bluuebunny/crossref_metadata_2025_split huggingface dataset:
Contribution of deviatoric stresses to metamorphic P‐T paths: an example appropriate to low‐P, high‐T metamorphism
Authors: STÜWE K. , SANDIFORD M. 
Published: May 2007

ABSTRACT P‐T paths for a simple situation appropriate to many low‐P, high‐T (LPHT) terranes in which metamorphism and deformation are localized by advection of heat in magmas, has been modelled assuming a medium with a power‐law rheology with an inverse exponential dependence of stress and temperature and capable of sustaining deviatoric stress, τ, in the order of 100 MPa at 400d̀ C and strain rates of up to 10‐13s‐1. Numerical simulations and analytical approximations for P‐T histories appropriate for simple convergent deformation histories show that the destruction of the deviatoric stress field around large intrusions may result in significant decompression near the metamorphic temperature peak. Moreover, for a specified strain rate and temperature evolution, P‐T paths may vary from clockwise to anticlockwise merely as a function of vertical distance from the heat source. Inasmuch as mounting independent evidence suggests that the crust can support deviatoric stresses of up to about 100 MPa at temperatures of 400‐500d̀ C, and that the shear strength of the crust is strongly temperature‐dependent in the range 400‐800d̀ C, these results suggest that caution should be taken in the tectonic interpretation of P‐T paths involving decompression of the order of 100 MPa or less in LPHT terranes. The results illustrate a plausible mechanism for the close spatial association of both clockwise and anticlockwise P‐T paths documented in some LPHT terranes.
Very low‐grade metamorphism of the Taveyanne greywacke, Glarus Alps, Switzerland
Authors: RAHN M. , MULLIS J. , ERDELBROCK K. , FREY M. 
Published: May 2007

ABSTRACTDetailed textural and chemical data for mineral assemblages on a regional scale are presented for the metaandesitic Eocene‐Oligocene Taveyanne greywacke of the Glarus Alps, Eastern Switzerland. Presented data indicate an increase of metamorphic grade from zeolite facies to prehnite‐pumpellyite and pumpellyite‐actinolite facies. Low‐grade outcrops contain laumontite, minor corrensite and pumpellyite (assemblage type 1), whereas outcrops of higher metamorphic grade contain prehnite and two populations of pumpellyite (type 2), prehnite—pumpellyite‐(Al)—white mica (type 3), a single outcrop shows pumpellyite‐actinolite facies (type 4). From the zeolite to prehnite‐pumpellyite/pumpellyite‐actinolite facies there are indications for an increase of the chemical equilibrium domain size for the critical paragenesis from a single detrital grain ≤1 mm) in type 1, to a few millimetres in type 2, and to a whole thin section in type 3. MetamorphicP‐Tconditions were determined by a combination of chlorite thermometry, fluid inclusion and vitrinite reflectance data. Peak temperatures range from 170‐190d̀ C for zeolite facies to 270‐310d̀ C for prehnite‐pumpellyite and pumpellyite‐actinolite facies. For the higher temperature range, pressures of 2‐3 kbar are derived indicating a geothermal gradient of 24‐32d̀ C km‐1. The well‐constrained temperature estimations derived for the assemblages provide a useful test of the different empirical calibrations of chlorite thermometers recently proposed. The best correspondence to the temperatures determined here is for the Cathelineau calibration. In addition, in the lower grade samples differences in textures and calculated temperatures provide a mean to distinguish between detrital and newly formed chlorites.
Chemographic analysis of assemblages involving pyrophyllite, chloritoid, chlorite, kaolinite, kyanite, quartz: application to metapelites in the Witwatersrand goldfields, South Africa
Authors: ZHOU T. , DONG C. , PHILLIPS G. N. 
Published: May 2007

ABSTRACTThe Witwatersrand goldfields contain abundant assemblages that include pyrophyllite, chloritoid, chlorite, kaolinite and/or kyanite, with quartz. A chemographic analysis of the system Fe(Mg)‐Al‐Si‐O‐H involving these minerals yields 22 potential phase diagrams. Using orientation criteria and thermodynamic calculations as further constraints, this list has been reduced to three possible diagrams. New thermodynamic data favour one of these in particular.This chemographic analysis demonstrates that formation of chloritoid is not restricted to the breakdown reaction of kaolinite plus chlorite in the F(M)ASH system, as stated by previous studies, but could be from pyrophyllite + chlorite → chloritoid + quartz + H2O.The metamorphic temperature variation between Witwatersrand goldfields exceeded 65d̀ C, based on chlorite and chloritoid compositions. The lower and upper pressure limits are constrained by the andalusite to kyanite, and the sudoite/chlorite to carpholite boundaries, i.e. 1.5–2.8, and 7 kbar, respectively. The widespread pyrophyllite, chlorite and Fe‐chloritoid in all the Witwatersrand goldfields, and the local occurrence of sudoite indicate a consistent low‐pressure environment in which Mg‐chloritoid would not be stable.
Synkinematic contact metasomatism: implications for the timing of pluton emplacement and regional deformation in the Scanlon shear zone, south‐eastern California
Authors: ROTHSTEIN D. A. , KARLSTROM K. E. , HOISCH T. D. , MORRISON J. 
Published: May 2007

