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Byline: John R. Bowman (1), John W. Valley (2), Noriko T. Kita (2) Abstract: Oxygen isotope ratios have been measured by ion microprobe and millimeter-scale dental drill along detailed sampling traverses across the boundary between periclase-bearing ([delt[a].sup.18]O = 11.8[per thousand]) and periclase-free ([delt[a].sup.18]O = 17.2[per thousand]) marble layers in the periclase (Per) zone of the Alta Stock aureole, Utah. These data define a steep, coherent gradient in [delt[a].sup.18]O that is displaced a short distance (~4 cm) into the periclase-free (Cal + Fo) layer. SEM and ion microprobe analyses show two isotopically and texturally distinct types of calcite at the grain scale. Clear (well polished) calcite grains are isotopically homogeneous (within analytical uncertainty +-0.27[per thousand], 2SD). More poorly polished (pitted), texturally retrograde 'turbid'-looking calcite has lower and more variable [delt[a].sup.18]O values, and replaces clear calcite along fractures, cleavage traces or grain boundaries. Despite significant lowering of the [delt[a].sup.18]O values in calcite throughout both layers during prograde metamorphism, ion microprobe analyses indicate that individual clear calcite grains are now isotopically homogeneous across the entire gradient in [delt[a].sup.18]O. Diffusion calculations indicate that conservative time scales required for isotopic homogenization of calcite grains by volume diffusion, 30,000--62,000 years at 575--600degC, exceed significantly the timescale (~1,250 years) estimated for the prograde development of the [delt[a].sup.18]O gradient at the boundary between these two marble layers. The ion microprobe data and these diffusion calculations suggest instead that surface reaction mechanisms accompanying recrystallization are responsible for the observed oxygen isotope homogeneity of these calcite grains. Thus, the ion microprobe data are consistent with the formation of calcite in oxygen isotope exchange equilibrium with infiltrating fluid during prograde reaction and recrystallization. Author Affiliation: (1) Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, 84112, USA (2) Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI, 53706, USA Article History: Registration Date: 20/06/2008 Received Date: 26/01/2008 Accepted Date: 20/06/2008 Online Date: 20/08/2008 Article note: Communicated by J. Hoefs. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-008-0321-1) contains supplementary material, which is available to authorized users.

Infiltration-driven metamorphism has produced the widespread development of forsterite in the siliceous dolomites of the Alta, Utah contact aureole. SIMS (secondary ion mass spectrometry) δ18O analyses show that in most of the middle to outer forsterite zone samples, forsterite, calcite and dolomite are homogenous in δ18O at the grain-scale, but forsterite and calcite exhibit minor intergranular heterogeneities of < 1‰ on the thin-section to hand sample-scales. In contrast, within ~ 300 m of the igneous contact (inner forsterite and periclase zones), grain-scale δ18O heterogeneities in forsterite are as large as 3.0‰, but forsterite crystals do not exhibit systematic center-to-edge decreases in δ18O due to skeletal growth and infilling. With one exception, forsterite, calcite and dolomite in all samples analyzed yield disequilibrium fractionations. The oxygen isotope disequilibrium commonly recorded among forsterite, calcite and dolomite may reflect the rapid growth of forsterite from increased reaction overstepping as temperature increased, or results from 18O/16O depletion in the matrix carbonate minerals during continued fluid infiltration after forsterite crystallization was complete, during the initial stages of cooling in the forsterite zone. In a traverse across the boundary between forsterite- and periclase-bearing marble layers in the periclase zone, forsterite and calcite SIMS δ18O profiles combined with the trend in forsterite textures indicate that these layers were not infiltrated simultaneously, nor continuously during both prograde reactions responsible for forsterite and periclase. Rather, the texture and SIMS data require infiltration and formation of forsterite first in the forsterite marble layer, followed by infiltration and formation of periclase in the periclase marble layer. As a consequence, the δ18O profile recorded by forsterite formed earlier than the δ18O profile recorded by calcite, but both profiles are prograde features—that is, both profiles formed in response to prograde reactions forming first forsterite and then periclase. These grain-scale δ18O profiles further suggest that these layers experienced significant changes in permeability that are linked to their sequential infiltration-reaction history. The asynchronous growth of these index minerals at the outcrop-scale during prograde heating may be more common during contact metamorphism of carbonate lithologies than currently recognized. [ABSTRACT FROM AUTHOR]

