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1.
Ingi Olafsson Eirik Sundvor Olav Eldholm Kjersti Grue 《Marine Geophysical Researches》1992,14(2):137-162
Analysis in both the x—t and —p domains of high-quality Expanded Spread Profiles across the Møre Margin show that many arrivals may be enhanced be selective ray tracing and velocity filtering combined with conventional data reduction techniques. In terms of crustal structure the margin can be divided into four main areas: 1) a thicker than normal oceanic crust in the eastern Norway Basin; 2) expanded crust with a Moho depth of 22 km beneath the huge extrusive complex constructed during early Tertiary breakup; 3) the Møre Basin where up to 13–14 km of sediments overlie a strongly extended outer part with a Moho depth at 20 km west of the Ona High; and 4) a region with a 25–27 km Moho depth between the high and the Norwegian coast. The velocity data restricts the continent-ocean boundary to a 15–30 km wide zone beneath the seaward dipping reflector wedges. The crust west of the landward edge of the inner flow is classified as transitional. This region as well as the adjacent oceanic crust is soled by a 7.2–7.4 km s–1 lower crustal body which may extend beneath the entire region that experienced early Tertiary crustal extension. At the landward end of the transect a 8.5 km s–1 layer near the base of the crust is recognized. A possible relationship with large positive gravity anomalies and early Tertiary alkaline intrusions is noted. 相似文献
2.
Eirik Sundvor 《Marine Geophysical Researches》1971,1(3):303-313
A seismic refraction survey along nine profiles has been carried out on the Norwegian continental shelf in the area between Andøya and Fugløybanken (69°–71°N). In all but one of the profiles the shelf is found to be covered with layered sediments. Average velocities are 1.85, 2.20, 2,55, 3.25, and 3.90 km/s probably representing sediments of Cenozoic and Mesozoic ages. An average velocity of 5.25 km/s represents a basement, which probably is the seaward continuation of the onshore Caledonian rocks. Except for an apparent depressional area just north of Andøya the sedimentary layers appear to dip towards the shelf edge. On the outer part of the shelf the 2.20 km/s layer appears at the sea-floor while more complex structures are found on the inner part of the shelf.Publication No. 3 in NTNF's Continental Shelf Project. 相似文献
3.
P. R. Vogt J. Gardner K. Crane E. Sundvor F. Bowles G. Cherkashev 《Geo-Marine Letters》1999,19(1-2):97-110
Numerous small (50- to 300-m-diameter) strong-backscatter objects were imaged on the 1200- to 1350-m deep crest of Vestnesa
Ridge (Fram Strait) and along the 900- to 1000-m deep northeast margin of the Storegga slide valley. Ground-truthing identified
most of these objects as 2- to 10-m-deep pockmarks, developed within soft, acoustically stratified silty clays (typical wet
bulk density: 1400–1600 kg m-3; sound speed: 1480– 1505 m s-1; porosity, 65–75%; shear strength: 5–10 kPa; water content: 80–120%; and thermal conductivity: 0.8–0.9 W m-1 deg C-1 in the top 3 m). Gas wipeouts, enhanced reflectors, and reflector discontinuities indicate recent or ongoing activity, but
the absence of local heat flow anomalies suggests that any upward fluid flows are modest and/or local. 相似文献
4.
The continental margin off the Lofoten-Vesterålen islands between 67° and 70°N becomes progressively narrower northwards. The continental shelf west of the islands and in the Vestfjord is underlain by a relatively thin sedimentary sequence which has been subjected to block faulting, forming local basins and highs. The structural deformation had ceased in the mid-Creataceous. The Tertiary sediments are generally missing, but reappear in the Træn Basin south of about 67.5°N. The continental margin seaward of the shelf edge changes structural style from south to north. In the north, the marginal subsidence is characterized by major faults, whereas minor faults and flexuring dominate south of 69°N. A smooth acoustic basement reflector, which in places is underlain by dipping sub-basement interfaces, is typical for the area between anomaly 23 and the Vøring Plateau Escarpment. In the northern area, the acoustic basement extends almost to the shelf edge. These observations relate to the early Tertiary history of rifting and passive margin formation within a preexisting epicontinental sea between Norway and Greenland. The abrupt change from continental to oceanic basement is defined by the extension of the Vøring Plateau Escarpment south of 69.1°N and by the change in magnetic character off Vesterålen. 相似文献
5.