ABSTRACTStructures in rocks altered by the infiltration of magmatic fluids provide key constraints on the relative timing of plutonism and regional deformation in the central Old Woman Mountains, south‐eastern California. In this well‐exposed area the Scanlon shear zone, a belt of attenuated, shallowly dipping, amphibolite facies Palaeozoic strata, is in contact with two tabular, Late Cretaceous (∼74 Ma) granitoid plutons. The shear zone contains massive wollastonite‐bearing skarns ∼40 m above the contact with the Old Woman granodiorite. Field evidence, petrological data and stable isotope compositions indicate that the mineral assemblages in these skarns formed when the granodiorite crystallized and exsolved water‐rich, magmatic fluids. Structural features in the skarns, which include transposed wollastonite foliations, syntectonic vesuvianite and garnet porphyroblasts, and quartz ± wollastonite veins, afford an opportunity to monitor the regional strain at the time of pluton crystallization. These structures yield a broad range of timing relationships that indicate synkinematic mineral growth with deformation ending first, at c. 74 Ma. The metasomatic structures are kinematically compatible with the regional deformation observed in other lithologies and no post‐tectonic features overprint the fabrics in the skarns. Observations of isoclinally folded and boudinaged dykes and pegmatites, granodiorite saddle reefs in isoclinal fold hinges, and undeformed, locally pegmatitic dykes also yield a broad range of timing relationships indicative of synkinematic plutonism, with deformation ending first. Our results show that coupling petrological and stable isotope data with structural analysis is effective for unravelling the relative timing of heat and mass transfer processes in pluton‐wallrock systems.
Multiple intrusions and low‐pressure metamorphism in the central Old Woman Mountains, south‐eastern California: constraints from thermal modelling
Authors: ROTHSTEIN D. A. , HOISCH T. D. 
Published: May 2007

ABSTRACTThe Old Woman Mountains in south‐eastern California are a Late Cretaceous low‐pressure metamorphic terrane where multiple magmatic intrusions generated broad regions of elevated metamorphic temperatures. In the Scanlon Gulch area, two sheet‐like, Late Cretaceous granitoid plutons are in contact with the Scanlon shear zone, a 1‐km‐thick sheet of isoclinally folded and transposed metamorphic rocks. The metaluminous Old Woman granodiorite underlies the shear zone and the peraluminous Sweetwater Wash granite overlies it. Both plutons record emplacement ages of ∼74 Ma. Thermobarometry and phase relations in the shear zone suggest that peak metamorphism was at 650 ± 50† C and 4.3 ± 0.5 kbar. Late Cretaceous metamorphic temperatures were less elsewhere in the Old Woman Mountains, away from the intrusions.One‐dimensional thermal models are used to investigate how differences in the time between the emplacement of plutons would affect the thermal evolution of the central Old Woman Mountains. The prediction of a thermal history inferred from petrological and thermochronological data requires the rapid emplacement of the two plutons around the shear zone; simulations with delays of more than 1 Myr in the emplacement of the second pluton failed to predict peak metamorphic temperatures. Calculations which consider only the emplacement of a single pluton yield metamorphic temperatures that are too low. The time separating the intrusions is by far the most sensitive parameter in the calculations; assumptions concerning the treatment of the initial geothermal gradient and the latent heat of crystallization have relatively small effects on the predicted thermal histories. Our results suggest that for certain geometries, relatively short‐lived magmatic events involving rapid emplacement of multiple intrusions can produce low‐pressure metamorphism.
Stable isotopic and trace element evidence for restricted fluid migration in 2 GPa eclogites
Authors: GETTY S. R. , SELVERSTONE J. 
Published: May 2007

