共查询到20条相似文献，搜索用时 31 毫秒
1.
Synoptic images of the Martian volcano Olympus Mons are of a quality and quantity that are unique for mars and, somewhat surprisingly, are appreciably better than image data that exist for many volcanoes on Earth. Useful information about the evolution of shield volcanoes on Earth can thus be derived from the investigation of this extraterrestrial example. We have used shadow-length measurements and photoclinometrically derived profiles to supplement and refine the topographic map of the Olympus Mons caldera. As much as 2.5 km of collapse took place within the 80×65 km diameter caldera and the elevation of the caldera rim varies by almost 2.0 km (low around the oldest collapse events, high around the youngest). An eight-stage evolutionary sequence for the caldera of Olympus Mons is identified which shows that caldera subsidence was a longterm process rather than the near-instantaneous event that has been interpreted from comparable terrestrial examples. Tectonic features on the caldera floor indicate a transition from an extensional environment (graben formation) around the perimeter of the caldera to compression (ridge formation) towards the caldera center. This transition from a compressional to extensional environment is surprisingly sudden, occurs at a radial distance of 17 km from the caldera center, and is import because it can be used to infer that the magma chamber was relatively shallow (thought to be at a depth of <16 km beneath the caldera floor; Zuber and Mouginis-Mark 1990). Ample evidence is also found within the Olympus Mons caldera for solidified lava lakes more than 30 km in width, and for the localzed overturning and/or withdrawal of lava within these lakes. 相似文献
2.
3.
J. Green 《Bulletin of Volcanology》1966,29(1):79-81
The most important lunar resource may be ignimbrite because of its water content. The variation of water in tuff as a function of degree of welding, oxidation and flow thickness is of direct significance to lunar basing in volcanic terrains on the moon. The fact that many calderas on earth have ignimbritic « aprons » extending from them is correlatable with the apron-type ray patterns around certain post-mare and highland craters on the moon. If lunar craters can be positively identified with associated ignimbritic flows then such areas are potentially water richer than impacted environments. Electrolytic hygrometry and static dehydration analysis of the Tumulo Creek, Wineglass, Bishop, Pelée and Gharvegh tuffs indicate a wide span in water content from 0.2 to 4.1 % even within one flow unit. Devitrification of the mesostasis of these tuffs expels water. Water content apparently varies as a function of flow geometry and possibly thickness. The lower portions of the Tumulo Creek tuff are more hydrous than the upper portions. A slight increase in water content is observed with increase in oxidation. Most of the water in all welded tuffs analysed with the hygrometer is driven off at around 300°C suggesting polymeric hydroxyl bonding with dissociation energies ranging from 2 to 8 kilocalories per mole. However, other types of bonding — Van der Waal, coordinated hydroxyl, free monomeric hydroxyl, etc. — are probably also present. No single, simple bond type controls water retention in rocks. Lunar exploration techniques for hydrous portions of ignimbrite flows include the lateral and vertical application of the epithermal log. 相似文献
4.
Richard J. Pike 《Earth and Planetary Science Letters》1974,23(3):265-271
Amendments to a quantitative scheme developed by T.R. McGetchin et al. (1973) for predicting the distribution of ejecta from lunar basins yield substantially thicker estimates of ejecta, deposited at the basin rim-crest and at varying ranges byond, than does the original model. Estimates of the total volume of material ejected from a basin, illustrated by Imbrium, also are much greater. Because many uncertainties affect any geometric model developed primarily from terrestrial analogs of lunar craters, predictions of ejecta thickness and volume on the Moon may range within at least an order of magnitude. These problems are exemplified by the variability ofT, thickness of ejecta at the rim-crest of terrestrial experimental craters. The proportion ofT to crater rim-height depends critically upon scaled depth-of-burst and whether the explosive is nuclear or chemical. 相似文献
5.