We have discovered a robust microcrystalline record of the early genesis of North American lithosphere preserved in the U-Pb age and oxygen isotope zoning of zircons from a lower crustal paragneiss in the Neoarchean Superior province. Detrital igneous zircon cores with [[delta].sup.18]O values of 5.1 [per thousand]-7.1 [per thousand] record creation of primitive to increasingly evolved crust from 2.85 [+ or -] 0.02 Ga to 2.67 [+ or -] 0.02 Ga. Sharp chemical unconformity between cores and higher [[delta].sup.18]O (8.4 [per thousand]-10.4 [per thousand]) metamorphic overgrowths as old as 2.66 [+ or -] 0.01 Ga dictates a rapid sequence of arc unroofing, burial of detrital zircons in hydrosphere-altered sediment, and transport to lower crust late in upper plate assembly. The period to 2.58 [+ or -] 0.01 Ga included ~80 m.y. of high-temperature (~700-650 [degrees]C), nearly continuous overgrowth events reflecting stages in maturation of the subjacent mantle root. Huronian continental rifting is recorded by the youngest zircon tip growth at 2512 [+ or -] 8 Ma (~ 600 [degrees]C) signaling magma intraplating and the onset of rigid plate behavior. This >150 m.y. microscopic isotope record in single crystals demonstrates the sluggish volume diffusion of U, Pb, and O in zircon throughout protracted regional metamorphism, and the consequent advances now possible in reconstructing planetary dynamics with zircon zoning. Keywords: zircon, U-Pb, oxygen isotopes, ion probe, lower crust, Kapuskasing, Archean.

A study of vocational training in Norway is conducted to explore the condition under which employers would cooperate to increase the skill level of their workforce. Two sets of insights into the political economy of training in coordinated market economies is generated, firstly by demonstrating the cooperation among employers and secondly the collective action problem with respect to the initial training of apprentices of the employer differs from that posed by extra training of workers.

Recent research indicates that centralized collective bargaining institutions are more resilient than predicted by the conventional wisdom, which viewed them as incompatible with new competitive conditions and new production strategies. Drawing on a case study of Norway, the author argues that one reason for this resilience is that centralized wage setting may be actively supported by employers because it serves important employer interests. It has helped moderate wage growth, reduced transaction costs, contributed to stable industrial relations, and provided political leverage for employer organizations. The author also argues that institutional change must be viewed in terms of its economic and institutional context. There has been some formal devolution of bargaining capacity to the level of the individual firm in Norway, Sweden, and Denmark. However, these changes have been accompanied by institutional changes, instigated by employers, that have increased the coordinating capacity of labor market actors. Labor markets in all three countries remain highly institutionalized.

1. INTRODUCTION Observers as disparate as Adam Smith and Friedrich Engels have agreed that because of their small numbers and the nature of their social relations, capitalists face no meaningful [...]

Calcite-dolomite geothermometry and oxygen isotope analyses of marbles in the southern contact aureole around the Alta stock, Utah, indicate that advective transport of oxygen isotopes and heat accompany cooling of the stock. Finite element models with a horizontal permeability barrier over the Alta-Grizzly thrust reproduce the observed thermal and delta-18O aureole profiles. Fluid circulation dynamics and hydrogeologic aspects of the aureole during prograde hydrothermal metamorphism are discussed.

Recent studies provide theoretical models for kinetically limited isotope exchange during fluid flow; however, few have attempted to apply these models to natural systems. In this paper, we interpret stable isotopic data from fossil hydrothermal systems in two different tectonic settings by using combined equations of mass transport and kinetically limited isotope exchange. Our models provide alternative interpretations for the geometry of flow responsible for the development of 18O depletion annuli surrounding epizonal intrusions and for the geometry of flow in shallow-level normal faults. Our models also provide information about relative isotope exchange rates and, by extension, mechanisms of isotope exchange. Our results indicate that dynamic recrystallization in fault zones promotes exchange by surface reaction, whereas exchange in chemically nonreactive and undeformed minerals may be limited by solid-state diffusion.

Introduction Geothermal waters constitute a small but important portion of the world's energy resources. Thermal waters hot enough to generate electricity form the most economically viable resources, yet these systems [...]

The thermal effect in the southern portion of the Alta aureole is influenced by advective heat transfer and the fluid flow involved in this advection is lateral to the intrusive contact during prograde metamorphism. The silicon dolomites in the contact aureole of the Alta stock undergo progressive metamorphic sequence, which can be observed by the application of calcite + dolomite geothermometry.

Variable isotopic compositions on the flowpath is a characteristic of the uniform exchange between explosive minerals and percolating liquids. This characteristic feature is obtained by solving the one-dimensional transport equations for isotopic tracers. A uniform exchange medium differentiates the upstream part of the flow column and the percolating water. The system is not characterized by regular boromodels of fluid rock interaction since large spatial variations are present.

