Shear band evolution and accumulated microstructural development in Cosserat media   总被引：1，自引：0，他引：1  

A. Tordesillas  J. F. Peters  B. S. Gardiner 《国际地质力学数值与分析法杂志》2004,28(10):981-1010

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The Geochemical Evolution of Riparian Ground Water in a Forested Piedmont Catchment   总被引：2，自引：0，他引：2  

Douglas A. Burns  L. Niel Plummer  Jeffrey J. McDonnell    Eurybiades Busenberg  Gerolamo C. Casile  Carol Kendall  Richard P. Hooper  James E. Freer  Norman E. Peters  Keith Beven  Peter Schlosser 《Ground water》2003,41(7):913-925

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Evolution of the West Andean Escarpment at 18°S (N. Chile) during the last 25 Ma: uplift, erosion and collapse through time     

Gerhard Wrner  Dieter Uhlig  Ingrid Kohler  Hartmut Seyfried 《Tectonophysics》2002,345(1-4)

The geological record of the Western Andean Escarpment (WARP) reveals episodes of uplift, erosion, volcanism and sedimentation. The lithological sequence at 18°S comprises a thick pile of Azapa Conglomerates (25–19 Ma), an overlying series of widespread rhyodacitic Oxaya Ignimbrites (up to 900 m thick, ca. 19 Ma), which are in turn covered by a series of mafic andesite shield volcanoes. Between 19 and 12 Ma, the surface of the Oxaya Ignimbrites evolved into a large monocline on the western slope of the Andes. A giant antithetically rotated block (Oxaya Block, 80 km×20 km) formed on this slope at about 10–12 Ma and resulted in an easterly dip and a reversed drainage on the block's surface. Morphology, topography and stratigraphic observations argue for a gravitational cause of this rotation. A “secondary” gravitational collapse (50 km³), extending 25 km to the west occurred on the steep western front of the Oxaya Block. Alluvial and fluvial sediments (11–2.7 Ma) accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall, indicating further shortening between 8 and 6 Ma. Flatlying Upper Miocene sediments (<5.5 Ma) and the 2.7 Ma Lauca–Peréz Ignimbrite have not been significantly shortened since 6 Ma, suggesting that recent uplift is at least partly caused by regional tilting of the Western Andean slope.  相似文献   

Spin-cast ZERODUR mirror substrates of the 8 m class and lightweight substrates for secondary mirrors     

Hartmut W. Hoeness  Rudolf Mueller  Erich W. Rodeck  Friedrich B. Siebers 《Astrophysics and Space Science》1989,160(1-2):193-197

For about 20 years SCHOTT has been supplying the glass ceramic ZERODUR, a material with very low thermal expansion. Besides many other applications, ZERODUR is excellently suited for the manufacture of mirror substrates for telescopes. About 80% of all telescopes in the western world with mirror diameters >1.8 m have been equipped with ZERODUR during the last 10 years. The development of modern astronomical telescopes is aimed at larger primary mirrors and lighter secondary mirrors.New techniques have been developed by SCHOTT for manufacture of thin monolithic mirror blanks of more than 8 m in diameter. The development of thin meniscus shaped shells using the spin-casting technique was successfully completed last year. During a test production several mirror substrates up to 4.1 m in diameter and down to 57 mm in thickness could be produced. The know-how has been acquired for the fabrication of mirror substrates of more than 8 m in diameter by the spin-casting technique.SCHOTT has also performed considerable developmental work in the field of lightweighted ZERODUR mirror substrates which can be generated using different techniques: forming of the lightweighted structure during casting, fusion of individual components to a total structure and lightweighting of a massive block by various mechanical machining methods.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.Registered trademark of SCHOTT Glaswerke, Mainz.  相似文献   

Compositional variability of ice‐rafted debris in Heinrich layers 1 and 2 on the northwest European continental slope identified by environmental magnetic analyses     

John Walden  Emilie Wadsworth  William E. N. Austin  Clare Peters  James D. Scourse  Ian R. Hall 《第四纪科学杂志》2007,22(2):163-172

