bluuebunny/crossref_metadata_2025 huggingface dataset:
Metamorphism of a Late Jurassic volcano‐plutonic arc, northern California, USA
Authors: BEIERSDORFER R. E.
Published: May 2007

Abstract
The metamorphic history of the Middle to Upper Jurassic volcanic and hypabyssal rocks exposed in the Klamath Mountains and Sierra Nevada of California is related, in part, to the rifting of a volcano‐plutonic arc. The Callovian to Kimmeridgian rocks exposed in the region consist of, from north‐west to south‐east, a back‐arc ophiolite, a rifted volcanic arc and a volcanic arc complex. All of these units have been metamorphosed and contain various combinations of the phases chlorite, amphibole, epidote, prehnite and pumpellyite. Projection of coexisting phases onto the composition plane MgO/(MgO + FeO) and Al2O3+ Fe2O3 ‐ 0.75 CaO ‐ Na2O through quartz, water, albite and epidote results in consistent mineralogical compatibilities within each region, but crossing tie‐lines between regions. This suggests that the volcanic and hypabyssal rocks from each region have equilibrated under different intensive conditions.

The back‐arc ophiolite in the north has suffered subseafloor high‐T/P hydrothermal metamorphism with geothermal gradients on the order of 100° C km−1. The rifted volcanic arc has undergone synchronous burial, hydrothermal and contact metamorphism. Metamorphic field gradients in the region pass through the prehnite‐pumpellyite and greenschist facies suggesting geothermal gradients on the order of 30° C km−1. The southernmost volcanic arc complexes contain metavolcanics of the pumpellyiteactinolite and greenschist facies suggesting moderate‐ to high‐P/T metamorphism and geothermal gradients on the order of 20° C km−1.

The apparent increase in rifting and calculated geothermal gradients from south‐east to north‐west suggest that the observed very low‐ and low‐grade metamorphism may be a response to enhanced thermal gradients during extension of the volcanic arc. This correlation between the extent of rifting and metamorphism is consistent with a model of diastathermal metamorphism of a propagating rift along the western margin of North America during the Late Jurassic. The plate tectonic setting may be analogous to the present‐day Andaman Sea region.
Metamorphism and tectonic evolution of the Lancang paired metamorphic belts, south‐western China
Authors: ZHANG RUYUAN , CONG BOLIN , MARUYAMA SHIGE , LIOU J. G.
Published: May 2007

Abstract
The Lancang metamorphic terrane consists of an eastern low‐P/T belt and a western high‐P/T belt divided by a N–S‐trending fault. Protoliths of both units are mid–late Proterozoic basement and its cover. The low‐P/T belt includes the Permian Lincang batholith, related amphibolite facies rocks of the Damenglong and Chongshan groups, and Permo‐Triassic volcanic and volcaniclastic rocks. Most whole‐rock Rb–Sr isochron and U–Pb zircon ages of the Lincang batholith are in the range 290–279 and 254–212 Ma, respectively. Metamorphism of the low‐P/T belt reaches upper amphibolite with local granulite facies (735°C at 5 kbar), subsequently retrogressed at 450–500°C during post‐Triassic time. The high‐P/T rocks grade from west to east from blueschist through transitional blueschist/greenschist to epidote amphibolite facies. Estimated P–T conditions follow the high‐P intermediate facies series up to about 550–600°C, at which oligoclase is stable. The 40Ar/39Ar plateau age of sodic amphibole in blueschist is 279 Ma.

The paired metamorphic belts combined with the spatial and temporal distribution of other blueschist belts lead us to propose a tentative tectonic history of south‐east Asia since the latest Precambrian. Tectonic juxtaposition of paired belts with contrasting P–T conditions, perhaps during collision of the Baoshan block with south‐east Asia, suggests that an intervening oceanic zone existed that has been removed. The Baoshan block is a microcontinent rifted from the northern periphery of Gondwana. Successive collision and amalgamation of microcontinents from either Gondwana or the Panthalassan ocean resulted in rapid southward continental growth of c. 500 km during the last 200 Ma. Hence, the Lancang region in south‐east Asia represents a suture zone between two contrasting microcontinents.
Compositional evolution in Ca‐amphibole in the Karmutsen metabasites, Vancouver Island, British Columbia, Canada
Authors: TERABAYASHI M.
Published: May 2007

Abstract
The 6‐km‐thick Karmutsen metabasites, exposed over much of Vancouver Island, were thermally metamorphosed by intrusions of Jurassic granodiorite and granite. Observations of about 800 thin sections from the Campbell River and Buttle Lake area show that the metabasites provide a complete succession of mineral assemblages ranging from the zeolite to pyroxene hornfels facies around the intrusion. The most important observations are as follows. (1) The compositional change of Ca‐amphiboles with increasing metamorphic grade is not straightforward. The tremolite component decreases from the prehnite–actinolite facies to the greenschist facies with a compensating tschermak component increase, but the tendency is not clear thereafter. Instead, the edenite component increases from the amphibolite facies to the pyroxene hornfels facies. (2) The most pargasitic Ca‐amphibole occurs in high‐Fe2+/Mg metabasite from the greenschist/amphibolite transition zone. (3) The reasons for such irregular compositional trends, even in the rather uniform MORB‐like composition of the Karmutsen metabasites, are non‐ideal solid solutions of Ca‐amphibole at low temperature and the effective control by bulk rock composition in the amphibolite facies. (4) The data from this study support, but do not prove, a transition loop for the actinolite–hornblende compositional gap rather than a solvus. If the gap is a solvus, its shape is asymmetric, and is highly dependent on the other compositional parameters such as Fe3+/Al and Fe2+/Mg. (5) The XNaA/XA±XAb) ratios between Ca‐amphibole and plagioclase are most useful as an indicator of metamorphic grade even within the amphibolite facies, and these change systematically from 0.2 to 0.5 from the greenschist to pyroxene hornfels facies. (6) The compositional trend of Ca‐amphibole from the Karmutsen metabasites indicates a typical low‐P/T metamorphic facies series on a Rbk–Gln–Tr–Ts diagram.
Prograde reactions and garnet zoning reversals in staurolite schist, British Columbia: significance for thermobarometric interpretations
Authors: WHITNEY D. L. , GHENT E. D.
Published: May 2007

