bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data
Authors: WARR L. N. , RICE A. H. N. 
Published: May 2007

ABSTRACTClay mineral crystallinity and crystallite (domain) size data determined by X‐ray diffraction (XRD) are methods extensively used in the characterization of very low‐grade metamorphic conditions. However, the lack of sufficient interlaboratory standardization has made comparisons between different research groups unreliable due to significant variations in numerical results obtained, a consequence of the different machine conditions, measurement methods and sample preparations used during analysis. A calibration approach to the standardization of data using rock chip standards is presented, which allows data sets produced by different research groups to be directly and quantitatively compared. A standardized scale, the crystallinity index standard (CIS), is proposed, with illite crystallinity anchizonal boundary limits of 0.25d̀Δ2θ and 0.42d̀Δ2θ, and equivalent illite crystallite sizes of 52 and 23 nm, respectively, determined by the Warren‐Averbach method. Calibrating both old and new data will enable more reliable comparisons between similar and contrasting geological environments, and should improve the accuracy and reliability of correlations made between XRD data and other indicators of very low‐grade metamorphism, hence increasing the value of such clay mineral studies.
Oxygen isotope exchange and closure temperatures in cooling rocks
Authors: JENKIN G. R. T. , FARROW C. M. , FALLICK A. E. , HIGGINS D. 
Published: May 2007

ABSTRACTRetrograde exchange of oxygen isotopes between minerals in igneous and metamorphic rocks by means of diffusion is explored using a finite difference computer model, which predicts both the zonation profile of δ18O within grains, and the bulk δ18O value of each mineral in the rock. Apparent oxygen isotope equilibrium temperatures that would be observed in these rocks are calculated from the δ18O values of each mineral pair within the rock. In systems which cool linearly from a sufficiently high temperature or at a low enough cooling rate, such that the final oxygen isotope values are not dependent upon the initial oxygen isotope values (‘slow cooling’), the apparent oxygen isotope temperature derived for a rock composed of a single mineral pair can be shown to be simply related to the Dodson closure temperatures (Tc) for the two phases and the mode of the rock. Adding a third phase into a system which undergoes ‘slow’ cooling will cause the apparent temperature derived for the two minerals already present to differ from the simple relationship for a two‐phase system. In some systems oxygen isotope reversals can be developed. If cooling is not ‘slow’, then the mineral δ18O values resulting from cooling will be partly dependent upon the initial temperature of the system concerned. The model successfully simulates the mineral δ18O values that are often observed in granitic rocks. Application of the model will help in assessing the validity of oxygen isotope thermometry in different geological settings, and allows quantitative prediction of the oxygen isotope fractionations that are developed in cooling closed systems.
Interdependence of deformation, fluid infiltration and reaction progress recorded in eclogitic metagranitoids (Sesia Zone, Western Alps)
Authors: FRÜH‐GREEN G. L. 
Published: May 2007

ABSTRACTThe effects of high‐strain deformation and fluid infiltration during Alpine eclogite facies metamorphism have been studied across ductile shear zones in relatively undeformed metagranitoids at Monte Mucrone (Sesia Zone, Western Alps, Italy). Microfabrics together with bulk rock and stable isotope data indicate that the mineralogical and chemical variations are related to the degree of deformation, rather than to changes in P‐T conditions or tectonic position. Transformation of meta‐quartz diorite to recrystallized eclogitic mylonites involved the breakdown of biotite and plagioclase and required the influx of H2O. Bulk‐rock geochemical data show that ductile deformation to form eclogitic mylonites involved an increase in volume with a weight percent gain in H2O and Si and variable loss of K, Na, Ca and Al. δ18O changes systematically across ductile shear zones into the undeformed country rocks. Constant values in shear zone centres indicate advection parallel to the shear zone and within 10 cm of the mylonites. A dominant component of diffusive oxygen exchange perpendicular to the shear zones produced isotopic fronts, evident from a gradual increase in δ18O values to the reference values of the country rocks. The degree of isotopic shift within the shear zones reflects increasing deformation and degree of reaction progress.Multiple phases of Alpine deformation and mineral growth are recognized in the Monte Mucrone metagranitoids, and in some cases, eclogite facies shear zones were reactivated under greenschist facies conditions. The results of this study suggest that high‐strain deformation provided pathways for both synkinematic and post‐kinematic metamorphic fluids which were necessary for complete reactions. Relict igneous fabrics, as well as the presence of corona textures around biotite and pseudomorphs after primary igneous plagioclase in the least deformed rocks, indicate a paucity of hydrous fluids and support the conclusion that fluid movement was channelled rather than pervasive.
Tectonic setting, petrology and geochronology of jadeite + glaucophane and chloritoid + glaucophane schists from north‐west Turkey
Authors: OKAY A. I. , KELLEY S. P. 
Published: May 2007

