Early Proterozoic regolith at Pasvik, NE Norway: palaeoenvironmental implications for the Baltic Shield

Regolith occurs at a number of localities along the northern margin of the early Proterozoic Pechenga Greenstone Belt marking a profound stratigraphic unconformity at the base of the 10 km thick Petsamo Supergroup. The age of regolith formation can be bracketed between 2.453 ± 42 Ga (Sm-Nd) and 2.330 ± 36 Ga (Rb-Sr). Regolith is developed on a varied substrate of Archaean rocks including early Proterozoic layered gabbros (2.45 Ga). The best example of the regolith occurs in the Pasvik valley at Brattli, Norway. Analogues are widespread on the Baltic Shield at the base of early Proterozoic 'greenstone belts' showing a low degree of chemical weathering and carbonatisation. Fluviatile deposits overlying the Brattli regolith preserve unweathered pyrite-magnetite boulders and terrigenous pyrite grains. These features are considered to relate an arid or semi-arid palaeoenvironment, possibly with some deficiency of oxygen in the atmosphere-hydrosphere system. A systematic and well-preserved regolith or palaeosaprolite at the base of the Petsamo Supergroup is proof that the northern boundary of the Pechenga Greenstone Belt is a fundamental first-order unconformity. This places constraints on geotectonic modelling of this early Proterozoic rift-basin.     

Great Barrier Island silver-gold deposits,Hauraki Province,New Zealand

The Great Barrier Island subvolcanic silver-gold deposits comprise a number of essentially east striking, quartz filled, mineralized fissures, which transect andesitic volcanics and an unconformably overlying, bedded sinter deposit of upper Tertiary to Quaternary age. Wall rock alteration is characterized by a propylitic assemblage in the least altered andesite, with argillic assemblages and silicification developed in close proximity to the veins. Some twentyfive hypogene and supergene ore minerals have been recognized, of which pyrite is the most common and finely disseminated pyrargyrite constitutes the main source of silver. The mineral assemblage is dominantly hypogene with minor supergene alteration occurring at surface exposures, and includes mainly sulfides, selenides and native metals. Fineness of electrum derived from two electron microprobe analyses is approximately 500, while total silver to gold ratio from a number of bulk chemical analyses is 30:1. Maximum depth of deposition is estimated to be in the order of 500 m and for some surface exposures 100 m. The mineralization is regarded as subvolcanic and along with other hydrothermal fissure deposits of Hauraki Province is considered to be of Pliocene-Pleistocene age, and hence is believed to be associated with the late phase extrusions and intrusions of acid magma in the volcanic belt.     

The cordierite isograd in archaean meta-sediments near yellowknife,N.W.T., Canada-variations on an experimentally established reaction

In the Slave Craton, meta-sediments commonly exhibit broad, Abukuma-type metamorphic aureoles round late, potassic plutons. The rocks are divided into low and medium metamorphic grades by sharply-defined cordierite isograds. Comparison of mineral assemblages above and below one such isograd indicates that chlorite and muscovite were reactants. Biotite is present below the isograd, and textural relations suggest that it participated in the reaction. Micro-probe analyses of biotites in cordierite-free and cordieritebearing rocks, considered in the light of established pro-grade compositional changes, indicate that the biotite changed in composition during the reaction, supplying Si in exchange for Al^IV, Fe and Mg in exchange for Al^VI, and K in exchange for Na. The reaction can be balanced in a fashion consistent with all the observable evidence. The balancing operation indicates that abundant quartz and traces of albite and ilmenite also reacted, and that biotite became more abundant during the reaction. Thus the complex reaction can be approximated by the formula Chl+Musc+Biot(1)+Qtz [+Albite+Ilm] →Cord+Biot(2)+Water It is of a type extensively studied in experimental haplo-pelitic systems but was modified in the natural system mainly because additional phases participated. In particular, pre-existing biotite was compositionally modified and increased in amount during the reaction.     

The tectonic implications of Solundian (Upper Devonian) magnetization of the Devonian rocks of Kvamshesten, western Norway

The allochthonous Old Red Sandstone of Kvamshesten, western Norway, records polyphase orogenic deformation, and palaeomagnetic results from both the Devonian sediments and mylonites associated with the basal thrust define a syn- (to post-) tectonic magnetization withD = 218°,I = +3° and₉₅ = 9.7°. The corresponding pole position (lat. 21°S, long. 324°E) suggests a Late Devonian/Early Carboniferous magnetization age (Solundian), and probably dates the time of thrust movements.     

