Creating an isotopically similar Earth–Moon system with correct angular momentum from a giant impact

The giant impact hypothesis is the dominant theory explaining the formation of our Moon. However, the inability to produce an isotopically similar Earth–Moon system with correct angular momentum has cast a shadow on its validity. Computer-generated impacts have been successful in producing virtual systems that possess many of the observed physical properties. However, addressing the isotopic similarities between the Earth and Moon coupled with correct angular momentum has proven to be challenging. Equilibration and evection resonance have been proposed as means of reconciling the models. In the summer of 2013, the Royal Society called a meeting solely to discuss the formation of the Moon. In this meeting, evection resonance and equilibration were both questioned as viable means of removing the deficiencies from giant impact models. The main concerns were that models were multi-staged and too complex. We present here initial impact conditions that produce an isotopically similar Earth–Moon system with correct angular momentum. This is done in a single-staged simulation. The initial parameters are straightforward and the results evolve solely from the impact. This was accomplished by colliding two roughly half-Earth-sized impactors, rotating in approximately the same plane in a high-energy, off-centered impact, where both impactors spin into the collision.     

Extension of the Paraná Basin to offshore Brazil: Implications for coalbed methane evaluation

Coalbed methane (CBM) is a worldwide exploration target of the petroleum industry. In Brazil, the most important coal-bearing succession is associated with the Permian Rio Bonito Formation of the Paraná Basin. The gas-prone areas are located at the southeastern margin of the Paraná Basin and possibly in the offshore region of the northern part of the Pelotas Basin. Coalfields end abruptly at the present day shoreline, a result of rifting of Gondwana and the evolution of the South Atlantic Ocean. All geologic indicators suggest that in pre-rift times the coal seams extended further eastwards, probably now lying deeply buried below the sedimentary succession of the Pelotas Basin. The present paper discusses structural, stratigraphic, seismic and aeromagenetic data that support the preservation of continental crust beneath ocean sediment. If the coal beds had similar lateral extent to known onshore coals, and coal beds extended across the projected extension of the Parana basin, and there was a conservative 5 m of cumulative coal thickness, then a potential methane volume can be estimated for this newly inferred resource. Average onshore coal gas content is 32 scf/ton (1.00 m³/ton). If this is similar in the offshore coal deposits, then the hypothetical methane volume in the offshore area could be in excess of 1.9 × 10¹² scf (56 × 10⁹ m³). Metamorphism from dikes associated with rifting are potential complicating factors in these deposits, and since no borehole reaching the deep-lying strata in the offshore area are available, this is a hypothetical gas resource with a certain level of uncertainty which should be tested in the future by drilling a deep borehole.     

Guiding ecological principles for marine spatial planning

The declining health of marine ecosystems around the world is evidence that current piecemeal governance is inadequate to successfully support healthy coastal and ocean ecosystems and sustain human uses of the ocean. One proposed solution to this problem is ecosystem-based marine spatial planning (MSP), which is a process that informs the spatial distribution of activities in the ocean so that existing and emerging uses can be maintained, use conflicts reduced, and ecosystem health and services protected and sustained for future generations. Because a key goal of ecosystem-based MSP is to maintain the delivery of ecosystem services that humans want and need, it must be based on ecological principles that articulate the scientifically recognized attributes of healthy, functioning ecosystems. These principles should be incorporated into a decision-making framework with clearly defined targets for these ecological attributes. This paper identifies ecological principles for MSP based on a synthesis of previously suggested and/or operationalized principles, along with recommendations generated by a group of twenty ecologists and marine scientists with diverse backgrounds and perspectives on MSP. The proposed four main ecological principles to guide MSP—maintaining or restoring: native species diversity, habitat diversity and heterogeneity, key species, and connectivity—and two additional guidelines, the need to account for context and uncertainty, must be explicitly taken into account in the planning process. When applied in concert with social, economic, and governance principles, these ecological principles can inform the designation and siting of ocean uses and the management of activities in the ocean to maintain or restore healthy ecosystems, allow delivery of marine ecosystem services, and ensure sustainable economic and social benefits.     

The relationship of elasticity and crystal structure in andalusite and sillimanite

The nine elastic constants of andalusite and sillimanite have been determined, using the technique of Brillouin scattering. They are, in megabars, for andalusite: c ₁₁=2.334, c ₂₂=2.890, c ₃₃=3.801, c ₄₄=0.995, c ₅₅=0.878, c ₆₆=1.123, c ₂₃=0.977, c ₁₃=1.162, c ₁₂=0.814; for sillimanite: c ₁₁=2.873, c ₂₂=2.319, c ₃₃=3.884, c ₄₄=1.224, c ₅₅=0.807, c ₆₆=0.893, c ₂₃=1.586, c ₁₃=0.834, c ₁₂=0.947. Both structures are characterized by chains of edge-linked coordination octahedra extending parallel to the crystallographic c direction, cross-linked by polyhedra of lower coordination. In each structure the stiffness measured parallel to c is greater than that measured normal to c. The shear moduli can be directly correlated with the relative rigidity of the cross-linking structures.     