Abstract
An outcrop of staurolite‐bearing pelitic schist from the Solitude Range in the south‐western Rocky Mountains, British Columbia, was examined in order to determine the nature of prograde garnet‐ and staurolite‐producing reactions using information from garnet zoning and inclusion mineralogy. Although not present as a matrix phase, chloritoid is present as inclusions in garnet and is interpreted to have participated in the simultaneous growth of garnet and staurolite by a reaction such as chloritoid + quartz = garnet + staurolite + H2O.

A garnet zoning trend reversal, which is most pronounced with respect to almandine and grossular components, is present in the outer core of garnets. The location of the zoning reversal corresponds to the outer limit of chloritoid inclusions in garnet. As there is no evidence for polymetamorphism, the zoning reversal is interpreted to indicate continued garnet growth by prograde reaction(s) during a single metamorphic event after the exhaustion of chloritoid as a matrix phase.

Metamorphic conditions recorded by mineral rim compositions are 550–600° C at 6–7 kbar. Because there is no evidence for partial resorption of garnet during production of staurolite, we interpret these results to represent peak conditions.
Progressive metamorphism in a crustal‐scale shear zone: an example from the Léon region, north‐west Brittany, France
Authors: JONES K. A.
Published: May 2007

This paper describes the progressive metamorphism and deformation of a series of metasediments, Le Conquet Schists and their higher grade equivalents, which occur as tectonically emplaced screens within a sequence of foliated gneisses, the Gneiss de Brest and Gneiss de Lesneven. The sequence exhibits a steep south to north increase in metamorphic grade from garnet‐staurolite schist to sillimanite gneiss and sillimanite‐K‐feldspar migmatite. The relationship of mineral growth to foliation development has been established for individual screens. At least five phases of deformation (D1‐D5) are preserved. Analysis of porphyroblast inclusion trails is used to demonstrate sequential mineral growth during the successive development of orthogonal foliations S1‐S4. Porphyroblasts continued to grow during the subsequent development of C‐S mylonite fabrics and extensional crenulation cleavages which are genetically related to a series of high‐strain zones (D5). Mineral assemblages, phase relations and mineral chemistry are consistent with porphyroblast growth being the result of continuous reactions. Microstructure‐porphyroblast relations are used to show that although mineral growth proceeded during continuous reactions, these only operated episodically. Phase relations, mineral chemistry and P‐T estimates are used to constrain P‐T trajectories and these are linked to the deformation histories within individual screens. A comparison between the resulting pressure‐temperature‐deformation paths is used to demonstrate that the metamorphic peak occurred progressively later and at successively lower pressures with increasing metamorphic grade. It is suggested that the early evolution of the belt is the result of crustal thickening by overthrusting. The subsequent history is one of progressive heating and unroofing of the higher grade rocks in a dextral strike‐slip transtensional shear zone.
Rotation of porphyroblasts in non‐coaxial deformation: insights from computer simulations
Authors: BJØRNERUD M. G. , ZHANG HUBAO
Published: May 2007

Porphyroblast inclusion trails have the potential to provide critical information about tectonometamorphic events. Recently, however, traditional interpretations of inclusion trails have been called into question by the suggestions that porphyroblasts do not rotate during non‐coaxial deformation and that apparent spiral inclusion trails can be generated in coaxial deformation. We present a new computer model that simulates inclusion trail development. Model results suggest: (1) that the extent of porphyroblast rotation is controlled by conditions at the porphyroblast‐matrix boundary; (2) that curved inclusion trails may develop in unrotated porphyroblasts; (3) that classic “snowball” inclusion trails are most simply explained by rotational growth histories; and (4) that some of the observations used to support the view that porphyroblasts do not rotate (e.g. weakly sigmoidal inclusion trails, apparent truncations of inclusion trails) can be accounted for by variations in the growth rate of rotating porphyroblasts.
Fluid migration and vein formation during deformation and greenschist facies metamorphism at Ormiston Gorge, central Australia
Authors: CARTWRIGHT I. , POWER W. L. , OLIVER N. H. S. , VALENTA R. K. , MCLATCHIE G. S.
Published: May 2007