Terrestrial chondrules,glass spherules and accretionary lapilli from the suevite,Ries Crater,Germany
Gu¨nther Graup 《Earth and Planetary Science Letters》1981,55(3):407-418
Until recently, no terrestrial analogues of meteoritic and lunar chondrules were known. Only rare glass spherules from the Lonar Crater, India, and black magnetic spherules from various localities have been recorded. The impact breccia suevite of the No¨rdlinger Ries Crater, Germany, contains both chondrules and glass spherules, and in addition, accretionary lapilli, all of which are found imbedded within the fine-grained matrix of the suevite. The chondrules display many of the textural features characteristic of meteoritic and lunar chondrules. Lithic chondrules and fluid drop chondrules are present, the latter having a composition quite similar to that of glass bombs and glass fragments in the suevite. Fluid drop chondrules developed from glass spherules by slow devitrification in the hot suevite ejecta masses after deposition. On the whole, fluid drop chondrules, lithic chondrules and glass spherules are rare in the suevite, with fluid drop chondrules prevailing. Detection of chondrules from a terrestrial impact crater supports theories of an impact origin for meteoritic and lunar chondrules. Accretionary lapilli also represent material formed as a result of impact. 相似文献
6.
《Journal of Volcanology and Geothermal Research》2007,159(1-3):164-178
Volcanic fields in the Pannonian Basin, Western Hungary, comprise several Mio/Pliocene volcaniclastic successions that are penetrated by numerous mafic intrusions. Peperite formed where intrusive and extrusive basaltic magma mingled with tuff, lapilli-tuff, and non-volcanic siliciclastic sediments within vent zones. Peperite is more common in the Pannonian Basin than generally realised and may be also important in other settings where sediment sequences accumulate during active volcanism. Hajagos-hegy, an erosional remnant of a maar volcano, was subsequently occupied by a lava lake that interacted with unconsolidated sediments in the maar basin and formed both blocky and globular peperite. Similar peperite developed in Kissomlyó, a small tuff ring remnant, where dykes invaded lake sediments that formed within a tuff ring. Lava foot peperite from both Hajagos-hegy and Kissomlyó were formed when small lava flows travelled over wet sediments in craters of phreatomagmatic volcanoes. At Ság-hegy, a large phreatomagmatic volcanic complex, peperite formed along the margin of a coherent intrusion. All peperite in this study could be described as globular or blocky peperite. Globular and blocky types in the studied fields occur together regardless of the host sediment. 相似文献
7.
《Earth and Planetary Science Letters》2007,253(1-2):291-303
The distribution of extraterrestrial chromite grains (> 63 μm) has been studied in the resurge deposit of the early Late Ordovician (458 Ma) Lockne impact structure in central Sweden. A 1-kg-sample of resurge sediment from the rim of the crater is extremely rich in extraterrestrial chromite. In total the sample contains > 125 chromium spinel grains kg− 1, most grains being chromite. Due to post-depositional alterations, the origin of several of the grains is dubious, although it is clear that the major part of the chromites is of extraterrestrial origin (> 75 grains kg− 1), most likely derived from the impactor. The alterations are primarily due to the hydrothermal system induced by the impactor, with zinc enrichment in the chromites as the most common characteristic. The element chemistry of the least altered chromite grains indicates that the impactor was an ordinary L chondrite. This concurs with a suggested increase in the flux of L chondritic asteroids to Earth, following the disruption of the L chondrite parent body at ca. 470 Ma.More than 170 impact craters are known from around the Earth, but only few of the impactors have been identified, mainly due to the low survival rate of projectile material. Further studies of impact craters will reveal if survival of extraterrestrial chromite is unique for the Lockne structure. 相似文献
8.
