首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Conventional K-Ar and 40Ar/39Ar total-fusion and incremental-heating ages from basalts recovered from the Ninetyeast Ridge confirm earlier indication from paleontology of basal sediments that basement crystallization ages increase systematically from south to north. A rate of migration of volcanism of 9.4 ± 0.3 cm/yr best fits the age-distance relationship determined from these basalts. The geometry, distribution of ages, paleomagnetism and geochemistry are most compatible with an origin of the Ninetyeast Ridge by northward movement of the Indian plate over a hotspot near Heard Island in the southern Indian Ocean, from mid-Cretaceous to Early Oligocene time. The Ninetyeast Ridge and nearly parallel Chagos-Laccadive Ridge provide an absolute frame of reference for the reconstruction of the eastern Indian Ocean.  相似文献   

2.
Parameters of the focal mechanisms of earthquakes, as well as their relations to the characteristics of seismicity and geological structure are analyzed in the regions of the Komandorskie Islands in the west of the Aleutian arc, the Fox Islands, and the Alaska Peninsula coast in the east of the arc. Different types of ruptures are revealed in the western and eastern parts of the Aleutian arc. The leading type of ruptures at the southern slope of the Komandorskie Islands is steep reverse faults crossing the arc at azimuths from submeridional to northeastern. A similar type of rupture occurs in abundance on the Rat Islands and is predominant on the Near Islands. Steep strike-slips with small components of the normal or reverse fault manifest themselves at the northern side of the block uplift of the Komandorskie Islands. Seismogenic ruptures in the region of the Komandorskie Islands do not contradict geological data on the rupture tectonics on Medny and Bering islands. At the southern slope of the Fox Islands, as well as in the Andreanof Islands, steep reverse faults striking longitudinally (along the arc) with the dip toward the deep-sea trench are the predominant type of seismogenic ruptures. This type of seismogenic ruptures is the leading type for the structures of island arcs with present-day volcanism; an example is the Kurile-Kamchatka island. Different types of predominant seismogenic ruptures in the western and eastern parts of the Aleutian island arc probably reflect different stages of the tectonic development of these regions of the arc. Possible positions and sizes of sources of the largest historical earthquakes in the eastern part of the Aleutian island arc are considered  相似文献   

3.
From the seismic point of view, the territory of Pakistan which lies between latitude 23°–37° N and longitude 61°–75° E is one of the most active zones in the world. The importance of this area lies in terms of movements of the Indian plate with respect to Eurasia on the west. Seismicity, as well as focal mechanism- solutions, throws a considerable light on the nature of forces acting in the area. All the available solutions, along with 12 new ones, have been considered for the present study. Their relationship to major faults in the area is discussed. The majority of the solutions in the central and northern parts show strike-slip faulting with a left-lateral sense of motion, followed by thrust faulting; few show normal faulting. This suggests that the Indian plate is moving with respect to the Eurasian plate along the Chaman fault, Quetta transverse zone, Sulaiman Ranges and the Hazara thrusts region joining the Hazara/Kashmir syntaxis. The orientations of P and T axes have been studied. It is seen that in a large number of cases compressive stress is acting nearly in NNW-SSE to N-S directions. The Hazara thrust region appears to be the most complex. Here, the influence of the Himalayan thrust front is evident to a large extent.The nature of faulting along the Chaman fault and Quetta transverse zone is to some extent similar to that of the San Andreas fault system of California. So far as the energy release is concerned, the maximum energy is being released in the form of strike-slip movements close to the Chaman fault and Quetta transverse ranges.  相似文献   

4.
An interpretation of the parameters of earthquake sources is proposed for the two large earthquakes in the Rat Islands of February 4, 1965 (M W = 8.7), and November 17, 2003 (M W = 7.7–7.8), based on the analysis of focal mechanisms, the manifestation of aftershocks, and the specific features of the geological structure of the island slope of the Rat Islands. The source of the earthquake of 1965 is a reverse fault of longitudinal strike, with a length of ～350 km. It is located in the lower part of the Aleutian Terrace and probably is genetically connected with the development of the Rat submarine ridge. The westward boundary of the earthquake source is determined by the Heck Canyon structures, and the eastward boundary is determined by the end of Rat Ridge in the region of λ ～ 179°E–179.5°E. The source of the earthquake of 2003 is a steep E-W reverse fault extending for about 100 km. It is located in the eastern part of the Rat Islands, higher on the slope than the source of the earthquake of 1965. The westward end of the earthquake source is determined by Rat Canyon structures, and the eastward end is an abrupt change in isobaths in the region of λ ～ 179°E. According to the aftershock hypocenters, the depth of occurrence of the reverse fault could reach ～60 km. According to our interpretation, on the southern slope of the Rat and Near islands, there is a complex system of seismogenic faults that is caused by tectonic development of different structural elements. The dominant types of faults here are reverse faults, as in other island arcs. During earthquakes, reverse faults oriented along the island arc and also faults that intersect it exhibit themselves. The reverse faults of northeastern strike that intersect the arc characterize the type of tectonic motions in a series of canyons of the western part of the Aleutian Islands.  相似文献   