The composition of ice‐rafted debris (IRD) within a sediment core from the European continental slope (core OMEX‐2K; 49° 5′ N, 13° 26′ W) has been examined using environmental magnetic analyses. The data demonstrate compositional variability of the IRD within Heinrich layers 2 (H2) and 1 (H1) and these differences are most readily explained by changes in the contribution of different IRD sources to the core site. Some IRD within the main Heinrich layers show magnetic signatures that are similar to IRD derived from the Laurentide ice sheet found in cores from within the main North Atlantic IRD‐belt. In contrast, other IRD‐rich layers, both prior to and within the main Heinrich layers, demonstrate different magnetic behaviour, suggesting a contribution from a non‐Laurentide sourced IRD, most likely derived from ice streams discharging from northeast Atlantic ice sheets such as the British and Fennoscandian ice sheets. These data are consistent with published compositional data from the same core and, given the rapid, highly sensitive and non‐destructive nature of the method, suggest that environmental magnetic analysis has considerable potential for characterising IRD materials within Heinrich layers for the purposes of defining provenance. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Distribution and sedimentary characteristics of tsunami deposits along the Cascadia margin of western North America   总被引：1，自引：0，他引：1  

Robert Peters  Bruce Jaffe  Guy Gelfenbaum 《Sedimentary Geology》2007,200(3-4):372-386

Tsunami deposits have been found at more than 60 sites along the Cascadia margin of Western North America, and here we review and synthesize their distribution and sedimentary characteristics based on the published record. Cascadia tsunami deposits are best preserved, and most easily identified, in low-energy coastal environments such as tidal marshes, back-barrier marshes and coastal lakes where they occur as anomalous layers of sand within peat and mud. They extend up to a kilometer inland in open coastal settings and several kilometers up river valleys. They are distinguished from other sediments by a combination of sedimentary character and stratigraphic context. Recurrence intervals range from 300–1000 years with an average of 500–600 years. The tsunami deposits have been used to help evaluate and mitigate tsunami hazards in Cascadia. They show that the Cascadia subduction zone is prone to great earthquakes that generate large tsunamis. The inclusion of tsunami deposits on inundation maps, used in conjunction with results from inundation models, allows a more accurate assessment of areas subject to tsunami inundation. The application of sediment transport models can help estimate tsunami flow velocity and wave height, parameters which are necessary to help establish evacuation routes and plan development in tsunami prone areas.  相似文献   

Sedimentary rock-hosted Au deposits of the Dian–Qian–Gui area, Guizhou, and Yunnan Provinces, and Guangxi District, China     

Stephen G. Peters  Huang Jiazhan  Li Zhiping  Jing Chenggui 《Ore Geology Reviews》2007,31(1-4):170

Sedimentary rock-hosted Au deposits in the Dian–Qian–Gui area in southwest China are hosted in Paleozoic and early Mesozoic sedimentary rocks along the southwest margin of the Yangtze (South China) Precambrian craton. Most deposits have characteristics similar to Carlin-type Au deposits and are spatially associated, on a regional scale, with deposits of coal, Sb, barite, As, Tl, and Hg. Sedimentary rock-hosted Au deposits are disseminated stratabound and(or) structurally controlled. The deposits have many similar characteristics, particularly mineralogy, geochemistry, host rock, and structural control. Most deposits are associated with structural domes, stratabound breccia bodies, unconformity surfaces or intense brittle–ductile deformation zones, such as the Youjiang fault system. Typical characteristics include impure carbonate rock or calcareous and carbonaceous host rock that contains disseminated pyrite, marcasite, and arsenopyrite—usually with μm-sized Au, commonly in As-rich rims of pyrite and in disseminations. Late realgar, orpiment, stibnite, and Hg minerals are spatially associated with earlier forming sulfide minerals. Minor base–metal sulfides, such as galena, sphalerite, chalcopyrite, and Pb–Sb–As–sulphosalts also are present. The rocks locally are silicified and altered to sericite–clay (illite). Rocks and(or) stream-sediment geochemical signatures typically include elevated concentrations of As, Sb, Hg, Tl, and Ba. A general lack of igneous rocks in the Dian–Qian–Gui area implies non-pluton-related, ore forming processes. Some deposits contain evidence that sources of the metal may have originated in carbonaceous parts of the sedimentary pile or other sedimentary or volcanic horizons. This genetic process may be associated with formation and mobilization of petroleum and Hg in the region and may also be related to As-, Au-, and Tl-bearing coal horizons. Many deposits also contain textures and features indicative of strong structural control by tectonic domes or shear zones and also suggest syndeformational ore deposition, possibly related to the Youjiang fault system. Several sedimentary rock-hosted Au deposits in the Dian–Qian–Gui area also are of the red earth-type and Au grades have been concentrated and enhanced during episodes of deep weathering.  相似文献   