Dávid Karátson Jean-Claude Thouret Ichio Moriya Alejandro Lomoschitz 《Bulletin of Volcanology》1999,61(3):174-193
The origin and development of erosion-modified, erosion-transformed, and erosion-induced depressions in volcanic terrains
are reviewed and systematized. A proposed classification, addressing terminology issues, considers structural, geomorphic,
and climatic factors that contribute to the topographic modification of summit or flank depressions on volcanoes. Breaching
of a closed crater or caldera generated by volcanic or non-volcanic processes results in an outlet valley. Under climates
with up to ∼2000–2500 mm annual rainfall, craters, and calderas are commonly drained by a single outlet. The outlet valley
can maintain its dominant downcutting position because it quickly enlarges its drainage basin by capturing the area of the
primary depression. Multi-drained volcanic depressions can form if special factors, e.g., high-rate geological processes,
such as faulting or glaciation, suppress fluvial erosion. Normal (fluvial) erosion-modified volcanic depressions the circular
rim of which is derived from the original rim are termed erosion craters or erosion calderas, depending on the pre-existing
depression. The resulting landform should be classed as an erosion-induced volcanic depression if the degradation of a cluster
of craters produces a single-drained, irregular-shaped basin, or if flank erosion results in a quasi-closed depression. Under
humid climates, craters and calderas degrade at a faster rate. Mostly at subtropical and tropical ocean-island and island-arc
volcanoes, their erosion results in so-called amphitheater valleys that develop under heavy rainfall (>∼2500 mm/year), rainstorms,
and high-elevation differences. Structural and lithological control, and groundwater in ocean islands, may in turn preform
and guide development of high-energy valleys through rockfalls, landsliding, mudflows, and mass wasting. Given the intense
erosion, amphitheater valleys are able to breach a primary depression from several directions and degrade the summit region
at a high rate. Occasionally, amphitheater valleys may create summit depressions without a pre-existing crater or caldera.
The resulting, negative landforms, which may drain in several directions and the primary origin of which is commonly unrecognizable,
should be included in erosion-transformed volcanic depressions.
Received: 4 January 1998 / Accepted: 18 January 1999 相似文献
9.
Dr. N. Richter 《Pure and Applied Geophysics》1951,20(1):15-23
Zusammenfassung Es wird gezeigt, dass wir einige irdische Vulkankrater kennen, deren morphologischer Aufbau nahezu identisch ist mit den typischen Formen der Mondkrater. Auf die Wichtigkeit dieses Befundes für das Problem der Entstehung der Mondkrater wird hingewiesen. Es ist zu vermuten, dass sich auf der Erde noch weitere Beispiele dieser Art werden finden lassen.
Summary It is shown, that some terrestrial volcanic craters are known, the morphological structure of which is practically identical with the typical shapes of lunar craters. The importance of this relation for the problem of the origin of lunar craters is pointed out. It may be expected, that some more examples of this kind might be found.相似文献
10.
Jeju Island, the largest Quaternary volcanic island in Korea, has formed mostly since the early Pleistocene, but its latest chronology of volcanism and sedimentation is still poorly constrained. Here we report optically stimulated luminescence (OSL) ages for two hydromagmatic volcanoes on the southwestern coast of Jeju Island, i.e., the Songaksan and Suwolbong tuff rings. The basaltic tuffs of these volcanoes contain abundant quartz sands from underlying marine sedimentary sequences. Two samples collected from the middle part of the Songaksan Tuff yielded highly reproducible quartz single-aliquot regenerative-dose (SAR) OSL ages of 7.0±0.3 ka, providing the first direct age estimate of Holocene volcanism in Jeju Island. The quartz OSL age estimate of 5.1±0.3 ka for the younger reworked basaltic tuff (the Hamori Formation) is comparable with previous radiocarbon and U-series disequilibrium dating of fossil mollusk shells. Two samples from the Suwolbong Tuff show quartz OSL age estimates of 18.3±0.7 and 18.6±0.9 ka, which are identical within error ranges and younger than the quartz OSL age estimate of 23.2±1.0 ka for the underlying Gosan Formation. This study confirms that volcanism and attendant sedimentation were active in Jeju Island until very recently. 相似文献
11.
Pristine samples from the lunar highlands potentially offer important information bearing on the nature of early crustal development on all the terrestrial planets. One apparently unique sample of this group of lunar crustal rocks, the feldspathic lherzolite 67667, was studied utilizing the Sm-Nd radiometric system in an attempt to define its age and the implications of that age for the evolution of the lunar highlands. Data for 67667 precisely define an isochron corresponding to an age of 4.18±0.07 AE. The observed lack of disturbance of the Sm-Nd system of this sample may suggest that this time marks its crystallization at shallow depth in the lunar crust. However, the possibility that this age, as well as those of other highland rocks, indicate the time of their impact-induced excavation from regions deep enough in the lunar crust to allow subsolidus isotopic equilibrium to be produced or maintained between their constituent minerals is also considered. Taken together, bulk rock Sm-Nd data for four “high-Mg” rocks, including 67667, indicate that the chemical characteristics of all their source materials were established 4.33±0.08 AE ago and were intimately associated with the parent materials of KREEP. This finding provides more support for the concept of a large-scale differentiation episode early in lunar history. The possible roles of the crystallization of a global magma ocean, endogenous igneous activity, and of planetesimal impact, in producing the observed geochemical and chronological aspects of lunar highland rocks are discussed. 相似文献
12.
