A compact representation of gamma-ray burst time series

Multiscale edge detection (MSED), using wavelet transform extrema, provides a robust method to compress the information in a transient signal. We apply this to gamma-ray burst (GRB) time series. Multiscale edge detection can be used to quantify the variability, identify structures (e.g. FREDs), and suppress noise. We present preliminary results of MSED applied to BATSE 64ms discsc data.     

Modeling outflow from the Ernest Henry Fe oxide Cu–Au deposit: implications for ore genesis and exploration

The Ernest Henry Fe oxide Cu–Au (IOCG) deposit (>ca. 1.51 Ga) is hosted by breccia produced during the waning stages of an evolving hydrothermal system that formed a number of tens of metres to a kilometre scale, pre- and syn-ore alteration halos, although no demonstrable patterns have been attributed to fluids expelled through the outflow zones. However, the recognition of a population of hypersaline fluid inclusions representing the ‘spent’ fluids after Cu–Au deposition at Ernest Henry provides the basis to model the geochemical characteristics of the deposit's outflow zones. Geochemical modeling at 300 °C was undertaken at both high and low fluid/rock ratios via FLUSH models involving three host rock types: (1) granite, (2) calc–silicate rock, and (3) graphitic schist. In models run at high fluid/rock ratios, all rock types are essentially fluid-buffered, and produce an albite–quartz–hematite–barite-rich assemblage, although in low fluid–rock environments, the pH, redox, and geochemical character of the host rock exerts a greater influence on the mineralogy of the alteration assemblages (e.g., andradite, Fe–chlorite, and magnetite). Significant sulphide mineralization was predicted in graphitic schist where sphalerite occurred in both low- and high-porosity models, which indicates the possibility of an association between high-temperature IOCG mineralization and lower temperature base metal mineralization.Cooling experiments (from 300 to 100 °C) using the ‘spent fluids’ predict early high-T (300–200 °C) Na-, Ca-, Fe-, and Mn-rich, magnetite-bearing hydrothermal associations, whereas with cooling to below 200 °C, and with progressive fluid–rock interaction, the system produces rhodochrosite-bearing, hematite–quartz–muscovite–barite-rich assemblages. These results show that the radical geochemical and mineralogical changes associated with cooling and progressive fluid influx are likely to be accompanied by major transformations in the geophysical expression (e.g., spectral and magnetic character) of the alteration in the outflow zone, and highlight the potential link between magnetite- and hematite-bearing IOCG hydrothermal systems.     

Review of the tectonics of the Levant Rift system: the structural significance of oblique continental breakup

The Levant Rift system is an elongated series of structural basins that extends for more than 1000 km from the northern Red Sea to southern Anatolia. The system consists of three major segments, the Jordan Rift in the south, El Gharb–Kara-Su Rift in the north, and the Lebanese Fault splay in between. The rifted parts of this structural system are accompanied by intensively uplifted margins that mirror-image the basinal pattern, namely, the deeper the basin—the higher its margins, and vice versa. Uplifts also occur along the fault splay section. The Jordan Rift comprises axial basins that diminish in size from the south northwards, and are separated from each other by shallow threshold zones along the axis of the rift, where the margins are also subdued. The Lebanese Fault splay consists of five faults that emerge from the northern edge of the Jordan Rift and trend like a fan between the north and the northeast. One of these faults connects the Jordan and El Gharb–Kara-Su rifts. The Levant Rift and its uplifted margins started to develop in the middle-late Miocene, and most of the structural development occurred in the Plio-Pleistocene.The Levant Rift system is characterized by its oblique displacement, and evidence for both dip-slip and strike-slip displacement was measured on its faults. Earthquakes also indicate that same mixed pattern, some of them show strike-slip offset, and others normal. It is generally conceded that the amount of normal offset along the boundary faults of the Rift system reaches 8–10 km, but the lateral displacement is disputed, and offsets ranging from 11 to 107 km were suggested. Assessment of the available data led us to suggest that the sinistral offset along the Levant Rift system is approximately 10–20 km. The similarity between the vertical and the lateral displacements, the basin and threshold structural pattern of the Rift, model experiments in oblique rifting, as well as the significant tectonic resemblance to the Red Sea and the East African rifts, indicate that the Levant Rift is the product of continental breakup, and it is probably an emerging oceanic spreading center.     

Calc-Alkaline Magmatism at the Archean Proterozoic Transition: the Caico Complex Basement (NE Brazil)

The Paleoproterozoic metaplutonic rocks of the CaicóComplex Basement (Seridó region, NE Brazil) provide importantand crucial insights into the petrogenetic processes governingcrustal growth and may potentially be a proxy for understandingthe Archean–Proterozoic transition. These rocks consistof high-K calc-alkaline diorite to granite, with Rb–Sr,U–Pb, Pb–Pb and Sm–Nd ages of c. 2·25–2·15Ga. They are metaluminous, with high Yb_N, K₂O/Na₂O and Rb/Sr,low I_Sr ratios, and are large ion lithophile elements (LILE)enriched. Petrographic and geochemical data demonstrate thatthey belong to differentiated series that evolved by low-pressurefractionation, thus resulting in granodioritic liquids. We proposea model in which the petrogenesis of the Caicó Complexorthogneisses begins with partial melting of a metasomaticallyenriched spinel- to garnet-bearing lherzolite (with high-silicaadakite melt as the metasomatic agent), generating a basic magmathat subsequently evolved at depth through fractional crystallizationof olivine, followed by low-pressure intracrustal fractionation.A subduction zone setting is proposed for this magmatism, toaccount for both negative anomalies in high field strength elements(HFSE) and LILE enrichment. Mantle-derived juvenile magmatismwith the same age is also known in the São Franciscoand West Africa cratons, as well as in French Guyana, and thusthe Archean–Proterozoic transition marks a very importantcontinental accretion event. It also represents a transitionfrom slab-dominated (in the Archean) to wedge-dominated post-Archeanmagmatism. KEY WORDS: calc-alkaline; magmatism; NE Brazil; Paleoproterozoic; petrogenesis     

