Pyrometamorphism of Phyllites by a Dolerite Plug

The progressive thermal metamorphism of Dalradian phyllitesadjacent to a Tertiary basic plug is traced petrographicallyfrom the initial stages of breakdown of micaceous minerals tothe eventual development, in places near the contact, of rheomorphicmaterial of granitic composition and complementary highly desilicatedferromagnesian residues. Chemical analyses of unmetamorphosedand thermally metamorphosed country rock, granophyres, and desilicatedresidues, are used to illustrate the chemistry of these metamorphicprocesses and to suggest approximate temperature-pressure conditionsunder which they took place. The petrological significance ofthe emery-like residues is discussed briefly.     

Basalt and Sediment Geochemistry and Magma Petrogenesis in a Transect from Oceanic Island Arc to Rifted Continental Margin Arc: the Kermadec--Hikurangi Margin, SW Pacific

Sediment mixing and recycling through a subduction zone canbe detected in lead isotopes and trace elements from basaltsand sediments from the Kermadec-Hikurangi Margin volcanic arcsystem and their coupled back-arc basins. Sr, Nd and Pb isotopesfrom the basalts delineate relatively simple, almost overlapping,arrays between back-arc basin basalts of the Havre Trough-NgatoroBasin (⁸⁷Sr/⁸⁶Sr = 0.70255; _Nd=+9.3; ²⁰⁶Pb/²⁰⁴Pb = 18.52; ²⁰⁸Pb/²⁰⁴Pb= 38.18), island arc basalts from the Kermadec Arc togetherwith basalts from Taupo Volcanic Zone (⁸⁷Sr/⁸⁶Sr 0.7042; _Nd= +5; ²⁰⁶Pb/²⁰⁴Pb= 18.81; ²⁰⁸Pb/²⁰⁴Pb = 38.61), and sedimentsderived from New Zealand's Mesozoic (Torlesse) basement (⁸⁷Sr/⁸⁶Sr 0.715; _Nd —4; ²⁰⁶Pb/²⁰⁴Pb 18.86; ²⁰⁸Pb/²⁰⁴Pb 38.8).Basalts from the arc front volcanoes have high Cs, Rb, Ba, Th,U and K, and generally high but variable Ba/La, Ba/Nb ratios,characteristic of subduction-related magmas, relative to typicaloceanic basalts. These signatures are diluted in the back-arcbasins, which are more like mid-ocean ridge basalts. Strongchemical correlations in plots of SiO₂ vs CaO and loss on ignitionfor the sediments (finegrained muds) are consistent with mixingbetween detrital and biogenic (carbonate-rich) components. Otherdata, such as Zr vs CaO, are consistent with the detrital componentcomprising a mixture of arc- and continent-derived fractions.In chondrite-normalized diagrams, most of the sediments havelight rare earth element enriched patterns, and all have negativeEu anomalies. The multielement diagrams have negative spikesat Nb, P and Ti and distinctive enrichments in the large ionlithophile elements and Pb relative to mantle. Isotopic measurementsof Pb, Sr and Nd reveal restricted fields of Pb isotopes butwide variation in Nd and Sr relative to other sediments fromthe Pacific Basin. Rare K-rich basalts from Clark Volcano towardthe southern end of the oceanic Kermadec Island Arc show unusualand primitive characteristics ( 2% K₂O at 50% SiO₂, Ba 600p.p.m., 9–10% MgO and Ni > 100 p.p.m.) but have highlyradiogenic Sr, Nd and Pb isotopes, similar to those of basaltsfrom the continental Taupo Volcanic Zone. These oceanic islandarc basalts cannot have inherited their isotope signatures throughcrustal contamination or assimilation—fractional crystallizationtype processes, and this leads us to conclude that source processesvia bulk sediment mixing, fluid and/or melt transfer or somecombination of these are responsible. Although our results showclear chemical gradients from oceanic island arc to continentalmargin arc settings (Kermadec Arc to Taupo Volcanic Zone), overlapbetween the data from the oceanic and continental sectors suggeststhat the lithospheric (crustal contamination) effect may beminimal relative to that of sediment subduction. Indeed, itis possible to account for the chemical changes by a decreasenorthward in the sediment flux into the zone of magma genesis.This model receives support from recent sediment dispersal studiesin the Southern Ocean which indicate that a strong bottom current(Deep Western Boundary Current) flows northward along the easterncontinental margin of New Zealand and sweeps continental derivedsediment into the sediment-starved oceanic trench system. Thetrace element and isotopic signatures of the continental derivedcomponent of this sediment are readily distinguished, but alsodiluted in a south to north direction along the plate boundary. KEY WORDS: subduction zone basalts; sediments; Sr-, Nd-, Pb-isotopes; trace elements ^*Present address: School of Earth Sciences, University of Melbourne, Parkville, Vic. 3052, Australia.     

