Costa Rica Rift hole deepened and logged
Keir BeckerHitoshi SakaiRussel B. MerrillAndrew C. AdamsonJoanne M. AlexandrovichJeffrey C. AltGilles GuérinDaniel BideauRobert S. GablePeter HerzigSimon D HoughtonHideo IshizukaHodaka KawahataHajimu KinoshitaMichael A. LovellJohn MalpasHarue MasudaRoger H. MorinMichael J. MottlJanet E. ParisoPhilippe PézardJoseph D. PhillipsJ. SparksStefan Uhlig
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Abstract:
During Leg 111 of the Ocean Drilling
Program, scientists on the
drilling vessel JOIDES Resolution
studied crustal structure and hydrothermal
processes in the eastern
equatorial Pacific. Leg 111 spent 43
days on its primary objective, deepening
and logging Hole 5048, a deep
reference hole in 5.9-million-year-old
crust 200 km south of the spreading
axis of the Costa Rica Rift. Even before
Leg 111 , Hole 5048 was the deepest
hole drilled into the oceanic crust,
penetrating 274.5 m of sediments and
1,075.5 m of pillow lavas and sheeted
dikes to a total depth of 1,350 m
below sea floor (mbsf). Leg 111 deepened
the hole by 212.3 m to a total
depth of 1,562.3 mbsf (1,287.8 m into
basement), and completed a highly successful suite of geophysical logs
and experiments, including sampling
of borehole waters.Keywords:
Dike
Pillow lava
Basement
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A seismic deep-refraction profile across the Arabian Shield provides new constraints for crustal models of the southwestern Shield and the structural transition from the Shield to Red Sea axial trough. The crust thins abruptly from 40 to 16 km at the eastern edge of the coastal plain, and further thins without any detected lateral disconformity to about 8 km (of which about half is composed of a Miocene evaporite sequence) beneath the Red Sea shelf. The upper crustal layer has a mean velocity of about 6.2 ± 0.2 kms/s on either side of the exposed Shield margin, and may be composed predominantly of diabase (analogous to the oceanic layer 2). The 16-km crustal thickness beneath the coastal plain and 6.2 km/s crustal velocity indicate that the crust is not typical oceanic crust, but the required total crustal thinning from 40 km on the Shield to 4 km (of non-evaporite crust) beneath the Red Sea shelf would seem to rule out a continental composition west of the Shield margin. This transitional crust, with an intermediate velocity, high density, and a thickness decreasing from that of attenuated crust (16 km) of an initial rift valley floor to that of a typical oceanic environment (4km), may be representative of crust produced during early stages of seafloor spreading. In general, such transitional crust is also a magnetic quiet zone, but, in the region traversed by the seismic refraction profile, magnetism was sufficiently localized with respect to a fixed axis of spreading to produce the distinct stripe anomalies. The seismic interpretation supports the hypotheses of (1) essentially shore-to-shore opening of the Red Sea between Aqaba and the Tihamat Asir; (2) two-stage extension; and (3) Miocene and younger crust beneath most of the Afar. INTRODUCTION A 1,000-km-long, deep-refraction seismic profile was recorded in early 1978 by the U.S. Geological Survey (USGS) and the Saudi Arabian Directorate General for Mineral Resources (DGMR) across southwestern Saudi Arabia. Its purpose was to provide estimates of crustal thickness and the bulk properties of the crust and upper mantle beneath the principal tectonic provinces of the Arabian Shield and its margins. The profile transects the Shield in a south and southwesterly direction, extending from Phanerozoic cover rock terrain of the Arabian platform, near Riyadh, to the JL/ U.S. Geological Survey, Menlo, Park, CA 2/ U.S. Geological Survey, Reston, VA outer edge of the Farasan Islands, in the southern Red Sea, less than 40 km from the edge of the Red Sea axial trough. Six shots were employed, and more than 500 recording stations were occupied. One hundred specially developed, portable, programmable instruments recorded the shots using 2-Hz vertical-component seismometers. A description of equipment, field j procedures, and initial results are contained in Blank and others (1979), and a general account of the results and their interpretation are given in Healy and others (1982$. The present report is concerned specifically with the interpretation of the southwesternmost 480 km of the recorded profile. The report focuses on the structural transition from Arabian Shield to oceanic crust of the central Red Sea and on the problem of the composition of the crust beneath the southern Red Sea shelf and coastal plain.