During the Alice Springs Orogeny, deformation at Ormiston Gorge, central Australia, occurred under lower‐ to middle‐greenschist facies conditions. Dolomites of the Bitter Springs Formation and quartzites. metagreywackes, and metapelites of the Heavitree Quartzite contain abundant early‐, syn‐, and post‐tectonic veins. However, though vein densities locally approach 15%, the distribution of veins and the oxygen isotope geochemistry of wallrocks and veins suggest that fluid movement was on a local scale. The Heavitree Quartzite contains quartz veins that, even along the main thrust plane, have similar δ18O values (13.5–16.9%o) to those of their wallrocks (13.6–16.9%o), with Δ18O(vein‐wallrock) values of ‐0.6 to 0.4%o. In contrast, the Bitter Springs Formation contains predominantly dolomite veins that have δ18O values of 23.4 to 27.7%o. These differences are observed even at the boundary between the Heavitree and Bitter Springs rocks, implying that significant fluid exchange between these rocks has not occurred, or that fluid flow was channelled through areas outside those sampled for this study. By contrast with the Heavitree Quartzite, δ18O values of wallrocks in individual samples of the Bitter Springs Formation are significantly higher (23.3–29.1%o) than those of the veins, with δ18O(vein‐wallrock) values up to ‐4%o (average of ‐2.1%o). These systematic differences in δ18O values most likely result from oxygen isotope fractionation caused by fluid immiscibility or disequilibrium dissolution. Smaller differences in δ13C values between some dolomite veins and wallrocks [δ13C(vein‐wallrock) up to ‐1.9%o, average of ‐0.5%o] are also explained by these processes. This study indicates that large volumes of veins may be produced by repeated fracturing and fluid migration within particular rock units, without involving large volumes of externally derived fluids.
Zoning patterns in orthopyroxene and garnet in granulites: implications for geothermometry
Authors: PATTISON D. R. M. , BÉGIN N. J.
Published: May 2007

Compositional maps of orthopyroxene and garnet of contrasting grain size and in contact with different minerals were made from two paragneiss granulites from the Minto terrane of northern Quebec. The compositional maps provide clear evidence of late exchange of Fe/(Fe + Mg) after Ca in garnet and Al in orthopyroxene had been quenched‐in. The extent of late Fe‐Mg exchange was controlled by neighbouring minerals, with negligible Fe‐Mg gradients against plagioclase and quartz, and substantial gradients against exchangeable Fe‐Mg minerals. Cores of grains in contact with exchangeable Fe‐Mg neighbours are progressively more reset in Fe/(Fe + Mg) as grain size decreases, whereas cores of even small grains surrounded by only plagioclase and quartz are not significantly different in Fe/(Fe + Mg) than cores of the largest grains. Gradients of Ca in garnet and of Al in orthopyroxene in grains of uniform Fe/(Fe + Mg) preserve a high‐temperature retrograde history during which intergranular exchange effected compositional uniformity of mineral rims and intragranular Fe‐Mg diffusion in garnet and orthopyroxene was rapid enough to homogenize Fe/(Fe + Mg). The transition from efficient intergranular exchange at relatively high temperatures to local Fe‐Mg exchange at lower temperatures may have been controlled by loss of an intergranular exchange medium in the rock, possibly an internally generated dehydration melt phase. Implications for geothermometry of granulites include the following (numerical values are particular to this study): (1) core compositions of garnet and orthopyroxene grains in contact with exchangeable neighbours may be reset in Fe/(Fe + Mg) relative to the most refractory compositions by an amount equivalent to 120d̀ C; (2) Fe‐Mg exchange thermometry using even the most refractory Fe/(Fe + Mg) compositions may not record peak granulite conditions, possibly recording instead the temperature at which an intergranular exchange medium was lost from the rock; and (3) temperature‐sensitive net transfer equilibria involving Al solubility in orthopyroxene yield temperatures up to 150d̀ C higher than maximum Fe‐Mg exchange temperatures, even in grains with flat Fe/(Fe ‐ Mg) compositional profiles, making them a better means of estimating peak granulite temperatures than Fe‐Mg exchange thermometry.
Microstructural timing of the Rosebery massive sulphides, Tasmania: evidence for a metamorphic origin through mobilization of disseminated base metals
Authors: AERDEN D. G. A. M.
Published: May 2007

Microstructural timing relationships indicate that the Rosebery massive sulphide ore, western Tasmania, Australia, formed by metasomatic replacement of ‘sericite’ schist during a Devonian deformation event (D3). This interpretation is contrary to earlier volcanogenic‐based interpretations, but accords with the discordant position and inferred structurally controlled emplacement of the orebody. The main timing criteria are: overprinting of S3 by the late ore minerals, replacement textures in undeformed mineral parageneses, and a D3 structural control from the microscopic to the macroscopic scales. The consistent observation of these criteria in the orebody and the complete lack of pre‐D3 ore argue against in situ dissolution of a primary orebody and local redeposition of sulphides by replacement.

D3 deformation at Rosebery is inferred to have been characterized by heterogeneous cleavage‐parallel extension, which resulted in localized microfracturing and selective replacement of zones of maximum strain rate. Continuous shifts in the strain‐rate distribution pattern during progressive mineralization led to the compositional ore banding.

Published Pb‐isotope data point towards a Cambrian source rock for the orebody. This suggests a metamorphogenic origin by regional‐scale dissolution of dispersed volcanogenic metals, focused solution transfer and concentrated redeposition in a structural trap.
Synmetamorphic veining: origin of andalusite‐bearing veins in the Vedrette di Ries contact aureole, Eastern Alps, Italy
Authors: CESARE B.
Published: May 2007

Discordant andalusite‐biotite‐quartz‐bearing veins occur in the contact aureole of the Vedrette di Ries pluton (Italian Eastern Alps), never outside the area of contact metamorphic andalusite development. Andalusite veins are found only within andalusite‐bearing hornfelses, and vein biotite occurs wherever host‐rock garnet is partially replaced by biotite. Veins formed during contact metamorphism, synchronously with the crystallization of andalusite and biotite within host rocks. Their pegmatitic structure and their orientation suggest that vein parageneses crystallized within fluid‐filled cavities that opened by hydraulic fracturing.