K. Crane E. Sundvor J. -P. Foucher M. Hobart A. M. Myhre S. LeDouaran 《Marine Geophysical Researches》1988,9(2):165-194
The northern Norwegian-Greenland Sea opened up as the Knipovich Ridge propagated from the south into the ancient continental Spitsbergen Shear Zone. Heat flow data suggest that magma was first intruded at a latitude of 75° N around 60 m.y.b.p. By 40–50 m.y.b.p. oceanic crust was forming at a latitude of 78° N. At 12 m.y.b.p. the Hovgård Transform Fault was deactivated during a northwards propagation of the Knipovich Ridge. Spreading is now in its nascent stages along the Molloy Ridge within the trough of the Spitsbergen Fracture Zone. Spreading rates are slower in the north than the south. For the Knipovich Ridge at 78° N they range from 1.5–2.3 mm yr-1 on the eastern flank to 1.9–3.1 mm yr-1 on the western flank. At a latitude of 75° N spreading rates increase to 4.3–4.9 mm yr-1.Thermal profiles reveal regions of off-axial high heat flow. They are located at ages of 14 m.y. west and 13 m.y. east of the northern Knipovich Ridge, and at 36 m.y. on the eastern flank of the southern Knipovich Ridge. These may correspond to episodes of increased magmatic activity; which may be related to times of rapid north-wards rise axis propagation.The fact that the Norwegian-Greenland Sea is almost void of magnetic anomalies may be caused by the chaotic extrusion of basalts from a spreading center trapped within the confines of an ancient continental shear zone. The oblique impact of the propagating rift with the ancient shear zone may have created an unstable state of stress in the region. If so, extension took place preferentially to the northwest, while compression occurred to the southeast between the opening, leaking shear zone and the Svalbard margin. This caused faster spreading rates to the northwest than to the southeast. 相似文献
6.
Heat flow taken between Svalbard and Greenland reveal three thermal provinces:
- 1. (1) the Molloy Ridge within the Spitsbergen Transform,
- 2. (2) the Yermak Plateau
- 3. (3) the northeastern margin of Svalbard (Nordaustlandet).
7.
Recent geophysical measurements, including multi-channel seismic reflection, on the Svalbard passive margin have revealed that it has undergone a complex geological history which largely reflects the plate tectonic evolution of the Greenland Sea and the Arctic Ocean. The western margin (75–80°N) is of a sheared-rifted type, along which the rifted margin developed subsequent to a change in the pole of plate rotation about 36 m.y. B.P. The north-trending Hornsund Fault on the central shelf and the eastern escarpment of the Knipovich Ridge naturally divide the margin into three structural units. These main marginal structures strike north, paralleling the regional onshore fault trends. This trend also parallels the direction of Early Tertiary plate motion between Svalbard and Greenland. Thus, the western Svalbard margin was initially a zone of shear, and the shear movements have affected the adjacent continental crust. Although, the nature and location of the continent—ocean crustal transition is somewhat uncertain, it is unlikely to lie east of the Hornsund Fault. The northern margin, including the Yermak marginal plateau, is terminated to the west by the Spitsbergen Fracture Zone system. This margin is of a rifted type and the preliminary analysis indicates that the main part of the investigated area is underlain by continental crust. 相似文献
8.
The concept of plate tectonics implies that the normal sea floor spreading stage is preceded by a sequence of events associated with the break-up of continental crust. Thus, evidence of the early development of “non-failed” rifts is to be found at passive continental margins. Of special interest is the question of the extent of the continental crust and the structural and compositional changes associated with the change in crustal type. In addressing these topics, we have focused attention on the Norwegian margin between the Jan Mayen and Senja fracture zones (66°–70°N) in an attempt to understand its history of rifting and early sea floor spreading. p ]The southern part of this rifted margin is characterized by a wide shelf and the marginal Vøring Plateau interrupts a gentle slope at a level of about 1500 m. However, the margin becomes progressively narrower towards the north and a typical narrow shelf and steep slope emerge off the Lofo—tenVesterålen Islands (Fig. 1). In a reconstructed pre-opening configuration (Talwani and Eldholm, 1977) the narrowest part of the juxtaposed EastGreenland margin is found in the south and a wide shelf and slope corresponds to the Lofoten-Vesterålen margin.The most prominent structural element is a buried basement high underneath the Vøring Plateau. The high is bounded landward by the Vøring Plateau Escarpment, a major structural boundary which defines typical changes in the geophysical parameters. These are: (1) a sudden increase of depth to acoustic basement; (2) changes in the velocity-depth function; (3) a gravity gradient; and (4) a magnetic edge anomaly separating sea-floor spreading type anomalies from a quiet zone on the landward side (Talwani and Eldholm, 1972). These observations were interpreted in terms of a sharp ocea—ncontinent crustal transition along the escarpment with sea-floor spreading commencing between anomaly 24 and 25 time (56–58 m.y. B.P.). Alternatively, the concept of ancient oceanic crust landward of this escarpment and the possible existence of continental crust under the outer basement high have been argued and we refer to Eldholm et al. (1979) for a detailed discussion. 相似文献
9.
