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T. J. Reston W. Weinrebe I. Grevemeyer E. R. Flueh N. C. Mitchell L. Kirstein C. Kopp H. Kopp participants of Meteor / 《Earth and Planetary Science Letters》2002,200(3-4):255-269
The structure of the Mid-Atlantic Ridge at 5°S was investigated during a recent cruise with the FS Meteor. A major dextral transform fault (hereafter the 5°S FZ) offsets the ridge left-laterally by 80 km. Just south of the transform and to the west of the median valley, the inside corner (IC – the region bounded by the ridge and the active transform) is marked by a major massif, characterized by a corrugated upper surface. Fossil IC massifs can also be identified further to the west. Unusually, a massif almost as high as the IC massif also characterizes the outside corner (OC) south of the inactive fracture zone and to the east of the median valley. This OC massif has axis-parallel dimensions identical to the IC massif and both are bounded on their sides closest to the spreading axis by abrupt, steep slopes. An axial volcanic ridge is well developed in the median valley both south of the IC/OC massifs and in an abandoned rift valley to the east of the OC massif, but is absent along the new ridge-axis segment between the IC and OC massifs. Wide-angle seismic data show that between the massifs, the crust of the median valley thins markedly towards the FZ. These observations are consistent with the formation of the OC massif by the rifting of an IC core complex and the development of a new spreading centre between the IC and OC massifs. The split IC massif presents an opportunity to study the internal structure of the footwall of a detachment fault, from the corrugated fault surface to deeper beneath the fault, without recourse to drilling. Preliminary dredging recovered gabbros from the scarp slope of the rifted IC massif, and serpentinites and gabbros from the intersection of this scarp with the corrugated surface. This is compatible with a concentration of serpentinites along the detachment surface, even where the massif internally is largely plutonic in nature. 相似文献
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Kopf A. Klaeschen D. Weinrebe W. Flueh E.R. Grevemeyer I. 《Marine Geophysical Researches》2001,22(3):225-234
The Ninetyeast Ridge is a well-studied hot spot trail in the Indian Ocean. A recent geophysical survey in its central portion
near 17° S included Hydrosweep bathymetric mapping, Parasound echosounder profiles, and high resolution seismic reflection
data. These data reveal a number of small cones of a few hundreds of meters in diameter and up to 200 m height. Seismic evidence
exists regarding a magmatic origin of these features. Different events of basaltic flow and tuff deposition intercalated with
hemipelagic oozes of Eocene to present age, as being known from nearby drilling, allow dating of these latest stages of volcanic
activity. An activity of at least 6 Ma longer than termination of the dominant constructional phase of the ridge can be demonstrated.
These eruptions occur at shallow water depth, and seem to be related to tectonic lineaments in the area. Transtensional stresses
together with a more durable magmatic source beneath this part of the ridge allow magma to ascend along pull-apart structures.
The age discrepancy found calls for special attention when trying to reconstruct global plate motions.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
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Reloca Slide: an ~24 km3 submarine mass‐wasting event in response to over‐steepening and failure of the central Chilean continental slope 
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下载免费PDF全文 Eduardo Contreras‐Reyes David Vlker Jrg Bialas Eduardo Moscoso Ingo Grevemeyer 《地学学报》2016,28(4):257-264
Reloca Slide is the relict of an ~24‐km3 submarine slope collapse at the base of the convergent continental margin of central Chile. Bathymetric and seismic data show that directly to the north and south of the slide the lower continental slope is steep (~10°), the deformation front is shifted landwards by 10–15 km, and the frontal accretionary prism is uplifted. In contrast, ~80 km to the north the lower continental margin presents a lower slope angle of about 4° and a wide frontal accretionary prism. We propose that high effective basal friction conditions at the base of the accretionary prism favoured basal accretion of sediment and over‐steepening of the continental slope, producing massive submarine mass wasting in the Reloca region. This area also spatially correlates with a zone of low coseismic slip of the 2010 Maule megathrust earthquake, which is consistent with high basal frictional coefficients. 相似文献