Counter point bar deposits: lithofacies and reservoir significance in the meandering modern Peace River and ancient McMurray Formation, Alberta, Canada

Counter point bar deposits in the meandering Peace River, North‐central Alberta, Wood Buffalo National Park, are distinct from point bar deposits in terms of morphology, lithofacies and reservoir potential for fluids. Previously referred to as the distal‐most parts of point bars, point bar tails and concave bank‐bench deposits, counter point bar deposits have concave morphological scroll patterns rather than convex as with point bars. The Peace is a large river (bankfull discharge 11 700 m³ sec^?1, width 375 to 700 m, depth 15 m, gradient 0·00004 or 4 cm km^?1) in which counter point bar deposits are dominated by silt (80% to 90%), which contrasts with sand‐dominant (90% to 100%) point bar deposits. Beginning at the meander inflection (transition from convex to concave), counter point bar deposit stratigraphy thickens as a wedge‐like architecture in the distal direction until the deposit is nearly as thick as the point bar deposits. The low permeability silt‐dominant lithofacies in counter point bar deposits will limit reservoir extent and movement of fluids in both modern and ancient subsurface fluvial deposits. In the exploration and extraction of bitumen and heavy oil in subsurface fluvial rocks, identification and mapping of reservoir potential of point bar deposits and counter point bar deposits is now possible in the fluvial‐dominated tidal estuarine Lower Cretaceous Middle McMurray Formation, North‐east Alberta. Recent geophysical advances have facilitated imaging of some ancient buried point bar deposits and counter point bar deposits which, on the basis of morphological shape of sedimentary bodies observed from seismic amplitude, can be interpreted and mapped as depositional elements or blocks that contain associated sandstone or siltstone dominant lithofacies, respectively. As counter point bar deposits exhibit poor permeability and thus limit reservoir potential for water, natural gas, light crude, heavy oil and bitumen, counter point bar deposits should be avoided in resource developments. Geophysical imaging, interpretation and mapping of point bar deposit and counter point bar deposit elements provide new opportunities to improve recovery of bitumen and heavy oil and reduce development costs in subsurface cyclic steam stimulation and steam‐assisted gravity drainage projects by not drilling into counter point bar deposits.     

A procedure for determining the nature of Mercury's core

Abstract— We review the assertion that the precise measurement of the second degree gravitational harmonic coefficients, the obliquity, and the amplitude of the physical libration in longitude, C₂₀, C₂₂, θ, and φ₀, for Mercury are sufficient to determine whether or not Mercury has a molten core (Peale, 1976). The conditions for detecting the signature of the molten core are that such a core not follow the 88‐day physical libration of the mantle induced by periodic solar torques, but that it does follow the 250 000‐year precession of the spin axis that tracks the orbit precession within a Cassini spin state. These conditions are easily satisfied if the coupling between the liquid core and solid mantle is viscous in nature. The alternative coupling mechanisms of pressure forces on irregularities in the core‐mantle boundary (CMB), gravitational torques between an axially asymmetric mantle and an assumed axially asymmetric solid inner core, and magnetic coupling between the conducting molten core and a conducting layer in the mantle at the CMB are shown for a reasonable range of assumptions not to frustrate the first condition while making the second condition more secure. Simulations have shown that the combination of spacecraft tracking and laser altimetry during the planned MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, Ranging) orbiter mission to Mercury will determine C₂₀, C₂₂, and θ to better than 1% and φ₀ to better than 8%—sufficient precision to distinguish a molten core and constrain its size. The possible determination of the latter two parameters to 1% or less with Earth‐based radar experiments and MESSENGER determination of C₂₀ and C₂₂ to 0.1% would lead to a maximum uncertainty in the ratio of the moment of inertia of the mantle to that of the whole planet, C_m/C, of ?2% with comparable precision in characterizing the extent of the molten core.     