Seafloor Spreading
Seismic refraction
Continental Margin
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Research Article| April 01, 2000 Impact-induced mass wasting at the K-T boundary: Blake Nose, western North Atlantic Adam Klaus; Adam Klaus 1Ocean Drilling Program and Department of Oceanography, Texas A&M University, 1000 Discovery Drive, College Station, Texas 77845, USA Search for other works by this author on: GSW Google Scholar Richard D. Norris; Richard D. Norris 2Mail Stop 23, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA Search for other works by this author on: GSW Google Scholar Dick Kroon; Dick Kroon 3Department of Geology and Geophysics, University of Edinburgh, Edinburgh, Scotland Search for other works by this author on: GSW Google Scholar Jan Smit Jan Smit 4Department of Sedimentology, Faculty of Earth Sciences, Vrije Universiteit, de Boelelaan 1085, 1081HV Amsterdam, Netherlands Search for other works by this author on: GSW Google Scholar Author and Article Information Adam Klaus 1Ocean Drilling Program and Department of Oceanography, Texas A&M University, 1000 Discovery Drive, College Station, Texas 77845, USA Richard D. Norris 2Mail Stop 23, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA Dick Kroon 3Department of Geology and Geophysics, University of Edinburgh, Edinburgh, Scotland Jan Smit 4Department of Sedimentology, Faculty of Earth Sciences, Vrije Universiteit, de Boelelaan 1085, 1081HV Amsterdam, Netherlands Publisher: Geological Society of America Received: 07 Oct 1999 Revision Received: 10 Jan 2000 Accepted: 14 Jan 2000 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2000) 28 (4): 319–322. https://doi.org/10.1130/0091-7613(2000)28<319:IMWATK>2.0.CO;2 Article history Received: 07 Oct 1999 Revision Received: 10 Jan 2000 Accepted: 14 Jan 2000 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Adam Klaus, Richard D. Norris, Dick Kroon, Jan Smit; Impact-induced mass wasting at the K-T boundary: Blake Nose, western North Atlantic. Geology 2000;; 28 (4): 319–322. doi: https://doi.org/10.1130/0091-7613(2000)28<319:IMWATK>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Seismic reflection data combined with results from ocean drilling document regional-scale slumping associated with the Cretaceous-Tertiary (K-T) impact event. The K-T boundary is biostratigraphically complete at three Ocean Drilling Program sites (1049, 1050, and 1052) located on Blake Nose (30°N, 75°W) off eastern Florida in water depths of 1300–2600 m. Maastrichtian chalk is folded and fractured below the K-T boundary at all three sites, whereas lowermost Paleocene clays and chalks are undeformed. Deformation is pervasive in Maastrichtian at the deepest water site (Site 1049), whereas at the shallower water sites (Sites 1050 and 1052) thick intervals of structurally intact Maastrichtian chalk are separated by thinner intervals of highly deformed sediments. Correlation of core to seismic reflection data indicates that the K-T boundary immediately overlies seismic facies characteristic of mass wasting that extend across most of the ∼55 km distance of the depth transect. Maastrichtian sediments appear to have moved as large slump blocks on the upper part of Blake Nose but deformed more uniformly in the deeper water parts of the transect. We suggest that mass wasting occurred on the Blake Nose >1600 km from the Chicxulub crater in response to the cataclysmic seismicity generated by the impact. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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A crustal and basin seismic study of the Nova Scotia shelf/slope and its transition to the oceanic crust of West Atlantic was performed by observing a 400 km long NW-SE oriented seismic profile covered by 100 Ocean Bottom Seismographs (OBS). Four different geological domains have been identified: A continental crust of 33 to 27 Km thickness covers the first 70 Km of the north western part of the line and is covered by 4,5 Km thick sediments. The next 100 Km consist of a stretched continental crust of 27 to 19 km, including 9 km of sediments. At the following 90 km the crust consists of igneous intrusions with Vp-velocity 7.2 to 7.3 Km/s, terminating the continental domain. Strong serpentinization occurs at the top of this intrusion. The last 140 km of the profile are floored by thin oceanic crust of 4 km thickness, which is covered by 4 to 5 km thick sediments. A salt basin extends over the last 60 Km of the stretched continental crust. The conjugate margin of Nova Scotia, which is the Moroccan margin north of Agadir, differs from that of the Canadian side since the stretched continental crust of the Moroccan margin is followed by seafloor spreaded oceanic crust without any igneous intrusions and serpentinized units.
