: evidence for A‐ and B‐type subduction
Authors: HANSEN V. L. 
Published: May 2007

Mineral composition and quantitative thermobarometric studies indicate that the Teslin‐Taylor Mountain and Nisutlin terranes within the Teslin suture zone (TSZ), Yukon, record widespread high‐P/T metamorphic conditions consistent with subduction zone dynamothermal metamorphism. The highest P–T conditions (575–750° C and 9–17 kbar) are preserved in tectonites formed during normal dip‐slip ductile shear. Dextral strike‐slip tectonites record lower P–T conditions (400–550° C and 5–8 kbar), and tectonites which show reverse shear have peak temperatures of c. 420° C and a minimum peak pressure of 3 kbar. Dynamothermal metamorphism took place in a west‐dipping B‐type subduction zone outboard of western North America in Permo‐Triassic time. TSZ tectonites were underplated against the hangingwall plate of the subduction zone. Following subduction of the ocean basin which separated North America from the hangingwall plate, TSZ tectonites were overthrust eastward as a coherent structural package as a result of A‐type subduction of Cassiar strata in early Jurassic time.(Par)autochthonous Cassiar tectonites, which comprised the leading edge of the western North American margin, record prograde moderate‐P, high‐T metamorphism (550–750° C and 7–13 kbar) synchronous with top‐to‐the‐east ductile shear. Metamorphism occurred as a result of subduction of the North American margin into the TSZ subduction zone in early Jurassic time. Following metamorphism Cassiar tectonites cooled slowly from 500 to 300° C during the period middle Jurassic to middle Cretaceous.TSZ and Cassiar tectonites were deformed during changing P–T conditions. Data from each of these tectonite packages indicate that grain‐scale strain partitioning may have allowed local recrystallization of individual minerals by the addition of mechanical energy. The composition of the new grains reflects the P–T conditions under which that particular grain was deformed.
Segregation of leucogranite microplutons during syn‐anatectic deformation: an example from the Taylor Valley, Antarctica
Authors: ALLIBONE A. H. , NORRIS R. J. 
Published: May 2007

ABSTRACTA suite of migmatites in uppermost amphibolite facies schists of the Koettlitz Group exposed in the Taylor Valley, Antarctica, provides direct evidence of the behaviour of partially molten rock during syn‐anatectic deformation. The geometry of the migmatites is directly related to their position relative to the hinge of a kilometre‐scale antiform. Migmatitic rocks on the fold limbs are characterized by extensional shears and fractures, filled with leucosome material, that intersect the pervasive foliation and millimetre‐thick stromatic leucosomes. Vein‐ and dyke‐like leucosomes become more common and thicker from the limb to the hinge region of the antiform. Rocks characterized by high leucosome‐to‐rock ratios near the antiform hinge are xenolithic in appearance. Major parasitic folds within the hinge contain leucogranite ‘microplutons’ up to 50 m across beneath refractory ‘cap‐rock’ layers.Angular boudinage structures in schists surrounded by leucosomes indicate a relatively low yield strength in the leucosome, which is compatible with a molten rather than solid leucosome. Leucogranite‐bearing extensional shears and fractures indicate that repeated extensional fracturing and shearing promoted by high fluid (melt) pressure is an important mechanism of melt segregation. Dilation in the hinges of developing folds aids the migration of melt into fold hinges and the development of 10–50‐m‐wide ‘microplutons’ of xenolith‐rich leucogranite.Lack of vapour‐absent melting and consequent low melt‐to‐rock ratios allowed the Koettlitz Group to maintain its structural coherency on a kilometre scale. Consequently, leucosome ‘microplutons’ did not exceed 50 m in width, and therefore observed leucosomes have not contributed to the development of adjacent plutonic‐scale granitoids.
Rotated staurolite porphyroblasts in the Littleton Schist at Bolton, Connecticut, USA
Authors: BUSA M. D. , GRAY N. H. 
Published: May 2007

ABSTRACTStaurolite porphyroblasts, 1.5–8cm in length and 0.3–2cm in width, in the Littleton Schist at Bolton, Connecticut, contain curved quartz inclusion trails which document synkinematic rotations of at least 135°. The orientations of long axes of these staurolite crystals define a weak preferred orientation in a plane approximately parallel to the external foliation. Serial sections of four differently orientated crystals and U‐stage measurements of the orientations of their inclusion trails demonstrate that the inflection hinge line and the statistical ‘symmetry axis’ characterizing the foliation within a porphyroblast are unrelated to the orientations of external crenulations and are, in all cases, parallel to the long axis of the porphyroblast. The cumulative rotation reflected in the curvature of the inclusion trails is a maximum in a c‐axis section through the initial core of a crystal. The amount of rotation about the c‐axis decreases linearly along the length of the crystal away from the nucleation site.The sense and amount of rotation recorded by a porphyroblast is related to its orientation. A tightly constrained transition from clockwise to anticlockwise rotation defines a slip direction that coincides with the preferred orientation of the staurolite c‐axes. The total rotation reflected by the inclusion trails increases as a function of the angle between the c‐axes of the staurolite crystals and the slip direction.Initially random staurolite porphyroblasts rotated during growth, as a consequence of laminar shear in the surrounding viscous matrix. This interpretation is quantitatively consistent with: the staurolite preferred orientation; its coincidence with the apparent slip direction; the correlation between both the sense and the amount of rotation and the orientation of the long axis of the porphyroblast; and the twisted conical shape of the family of surfaces defined by the inclusion trails.
Origin of CO2‐rich fluid inclusions in leucosomes from the Skagit migmatites, North Cascades, Washington, USA
Authors: WHITNEY D. L. 
Published: May 2007

CO2–CH4 fluid inclusions are present in anatectic layer‐parallel leucosomes from graphite‐bearing metasedimentary rocks in the Skagit migmatite complex, North Cascades, Washington. Petrological evidence and additional fluid inclusion observations indicate, however, that the Skagit Gneiss was infiltrated by a water‐rich fluid during high‐temperature metamorphism and migmatization.CO2‐rich fluid inclusions have not been observed in Skagit metasedimentary mesosomes or melanosomes, meta‐igneous migmatites, or unmigmatized rocks, and are absent from subsolidus leucosomes in metasedimentary migmatites. The observation that CO2‐rich inclusions are present only in leucosomes interpreted to be anatectic based on independent mineralogical and chemical criteria suggests that their formation is related to migmatization by partial melting. Although some post‐entrapment modification of fluid inclusion composition may have occurred during decompression and deformation, the generation of the CO2‐rich fluid is attributed to water‐saturated partial melting of graphitic metasedimentary rocks by a reaction such as biotite + plagioclase + quartz + graphite ± Al2SiO5+ water‐rich fluid = garnet + melt + CO2–CH4. The presence of CO2‐rich fluid inclusions in leucosomes may therefore be an indication that these leucosomes formed by anatexis.Based on the inferences that (1) an influx of fluid triggered partial melting, and (2) some episodes of fluid inclusion trapping are related to migmatization by anatexis, it is concluded that a free fluid was present at some time during high‐temperature metamorphism. The infiltrating fluid was a water‐rich fluid that may have been derived from nearby crystallizing plutons. Because partial melting took place at pressures of at least 5 kbar, abundant free fluid may have been present in the crust during orogenesis at depths of at least 15 km.