Origin of fine-scale sheeted granites by incremental injection of magma into active shear zones: examples from the Pilbara Craton, NW Australia

In the Archaean Pilbara Craton of Western Australia, three zones of heterogeneous centimetre- to metre-scale sheeted granites are interpreted to represent high-level, syn-magmatic shear zones. Evidence for the syn-magmatic nature of the shear zones include imbricated and asymmetrically rotated metre-scale orthogneiss xenoliths that are enveloped by leucogranite sheets that show no significant internal strain. At another locality, granite sheets have a strong shape-preferred alignment of K-feldspar, suggesting magmatic flow, while the asymmetric recrystallisation of the grain boundaries indicates that non-coaxial deformation continued acting upon the sheets under sub-solidus conditions. Elsewhere, randomly oriented centimetre-wide leucogranite dykes are realigned at a shear zone boundary to form semi-continuous, layer-parallel sheets within a magma-dominated, dextral shear zone.

It is proposed that the granite sheets formed by the incremental injection of magmas into active shear zones. Magma was sheared during laminar flow to produce the sheets that are aligned sub-parallel to the shear zone boundary. Individual sheets are fed by individual dykes, with up to 1000s of discrete injections in an individual shear zone. The sheets often lack microstructural evidence for magmatic flow, either because the crystal content of the magma was too low to record internal strain, or because of later recrystallisation.     

Os-Os systematics of Hawaiian picrites revisited: New insights into Os isotopic variations in ocean island basalts

Eighteen picrites (MgO > 13 wt.%) and three related basalts from six Hawaiian volcanoes were analyzed for ¹⁸⁷Os/¹⁸⁸Os and ¹⁸⁶Os/¹⁸⁸Os. Variations in these ratios reflect long-term Re/Os and Pt/Os differences in the mantle source regions of these volcanoes. ¹⁸⁷Os/¹⁸⁸Os ratios vary from ∼0.129 to 0.136, consistent with the range defined by previous studies of Hawaiian picrites and basalts. Samples with lower ¹⁸⁷Os/¹⁸⁸Os are mainly from Kea trend volcanoes (Mauna Kea and Kilauea), and the more radiogenic samples are mainly from Loa trend volcanoes (Mauna Loa, Hualalai, Koolau and Loihi). As previously suggested, differences in ¹⁸⁷Os/¹⁸⁸Os between volcanic centers are most consistent with the presence of variable proportions of recycled materials and/or pyroxenitic components in the Hawaiian source.¹⁸⁶Os/¹⁸⁸Os ratios vary from 0.1198332 ± 26 to 0.1198480 ± 20, with some samples having ratios that are significantly higher than current estimates for the ambient upper mantle. Although the range of ¹⁸⁶Os/¹⁸⁸Os for the Hawaiian suite is consistent with that reported by previous studies, the new data reveal significant heterogeneities among picrites from individual volcanoes. The linear correlation between ¹⁸⁷Os/¹⁸⁸Os and ¹⁸⁶Os/¹⁸⁸Os reported by a previous study is no longer apparent with the larger dataset. The postulated recycled materials and pyroxenites responsible for the dominant variations in ¹⁸⁷Os/¹⁸⁸Os are likely not responsible for the variations in ¹⁸⁶Os/¹⁸⁸Os. Such materials are typically characterized by both insufficiently high Os concentrations and Pt/Os to account for the ¹⁸⁶Os/¹⁸⁸Os heterogeneities. The lack of correspondence between ¹⁸⁶Os/¹⁸⁸Os variations and the Kea and Loa trends supports this conclusion.The primary cause of ¹⁸⁶Os/¹⁸⁸Os variations are evaluated within the framework of two mixing scenarios: (1) metasomatic transport of Pt and/or ¹⁸⁶Os-rich Os into some portions of the Hawaiian source, and (2) interaction between an isotopically complex plume source with a common, Os- and ¹⁸⁶Os-enriched reservoir (COs). Both scenarios require large scale, selective transport of Pt, Re and/or Os. Current estimates of HSE concentrations in the mantle source of these rocks, however, provide little evidence for either process, so the dominant cause of the ¹⁸⁶Os/¹⁸⁸Os variations remains uncertain.     

Coupled dynamics of tethered buoy systems

The three-dimensional coupled behavior during the interaction of buoys with their mooring systems is numerically analyzed. A time-domain model was developed to predict the response of a tethered buoy subject to hydrodynamic loadings. External loadings include hydrodynamic forces, tethers tensions, wind loadings and weight. System nonlinearities include large rotational and translational motions, and non-conservative fluid loadings. The mooring problem is formulated as a combined nonlinear initial-value and two-point-boundary-value problem which is directly integrated both in time and space. Buoy equations of motion are derived using small Eulerian angles. Coupling between rotational and translational degrees of freedom is included and coupling between the buoy and cable is effected by adopting the buoy equations of motion as boundary conditions at one end for the mooring problem. Numerical examples are provided to validate the formulation and solution technique; predicted responses of three types of buoy (sphere, spar, and disc) are compared with experimental results.     