A mechanism of synmetamorphic veining is proposed to explain rock failure and subsequent mineral deposition within veins. During hydrofracturing induced by dehydration reactions in response to heating in the aureole, fissures were immediately filled with locally derived fluids. The lack of large‐scale flux, together with high fluid pressures required by hydrofracturing, suggest fluid in the cavities was a virtually stagnant, passive medium, and that mass‐transport toward fractures was driven by intergranular diffusion. Because temperature and Pf values within veins are similar to those in the host rock, vein assemblages are interpreted as the stable, high‐T side of reactions taking place within pelitic schists, at the time when fractures opened. Once nucleation of product phases occurred, chemical components released by dissolution of reactant minerals were driven to precipitation sites by chemical potential gradients. Since nucleation was favoured at the strained grains of vein walls, andalusite and biotite simultaneously grew in vein and host rock.

The proposed genetic model contrasts with generally adopted metasomatic mechanisms for the genesis of Al2SiO5‐bearing veins, in not requiring large fluid/rock ratios or a highly ‘aggressive’ fluid composition. The mechanism of synmetamorphic veining may be particularly useful in the interpretation of vein occurrences in medium‐ and deep‐crustal rocks which have undergone extensive devolatilization.
Interpretation of porphyroblast inclusion trails: limitations imposed by growth kinetics and strain rates
Authors: BARKER A. J.
Published: May 2007

Porphyroblast inclusion trails provide important information about the tectonometamorphic evolution of a metamorphic rock. However, there remains considerable controversy over whether porphyroblasts rotate during bulk non‐coaxial deformation.

With reference to an area of the Scandinavian Caledonides and utilizing existing data from theoretical and experimental modelling, this study demonstrates that both ‘straight’ and ‘S‐shaped’ inclusion trails are consistent with an interpretation in terms of syndeformational porphyroblast growth in a regime approximating to Newtonian simple shear. At crustal strain rates of 10‐14 s‐1 and porphyroblast growth times of 0.1–1.0 Ma, it is shown that a maximum of 5d̀‐9d̀ angular rotation would occur during growth. At faster strain rates of 10‐12 s‐1 (e.g. those in a shear zone) porphyroblast angular rotations of 90d̀ are shown to occur in 0.1–0.25 Ma (i.e. times comparable with or faster than porphyroblastesis). In view of this, ‘S‐shaped’ inclusion trails are to be expected in porphyroblasts growing in active shear zones or other situations of high shear strain, whereas ‘straight’ inclusion trails can be interpreted as static overgrowth of an existing fabric or as syndeformational porphyroblastesis at low strain rates.
The effects of ferromagnesian components on the paragonite‐muscovite solvus: a semiquantitative analysis based on chemical data for natural paragonite‐muscovite pairs
Authors: GUIDOTTI C. V. , SASSI F. P. , SASSI R. , BLENCOE J. G.
Published: May 2007

Chemical data for 139 natural paragonite‐muscovite (Pg‐Ms) pairs illustrate the effects of ferromagnesian components on theP‐T‐Xtopology of the Pg‐Ms solvus. The pairs were selected on the basis of: reasonably accurate knowledge of theP‐Tconditions of formation; evidence for close approach to equilibrium at peak metamorphic conditions; exclusion of pairs in which paragonite contains more than 5 mol% margarite; and exclusion of pairs from polymetamorphic rocks that contain more than one set of cogenetic Pg‐Ms pairs. Graphical analysis reveals considerable scatter in the data; nevertheless, it is evident that the muscovite limb of the solvus shifts markedly toward end‐member muscovite with increasing pressure from approximately 7 kbar to 21 kbar. This shift is attributed to a pressure‐induced increase of the ferromagnesian content of muscovite, which increases the size of the XII alkali site ‐ to the effect that K is more readily accommodated than Na. The data also suggest that the paragonite limb of the solvus migrates slightly toward end‐member paragonite with increasing pressure. Broadening of the Pg‐Ms solvus with increasing pressure reflects increasingly nonideal Na‐K mixing as the phengite content of muscovite increases. Due to the wide scatter of data for Pg‐phengitic‐Ms pairs, it is concluded that, at the present time, Pg‐Ms solvus thermometry is only viable for quasibinary Pg‐Ms pairs.
Metamorphic P‐T paths from calcic pelitic schists from the Strafford Dome, Vermont, USA
Authors: MENARD T. , SPEAR F. S.
Published: May 2007

Metamorphism of the Gile Mountain Formation and Waits River Formation in the Strafford Dome and Townshend‐Brownington Syncline in east‐central Vermont records two nappe‐style events, D1 and D2, followed by doming. D1 formed a muscovite + biotite ± ilmenite schistosity subparallel to compositional layering, SO, and was followed by heating to garnet grade. The temperature and pressure at the end of D1 are estimated to be c. 450d̀ C and 6‐8 kbar. D2 variably crenulated and folded S1 during a nearly isothermal pressure increase of 1‐2 kbar, calculated from compositions of garnet, which have inclusions trails with progressive crenulation and rotation of the S1 fabric. Similar P‐T paths are computed for most of the area, suggesting that the later schistosity developed during emplacement of a regional nappe 3‐6 km thick. There is a general lack of D3 (dome‐stage) microstructures.