5.
Most estimates of the epicentre of the Long Shot explosion (29 October 1965, Aleutian Islands) are biased to the north of the true epicentre, this bias being much larger than formal uncertainty estimates. The bias is interpreted by some as evidence that the P-wave speeds in the upper mantle in the source region are higher to the north than to the south; that is, the difference between estimated and true epicentre is a source bias. Others argue that much of the bias can be explained by station anomalies, i.e. differences in the wave speeds in the upper mantle at stations to the north relative to those to the south. Bias may also be introduced by measurement error if signal-to-noise ratio (SNR) is lower on average at stations to the south compared to those to the north and times are read late at the low SNR stations. Here I locate Long Shot and the other two Aleutian Island explosions (Milrow and Cannikin) using P times from small networks of stations all on continents. The results support the view that a large component of the bias in the epicentres of the three explosions is due to station anomalies and not source bias, but that for the Long Shot explosion (the lowest magnitude of the three explosions), measurement error due to systematic variations in the SNR between stations to the north and south also contributes to the bias.  相似文献   

6.
Over the last twenty years, Chagos Bank has a seismicity rate disproportionate to its supposed intraplate location. Earthquake relocation also shows a high seismicity rate in pre-WWSSN time (1912–1963), with seven events located off of the Central Indian Ridge, including large events in 1912 (M = 6.8) and 1944 (M = 7.2). This study uses the moment variance technique, a systematic search for the mechanism which best fits P, PP, SH, Love and Rayleigh amplitudes, to determine the focal mechanisms of two pre-WWSSN earthquakes. A test with a recent event of known mechanism demonstrates that accurate focal parameter determination is possible even when only a few good records are available. Moment variance analysis shows a thrust faulting mechanism for the 1944 event, northeast of Chagos Bank near the Chagos-Laccadive ridge, and a strike-slip focal mechanism for a smaller 1957 event west of Chagos Bank. The 1944 event, one of the largest oceanic “intraplate” earthquakes known (moment 1.4 × 1027 dyne-cm), indicates that the Chagos seismicity reflects not an isolated occurrence of normal faulting as previously thought, but rather regional tectonic deformation extending northeast of Chagos Bank and including thrust, normal and strike-slip events. This seismicity and previously studied seismicity near the Ninetyeast Ridge and Central Indian Basin suggest a broad zone of deformation stretching across the equatorial Indian Ocean. This zone contains all known magnitude seven oceanic “intraplate” earthquakes not associated with subduction zones or continental margins, suggesting that elsewhere such extensive deformation occurs only along plate boundaries. This study proposes that a slow, diffuse plate boundary extends east from the Central Indian Ridge to the Ninetyeast Ridge and north to the Sumatra Trench. A recent plate motion study confirms this boundary and suggests that it separates the Australian plate from a single Indo-Arabian plate.  相似文献   