ABSTRACTThe north‐west Turkish blueschists represent a subducted passive continental margin sequence dominated by metaclastic rocks and marble. The depositional age of the blueschist protoliths are probably Palaeozoic to Mesozoic, while the age of the high‐pressure/low‐temperature metamorphism is Late Cretaceous. Blueschists are tectonically overlain by a volcanosedimentary sequence made up of accreted oceanic crustal material that locally shows incipient blueschist metamorphism and by spinel peridotite slices.The metaclastic rocks with regional jadeite and glaucophane, which comprise the lower part of the blueschist unit, make up an over 1000‐m‐thick coherent sequence in the Kocasu region of north‐west Turkey. Rare metabasic horizons in the upper parts of the metaclastic sequence with sodic amphibole + Iawsonite but no garnet indicate lawsonite blueschist facies metamorphism. The blueschist metaclastics in the Kocasu region are practically free of calcium and ferric iron and closely approximate the NFMASH system in bulk composition. Two low‐variance mineral assemblages (with quartz and phengite) are jadeite + glaucophane + chlorite + paragonite and chloritoid + glaucophane + paragonite. The metaclastics comprise up to several‐metres‐thick layers of jadeite schist with quartz, phengite and nearly 100 mol% jadeite. Phase relations in the metaclastics show that the chloritoid + glaucophane assemblage, even in Fe2+‐rich compositions, is stable in the jadeite stability field. In the NFASH system the above assemblage without the accompanying garnet has a narrow thermal stability field.Mineral equilibria in the metaclastics involving chloritoid, glaucophane, jadeite, paragonite and chlorite indicate metamorphic P‐T conditions of 20 ± 2 kbar and 430 ± 30 d̀ C, yielding geothermal gradients close to 5d̀ C km‐1, one of the lowest geotherms recorded. Blueschists in the Kocasu region, which have been buried to 70 km depth, are tectonically overlain by the volcanosedimentary sequence and by peridotite buried not deeper than 30 km.Phengites from two jadeite schists were dated by Ar/Ar laser probe; they give an age of 88.5 ± 0.5 Ma, interpreted as the age of metamorphism. Blueschists and the overlying peridotite bodies are intruded by 48‐53‐Ma‐old granodiorite bodies that were emplaced at 10 km depth. This suggests that the exhumation of blueschists by underplating of cold continental crust, and normal faulting at the blueschist‐peridotite, interface occurred during the Late Cretaceous to Palaeocene (88‐53 Ma).
Fluid‐mineral equilibria in prehnite‐pumpellyite to greenschist facies metabasites near Flin Flon, Manitoba, Canada: implications for petrogenetic grids
Authors: DIGEL S. , GHENT E. D. 
Published: May 2007

ABSTRACTA sequence of regional metamorphic isograds indicating a range from prehnite‐pumpellyite to lower amphibolite facies was mapped in metabasites near Flin Flon, Manitoba. The lowest grade rocks contain prehnite + pumpellyite and are cut by younger brittle faults containing epidote + chlorite + calcite. Isobaric temperature‐XCO2 and pressure‐temperature (constant XCO2) diagrams were calculated to quantify the effects of CO2 in the metamorphic fluid on the stability of prehnite‐pumpellyite facies minerals in metabasites containing excess quartz and chlorite. Prehnite and, to a lesser extent, pumpellyite are stable only in fluids with Xco2 <0.002. For Xco2>0.002, epidote + chlorite + calcite assemblages are stable. Our calculated phase relations are consistent with regional metamorphism in the Flin Flon area in the presence of an H2O‐rich fluid and a more CO2‐rich fluid in the later fault zones. We believe that the potential effects of small amounts of CO2 in the metamorphic fluid should be assessed when considering the pressure‐temperature implications of mineral assemblages in low‐grade metabasites.
Deformation‐induced reconstitution and local resetting of mineral equilibria in polymetamorphic gneisses: tectonic and metamorphic implications
Authors: MOECHER D. P. , WINTSCH R. P. 
Published: May 2007

