The breakdown of potassium feldspar at high water pressures   总被引：1，自引：0，他引：1  

Pauline Thompson  Ian Parsons  Colin M. Graham  Brian Jackson 《Contributions to Mineralogy and Petrology》1998,130(2):176-186

The equilibrium position of the reaction between sanidine and water to form “sanidine hydrate” has been determined by reversal experiments on well characterised synthetic starting materials in a piston cylinder apparatus. The reaction was found to lie between four reversed brackets of 2.35 and 2.50 GPa at 450 °C, 2.40 and 2.59 GPa at 550 °C, 2.67 and 2.74 GPa at 650 °C, and 2.70 and 2.72 GPa at 680 °C. Infrared spectroscopy showed that the dominant water species in sanidine hydrate was structural H₂O. The minimum quantity of this structural H₂O, measured by thermogravimetric analysis, varied between 4.42 and 5.85 wt% over the pressure range of 2.7 to 3.2 GPa and the temperature range of 450 to 680 °C. Systematic variation in water content with pressure and temperature was not clearly established. The maximum value was below 6.07 wt%, the equivalent of 1 molecule of H₂O per formula unit. The water could be removed entirely by heating at atmospheric pressure to produce a metastable, anhydrous, hexagonal KAlSi₃O₈ phase (“hexasanidine”) implying that the structural H₂O content of sanidine hydrate can vary. The unit cell parameters for sanidine hydrate, measured by powder X-ray diffraction, were a = 0.53366 (±0.00022) nm and c = 0.77141 (±0.00052) nm, and those for hexasanidine were a = 0.52893 (±0.00016) nm and c = 0.78185 (±0.00036) nm. The behaviour and properties of sanidine hydrate appear to be analogous to those of the hydrate phase cymrite in the equivalent barium system. The occurrence of sanidine hydrate in the Earth would be limited to high pressure but very low temperature conditions and hence it could be a potential reservoir for water in cold subduction zones. However, sanidine hydrate would probably be constrained to granitic rock compositions at these pressures and temperatures. Received: 6 May 1997 / Accepted: 2 October 1997  相似文献   

A complete infrared Einstein ring in the gravitational lens system B1938 + 666     

L.J. King  N. Jackson  R.D. Blandford  M.N. Bremer  I.W.A. Browne  A.G. de Bruyn  C. Fassnacht  L. Koopmans  D. Marlow  P.N. Wilkinson 《Monthly notices of the Royal Astronomical Society》1998,295(2):L41-L44

We report the discovery, using NICMOS on the Hubble Space Telescope , of an arcsec-diameter Einstein ring in the gravitational lens system B1938+666. The lensing galaxy is also detected, and is most likely an early-type galaxy. Modelling of the ring is presented and compared with the radio structure from MERLIN maps. We show that the Einstein ring is consistent with the gravitational lensing of an extended infrared component, centred between the two radio components.  相似文献   

B0712+472: a new radio four-image gravitational lens     

N. Jackson  S. Nair  I. W. A. Browne  P. N. Wilkinson  T. W. B. Muxlow  A. G. de Bruyn  L. Koopmans  M. Bremer  I. Snellen  G. K. Miley  R. T. Schilizzi  S. Myers  C. D. Fassnacht  D. S. Womble  A. C. S. Readhead  R. D. Blandford  & T. J. Pearson 《Monthly notices of the Royal Astronomical Society》1998,296(3):483-490

A new four-image gravitational lens system, B0712+472, has been discovered during the Cosmic Lens All-Sky Survey. This system consists of four flat-spectrum radio images that are also seen on a Hubble Space Telescope ( HST ) image, together with the lensing galaxy. We present MERLIN, VLA and VLBA maps and WHT spectra of the system as well as the HST images. The light distribution of the lensing galaxy is highly elongated and so too is the mass distribution deduced from modelling. We suggest a redshift of ∼1.33 for the lensed object; the lens redshift will require further investigation. The discovery of this new system further increases the ratio of four-image to two-image lens systems currently known, exacerbating problems of required ellipticity of matter distributions in lensing galaxies.  相似文献   

Resistance of quartz silt to isotopic exchange under burial and intense weathering conditions   总被引：1，自引：0，他引：1  

Robert N. Clayton  M.L. Jackson  K. Sridhar 《Geochimica et cosmochimica acta》1978,42(10):1517-1522

