The evolution of fluorine-rich felsic magmas: source dichotomy, magmatic convergence and the origins of topaz granite

Topaz granite is alkali-feldspar granite that contains essential albite, quartz, K-feldspar, lithium-mica, and topaz. As a group topaz granites are characterized by their extreme enrichment in F (up to 3 wt%) and a wide variety of lithophile elements. They can be subdivided into a 'low-P₂O₅ subtype' (P₂O₅ < 0.1 wt%, Al₂O₃ < 14.5 wt%, SiO₂ > 73 wt%) and a 'high-P₂O₅ subtype' (P₂O₅ > 0.4 wt%, Al₂O₃ > 14.5 wt%, SiO₂ < 73 wt%), the δ¹⁸O values of which indicate a dichotomy of source rock: the low-P₂O₅ subtype (δ¹⁸O < 10‰) having a meta-igneous protolith and the high-P₂O₅ subtype (δ¹⁸O > 10 ‰) a source with a significant component of pelitic material. The unusually high F contents enhance the efficacy of melt segregation and crystal-melt fractionation and so facilitate extreme differentiation in topaz granite magmas. Very low melt volumes restrict the bulk composition of the partial melts regardless of the nature of the source; and extreme fractionation forces them along a path of magmatic convergence, to produce a group of granitic rocks with near-minimum compositions so enriched in a variety of lithophile elements (Li, Nb, Ta, Sn) that economic mineralization often results.     

Angular distribution of photoelectrons from atomic oxygen,nitrogen and carbon

The angular distributions of photoelectrons from atomic oxygen, nitrogen and carbon are calculated. Both Hartree-Fock and Hartree-Slater (Herman-Skillman) wave functions are used for oxygen and the agreement is excellent; thus only Hartree-Slater functions are used for carbon and nitrogen. The pitch angle distribution of photoelectrons is discussed and it is shown that previous approximations of energy independent isotropic or sin² θ distributions are at odds with our results, which vary with energy. This variation with energy is discussed as is the reliability of these calculations.     

Atmospheric tides and the rotation of Venus II. Spin evolution

Tides in the atmosphere of Venus may help to stabilize its slow retrograde rotation. The frequency dependence of the body tides also affects its rotational stability. However, the obliquity is probably maintained near 180° by friction between the core and mantle of Venus. In any case, it appears most likely that Venus originated with an obliquity greater than 90°.     

Neogene sedimentation patterns in north-central peninsular Florida

Sea level fluctuations and shoreline migrations are responsible for commonly oriented ridges and hills of north-central Florida. Lake Wales Ridge is the principal geomorphic feature of the region, with younger ridges, including Trail Ridge, occurring to the north and east.Sand is the dominant sediment size of the deposits forming these ridges, but gravels and clay beds also occur. Cross-laminations and burrowing are prominent in certain horizons. Generalized sections resemble marine regressive patterns and a marine barrier environment. The deposits reflect a prograding shoreline and the subaerial evolution of the Florida peninsula.     

Plasma and the universe: large scale dynamics,filamentation, and radiation

One of the earliest predictions about the morphology of the universe is that it be filamentary (Alfvén, 1950). This prediction followed from the fact that volumewise, the universe is 99.999% matter in the plasma state. When the plasma is energetic, it is generally inhomogeneous with constituent parts in motion. Plasmas in relative motion are coupled by the currents they drive in each other and nonequilibrium plasma often consists of current-conducting filaments.In the laboratory and in the Solar System, filamentary and cellular morphology is a well-known property of plasma. As the properties of the plasma state of matter is believed not to change beyond the range of our space probes, plasma at astrophysical dimensions must also be filamentary.During the 1980s a series of unexpected observations showed filamentary structure on the Galactic, intergalactic, and supergalactic scale. By this time, the analytical intractibility of complex filamentary geometries, intense self-fields, nonlinearities, and explicit time dependence had fostered the development of fully three-dimensional, fully electromagnetic, particle-in-cell simulations of plasmas having the dimensions of galaxies or systems of galaxies. It had been realized that the importance of applying electromagnetism and plasma physics to the problem of radiogalaxy and galaxy formation derived from the fact that the universe is largely aplasma universe. In plasma, electromagnetic forces exceed gravitational forces by a factor of 10³⁶, and electromagnetism is 10⁷ times stronger than gravity even in neutral hydrogen regions, where the degree of ionization is a miniscule 10^–4.The observational evidence for galactic-dimensioned Birkeland currents is given based on the direct comparison of the synchrotron radiation properties of simulated currents to those of extra-galactic sources including quasars and double radio galaxies.     

