Effect of sea-level lowering on ELA depression during the LGM     

Brian Hanson  Roger LeB. Hooke 《Quaternary Research》2011,75(3):406-410

Decreases in equilibrium-line altitudes (ELAs) varied geographically during the last glacial maximum (LGM), with a mid-range value of ~ 900 m commonly deduced from altitude ratio and accumulation–area ratio calculations. Sea level, however, was 120 m lower during the LGM, so the ELA lowering relative to sea level would only be 780 m for a 900-m absolute lowering. With a lapse rate of 0.006°C m⁻¹, this implies a 4.7°C lowering of global temperature. It has been argued that this correction for sea-level change is unnecessary, but the logic on which this is based requires adiabatic compression to apply over much longer time scales than is typically invoked. We find that the correction is necessary. In addition, geometric changes in the atmosphere during the LGM, pointed out by Osmaston (2006), could lead to 0.4°C decrease in the average temperature of the troposphere. Additionally, orographic effects could significantly change the snow distribution on mountain masses near sea level.  相似文献   

Numerical computations of a theoretical model of ribbed moraine formation     

Michael Chapwanya  Chris D. Clark  Andrew C. Fowler 《地球表面变化过程与地形》2011,36(8):1105-1112

We develop numerical solutions of a theoretical model which has been proposed to explain the formation of subglacial bedforms. The model has been shown to have the capability of producing bedforms in two dimensions, when they may be interpreted as ribbed moraine. However, these investigations have left unanswered the question of whether the theory is capable of producing fully three‐dimensional bedforms such as drumlins. We show that, while the three‐dimensional calculations show realistic quasi‐three‐dimensional features such as dislocations in the ribbing pattern, they do not produce genuine three‐dimensional drumlins. We suggest that this inadequacy is due to the treatment of subglacial drainage in the theory as a passive variable, and thus that the three‐dimensional forms may be associated with conditions of sufficient subglacial water flux. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Carbonatite melt inclusions in coexisting magnetite,apatite and monticellite in Kerimasi calciocarbonatite,Tanzania: melt evolution and petrogenesis   总被引：1，自引：0，他引：1  

Tibor Guzmics  Roger H. Mitchell  Csaba Szabó  Márta Berkesi  Ralf Milke  Rainer Abart 《Contributions to Mineralogy and Petrology》2011,161(2):177-196

Kerimasi calciocarbonatite consists principally of calcite together with lesser apatite, magnetite, and monticellite. Calcite hosts fluid and S-bearing Na–K–Ca-carbonate inclusions. Carbonatite melt and fluid inclusions occur in apatite and magnetite, and silicate melt inclusions in magnetite. This study presents statistically significant compositional data for quenched S- and P-bearing, Ca-alkali-rich carbonatite melt inclusions in magnetite and apatite. Magnetite-hosted silicate melts are peralkaline with normative sodium-metasilicate. On the basis of our microthermometric results on apatite-hosted melt inclusions and forsterite–monticellite phase relationships, temperatures of the early stage of magma evolution are estimated to be 900–1,000°C. At this time three immiscible liquid phases coexisted: (1) a Ca-rich, P-, S- and alkali-bearing carbonatite melt, (2) a Mg- and Fe-rich, peralkaline silicate melt, and (3) a C–O–H–S-alkali fluid. During the development of coexisting carbonatite and silicate melts, the Si/Al and Mg/Fe ratio of the silicate melt decreased with contemporaneous increase in alkalis due to olivine fractionation, whereas the alkali content of the carbonatite melt increased with concomitant decrease in CaO resulting from calcite fractionation. Overall the peralkalinity of the bulk composition of the immiscible melts increased, resulting in a decrease in the size of the miscibility gap in the pseudoquaternary system studied. Inclusion data indicate the formation of a carbonatite magma that is extremely enriched in alkalis with a composition similar to that of Oldoinyo Lengai natrocarbonatite. In contrast to the bulk compositions of calciocarbonatite rocks, the melt inclusions investigated contain significant amount of alkalis (Na₂O + K₂O) that is at least 5–10 wt%. The compositions of carbonatite melt inclusions are considered as being better representatives of parental magma composition than those of any bulk rock.  相似文献   