Continental Margin
Seafloor Spreading
Nova scotia
Oceanic basin
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Hotspot (geology)
geodynamics
Seismic Tomography
Slab window
Island arc
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Trough (economics)
Continental Margin
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End_Page 304------------------------------In November to December 1983, the University of Texas and the U.S. Geological Survey conducted a seismic experiment that attempted to measure crustal and upper mantle depths and velocities along a transect of the Gulf of Mexico south of Galveston, Texas. The transect is composed of 5 along-strike lines spaced to span the continental shelf and slope and reaching the deep basin. Two 2,000-in.3, 2,000-psi air guns were fired simultaneously at 30-sec intervals at 5 knots for a shot spacing of 77 m. The signals were recorded by digital ocean-bottom seismographs with vertical geophones. Four seismographs were placed along each 90-km line. The seismic sections obtained are densely sampled and fully reversed, about half showing seismic arrivals at the full range of the line. We find that the deep Gulf of Mexico is, as expected, underlain by oceanic crust. On the outer slope, we see deeply penetrating arrivals from below thick salt, and we find that this crust is thicker than the oceanic crust. North of the thick salt, we see the crust thinning to nearly the thickness of oceanic crust. Although this crust may be seismically indistinguishable from oceanic crust, we believe it to be highly extended continental crust. We interpret the two northern lines to show northward thickening, extended continental crust. End_of_Article - Last_Page 305------------
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The following is an extended abstract of a paper presented at the Marine Studies Group meeting ‘Structure of Continent-Ocean Boundaries’ , 11 December 1985. Ocean Drilling Program (ODP) Leg 104 successfully completed a number of deep drill holes on the Outer V0ring Plateau and the Vering Basin during July and August 1985 (Fig. 1; Eldholm, Thiede, Taylor et al. 1986). One of the principal objectives of the leg was to drill and sample a thick oceanward-dipping wedge of seismic reflectors, known to characterize much of the multichannel seismic (MCS) profile data recorded across ocean-continent transitions in the NE Atlantic north of 55°N. Elsewhere, these reflectors have previously been the target of deep drilling during Legs 48 and 81 of the International Phase of Ocean Drilling IPOD (Montadert, Roberts et al. 1979; Roberts, Schnitker et al. 1984). These efforts met with some success, sampling only the uppermost part of the sequence and identifying a series of tholeiitic lava flows. Over the Outer V~ring Plateau, a number of MCS profiles reveal a distinct change in seismic character at the base of the well-stratified dipping reflector sequence, where an irregular surface characterized by a band of low-frequency, high-amplitude reflectors occurs. This surface is referred to as K. Prior to Leg 104, therefore, relatively little was known regarding the variation in petrographic character of the flows at depth, their evolution and origin, and particularly the character of the material below the reflector sequence. A single deep drillhole (642E) successfully recovered a section through the
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Large aperture seismic data were collected on several ocean bottom seismometers (OBS) deployed along a deep crustal seismic profile that was shot across the central California continental margin. The line of shots extends from the oceanic crust seaward of the Santa Lucia Escarpment to the California coast near Morro Bay and crosses the Santa Lucia Basin, Santa Lucia Bank, Santa Maria Basin, and Hosgri fault zone. The OBS data permit us to trace the subducted oceanic crust from seaward of the Santa Lucia Escarpment to beneath the central part of the Santa Maria Basin. A complementary study using onshore recordings of the same shots extends the crustal model onshore. Just seaward of the Santa Lucia Escarpment, the oceanic crust is subhorizontal and covered by a thin layer of low‐velocity sediment. The velocity (4.5 km/s) and gradient (1.20–1.25 km/s/km) of the upper oceanic crust in this region are well determined and agree with earlier determinations of the crustal structure of the eastern Pacific. Beneath the Santa Lucia Escarpment and Santa Lucia Basin, the oceanic crust dips approximately 16° to the east. It is overlain by material with a velocity that increases from 4.8 to 6.4 km/s at a depth of 1.7–5.5 km below the seafloor beneath the Santa Lucia Basin. A low‐velocity zone may be sandwiched between the subducted crust and this shallow high‐velocity material, which we interpret to represent obducted oceanic crustal material. Beneath the eastern edge of Santa Lucia Basin, the dip of the subducted oceanic crust decreases to less than 2°. The configuration of the subducted crust in this region is consistent with imbrication of the subducted crust, as suggested by others based on common midpoint reflection data. Beneath the central Santa Maria Basin, the top of the subducted oceanic crust is at a depth of about 14–16 km and the Moho is at 19–21 km.
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Seafloor Spreading
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Trough (economics)
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Seafloor Spreading
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