The dependence of the Fe2+-Mg cation-partitioning between olivine and basaltic liquid on pressure,temperature and composition

The equilibrium partitioning of Fe²⁺ and Mg between olivine and liquid along a liquid line of descent has been determined for a calc-alkaline system, ranging in composition from picritic to andesitic. Experiments were conducted between 1000–1450° C and 1 bar to 30 kbar. Within the compositional range investigated and , the compositional dependence of the Fe²⁺ and Mg partitioning is a function of the Mg-content of the liquid. The Mg-content of the liquid correlates strongly with temperature. The variation of the Fe²⁺ and Mg partitioning were therefore evaluated individualy as functions of composition and temperature alone. The composition dependence of the cation-partitioning coefficients (Kd) is given by the following two equations:

Geochemistry of Tertiary tholeiites and picrites from Qeqertarssuaq (Disko Island) and Nuussuaq, West Greenland with implications for the mineral potential of comagmatic intrusions

Tertiary continental flood basalts on Qeqertarssuaq and Nuussuaq in West Greenland contain ～3?km of picrites and variably contaminated tholeiites. The picrites are in the Naujánguit member of the Vaïgat Formation and they have 7–29?wt% MgO, La/Sm?=?0.9–2.1, and ¹⁴³Nd/¹⁴⁴Nd?=?0.51263–0.51307. They appear to have crystallised from high-Mg parental magmas (14.4–16.4?wt% MgO) with isotope and trace element ratios similar to recent Icelandic picrites. Discrete horizons of tholeiites, including the Asûk and?Kûgánguaq, have elevated SiO₂ (50–58 wt%), La/Sm?=?3–7, ⁸⁷Sr/⁸⁶Sr?=?0.70550–0.71224, and low ¹⁴³Nd/¹⁴⁴Nd?=?0.51234–0.51174. These lavas have low Cu and Ni abundances (typically 10–50?ppm Ni or Cu), and in the case of the Asûk on Qeqertarssuaq, they contain droplets of native iron. The low Cu and Ni contents are attributed to scavenging by magmatic sulphides formed in response to crustal contamination of picritic magmas. Two contamination trends are recognised, one to a sediment end-member with high Th/Nb and Archaean model Nd ages, and the other to a meta-igneous component with high La/Sm, low Th/Nb and Rb/Nb, and Proterozoic source ages. Overall, ²⁰⁶Pb/²⁰⁴Pb varies from 16.47–21.68. Both contamination trends are associated with low Cu and Ni, and high SiO₂, and it is argued that the magmatic sulphides were triggered by the increases in silica, rather than simply by the introduction of additional crustal-derived sulphur. Geochemically, the Asûk and Kûgánguaq rocks resemble the most contaminated Nadezhdinsky lavas of the Siberian Trap, which are widely regarded as the source of the Ni and Cu mineralisation in the giant Noril'sk deposits. Mass balance considerations indicate that the parental liquids to the contaminated magmas contained sufficient Ni, Cu, S and platinum group elements to form substantial magmatic sulphide deposits. However, unlike the lavas at Noril'sk, the contaminated (low Cu and Ni) West Greenland basalts are in isolated units with no evidence for a gradual recovery in Ni and Cu abundances with height in the lava column. Comparison with Noril'sk suggests that although significant quantities of metals were scavenged by sulphides in West Greenland, the metal contents of the sulphides may not have been upgraded by continued interaction with subsequent magma batches.     

Eastern Altantic fracture zones as potential disposal sites for radioactive waste

Disposal of radioactive waste in the sea floor of fracture zones associated with the flanks of the Mid-Atlantic Ridge may be a satisfactory alternative to land disposal. Effective physiographic, sedimentary, chemical, and oceanographic barriers exist in these aseismic deep canyons, especially in the eastern Atlantic. In addition, the major producers of radioactive wastes are likely to be near the Atlantic Ocean. If such a disposal strategy is adopted, intensive study of the sedimentologic and oceanographic properties of oceanic fracture zones will be necessary.     