ABSTRACTMineral stable isotopic and trace element studies in 2 GPa banded eclogites of the Tauern Window, eastern Alps, record mm‐ to cm‐scale heterogeneities that reflect compositional variations in the accompanying metamorphic fluids. A close correlation between dolomite mode and dolomite δ18O is consistent with equilibrium partitioning among coexisting minerals and fluids. Small variations in dolomite δ13C values correspond with δ18O variations, but an overall decrease in dolomite δ13C by c. 1%o across a 12‐cm sample is a relict feature that pre‐dates eclogite equilibration. Garnet, omphacite, and clinozoisite rims show little systematic mineral‐mineral partitioning behaviour for Ti, V, Cr, Y, Sr, or Zr; major elements, however, are well equilibrated among these same minerals. Despite the apparent lack of mineral‐mineral trace element equilibration, most of the trace elements vary systematically with water activity calculated in each layer. Trace element behaviour during the eclogite metamorphism thus appears to have been controlled largely by mineral‐fluid interactions along grain boundaries.Shallow structural levels in other subduction complexes (c. 10‐45 km) typically exhibit fracture‐controlled permeability and extensive metasomatism, but there is no field or geochemical evidence for extensive fluid advection during high‐pressure metamorphism in the Tauern eclogites. Because most dewatering and devolatilization during tectonic burial occurs prior to eclogite conditions, the volumetric fluid/rock ratio in eclogites should generally be low. Low fluid/rock ratios, coupled with the possible non‐wetting nature of the fluids, permits the production and preservation of fine‐scale chemical heterogeneities in deeply subducted eclogites and associated fluids. However, the eventual breakdown at greater depth of volatile‐bearing dolomite, phengite, clinozoisite, zoisite, or amphibole could lead to renewed fracture‐controlled fluid release from the subducted rocks to regions appropriate for arc magma generation.
Prograde amphiboles in hematite‐bearing basic and quartz schists in the Sanbagawa belt, central Shikoku: relationship between metamorphic field gradient and P‐T paths of individual rocks
Authors: NAKAMURA C. , ENAMI M. 
Published: May 2007

ABSTRACTThe prograde amphibole that coexists with chlorite, epidote, muscovite, albite, quartz and hematite in Sanbagawa schists was examined to investigate the relationship between the prograde P‐T paths of individual rocks and the metamorphic field gradient in the Sanbagawa metamorphic belt, central Shikoku. The amphibole changes from actinolite, through ferri‐winchite and crossite, to barroisite and hornblende with increasing grade along the metamorphic field gradient. However, the sequence of prograde amphibole compositions in each sample varies in different mineral zones. The general scheme can be summarized as: magnesioriebeckite‐riebeckite crossite in the upper chlorite zone of lower‐grade rocks; crossite or glaucophane barroisite in the garnet zone of medium‐grade rocks; and actinolite or winchite barroisite hornblende in the albite‐biotite zone of higher‐grade rocks. Changes of amphibole composition indicate that the prograde P‐T path recorded in the higher‐grade rocks was situated on the higher‐temperature side of that of the lower‐grade rocks and on the lower‐pressure side of the metamorphic field gradient. The systematic change of P‐T paths implies an increasing dP/dT during continuous subduction. These features can be interpreted as documenting prograde metamorphism within a young subduction zone that has a non‐steady‐state geotherm.
40Ar/39Ar traverse — Grenville Front Tectonic Zone to Britt Domain, Grenville Province, Ontario, Canada*
Authors: REYNOLDS P. H. , CULSHAW N. G. , JAMIESON R. A. , GRANT S. L. , McKENZIE K. J. 
Published: May 2007

Abstract
40Ar/39Ar data (on hornblende, muscovite and K‐feldspar) are presented for samples from the western Grenville Province taken along a 140‐km traverse from the Grenville Front into the Britt domain. Our interpretation is based on 28 new analyses, synthesized with 20 previously reported from the traverse area.In regions where comparisons are possible, muscovite and (large domain) K‐feldspar apparent ages appear similar (at c. 920–930 Ma), but throughout the traverse, these are c. 60–70 Myr younger than the hornblende ages. The inferred cooling rate over the c. 350–500°C temperature range, c.2°C Myr‐1, is appropriate for exhumation controlled by post‐orogenic erosional unroofing. At the Grenville Front Tectonic Zone (GFTZ) — Britt domain boundary there is a c. 25‐Myr offset in both hornblende and muscovite/K‐feldspar ages. We interpret the lower ages in the Britt domain to reflect variations in crustal thickness and geothermal gradient between the flank and interior of a thick orogen.The argon data from the GFTZ are interpreted in the context of an asymmetric crustal‐scale antiformal structure developed during a late episode of convergence. Hornblende from rocks on either side of the core of the antiform has an apparent age of c. 990 Ma, our estimate of the age of the compressional event. In the west, we infer that these date the short‐lived thermal event associated with the development of the crustal‐scale antiform previously postulated. In the east, the ages reflect the cooling of material brought toward the surface in the flank of the antiform. Hornblendes from the antiform core appear to contain excess radiogenic argon. We suggest that this was the ambient argon in rocks transported from depth that was subsequently trapped when the rocks cooled rapidly.
Syndeformational fluid trapping in quartz: determining the pressure‐temperature conditions of deformation from fluid inclusions and the formation of pure CO2 fluid inclusions during grain‐boundary migration
Authors: JOHNSON E. L. , HOLLISTER L. S. 
Published: May 2007

