Tion Zone Research Articles

Extra-basinal fluid infiltration, mass transfer, and volume strain during folding: Insights from the Idaho-Montana thrust belt

Finite strain and geochemical variations along strain gradients were used to study cleavage development in carbonates in the Lost River Range, Idaho. Deformation accommodating layer-parallel shear was partitioned into thin deforma- tion zones during folding of Willow Creek anticline. Cleavage intensity is strong to very strong in deformation zones and weak in surrounding rocks. Strain magnitudes range from e s0.32 (1.15:0.93:0.73; x, y, z, principal axes of strain) outside, to e s0.64 (1.29:0.80:0.52) inside, deformation zones. We found a positive linear correlation between strain, cleavage development, and negative dilation. Volume loss, at a cubic centimeter scale, ranges from 12 percent to 49 percent. Cleavage selvages are depleted in Ca and 18 O and enriched in other elements relative to microlithons and less deformed protolith carbonates. Mass-balance considerations indicate that cleavage was formed by incongruent pressure solution leading to a passive concentration of less soluble components during Ca loss and metasomatic additions of Si, Al, and K to produce authigenic clay minerals in selvages. Data for the Willow Creek locality and elsewhere in the Lost River Range (Davidson and others, 1998), Pioneer Mountains, and the Tendoy Range (Bebout and others, 2001), show that across the Sevier orogen, fluid infiltration was heterogeneous at centimeter-kilometer scales and resulted from positive feedback between deforma- tion and far-traveled surficial fluids. Metasomatic strain softening enhanced deforma- tion zone development, which generated increased permeability as the thrust belt evolved from a porosity-based closed system to a discontinuity-based open system. Increased fluid infiltration and isotopic exchange was associated with volume loss, increasingly prolate strains, and crystallization of clays, to produce the cleavage selvages. Mass transfer was accommodated by diffusion early and advection later in the deformation history. Mesoscopic structures (deformation zones, faults, veins) focused fluid flow and were kinematically related to larger-scale structures (faults, fault- related folds). The inferred addition of surficial fluids to depths of >7 kilometers in the thrust belt implies a fluid regime involving significant topographically driven recharge. Deformed whole-rocks and microsamples are lower in 18 O than unde- formed samples which have O- and C-isotope compositions similar to those of marine carbonates. Veins are even lower in 18 OV-SMOW, with minimum values of 5 permil reflecting penetration of the crust by ocean-derived precipitation with 18 O near to somewhat lower than 0 permil (range of 7.5 to 2.5‰ calculated for H2 Oi n equilibrium with these veins). The inferred penetration, into the thrust belt, of nearshore meteoric waters is consistent with proximity to the reconstructed Western Interior Seaway. Later fluid infiltration locally lowered the 18 O of carbonates even further, based on the O-isotope compositions of veins related to younger compres- sional deformation and to the onset of crustal-scale extension in the Eocene. This progression toward lowered 18 O of the surficial waters is compatible with the retreat of the seaway during emergence of the thrust wedge and Paleogene extension, uplift, and subaerial volcanism.

Influence of taxonomic resolution, biological attributes and data transformations on multivariate comparisons of rocky macrofaunal assemblages

Multivariate comparisons of impacted and non-impacted biotic assemblages require decisions to be made about the taxonomic resolution to be used, biological attributes to be measured and whether the contributions of common, or combinations of common, intermediate and rare taxa should be emphasised. This study shows how these decisions affect comparisons of exploited and non-exploited rocky infratidal macrofaunal assemblages distributed across a biogeographic transi- tion zone on the south-east coast of South Africa. Two-way crossed ANOSIM tests were used to test for differences in the structure of assemblages among regions of the coast and between exploited and non-exploited localities. In tests based on presence/absences, significant differences in assemblages among regions and between treatments were evident only at the species level. In tests based on den- sities and biomasses, regional differences were evident at the species, order, class and phylum level, and were irrespective of whether dominant or combinations of dominant, intermediate and rare taxa were emphasised. Significant differences in exploited and non-exploited assemblages were evident in all of the comparisons except those in which numerically dominant higher taxa were emphasised. These results do not suggest that the natural environmental gradient influences the fauna more by species replacements than by changes to the proportions of higher taxa, nor do they indicate that natural environmental variations and anthropogenic disturbances modify macrofaunal assemblages at different taxonomic levels. Further studies are needed to establish whether the taxonomic level, at which modification of assemblages occurs, varies with the type of disturbance (e.g. pollution vs exploitation, strong vs weak gradients) or biotic component (e.g. rocky vs soft-bottom assemblages) under consideration.