Bioaccumulation of trace metals in the Antarctic amphipod Orchomene plebs: evaluation of toxicokinetic models

Bioaccumulation of Cd, Co, Cu, Ni, Pb and Zn in Antarctic gammaridean amphipod collectives, Orchomene plebs (Hurley, 1965), was investigated during a cruise of RV "Polarstern" to the Wedell Sea. With the sole exception of Cd the organisms accumulated metals during exposure and depurated them in uncontaminated seawater. Four independent toxicokinetic experiments and one field study were modelled simultaneously to calculate the following size-dependent bioconcentration factors for organisms with body length 10 mm (BCF(10 mm)): 130 (Co), 4030 (Cu), 190 (Ni), 2900 (Pb), and 5210 (Zn). On the time scale of our experiments the data suggest an increased metal uptake by previously exposed test organisms. The collectives investigated may be regarded as potentially suitable biomonitors for Co, Cu, Ni, Pb and Zn but not for Cd. An approach to evaluate the sensitivity of Orchomene plebs as a biomonitor of waterborne metals in the field indicates minimal increments of the ambient exposure concentrations of 0.01 microg Co l(-1), 0.2 microg Cu l(-1), 0.4 microg Ni l(-1), 0.6 microg Pb l(-1) and 0.3 microg Zn l(-1).     

Assessment of the effects of climate and land cover changes on river discharge and sediment yield,and an adaptive spatial planning in the Jakarta region

In Jakarta, climate change has been detected through rising air temperatures, increased intensity of rainfall in the wet season, and sea level rise. The coupling of such changes with local anthropogenic driven modifications in the environmental setting could contribute to an increased probability of flooding, due to increase in both extreme river discharge and sedimentation (as a result of erosion in the watersheds above Jakarta and as indicated by sediment yield in the downstream area). In order to respond to the observed and projected changes in river discharge and sediment yield, and their secondary impacts, adaptation strategies are required. A possible adaptation strategy is through policy making in the field of spatial planning. For example, in Indonesia, presidential regulation number 54 year 2008 (Peraturan Presiden Nomor 54 Tahun 2008—Perpres 54/2008) was issued as a reference for the implementation of water and soil conservation. This paper assesses the impact of climate and land cover change on river discharge and sediment yield, as well as the effects of Perpres 54/2008 on that river discharge and sediment yield. The spatial water balance model Spatial Tools for River Basins and Environmental and Analysis of Management Option was used for the runoff computations, whilst the Spatial Decision Assistance of Watershed Sedimentation model was used to simulate erosion, Sediment Delivery Ratio, and sediment yield. The computation period is from January 1901 to December 2005, at the scale of the following watersheds: Ciujung, Cisadane, Ciliwung, and Citarum. During the twentieth century, computed average discharge in the downstream area (near Jakarta) increased between 2.5 and 35 m³/s/month, and sediment yield increased between 1 × 10³ and 42 × 10³ tons/year. These changes were caused by changes in both land cover and climate, with the former playing a stronger role. Based on a computation under a theoretical full implementation of the spatial plan proposed by Perpres 54/2008, river discharge would decrease by up to 5 % in the Ciliwung watershed and 26 % in the Cisadane watershed. The implementation of Perpres 54/2008 could also decrease the sediment yield, by up to 61 and 22 % in the Ciliwung and Cisadane watersheds, respectively. These findings show that the implementation of the spatial plan of Perpres 54/2008 could significantly improve watershed response to runoff and erosion. This study may serve as a tool for assessing the reduction in climate change impacts and evaluating the role of spatial planning for adaptation strategies.     

USGS Reference Samples Attapulgite ATT-1 and Bentonite CSB-1

The U.S. Geological Survey has prepared an attapulgite and a bentonite as reference samples because of their economic importance. The attapulgite (ATT-1) is from the Meigs-Attapulgite-Quincy fuller's earth district of Georgia and Florida, and the bentonite (CSB-1) is from the Northern Black Hills bentonite district of Wyoming, Montana, and South Dakota. The chemical and mineralogical properties of these two samples are quite different. Provisional values calculated from the few analytical data and the X-ray diffraction mineralogy are presented for those who wish to use the clays as reference samples.     

A Possible Detection of the 26 December 2004 Great Sumatra-Andaman Islands Earthquake with Solution Products of the International GNSS Service

The main goal of this work is to critically review the IGS solution products and Precise Point Positioning (PPP) in order to demonstrate their potential to contribute to studies of large earthquakes such as the one that devastated Southeast Asia on December 26th, 2004. In view of a possible detection of the Mw 9.0 Sumatra-Andaman Islands Earthquake of December 26, 2004, position solutions, ranging from intervals of years to one second, of four International GNSS Service (IGS) stations within 3000 km of the epicenter were examined. The IGS combined, cumulative solution product (IGS04P51), consisting of epoch and station velocity solutions and based on data spans of several years prior to the earthquake, was used as a reference. Four IGS combined weekly position solutions (igs04P1301-4), two weeks before and after the earthquake, were utilized for the weekly solution resolution. PPP static and kinematic solutions with IGS Final combined orbits and clocks were used for the mean daily and instantaneous 5-min and 1-sec epoch solutions, respectively. The most significant changes, detected by both weekly and daily solutions occurred in longitude. The nearest IGS station ntus, about 1000 km east of the epicenter, moved westward about 15 mm, while the more distant Indian station iisc (∼ 2300 km NW from the epicenter), shifted about 15 mm eastward. In spite of position errors caused by interpolation of the 5-min IGS clocks, the 1-sec solutions, based on separate data sets, available only for two stations (iisc, dgar), still showed seismic surface waves, in particular at the Indian station iisc. Precise daily IGS combined polar motion and length-of-day products, after correcting for the atmospheric effects, also likely detected, statistically significant, anomalistic excitations on December 26, 2004 that could be caused by this great earthquake.