Geophysical consequences of planetary-scale impacts into a Mars-like planet     

Margarita M. Marinova  Oded Aharonson 《Icarus》2011,211(2):960-8

All planetary bodies with old surfaces exhibit planetary-scale impact craters: vast scars caused by the large impacts at the end of Solar System accretion or the late heavy bombardment. Here we investigate the geophysical consequences of planetary-scale impacts into a Mars-like planet, by simulating the events using a smoothed particle hydrodynamics (SPH) model. Our simulations probe impact energies over two orders of magnitude (2 × 10²⁷-6 × 10²⁹ J), impact velocities from the planet’s escape velocity to twice Mars’ orbital velocity (6-50 km/s), and impact angles from head-on to highly oblique (0-75°). The simulation results confirm that for planetary-scale impacts, surface curvature, radial gravity, the large relative size of the impactor to the planet, and the greater penetration of the impactor, contribute to significant differences in the geophysical expression compared to small craters, which can effectively be treated as acting in a half-space. The results show that the excavated crustal cavity size and the total melt production scale similarly for both small and planetary-scale impacts as a function of impact energy. However, in planetary-scale impacts a significant fraction of the melt is sequestered at depth and thus does not contribute to resetting the planetary surface; complete surface resetting is likely only in the most energetic (6 × 10²⁹ J), slow, and head-on impacts simulated. A crater rim is not present for planetary-scale impacts with energies >10²⁹ J and angles ?45°, but rather the ejecta is more uniformly distributed over the planetary surface. Antipodal crustal removal and melting is present for energetic (>10²⁹ J), fast (>6 km/s), and low angle (?45°) impacts. The most massive impactors (with both high impact energy and low velocity) contribute sufficient angular momentum to increase the rotation period of the Mars-sized target to about a day. Impact velocities of >20 km/s result in net mass erosion from the target, for all simulated energies and angles. The hypothesized impact origin of planetary structures may be tested by the presence and distribution of the geochemically-distinct impactor material.  相似文献   

New result of the seismic facies analysis of the Quaternary deposits in the western Atlantic     

O. V. Levchenko  I. O. Murdmaa  E. V. Ivanova  A. D. Mutovkin  E. V. Blinova  D. G. Borisov  S. A. Dremuchev  S. M. Isachenko  N. P. Konstantinova  L. V. Lapidus  Yu. G. Marinova  A. V. Firstova  T. N. Frantseva  V. V. Yutsis 《Doklady Earth Sciences》2014,458(2):1256-1260

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Geologic evolution of the Donguinyó-Huichapan caldera complex,central Mexican Volcanic Belt,Mexico     

Gerardo J. Aguirre-Díaz  Margarita López-Martínez 《Journal of Volcanology and Geothermal Research》2009,179(1-2):133-148

The Donguinyó-Huichapan caldera complex is located 110 km to the NNW of Mexico City, in the central sector of the Mexican Volcanic Belt. It is a 10 km in diameter complex apparently with two overlapping calderas, each one related to an ignimbrite sequence that contrasts in composition, mineralogy, welding, distribution, and physical aspect. The geologic evolution of this complex includes the following phases, 1) A first caldera formed at 5.0 ± 0.3 Ma, with the eruption of several discrete pulses of andesitic to trachydacitic pyroclastic flows that produced a series of densely welded ignimbrites; 2) At 4.6 ± 0.3 Ma, several small shield volcanoes and cinder cones built the rim of this caldera and erupted basaltic-andesite and andesitic lava flows; 3) At 4.2 ± 0.2 Ma, a second caldera was formed associated to the eruption of the Huichapan Tuff, which is a rhyolitic pyroclastic sequence consisting of minor unwelded ignimbrites, pumice fall and surge deposits, and a voluminous welded ignimbrite; 4) Also yielding an age of 4.2 ± 0.2 Ma, several trachydacitic lava domes were extruded along the new ring fracture and formed the rim of the Huichapan caldera, as well as five intra-caldera domes of dacitic and trachydacitic composition. Peripheral volcanism includes a large 2.5 ± 0.1 Ma shield volcano that was emplaced on the Huichapan caldera rim.The two calderas that form the Donguinyó-Huichapan complex have contrasting differences in volcanic styles that were apparently due to their differences in composition. Products erupted by the Donguinyó caldera are basaltic-andesite to trachydacitic in composition, whereas Huichapan caldera products are all high-silica rhyolites.  相似文献   

Permafrost-associated natural gas hydrate occurrences on the Alaska North Slope   总被引：7，自引：0，他引：7  