Oxygen isotopic compositions of quartz from silty sediments buried to 5400 m depth from two wells in the Gulf of Mexico each showed δ5¹⁸O variations of less than 1.7%. Clay diagenesis has been reported within this depth. The observed variations in the quartz do not appear to be primarly diagenetic effects, but rather are mainly depositional features reflecting variations in the sources of the sediments. Sources may be influenced by the variation of distance from the shore at different depths in a given sampling location and by sediment production by continental glaciations. Stability of the oxygen isotopic composition of quartz in the 10–20 μm size range under long-time humid, temperate weathering conditions was studied by analysis of saprolites formed from Pennsylvanian to Precambrian crystalline rocks. In four of the five cases, the 10–20 μm fraction was found to have only 0.1–0.5%. greater δ¹⁸O than the corresponding 20–50 μm fraction. This increase may be attributable either to a slight oxygen isotopic exchange with ambient ground waters or original differences within the rock since the saprolites were sufficiently coherent to make an influx of extraneous detrital silt unlikely. The amount of oxygen isotopic exchange in silt size quartz over periods of many million years of shallow burial or weathering appears to be small enough to permit the use of the oxygen isotopic ratio of quartz in tracing the origin of eolian and fluvial additions of minerals to continental soils and pelagic sediments.  相似文献   

Summer Field Meeting in west Cornwall: 15–20 September 1974     

A. Hall  N.J. Jackson 《Proceedings of the Geologists' Association. Geologists' Association》1975,86(1):95-102

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Shock-wave compression of vitreous and rutile-type GeO2: A comparative study     

Ian Jackson  Thomas J. Ahrens 《Physics of the Earth and Planetary Interiors》1979,20(1):60-70

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Relations between surface deformation,fault geometry,seismicity, and rupture characteristics during the El Asnam (Algeria) earthquake of 10 October 1980     

G. Yielding  J.A. Jackson  G.C.P. King  H. Sinvhal  C. Vita-Finzi  R.M. Wood 《Earth and Planetary Science Letters》1981

The El Asnam earthquake of October 10, 1980 (M_s=7.3) produced surface faulting on a northeast-trending thrust fault of 30 km length with displacements of up to 6.5 m, though average displacements were about 3 m. In addition, widespread tensional features were formed, some in clear association with folding above the thrust, and others, in an area beyond the exposure of the thrust at the surface, which may be related to buried reverse faults.The observed thrust fault is split into southern, central and northern segments. Local and teleseismic data are examined to show that the main shock nucleated at the southwest end of the fault, and propagated 12 km northeast where a second rupture of approximately equal moment occurred, continuing the faulting a further 12 km northeast along the central segment. Both ruptures nucleated at about 8–10 km depth. Displacements were largest on the central segment, where they were probably enlarged by aftershocks, including one of m_b=6.1 three hours after the main shock. The northern segment was much shorter than the other two, and showed smaller displacement.The junctions between fault segments are marked by distinct geomorphological characteristics and a change in strike of the faulting, as well as a sudden drop in the observed displacement. It appears that the rupture development is influenced by the changes in fault geometry between segments, and that such junctions or barriers have persisted through much of the late Quaternary.  相似文献   

Simulation of the spatio‐temporal extent of groundwater flooding using statistical methods of hydrograph classification and lumped parameter models     

K. A. Upton  C. R. Jackson 《水文研究》2011,25(12):1949-1963

This article presents the development of a relatively low cost and rapidly applicable methodology to simulate the spatio‐temporal occurrence of groundwater flooding in chalk catchments. In winter 2000/2001 extreme rainfall resulted in anomalously high groundwater levels and groundwater flooding in many chalk catchments of northern Europe and the southern United Kingdom. Groundwater flooding was extensive and prolonged, occurring in areas where it had not been recently observed and, in places, lasting for 6 months. In many of these catchments, the prediction of groundwater flooding is hindered by the lack of an appropriate tool, such as a distributed groundwater model, or the inability of models to simulate extremes adequately. A set of groundwater hydrographs is simulated using a simple lumped parameter groundwater model. The number of models required is minimized through the classification and grouping of groundwater level time‐series using principal component analysis and cluster analysis. One representative hydrograph is modelled then transposed to other observed hydrographs in the same group by the process of quantile mapping. Time‐variant groundwater level surfaces, generated using the discrete set of modelled hydrographs and river elevation data, are overlain on a digital terrain model to predict the spatial extent of groundwater flooding. The methodology is applied to the Pang and Lambourn catchments in southern England for which monthly groundwater level time‐series exist for 52 observation boreholes covering the period 1975–2004. The results are validated against observed groundwater flood extent data obtained from aerial surveys and field mapping. The method is shown to simulate the spatial and temporal occurrence of flooding during the 2000/2001 flood event accurately. British Geological Survey © NERC 2011. Hydrological Processes © 2011 John Wiley & Sons, Ltd.  相似文献   