Industrial relocation of Hong Kong manufacturing firms: towards an expanding industrial space beyond the Pearl river delta   总被引：2，自引：0，他引：2  

Haifeng Felix Liao  Roger C. K. Chan 《GeoJournal》2011,76(6):623-639

This paper explores the recent industrial relocation of Hong Kong manufacturing firms in the Pearl River Delta. Based on a combination of recent surveys, four in-depth case studies and nearly 20 firm interviews through the end of 2008, the paper argues that in response to a dynamic business environment in the region, some Hong Kong manufacturing firms in the PRD are forced to design new spatial strategies. The paper also identifies the different relocation strategies adopted by Hong Kong manufacturing firms, namely, total relocation, stratified relocation and “pseudo relocation”. The industrial space of Hong Kong manufacturing firms will be expanded beyond the PRD. In addition, the new round of relocation of Hong Kong manufacturers is a response to the initiative ushered in by the provincial and local governments in order to achieve the objectives of industrial upgrading, sustainable environment and regional balanced development.  相似文献   

Experiments on liquid immiscibility in silicate melts with H2O, P, S, F and Cl: implications for natural magmas     

G. W. Lester  A. H. Clark  T. K. Kyser  H. R. Naslund 《Contributions to Mineralogy and Petrology》2013,166(1):329-349

Isobaric (200 MPa) experiments have been performed to investigate the effects of H₂O alone or in combination with P, S, F or Cl on liquid-phase separation in melts in the systems Fe₂SiO₄–Fe₃O₄–KAlSi₂O₆–SiO₂, Fe₃O₄–KAlSi₂O₆–SiO₂ and Fe₃O₄–Fe₂O₃–KAlSi₂O₆–SiO₂ with or without plagioclase (An₅₀). Experiments were heated in a rapid-quench internally heated pressure vessel at 1,075, 1,150 or 1,200 °C for 2 h. Experimental fO₂ was maintained at QFM, NNO or MH oxygen buffers. H₂O alone or in combination with P, S or F increases the temperature and composition range of two-liquid fields at fO₂ = NNO and MH buffers. P, S, F and Cl partition preferentially into the Fe-rich immiscible liquid. Two-liquid partition coefficients for Fe, Si, P and S correlate well with the degree of polymerization of the SiO₂-rich liquid and plot on similar but distinct power-law curves compared with equivalent anhydrous or basaltic melts. The addition of 2 wt% S to the system Fe₃O₄–Fe₂O₃–KAlSi₂O₆–SiO₂ stabilizes three immiscible melts with Fe-, FeS- and Si-rich compositions. H₂O-induced suppression of liquidus temperatures in the experimental systems, considered with the effects of pressure on the temperature and composition ranges of two-liquid fields in silicate melts, suggests that liquid-phase separation may be stable in some H₂O-rich silicate magmas at pressures in excess of 200 MPa.  相似文献   

Refinement of the time-space evolution of the giant Mio-Pliocene Río Blanco-Los Bronces porphyry Cu–Mo cluster, Central Chile: new U–Pb (SHRIMP II) and Re–Os geochronology and 40Ar/39Ar thermochronology data     

Katja Deckart  Alan H. Clark  Patricio Cuadra  Mark Fanning 《Mineralium Deposita》2013,48(1):57-79