Timothy S. Collett  Myung W. LeeWarren F. Agena  John J. MillerKristen A. Lewis  Margarita V. ZyrianovaRay Boswell  Tanya L. Inks 《Marine and Petroleum Geology》2011,28(2):279-294

In the 1960s Russian scientists made what was then a bold assertion that gas hydrates should occur in abundance in nature. Since this early start, the scientific foundation has been built for the realization that gas hydrates are a global phenomenon, occurring in permafrost regions of the arctic and in deep water portions of most continental margins worldwide. In 1995, the U.S. Geological Survey made the first systematic assessment of the in-place natural gas hydrate resources of the United States. That study suggested that the amount of gas in the gas hydrate accumulations of northern Alaska probably exceeds the volume of known conventional gas resources on the North Slope. Researchers have long speculated that gas hydrates could eventually become a producible energy resource, yet technical and economic hurdles have historically made gas hydrate development a distant goal. This view began to change in recent years with the realization that this unconventional resource could be developed with existing conventional oil and gas production technology. One of the most significant developments was the completion of the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well on the Alaska North Slope, which along with the Mallik project in Canada, have for the first time allowed the rational assessment of gas hydrate production technology and concepts. Almost 40 years of gas hydrate research in northern Alaska has confirmed the occurrence of at least two large gas hydrate accumulations on the North Slope. We have also seen in Alaska the first ever assessment of how much gas could be technically recovered from gas hydrates. However, significant technical concerns need to be further resolved in order to assess the ultimate impact of gas hydrate energy resource development in northern Alaska.  相似文献   

Large-scale tracer profiles in a deep claystone formation (Opalinus Clay at Mont Russelin,Switzerland): Implications for solute transport processes and transport properties of the rock     

Margarita Koroleva  Peter Alt-Epping  Martin Mazurek 《Chemical Geology》2011,280(3-4):284-296

Natural tracers (Cl^? and stable water isotopes) in pore water of the Opalinus Clay and adjacent formations were studied in the motorway tunnel at Mont Russelin, Switzerland. The Opalinus Clay occurs in the core of an anticline which is cut by a complex system of thrust faults. Concentration profiles of natural tracers were taken from 17 boreholes along a 363 m long section. Pore waters of drillcore samples were analysed with indirect and direct methods. The Cl^? and stable water isotope distribution in the pore water shows a regular and well defined profile, with a conspicuous decrease towards the overlying Dogger limestone aquifer. The highest Cl^? values (approximately 23,000 mg/L) are found in the core of the anticline in Liassic claystones underlying the Opalinus Clay. To quantify the large-scale transport properties of the Opalinus Clay formation, a 2D transport model was constructed and used to reproduce the observed concentration profiles. The calculations indicate that the observed tracer distributions are consistent with diffusion as the dominant transport process. Groundwater flow in the overlying Dogger aquifer was initiated about 2–4 Ma ago, which is long after the folding of the Jura Mountains and probably coincides with the exposure of the aquifer to freshwater recharge following continued erosion of the anticline. The calculations suggest that tracer distributions are controlled by 1) the timing of freshwater recharge in the overlying limestone aquifer, 2) the shape of the anticline and 3) the magnitude and the anisotropy ratio of diffusion coefficients.  相似文献   

Tectonics of the Ninety-East Ridge     

O. V. Levchenko  I. M. Sborshchikov  Yu. G. Marinova 《Oceanology》2014,54(2):231-244

New multibeam bathymetry data and multichannel seismic profiles over 7 detailed survey sites collected during cruise no. KNOXRR06 of the R/V Rodger Revelle in 2007 fundamentally expanded the concepts about the structure of the sedimentary cover of the Ninety-East Ridge, which were based on the results of previous studies. They allow making a step forward in interpreting the nature of the unconformities and deformations. The deformation pattern of the sedimentary cover suggests three stages of tectonic activity over the ridge during the Paleocene, Eocene, and Late Miocene. As suggested by the high present-day seismicity, the last stage might continue to the present time. In addition, indirect criteria indicate young intraplate volcanism at the last stage. New data is reviewed in the context of two models of the ridge formation. The first model follows a well-known concept of the ridge representing a trace of the Kerguelen hotspot. The second one relates large outflows of basalts to the development of a giant fracture under conditions of global extension, which continued later during the sedimentary cover formation. Additional integrated geological and geophysical studies are required for understanding the nature of this unique feature.  相似文献   

Dynamic hybrid terrain representation based on convexity limits identification     

Montserrat Bóo  Margarita Amor 《International journal of geographical information science》2013,27(4):417-439

