Role of melt during deformation in the deep crust

Deformation in the deep crust is strongly influenced by the presence of melt. Injected melt (or magma) weakens the crust because strain will tend to localize where melt is present. The amount of strain a pluton may accommodate is dependent on the length of time it takes for a pluton to crystallize and the strain rate. For plutons that intrude into rocks which are near the solidus temperature of the melt, crystallization times can be quite long (> 1Myr).
Partial melting of deep crustal rocks can lead to melt-enhanced embrittlement. This occurs because the volume change for most melting reactions is positive. Therefore, when the rate of melt production outpaces the rate at which melt can leave the system, the melt pressure increases. Eventually, the melt pressure may become sufficiently high that the melting rocks behave in a brittle fashion and fracture.
Conjugate sets of dilatant shear fractures filled with melt occur in migmatite from the Central Gneiss belt (Canada); this suggests that melt-enhanced embrittlement occurred in these rocks. An expression which relates the magnitude of differential stress to the angle between conjugate dilatant shear fractures is derived. Assuming that migmatite has a small tensile strength, differential stresses are ≤ 20 MPa in migmatitic rocks at the time melt-enhanced embrittlement occurs. The occurrence of melt-enhanced embrittlement shows that a switch in deformation mechanism from plastic flow to cataclasis is possible in the deep crust during melting. Furthermore, repeated episodes of melt-enhanced embrittlement in migmatitic rocks may be an efficient mechanism for extracting melt from partially melted terrains.     

A Pool-Based Model of the Spatial Distribution of Undiscovered Petroleum Resoufrces

An approach is proposed to predict the spatial distributions of undiscovered petroleum resources. Each pool is parameterized as a marked-point. The independence chain of the Hastings algorithm is used to generate an appropriate structure for pool combinations in a play. Petroleum-bearing favorability estimated from geological observations is used to represent the sampling probabilities of pool locations. An objective function measuring the distance between characteristics of the realization and constraints is constructed from both the pool size distribution and entropy maximum criterion, in which the entropy criterion places all undiscovered pools in the most favorable positions. The geometrical convergence property of the proposed Hastings algorithm is presented. The method is illustrated by a case study from the Western Canada Sedimentary Basin.     

Boninite primary magmas: Evidence from the Cape Vogel Peninsula,PNG

Boninites from Cape Vogel, PNG, are dominantly pyroxene-glass rocks, but many contain olivine, sometimes as refractory as Fo₉₄. We derive a parental magma for this suite (in equilibrium with Fo₉₄) which contains 20 wt.% MgO and is quartz-normative. This liquid is hydrous, and from petrographie evidence and whole rock H₂O⁺ values, we estimate it to contain 2–3 wt.% H₂O. These data suggest olivine fractionation and primary magmatic water are important in boninite genesis, but both are often obscured by later alteration. The derived parental magma has probably formed at 1,250–1,300° C and low pressures (< ?10kB) and is similar to those which gave rise to olivine-clinoenstatite phyric boninites from New Caledonia and from Howqua, Australia, and possibly to a proposed parental magma for the Bushveld Complex.     

Nonstoichiometry in sillimanite: Mullite compositions with sillimanite-type superstructures

Complete solid solution between sillimanite and mullite is shown to occur when Fe³⁺, in the virtual absence of Ti, replaces Al^VI. All members of the series adopt the sillimanite (Al, Si)^IV ordering scheme in preference to the modulated structure typical of synthetic and titaniferous natural mullites.     

Olivine-matrix reactions in thermally metamorphosed Apollo 14 breccias

Olivine clasts, which have mantles formed by reaction of the olivine with the breccia matrix, are present in the high-grade thermally metamorphosed Apollo 14 breccias. The mantled olivine clasts are most abundant in 14311, but they are also present in 14304 and 14319. Typically the mantles consist of two zones: an inner corona containing pyroxene, ilmenite and commonly plagioclase, and an outer light-colored halo where the matrix is depleted in ilmenite. The growth of the coronas involved matrix-to-corona diffusion of TiO₂ and corona-to-matrix diffusion of MgO and FeO. These diffusive fluxes can be attributed to chemical potential gradients developed between mineral assemblages in local equilibrium at the olivine-corona boundary and the matrix.     

Future heat vulnerability in California, Part II: projecting future heat-related mortality

Through the 21^st century, a significant increase in heat events is likely across California (USA). Beyond any climate change, the state will become more vulnerable through demographic changes resulting in a rapidly aging population. To assess these impacts, future heat-related mortality estimates are derived for nine metropolitan areas in the state for the remainder of the century. Heat-related mortality is first assessed by initially determining historical weather-type mortality relationships for each metropolitan area. These are then projected into the future based on predicted weather types created in Part I. Estimates account for several levels of uncertainty: for each metropolitan area, mortality values are produced for five different climate model-scenarios, three different population projections (along with a constant-population model), and with and without partial acclimatization. Major urban centers could have a greater than tenfold increase in short-term increases in heat-related mortality in the over 65 age group by the 2090s.     