《Journal of Volcanology and Geothermal Research》2007,159(1-3):153-163
Detailed gravity and aeromagnetic data over maars in the Auckland volcanic field reveal contrasting anomalies, even where surface geology is similar. Pukaki and Pukekiwiriki, almost identical maars marked by sediment-filled craters and tuff rings, have gravity and magnetic anomalies of − 6 g.u. and 20 nT, and 8 g.u. and 160 nT, respectively. The Domain and Waitomokia maars, with similar tuff rings but each with a small central scoria cone, have gravity and magnetic anomalies of 32 g.u. and 300 nT, and 21 g.u. and 310 nT, respectively. These differences in geophysical expression are attributed to varying volumes of dense, magnetic basalt in the form of shallow bowl-shaped bodies up to several hundreds of metres in diameter and up to 140 m thick beneath the maar centres. These bodies are interpreted as solidified magma that ponded into early-formed phreatomagmatic explosion craters. Where magma supply was limited relative to groundwater availability, no residual subsurface basalt occurs (as at Pukaki); continued magma supply, but limited groundwater, resulted in ponding (e.g. at Pukekiwiriki) and eventually the building of a scoria cone (as at Domain and Waitomokia). There is no evidence in these geophysical data for diatreme structures below the maars or for shallow and/or extensive feeder dykes associated with these maars. If diatreme structures do occur, their lack of geophysical signature must be a consequence of either their small geophysical contrast with host Miocene sediments and/or masking by the stronger anomalies associated with the subsurface basalt. In addition, any magma conduits appear to be confined centrally beneath the maars, at least to shallow depths (upper 100 m). 相似文献
13.
月球目前的同步旋转轨道状态使得形成的撞击坑分布满足一定的不对称性.本文利用最新的LRO影像和地形数据,结合早期的Clementine影响数据,分析了月球辐射状撞击坑经度方向成坑率分布,结果表明所识别的辐射状撞击坑的.年龄为O.9 Ga内,西一东半球方向存在明显不对称性,比值约为1.35~1.53;同时利用辐射状撞击坑模拟了0.9 Ga内的同步旋转轨道的平均状态,得到该时间内月球的向点-背点为70°W—110°E附近;最后利用撞击坑数据库资料对月球形成以来各地质世纪时间尺度内的撞击坑进行了成坑率分布分析,结论表明月球在大爆炸中后期间可能处于过近似的同步轨道旋转状态,但是与现在的轨道运行状态相反,月球在之后的地质时期内经历了翻转,其诱因可能是雨海和东方海盆地遭受的撞击. 相似文献
14.
Daniela Tirsch Robert Anthony Craddock Thomas Platz Alessandro Maturilli Jörn Helbert Ralf Jaumann 《地球表面变化过程与地形》2012,37(4):434-448
Dark aeolian deposits on Mars are thought to consist of volcanic materials due to their mineral assemblages, which are common to basalts. However, the sediment source is still debated. Basaltic dunes on Earth are promising analogs for providing further insights into the assumed basaltic sand dunes on Mars. In our study we characterize basaltic dunes from the Ka'u Desert in Hawaii using optical microscopes, electron microprobe, and spectral analyses. We compare the spectra of terrestrial and Martian dune sands to determine possible origins of the Martian dark sediments. Our results show that the terrestrial sands consist primarily of medium to coarse sand‐sized volcanic glass and rock fragments as well as olivine, pyroxene, and plagioclase minerals. Grain shapes range from angular to subrounded. The sample composition indicates that the material was derived from phreatomagmatic eruptions partially with additional proportions of rock fragments from local lava flows. Grain shape and size indicate the materials were transported by aeolian processes rather than by fluvial processes. Spectral analyses reveal an initial hydration of all terrestrial samples. A spectral mineralogical correlation between the terrestrial and Martian aeolian sands shows a similarity consistent with an origin from volcanic ash and lava. We suggest that the Martian deposits may contain similar abundances of volcanic glass, which has not yet been distinguished in Martian spectral data. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
15.