Chalcophile and platinum-group element (PGE) concentrations in the sulfide minerals from the McCreedy East deposit,Sudbury, Canada,and the origin of PGE in pyrite

Magmatic sulfide deposits consist of pyrrhotite, pentlandite, chalcopyrite (± pyrite), and platinum-group minerals (PGM). Understanding the distribution of the chalcophile and platinum-group element (PGE) concentrations among the base metal sulfide phases and PGM is important both for the petrogenetic models of the ores and for the efficient extraction of the PGE. Typically, pyrrhotite and pentlandite host much of the PGE, except Pt which forms Pt minerals. Chalcopyrite does not host PGE and the role of pyrite has not been closely investigated. The Ni–Cu–PGE ores from the South Range of Sudbury are unusual in that sulfarsenide PGM, rather than pyrrhotite and pentlandite, are the main carrier of PGE, probably as the result of arsenic contribution to the sulfide liquid by the As-bearing metasedimentary footwall rocks. In comparison, the North Range deposits of Sudbury, such as the McCreedy East deposit, have As-poor granites in the footwall, and the ores commonly contain pyrite. Our results show that in the pyrrhotite-rich ores of the McCreedy East deposit Os, Ir, Ru, Rh (IPGE), and Re are concentrated in pyrrhotite, pentlandite, and surprisingly in pyrite. This indicates that sulfarsenides, which are not present in the ores, were not important in concentrating PGE in the North Range of Sudbury. Palladium is present in pentlandite and, together with Pt, form PGM such as (PtPd)(TeBi)₂. Platinum is also found in pyrite. Two generations of pyrite are present. One pyrite is primary and locally exsolved from monosulfide solid solution (MSS) in small amounts (<2 wt.%) together with pyrrhotite and pentlandite. This pyrite is unexpectedly enriched in IPGE, As (± Pt) and the concentrations of these elements are oscillatory zoned. The other pyrite is secondary and formed by alteration of the MSS cumulates by late magmatic/hydrothermal fluids. This pyrite is unzoned and has inherited the low concentrations of IPGE and Re from the pyrrhotite and pentlandite that it has replaced.     

Salt kinematics and regional tectonics across a Permian gas field: a case study from East Frisia, NW Germany

This study presents a reconstruction of the tectonic history of an Upper Rotliegend tight gas field in Northern Germany. Tectonism of the greater study area was influenced by multiple phases of salt movement, which produced a variety of salt-related structural features such as salt walls, salt diapirs as well as salt glaciers (namakiers). A sequential 2D retro-deformation and stratal backstripping methodology was used to differentiate mechanisms inducing salt movement and to discuss their relation to regional tectonics. The quantitative geometric restoration included sedimentary balancing, decompaction, fault-related deformation, salt movement, thermal subsidence, and isostasy to unravel the post-depositional tectonic overprint of the Rotliegend reservoir rock. The results of this study indicate that reactive salt diapirism started during an Early Triassic interval of thin-skinned extensional tectonics, followed by an active diapirism stage with an overburden salt piercement in the Late Triassic, and finally a period of intensive salt surface extrusion and the formation of salt glaciers (namakiers) in Late Triassic and Jurassic times. Since the Early Cretaceous, salt in the study area has been rising by passive diapirism.     

The locational policies and geographical expansion of multiple retail companies: A case study of M.F.I.

M.F.I. has emerged as the major retailer of self-assembly furniture in the United Kingdom and their trading philosophy has led to a search for suburban retail sites. This paper outlines M.F.I.'s locational policies and traces the company's geographical expansion.     

Modeling the Population Effects of Hypoxia on Atlantic Croaker (<Emphasis Type="Italic">Micropogonias undulatus</Emphasis>) in the Northwestern Gulf of Mexico: Part 1—Model Description and Idealized Hypoxia

We developed a spatially explicit, individual-based model to analyze how hypoxia effects on reproduction, growth, and mortality of Atlantic croaker in the northwestern Gulf of Mexico lead to population-level responses. The model follows the hourly growth, mortality, reproduction, and movement of individuals on a 300 × 800 spatial grid of 1-km² cells for 140 years. Chlorophyll-a concentration, water temperature, and dissolved oxygen (DO) were specified daily for each grid cell and repeated for each year of the simulation. A bioenergetics model was used to represent growth, mortality was assumed stage- and age-dependent, and the movement behavior of juveniles and adults was modeled based on temperature and avoidance of low DO. Hypoxia effects were imposed using exposure effect submodels that converted time-varying exposures to low DO to reduced hourly growth, increased hourly mortality, and reduced annual fecundity. Results showed that 100 years of either mild or intermediate hypoxia produced small reductions in population abundance, while repeated severe hypoxia caused a 19% reduction in long-term population abundance. Relatively few individuals were exposed to low DO each hour, but many individuals experienced some exposure. The response was dominated by a 5% average reduction in annual fecundity of individuals. Under conditions of random sequences of mild, intermediate, and severe hypoxia years occurring in proportion to their historical frequency, the model predicted a 10% decrease in the long-term population abundance of croaker. A companion paper substitutes hourly DO values from a three-dimensional water quality model for the idealized hypoxia and results in a more realistic population reduction of about 25%.