Representing one of the largest known (estimated >5 Gt at 1 % Cu and 0.02 % Mo) porphyry system, the Río Blanco-Los Bronces deposit incorporates at least five hypabyssal intrusive and hydrothermal centres, extending for about 5 km from the Río Blanco and Los Bronces mines in the north, through the Don Luis mine, to the Sur Sur mine, La Americana and Los Sulfatos in the south. The new geochronology data, which now include data on different molybdenite vein types, confirm the U–Pb ages of the pre-mineralisation intrusions but slightly increase their age range from 8.8 to 8.2 Ma. The distinct magmatic pulses of the mineralisation-associated porphyritic intrusives (Late Porphyries) indicate an age interval instead of the previously suggested individual ages: the quartz monzonite porphyry ranges from 7.7 to 6.1 Ma (Sur Sur 5.74?±?0.13 Ma), the feldspar porphyry shows an interval from 5.8 to 5.2 Ma and the Don Luis porphyry from 5.2 to 5.0 Ma. The new Re–Os data on distinct molybdenite vein types confirm the protracted history of Cu(–Mo) mineralisation, inferred previously. The vein development occurred at least from 5.94 to 4.50 Ma, indicating a time-span of 1.5 Ma for the hydrothermal activity. Hydrothermal minerals dated by the ⁴⁰Ar/³⁹Ar method are generally too young to record the age of early, high-temperature mineralisation. The majority of the ⁴⁰Ar/³⁹Ar data in the Río Blanco porphyry cluster record reheating by either the youngest member of the Late Porphyry suite or the post-mineralisation dacite or rhyolite plug formations at around 4.9–4.7 Ma.  相似文献   

Widespread overspill from a saline density‐current channel and its interaction with topography on the south‐west Black Sea shelf     

Richard N. Hiscott  Ali E. Aksu  Roger D. Flood  Vladimir Kostylev  Doğan Yaşar 《Sedimentology》2013,60(7):1639-1667

Seaward of the Bosphorus Strait, the south‐west Black Sea shelf is dominated by the world's largest channel network maintained by a quasi‐continuous saline (ca 35 → 31 psu) underflow. Calculations indicate that >85% of the initial discharge of ca 10⁴ m³s^?1 spills overbank before the shelf edge. This paper documents interaction of the overspill with sea bed topography using multibeam bathymetry, echo‐sounder images of the water column, conductivity–temperature–depth profiles and sediment cores. Overbank spill is widespread, particularly through crevasse channels and on the middle shelf where confinement by channel banks is negligible. Towards the outer shelf, the wind‐driven Rim Current advects mud along the shelf, contributing to levée successions and deposition on stoss sides of elongate transverse ridges. Echo‐sounder profiles reveal metre‐scale eddies over megaflutes, and breaking lee waves and internal hydraulic jumps over ridges. Megaflutes reach 600 m long and 7 m deep, yet form where the underflow, outside the flute, is no thicker than ca 2 to 5 m. Two types of elongate seaward‐facing ridges are recognized. Type 1 ridges, 2 to 5 m high, consist of bivalve‐rich muddy sand in low‐angle (3·5° to 6°) cross‐sets created by the underflow. Type 2 ridges, ca 5 m high, have crests up to 2 km long and a buried wedge‐shaped foundation (the ‘ridge‐core’) comprised of facies similar to Type 1 ridges. These ridge‐cores are blanketed on the landward side by stratified muds, and are capped by obliquely oriented ribs supporting a diverse benthic community. This facies distribution is interpreted to result from stoss‐side and lee‐side velocity and turbulence fluctuations induced by internal hydraulic jumps and breaking lee waves in overspilling portions of the underflow. Experimental results published by W.H. Snyder and co‐workers effectively explain ridge evolution and flow across the ridges, and therefore can be applied with confidence to less easily studied deep‐marine settings swept by turbidity currents.  相似文献   

Remote sensing and the search for surface rupture, Haiti 2010     

Roger Bilham  Eric Fielding 《Natural Hazards》2013,68(1):213-217

Minutes after the January 12, 2010 Haiti earthquake, most geologists and seismologists assumed that from its shallow teleseismic location and its largely strike-slip mechanism that a significant rupture must have occurred on the transform plate boundary south and west of Port au Prince. Within hours, plans were being made by geologists to map the anticipated rupture and, if possible, to trench it to obtain a record of paleoseismic slip. However, remote sensing images available a few days after the earthquake revealed raised corals and no significant plate boundary slip, and we now know that shallow slip was transpressive and that no surface rupture occurred. A week after the earthquake, it was clear that scientific visits to the region would be much delayed by the continuing needs of emergency response teams and military support who had commandeered access to the airport at Port au Prince. Serendipitously on 20 January, one of the authors accompanied a film crew on a chartered flight from nearby Santo Domingo with the quest to record the tectonic reasons for the disaster and to document the details of structural damage. At the time, there was still no clear idea of whether the transform boundary had a surface rupture, but there was abundant evidence for surface deformation from Google Earth images showing raised corals and collapsed coastlines along the Lêogáne coast. This article briefly describes communications between remote geologists and the ground-based crew who were guided to critical areas in the search for surface deformation using remote sensing data.  相似文献   