Evolution of three unconformity‐bounded sandy carbonate successions in the McArthur River region of northern Australia: The Lawn,Wide and Doom Supersequences in a proximal part of the Isa Superbasin     

M. J. Jackson  P. N. Southgate 《Australian Journal of Earth Sciences》2013,60(3):625-635

Gamma‐ray curves from surface outcrops together with U–Pb SHRIMP zircon dating are used to redefine the evolution of a Palaeoproterozoic sandy dolostone succession from northern Australia. This case history indicates that gamma‐ray logging of surface sections should accompany lithostratigraphic logging or an inadequate interpretation of stratigraphic evolution is a likely outcome. The 1200 m‐thick Nathan Group from the McArthur River area had previously been interpreted as a more‐or‐less continuous package of carbonates deposited in lacustrine and associated shallow‐water environments. Now it is seen to comprise the preserved remnants of three truncated, second‐order supersequences—the Lawn, Wide and Doom Supersequences—each a few hundred metres thick and each deposited over a time period of a few million years. These supersequences are separated by major stratigraphic breaks each approaching probably 10 million years duration. Each supersequence comprises several third‐order sequences which themselves contain higher‐order cycles. These were deposited in a series of continental, shoreline, and inner to outer carbonate platform environments. Transgressive, high‐energy, fluvial to marginal marine, mixed clastic‐carbonate facies dominate most of the sequences. The middle, Wide Supersequence, however, preserves deeper water (mostly sub‐storm‐wave‐base) stromatolitic facies in one sequence, and storm‐reworked clastics in another. These are interpreted as condensed intervals deposited around their respective maximum flooding surfaces and are succeeded by regressive facies that probably represent highstand systems tracts. New correlations between these 1615–1575 Ma sandy carbonate successions of the McArthur Basin (Amos, Balbirini and Dungaminnie Formations) and time‐equivalent largely clastic successions in the Lawn Hill area (Lawn Hill and Doomadgee Formations), some 400 km to the southeast, are proposed.  相似文献   

Salt thickness and composition influence rift structural style,northern North Sea,offshore Norway     

Christopher A.‐L. Jackson  Gavin M. Elliott  Elisabeth Royce‐Rogers  Robert L. Gawthorpe  Tor E. Aas 《Basin Research》2019,31(3):514-538

“Salt” giants are typically halite‐dominated, although they invariably contain other evaporite (e.g. anhydrite, bittern salts) and non‐evaporite (e.g. carbonate, clastic) rocks. Rheological differences between these rocks mean they impact or respond to rift‐related, upper crustal deformation in different ways. Our understanding of basin‐scale lithology variations in ancient salt giants, what controls this and how this impacts later rift‐related deformation, is poor, principally due to a lack of subsurface datasets of sufficiently regional extent. Here we use 2D seismic reflection and borehole data from offshore Norway to map compositional variations within the Zechstein Supergroup (ZSG) (Lopingian), relating this to the structural styles developed during Middle Jurassic‐to‐Early Cretaceous rifting. Based on the proportion of halite, we identify and map four intrasalt depositional zones (sensu Clark et al., Journal of the Geological Society, 1998, 155, 663) offshore Norway. We show that, at the basin margins, the ZSG is carbonate‐dominated, whereas towards the basin centre, it becomes increasingly halite‐dominated, a trend observed in the UK sector of the North Sea Basin and in other ancient salt giants. However, we also document abrupt, large magnitude compositional and thickness variations adjacent to large, intra‐basin normal faults; for example, thin, carbonate‐dominated successions occur on fault‐bounded footwall highs, whereas thick, halite‐dominated successions occur only a few kilometres away in adjacent depocentres. It is presently unclear if this variability reflects variations in syn‐depositional relief related to flooding of an underfilled presalt (Early Permian) rift or syn‐depositional (Lopingian) rift‐related faulting. Irrespective of the underlying controls, variations in salt composition and thickness influenced the Middle Jurassic‐to‐Early Cretaceous rift structural style, with diapirism characterising hangingwall basins where autochthonous salt was thick and halite‐rich and salt‐detached normal faulting occurring on the basin margins and on intra‐basin structural highs where the salt was too thin and/or halite‐poor to undergo diapirism. This variability is currently not captured by existing tectono‐stratigraphic models largely based on observations from salt‐free rifts and, we argue, mapping of suprasalt structural styles may provide insights into salt composition and thickness in areas where boreholes are lacking or seismic imaging is poor.  相似文献