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1.
G. Leitchenkov J. Guseva V. Gandyukhin G. Grikurov Y. Kristoffersen M. Sand A. Golynsky N. Aleshkova 《Marine Geophysical Researches》2008,29(2):135-158
About 16,000 km of multichannel seismic (MCS), gravity and magnetic data and 28 sonobuoys were acquired in the Riiser-Larsen
Sea Basin and across the Gunnerus and Astrid Ridges, to study their crustal structure. The study area has contrasting basement
morphologies and crustal thicknesses. The crust ranges in thickness from about 35 km under the Riiser-Larsen Sea shelf, 26–28 km
under the Gunnerus Ridge, 12–17 km under the Astrid Ridge, and 9.5–10 km under the deep-water basin. A 50-km-wide block with
increased density and magnetization is modeled from potential field data in the upper crust of the inshore zone and is interpreted
as associated with emplacement of mafic intrusions into the continental margin of the southern Riiser-Larsen Sea. In addition
to previously mapped seafloor spreading magnetic anomalies in the western Riiser-Larsen Sea, a linear succession from M2 to
M16 is identified in the eastern Riiser-Larsen Sea. In the southwestern Riiser-Larsen Sea, a symmetric succession from M24B
to 24n with the central anomaly M23 is recognized. This succession is obliquely truncated by younger lineation M22–M22n. It
is proposed that seafloor spreading stopped at about M23 time and reoriented to the M22 opening direction. The seismic stratigraphy
model of the Riiser-Larsen Sea includes five reflecting horizons that bound six seismic units. Ages of seismic units are determined
from onlap geometry to magnetically dated oceanic basement and from tracing horizons to other parts of the southern Indian
Ocean. The seaward edge of stretched and attenuated continental crust in the southern Riiser-Larsen Sea and the landward edge
of unequivocal oceanic crust are mapped based on structural and geophysical characteristics. In the eastern Riiser-Larsen
Sea the boundary between oceanic and stretched continental crust is better defined and is interpreted as a strike-slip fault
lying along a sheared margin. 相似文献
2.
Recent structures in the Alboran Ridge and Yusuf fault zones based on swath bathymetry and sub-bottom profiling: evidence of active tectonics 总被引:2,自引:2,他引:0
The seafloor of the Alboran Sea in the western Mediterranean is disrupted by deformations resulting from convergence between
the African and Eurasian plates. Based on a compilation of existing and new multibeam bathymetry data and high-resolution
seismic profiles, our main objective was to characterize the most recent structures in the central sector, which depicts an
abrupt morphology and was chosen to investigate how active tectonic processes are shaping the seafloor. The Alboran Ridge
is the most prominent feature in the Alboran Sea (>130 km in length), and a key element in the Gibraltar Arc System. Recent
uplift and deformation in this ridge have been caused by sub-vertical, strike-slip and reverse faults with associated folding
in the most recent sediments, their trend shifting progressively from SW–NE to WNW–ESE towards the Yusuf Lineament. Present-day
transtensive deformation induces faulting and subsidence in the Yusuf pull-apart basin. The Alboran Ridge and Yusuf fault
zones are connected, and both constitute a wide zone of deformation reaching tens of kilometres in width and showing a complex
geometry, including different active fault segments and in-relay folds. These findings demonstrate that Recent deformation
is more heterogeneously distributed than commonly considered. A narrow SSW–NNE zone with folding and reverse faulting cuts
across the western end of the Alboran Ridge and concentrates most of the upper crustal seismicity in the region. This zone
of deformation defines a seismogenic, left-lateral fault zone connected to the south with the Al Hoceima seismic swarm, and
representing a potential seismic hazard. Newly detected buried and active submarine slides along the Alboran Ridge and the
Yusuf Lineament are clear signs of submarine slope instability in this seismically active region. 相似文献
3.