On the response of yielding seismically isolated structures

This paper investigates the seismic response of yielding isolated structures. To establish a general understanding of the nonlinear response of seismically isolated structures, this study first investigates the nonlinear response of isolated structures subjected to steady‐state harmonic motion and nonlinear transient ground excitation. The response of both viscously damped and hysteretically damped isolation systems is investigated in three phases. Initially, basic insights are gained through simple nonlinear two degrees of freedom (2‐DOF) models subjected to harmonic motion of varying frequencies. Next, the transient response analysis of the nonlinear 2‐DOF model is investigated for a wide range of isolation system and superstructure properties. The results obtained from both approaches indicate that the yielding behavior of a structure on an isolation system is significantly different from that of the comparable fixed‐base structure. Finally, the response of the nonlinear 2‐DOF system model is compared with that of a 15‐story, three‐dimensional model. Based on the results of these analytical investigations, some important considerations for the design of seismically isolated structures are presented. Copyright © 2007 John Wiley & Sons, Ltd.     

The petrology and origin of coals from the lower Carboniferous Mattson formation, southwestern district of Mackenzie, Canada

Petrographic analyses were carried out on thin coals and coaly sediments from the Lower Carboniferous Mattson Formation at Clausen Creek and Jackfish Gap-Yohin Ridge in the northern part of the Liard Basin, northern Canada. The composition and optical characteristics indicate that the coals are high-volatile bituminous B, predominantly sapropelic (canneloid) and accumulated subaquatically.The coals are dominantly composed of inertinite-rich and exinite-rich durities with subsidiary inertites and clarodurites; vitrite is minor and liptite is rare. The inertinite-rich microlithotypes are dominated by semifusinite, but micrinite, semimacrinite and ?resino-inertinites are abundant. Sporinite, comprising megaspores, crassispores, tenuispores and miospores, is the dominant liptinite maceral with subsidiary cutinite and minor alginite. Except for pyrite, mineral matter is minimal.Three populations of telocollinite are observed: a low-reflectance variety (I), commonly associated with micrinite (as vitrinertite), displays weak brown fluorescence and a reflectance some 0.4-0.5% lower than type II; type II is non-fluorescing telocollinite, with intermediate reflectance (0.67-0.74% R_om), it occurs as vitrite and is also associated with micrinite; and a higher-reflectance telocollinite (III), having no fluorescence or association with micrinite, has variable reflectance (0.74-0.8% R_om) implying higher oxidation or gelification levels.The abundance of semimacrinite, macrinite and ?resino-inertinites in inertites and durites (I) suggests that much of the peat accumulated subaquatically. Furthermore, fluorescing vitrinite and an abundance of micrinite (derived by oxidation or coalification of bituminite), suggest that the coal accumulated under anaerobic conditions. The predominance of semifusinite in humic laminae and micrinite in sapropelic layers suggests extensive surface or near-surface oxidation of the peat. Oxidised sporinites suggest that they were wind-borne.Depositional environment is interpreted as marginal marine, perhaps in shallow lakes in the middle to upper delta plain. Peat accumulations probably began subaquatically at the oxygen-hydrogen sulphide interface, but periodic subaerial exposure and natural oxidation gave rise to the high inertinite coals. Upper Mattson coals are interbedded with algal laminites and probably accumulated in a lagoonal setting.     

Crisis? What crisis? Displacing the spatial imaginary of the fiscal state

This paper argues that there is an immanent and evolving relationship between the prevailing form of taxation and the economic geographies of the state. Despite this, the geographic significance of taxation has been obscured by the language in which its historic transformation tends to be couched. Prevailing fiscal systems tend to be presented as essentially static – institutionally and spatially fixed and routinely inscribed within the fixed boundaries and territories of the ‘sovereign’ fiscal state. Any threat to, or change in the nature or geography of the fiscal state tends to be couched in terms of ‘crisis’ – of negative and discontinuous change. This paper contends that these related and essentially conservative discourses of fiscal geography mask the degree to which fiscal spaces are both multiple and continuously evolving. More importantly, it argues, this fluidity and multiplicity does not threaten the stability and viability of state form, but it is an essential process in its maintenance and reproduction. Running counter to the prevailing discourse of the ‘national economy’, the practice of fiscal geography is an under-analysed but key aspect of the historical evolution and transformation of the imagined geographies of economies.