Sedimentation and palaeoenvironments of Late Cretaceous crater-lake deposits in Bushmanland, South Africa

A large diameter borehole core from an epiclastic kimberlite remnant on the farm Stompoor in the Prieska district, Cape Province, contains a continuous 76 m section of fossiliferous sediments interpreted as having accumulated within a crater-lake during the Late Cretaceous. Three distinct facies associations reflect depositional processes that prevailed in offshore areas of the original lake. Facies Association A: matrix-supported pebble conglomerates comprising a chaotic assemblage of pyroclastic, basement and country rocks set in a fine-grained matrix. Flat, non-erosional basal surfaces with ‘frozen’ rip-up clasts, the protrusion of matrix-supported clasts above the upper surfaces and a direct relationship between maximum clast size and bed thickness suggest deposition from debris flows that originated subaerially on pyroclastic talus cones surrounding the crater. Facies Association B: alternating thin beds of matrix-supported granule conglomerate, structureless fine-grained sandstone and parallel laminated mudrock. Small fining-upward sequences within these beds are comparable to turbidite Bouma Tade, Tde. Numerous partings display petrified fish and frog skeletons, as well as bivalve, gastropod and ostracode shells, leaf impressions, insect wings and a possible bird bone. These beds were deposited by thin debris-flows and turbidity underflows interspersed with periods of ‘pelagic’ sedimentation. Facies Association C: microlaminated mudstone beds containing scattered ‘dropstone lapilli’. The lamination is imparted by alternating Ca-rich/Ca-poor layers which may reflect climatic seasonality. They are interpreted as the result of seasonally influenced suspension settling through a thermally stratified water column. Short-term periodicities in conglomerate bed thicknesses are interpreted as the result of successive block caving of a slump scar giving rise to several debris flows from the same source area. Seismic shock from nearby volcanism may have simultaneously triggered slumps on both subaerial and subaqueous slopes. Dropstone lapilli in Type C beds and the preponderance of load casting in Type B beds support this interpretation. An estimate of the time span involved in accumulating 76 m of crater lake sediments based on the possible seasonal imprint of Type C beds gives a figure of some 220,000 yr.     

NUMERICAL MODELING OF HEAVY METAL POLLUTANT TRANSPORT-TRANSFORMATION IN FLUVIAL RIVERS：A REVIEW

A detailed discussion of existing three kinds of mathematical models of heavy metal pollutant transport-transformation in fluvial rivers is presented, with an emphasis on the mathematical model of heavy metal pollutant transport-transformation dynamics. The imperfection of two kinds of mathematical models, that is, mathematical model of chemical thermodynamic equilibrium and that of chemical reaction kinetics, and the shortcoming of existing mathematical models of heavy metal pollutant transport-transformation dynamics are pointed out. Furthermore, the structure of mathematical model of heavy metal pollutant transport-transformation dynamics in fluvial rivers is suggested. Equations in the mathematical model of heavy metal pollutant transport-transformation dynamics in fluvial rivers will be discussed in the following paper.     

Ideal shocks in 2‐layer flow Part II: Under a passive layer

In this second part of the study, ideal shock theory in two‐layer stratified flow is extended to include a third passive layer (i.e., a two and a half layer system). With the presence of a passive layer, two linear wave modes and "viscous tail modes" exist, complicating the solubility conditions and uniqueness proofs for two layer shocks. It is found however, that shocks can be unambiguously classified as external or internal based on the states of criticality that they connect. The steepening condition, while still necessary, provides a less restrictive constraint than it did with a rigid lid. Thus, we have to rely more on solutions to the full viscous shock equations to establish shock existence. The detailed structure, momentum exchange, and Bernoulli loss in a viscous shock are examined using an analytical weak shock solution and a set of numerical solutions for shocks with finite amplitudes. A shock regime diagram ( F ₁ by F ₂) is constructed based on the numerical integration of the full viscous shock equations. For strong external jumps, a cusp region (i.e., in the sense of catastrophe theory) is identified on the regime diagram. For pre‐shock states within the cusp, three end states are possible and two of these are realizable. The cusp has several physical implications. It indicates that an equal distribution of dissipation between the two layers in shocks is mathematically possible but physically inaccessible. It also allows hysteresis in time varying flows, and promotes the occurrence of double shocks (i.e., closely spaced shocks of different character). The results are compared with classical shock solutions and a set of time dependent numerical experiments.     

Cross-Calibration and Long-Term Monitoring of the Microwave Radiometers of ERS,TOPEX, GFO,Jason, and Envisat

The radiometers on board the satellites ERS-1, TOPEX/Poseidon, ERS-2, GFO, Jason-1, and Envisat measure brightness temperatures at two or three different frequencies to determine the total columnal water vapor content and wet tropospheric path delay, a major correction to the altimeter range measurements. In order to asses the long-term stability of the path delay, the radiometers are calibrated against vicarious cold and hot references, against each other, and against several atmospheric models. Four of these radiometers exhibit significant drifts in at least one of the channels, resulting in yet unmodeled errors in path delay of up to 1 mm/year, thus limiting the accuracy at which global sea level rise can be inferred from the altimeter range measurements.