Larry Jay Friesen 《Physics of the Earth and Planetary Interiors》1977,14(3):274-275
Both lunar transient phenomena and 222Rn/210Po anomalies observed by Apollo-15 and -16 orbital alpha spectrometers display preferences for certain kinds of locations: rims of circular maria and craters with central peaks and/or dark floors. If these classes of observations are due to lunar gas venting, why are these types of locations preferred? The hypothesis offered is that these are locations at which cracks or channels exist extending deep enough into the moon to tap lunar volatile reservoirs. Possible channels include circumferential cracks around circular maria, old lava tubes for dark-floor and volcanic central peak craters, and shattered subsurface rock structure for impact central peak craters. 相似文献
16.
J. Borg G.M. Comstock Y. Langevin M. Maurette B. Jouffrey C. Jouret 《Earth and Planetary Science Letters》1976,29(1):161-174
The theoretical motion of individual dust grains in the lunar regolith is analyzed by using a Monte Carlo statistical code where the variables are the mass and speed distribution of meteorites at the lunar surface and the geometrical shape of impact craters. From these computations the detailed irradiation history of the grains in the ancient solar wind is traced back, over a period of 4 billion years, as a function of the grain size. Then by combining this irradiation scheme with the result of solar wind simulation experiments, the time and depth dependent accumulation of solar wind effects in the theoretical grains (solar wind maturation) is inferred. Finally, the validity of these predictions is tentatively checked by discussing a variety of physical and chemical solar wind effects which are registered in the surface layers of lunar dust grains. Therefore these studies give a tentative scenario for the “maturation” of the lunar regolith with respect to solar wind effects, but they also reveal useful guidelines to deduce meaningful information from such effects. In particular, they suggest a “lunar skin” sampling technique for extracting dust grains in lunar core tubes which could help in deciphering the past activity of the ancient solar wind over a time scale of several billion years. 相似文献
17.
《Earth and Planetary Science Letters》2006,241(3-4):663-671
Understanding spin orbital parameter-driven climate change on Mars prior to ∼ 20 Ma ago requires geological evidence because numerical solutions for that period are chaotic and non-unique. We show geological evidence that lineated valley fill at low mid-latitudes in the northern hemisphere of Mars (∼ 37.5° N) originated through regional snow and ice accumulation and underwent glacial-like flow. Breached upland craters and theater-headed valleys reveal features typical of erosion in association with terrestrial glaciers. Parallel, converging and chevron-like lineations in potentially ice-rich deposits on valley floors indicate that flow occurred through constrictions and converged from different directions at different velocities. Together, these Martian deposits and erosional landforms resemble those of intermontaine glacial systems on Earth, particularly in their major morphology, topographic shape, planform and detailed surface features. An inferred Late Amazonian age, combined with predictions of climate models, suggest that the obliquity of Mars exceeded a mean of 45° for a sustained period. During this time, significant transfer of ice occurred from ice-rich regions (e.g., the poles) to mid-latitudes, causing prolonged snow and ice accumulation there and forming an extensive system of valley glaciers. 相似文献
18.