The comparative estimation of the parameters of the lithosphere of the Mid-Ocean Southwestern Indian range in the areas westwards
and eastwards of the Atlantis II transform fault zone shows that, within this zone, an alteration in the basalt composition
occurred. Eastwards of this zone, a decrease of the anomaly of the magnetic field occurred and increased average depths of
the axial part (4.7 km) and thinning (up to 4–5 km) of the ocean crust with increased rates of seismic waves in the upper
mantle were observed. This, first of all, indicates an anomalously cold mantle below the oceanic crust. The changes that occurred
in the location of the Euler pole within the last millions of years resulted in slanting spreading in the area of the investigation
with rates of opening lower than 1.8 cm/year probably accompanied by the phenomena of transtension in the active parts of
the transform faults. The interaction between the Landly and Somali lithosphere plates occurred along the diffusion boundary
and was accompanied by problems with tracing the chrones between the neighboring profiles of geomagnetic observations. Consequently,
the more detailed investigation of the configuration of the diffusion boundary will contribute to the more accurate reconstruction
of the paleogeodynamics of the central part of the Indian Ocean. 相似文献
4.
The distinguishing features of the seismicity throughout South Kamchatka and within the Avacha Bay seismic gap in the 20th century are considered. The evolution of the evaluation of the magnitudes of the strongest earthquakes for this gap from M = 7.25–7.5 in 1965–1980 to 7.75–8.0 after 1980 is discussed. On the basis of the method for studying the characteristic features of the seismicity within a seismic gap developed for the Central Kuriles, the seismicity of South Kamchatka is considered for depths of 0–100, 101–200, and more than 200 km according to the data from the New Catalog [6] for the period from 1901 to 1974 (M ≥ 6.1), the Special Catalog for North Eurasia [3] for the period from 1975 to 1993 (M ≥ 4.5), and additional data from the Kamchatka stations for the period from 1994 to 1997. It was found that the seismic process within the region of South Kamchatka is typical of the island arcs; i.e, most of the earthquakes considered and the maximum of the seismic energy released are concentrated in the lithosphere at depths of 0–100 km. The seismological situation in the zone of Avacha Bay is found to be similar to that within the second kind of the seismic gap during the precursory seismic quiescence of the 1978 Oaxac earthquake with M = 7.8 in Central Mexico. This allows us to consider the zone of Avacha Bay as a possible seismic gap of the second kind. Such a result can be considered as a suggestion of the possibility of the occurrence in Avacha Bay of an earthquake with M ~ 8 according to the long-term forecast for the region of the Kuriles and Kamchatka made by S.A. Fedotov. 相似文献
5.
D. Dusunur J. Escartín V. Combier T. Seher W. Crawford M. Cannat S. C. Singh L. M. Matias J. M. Miranda 《Marine Geophysical Researches》2009,30(2):105-120
The crust at mid-ocean ridges is formed through a combination of magmatic and tectonic processes. Along slow-spreading ridges,
magmatism is inferred to be discontinuous and episodic, and lithospheric faulting may strongly interact with the melt supply
system. These interactions can be studied for the first time at the Lucky Strike segment along the Mid-Atlantic Ridge (MAR),
where a 3.4 km deep magma chamber (AMC) extending ~6 km along-axis is found at its centre (Singh et al. in Earth Planet Sci
Lett 246:353–366, 2006). With an array of ocean bottom seismometers we have detected along this ridge segment approximately 400 microseismic events
during a total of 6 days, and located 71 of them, whose local magnitudes ranged from 0.2 to 1.8. While most of the events
were concentrated at non-transform offset and inside corners, three events with well-constrained locations were detected beneath
the central volcano and at the edges of the AMC. Two of the microearthquakes, which occur in a brittle lithosphere and therefore
at temperatures lower than 750°C, are deeper than the AMC and therefore very steep thermal gradients both along- and across-axis.
Regionally seismicity deepens from ~6 km at the segment center to >10 km towards the ends. 相似文献
6.
In this paper we focused on understanding the isostatic compensation of the Ninetyeast Ridge in the overall context of the
Bay of Bengal oceanic lithosphere and the interaction of the ridge system with the north Andaman subduction zone from north
of 7–18°N. This region is characterized by the initial interaction of the Kerguelen hotspot with the Bay of Bengal oceanic
lithosphere. We used satellite altimeter-derived marine geoid, as it should comprehensively reflect the compensations caused
by large spatial wavelength dominated deeper anomaly sources in a hotspot affected lithospheric load like the Ninetyeast Ridge.