Near the Strafford‐Willoughby Arch, staurolite and kyanite overgrew S2 in pelites, and plagioclase with increasing XAn overgrew S2 in calcic pelites, reflecting post‐D2 heating to a maximum of 550‐600d̀ C. Metamorphic pressures at the end of D2 are fairly constant on the west side of the dome, indicating minor dome‐stage uplift. In contrast, pressures at the thermal peak of metamorphism decrease by more than 4 kbar east of the dome. The observed pattern of isotherms and isobars is mainly the result of post‐metamorphic, differential uplift and unroofing.

Finally, a minor, retrograde metamorphism produced the assemblage albite + epidote + K‐feldspar + muscovite + chlorite, with grade increasing east toward the Connecticut River.
Stepping stones and pitfalls in the determination of an anticlockwise P‐T‐t‐deformation path: the low‐P, high‐T Cooma Complex, Australia
Authors: JOHNSON S. E. , VERNON R. H.
Published: May 2007

Abstract
Low‐pressure/high‐temperature (low‐P/high‐T) metamorphic rocks of the Cooma Complex, southeastern Australia, show evidence of an anticlockwise pressure‐temperature‐time‐deformation (P‐T‐t‐D) path, similar to those of some other low‐P/high‐T metamorphic areas of Australia. Prograde paths are reasonably well constrained in cordierite‐andalusite schists, cordierite‐K‐feldspar gneisses and andalusite‐K‐feldspar gneisses. These paths are inferred to be convex to the temperature axis, involving increase in pressure with increase in temperature. Evidence of the retrograde path is inconclusive, but is consistent with approximately isobaric cooling, as are available isotopic data on the Cooma Granodiorite, which indicate initially rapid cooling following attainment of peak temperatures. The retrograde path is inconsistent with either a clockwise P‐T‐t‐D path involving rapid or even moderate decompression immediately post‐dating the peak of metamorphism, or a path in which the retrograde component simply reverses the prograde component, because both these paths should cross reactions forming cordierite from aluminosilicate, for which no evidence has been observed.

Determination of the deformational‐metamorphic history of the complex is not straightfoward and depends on careful examination of critical samples. Evidence necessary for successful elucidation of the prograde, and part of the retrograde, deformational‐metamorphic history in the Cooma Complex includes: (1) sequentially grown porphyroblasts that can be timed relative to surrounding foliations; (2) partial replacement microstructures providing relative timing of metamorphic reactions that cannot be timed relative to foliation development; (3) a tectonic marker foliation (S4 at Cooma) that allows correlation of foliations from one location to another; and (4) single samples containing all of the foliations and all generations of porphyroblast growth within a single metamorphic zone. The latest two or three foliations involve low strain accumulation, allowing relative timing relationships between foliations and porphyroblasts to be more clearly determined.

Sequential porphyroblast growth and foliation development in the cordierite‐andalusite schists is examined for situations involving rotation and non‐rotation of porphyroblasts relative to geographically fixed coordinates. Although the number of foliations developed varies in the rotational situation, depending on the deformation history proposed, the sequential order of porphyroblast growths does not differ from the non‐rotational situation. Thus, whether or not porphyroblasts rotated in the Cooma rocks, the sequence of reactions, and therefore P‐T‐t paths inferred from the relative timing of porphyroblast growths, remain the same, for the deformational histories evaluated.
North‐west propagation of the Grenville orogen: Grenvillian structure and metamorphism near Key Harbour, Georgian Bay, Ontario, Canada*
Authors: JAMIESON R. A. , CULSHAW N. G. , CORRIGAN D.
Published: May 2007

Abstract
We report structural and metamorphic data from a c. 25‐km transect across the eastern Grenville Front Tectonic Zone (GFTZ) to the Britt domain at the northern end of Georgian Bay near Key Harbour, Ontario. Constrasting Grenvillian structural and fabric elements characterize the eastern GFTZ, northern Britt domain and a narrow Transition Zone between them.

Moderately to steeply dipping foliations with strong down‐dip lineations in all three divisions appear to be associated with NW‐directed thrusting. In the Transition Zone and northern Britt domain, early S = L fabrics with steep lineations are overprinted by younger structures (S > L) with shallow, SE‐SSE‐plunging lineations in which sparse, dominantly (but not exclusively) normal‐sense kinematic indicators are recognized. Pressure and temperature estimates from Grenvillian metamorphic assemblages in metadi‐abase indicate that conditions of P ± 12 kbar and T c 800° C were achieved before or during the thrust‐related deformation, with P‐T‐t paths that indicate near‐isothermal decompression to P c. 4 kbar and T c. 700° C. Correlation of fabric elements with points on the P‐T‐t paths suggests that exhumation occurred during two stages, the first associated with thrusting (≥1035 Ma) and the second with extension and thrusting (pre‐1003 Ma).

The GFTZ contains steeply to moderately dipping, thrust‐related fabrics and lacks shallow, extensional structures; the latest episode of thrusting in the GFTZ is inferred to have taken place at 990‐980 Ma. The data are interpreted in terms of a tectonic model involving two stages of propagation of the Grenville orogen towards its foreland (≥1035 Ma and ≥980 Ma), with an intervening period of extension, although the tectonic regime probably remained compressional on the scale of the orogen.
Trace element redistribution in high‐temperature deformed gabbros from East Ligurian ophiolites (Northern Apennines, Italy): constraints on the origin of syndeformation fluids
Authors: TRIBUZIO R. , RICCARDI M. P. , OTTOLINI L.
Published: May 2007

Abstract
Mg‐gabbros from East Ligurian ophiolites (Northern Apennines, Italy) display a high‐temperature/low‐pressure recrystallization localized along ductile shear zones. In deformed gabbros, the igneous diopside is recrystallized into granoblastic aggregates of neoblastic diopside and minor red‐brown amphibole. The latter displays a pargasitic composition, with high amounts of AlIV Na(A) and Ti (± 1.8, 0.7 and 0.4 atoms per formula unit, respectively). Major element composition of neoblastic minerals highlight equilibration temperature conditions in the range 800–950° C. Red‐brown Ti‐pargasite also occurs as a minor interstitial constituent, presumably growing from a residual trapped liquid, in the differentiated lithologies (Fe‐Ti‐diorites) of the plutonic ophiolitic complex.