Volatile characteristics of peralkaline rhyolites from Kenya: an ion microprobe,infrared spectroscopic and hydrogen isotope study

Peralkaline rhyolites of the Greater Olkaria Volcanic Complex, Kenya Rift Valley, were derived from separated, though closely related, magma chambers. Ion microprobe analyses of glass inclusions in quartz phenocrysts show pre-eruptive water contents of up to 3.4 wt% contrasting with previous estimates that the magmas were anhydrous. The values approach predicted solubility levels corresponding to water saturation at low crustal pressures (1 kbar). The glass matrices of the rhyolites have low water contents, ranging from 0.07 to 0.46 wt%, suggesting significant degassing during, or prior to, eruption. Infrared measurements of the matrix glasses show variation in the relative proportions of the two hydrous species dissolved in the glasses. The amount of molecular water, determined semi-quantitatively, apparently increases with increased fluorine content and peralkalinity. This suggests a competition between hydroxyl groups and fluoride ions for similar sites within the melt structure. The mechanism of degassing has been investigated using hydrogen isotopes. The range of D values in most rocks can be produced by varied degrees of open-system degassing of rhyolite melt initially in equilibrium with water of a fixed, or limited, D value. There is evidence to suggest that closed-system degassing may also have been a significant component in some rhyolites. The exact mechanisms of degassing remain uncertain. Particular problems include the relative contribution of open-and closed-system degassing during eruption and the initial vapour compositions and solubility relationships.     

Petrology of the Chilliwack batholith,North Cascades,Washington: generation of calc-alkaline granitoids by melting of mafic lower crust with variable water fugacity

Calc-alkaline granitoid rocks of the Oligocene-Pliocene Chilliwack batholith, North Cascades, range from quartz diorites to granites (57–78% SiO₂), and are coeval with small gabbroic stocks. Modeling of major element, trace element, and isotopic data for granitoid and mafic rocks suggests that: (1) the granitoids were derived from amphibolitic lower crust having REE (rare-earth-element) and Sr-Nd isotopic characteristics of the exposed gabbros; (2) lithologic diversity among the granitoids is primarily the result of variable water fugacity during melting. The main effect of f_{H 2 O} variation is to change the relative proportions of plagioclase and amphibole in the residuum. The REE data for intermediate granitoids (quartz diorite-granodiorite; Eu/Eu^*=0.84–0.50) are modeled by melting with f_{H 2 O}<1 kbar, leaving a plagioclase + pyroxene residuum. In contrast, data for leucocratic granitoids (leuco-granodiorites and granites; Eu/Eu^* =1.0–0.54) require residual amphibole in the source and are modeled by melting with f_{H 2 O}=2–3 kbar. Consistent with this model, isotopic data for the granitoids show no systematic variation with rock type (⁸⁷Sr/⁸⁶Sr_i =0.7033–0.7043; Nd(0)=+3.3 to +5.5) and overlap significantly with data for the gabbroic rocks (⁸⁷Sr/⁸⁶Sr_i =0.7034–0.7040; Nd(0)=+3.3 to +6.9). The f_{H 2 O} variations during melting may reflect additions of H₂O to the lower crust from crystallizing basaltic magmas having a range of H₂O contents; Chillwack gabbros document the existence of such basalts. One-dimensional conductive heat transfer calculations indicate that underplating of basaltic magmas can provide the heat required for large-scale melting of amphibolitic lower crust, provided that ambient wallrock temperatures exceed 800°C. Based on lithologic and geochemical similarities, this model may be applicable to other Cordilleran batholiths.     

Electric space: Evolution of the plasma universe

Contrary to popular and scientific opinion of just a few decades ago, space is not an empty void. It is actually filled with high energy particles, magnetic fields, and highly conducting plasma. The ability of plasmas to produce electric fields, either by instabilities brought about by plasma motion or the movement of magnetic fields, has popularized the term Electric Space in recognition of the electric fields systematically discovered and measured in the solar system. Today it is recognized that 99.999% of all observable matter in the universe is in the plasma state and the importance of electromagnetic forces on cosmic plasma cannot be overstated; even in neutral hydrogen regions (10^–4 parts ionized), the electromagnetic force to gravitational force ratio is 10⁷.An early prediction about the morphology of the universe is that it be filamentary (Alfvén, 1950). Plasmas in electric space are energetic (because of electric fields) and they are generally inhomogeneous with constituent parts in motion. Plasmas in relative motion are coupled by the currents they drive in each other and nonequilibrium plasma often consists of current-conducting filaments. This paper explores the dynamical and radiative consequences of the evolution of galactic-dimensioned filaments in electric space.