Our analyses of the geoid-to-topography ratio (GTR), residual geoid, gravity-to-topographic kernel and upward continuation
of anomalies show the existence of two different types of source compensation bodies beneath the northern (12–18°N) and southern
(7–12°N) Ninetyeast Ridge. In the northern region, the geoid to topography ratio varies from 0.63 ± 0.05 to 0.44 ± 0.03, while
in the southern region it ranges from 1.34 ± 0.09 to 1.31 ± 0.07 which resulted in a north to south increase in the apparent
compensation depth from ~9 to 28 km. The presence of a shallow Moho, low GTR, broader gravity to topography kernel and the
absence of a ridge anomaly from the mantle density dominated upward continued anomaly at z = 300 km indicates that at the northern segment the underplated low density crustal melt is the dominant isostatic compensating
body. However, at the southern ridge segment the high GTR, strong gravity-to-topography kernel and the subsistence of the
anomaly at long wavelengths, even at z = 300 km represents the existence of large volumes of hotspot related underplated dense material as the source of compensation.
The proximity of the dense source compensating body of the southern Ninetyeast Ridge to the Andaman subduction zone affected
the regional mantle driven density gradient flow, as observed from the z = 300 km continued gravity anomaly. The existence of a southern Ninetyeast Ridge in such a transpressional regime has caused
the formation of a forearc sliver at its eastern flank, which is a major crustal deformational structure developed as a result
of ridge-trench collision. 相似文献
7.
D. Gopala Rao G. C. Bhattacharya M. V. Ramana V. Subrahmanyam T. Ramprasad K. S. Krishna A. K. Chaubey G. P. S. Murty K. Srinivas Maria Desa S. I. Reddy B. Ashalata C. Subrahmanyam G. S. Mital R. K. Drolia S. N. Rai S. K. Ghosh R. N. Singh R. Majumdar 《Marine Geophysical Researches》1994,16(3):225-236
Analysis of the multi-channel seismic reflection, magnetic and bathymetric data collected along a transect, 1110 km long parallel to 13° N latitude across the Bay of Bengal was made. The transect is from the continental shelf off Madras to the continental slope off Andaman Island in water depths of 525 m to 3350 m and across the Western Basin (bounded by foot of the continental slope of Madras and 85° E Ridge), the 85° E Ridge, the Central Basin (between the 85° E Ridge and the Ninetyeast Ridge), the Ninetyeast Ridge and the Sunda Arc. The study revealed eight seismic sequences, H1 to H8 of parallel continuous to discontinuous reflectors. Considering especially depth to the horizons, nature of reflection and on comparison with the published seismic reflection results of Currayet al. (1982), the early Eocene (P) and Miocene (M) unconformities and the base of the Quaternary sediments (Q) are identified on the seismic section. Marked changes in velocities also occur at their boundaries.In the Western Basin the acoustic basement deepening landward is inferred as a crystalline basement overlain by about 6.7 km of sediment. In the Central Basin possibly thicker sediments than in the Western Basin are estimated. The sediments in the Sunda Arc area are relatively thick and appears to have no distinct horizons. But the entire sedimentary section appears to be consisting of folded and possibly faulted layers.The comparatively broader wavelength magnetic anomalies of the Central Basin also indicate deeper depth of their origin. Very prominent double humped feature of the 85° E Ridge and broad basement swell of the Ninetyeast Ridge are buried under about 2.8 km thick sediments except over the prominent basement high near 92° E longitude. The positive structural relief of the buried 85° E Ridge in the area is reflected in magnetic signature of about 450 nT amplitude. Flexural bulge of the 85° E Ridge and subsidence of the Ninetyeast Ridge about 24 cm my–1 rate since early Eocene period have been inferred from the seismic sequence analysis. 相似文献
8.
The Blake Outer Ridge is a 480–kilometer long linear sedimentary drift ridge striking perpendicular to the North American
coastline. By modeling free-air gravity anomalies we tested for the presence of a crustal feature that may control the location
and orientation of the Blake Outer Ridge. Most of our crustal density models that match observed gravity anomalies require
an increase in oceanic crustal thickness of 1–3 km on the southwest side of the Blake Outer Ridge relative to the northeast
side. Most of these models also require 1–4 km of crustal thinning in zone 20–30 km southwest of the crest of the Blake Outer
Ridge. Although these features are consistent with the structure of oceanic fracture zones, the Blake Outer Ridge is not parallel
to adjacent known fracture zones. Magnetic anomalies suggest that the ocean crust beneath this feature formed during a period
of mid-ocean ridge reorganization, and that the Blake Outer Ridge may be built upon the bathymetric expression of an oblique
extensional feature associated with ridge propagation. It is likely that the orientation of this trough acted as a catalyst
for sediment deposition with the start of the Western Boundary Undercurrent in the mid-Oligocene. 相似文献
9.