Ground-Motion Attenuation Relationships for Cascadia Subduction Zone Megathrust Earthquakes Based on a Stochastic Finite-Fault Model

The number of strong ground motion recordings available for regression analysis in developing empirical attenuation relationships has rapidly grown in the last 10 years. However, the dearth of strong-motion data from the Cascadia subduc- tion zone has limited this development of relationships for the Cascadia subduction zone megathrust, which can be used in the calculation of design spectra for engi- neered structures. A stochastic finite-fault ground-motion model has been used to simulate ground motions for moment magnitude (M) 8.0, 8.5, and 9.0 megathrust earthquakes along the Cascadia subduction zone for both rock-and soil-site condi- tions. The stochastic finite-fault model was validated against the 1985 M 8.0 Mi- choacan, Mexico, and the 1985 M 8.0 Valpariso, Chile, earthquakes. These two subduction zone megathrust earthquakes were recorded at several rock sites located near the fault rupture. For the Cascadia megathrust earthquakes, three different rup- ture geometries were used to model the M 8.0, 8.5, and 9.0 events. The geometries only differ in their respective fault lengths. A fault dip of 9 to the east with a rupture width of 90 km was selected to represent average properties of the Cascadia sub- duction zone geometry. A regional crustal damping and velocity model was used with the stochastic finite-fault model simulations. Ground motions were computed for 16 site locations. The parametric uncertainties associated with the variation in source, path, and site effects were included in the development of the ground motions. A functional form was fit to the ground-motion model simulations to develop region- specific attenuation relationships for the Cascadia megathrust rupture zone for both rock and soil site conditions. The total uncertainty was based on a combination of the modeling and parametric uncertainties (sigmas). These newly developed atten- uation relationships for Cascadia subduction zone megathrust earthquakes can be used in both the probabilistic and deterministic seismic-hazard studies for engineer- ing design for the Pacific Northwest.

Middle Miocene tectonic development of the Transition Zone, Salta Province, northwest Argentina: Magnetic stratigraphy from the Metán Subgroup, Sierra de González

Magnetostratigraphy, isotopic dating, and sandstone petrography establish age limits on the depositional history of 2100 m of foreland basin strata in the Neogene Metan Subgroup of northwest Argentina. The strata were deposited between ca. 15.1 and 9.7 Ma in the eastern Sistema de Santa Barbara. The region is positioned above the Cretaceous Salta rift basin, in the Transi- tion Zone between modern relatively steep and flat subducting segments of the Nazca plate. Formations within the subgroup are shown to be diachronous over a 60 km dis- tance; the younger ages are in the east. Changes in paleocurrent flow directions and the lithic clast component of sandstones collected from the Arroyo Gonzalez section suggest that basal fluvial strata were de- rived from the craton to the east beginning in middle Miocene time, just prior to 15.1 Ma. By ca. 14.5 Ma, the paleocurrent flowed from a source in the west and sedi- ment accumulation rates increased dramat- ically. These changes correlate with con- temporaneous tectonism in the west. A local increase in basin accommodation may be partly related to a zone of weakness near the eastern boundary of the Salta rift. Uplift in the western Cordillera Oriental apparently began by 13.7 Ma and thrusting rapidly migrated eastward. The eastern Cordillera Oriental ranges began to rise be- tween 25 and 26S ca. 10 Ma. As thrusting migrated eastward, low-energy depositional environments were overwhelmed ca. 13.7 Ma. Above an erosional unconformity that removed strata to an age of ca. 9.7 Ma, bas- al strata from the overlying Jujuy Sub- group were deposited beginning after 9 Ma. Sandstones from Ro ´o Yacones suggest that the Cordillera Oriental uplift contin- ued for several million years longer be- tween 24 and 25S. Uplift of the Sistema de Santa Barbara, in the distal portion of the foreland, did not begin until after ca. 9 Ma.

