鼓丘和巨型冰川线理的冰川摩擦学:剥蚀和沉积的争论之谜得到解决?     

周维维  Nick EYLES  Shane SOOKHAN  Niko PUTKINEN 《地质学报》2021,95(8):2306-2317

冰流是指冰盖中快速流动(高达10 km/a)的区域.冰流通常长达1000 km,宽200 km,嵌入在冰盖中.沿其流动方向形成了低幅度波纹状基岩床.这些波纹状基岩床由一些高度拉伸的沿着流向呈平行状分布的脊和沟槽(巨型冰川线理)组成.这些巨型冰川线理在空间上继承自体积大、拉伸程度低的鼓丘.由于鼓丘核部的地质条件复杂多变且不存在特征性的岩相,同时很难直接观察到现代冰盖下鼓丘的形成,因而鼓丘的起源在世界上仍然是未解之谜.基于新的高分辨率(0.5 m)LiDAR数据绘制的地形图和对更新世古冰流岩床进行野外地质考察表明,鼓丘和巨型冰川线理是底形连续体(后者由前者演化而来).它们由基岩或部分岩石和早期较老的沉积物组成,基于此部分学者提出了鼓丘的侵蚀起源说.本文重点介绍了类似鼓丘和巨型冰川线理的椭圆-流线型和带有沟槽的表面,这些表面广泛形成于多种非冰川的地质环境中(无论是在地球上还是在火星上),它们是由于受限剪切作用下颗粒状碎屑对基底面的磨损所产生的.变质核杂岩中的大型滑脱断层和俯冲带巨型逆冲断层的表面显示出槽状表面,其形状和规模能够与巨型冰川线理相类比.多尺度的断层面上都表现出了逐渐消除的类似鼓丘状的"椭圆形凸起",形成带凹槽的岩石光滑面,从而减少了阻力并允许继续滑动.现代冰流岩床记录的冰下地震的独特"纹理"与凹槽内基底面遭受的局部侵蚀和剪切一致,冰下地貌特征加强了与断层运动学的联系.火山碎屑流、陨石撞击坑周围的溅射毯以及滑坡和块体搬运沉积体系的滑动,它们的下垫面都会形成类似巨型冰川线理的沟槽.在人造和生物材料的摩擦接触表面上,也可以重现这些由粒状"磨损碎屑"(被定义为"第三层")切割形成的类似鼓丘的椭圆形凸起和类似巨型冰川线理的沟槽表面.因此,我们提议将鼓丘和巨型冰川线理作为冰川动力学研究的相关组成部分,可以称之为"磨损痕迹"或者"流向剪切痕".它们是由于不同的冰流速度拖曳粗颗粒的变形冰碛物切割底面(沉积物或者岩石(或其他岩相组合))形成的.地学界颇具争议的鼓丘-冰川线理成因谜团已逐渐清晰.  相似文献   

Area studies,asian studies,and the pacific basin          下载免费PDF全文

Shane J. Barter 《Geographical review》2015,105(1):105-119

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Range extension of two invasive crab species in eastern Australia: Carcinus maenas (Linnaeus) and Pyromaia tuberculata (Lockington)     

Ahyong ST 《Marine pollution bulletin》2005,50(4):460-462

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Millennial timescale resolution of rhyolite magma recharge at Tarawera volcano: insights from quartz chemistry and melt inclusions   总被引：4，自引：4，他引：0  

Phil Shane  Victoria C. Smith  Ian Nairn 《Contributions to Mineralogy and Petrology》2008,156(3):397-411