ABSTRACTA sequence of at least three Al2SiO5‐bearing mineral assemblages are preserved in successively overprinted ductile shear zones in the Willimantic window, Connecticut. The ductile deformation, localized at and near the boundary between the Putnam‐Nashoba terrane and underlying Avalon terrane is characterized by a network of anastomozing shear zones that outline metre‐scale tectonic blocks of migmatitic Kfs + Sil + Gt + Bi + Pg + Qtz + Ilm + Ru gneiss. These assemblages record Acadian or older metamorphic conditions of 6 kbar, 700d̀ C. Mylonitic gneisses in shear zones that define block margins were formed by reconstitution and recrystallization of the migmatitic gneiss. The reconstituted rocks exhibit relict Ky + St + Grt (+Pl + Bt + Qtz + Rt + Ilm) assemblages and require a minimum pressure for the Ky‐Str grade metamorphism of 8.5 kbar. Kyanite in block margins is widely replaced by sillimanite, and locally by andalusite, during a period of post‐Alleghanian ductile deformation. The interiors of blocks do not record this sequence of polymorphs. The pattern of reconstitution is accounted for by localization of strain along block margins within a regionally extensive terrane‐bounding fault zone. Strain provided the activation energy for recrystallization and retrograde mineral reactions. The P‐T conditions of post‐Alleghanian ductile deformation evolved from 600d̀ C and 6 kbar to 550d̀ C and 3 kbar.The occurrence of Ky + Str‐bearing assemblages, overprinting Acadian Kfs + Sil‐bearing assemblages and subsequently overprinted by Alleghanian sillimanite‐ and andalusite‐bearing assemblages, along with reset hornblende 40Ar/39 Ar mineral ages from Mississippian to Permian, requires a prograde Alleghanian metamorphism of rocks previously metamorphosed during the Acadian. Thus, mineral assemblages from gneisses in the Willimantic fault zone retain evidence of a protracted tectonothermal evolution that included high‐grade Acadian orogenesis, tectonic loading resulting from Alleghanian collision of Avalon with North America, and tectonic exhumation in Permo‐Triassic time. The c.3‐kbar pressure decrease between prograde and retrograde Alleghanian metamorphic conditions corresponds to 10 km of crust that must have been tectonically excised from the base of the Putnam‐Nashoba terrane cover sequence following Alleghanian orogenesis in south‐eastern New England.
Reworking of deep‐seated gabbros and associated contact metamorphosed paragneisses in the southeastern part of the Seiland Igneous Province, northern Norway
Authors: ELVEVOLD S. , REGINIUSSEN H. , KROGH E. J. , BJØRKLUND F. 
Published: May 2007

ABSTRACTThe Seiland Igneous Province of the North Norwegian Caledonides consists of a suite of deep‐seated rift‐related magmatic rocks emplaced into paragneisses during late Precambrian to Ordovician time. In the south‐eastern part of the province, contact metamorphism of the paragneisses and later reworking of intrusives and associated contact aureoles have resulted in the development of three successive metamorphic stages. The contact metamorphic assemblage (M1) Opx + Grt + Qtz + Pl + Kfs + Hc + Ilm ± Crd is preserved in xenolithic rafts of paragneiss within metagabbro. Geothermobarometric calculations yield 930‐960d̀ C and 5‐6.5 kbar for the contact metamorphism. M1 was followed by cooling, accompanied by strong shearing, formation of the gneiss foliation and recrystallization at intermediate‐P granulite facies conditions (M2). Stable M2 phases are Cpx + Opx + Pl +Ilm ± Hbl in metagabbro and Grt ± Sil ± Opx + Kfs + Qtz + Pl ± Bt + Ilm in host paragneiss. The M2 conditions are estimated to 700‐750d̀ C and 5‐7 kbar. A subsequent pressure increase is recorded in the M3 episode, which is associated with recrystallization in narrow ductile shear zones and secondary growth on M2 minerals. M3 is defined by the assemblages Grt + Cpx ± Opx + Pl + Ru + Qtz in metagabbro, and Grt ± Ky + Qtz + Pl ± Kfs + Bt + Ru in host paragneiss. M3 conditions are estimated to 650‐700d̀ C and 8‐10 kbar. The substantial pressure increase related to the M2 → M3 transition is interpreted to be a result of (early?) Caledonian overthrusting. Chemical zoning in cordierite and biotite suggest rapid cooling following the M3 event. The proposed P‐T‐t evolution implies that the tectonic evolution of the Seiland Igneous Province was long (at least 330 Ma) and complex and involved initial rifting and extension followed by crustal thickening and compression.
Garnet coronas in scapolite‐wollastonite calc‐silicates from East Antarctica: the application and limitations of activity‐corrected grids
Authors: FITZSIMONS I. C. W. , HARLEY S. L. 
Published: May 2007