Strengthening Western Gondwanan correlations: A Brazilian Dicynodont (Synapsida,Anomodontia) in the Middle Triassic of Namibia     

Fernando Abdala  Claudia A. Marsicano  Roger M.H. Smith  Roger Swart 《Gondwana Research》2013,23(3):1151-1162

Terrestrial Middle Triassic strata occur throughout continental Africa and are particularly well exposed in South Africa, Tanzania, Zambia, and Namibia. The youngest age for all these African deposits is widely accepted as early Middle Triassic (Anisian). Fossils collected recently from the uppermost strata of the upper Omingonde Formation in Namibia highlighted the presence of Chiniquodon, a carnivorous cynodont previously only found in Ladinian-Carnian aged rocks of South America. In addition, work in progress indicates that a large archosaur, originally reported as Erythrosuchus, also discovered from levels close to the top of this unit, is in fact a rauisuchian, a group of archosaurs well known from Ladinian-Carnian beds of southern South America. Here we present the first record of the tuskless dicynodont Stahleckeria potens from the top of the upper Omingonde Formation in central Namibia. This taxon was up until now only known from the Ladinian Dinodontosaurus Assemblage Zone of the Santa Maria Formation in southern Brazil. Thus, compelling evidence for a Ladinian age for the upper levels of the upper Omingonde Formation is provided by two therapsid and one archosaur taxa. The tetrapod fauna of the upper Omingonde Formation partially fills the gap of the well-documented hiatus (Ladinian gap), prevalent throughout the Karoo basins of south and central Africa. The presence of the same therapsid taxa in the Namibian Waterberg Basin and the Paraná Basin of Brazil during Middle Triassic suggests that these basins were biogeographically linked through a series of interconnecting lowlands, with no major ecological, climatic and/or physical barriers.  相似文献   

Nature and degree of aqueous alteration in CM and CI carbonaceous chondrites     

Driss Takir  Joshua P. Emery  Harry Y. Mcsween Jr.  Charles A. Hibbitts  Roger N. Clark  Neil Pearson  Alian Wang 《Meteoritics & planetary science》2013,48(9):1618-1637

We investigated the petrologic, geochemical, and spectral parameters that relate to the type and degree of aqueous alteration in nine CM chondrites and one CI (Ivuna) carbonaceous chondrite. Our underlying hypothesis is that the position and shape of the 3 μm band is diagnostic of phyllosilicate mineralogy. We measured reflectance spectra of the chondrites under dry conditions (elevated temperatures) and vacuum (10^?8 to 10^?7 torr) to minimize adsorbed water and mimic the space environment, for subsequent comparison with reflectance spectra of asteroids. We have identified three spectral CM groups in addition to Ivuna. “Group 1,” the least altered group as determined from various alteration indices, is characterized by 3 μm band centers at longer wavelengths, and is consistent with cronstedtite (Fe‐serpentine). “Group 3,” the most altered group, is characterized by 3 μm band centers at shorter wavelengths and is consistent with antigorite (serpentine). “Group 2” is an intermediate group between group 1 and 3. Ivuna exhibits a unique spectrum that is distinct from the CM meteorites and is consistent with lizardite and chrysotile (serpentine). The petrologic and geochemical parameters, which were determined using electron microprobe analyses and microscopic observations, are found to be consistent with the three spectral groups. These results indicate that the distinct parent body aqueous alteration environments experienced by these carbonaceous chondrites can be distinguished using reflectance spectroscopy. High‐quality ground‐based telescopic observations of Main Belt asteroids can be expected to reveal not just whether an asteroid is hydrated, but also details of the alteration state.  相似文献