The Lough Talt and Easky adamellites in the north-central Ox Mountains inlier were originally regarded as being nearly synchronous in age of emplacement with the more strongly deformed c. 480 Ma Ox Mountains granodiorite. They are now shown by Rb-Sr whole-rock dating to be significantly younger at c. 400 Ma. This recognition of the emplacement of late Silurian/early Devonian Newer Caledonian granites in the central Ox Mountains inlier indicates that the thermal overprinting by the adamellites of the regionally metamorphosed Ox Mountains succession is not an early Ordovician event. Earlier interpretations, using deformationai events and igneous intrusions, advanced by others to suggest that the Ox Mountains succession is pre-Caledonian are now greatly weakened since the deformationai sequence in the Ox Mountains succession is now known to span a longer period of time, ranging from Grampian (late Cambrian to early Ordovician) to Caledonian sensu stricto, and therefore leaves fewer events to have occurred prior to the early Ordovician emplacement of the Ox Mountains granodiorite. 相似文献
We estimate the losses due to 10 scenario earthquakes in 150 settlements of the United Arab Emirates (UAE). For southern Iran, we use four source zones and the maximum magnitudes in them as determined by GSHAP (7.2 M 8.1). For six local scenario earthquakes, we use the range 5.5 M 6.5, place the sources mainly on mapped faults and vary the distance to major cities from 10 to 60 km. In the test case of the Masafi earthquake (M5, 11 March 2002), the method and data bank we use yield the correct results, suggesting that our approach to the problem is valid for the UAE. The sources in Iran are expected to cause only minor damage, except for an M8.1 earthquake in the Makran region. For such an event we expect some deaths, several hundred injured and a loss of 3–6% of the value to the building stock in the northeastern UAE, including Oman. The losses for local scenarios with epicenters in the unpopulated areas of the UAE and for scenarios with M < 5.8 are estimated to be minor. Because the two major mapped faults run through several of the large cities, scenarios with short epicentral distances from cities have to be considered. Scenarios with M6 near cities lead to estimates of about 1000 ± 500 deaths, and several thousand injured. Most buildings are expected to be damaged to a moderate degree and the loss to buildings is estimated around 1/4of their value. If the magnitude should reach 6.5, the losses to humans and to building value could be staggering. These estimates are approximate because: (1) there exists no local seismograph network that could map active faults by locating microseismicity; (2) there exist no historically old buildings that could serve as tests for effects due to strong ground motion in the past; (3) there exist no microzonation of the subsurface properties in this region of unconsolidated building ground; (4) there exist no detailed inventory of building fragility. Nevertheless, our conclusion that there exists a substantial seismic risk in the UAE is reliable, because our method yields accurate results in the cases of earthquakes with known losses during the last several decades in the Middle East. 相似文献
A previously unsuspected source of fuel for the global firestorm recorded by soot in the Cretaceous–Tertiary impact layer
may have resided in methane gas associated with gas hydrate in the end-Cretaceous seafloor. End-Cretaceous impact-generated
shock and megawaves would have had the potential to initiate worldwide oceanic methane gas blow-outs from these deposits.
The methane would likely have ignited and incompletely combusted. This large burst of methane would have been followed by
longer-term methane release as a part of a positive thermal feedback in the disturbed ocean-atmosphere system.
Received: 16 September 1998 / revision received: 11 January 1999 相似文献
Phenocrysts of phlogopite from a micaceous kimberlite contain finely interlayered serpentine. These phenocrysts occur in the kimberlite groundmass and are altered along the mica layers and are slightly deformed. Lizardite is the predominant serpentine mineral, but chrysotile and mixed structures also occur. The lizardite occurs as lamellae within phlogopite, oriented such that (001) layers of the two minerals are parallel and the [100] direction of lizardite is parallel to the [100] or 110 directions of phlogopite. The serpentinized regions of phlogopite are localized and extensive along the (001) layers. Chrysotile fibers and chrysotile-like curled serpentine occur within regions of disrupted material, and polygonal structures occur in folded lizardite lamellae. Textural relations suggest three events: 1) replacement of phlogopite by lizardite, 2) deformation of the phenocrysts, and 3) partial transformation of the lizardite to chrysotile-like structures. Deformation features include openings along (001), folds, and regions of disrupted or broken material. The folded and broken material consists of lamellar lizardite and phlogopite, indicating that lamellar replacement preceded deformation. Intergrowths of lizardite and curled serpentine are associated with cleavage openings and voids in disrupted material, suggesting that a partial transformation of lizardite to chrysotile occurred within openings created by deformation. Clay minerals also occur within phlogopite as either a minor product of serpentinization or of late-stage alteration. 相似文献
A previously unsuspected source of fuel for the global firestorm recorded by soot in the Cretaceous–Tertiary impact layer may have resided in methane gas associated with gas hydrate in the end-Cretaceous seafloor. End-Cretaceous impact-generated shock and megawaves would have had the potential to initiate worldwide oceanic methane gas blow-outs from these deposits. The methane would likely have ignited and incompletely combusted. This large burst of methane would have been followed by longer-term methane release as a part of a positive thermal feedback in the disturbed ocean-atmosphere system. 相似文献
This study presents an innovative technique of executing soil nails called sectorized post grouting (SPG). The most utilized technique of soil nail grouting is gravity grouting, with the literature reporting advances in pressurized grouting. Although obtaining higher pullout resistance of soil nails, pressurized grouting, mostly done in single-stage grouting, does not compensate for exudation and its use in higher nail lengths is difficult. Thus, a technique has been developed that compensates for exudation, with easier application in lengthier nails. The technique was qualitatively assessed to evaluate its surface roughness and later applied in seven real soil nailing works, where it could be quantitatively assessed. The results show that sectorized post-grouted nails obtained greater pullout resistances than gravity grouted and single-stage grouted nails. Although similar improvement was found in tube-à-manchette (TAM) grouted nails, this method presents lower economic efficiency than sectorized post grouting. The pullout resistance results obtained in this study can be utilized in future soil nailing works executed utilizing SPG.
21-cm tomography is emerging as a promising probe of the cosmological dark ages and the epoch of reionization, as well as a tool for observational cosmology in general. However, serious sources of foreground contamination must be subtracted for experimental efforts to be viable. In this paper, we focus on the removal of unresolved extragalactic point sources with smooth spectra, and evaluate how the residual foreground contamination after cleaning depends on instrumental and algorithmic parameters. A crucial but often ignored complication is that the synthesized beam of an interferometer array shrinks towards higher frequency, causing complicated frequency structure in each sky pixel as 'frizz' far from the beam centre contracts across unresolved radio sources. We find that current-generation experiments should none the less be able to clean out this point source contamination adequately, and quantify the instrumental and algorithmic design specifications required to meet this foreground challenge. 相似文献