7.
Continuous MF and meteor radar observations allow detailed studies of winds in the mesosphere and lower thermosphere (MLT) as well as temperatures around the mesopause. This height region is characterized by a strong variability in winter due to enhanced planetary wave activity and related stratospheric warming events, which are distinct coupling processes between lower, middle and upper atmosphere. Here the variability of mesospheric winds and temperatures is discussed in relation with major and minor stratospheric warmings as observed during winter 2005/06 in comparison with results during winter 1998/99.Our studies are based on MF radar wind measurements at Andenes (69°N, 16°E), Poker Flat (65°N, 147°W) and Juliusruh (55°N, 13°E) as well as on meteor radar observations of winds and temperatures at Resolute Bay (75°N, 95°W), Andenes (69°N, 16°E) and Kühlungsborn (54°N, 12°E). Additionally, energy dissipation rates have been estimated from spectral width measurements using a 3 MHz Doppler radar near Andenes. Particular attention is directed to the changes of winds, turbulence and the gravity wave activity in the mesosphere in relation to the planetary wave activity in the stratosphere.Observations indicate an enhancement of planetary wave 1 activity in the mesosphere at high latitudes during major stratospheric warmings. Daily mean temperatures derived from meteor decay times indicate that strong warming events are connected with a cooling of the 90 km region by about 10–20 K. The onset of these cooling processes and the reversals of the mesospheric circulation to easterly winds occur some days before the changes of the zonal circulation in the stratosphere start indicating a downward propagation of the circulation disturbances from the MLT region to the stratosphere and troposphere during the stratospheric warming events. The short-term reversal of the mesospheric winds is followed by a period of strong westerly winds connected with enhanced turbulence rates and an increase of gravity wave activity in the altitude range 70–85 km.  相似文献   

8.
Floating pumice masses have been observed several times near the central part of Ninety-East Ridge, Indian Ocean, in 1879 and in 1883. The author is of the opinion that the source of these pumice masses cannot have been the volcano Krakatau in the Sunda Strait - as has been suggested earlier by other authors -, but that they originated in situ. Examples of floating pumice observed over submarine volcanoes lying at depths of 1500 m or even more, are mentioned briefly by other authors, suggesting that eruptions in deep water may indeed lead to its formation.The suspected submarine volcano may coincide with an elongated but rather flat elevation a little north of the central part of Ninety-East Ridge. The center of this elevation is located approximately at 6° 05′ S, 89° 10 E. A roughly NW-SE profile of this area shows the presence of this shield-like feature very near the site where floating pumice was seen on three occasions. The inferred submarine volcanic center is lying within the belt of heat flow anomaly (called belt I). A particular “hot spot” with an unusually high heat flow value (7.61 HFU) is located southeast of the feature in question. The heat flow values measured in belt I are well above the world-average. This belt may be the result of the presence of linearly arranged magma chambers at a relatively shallow depth, probably within the oceanic crust. This belt has a length of 1100 km.The seismic activity of the area investigated is similarly remarkable. Numerous powerful shocks have taken place there. Belt I represents the axis of the seismic zone, extending from points b to c (Fig. 5). The seismic belt is regarded as a zone of weakness within which fractures can originate, permitting rock-melts to emerge from depth towards the surface.  相似文献   

9.
Age of Seychelles–India break-up   总被引：1，自引：0，他引：1  
Many continental flood basalt provinces are spatially and temporally linked with continental break-up. Establishing the relative timing of the two events is a key step in determining their causal relationship. Here we investigate the example of the Deccan Traps and the separation of India and the Seychelles. Whilst there has been a growing consensus as to the age of the main phase of the Deccan emplacement (65.5 ± 1 Ma, chron 29r), the age of the rifting has remained unclear. We resolve this issue through detailed seafloor magnetic anomaly modeling (supported by wide-angle and reflection seismic results) of the north Seychelles and conjugate Laxmi Ridge/Gop Rift margins, and geochemistry and 40Ar/39Ar geochronology of rocks from the north Seychelles margin. We show that syn-rift volcanics offshore the Seychelles Islands in the form of seaward-dipping reflectors were most likely erupted during chron 28n, and the first organized seafloor spreading at the Carlsberg Ridge also initiated during this chron at 63.4 Ma. The severing of the Seychelles occurred by a south-eastward ridge propagation that was completed by the start of chron 27n (~ 62 Ma). A brief, pre-28r phase of seafloor spreading occurred in the Gop Rift, possibly as early as 31r–32n (~ 71 Ma). Initial extension at the margin therefore preceded or was contemporaneous with the Deccan emplacement, and separation of the Seychelles was achieved less than 3.5 Ma afterwards. This is the shortest time interval between flood basalt emplacement and break-up yet reported for any continental flood basalt-rifted margin pair. A contributing factor to the apparently short interval in the Deccan case may be that rifting occurred by a ridge jump into already thinned continental lithosphere. However, we conclude that external plate-boundary forces, rather than the impact of a mantle plume, were largely responsible for the rifting of the Seychelles from India.  相似文献   