Most rhyolite eruption episodes of Tarawera volcano have emitted several physiochemically distinct magma batches (∼1–10 km³). These episodes were separated on a millennial timescale. The magma batches were relatively homogeneous in temperature and composition at pumice scale (>4 cm), but experienced isolated crystallisation histories. At the sub-cm scale, matrix glasses have trace element compositions (Sr, Ba, Rb) that vary by factors up to 2.5, indicating incomplete mixing of separate melts. Some quartz-hosted melt inclusions are depleted in compatible trace elements (Sr, Ti, Ba) compared to enclosing matrix glasses. This could reflect re-melting of felsic crystals deeper in the crystal pile. Individual quartz crystals display a variety of cathodoluminescence brightness and Ti zoning patterns including rapid changes in melt chemistry and/or temperature (∼50–100°C), and point to multi-cycle crystallisation histories. The Tarawera magma system consisted of a crystal-rich mass containing waxing and waning melt pockets that were periodically recharged by silicic melts driven by basaltic intrusion. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Canadian Shield brine from the Con Mine, Yellowknife, NT, Canada: Noble gas evidence for an evaporated Palaeozoic seawater origin mixed with glacial meltwater and Holocene recharge     

Shane Greene  Nick Battye  Ian Clark  Tom Kotzer  Dennis Bottomley 《Geochimica et cosmochimica acta》2008,72(16):4008-4019

Dissolved noble gas concentrations were measured in high salinity (270 g/L) Ca(Na)-Cl groundwaters from the Con Mine, Yellowknife, Canada in an effort to discriminate between two possible origins, as either a brine generated by evaporative enrichment in a Paleozoic inland sea, or marine water concentrated by freezing during glacial times. Major ion and isotope geochemistry indicate that brines from the deepest level remain relatively undisturbed by mixing with modern water introduced by mining. Mixing calculations are used to quantify fractions of brine, glacial meltwater and modern water. From this, noble gas concentrations were corrected for excess air with Ne and normalized to 100% brine solution. Over-pressuring of helium and argon in the brine provide age constraints based on the accumulation of geogenic ⁴He and ⁴⁰Ar. Radiogenic age calculations together with the local geological history suggest brine emplacement during early Palaeozoic time, likely during the Devonian when evaporitic inland seas existed in this region. The concentrations of the atmospherically derived noble gases in the brine fraction (Kr = 1.4E-8, Xe = 8.5E-10 cc_STP/cc_H2O) are close to atmospheric equilibrium for brine at 25 °C (Kr = 7.3E-9, Xe = 8.0E-10 cc_STP/cc_H2O), but are far lower than would be expected for closed-system concentration of seawater by freezing (Kr = 2.8E-6, Xe = 4.2E-7 cc_STP/cc_H2O). Thus, despite the complicated mixing history of the brine, the atmospheric and geogenic noble gases provide strong evidence for an origin as air-equilibrated brine from evaporated Paleozoic seawater, which infiltrated via density displacement through existing fractures and faults into the Canadian Shield.  相似文献   

Predicting the effects of shade on water temperature in small streams     

J. Christopher Rutherford  Shane Blackett  Colin Blackett  Laurel Saito  Robert J. Davies‐Colley 《新西兰海洋与淡水研究杂志》2013,47(5):707-721

A computer model for stream water temperature was developed, and tested in a small pasture stream near Hamilton, New Zealand. The model quantifies shading by riparian vegetation, hillsides, and stream banks using three coefficients: canopy angle, topography angle, and canopy shade factor. Shade was measured directly and found to vary significantly along the channel. Using the maximum measured shade, a close match was achieved between observed and predicted daily maximum and minimum water and bed sediment temperature. Model predictions of incoming and outgoing long‐wave radiation flux closely matched measurements, but there were unexplained discrepancies in short‐wave radiation flux. Model predictions indicate that moderate shade levels (c. 70%) may be sufficient in temperate climates to restore headwater pasture stream temperatures to 20°C, an estimate of the thermal tolerance for sensitive invertebrates.  相似文献   

Biodegradation of petroleum products in experimental plots in Antarctic marine sediments is location dependent     

Powell SM  Harvey PM  Stark JS  Snape I  Riddle MJ 《Marine pollution bulletin》2007,54(4):434-440