The 85°E Ridge, located in the Bay of Bengal of the northeastern Indian Ocean is an enigmatic geological feature as it possesses unusual geophysical signatures. The ridge's internal structure and mode of eruptions are unknown due to lack of deep seismic reflection and borehole data control. Here, we analyze 10 km of long-streamer seismic reflection data to unravel the ridge's internal structure, and thereby to enhance the understanding of how the ridge was originated and grew over a geologic time. Seismic facies analysis reveals the ridge structure consisting of volcanic vent and several stratigraphic units including packs of prograding clinoforms. The clinoform sequences are interpreted as volcanic successions, and led to the formation of lava-delta fronts. Interpreted features of lava-fed deltas and intervening erosional surfaces, and mass flows along ridge flanks suggest that the 85°E Ridge is a volcanic construct, and was built by both subaqueous and multiphase sub-marine volcanism during the Late Cretaceous (approximately from 85 to 80 Ma). At later time, from Oligocene-Miocene (∼23 Ma) onwards the ridge was buried under the thick sediments of the Bengal Fan system. 相似文献
10.
Bathymetry, satellite-derived gravity, and interpreted seismic reflection data across the northern Falkland/Malvinas Plateau
fossil continent–ocean transform rim may record the degree of mechanical coupling across the boundary after ridge–transform
intersection time. The rim comprises a broad microcontinental block in the east and a continental marginal fracture ridge
50–100 km wide elsewhere. Free-air gravity anomalies tentatively suggest that the fracture ridge is locked against oceanic
elastic lithosphere both to the north (Argentine Basin) and south (Central Falkland Basin).
Received: 18 January 1996 / Revision received: 25 March 1995 相似文献
11.
Wilfried Jokat Oliver Ritzmann Christian Reichert Karl Hinz 《Marine Geophysical Researches》2004,25(3-4):283-304
This study presents the results of a seismic refraction experiment that was carried out off Dronning Maud Land (East Antarctica)
along the Explora Escarpment (14° W–12° W) and close to Astrid Ridge (6°E). Oceanic crust of about 10 km thickness is observed
northwest of the Explora Escarpment. Stretched continental crust, observed southeast of the escarpment, is most likely intruded
by volcanic material at all crustal levels. Seismic velocities of 7.0–7.4 km/s are modelled for the lower crust. The northern
boundary of this high velocity body coincides approximately with the Explora Escarpment. The upper crystalline crust is overlain
by a 4-km thick and 70-km wide wedge of volcanic material: the Explora Wedge. Seismic velocities for the oceanic crust north
of the Explora Escarpment are in good agreement with global studies. The oceanic crust in the region of the Lazarev Sea is
also up to 10-km thick. The lower crystalline crust shows seismic velocities of up to 7.4 km/s. This, together with the larger
crustal thickness might point to higher mantle temperatures during the formation of the oceanic crust. The more southerly
rifted continental crust is up to 25-km thick, and also has seismic velocities of 7.4 km/s in the lower crystalline crust.
This section is interpreted to consist of stretched continental crust, which is heavily intruded by volcanic material up to
approximately 8-km depth. Multichannel seismic data indicate that, in this region, two volcanic wedges are present. The wedges
are interpreted to have evolved during different time/rift periods. The wedges have a total width of at least 180 km in the
Lazarev Sea. Our results support previous findings that the continental margin off Dronning Maud Land between ≈2°E and ≈13°E
had a complex and long-lived rift history. Both continental margins can be classified as rifted volcanic continental margins
that were formed during break-up of Gondwana. 相似文献
12.
Crustal structure of the Co^te d’Ivoire–Ghana marginal ridge and its transition with oceanic lithosphere are deduced from
multichannel seismic reflection, wide-angle seismic, and gravity data. The CIGMR is cut into rotated blocks and displays a
crustal structure quite similar to that of the nearby northern Ivorian extensional basin. These results strongly support that
the CIGMR represents an uplifted fragment of continental crust. Transition with the oceanic crust appears sharp; continental
crustal thinning occurs over less than 5 km. We did not find evidence for underplating and/or contamination as anticipated
from such a sharp contact between continental and oceanic crust.