O. Eldholm E. Sundvor P. R. Vogt B. O. Hjelstuen K. Crane A. K. Nilsen T. P. Gladczenko 《Geo-Marine Letters》1999,19(1-2):29-37
The high thermal gradient and heat flow >1000?mW?m-2 on Håkon Mosby Mud Volcano are ascribed to rapid transport of pore water, mud, and gas in a narrow, deep conduit within a 3.1-km-thick glacial sediment unit. The instability is caused by rapid loading of dense glacial sediments on less dense oozes. Changes in pressure–temperature conditions by sudden, large-scale downslope mass movement may induce structural deformation, opening transient pathways from the base of the glacial sediments to the sea floor. This model may also explain slope maxima elsewhere on the margin. 相似文献
10.
The role of the Spitsbergen shear zone in determining morphology,segmentation and evolution of the Knipovich Ridge 总被引：1，自引：1，他引：1
Crane Kathleen Doss Hany Vogt Peter Sundvor Eirik Cherkashov Georgy Poroshina Irina Joseph Devorah 《Marine Geophysical Researches》2001,22(3):153-205
In 1989–1990 the SeaMARC II side-looking sonar and swath bathymetric system imaged more than 80 000 km2 of the seafloor in the Norwegian-Greenland Sea and southern Arctic Ocean. One of our main goals was to investigate the morphotectonic
evolution of the ultra-slow spreading Knipovich Ridge from its oblique (115° ) intersection with the Mohns Ridge in the south
to its boundary with the Molloy Transform Fault in the north, and to determine whether or not the ancient Spitsbergen Shear
Zone continued to play any involvement in the rise axis evolution and segmentation.
Structural evidence for ongoing northward rift propagation of the Mohns Ridge into the ancient Spitsbergen Shear Zone (forming
the Knipovich Ridge in the process) includes ancient deactivated and migrated transforms, subtle V-shaped-oriented flank faults
which have their apex at the present day Molloy Transform, and rift related faults that extend north of the present Molloy
Transform Fault. The Knipovich Ridge is segmented into distinct elongate basins; the bathymetric inverse of the very-slow
spreading Reykjanes Ridge to the south. Three major fault directions are detected: the N-S oriented rift walls, the highly
oblique en-echelon faults, which reside in the rift valley, and the structures, defining the orientation of many of the axial
highs, which are oblique to both the rift walls and the faults in the axial rift valley.
The segmentation of this slow spreading center is dominated by quasi stationary, focused magma centers creating (axial highs)
located between long oblique rift basins. Present day segment discontinuities on the Knipovich Ridge are aligned along highly
oblique, probably strike-slip faults, which could have been created in response to rotating shear couples within zones of
transtension across the multiple faults of the Spitsbergen Shear Zone. Fault interaction between major strike slip shears
may have lead to the formation of en-echelon pull apart basins. The curved stress trajectories create arcuate faults and subsiding
elongate basins while focusing most of the volcanism through the boundary faults. As a result, the Knipovich Ridge is characterized
by Underlapping magma centers, with long oblique rifts.
This style of basin-dominated segmentation probably evolved in a simple shear detachment fault environment which led to the
extreme morphotectonic and geophysical asymmetries across the rise axis. The influence of the Spitsbergen Shear Zone on the
evolution of the Knipovich Ridge is the primary reason that the segment discontinuities are predominantly volcanic.
Fault orientation data suggest that different extension directions along the Knipovich Ridge and Mohns Ridge (280° vs. 330°,
respectively) cause the crust on the western side of the intersection of these two ridges to buckle and uplift via compression
as is evidenced by the uplifted western wall province and the large 60 mGal free air gravity anomalies in this area.
In addition, the structural data suggest that the northwards propagation of the spreading center is ongoing and that a `normal'
pure shear spreading regime has not evolved along this ridge.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献