Mafic peperite from the Gold Creek Volcanics in the Middle Proterozoic McArthur Basin,Northern Territory

Peperite is a non‐genetic term used to describe volcanic breccia in which a texture of dark blocks in a light matrix resembles a mixture of salt and pepper. In the Gold Creek Volcanics, peperite is a mixture of partly vesiculated basalt clasts in a mudstone‐sandstone matrix. It is formed by the buoyant intrusion of basaltic magma into wet unconsolidated sediment. The intruding bodies deform and quench, giving rise to discordant masses of hyaloclastic breccia, confined largely to the subsurface. These basalt masses may remain hot enough to locally superheat pore water and produce convective systems where the basalt clasts and fluidized sediment become mixed, forming the distinctive peperite.     

Stochastic interpolation as a means to estimate oceanic fields

Abstract

The method of stochastic interpolation (conditional simulation) is introduced as a means to interpolate / extrapolate a scalar or vector field of an oceanic variable, e.g. currents. Conditional simulation produces the synthesis of a random field that is forced to agree with simultaneous measurements in the same time interval and area where the input data are being synthesized. The conditional simulation is applied to the vector field for two California current measurement programs (Coastal Ocean Dynamics Experiment (CODE) and Central California Coastal Circulation Study fccccsj, north and south of San Francisco, respectively). These field programs covered different areas and were characterized by different instrument spacings. The influence of these spatial factors shows up in the quality of the conditional simulations, i.e. a smaller area and a tighter mooring array led to more physically reasonable flow realizations. The various realizations provided by a series of conditional simulations allow confidence intervals to be defined. Other uses for this technique include optimization of current‐meter (or other sensor) placement and the specification of initial or boundary conditions for numerical models. This latter function could be invoked when real data are sparse or when the data that are available are overly smooth and do not contain enough of the variability of the natural system.     

Thermodynamically Constrained Averaging Theory Approach for Modeling Flow and Transport Phenomena in Porous Medium Systems: 8. Interface and Common Curve Dynamics

This work is the eighth in a series that develops the fundamental aspects of the thermodynamically constrained averaging theory (TCAT) that allows for a systematic increase in the scale at which multiphase transport phenomena is modeled in porous medium systems. In these systems, the explicit locations of interfaces between phases and common curves, where three or more interfaces meet, are not considered at scales above the microscale. Rather, the densities of these quantities arise as areas per volume or length per volume. Modeling of the dynamics of these measures is an important challenge for robust models of flow and transport phenomena in porous medium systems, as the extent of these regions can have important implications for mass, momentum, and energy transport between and among phases, and formulation of a capillary pressure relation with minimal hysteresis. These densities do not exist at the microscale, where the interfaces and common curves correspond to particular locations. Therefore, it is necessary for a well-developed macroscale theory to provide evolution equations that describe the dynamics of interface and common curve densities. Here we point out the challenges and pitfalls in producing such evolution equations, develop a set of such equations based on averaging theorems, and identify the terms that require particular attention in experimental and computational efforts to parameterize the equations. We use the evolution equations developed to specify a closed two-fluid-phase flow model.     

Regional sea level changes projected by the NASA/GISS Atmosphere-Ocean Model

Sea level has been rising for the past century, and coastal residents of the Earth will want to understand and predict future sea level changes. In this study we present sea level changes from new simulations of the Goddard Institute for Space Studies (GISS) global atmosphere-ocean model from 1950 to 2099. The free surface, mass conserving ocean model leads to a straightforward calculation of these changes. Using observed levels of greenhouse gases between 1950 and 1990 and a compounded 0.5% annual increase in CO₂ after 1990, model projections show that global sea level measured from 1950 will rise by 61?mm in the year 2000, by 212?mm in 2050, and by 408?mm in 2089. By 2089, 64% of the global sea level rise will be due to thermal expansion and 36% will be due to ocean mass changes. The Arctic Ocean will show a greater than average sea level rise, while the Antarctic circumpolar region will show a smaller rise in agreement with other models. Model results are also compared with observed sea level changes during the past 40 years at 12 coastal stations around the world.     