Structure of the crust and upper mantle in Canada

The seismic probing of the crust and upper mantle in Canada started in 1938 and since then has involved many government and university groups using a wide variety of techniques. These have included simple profiling with both wide and narrow station spacing, areal time-term surveys, detailed deep reflection experiments, very long-range refraction studies and the analysis of surface wave dispersion between stations of the Canadian Standard Network.

A review of the published interpretation leads to the general conclusion that:

1. (1) P_n-velocities vary from a value possibly as low as 7.7 km/sec under Vancouver Island to 8.6 km/sec and higher in the extreme eastern part of the shield and some parts of the Atlantic coast.

2. (2) Large areas of Canada have a crustal thickness of 30–40 km, with Vancouver Island, the southwestern Prairies, the Lake Superior basin and parts of the eastern shield of Quebec being thicker. No continental area in Canada is known to have a crust thinner than 29 km.

3. (3) The Riel discontinuity — a deep intra-crustal reflector and sometime refractor, is widely reported in the Prairies and Manitoba. It is not seen to the north in the vicinity of Great Slave Lake, nor in the Hudson Bay, Lake Superior and Maritime regions, nor in the interior of British Columbia. It may be present in some areas of the eastern shield.

4. (4) As experiments have become more detailed, crustal structures of greater complexity have been revealed. The concept that crustal structure becomes simpler with increasing depth is apparently unfounded.

Long-range refraction studies suggest that the Gutenberg P-wave low-velocity channel is poorly developed under the Canadian Shield. The analysis of the dispersion of surface waves, however, suggests that the channel is better developed for S-waves, and is present throughout the country. The lid of the channel is deepest under the central shield and shallowest under the Cordillera.     

The variation of tetrahedral bond lengths in sodic plagioclase feldspars

Multiple linear regression analysis has been applied to the geometric and chemical variables in sodic plagioclases in order to determine their relative effects on individual T-O bond lengths in the Al_1+xSi_3?xO₈ tetrahedral framework. Using data from crystal structure analyses of low and high albite, An₁₆ and An₂₈, and assuming that low albite is completely ordered, 1 $$\begin{gathered} {\text{T}} - {\text{O = 1}}{\text{.568}} + {\text{[(0}}{\text{.122) x (Al content of the T site)]}} \hfill \\ {\text{ }} - {\text{[(0}}{\text{.037) x (}}\Delta {\text{{\rm A}l}}_{{\text{br}}} )] + [0.063){\text{ x }}(\Sigma {\text{[}}q{\text{/(Na,Ca}} - {\text{O)}}^{\text{2}} ])] \hfill \\ {\text{ }} + {\text{[(0}}{\text{.029) x (}} - {\text{1/cosT}} - {\text{O}} - {\text{T)]}} \hfill \\ \end{gathered}$$ where the Al content of a particular tetrahedral (T) site can be estimated from empirically-derived determinative curves, where Δ Al_br is a linkage factor to account for the Al content of adjacent tetrahedral sites, where the formal charge on the (Na_1?xCa_x) atom is q=1+x, and where T-O-T is the inter-tetrahedral angle involving the T-O bond. For sodic plagioclases it is essential to know only the anorthite content and the 2Θ₁₃₁-2Θ_1¯31 spacing (CuK _α radiation) in order to determine the independent variables in this equation and thus to evaluate the individual T-O distances. The 64 individual T-O distances predicted for the four sodic plagioclases by this equation agree well with the observed T-O bond lengths (σ=0.004 Å; r=0.994), and the method has been used by way of example to rationalize the T-O bond lengths in analcime (cf. Ferraris, Jones and Yerkess, 1972).     

Abundance of Boron in International Geochemical Standards by Prompt-Gamma Neutron Activation Analysis

Eighteen international reference standards, mostly geochemical standards, have been analysed for boron using prompt-gamma neutron activation analysis (PGNAA). There is good agreement between the results for samples with high boron abundances and the few published values using PGNAA and other methods. However, correlation is poor at low boron abundances, especially in those standards with low boron/sodium ratios. Corrections for sodium interference on boron have been critically evaluated and the data corrected using two different methods.