Received: 12 March 1995/Revision received: 2 July 1996 相似文献
13.
Yoshifumi Nogi Kumiko Nishi Nobukazu Seama Yoichi Fukuda 《Marine Geophysical Researches》2004,25(3-4):221-231
The seafloor spreading evolution in the Southern Indian Ocean is key to understanding the initial breakup of Gondwana. We
summarize the structural lineaments deduced from the GEOSAT 10 Hz sampled raw altimetry data as well as satellite derived
gravity anomaly map and the magnetic anomaly lineation trends from vector magnetic anomalies in the West Enderby Basin, the
Southern Indian Ocean. The gravity anomaly maps by both Sandwell and Smith 1997, J. Geophys. Res. 102, 10039–10054 and 10 Hz raw altimeter data show almost the same general trends. However, curved structural trends, which turn
from NNW–SSE in the south to NNE–SSW in the north, are detected only from gravity anomaly maps by 10 Hz raw altimeter data
just to the east of Gunnerus Ridge. NNE–SSW structural trends and magnetic anomaly lineation trends that are perpendicular
to them are observed between the Gunnerus Ridge and the Conrad Rise. To the west of Gunnerus Ridge, structural elements trend
NNE–SSW and magnetic polarity changes are normal to them. In contrast, almost NNW–SSE structural trends and ENE–WSW magnetic
polarity reversal strikes are dominant to the east of Gunnerus Ridge. Curved structural trends, which turn from WNW–ESE direction
in the south to NNE–SSW direction in the west, and magnetic polarity reversal strikes that are almost perpendicular to them
are observed just south of Conrad Rise. The magnetic polarity reversals may be parts of the Mesozoic magnetic anomaly sequence
that formed along side of the structural lineaments before the long Cretaceous normal polarity superchron. Curved structural
trends, detected only from gravity anomaly maps by 10 Hz raw altimeter data, most likely indicate slight changes in spreading
direction from an initial NNW–SSE direction to NNE–SSW. Our results also suggest that these curved structural trends are fracture
zones that formed during initial breakup of Gondwana. 相似文献
14.
A newly discovered area of mud volcanism, about 170 km south of Crete, in the central–eastern part of the Mediterranean Ridge,
was named the “United Nations Rise” (UNR). A survey of the UNR area with the deep-towed ORE tech side-scan sonar equipped
with a subbottom profiler revealed the presence of some mud volcanoes and also showed various other sea-floor features, including
slumps, escarpments and pockmark-type depressions. Several of our interpretations were ground-truthed by coring. The UNR area
appears to belong to the Inner deformation front of the Mediterranean Ridge. 相似文献
15.
We report the occurrence of ferrobasalts recovered from the Central Indian Ocean Basin crust generated at the Southeast Indian
Ridge during a phase of moderate to fast spreading accretion (∼110–190 mm/yr, full rate).The rocks are rich in plagioclase,
FeO* (13–19%), and TiO2 (2.27–2.76%), poor in olivine and MgO (3.44–6.20%), and associated with topographic highs and increased amplitude magnetic
anomalies corresponding to chrons A25 and A24. We suggest that secon dary eruptions from ancient N-MORB magma, which may have
been trapped at a shallow depth in a horizon of neutral buoyancy, could have produced the ferrobasalts.
Received: 27 January 1998 / Revision received: 25 May 1998 相似文献
16.