10.
The Blackfoot Reservoir region in southeastern Idaho is recognized as a potential geothermal area because of the presence of several young rhyolite domes (50,000 years old), Quaternary basalt flows, and warm springs. North- to northwest-trending high-angle normal faults of Tertiary to Holocene age appear to be the dominant structural control of spring activity. Surface spring-water temperatures average 14°C except for a group of springs west of the Reservoir Mountains which average 33°C. Chemical geothermometers applied to fifty water samples give temperatures less than 75°C except for eight springs along the Corral Creek drainage. The springs along Corral Creek have Na-K-Ca temperatures that average 354°C, a direct result of high potassium concentrations in the water. A correction for carbon dioxide applied to the Na-K-Ca geothermometer lowers the estimated temperatures of the anomalous springs to near the measured surface temperatures, and Na-K-Ca-Mg temperatures for the anomalous springs are near 100°C. Mixing model calculations suggest that hot water with a temperature of approximately 120°C may be mixing with cooler, more dilute water in the springs from the Corral Creek drainage, a temperature supported by Na-K-Ca-Mg temperatures and mineral saturation temperatures.Stability relations of low-temperature phases in the system indicate that the large concentrations of potassium in the eight anomalous springs are derived from reactions with the potassium-bearing minerals muscovite and K-feldspar. Carbon dioxide and hydrogen sulfide gases may be derived through the oxidation of organic matter accompanied by the reduction of sulfate. Concentrations of major and minor elements, and gases found in springs of the Blackfoot Reservoir region are due to water-rock reactions at temperatures less than 100°C.Based on spring geochemistry, a geothermal reservoir of 100°C up to 120°C may exist at shallow (less than 2 km) depths in the Blackfoot Reservoir region.  相似文献   

11.
An interpretation of the type, size, and interrelations of sources is proposed for the three large Aleutian earthquakes of March 9, 1957, May 7, 1986, and June 10, 1996, which occurred in structures of the Andreanof Islands. According to our interpretation, the earthquakes were caused by steep reverse faults confined to different structural units of the southern slope of the Andreanof Islands and oriented along the strike of these structures. An E-W reverse fault that generated the largest earthquake of 1957 is located within the Aleutian Terrace and genetically appears to be associated with the development of the submarine Hawley Ridge. The western and eastern boundaries of this source are structurally well expressed by the Adak Canyon in the west (～177°W) and an abrupt change in isobaths in the east (～173°W). The character of the boundaries is reflected in the focal mechanisms. The source of the earthquake of 1957 extends for about 300 km, which agrees well with modern estimates of its magnitude (M w = 8.6). Because the earthquake of 1957 caused, due to its high strength, seismic activation of adjacent areas of the Aleutian island arc, its aftershock zone appreciably exceeded in size the earthquake source. Reverse faults that activated the seismic sources of the earthquakes of 1986 and 1996 were located within the southern slope of the Andreanof Islands, higher than the Aleutian Terrace, outside the seismic source of the 1957 earthquake. The boundaries of these sources are also well expressed in structures and focal mechanisms. According to our estimate, the length of the 1986 earthquake source does not exceed 130–140 km, which does not contradict its magnitude (M w = 8). The length of the 1996 earthquake source is ～100 km, which also agrees with the magnitude of the earthquake (M w = 7.8).  相似文献   

12.
Phil Dyke 《Ocean Dynamics》2005,55(3-4):238-247
Wave trapping and induced flow around an island is examined. The exactly circular island solutions are reprised and the solutions extended, and shown to apply to a stratified sea. The homogeneous solutions are then used to deduce the wave trapping and flow around a near circular island. It turns out that the cotidal pattern for a perfectly circular island is relatively immune to variations in geometry and radially dependent depth variations. This helps explain the similarity in the behaviour of the tides around various islands (the Pribilof Islands near Alaska, Oahu in Hawaii, Cook Island off north west Australia, Bermuda off the eastern coast of the USA, and Bear Island in the Norwegian Sea). The dominant steady drift and its rate of decay off-shore is also calculated.  相似文献   