ABSTRACTCalc‐silicate boudins within Proterozoic granulite facies gneisses of the northern Prince Charles Mountains, East Antarctica, preserve a number of reaction textures including garnet coronas between calcite and scapolite; garnet‐quartz coronas between scapolite and wollastonite and between plagioclase and wollastonite; calcite‐quartz intergrowths in wollastonite; and calcite‐plagioclase symplectites in scapolite. These textures have been modelled using petrogenetic grids for reactions in the CaO‐Al2,O3‐SiO2‐CO2 system, but with reduced mineral activities to account for additional components in real mineral compositions. Such fixed‐composition reduced‐activity grids are strictly valid only at the point in P‐T‐aCO2 space where an assemblage last equilibrated, and do not show the true positions of reactions away from this point because mineral compositions change with reaction progress. In this case, however, mineral compositions close to end‐member values and low extents of reaction progress mean that compositional change was limited and the grids are good approximations to true pseudosections over the entire P‐T‐aco2 range of interest.The grids show that the textures are consistent with near‐isobaric cooling from about 850 to 700d̀ C at 7 kbar, a P‐T path compatible with thermobarometric studies of other lithologies from the area. Phase relationships indicate that CO2 activities were buffered by the local mineral assemblage during peak and retrograde metamorphism, either under fluid‐absent conditions or within a non‐pervasive fluid phase. Previous studies of garnet coronas in scapolite‐wollastonite calc‐silicates have used qualitative grids based on limited experimental data to invoke garnet growth during water infiltration at high temperature, but the grids used here show that garnet coronas can form on cooling, without any need for water influx.
Formation of corrensite, chlorite and chlorite‐mica stacks by replacement of detrital biotite in low‐grade pelitic rocks
Authors: JIANG WEI‐TEH , PEACOR DONALD R. 
Published: May 2007

ABSTRACTTransmission and scanning electron microscopy were utilized to investigate the nature and mechanisms of alteration of abundant detrital biotite of volcanic origin and progressive modification of phyllosilicate aggregates in a prograde sequence of pelitic rocks (illite crystallinity index = 0.19–0.58d̀λ2θ) from the Gaspé Peninsula in Quebec.Detrital biotite has been diagenetically altered to form corrensite and chlorite through two mechanisms; (1) layer‐by‐layer replacement gave rise to interstratification of packets of layers and complex mixed layering via several kinds of layer transitions between biotite and chlorite, corrensite or smectite; (2) dissolution‐transport‐precipitation resulted in the formation of relatively coarse‐grained aggregates of randomly orientated, corrensite‐rich flakes and fine‐grained corrensite intergrown with chlorite and illite in the matrix.The data show that stacks consisting of alternating packets of trioctahedral and dioctahedral phyllosilicates originated during early diagenesis when lenticular fissures in strained altering biotite were filled by dioctahedral clays. Subsequent prograde evolution of dioctahedral clays occurred through deformation, dissolution and crystallization, and overgrowth. Illite evolved to muscovite, with K in part provided through biotite alteration, and corrensite/chlorite to homogeneous chlorite. The alteration of detrital biotite is closely related to the formation of titanite and magnetite in diagenetic rocks, and pyrite, calcite and anatase or rutile in the higher grade rocks.The observations demonstrate that detrital biotite of volcanic origin may be the principal precursor of chlorite in chlorite‐rich metapelites originating in marginal basins. The mineral parageneses suggest that the transitions from corrensite to chlorite and illite to muscovite may be a function of local chemistry and time.
40Ar/39Ar geochronology and P‐T‐t paths from the Cordillera Darwin metamorphic complex, Tierra del Fuego, Chile
Authors: KOHN M. J. , SPEAR F. S. , HARRISON T. M. , DALZIEL I. W. D. 
Published: May 2007