The Carlsberg Ridge lies between the equator and the Owen fracture zone. It is the most prominent mid-ocean ridge segment
of the western Indian Ocean, which contains a number of earthquake epicenters. Satellite altimetry can be used to infer subsurface
geological structures analogous to gravity anomaly maps generated through ship-borne survey. In this study, free-air gravity
and its 3D image have been generated over the Carlsberg Ridge using a very high resolution data base, as obtained from Geosat
GM, ERS-1, Seasat and TOPEX/POSEIDON altimeter data. As observed in this study, the Carlsberg Ridge shows a slow spreading
characteristic with a deep and wide graben (average width ∼15 km). The transform fault spacing confirms variable slow to intermediate
characteristics with first and second order discontinuities. The isostatically compensated region of the Carlsberg Ridge could
be demarcated with near zero contour values in the free-air gravity anomaly images over and along the Carlsberg Ridge axes
and over most of the fracture zone patterns. Few profiles have been generated across the Carlsberg Ridge and the characteristics
of slow/intermediate spreading ridge of various orders of discontinuity could be identified. It has also been observed in
zero contour image as well as in the characteristics of valley patterns along the ridge from NW to SE that different spreading
rates, from slow to intermediate, are occurring in different parts of the Carlsberg ridge. It maintains the morphology of
a slow spreading ridge in the NW, where the wide and deep axial valley (∼1.5–3 km) also implies the pattern of a slow spreading
ridge. However, a change in the morphology/depth of the axial valley from NW to SE indicates the nature of the Carlsberg Ridge
as a slow to intermediate spreading ridge.
For the prevailing security restrictions, lat./lon. coordinates have been omitted in few images. 相似文献
17.
A. Maldonado F. Bohoyo J. Galindo-Zaldívar J. Hernández-Molina A. Jabaloy F. J. Lobo J. Rodríguez-Fernández E. Suriñach J. T. Vázquez 《Marine Geophysical Researches》2006,27(2):83-107
The distribution of seismic units in deposits of the basins near the Antarctic–Scotia plate boundary is described based on
the analysis of multichannel seismic reflection profiles. Five main seismic units are identified. The units are bounded by
high-amplitude continuous reflectors, named a to d from top to bottom. The two older units are of different age and seismic
facies in each basin and were generally deposited during active rifting and seafloor spreading. The three youngest units (3
to 1) exhibit, in contrast, rather similar seismic facies and can be correlated at a regional scale. The deposits are types
of contourite drift that resulted from the interplay between the northeastward flow of Weddell Sea Bottom Water (WSBW) and
the complex bathymetry in the northern Weddell Sea, and from the influence of the Antarctic Circumpolar Current and the WSBW
in the Scotia Sea. A major paleoceanographic event was recorded by Reflector c, during the Middle Miocene, which represents
the connection between the Scotia Sea and the Weddell Sea after the opening of Jane Basin. Unit 3 (tentatively dated ∼Middle
to Late Miocene) shows the initial incursions of the WSBW into the Scotia Sea, which influenced a northward progradational
pattern, in contrast to the underlying deposits. The age attributed to Reflector b is coincident with the end of spreading
at the West Scotia Ridge (∼6.4 Ma). Unit 2 (dated ∼Late Miocene to Early Pliocene) includes abundant high-energy, sheeted
deposits in the northern Weddell Sea, which may reflect a higher production of WSBW as a result of the advance of the West
Antarctic ice-sheet onto the continental shelf. Reflector a represents the last major regional paleoceanographic change. The
timing of this event (∼3.5–3.8 Ma) coincides with the end of spreading at the Phoenix–Antarctic Ridge, but may be also correlated
with global events such as initiation of the permanent Northern Hemisphere ice-sheet and a major sea level drop. Unit 1 (dated
∼Late Pliocene to Recent) is characterized by abundant chaotic, high-energy sheeted deposits, in addition to a variety of
contourites, which suggest intensified deep-water production. Units 1 and 2 show, in addition, a cyclic pattern, more abundant
wavy deposits and the development of internal unconformities, all of which attest to alternating periods of increased bottom
current energy. 相似文献
18.