UBVRI photometry of the FK5 Extension Catalogue Stars

UBVRIphotometry in the Kron-Cousins sys- tem for 272 stars of the Extension Catalogue of the Fifth Fundamental Star Catalogue (FK5 stars) in the declina- tion zone +7 to 90 is presented.

Vegetation, environmental characteristics and ideas on the maintenance of alvars on the Bruce Peninsula, Canada

Abstract.Despite international recognition that alvar habitats are important reservoirs of biodiversity, they remain little studied in North America. In this paper, the results are reported on an investigation of alvars in the central portion of their known distribution on this continent. 210 plots were distributed among seven sites and were quantitatively sampled for vascular plants, lichens, bryophytes and a suite of environmental variables. Detrended and Canonical Correspondence Analyses and other methods were used to investigate differences among alvars, within alvars and between alvars and adjacent forested habitats. The plant communities and environmental conditions were highly similar among sites in the study region, yet very different from surrounding habitats. There were abrupt changes in vegetation and environmental conditions from alvar to forest, without the presence of transition zones in the vegetation or environmental gradients as the forest was approached. The environmental factors associated with the change from alvar to forest and with variation within alvar habitat were examined. Some alvars in the study were found to contain stunted, slow‐growing trees reaching ages of 524 yr. These same sites appear to have remained unburned for several centuries, while other sites likely burned 90 yr ago. The plant communities were very similar between the alvars that lacked a major, biomass‐removing disturbance in centuries and alvars that had experienced catastrophic fire relatively recently. Maintenance of the plant communities and open nature of alvars appears site‐specific rather than habitat specific.

The Effects of Curing Temperature On Deformation and Fracture Toughness in Thin Films of Larc™ Rp46 Polyimide

A processing-property relationship was studied by varying the final cure temperature for thin films of LaRC™ RP46 polyimide, a new PMR-15-like material. This new material incorporates a low toxicity diamine 3,4'-oxydianiline instead of the mutagenic 4,4'-methylenedianiline. Thin films of RP46 were cured at a final temperature of 316°C, 325 ° C, 350 ° C, and 371 ° C. Physical properties-including fracture toughness, size of plane-stress deforma tion zone, and tensile strength-were determined as a function of the final cure temperature. At lower cure temperatures (316°C and 325 ° C), the plastic defor mation zones exhibited diffuse shear yielding, similar to a semi-interpene trating polymer network. At higher cure temperatures (350 ° C and 371°C), the degree of crosslinking increased and as a consequence the size of the deforma tion zone was significantly diminished. The higher cure temperatures also decreased fracture toughness and tensile strength.

Thermal structure of solid flames

Abstract

Velocity Profiles in the Injection Zone of an EHD Generator and Efficiency Considerations

Electrical measurements taken in a cell modeling the injection zone of an EHD generator showed the existence of two flows regimes. In our wire-two plate geometry, either the electrical forces dominate or the hydrodynamic ones do, depending on the applied voltage and the Reynolds number of the forced flow through the cell. In the former case entrainment of ions out of the injection tion zone is very poor, whereas, in the latter regime, entrainment of the injected space charge is considered complete. We present here a more advanced study based on velocity measurements by laser doppler anemometry. Velocity profiles have been determined in the following three situations: (1) the convective four-roll case obtained with no forced flow; (2) the dominant electric force regime (high applied voltage and low flowrate) and (3) the entrainment regime (low applied voltage and high flowrate). We discuss the experimental observations in the light of what is known about wall jets (case (1)); wakes (case (3)); and EHD migration of space charge (case (2)). The functioning of an= EHD generator is then considered with these measurements in mind and the theoretical one-dimensional model of Stuetzer for the conversion zone is reappraised and modified to give an expression for conversion efficiency. This goes some way to explaining the low efficiency obtained with these machines previously.