13.
Paleomagnetic data from 46 sites (674 specimens) of the Westcoast Crystalline Gneiss Complex on the west coast of Vancouver Island using AF and thermal demagnetization methods yields a high blocking temperature WCB component (> 560°C) with a pole at 335°W, 66°N (δp = 4°, δm = 6°) and a lower coercivity WCA component ( 25 mT, < 500°C) with a pole at 52°W, 79°N (δp = 7°, δm = 8°). Further thermal demagnetization data from 24 sites in the Jurassic Island Intrusions also defines two high blocking temperature components. The IIA component pole is at 59°W, 79°N (δp = 7°, δm = 8°) and IIB pole at 130°W, 73°N (δp = 12°, δm = 13°). Combined with previous data from the Karmutsen Basalts and mid-Tertiary units on Vancouver Island and from the adjacent Coast Plutonic Complex, the geotectonic motions are examined for the Vancouver Island segment of the Wrangellian Subterrane of composite Terrane II of the Cordillera. The simplest hypothesis invokes relatively uniform translation for Terrane II from Upper Triassic to Eocene time producing 39° ± 6° of northward motion relative to the North American craton, combined with 40° of clockwise rotation during the Lower Tertiary.  相似文献   

14.
Izvestiya, Physics of the Solid Earth - Abstract—A new model of the rupture surface of the Mw = 7.8 Near Islands Aleutian earthquake that occurred on July 17, 2017 in the region of the...  相似文献   

15.
The 1964 Prince William Sound earthquake (March 28, 1964;M w =9.2) caused crustal deformation over an area of approximately 140,000 km2 in south central Alaska. In this study geodetic and geologic measurements of this surface deformation were inverted for the slip distribution on the 1964 rupture surface. Previous seismologic, geologic, and geodetic studies of this region were used to constrain the geometry of the fault surface. In the Kodiak Island region, 28 rectangular planes (50 by 50 km each) oriented 218°N, with a dip varying from 8o nearest the Aleutian trench to 9o below Kodiak Island, define the rupture surface. In the Prince William Sound region 39 planes with variable dimensions (40 by 50 km near the trench, 64 by 50 km inland) and orientation (218°N in the west and 270°N in the east) were used to approximate the complex faulting. Prior information was introduced to constrain offshore dip-slip values, the strike-slip component, and slip variation between adjacent planes. Our results suggest a variable dip-slip component with local slip maximums occurring near Montague Island (up to 30 m), further to the east near Kayak Island (up to 14 m), and trenchward of the northeast segment of Kodiak Island (up to 17m). A single fault plane dipping 30°NW, corresponding to the Patton Bay fault, with a slip value of 8 m modeled the localized but large uplift on Montague Island. The moment calculated on the basis of our geodetically derived slip model of 5.0×1029 dyne cm is 30% less than the seismic moment of 7.5×1029 dyne cm calculated from long-period surface waves (Kanamori, 1970) but is close to the seismic moment of 5.9×1029 dyne cm obtained byKikuchi andFukao (1987).  相似文献   

16.
We have constructed a new bathymetric chart of part of the Chile transform system, based mainly on an R/V “Endeavor” survey from 100°W to its intersection with the East Ridge of the Juan Fernandez microplate at 34°30′S, 109°15′W. A generally continuous lineated trend can be followed through the entire region, with the transform valley being relatively narrow and well-defined from 109°W to approximately 104°30′W. The fracture zone then widens to the east, with at least two probable en echelon offsets to the south at 104° and 102°W. Six new strike-slip mechanisms along the Chile Transform and one normal fault mechanism near the northern end of the Chile Rise, inverted together with other plate motion data from the eastern portion of the boundary, produce a new best fit Euler pole for the Nazca-Antarctic plate pair, providing tighter constraints on the relative plate motions.  相似文献   

17.
Tal Ezer  Lie-Yauw Oey 《Ocean Dynamics》2013,63(2-3):243-263
A high-resolution numerical ocean circulation model of the Bering Sea (BS) is used to study the natural variability of the BS straits. Three distinct categories of strait dynamics have been identified: (1) Shallow passages such as the Bering Strait and the Unimak Passage have northward, near barotropic flow with periodic pulses of larger transports; (2) wide passages such as Near Straits, Amukta Pass, and Buldir Pass have complex flow patterns driven by the passage of mesoscale eddies across the strait; and (3) deep passages such as Amchitka Pass and Kamchatka Strait have persistent deep return flows opposite in direction to major surface currents; the deep flows persist independent of the local wind. Empirical orthogonal function analyses reveal the spatial structure and the temporal variability of strait flows and demonstrate how mesoscale variations in the Aleutian passages influence the Bering Strait flow toward the Arctic Ocean. The study suggests a general relation between the barotropic and baroclinic Rossby radii of deformations in each strait, and the level of flow variability through the strait, independent of geographical location. The mesoscale variability in the BS seems to originate from two different sources: a remote origin from variability in the Alaskan Stream that enters the BS through the Aleutian passages and a local origin from the interaction of currents with the Bowers Ridge in the Aleutian Basin. Comparisons between the flow in the Aleutian passages and flow in other straits, such as the Yucatan Channel and the Faroe Bank Channel, suggest some universal topographically induced dynamics in strait flows.  相似文献   