By means of ion microprobe (SIMS technique), rare earth (La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb) and selected trace elements (Sr, Y, Cr, V, Sc, Zr, Ti) have been analysed in igneous and neoblastic diopside, as well as in Ti‐pargasites. Ti‐pargasites have also been analysed for F and Cl, and compared with the halogen composition of the amphiboles, mainly hornblendes to actinolites, which are related to the subsequent low‐temperature brittle evolution.

Neoblastic Ti‐pargasite from deformed Mg‐gabbros bears close compositional similarities with igneous Ti‐pargasite from undeformed Fe‐Ti‐diorites, whereas it is geochemically distinct from the amphiboles post‐dating the ductile event. In particular, Ti‐pargasites have relatively high contents of F, REE, Y, Zr and Sr, which are not consistent with crystallization in the presence of seawater‐derived hydrothermal fluids.

High‐grade recrystallization probably developed in the presence of volatile‐rich igneous fluids, either trapped between the cumulus minerals or injected into the ductile shear zones from outside the local system. An alternative hypothesis comprises the absence of fluid phase and the development of ductile shear zones in Ti‐pargasite‐rich layers. The petrological features of deformed gabbros recovered from present‐day slow‐spreading ridges and fracture zones bear close similarities with the investigated ophiolitic metagabbros. In East Ligurian ophiolites, high‐grade ductile shear zones have been related to the initial stages of the uplift of the gabbro‐peridotite complex to the sea‐floor.
Continuous reactions with amphibole, garnet and plagioclase
Authors: ZINGG A. J.
Published: May 2007

Abstract
End‐member, continuous and degenerate reactions are derived for the multisystem with the six components Na2O, CaO, (Mg/Fe)O, Al2O3, SiO2, H2O among the phases plagioclasess, garnetss, amphiboless, cpx, opx, olivine, spinel, quartz and an aqueous fluid. The chemography of this system is degenerate due to the co‐linearity 2Opx = Ol + Qtz. This co‐linearity has its implications both on reaction space and phase equilibria.

From a total of 28 reaction systems, reaction space is derived for nine subsystems (phases in parentheses are absent):

Case A1: (Cpx,Ol) (Cpx,Opx) and (Cpx,Qtz),

Case A2: (Spl,Ol) (Spl,Opx) and (Spl,Qtz),

Case B: (Ol,Opx) (Ol,Qtz) and (Opx,Qtz).

In the absence of either cpx or spl (case A), three reactions form an invariant point, either [Cpx] or [Spl], where the co‐linear phases olivine, opx and quartz coexist on the transformation line 2Opx = Ol + Qtz. Changing mineral compositions force invariant points to move along the line with the different reaction curves changing their relative position according to Schreinemakers’rules. Zero contours, i.e. the location where (a) phase(s) disappear(s) in reaction space correspond to singular points in phase diagrams. Two types are distinguished; singular points of indispensable and of substitutable phases. In the first case the phase disappears from the entire bundle while in the second it disappears from a single reaction. In the specific case where the substitutable phases are also the co‐linear ones, two of the three co‐linear phases disappear simultaneously. Two of the three reaction curves coincide.

In the system including Cpx and Spl (Case B) three reactions, (Ol,Opx) (Ol,Qtz) and (Opx,Qtz), oppose three invariant points, [Ol], [Opx] and [Qtz]. Invariant points no longer move along the line 2Opx = Ol + Qtz. The coincidence of the zero contours of all three co‐linear phases in reaction space‐the result of the chemographic degeneracy‐causes the respective singular points to coincide in the phase diagrams. This is the location where curves must be rearranged in a bundle to conform Schreinemakers’rules.

The reaction Grs1Prp2= 2 Ol + An is fourth order degenerate and part of all nine subsystems (cases A and B). It can be used to relate the different phase diagrams to one another.
Metamorphic interpretation of high‐pressure‐temperature metapelites with preserved growth zoning in garnet, eastern Grenville Province, Canadian Shield
Authors: INDARES A.
Published: May 2007

Abstract
High‐pressure‐temperature metapelites that occur in close proximity to eclogitized mafic rocks in the southern part of the Gagnon terrane (Parautochthonous Belt, eastern Grenville Province) were investigated in order to constrain depths of burial and P‐T paths. Mineral assemblages and partial melting relationships in these metapelites are consistent with peak temperatures in the range between 700 and 800° C. However, growth zoning is apparently well preserved in garnets and only narrow rims (width = 100–500 μm) are obviously affected by diffusional retrograde resetting. Despite uncertainties regarding mineral assemblages and compositions of matrix minerals at early stages of garnet growth, it can be shown that the observed growth zoning profiles of garnets imply increase of both pressure and temperature up to a common maximum at pressures between 1300 and 1600 MPa, and that thermal relaxation did not occur during the initial stages of unloading. On the other hand, calculated retrograde P‐T conditions are consistent with steep decompression paths. The inferred ‘hair‐pin’‐shaped P‐T path is consistent with independent evidence of rapid, tectonically driven exhumation, resulting in the preservation of growth zoning in garnets from such a high‐temperature regime.
Variscan Sm‐Nd and Ar‐Ar ages of eclogite facies rocks from the Erzgebirge, Bohemian Massif
Authors: SCHMÄDICKE E. , MEZGER K. , COSCA M. A. , OKRUSCH M.
Published: May 2007