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A.?FreundtEmail author I.?Grevemeyer W.?Rabbel T.?H.?Hansteen C.?Hensen H.?Wehrmann S.?Kutterolf R.?Halama M.?Frische 《International Journal of Earth Sciences》2014,103(7):2101-2127
After more than a decade of multidisciplinary studies of the Central American subduction zone mainly in the framework of two large research programmes, the US MARGINS program and the German Collaborative Research Center SFB 574, we here review and interpret the data pertinent to quantify the cycling of mineral-bound volatiles (H2O, CO2, Cl, S) through this subduction system. For input-flux calculations, we divide the Middle America Trench into four segments differing in convergence rate and slab lithological profiles, use the latest evidence for mantle serpentinization of the Cocos slab approaching the trench, and for the first time explicitly include subduction erosion of forearc basement. Resulting input fluxes are 40–62 (53) Tg/Ma/m H2O, 7.8–11.4 (9.3) Tg/Ma/m CO2, 1.3–1.9 (1.6) Tg/Ma/m Cl, and 1.3–2.1 (1.6) Tg/Ma/m S (bracketed are mean values for entire trench length). Output by cold seeps on the forearc amounts to 0.625–1.25 Tg/Ma/m H2O partly derived from the slab sediments as determined by geochemical analyses of fluids and carbonates. The major volatile output occurs at the Central American volcanic arc that is divided into ten arc segments by dextral strike-slip tectonics. Based on volcanic edifice and widespread tephra volumes as well as calculated parental magma masses needed to form observed evolved compositions, we determine long-term (105 years) average magma and K2O fluxes for each of the ten segments as 32–242 (106) Tg/Ma/m magma and 0.28–2.91 (1.38) Tg/Ma/m K2O (bracketed are mean values for entire Central American volcanic arc length). Volatile/K2O concentration ratios derived from melt inclusion analyses and petrologic modelling then allow to calculate volatile fluxes as 1.02–14.3 (6.2) Tg/Ma/m H2O, 0.02–0.45 (0.17) Tg/Ma/m CO2, and 0.07–0.34 (0.22) Tg/Ma/m Cl. The same approach yields long-term sulfur fluxes of 0.12–1.08 (0.54) Tg/Ma/m while present-day open-vent SO2-flux monitoring yields 0.06–2.37 (0.83) Tg/Ma/m S. Input–output comparisons show that the arc water fluxes only account for up to 40 % of the input even if we include an “invisible” plutonic component constrained by crustal growth. With 20–30 % of the H2O input transferred into the deeper mantle as suggested by petrologic modeling, there remains a deficiency of, say, 30–40 % in the water budget. At least some of this water is transferred into two upper-plate regions of low seismic velocity and electrical resistivity whose sizes vary along arc: one region widely envelopes the melt ascent paths from slab top to arc and the other extends obliquely from the slab below the forearc to below the arc. Whether these reservoirs are transient or steady remains unknown. 相似文献
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The construction of S-wave velocity models of marine sediments down to hundreds of meters below the seafloor is important
in a number of disciplines. One of the most significant trends in marine geophysics is to use interface waves to estimate
shallow shear velocities which play an important role in determining the shallow crustal structure. In marine settings, the
waves trapped near the fluid–solid interface are called Scholte waves, and this is the subject of the study. In 1998, there
were experiments on the Ninetyeast Ridge (Central Indian Ocean) to study the shallow seismic structure at the drilled site.
The data were acquired by both ocean bottom seismometer and ocean bottom hydrophone. A new type of seafloor implosion sources
has been used in this experiment, which successfully excited fast and high frequency (>500 Hz) body waves and slow, intermediate
frequency (<20 Hz) Scholte waves. The fundamental and first higher mode Scholte waves have both been excited by the implosion
source. Here, the Scholte waves are investigated with a full waveform modeling and a group velocity inversion approach. Shear
wave velocities for the uppermost layers of the region are inferred and results from the different methods are compared. We
find that the full waveform modeling is important to understand the intrinsic attenuation of the Scholte waves between 1 and
20 Hz. The modeling shows that the S-wave velocity varies from 195 to 350 m/s in the first 16 m of the uppermost layer. Depths
levels of high S-wave impedance contrasts compare well to the layer depth derived from a P-wave analysis as well as from drilling
data. As expected, the P- to S-wave velocity ratio is very high in the uppermost 16 m of the seafloor and the Poisson ratio
is nearly 0.5. Depth levels of high S-wave impedance contrasts are comparable to the layer depth derived from drilling data. 相似文献
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