Stable carbon- and oxygen-isotope variations in Holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern Great Basin, United States, a region with a semi-arid climate. Our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate, ecological variations, differences in parent material, and soil depth. [delta][sup.13.C] in deep pedogenic carbonate ([is greater than]50 cm) varies by about 12 per mil over a 2,440-m elevation range, being enriched in [sup.13.C] at the lowest elevations. The slope of [delta][sup.13.C] for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials: depletion by 4.6 to 4.7 per mil per 1,000 m increase in altitude between 300 to 2,740 m above mean sea level for the localities studied. This concordance makes it likely that there has been complete isotopic exchange between [HCO.sub.3]-in solution and soil [CO.sub.2] prior to carbonate precipitation. soil [CO.sub.2] and soil-respiration rates increase systematically with elevation. The plant-derived component of soil [CO.sub.2] indicates that [C.sub.3] plants dominate the biomass at most measured sites, in agreement with plant surveys. Calculated equilibrium fractionation factors between soil [CO.sub.2] and soil carbonate are very similar to those observed, again indicating complete isotopic exchange between carbon species. In all, the soil [CO.sub.2] and soil-carbonate data suggest that the [delta][sup.13.C] variation with elevation observed in the soil carbonates results from differing soil-respiration rates at each site, as well as from variations in the proportion of [C.sub.3] to [C.sub.4] and CAM plants in each site's surface biomass. [delta][sup.18.O] values in pedogenic carbonates are higher at lower elevations, due in part to the more positive [delta][sup.18.O] values for meteoric waters at lower elevations. The average [delta][sup.18.O] value of deep ([is greater than]50 cm) pedogenic carbonate at all sites, however, is enriched 2.4 to 3.7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters. This suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate, or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place. One or both of these processes also may explain the [delta][sup.18.O] decrease in soil carbonate with depth observed in two of three soil profiles.

Coordinated cathodoluminescence (CL) imaging and ion microprobe (SHRIMP and CAMECA 1280) analysis document micron-scale U-Pb-O isotope and trace element zoning in zircons from deep crust exposed to 80 m.y. of high temperature and pressure metamorphism. Three, along-strike paragneiss samples across the amphibolite to granulite facies transition in the Kapuskasing Uplift crustal cross-section in the Archean Superior province yield detrital, originally igneous zircon cores overgrown by progressively larger volumes of metamorphic zircon with increasing grade. The cores generally retain primary age (2.85 ±0.03 to 2.67 ±0.02 Ga), oxygen isotope (5.1 to 7.0%c) and trace element compositions similar to those reported for magmatic arc sources. Dark CL, metamorphic zircon rims record nearly continuous overgrowth events for ~80 m.y. from 2.66±0.01 to 2.58±0.01 Ga during uppermost amphibolite to granulite facies regional metamorphism. These rims have significantly higher δ18O values (8.4 to 10.4%e) and trace element compositions quite distinct from those of the cores; these differences indicate that their δ18O O and trace element compositions were not inherited from the igneous cores, consistent with extensive textural evidence for rim formation as metamorphic overgrowths. Multi-spot traverses record steep oxygen isotope discontinuities (4%e over <10 µm) at core-rim boundaries, confirming the extremely sluggish rates of volume diffusion of O in non-metamict zircon during extended (~80 m.y.) granulite-grade metamorphism (peak T=750-800 °C) at substantial f(H2O) but water-undersaturated (fluid-absent) conditions. Likewise no evidence of significant diffusive exchange of δ18O could be detected along deformation microstructures such as annealed fractures in cores infilled with high δ18O zircon. Application of simple diffusion models to detailed δ18O profiles in a large number of zircon grains constrain maximum values of the diffusivity of oxygen in zircon (logDZrcox) to the range -27.5 to -26.4 m²/s. For the estimated 80 m.y. and 700 to 800 °C time-T window of rim formation, these maximum values are similar to or slower than values reported by Page and others (2007, 2010) and the experimentally-determined "dry" diffusivity of oxygen in zircon (Watson and Cherniak, 1997), but are markedly slower than the experimentally-determined "wet" diffusivity of oxygen in zircon (Watson and Cherniak, 1997). Fast diffusion of oxygen in zircon predicted by hydrothermal experiments may, in nature, require the presence of a hydrous fluid rather than a threshold value of f(H2O). Our test demonstrates that unrecrystallized metamorphosed igneous zircons and metamorphic zircons will retain the geochemical (U-Pb age, trace element and δ18O) record of their origin and evolution despite prolonged, high-grade metamorphism at significant f (H2O) but water under-saturated (fluid-absent) conditions. Such zircons, particularly those that exhibit δ18O zoning, are micron-scale records for the T-time-fluid interaction history of deep crustal rocks. Such records will not be preserved in less refractory phases and promise new insights into the processes of continent formation and evolution. [ABSTRACT FROM AUTHOR]