Hybrid digital terrain models combine terrain data with different topologies and resolutions. Cartographic digital terrain models are typically composed of regular grid data that can be locally refined by adding a Triangulated Irregular Network (TIN) that represents morphologically complex terrain parts. Direct rendering of both datasets to visualize the digital terrain model generates discontinuities, as the meshes are disconnected. The utilization of complete/partial precomputed tessellation solutions solves the problem of quality, but limits the applicability of the representation to models with a fixed relative position between datasets. In this paper, we present a new scheme for hybrid terrain representation that permits the dynamic generation of the adaptive tessellation required to join the grid and TIN models. Our proposal permits the dynamic modification of the relative position between datasets. This increases the representation capabilities for those applications where this property is interesting as, for example, urban and landscape planning applications. The algorithm we propose is based on the identification of convex areas on the TIN and the efficient generation of triangles to join the models based on this convex structure. As a result, high quality models without discontinuities are obtained, increasing the flexibility of previous solutions based on fixed precomputations.  相似文献   

Modelling the impact of Black Sea water inflow on the North Aegean Sea hydrodynamics     

Margarita Tzali  Sarantis Sofianos  Anneta Mantziafou  Nikolaos Skliris 《Ocean Dynamics》2010,60(3):585-596

The impact of the Black Sea Water (BSW) inflow on the circulation and the water mass characteristics of the North Aegean Sea is investigated using a high-resolution 3D numerical model. Four climatological numerical experiments are performed exploring the effects of the exchange amplitude at the Dardanelles Straits in terms of the mean annual volume exchanged and the amplitude of its seasonal cycle. Larger inflow of low salinity BSW influences the water characteristics of the whole basin. The largest salinity reduction is encountered in the upper layers of the water column, and the most affected region is the northeastern part of the basin. The winter insulation character of the BSW layer (low-salinity layer) is reduced by the seasonal cycle of the inflow (minimum during winter). The maximum atmospheric cooling coincides with the minimum BSW inflow rate, weakening the vertical density gradients close to the surface and thus facilitating the vertical mixing. The inflow rate of BSW into the North Aegean Sea constitutes an essential factor for the circulation in the basin. Increased inflow rate results into considerably higher kinetic energy, stronger circulation and reinforcement of the mesoscale circulation features. Although the position of the front between BSW and waters of Levantine origin does not vary significantly with the intensity of the BSW inflow rate, the flow along the front becomes stronger and more unstable as the inflow rate increases, forming meanders and rings. The changes in the intensity of BSW inflow rate overpower the wind and thermohaline forcing and largely determine the general circulation of the North Aegean Sea.  相似文献   

Performance evaluation of underwater platforms in the context of space exploration     

A.L. Forrest  B.E. Laval  D.R. Williams  M.M. Marinova  A.L. Brady  M.L. Gernhardt 《Planetary and Space Science》2010,58(4):706-716

Robotic platforms are essential for future human planetary and lunar exploration as they can operate in more extreme environments with a greater endurance than human explorers. In this era of space exploration, a terrestrial analog that can be used for development of the coordination between manned and robotic vehicles will optimize the scientific return of future missions while concurrently minimizing the downtime of both human explorers and robotic platforms. This work presents the use of underwater exploratory robots - autonomous underwater vehicles (AUV), remotely operated vehicles (ROV), and manned submersibles - as analogues for mixed human-robot exploration of space. Subaqueous settings present diverse challenges for navigation, operation and recovery that require the development of an exploration model of a similar complexity as required for space exploration. To capitalize on the strengths of both robotic and human explorers this work presents lessons learnt with respect to the fields of human-robotic interface (HRI) and operator training. These are then used in the development of mission evaluation tools: (1) a task efficiency index (TEI), (2) performance metrics, and (3) exploration metrics. Although these independent evaluations were useful for specific missions, further refinement will be required to fully evaluate the strengths and capabilities of multiple platforms in a human-robotic exploration campaign in order to take advantage of unforeseen science opportunities in remote settings.  相似文献   

New Data on the Geology of Osborn Plateau,Indian Ocean     

Levchenko  O. V.  Marinova  Yu. G.  Portnyagin  M. V.  Werner  R.  Lobkovsky  L. I. 《Doklady Earth Sciences》2019,489(2):1469-1473

Doklady Earth Sciences - The Osborn Plateau is a large intraplate rise in the eastern part of the Indian Ocean, which has been poorly studied by the geological and geophysical methods. In cruise...  相似文献