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Doklady Earth Sciences - Using observations from a large-scale seismic station network, we built a seismic tomography model of velocity anomalies for longitudinal (P-wave) and transverse (S-wave)... 相似文献
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Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions
B?rje Dahren Valentin R. Troll Ulf B. Andersson Jane P. Chadwick Màiri F. Gardner Kairly Jaxybulatov Ivan Koulakov 《Contributions to Mineralogy and Petrology》2012,163(4):631-651
Understanding magma plumbing is essential for predicting the behaviour of explosive volcanoes. We investigate magma plumbing
at the highly active Anak Krakatau volcano (Indonesia), situated on the rim of the 1883 Krakatau caldera by employing a suite
of thermobarometric models. These include clinopyroxene-melt thermobarometry, plagioclase-melt thermobarometry, clinopyroxene
composition barometry and olivine-melt thermometry. Petrological studies have previously identified shallow magma storage
in the region of 2–8 km beneath Krakatau, while existing seismic evidence points towards mid- to deep-crustal storage zone(s),
at 9 and 22 km, respectively. Our results show that clinopyroxene in Anak Krakatau lavas crystallized at a depth of 7–12 km,
while plagioclase records both shallow crustal (3–7 km) and sub-Moho (23–28 km) levels of crystallization. These magma storage
regions coincide with well-constrained major lithological boundaries in the crust, implying that magma ascent and storage
at Anak Krakatau is strongly controlled by crustal properties. A tandem seismic tomography survey independently identified
a separate upper crustal (<7 km) and a lower to mid-crustal magma storage region (>7 km). Both petrological and seismic methods
are sensitive in detecting magma bodies in the crust, but suffer from various limitations. Combined geophysical and petrological
surveys, in turn, offer increased potential for a comprehensive characterization of magma plumbing at active volcanic complexes. 相似文献
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Seismic-tomography studies were conducted in the Kyrgyz Tien Shan using two different observation schemes. The first was based on the arrival times of P and S waves from regional earthquakes recorded with local seismological networks (local scheme). Nonlinear tomographic inversion based on the LOTOS algorithm was used to construct the 3D distributions of P and S wave velocities in the crust beneath the Kyrgyz Tien Shan and to refine the earthquake locations. The second scheme was used to study the upper-mantle structure based on data from global earthquake catalogs (regional scheme). All the data on waves which at least partly travel within the volume studied were used here, including (1) those from regional earthquakes recorded at world seismic stations and (2) teleseisms recorded at the local stations. This approach was earlier applied to calculate the upper-mantle structure beneath Asia. We used a fragment of this structure beneath the Tien Shan and adjacent areas. A series of synthetic tests was performed to estimate the resolution provided by both schemes. The tomography shows traces of the delamination of the Tarim mantle lithosphere from south to north. Also, the local and regional schemes reveal evidence for cold-matter descent from north to south in the northern Tien Shan but on a much smaller scale. Low velocities in the upper mantle beneath the Tien Shan might indicate lithospheric thinning. These data suggest that mantle-lithosphere delamination is taking place underneath both the northern and the southern margins of the Tien Shan collision belt. Lack of the mantle lithosphere beneath the Tien Shan leads to lithospheric weakening and active deformation, thus causing intense orogeny. 相似文献
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I.Yu. Koulakov C. Gaina N.L. Dobretsov A.N. Vasilevsky N.A. Bushenkova 《Russian Geology and Geophysics》2013,54(8):859-873
Based on the analysis of various geophysical data, namely, free-air gravity anomalies, magnetic anomalies, upper mantle seismic tomography images, and topography/bathymetry maps, we single out the major structural elements in the Circum Arctic and present the reconstruction of their locations during the past 200 million years. The configuration of the magnetic field patterns allows revealing an isometric block, which covers the Alpha–Mendeleev Ridges and surrounding areas. This block of presumably continental origin is the remnant part of the Arctida Plate, which was the major tectonic element in the Arctic region in Mesozoic time. We believe that the subduction along the Anyui suture in the time period from 200 to 120 Ma caused rotation of the Arctida Plate, which, in turn, led to the simultaneous closure of the South Anyui Ocean and opening of the Canadian Basin. The rotation of this plate is responsible for extension processes in West Siberia and the northward displacement of Novaya Zemlya relative to the Urals–Taimyr orogenic belt. The cratonic-type North American, Greenland, and European Plates were united before 130 Ma. At the later stages, first Greenland was detached from North America, which resulted in the Baffin Sea, and then Greenland was separated from the European Plate, which led to the opening of the northern segment of the Atlantic Ocean. The Cenozoic stage of opening of the Eurasian Basin and North Atlantic Ocean is unambiguously reconstructed based on linear magnetic anomalies. The counter-clockwise rotation of North America by an angle of ~ 15° with respect to Eurasia and the right lateral displacement to 200–250 km ensure an almost perfect fit of the contours of the deep water basin in the North Atlantic and Arctic Oceans. 相似文献
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Ivan Koulakov 《Geophysical Journal International》1998,133(2):467-489
This work is a study of the upper-mantle seismic structure beneath the central part of the Eurasian continent, including the northern Mongolia, Altai and Sayan orogenic areas and the Baikal rift zone. Seismic velocity models are reconstructed using the inverse teleseismic scheme. This scheme uses information from earthquakes located within the study area recorded by the Worldwide Network. The seismic anomaly structure is obtained for different volumes in the study area that partially overlap one another. Special attention has been paid to the reliability of the results: several noise and resolution comparisons are made.