《Journal of Volcanology and Geothermal Research》2007,159(1-3):138-152
Neogene alkaline basaltic rocks in the western Pannonian Basin are eroded remnants of maars, tuff rings, tuff cones, scoria cones and lava fields. The erosion level of these volcanoes is deep enough to expose diatreme zones associated with the phreatomagmatic volcanoes. The erosion level is deeper yet in the west, exposing shallow dyke and sill swarms related to former intra-plate volcanoes. The basanitic sills are irregular in shape and their lateral extent is highly variable. Individual sills reach a thickness of a few tens of metres and they commonly form dome-like structures with rosette-like radial columnar joint patterns. The largest sill system identified in this region is traceable over kilometres, and forms a characteristic ridge running north-east to south-west. Elevation differences in the position of the basanitic sills within an otherwise undisturbed “layer cake-like” siliciclastic succession indicate emplacement of the basanite magma at multiple levels over kilometre-scale distances. The margins of sills in the system are irregular at a dm-to-mm-scale. Undulating contacts of the sills together with gentle thermal alteration in the host sediment over cm-to-dm distances indicate the soft, but not necessarily wet state of the host deposits at the time sills were intruded. Parts of the sill complex show a complicated relationship with the host sediment in form of peperitic zones and irregularly shaped, disrupted, peperite textures. This is interpreted to reflect inhomogenities in water content and rheology of the siliciclastic deposits during intrusion. The current summit of the longest continuous ridge preserves a small diatreme that seems to cut through an otherwise disk-like sill indicating of relationship between sill emplacement and phreatomagmatic explosive eruptions. 相似文献
19.
C. A. Wood 《Bulletin of Volcanology》1974,38(1):149-172
The Pinacate volcanic field of northwest Sonora, Mexico contains eleven tuff-rimmed explosion craters as well as hundreds of cinder cones. A multiphase eruptive and collapse history for each of the craters is evidenced by: cinder cones exposed in cross-section in crater rims, rim-breaking cinder cones, major eccentric vents, erosion hiatuses between tuff deposition, and coalescing craters exhibiting differeng degrees of erosion. Basaltic intrusions occurred along ring fractures and in the center of at least one crater. Magnetic surveys indicate that explosion craters have tuffaceous feeder vents whereas cinder cones have basaltic, highly magnetic plugs. Computer models illustrate that magnetic terrain effects can contribute to anomalies observed associated with craters, and need to be considered where magnetic surveys include irregularities such as rims or peaks. 相似文献
20.
《Journal of Volcanology and Geothermal Research》2007,159(1-3):179-197
The Atexcac maar is located in the central part of the Serdán–Oriental lacustrine/playa basin in the eastern Mexican Volcanic Belt. It is part of a dispersed and isolated monogenetic field consisting of maar volcanoes, basaltic cinder cones and rhyolitic domes. Atexac is a maar volcano excavated into pyroclastic deposits, basaltic lava flows and the flanks of a cinder cone cluster, which itself was built on a topographic high consisting of limestone. It has an ENE-trending elliptical shape with beds, mostly unconsolidated deposits that dip outward at 16–22°. The Atexcac crater was formed from vigorous phreatomagmatic explosions in which fluctuations in the availability of external water, temporal migration of the locus of the explosion, and periodic injection of new magma were important controls on the evolution of the maar crater. Variations in grain sizes and component proportions of correlated deposits from the different sections suggest a migration of the locus of explosions, producing different eruptive conditions with fluctuating water–magma interactions. Deposits rich in large intrusive and limestone blocks are associated with a matrix enriched in small andesitic lapilli. This could suggest differential degrees of fragmentation due to inherited (previously acquired) fragmentation and/or relative distance to the locus of explosions. Initial short-lived phreatic explosions started at the southwest part of the crater and were followed by an ephemeral vertical column and the influx of external water that led to relatively shallow explosive interactions with the ascending basaltic magma. Drier explosions progressed downward and/or laterally northward, sampling subsurface rock types, particularly intrusive, limestone and andesitic zones as well as localized altered zones (N-NE), caused by repetitive injection of basaltic magma. A final explosive phase involved a new injection of magma and a new influx of external water producing wetter conditions at the end of the maar formation. We infer the aquifer was formed by fractured rocks, predominantly andesitic lava flows and limestone rocks. Andesitic accessory clasts dominate in all stratigraphic levels but these rocks are not exposed in the nearby area. These local hydrogeological conditions contrast with those at nearby maar volcanoes, where the water for the magma/water interactions apparently mostly came from a dominantly unconsolidated tuffaceous aquifer, producing tuff rings with a much lower profile than Atexcac. 相似文献