Abstract
The Erzgebirge Crystalline Complex (ECC) is a rare example where both‘crustal’eclogites and mantle‐derived garnet‐bearing ultramafic rocks (GBUs) occur in the same tectonic unit. Thus, the ECC represents a key complex for studying tectonic processes such as crustal thickening or incorporation of mantle‐derived material into the continental crust. This study provides the first evidence that high‐pressure metamorphism in the ECC is of Variscan age. Sm‐Nd isochrons define ages of 333 ± 6 (Grt‐WR), 337± 5 (Grt‐WR), 360± 7 (Grt‐Cpx‐WR) (eclogites) and 353 ± 7 Ma (Grt‐WR) (garnet‐pyroxenite). 40Ar/39Ar spectra of phengite from two eclogite samples give plateau ages of 348 ± 2 and 355 ± 2 Ma. The overlap of ages from isotopic systems with blocking temperatures that differ by about 300 ° C indicates extremely fast tectonic uplift rates. Minimum cooling rates were about 50° C Myr‐1. As a consequence, the closure temperature of the specific isotopic system is of minor importance, and the ages correspond to the time of high‐pressure metamorphism. Despite textural equilibrium and metamorphic temperatures in excess of 800° C, clinopyroxene, garnet and whole rock do not define a three‐point isochron in three of four samples. The metamorphic clinopyroxenes seem to have inherited their isotopic signature from magmatic precursors. Rapid tectonic burial and uplift within only a few million years might be the reason for the observed Sm‐Nd disequilibrium. The εNd values of the eclogites (+4.4 to +6.9) suggest the protoliths were derived from a long‐term depleted mantle, probably a MORB source, whereas the isotopically enriched garnet‐pyroxenite (εNd–2.9) might represent subcontinental mantle material, emplaced into the crust prior to or during collision. The similarity of ages of the two different rock types suggests a shared metamorphic history.
Local disequilibrium of plagioclase in high‐temperature shear zones of the Ivrea Zone, Italy
Authors: ALTENBERGER U.
Published: May 2007

AbstractMicrostructural and chemical analysis of plagioclase in 20 superficially similar amphibolite facies ductile shear zones in metagabbors and amphibolites of the Ivrea Zone in Italy reveals significant differences in An and Ba contents. Plagioclase, which was deformed atP‐Tconditions lower than those of the wall rocks, occurs in the following four different microstructural situations with different chemical compositions: (i) relatively undeformed porphyroclasts, (ii) dynamically recrystallized grains and subgrains rimming the porphyroclasts, (iii) infill of microcracks cross‐cutting the porphyroclasts and (iv) fine‐grained recrystallized grains in the matrix of the shear zones. The differences in the An and Ba contents are caused by partial chemical equilibration of plagioclase in the shear zones during and partly after deformation. Changes in An and Ba contents were caused by fluid‐assisted grain‐boundary migration recrystallization, as well as by solid‐state diffusion, while fluid activity was high. The relation between the composition and microstructures of the plagioclase in the shear zones indicates that in the different shear zones, fluids ceased to be active during different stages in the late shear zone deformation history.

The interpretation of the variations in composition and microstructures reveals that only grains that developed by grain‐boundary migration recrystallization and that are not adjacent to porphyroclasts reflectP‐Tconditions during the dominant shear‐zone deformation.
An evaluation of the inverted metamorphic gradient at Langtang National Park, Central Nepal Himalaya
Authors: MACFARLANE A. M.
Published: May 2007

AbstractThe crystalline core of the Himalayan orogen in the Langtang area of Nepal, located between the Annapurna‐Manaslu region and the Everest region, contains middle to upper amphibolite grade pelitic gneisses and schists. These rocks are intimately associated with the Main Central Thrust (MCT), one of the major compressional structures in the northern Indian plate, which forms a 3.7‐km‐wide zone containing rocks of both footwall and hangingwall affinity. An inverted metamorphic gradient is noticeable from upper footwall through hangingwall rocks, where metamorphic conditions increase from garnet grade near the MCT zone to sillimanite + K‐feldspar grade in the upper hangingwall. Petrographic data distinguish two metamorphic episodes that have affected the area: a high‐pressure, moderate‐temperature episode (M1) and a moderate‐pressure, high‐temperature episode (M2). Comparison with appropriate reaction boundaries suggests that conditions for M1 in the hangingwall were approximately 900–1200 MPa and 425–525°C. Thermobarometric results for 24 samples from the footwall, MCT zone and hangingwall reflectP‐Tconditions during the M2 phase of 400–1200 MPa and 490–660° C. The decrease in estimated palaeopressures from footwall to hangingwall approximate a lithostatic gradient of 27 MPa km‐1, with slight fluctuations in the MCT zone reflecting structural discontinuities. In contrast to the palaeopressures, palaeotemperatures are indistinguishable across the entire area sampled. Although field evidence suggests the presence of the inverted palaeothermal gradient well known in the Himalaya, quantitative thermobarometry indicates that temperatures of final equilibration were all within error of each other across 17 km of section. At Langtang, change in pressure is responsible for the presence of the sequence of index minerals through the section. I interpret these data to reflect diachronous attainment of equilibrium temperature conditions in a lithostatic palaeopressure profile after ductile faulting of the sequence.
Funding Home Care in a Climate of Cost Containment
Authors: Knollmueller Ruth N.
Published: May 2007