Metallogeny and tectonic development of the Tasman Fold Belt System in Victoria

Current evidence suggests that most of Victoria is underlain by a relatively thick (20 km +) basement of sialic composition of assumed Proterozoic age. This basement is nowhere exposed and its structural relationship with exposed Palaeozoic rocks is conjectural. This uncertainty has resulted in both ensimatic and ensialic tectonic models being proposed for Victoria during the Cambrian.Mineralization associated with Cambrian igneous activity shows a variety of styles from minor orthomagmatic chromite deposits, through Au and Cu deposits of syngenetic or epigenetic origin, to Fe---Mn, Ba occurrences of exhalative volcanogenic affiliation.Cambrian volcanism and associated sedimentation was followed by the deposition of dominantly quartz-rich turbidites with interbedded shale and siliceous units. Subsequent to the epi-Ordovician Benambran Orogeny, late Silurian crustal extension caused several rifts to open along roughly orthogonal NW and NE aligned fractures. Within these fault-bounded depressions, thick acid volcanic sequences were deposited in close association with shallow-marine sediments. Mineralization in these Upper Silurian rocks comprises polymetallic base-metal sulphide lenses and minor disseminations, at least some of which are of exhalative volcanogenic affiliation.The Silurian rifts were obliterated and their rocks strongly deformed during the Bindian (Bowning) deformation during late Silurian to early Devonian time. This in turn was followed by another episode of crustal extension and rifting, during which the formation of a broad meridional trough marks the Buchan Rift. A very thick sequence of largely subaerial bimodal volcanics is overlain by shelf limestone and mudstone. A variety of minor base metal, barite, manganese, and iron mineralization is hosted by these volcanics and shelf sediments.The mid-Devonian Tabberabberan Orogeny was followed in the Late Devonian by bimodal volcanism and granite intrusion, and “red-bed”-type non-marine sedimentation. In Central Victoria, thick bimodal volcanics were erupted into a series of cauldron subsidences and intruded by comagmatic granites. Bimodal volcanism also occurred in the Mount Howitt Province farther east, but was followed by deposition of extensive fluviatile and lacustrine sediments (mainly mudstone, sandstone, and minor conglomerate). In the Mansfield Basin, these contain minor sedimentary copper occurrences.There are four distinct episodes of granite emplacement in Victoria, namely Late Cambrian -Early Ordovician (Delamerian) in the Glenelg Zone; Early Silurian (Benambran) in the Highlands Zone; Early Devonian (Bindian) in the Grampians, Ararat-Bendigo, Highlands, and Mallacoota Zones; and Middle Devonian-Carboniferous (post Tabberabberan) in the Ararat- Bendigo, Melbourne, Howqua, and Highlands Zones. Data for the Delamerian granitoids are sketchy, but in the remaining groups S-type granitoids predominate with the exception of eastern Victoria, east of the Yalmy Fault (I-S line), where only I- and A-type granitoids occur. A variety of Sn, Mo, W deposits and prospects are associated with the Benambran and younger intrusive phases.Victoria is a major gold province which has produced nearly 2.5 × 10⁶ kg gold. Primary gold occurs in a number of geological settings including veins and disseminations spatially associated with mafic Cambrian volcanism, vein deposits in turbiditic sequences of central and eastern Victoria, veins associated with mafic and intermediate intrusives of Mid to Late Devonian age, and minor amounts associated with a variety of granitoids and porphyry dykes.     

Re‐creation of the 1744 Heylyn and Frye ceramic patent wares using Cherokee clay: Implications for raw materials,kiln conditions,and the earliest English porcelain production

Porcelain wares have been produced following the directions contained in the Heylyn and Frye patent of 1744, using Cherokee clay and a lime‐alkali glass frit. The wares were fired to the bisque (˜ 950°C), glazed using a clay‐glass mixture, and then fired to a “heat‐work” level of Orton cone 9–90° deflection at 150°C per hour (1279°C). Modal mineralogy comprises Caplagioclase and two glass phases, one relict frit and the other a melt phase. The bulk chemistry of the body comprises 64.3 wt % SiO₂, 21.7 wt % Al₂O₃, and 5.6 wt % CaO. Molecular ratios are SiO₂:Al₂O₃ 5.0 and SiO₂:CaO 10.7. It is concluded that the patent, whose significance has been questioned over many years, was a practical working recipe, that close comparison may be made with porcelains of the “A”‐marked group, and that the patent represents a remarkable landmark in English ceramic history. © 2004 Wiley Periodicals, Inc.     

Demersal fishing disturbance increases predation risk for whelks (Buccinum undatum L.)

Field observations by divers indicated that a high rate of predation of whelks (Buccinum undatum) by starfish (Asterias rubens) occurred in an area disturbed by scallop dredging, although these whelks mostly appeared to be alive and externally undamaged. The ability of whelks to escape from starfish was tested in the laboratory after they were dropped or rolled to simulate direct physical contact with bottom fishing gear. Dropping whelks did not significantly affect their escape behaviour, but whelks which had been rolled took significantly longer to right themselves and were significantly less likely to perform an escape response than whelks that had not experienced this treatment. This study suggests that demersal fishing may indirectly increase whelk mortality by increasing their risk of predation.     

Determining the mass of the accreting white dwarf in magnetic cataclysmic variables using RXTE data

We have extracted spectra of 20 magnetic cataclysmic variables (mCVs) from the RXTE archive and best fitted them using the X-ray continuum method of Cropper et al. to determine the mass of the accreting white dwarf in each system. We find evidence that the mass distribution of these mCVs is significantly different from that of non-magnetic isolated white dwarfs, with the white dwarfs in mCVs being biased towards higher masses. It is unclear if this effect is a result of selection or whether this reflects a real difference in the parent populations.     

High-speed energy-resolved STJ photometry of the eclipsing binary UZ For

We present high-time-resolution optical photometry of the eclipsing binary UZ For using a superconducting tunnel junction (STJ) device, a photon-counting array detector with intrinsic energy resolution. Three eclipses of the ∼18-mag 126.5-min orbital binary were observed using a 6×6 array of tantalum STJs at the 4.2-m William Herschel Telescope on La Palma. The detector presently provides individual photon arrival-time accuracy to about 5 μs, and a wavelength resolution of about 60 nm at 500 nm, with each array element capable of counting up to ∼5000 photon s⁻¹. The data allow us to place accurate constraints on the accretion geometry from our time- and spectrally resolved monitoring, especially of the eclipse ingress and egress. We find that there are two small accretion regions, located close to the poles of the white dwarf. The positions of these are accurately constrained, and show little movement from eclipse to eclipse, even over a number of years. The colour of the emission from the two regions appears similar, although their X-ray properties are known to be significantly different: we argue that the usual accretion shock may be absent at the non-X-ray-emitting region, and instead the flow here interacts directly with the white dwarf surface; alternatively, a special grazing occultation of this region is required. There is no evidence for any quasi-periodic oscillations on time-scales of the order of seconds, consistent with relatively stable cyclotron cooling in each accretion region.