Determining meteoroid bulk densities using a plasma scattering model with high-power large-aperture radar data

We present an improved technique for calculating bulk densities of low-mass (<1 g) meteoroids using a scattering model applied to the high-density plasma formed around the meteoroid as it enters Earth’s atmosphere. These plasmas, referred to as head echoes, travel at or near the speed of the meteoroid, thereby allowing the determination of the ballistic coefficient (mass divided by physical cross-section), which depends upon speed and deceleration. Concurrently, we apply a scattering model to the returned signal strength of the head echo in order to correlate radar-cross-section (RCS) to plasma density and meteoroid mass. In this way, we can uniquely solve for the meteoroid mass, radius and bulk density independently. We have applied this new technique to head echo data collected in 2007 and 2008 simultaneously at VHF (160 MHz) and UHF (422 MHz) at ALTAIR, which is a high-power large-aperture radar located on the Kwajalein Atoll. These data include approximately 20,000 detections with dual-frequency, dual-polarization, and monopulse (i.e. angle) returns. From 2000 detections with the smallest monopulse errors, we find a mean meteoroid bulk density of 0.9 g/cm³ with observations spanning almost three orders of magnitude from 0.01 g/cm³ to 8 g/cm³. Our results show a clear dependence between meteoroid bulk density and altitude of head echo formation, as well as dependence between meteoroid bulk density and 3D speed. The highest bulk densities are detected at the lowest altitudes and lowest speeds. Additionally, we stipulate that the approximations used to derive the ballistic parameter, in addition to neglecting fragmentation, suggest that the traditional ballistic parameter must be used with caution when determining meteoroid parameters.     

Broadening participation,creating community,and learning that it never goes as planned

This paper presents the experience of a service-learning course which used community geography to study a proposed research and community center in DeKalb, IL. The center was proposed as a jointly-developed project by the Northern Illinois University and local governmental entities. The original goal of the course was to explore the viability of the proposed project and solicit feedback from the community through traditional engaged planning and public participation. As students began interacting with university and residential communities, it became clear that both communities had input for the center, and found similarities in their experiences and perceptions. While noted divisions in interest groups are known in DeKalb, both communities found themselves surprisingly interested in meaningful discussion to better understand each other through their shared experiences. In response, our theoretical approach shifted to community geography. Students, university employees, and local residents introduced and analyzed questions together as researchers and participants, and developed recommendations to address shared concern. Students then prepared a report advocating for those concerns to submit to university and community leaders. Following the evolution of this project, this paper presents lessons learned and areas for application of community geography as a pedagogical technique, as an important component of geography curriculum, and as a research framework for town-gown relationship inquiry.

     

A new framework to determine general multimodal soil water characteristic curves

Acta Geotechnica - A soil water characteristic curve (SWCC) model named as discrete-continuous multimodal van Genuchten model with a convenient parameter calibration method is developed to describe...     

Deep mantle roots and continental emergence: implications for whole-Earth elemental cycling,long-term climate,and the Cambrian explosion

Elevations on Earth are dominantly controlled by crustal buoyancy, primarily through variations in crustal thickness: continents ride higher than ocean basins because they are underlain by thicker crust. Mountain building, where crust is magmatically or tectonically thickened, is thus key to making continents. However, most of the continents have long passed their mountain building origins, having since subsided back to near sea level. The elevations of the old, stable continents are lower than that expected for their crustal thicknesses, requiring a subcrustal component of negative buoyancy that develops after mountain building. While initial subsidence is driven by crustal erosion, thermal relaxation through growth of a cold thermal boundary layer provides the negative buoyancy that causes continents to subside further. The maximum thickness of this thermal boundary layer is controlled by the thickness of a chemically and rheologically distinct continental mantle root, formed during large-scale mantle melting billions of years ago. The final resting elevation of a stabilized continent is controlled by the thickness of this thermal boundary layer and the temperature of the Earth’s mantle, such that continents ride higher in a cooler mantle and lower in a hot mantle. Constrained by the thermal history of the Earth, continents are predicted to have been mostly below sea level for most of Earth’s history, with areas of land being confined to narrow strips of active mountain building. Large-scale emergence of stable continents occurred late in Earth’s history (Neoproterozoic) over a 100–300 million year transition, irreversibly altering the surface of the Earth in terms of weathering, climate, biogeochemical cycling and the evolution of life. Climate during the transition would be expected to be unstable, swinging back and forth between icehouse and greenhouse states as higher order fluctuations in mantle dynamics would cause the Earth to fluctuate rapidly between water and terrestrial worlds.