The health care industry is preoccupied with increased costs because total expenditures for health services in the United States more than tripled between 1971 and 1981. Policy makers and health providers are looking at what contributes to these expenditures and ways to contain the escalating costs. One solution suggested has been the consideration of alternatives to institutional care, particularly home care. Historically, home care was provided by official or voluntary nursing agencies. Recently, proprietary, private, not‐for‐profit organizations have entered the home care arena. Home care reimbursement methods are a patchwork, causing confusion and cash flow problems. Public funds are administered by different levels of government, by several agencies within each level, and with various eligibility requirements. Private insurance coverage is uneven and limited.
A Model of Community‐Focused Nursing
Authors: Storfjell Judith Lloyd , Cruise Patrice Artress
Published: May 2007

Theoretically, the focus of community health nursing is the community; however, the nature of the practice has not been well documented. The purpose of this study was to develop a community‐focused model by identifying appropriate behaviors and activities for staff‐level community health nurses. A list of suggested behaviors and activities was compiled by means of brainstorming sessions and sent to a sample of community health nursing administrators, educators, and staff nurses in Michigan. Responses were analyzed using nonmetric multidimensional scaling techniques to uncover and define the primary underlying dimensions of perceived community‐focused practice of community health nursing. Three specific regions were identified and labeled: (1) client‐oriented services; (2) aggregate needs identification; and (3) aggregate planning and intervention. These regions (concepts) have been illustrated graphically in a proposed model for community focused nursing entitled the S‐C model. In addition, discrepancies among the three respondent groups were identified.
The Effects of Education on Self‐Care Agency
Authors: Stockdale‐Woolley Rebecca
Published: May 2007

This study examined the effects of group education classes on self‐care agency (SCA) of individuals with chronic obstructive pulmonary disease (COPD) and assessed the four independent variables of presence of a significant other, severity of disease, social status, and type of lung disease, and the persons' relationships to SCA and to the change in SCA after education. A sample of 25 individuals with COPD who attended group education classes offered by the American Lung Association of Connecticut served as subjects. Prior to and at the conclusion of the series of classes, they were given questionnaires eliciting perceptions of SCA and biographic data. From the questionnaires, two SCA scores were calculated. A paired t test demonstrated that these individuals had a significantly greater SCA at the conclusion of the classes than at the beginning. Stepwise multiple regression analysis of the biographic variables identified above and SCA revealed a significant negative correlation between chronic bronchitis and/or emphysema and SCA. There were no correlations between biographic variables and the change in SCA scores. It was concluded that teaching increases SCA; the need to direct rehabilitative efforts with greater emphasis toward individuals with chronic bronchitis and/or emphysema was suggested.
BOOK REVIEW
Authors: Yanni Celeste
Published: May 2007

Nurses and families: A guide to family assessment. Lorraine M. Wright, and Maureen Leahey Philadelphia: F. A. Davis, 1983; 250 pp., $14.95.
The Use of Partners in Undergraduate Public Health Nursing
Authors: Edwards Linda H. , Eyer Jane , Kahn Evelyn H.
Published: May 2007

This study assessed undergraduate student perceptions regarding homevisitingwithpartnersdutingthepublkh ealthnursing clinical experience. Approximately 130 public health nursing students completed a self‐administered questionnaire at the end of their clinical experience. Students identified positive aspects of visiting with partners as support, safety, and collaboration. On ranked items, they identified support as the most important benefit from visiting in pairs. Feedback, safety, and ventilation were next in importance, while expertise of the partner and economic considerations wererankedasleastimportant Visitingwith oneconsistent partner was first choice in making visits, fonOWed by visits with rotating partners, and finally, visits with staff nurses or alone. These findings suggest that making home visits with a parlner can be a beneficial experience, increasing the support perceived by undergraduate students and enhancing learning through feedback and collaboration.
Health Status and Resources of Recently Bereaved Older Persons
Authors: Yeaworth Rosalee C. , Valanis Barbara
Published: May 2007

This prospective, comparative study investigated variables in 60 recently widowed older men and women at three to four months and nine to 10 months after bereavement and compared them with an age‐matched of nonbereaved. Major sections of the Duke University Older Americans' Resources and Services multidimensional functional assessment questionnaire were used to measure physical and mental health and social and economic resources. The Zung self‐rating depression. scale (ZSDS) was used to evaluate the amount of depression. Subjects' scores were compared at Times 1 and 2 with scores of the comparison group. The bereaved were most impaired on physical health and economic resources: 18 percent were classified as moderately to severely depressed by the ZSDS and at both Times 1 and 2 they had significantly poorer scores than nonbereaved on all variables except social resources. For both groups, social and economic resources correlated highly with physical and mental health. Only for nonbereaved did age show a relationship to physical health and depression. Further research should focus on specific components of social resources and on evaluating interventions to reestablish social networks and mobilize social resources.
Nuclear Freeze and Disarmament: A Mandate for Community Health Nursing
Authors: McCarty Terry Lynn , Pratt Mary Alice
Published: May 2007

Nuclear war is presented as the “ultimate epidemic,” and requires the involvement of community health nurses in preventing it. The health consequences of nuclear war as well as present costs to human health of the current arms race are enormous. Nursing actions and primary prevention are discussed.