The circulation of intermediate and deep waters in the Philippine Sea west of the Izu-Ogasawara-Mariana-Yap Ridge is estimated
with use of an inverse model applied to the World Ocean Circulation Experiment (WOCE) Hydrographic Program data set. Above
1500 m depth, the subtropical gyre is dominant, but the circulation is split in small cells below the thermocline, causing
multiple zonal inflows of intermediate waters toward the western boundary. The inflows along 20°N and 26°N carry the North
Pacific Intermediate Water (NPIW) of 11 × 109 kg s−1 in total, at the density range of 26.5σθ–36.7σ2 (approximately 500–1500 m depths), 8 × 109 kg s−1 of the NPIW circulate within the subtropical gyre, whereas the rest is conveyed to the tropics and the South China Sea. The
inflow south of 15°N carries the Tropical Salinity Minimum water of 35 × 109 kg s−1, nearly half of which return to the east through a narrow undercurrent at 15–17°N, and the rest is transported into the lower
part of the North Equatorial Countercurrent. Below 1500 m depth, the deep circulation regime is anti-cyclonic. At the density
range of 36.7σ2, – 45.845σ4 (approximately 1500–3500 m depths), deep waters of 17 × 109 kg s−1 flow northward, and three quarters of them return to the east at 16–24°N. The remainder flows further north of 24°N, then
turns eastward out of the Philippine Sea, together with a small amount of subarctic-origin North Pacific Deep Water (NPDW)
which enters the Philippine Sea through the gap between the Izu Ridge and Ogasawara Ridge. The full-depth structure and transportation
of the Kuroshio in total and net are also examined. It is suggested that low potential vorticity of the Subtropical Mode Water
is useful for distinguishing the net Kuroshio flow from recirculation flows.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
Ingrid Marie Hasle Amundsen Maria Blinova Berit Oline Hjelstuen Rolf Mjelde Haflidi Haflidason 《Marine Geophysical Researches》2011,32(4):441-453
The northeastern high-latitude North Atlantic is characterised by the Bellsund and Isfjorden fans on the continental slope
off west Svalbard, the asymmetrical ultraslow Knipovich spreading ridge and a 1,000 m deep rift valley. Recently collected
multichannel seismic profiles and bathymetric records now provide a more complete picture of sedimentary processes and depositional
environments within this region. Both downslope and alongslope sedimentary processes are identified in the study area. Turbidity
currents and deposition of glacigenic debris flows are the dominating downslope processes, whereas mass failures, which are
a common process on glaciated margins, appear to have been less significant. The slide debrite observed on the Bellsund Fan
is most likely related to a 2.5–1.7 Ma old failure on the northwestern Barents Sea margin. The seismic records further reveal
that alongslope current processes played a major role in shaping the sediment packages in the study area. Within the Knipovich
rift valley and at the western rift flank accumulations as thick as 950–1,000 m are deposited. We note that oceanic basement
is locally exposed within the rift valley, and that seismostratigraphic relationships indicate that fault activity along the
eastern rift flank lasted until at least as recently as 1.5 Ma. A purely hemipelagic origin of the sediments in the rift valley
and on the western rift flank is unlikely. We suggest that these sediments, partly, have been sourced from the western Svalbard—northwestern
Barents Sea margin and into the Knipovich Ridge rift valley before continuous spreading and tectonic activity caused the sediments
to be transported out of the valley and westward. 相似文献
20.
Audun Libak Rolf Mjelde Henk Keers Jan Inge Faleide Yoshio Murai 《Marine Geophysical Researches》2012,33(2):185-207
This paper describes results from a geophysical study in the Vestbakken Volcanic Province, located on the central parts of the western Barents Sea continental margin, and adjacent oceanic crust in the Norwegian-Greenland Sea. The results are derived mainly from interpretation and modeling of multichannel seismic, ocean bottom seismometer and land station data along a regional seismic profile. The resulting model shows oceanic crust in the western parts of the profile. This crust is buried by a thick Cenozoic sedimentary package. Low velocities in the bottom of this package indicate overpressure. The igneous oceanic crust shows an average thickness of 7.2 km with the thinnest crust (5–6 km) in the southwest and the thickest crust (8–9 km) close to the continent-ocean boundary (COB). The thick oceanic crust is probably related to high mantle temperatures formed by brittle weakening and shear heating along a shear system prior to continental breakup. The COB is interpreted in the central parts of the profile where the velocity structure and Bouguer anomalies change significantly. East of the COB Moho depths increase while the vertical velocity gradient decreases. Below the assumed center for Early Eocene volcanic activity the model shows increased velocities in the crust. These increased crustal velocities are interpreted to represent Early Eocene mafic feeder dykes. East of the zone of volcanoes velocities in the crust decrease and sedimentary velocities are observed at depths of more than 10 km. The amount of crustal intrusions is much lower in this area than farther west. East of the Kn?legga Fault crystalline basement velocities are brought close to the seabed. This fault marks the eastern limit of thick Cenozoic and Mesozoic packages on central parts of the western Barents Sea continental margin. 相似文献