Abstract
Observations and microthermometric data on fluid inclusions from a terrane that underwent deformation following peak metamorphic conditions show that grain‐boundary migration recrystallization favours the entrapment of carbonic inclusions whereas microfracturing during brittle deformation favours the infiltration and eventual entrapment of aqueous fluids. Our results imply that pure CO2 fluid inclusions in metamorphic rocks are likely to be the residue of deformation‐recrystallization process rather than representing a primary metamorphic fluid.Where the temperature of deformation can be deduced by other means, the densities of fluid inclusions trapped during recrystallization, which we call recrystallization‐primary fluid inclusions, can be used to constrain the ambient pressure during deformation. Using these constraints, the data imply that the post‐metamorphic Hercynian exhumation in Sardinia brought rocks at 300° C to within 3km of the surface. This conclusion is similar to that described for the rapidly uplifted Southern Alps in New Zealand.
Mesozoic tectonothermal development of the Sambagawa, Mikabu and Chichibu belts, south‐west Japan: evidence from 40Ar/39Ar whole‐rock phyllite ages
Authors: DALLMEYER R. D. , TAKASU A. , YAMAGUCHI K. 
Published: May 2007

Abstract
Five whole‐rock 40Ar/39Ar plateau ages from low‐grade sectors of the Sambagawa belt (Besshi nappe complex) range between 87 and 97 Ma. Two whole‐rock phyllite samples from the Mikabu greenstone belt record well‐defined 40Ar/39Ar plateau ages of 96 and 98 Ma. Together these ages suggest that a high‐pressure metamorphism occurred in both the Sambagawa and Mikabu belts at c. 90–100 Ma. The northern Chichibu sub‐belt may consist of several distinct geochronological units because metamorphic ages increase systematically from north (c. 110 Ma) to south (c. 215 Ma). The northern Chichibu sub‐belt is correlated with the Kuma nappe complex (Sambagawa belt). Two whole‐rock phyllite samples from the Kurosegawa terrane display markedly older metamorphic ages than either the Sambagawa or the Chichibu belts.Accretion of Sambagawa‐Chichibu protoliths began prior to the middle Jurrasic. Depositional ages decrease from middle Jurassic (Kuma‐Chichibu nappe complex) to c. 100 Ma (Oboke nappe complex) toward lower tectonostratigraphic units. The ages of metamorphic culmination also decrease from upper to lower tectonostratigraphic units. The Kurosegawa belt and the geological units to the south belong to distinctly different terrances than the Sambagawa‐Chichibu belts. These have been juxtaposed as a result of transcurrent faulting during the Cretaceous.
Petrology of Fe‐Mg‐carpholite‐bearing metasediments from NE Oman
Authors: EL‐SHAZLY ALEY EL‐DIN K. 
Published: May 2007

Abstract
Fe‐Mg carpholite occurs in metasediments of tectonically disrupted basement, shelf and foreland basin units that structurally underlie the Semail ophiolite in NE Oman. In the lower grade, structurally higher units, Fe‐rich carpholite coexists with paragonite, quartz, illite, kaolinite and chlorite, whereas in deeper units, Fe‐Mg carpholite occurs with pyrophyllite, sudoite, phengite and/or chloritoid. Mineral compositions in these units indicate that chlorite is more magnesian than coexisting Fe‐Mg carpholite at low temperatures and pressures but, at higher metamorphic grades, XMg decreases in the order sudoite > carpholite > chlorite > chloritoid. This suggests a reversal in Fe‐Mg partitioning between Fe‐Mg carpholite and chlorite at temperatures below or close to those of the breakdown of kaolinite + quartz to pyrophyllite and at XMg= 0.35.Phase relations and mineral equilibria indicate that the P‐T conditions of formation of the Fe‐Mg‐carpholite‐bearing rocks of NE Oman range from 280–315° C, 3–6 kbar for the structurally highest units to 325–440° C, 6–9.5 kbar for the deepest units, indicating a systematic down‐section increase in metamorphic grade. Textural relations in these rocks, interpreted in the context of pertinent equilibria, are consistent with the clockwise P‐T paths previously constrained for these units from petrological studies of interlayered isofacial mafic rocks.
The smectite to chlorite transition in a fossil seamount hydrothermal system: the Basement Complex of La Palma, Canary Islands
Authors: SCHIFFMAN P. , STAUDIGEL H. 
Published: May 2007