Abstract
40Ar/39Ar data collected from hornblende, muscovite, biotite and K‐feldspar constrain the P‐T‐t history of the Cordillera Darwin metamorphic complex, Tierra del Fuego, Chile. These data show two periods of rapid cooling, the first between c. 500 and c. 325° C at rates ≥25° C Ma‐1, and the second between c. 250 and c. 200°C. For high‐T cooling, 40Ar/39Ar ages are spatially disparate and depend on metamorphic grade: rocks that record deeper and hotter peak metamorphic conditions have younger 40Ar/39Ar ages. Sillimanite‐ and kyanite‐grade rocks in the south‐central part of the complex cooled latest: 40Ar/39Ar Hbl = 73–77 Ma, Ms = 67–70 Ma, Bt = 68 Ma, and oldest Kfs = 65 Ma. Thermobarometry and P‐T path studies of these rocks indicate that maximum burial of 26–30 km at 575–625° C may have been followed by as much as 10 km of exhumation with heating of 25–50° C. Staurolite‐grade rocks have intermediate 40Ar/39Ar ages: Hbl = 84–86 Ma, Ms = 71 Ma, Bt = 72–75 Ma, and oldest Kfs = 80 Ma. Thermobarometry on these rocks indicates maximum burial of 19–26 km at temperatures of 550–580° C. Garnet‐grade rocks have the oldest ages: Ms = 72 Ma and oldest Kfs = 91 Ma; peak P‐T conditions were 525–550° C and 5–7 kbar. Regional metamorphic temperatures for greenschist facies rocks south of the Beagle Channel did not exceed c. 300–325° C from 110 Ma to the present, although the rocks are only 2 km from kyanite‐bearing rocks to the north.One‐dimensional thermal models allow limits to be placed on exhumation rates. Assuming a stable geothermal gradient of 20–25° C km‐1, the maximum exhumation rate for the St‐grade rocks is c. 2.5 mm yr‐1, whereas the minimum exhumation rate for the Ky + Sil‐grade rocks is c. 1.0 mm yr‐1. Uniform exhumation rates cannot explain the disparity in cooling histories for rocks at different grades, and so early differential exhumation is inferred to have occurred. Petrological and geochronological comparisons with other metamorphic complexes suggest that single exhumation events typically remove less than c. 20 km of overburden. This behaviour can be explained in terms of a continental deformation model in which brittle extensional faults in the upper crust are rooted to shallowly dipping ductile shear zones or regions of homogeneous thinning at mid‐ to deep‐crustal levels. The P‐T‐t data from Cordillera Darwin (1) are best explained by a ‘wedge extrusion’model, in which extensional exhumation in the southern rear of the complex was coeval with thrusting in the north along the margin of the complex and into the Magallanes sedimentary basin, (2) suggest that differential exhumation occurred initially, with St‐grade rocks exhuming faster than Ky + Sil‐grade rocks, and (3) show variations in cooling rate through time that correlate both with local deformation events and with changes in plate motions and interactions.
Reaction relationships during retrograde metamorphism at Olary, South Australia
Authors: CLARKE G. L. , POWELL R. , VERNON R. H. 
Published: May 2007

Abstract
In metapelitic schists of the north‐eastern Weekeroo Inliers, Olary Block, Willyama Supergroup, South Australia, syn‐S1 and syn‐S2 assemblages involving staurolite, garnet, biotite and another mineral, most probably cordierite, were overgrown by large syn‐S3 andalusite porphyroblasts, owing to isobaric heating from metamorphic conditions that existed during the development of S2. Conditions during the development of S3 probably just reached the andalusite—sillimanite transition. During the development of S4, at somewhat lower temperatures than those that accompanied the development of S3, the following reaction occurred:staurolite + chlorite + muscovite ± biotite + andalusite + quartz + H2O.The amount of retrogression is controlled primarily by the amount of H2O added by infiltration. As the syn‐S3 matrix assemblage was stable during the development of S4, but the andalusite porphyroblasts were no longer stable with the matrix when H2O was added, the retrogression is focused in and around the porphyroblasts. With enough H2O available, and if quartz was consumed before biotite in a porphyroblast, then the following reaction occurred:staurolite + chlorite + muscovite + corundum ± biotite + andalusite + H2O.This reaction allowed corundum inclusions in the andalusite to grow, regardless of the presence of quartz in the matrix assemblage.
The Press Image of Community Health Nurses
Authors: Kalisch Philip A. , Kalisch Beatrice J. 
Published: May 2007

AbstractThe informational quality of press news about community health nurses is a critical factor in gaining the required public support for the scarce resources needed to advance community health nursing practice. Using content analyses, 2,561 articles on community health nursing for the period 1978–1981 were coded for key message themes and compared with articles on other nursing subjects. Results reveal that although the subject of community health nursing comprised the largest share of all clinical nursing articles, they are (1) less visible in newspapers, (2) distributed unevenly per capita among the various states, and (3) written so as to communicate low‐quality information. Analysis of annual trends shows that community health nursing articles, while expanding in absolute numbers, constitute a declining proportion of nursing articles overall, and that the quality of information in current press coverage is diminishing. It is recommended that community health nurses embark on a concerted campaign to improve the quality of information carried in newspapers about their clinical specialty.