Clean sediment collected from O'Brien Bay, East Antarctica, was artificially contaminated with a mix of Special Antarctic Blend diesel fuel and lubricating oil and deployed in two uncontaminated locations (O'Brien and Sparkes Bays) and a previously contaminated bay (Brown Bay) to evaluate whether a history of prior contamination would influence the biodegradation process. Detailed analysis of the hydrocarbon composition in the sediment after 11 weeks revealed different patterns of degradation in each bay. Biodegradation indices showed that hydrocarbon biodegradation occurred in all three bays but was most extensive in Brown Bay. This study shows that even within a relatively small geographical area, the longevity of hydrocarbons in Antarctic marine sediments can be variable. Our results are consistent with faster natural attenuation of spilt oil at sites with previous exposure to oil but further work is needed to confirm this. Such information would be useful when evaluating the true risk and longevity of oils spills.  相似文献   

Deep Impact: Optical spectroscopy and photometry obtained at MIRA     

Russell G. Walker  Wm. Bruce Weaver  W.W. Shane  Arthur Babcock 《Icarus》2007,187(1):285-295

We present spectroscopic and photometric observations, spanning the optical UV to the far red, before, during, and after the NASA Deep Impact event of July 4, 2005. The inner 2000 km of the pre- and post-impact coma was about 0.3 magnitude redder in B-R than in the outer coma. The pre-impact spectrum was a faint reflected solar spectrum dominated by molecular emissions extending >40,000 km from the nucleus. The post-impact light curve in R and I showed a rapid rise consistent with an expanding optically thick cloud during the first 18 min after impact. During the next 8 min the cloud became optically thin. Sixty minutes after impact the impact R-band flux reached a plateau at , the comet brightening by a factor of ∼4.3 above its pre-impact value observed in a 15″ aperture. The mean expansion velocity of the grains during the first 49 min was . The spectrum became dominated by scattered sunlight during the first hour after impact. The volume scattering function (VSF) observed 32 min after impact shows strong reddening. At 49 min, however, the VSF shows an additional twofold increase in the blue but only a 20% increase at 5500 Å. Post-impact spectra and R-I photometry showed rapid reddening. The particle size distribution, dominated by 1-2.5 μm particles shortly after impact, changed dramatically during the first hour due to sublimation of water-ice particles of this size. On the night following impact the comet was still substantially brighter than before impact, but R-I had returned to its pre-impact value. B-R remained significantly redder. The ejecta 25 h after impact was fan-shaped subtending ∼180° roughly symmetrical about position angle 225°. The mean expansion velocity 90° from the direction to the Sun was .  相似文献   

Construction of the North Head (Maungauika) tuff cone: a product of Surtseyan volcanism,rare in the Auckland Volcanic Field,New Zealand     

Javier Agustín-Flores  Károly Németh  Shane J. Cronin  Jan M. Lindsay  Gábor Kereszturi 《Bulletin of Volcanology》2015,77(2):1-17

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On Selection of Analog Volcanoes     

Armando Rodado  Mark Bebbington  Alasdair Noble  Shane Cronin  Gill Jolly 《Mathematical Geosciences》2011,43(5):505-519

Estimating the occurrence probability of volcanic eruptions with VEI ??3 is challenging in several aspects, including data scarcity. A?suggested approach has been to use a simple model, where eruptions are assumed to follow a Poisson process, augmenting the data used to estimate the eruption onset rate with that from several analog volcanoes. In this model the eruption onset rate is a random variable that follows a gamma distribution, the parameters of which are estimated by an empirical Bayes analysis. The selection of analog volcanoes is an important step that needs to be explicitly considered in this model, as we show that the analysis is not always feasible due to the required over-dispersion in the resulting negative binomial distribution for the numbers of eruptions. We propose a modification to the method which allows for both over-dispersed and under-dispersed data, and permits analog volcanoes to be chosen on other grounds than mathematical tractability.  相似文献