AbstractThe hydrothermal metamorphism of a sequence of Pliocene‐aged seamount extrusive and volcanoclastic rocks on La Palma includes a relatively complete low‐P‐Tfacies series encompassing the zeolite, prehnite‐pumpellyite, and greenschist facies. The observed mineral zonations imply metamorphic gradients of 200–300° C km‐1.The transition from smectite to chlorite in the La Palma seamount series is characterized by discontinuous steps between discrete smectite, corrensite and chlorite, which occur ubiquitously as vesicles and, to a much lesser extent, vein in‐fillings. Trioctahedral smectites [(Mg/(Fe + Mg) = 0.4–0.75] occur with palagonite and Na‐Ca zeolites such as analcime and a thompsonite/natrolite solid solution. Corrensite [(Mg/(Fe + Mg) = 0.5–0.65] first appears at stratigraphic depths closely corresponding to the disappearance of analcime and first appearance of pumpellyite. Discrete chlorite [(Mg/(Fe + Mg) = 0.4–0.6] becomes the dominant layer silicate mineral coincident with the appearance of epidote and andraditic garnet.Within the stratigraphic section there is some overlap in the distribution of the three discrete layer silicate phases, although random interstratifications of these phases have not been observed. Although smectite occurs as both low‐ and high‐charge forms, the La Palma corrensite is a compositionally restricted, 1:1 mixture of low‐charge, trioctahedral smectite and chlorite. Electron microprobe analyses of coarse‐grained corrensite yield structural formulae close to ideal values based on 50 negative charge recalculations. Calcium (average 0.20 cations/formula unit) is the dominant interlayer cation, with lesser Mg, K and Na.The absence of randomly interlayered chlorite/smectite in the La Palma seamount series may reflect high, time‐integrated fluid fluxes through the seamount sequence. This is consistent with the ubiquity of high‐variance metamorphic mineral assemblages and the general absence of relict igneous minerals in these samples.
Chains of Impact from Reaganomics on Primary Care Policies
Authors: Milio Nancy 
Published: May 2007

AbstractThis article analyzes the effects of federal fiscal policy in the Reagan administration on primary care programs. Within the context of the national economy and federal policy priorities, states responded to budget cuts and block grants with fiscal and administrative restrictions that fell disproportionately on disadvantaged groups. A wide array of primary care services became less available and accessible, thereby limiting their cost‐savings potential and their effectiveness in supporting people's health. These program deficits, together with lowered living standards among large segments of the population, resulted in rising rates of infant mortality in many states. A perspective that can interrelate federal and state policy actions, and broad public policies with traditional health policies, will improve public health nurses' understanding of policy‐making and policy impacts, and thereby can guide renewed efforts toward health improvement.
Expanding Nursing's Practice Terrain: Imperatives for Future Viability
Authors: Dugan Anna Baziak 
Published: May 2007

AbstractChanges in perceptions of health needs, which are increasingly sociocultural in nature, and changes in health services shifting from medical control to entrepreneurial opportunities and corporate business control will necessarily have an impact on nursing. Nurses can capitalize on this, expanding their practice dimensions within the boundaries of current employment as well as joining in competitive health marketplace ventures. This will ensure relevance and continued viability of the profession in a dynamic, open, health services field.
Nurse‐patient Interaction in the Home Setting
Authors: Morgan Barbara S. , Barden Martha E. 
Published: May 2007

AbstractNurses' interactive behaviors with perinatal patients in the home setting, as well as nurse‐patient perceptions of home visits were examined. Data were obtained from 18 public health nurses and 55 perinatal patients. Results based on Bales's interaction process analysis revealed that 53.8 percent of the nurses' visits were related to asking for or giving information, while only 7.9 percent were categorized as friendly. Patients, however, perceived the nurses as friendly to them and others present. Although other differences in perceptions did emerge between nurses and patients, both groups were uncertain whether they had agreed on goals to work toward, which suggests the need for consumer involvement in the nursing process.