The stress dependent elastic properties of thermally induced microfractures in aeolian Rotliegend sandstone     

Colin MacBeth  Hartmut Schuett 《Geophysical Prospecting》2007,55(3):323-332

The impact of thermally induced microfractures on the stress‐sensitive elastic wave properties of aeolian Rotliegend sandstone samples is analysed. It is found that to identify the effects of the microfracture contribution accurately, a correction must first be made to account for water loss (representing a mass loss of 4–6%) from the pore throats and clays due to the heating process, despite care being taken to ensure that the thermally fractured samples re‐adsorb room moisture. Both the original and thermally fractured rocks are stress‐sensitive at the ultrasonic wave frequencies of the laboratory. However, a distinct shift in the estimated distribution of internal rock compliance indicates that the population of thermal microfractures differs in nature from that caused solely by core‐plug extraction damage. In particular, the ratio of normal to tangential compliance is observed to be higher for the thermally generated microfractures than for the broken grain‐grain contacts created by extraction unloading. This can be explained by the intragranular thermal‐fracture surfaces being smoother when compared to the intergranular boundaries. Mechanical hysteresis is observed between the up‐ and downgoing test cycles for both the original and, to a greater extent, the thermally fractured rock. This indicates that there is compaction‐induced movement of the fractures in the samples during application of stress in the laboratory.  相似文献   

A Search for Variability in the HCCN to H2CO Ratio in Comet Hale-Bopp     

M. D. Hofstadter  P. Hartogh  J. P. McMullin  R. N. Martin  C. Jarchow  W. Peters 《Earth, Moon, and Planets》1997,78(2):53-61

We observed submillimeter lines of H₂CO and HCN in comet Hale-Bopp near perihelion. One of our goals was to search for short term variability. Our observations are suggestive, but not conclusive, of temporal and/or spatial changes in the coma's HCN/H₂CO abundance ratio of ～25%. If due to spatial variability, the ratio on the sunward side of the coma is enhanced over other regions. If due to temporal variability, we find the bulk ratio in the coma changed in less than 16 hours.  相似文献   

The photospheric barium spectrum: Solar abundance and collision broadening of Baii lines by hydrogen     

Hartmut Holweger  Edith A. Müller 《Solar physics》1974,39(1):19-30

A study of the solar Ba ii spectrum leads to a solar abundance of barium of log ba = = 2.11±0.12, on the scale log h = 12. The observed asymmetry of the resonance line 4554 is consistent with an isotopic abundance ratio equal to the terrestrial one. The meteoritic Ba/Si abundance ratio found in carbonaceous chondrites appears to exceed the solar ratio by 0.1 to 0.2 dex (Section 5).The broadening by collisions with hydrogen atoms is determined from the solar spectrum (Section 4). Damping half-widths, h, of the three stronger Ba ii lines turn out to be larger by a factor of about 3.0 than predicted from pure van der Waals interaction of dipoles. Departures from LTE appear to be present in the cores of the resonance lines and of the lines arising from the metastable 5D levels (Section 6). The equivalent widths, however, remain practically unaffected.Equivalent widths of neutral barium lines are predicted and some new identifications of photospheric Ba i lines are suggested (Section 7).  相似文献