The main results are as follows. (1) A cell structure of anomalies is observed beneath the Altai–Sayan region: positive, cold anomalies correspond to regions of recent orogenesis, negative anomalies are located beneath the depression of the Great Lakes in Mongolia and Hubsugul Lake. (2) A large negative anomaly is observed beneath the Hangai dome in Mongolia. (3) Strong velocity variations are obtained in a zone around Baikal Lake. A large negative anomaly is traced beneath the southern margin of the Siberian craton down to a depth of 700 km. Contrasting positive anomalies (4–5 per cent) are observed at a depth of 100–300 km beneath the Baikal rift. Our geodynamical interpretation of the velocity structure obtained beneath central Asia involves the existence of two processes in the mantle: thermal convection with regular cells, and a narrow plume beneath the southern border of the Siberian plate. 相似文献
The main results are as follows. (1) A cell structure of anomalies is observed beneath the Altai–Sayan region: positive, cold anomalies correspond to regions of recent orogenesis, negative anomalies are located beneath the depression of the Great Lakes in Mongolia and Hubsugul Lake. (2) A large negative anomaly is observed beneath the Hangai dome in Mongolia. (3) Strong velocity variations are obtained in a zone around Baikal Lake. A large negative anomaly is traced beneath the southern margin of the Siberian craton down to a depth of 700 km. Contrasting positive anomalies (4–5 per cent) are observed at a depth of 100–300 km beneath the Baikal rift. Our geodynamical interpretation of the velocity structure obtained beneath central Asia involves the existence of two processes in the mantle: thermal convection with regular cells, and a narrow plume beneath the southern border of the Siberian plate. 相似文献
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Doklady Earth Sciences - The peculiarities of the junction between the Kuril–Kamchatka and Aleutian island arcs are studied using different techniques and experimental data. The models of... 相似文献
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A.V. Jakovlev N.A. Bushenkova I.Yu. Koulakov N.L. Dobretsov 《Russian Geology and Geophysics》2012,53(10):963-971
We present a new three-dimensional model of P-velocity anomalies in the upper mantle beneath the Circum-Arctic region based on tomographic inversion of global data from the catalogues of the International Seismological Center (ISC, 2007). We used travel times of seismic waves from events located in the study area which were recorded by the worldwide network, as well as data from remote events registered by stations in the study region. The obtained mantle seismic anomalies clearly correlate with the main lithosphere structures in the Circum-Arctic region. High-velocity anomalies down to 250–300 km depth correspond to Precambrian thick lithosphere plates, such as the East European Platform with the adjacent shelf areas, Siberian Plate, Canadian Shield, and Greenland. It should be noted that lithosphere beneath the central part of Greenland appears to be strongly thinned, which can be explained by the effect of the Iceland plume which passed under Greenland 50–60 million years ago. Beneath Chukotka, Yakutia, and Alaska we observe low-velocity anomalies which represent weak and relatively thin actively deformed lithosphere. Some of these low-velocity areas coincide with manifestations of Cenozoic volcanism. A high-velocity anomaly at 500–700 km depth beneath Chukotka may be a relic of the subduction zone which occurred here about 100 million years ago. In the oceanic areas, the tomography results are strongly inhomogeneous. Beneath the North Atlantic, we observe very strong low-velocity anomalies which indicate an important role of the Iceland plume and active rifting in the opening of the oceanic basin. On the contrary, beneath the central part of the Arctic Ocean, no significant anomalies are observed, which implies a passive character of rifting. 相似文献