18.
We present new paleomagnetic results from the well dated Miyako Cretaceous sediments (100–110 Ma) from Northeast Japan. These results, combined with those of Tosha [1], yield an in-situ characteristic directionD = 321°,I = 54.5° (α95 = 4.5°),N = 14 sites; reduced to a reference point at 40°N, 142°E). This direction is found to coincide with that of most older plutonic and sedimentary rocks of Devonian to lower Cretaceous age. It is also identical with the westerly pre-folding direction which is preserved in many Oligocene (20–40 Ma) formations from Northeast Japan [1,2]. In contrast, all recent formations (0–17 Ma) have been magnetized in the direction of the present axial dipole field. Only the Oligocene and Miocene results appear to be primary, or at least pre-folding. The Miyako sulfide-bearing sediments and lower Cretaceous (110–125 Ma) magnetite-bearing granites could either still bear a primary magnetization or be completely remagnetized by a low temperature chemical event. Evidence for such events is now found in many places, and as close as South Korea. Available data constrain the Oligo-Miocene history of Northeast Japan and indicate at least20/30° counterclockwise rotation with respect to mainland Asia during the opening of the Sea of Japan. On the other hand, the pre-40 Ma history of Northeast Japan is not well constrained and three models are proposed which are compatible with various interpretations of the data. None of them can presently document pro-Oligocene motion of Northeast Japan with respect to Asia. The most “economical” model implies widespread remagnetization. We conclude that, because of the scarcity of well tested primary magnetization directions, the classical bending of the Japanese Islands rests on weaker grounds than generally realized and that no pre-40 Ma apparent polar wander path of the Japanese Islands can safely be proposed.  相似文献   

19.
226Ra profiles have been measured in the western Indian Ocean as part of the 1977–1978 Indian Ocean GEOSECS program. These profiles show a general increase in deep and bottom water Ra concentration from the Circumpolar region to the Arabian Sea. A deep Ra maximum which originates in the Arabian Sea and in the Somali basin at about 3000 m depth spreads southward into the Mascarene basin and remains discernible in the Madagascar and Crozet basins. In the western Indian Ocean, the cold Antarctic Bottom Water spreads northward under the possibly southward-flowing deep water, forming a clear benthic front along the Crozet basin across the Southwest Indian Ridge into the Madagascar and Mascarene basins. The Antarctic Bottom Water continues to spread farther north to the Somali basin through the Amirante Passage at 10°S as a western boundary current. The benthic front and other characteristic features in the western Indian Ocean are quite similar to those observed in the western Pacific where the benthic front as a distinctive feature was first described by Craig et al. [15]. Across the Mid-Indian Ridge toward the Ceylon abyssal plain near the triple junction, Ra profiles display a layered structure, reflecting the topographic effect of the mid-ocean ridge system on the mixing and circulation of the deep and bottom waters. Both Ra and Si show a deep maximum north of the Madagascar basin. Linear relationships between these two elements are observed in the deep and bottom water with slopes increasing northward. This suggests a preferential input of Ra over Si from the bottom sediments of the Arabian Sea and also from the flank sediments of the Somali basin.  相似文献   

20.
Low18O/16O values have been found in rocks from the Captains Bay pluton and surrounding country rocks on Unalaska Island in the Aleutian Islands. The pluton is surrounded by a metamorphic aureole in which the country rocks have been domed, faulted and chaotically fractured. Samples with lower18O/16O values (δ18O = ?4.1 to +2.7‰, SMOW) commonly have interstitial micrographic intergrowths of quartz and turbid potassium feldspar. These facts suggest extensive interaction of circulating meteoric waters with the pluton. Unalaska Island must have been subaerially exposed at or shortly after the time of intrusion of the pluton. The pervasive low-grade metamorphism of the “early series” volcanic rocks of all of the Aleutian Islands might be a result of the interaction of intrusive bodies with meteoric waters rather than the consequence of ridge subduction.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号