Present Evidence for Intermediate Mass Black Holes in ULXs and Future Prospects

In a number of the most luminous ULXs (those with L_X ∼ 10⁴⁰ erg s⁻¹) in nearby galaxies, observations with XMM-Newton and Chandra are revealing evidence which suggests that these ULXs may harbor intermediate-mass black holes (IMBHs). The detection of accretion disk spectral components with temperatures 5–10 times lower than the temperatures observed in stellar-mass black hole binaries near to their Eddington limit may be particularly compelling evidence for IMBH primaries, since T ∝ M^−1/4 for disks around black holes. In some sources, X-ray timing diagnostics also hint at IMBHs. Evidence for IMBHs in a subset of the most luminous ULXs, a discussion of the robustness of this evidence and alternatives to the IMBH interpretation, and prospects for better determining the nature of these sources in the future, are presented in this work.     

Parameter sensitivity of automated baseflow separation for snowmelt‐dominated watersheds and new filtering procedure for determining end of snowmelt period

Automation in baseflow separation procedures allowed fast and convenient baseflow and baseflow index (BF and BFI) estimation for studies including multiple watersheds and covering large spatio‐temporal scales. While most of the existing algorithms are developed and tested extensively for rainfall‐ and baseflow‐dominated systems, little attention is paid on their suitability for snowmelt‐dominated systems. Current publishing practice in regional‐scale studies is to omit BF and BFI uncertainty evaluation or sensitivity analysis. Instead, “standard” and “previously recommended” parameterizations are transferred from rainfall/BF to snowmelt‐dominated systems. We believe that this practice should be abandoned. First, we demonstrate explicitly that the three most popular heuristic automated BF separation methods—Lyne–Hollick and Eckhardt recursive digital filters, and the U.K. Institute of Hydrology smoothed minima method—produce a wide range of annual BF and BFI estimates due to parameter sensitivity during the annual snowmelt period. Then, we propose a solution for cases when BF and BFI calibration is not possible, namely excluding the snowmelt‐dominated period from the analysis. We developed an automated filtering procedure, which divides the hydrograph into pre‐snowbelt, post‐snowmelt, and snowmelt periods. The filter was tested successfully on 218 continuous water years of daily streamflow data for four snowmelt‐dominated headwater watersheds located in Wyoming (60–837 km²). The post‐snowmelt BF and BFI metric can be used for characterizing summer low‐flows for snowmelt‐dominated systems. Our results show that post‐snowmelt BF and BFI sensitivity to filter parameterization is reduced compared with the sensitivity of annual BF and BFI and is similar to the sensitivity levels for rainfall/baseflow systems.     

The crustal evolution of South America from a zircon Hf‐isotope perspective

Hf‐isotope data of >1100 detrital zircon grains from the Palaeozoic, south‐central Andean Gondwana margin record the complete crustal evolution of South America, which was the predominant source. The oldest grains, with crustal residence ages of 3.8–4.0 Ga, are consistent with complete recycling of existing continental crust around 4 Ga. We confirm three major Archaean, Palaeoproterozoic (Transamazonian) and late Mesoproterozoic to early Neoproterozoic crust‐addition phases as well as six igneous phases during Proterozoic to Palaeozoic time involving mixing of juvenile and crustally reworked material. A late Mesoproterozoic to early Neoproterozoic, Grenville‐age igneous belt can be postulated along the palaeo‐margin of South America. This belt was the basement for later magmatic arcs and accreted allochthonous microcontinents as recorded by similar crustal residence ages. Crustal reworking likely dominated over juvenile addition during the Palaeozoic era, and Proterozoic and Archaean zircon was mainly crustally reworked from the eroding, thickened Ordovician Famatinian arc.