41 research outputs found
The origin and tectonic history of the Southwest Philippine Sea
Submitted in partial fulfillment of the requirements for
the degree of Doctor of Philosophy
at the
Massachusetts Institute of Technology
and the
Woods Hole Oceanographic Institution
September 1976This thesis is a collection and analysis of seafloor
magnetic anomalies, bathymetry, and the paleomagnetism
of DSDP sediments and basalt in the West Philippine Basin,
in an attempt to resolve questions about its origin as a
marginal basin. Our results suggest that this basin was
formed in an Eocene pulse of rapid spreading (v1/2 = 41-44 mm/yr)
in a direction (N 21°E) significantly different from later
pulses which opened the more eastern basins of the Philippine
Sea. The Central Basin Fault appears to be intimately
associated with this spreading by nature of its structure
and trend, and it may be a remanent of a former ridge system.
Our preliminary calculation of paleopole positions also
suggests that there was a large amount (60°) of clockwise rotation between this basin and the magnetic pole. This is
consistent with rotations of the Pacific plate with respect
to the magnetic pole and current directions of Philippine-
Pacific'relative rotations. Basement depths of 6 km in the
West philippine Basin imply that its crustal and/or lithospheric
structure is different from Pacific structure of the
same age
Structure of the ultraslow-spreading Southwest Indian Ridge at 64°30’E from coincident multichannel and wide-angle seismic data
Iceland, the Farallon slab, and dynamic topography of the North Atlantic
ABSTRACT Upwelling or downwelling flow in Earth's mantle is thought to elevate or depress Earth's surface on a continental scale. Direct observation of this ''dynamic topography'' on the seafloor, however, has remained elusive because it is obscured by isostatically supported topography caused by near-surface density variations. We calculate the nonisostatic topography of the North Atlantic by correcting seafloor depths for lithospheric cooling and sediment loading, and find that seafloor west of the Mid-Atlantic Ridge is an average of 0.5 km deeper than it is to the east. We are able to reproduce this basic observation in a model of mantle flow driven by tomographically inferred mantle densities. This model shows that the Farallon slab, currently in the lower mantle beneath the east coast of North America, induces downwelling flow that deepens the western North Atlantic relative to the east. Our model also predicts dynamic support of observed topographic highs near Iceland and the Azores, but suggests that the Icelandic high is due to local upper-mantle upwelling, while the Azores high is part of a plate-scale lower-mantle upwelling to the south. An anomalously deep area off the coast of Nova Scotia may be associated with the downwelling component of edge-driven convection at the continental boundary. Thus, several of the seafloor's topographic features can only be understood in terms of dynamic support from flow in Earth's mantle
Correction to “Evidence for asymmetric nonvolcanic rifting and slow incipient oceanic accretion from seismic reflection data on the Newfoundland margin”
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): B12403, doi:10.1029/2006JB004769
Crustal structure across the Grand Banks–Newfoundland Basin Continental Margin – II. Results from a seismic reflection profile
Author Posting. © Blackwell, 2006. This is the author's version of the work. It is posted here by permission of Blackwell for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 167 (2006): 157-170, doi:10.1111/j.1365-246X.2006.02989.x.New multi-channel seismic (MCS) reflection data were collected over a 565km
transect covering the non-volcanic rifted margin of the central eastern Grand Banks and the Newfoundland Basin in the northwestern Atlantic. Three major crustal zones are interpreted from west to east over the seaward 350-km of the profile: (1) continental crust; (2) transitional basement; (3) oceanic crust. Continental crust thins over a wide zone (~160 km) by forming a large rift basin (Carson Basin) and seaward fault block, together with a series of smaller fault blocks eastward beneath the Salar and Newfoundland basins. Analysis of selected previous reflection profiles (Lithoprobe 85-4, 85-2 and Conrad NB-1) indicates that prominent landward-dipping reflections observed under the continental slope are a regional phenomenon. They define the landward edge of a deep serpentinized mantle layer, which underlies both extended continental crust and transitional basement. The 80-km-wide transitional basement is defined landward by a basement high that may consist of serpentinized peridotite and seaward by a pair of basement highs of unknown crustal origin.
Flat and unreflective transitional basement most likely is exhumed, serpentinized mantle,
although our results do not exclude the possibility of anomalously thinned oceanic crust. A Moho reflection below interpreted oceanic crust is first observed landward of magnetic
anomaly M4, 230 km from the shelf break. Extrapolation of ages from chron M0 to the edge of interpreted oceanic crust suggests that the onset of seafloor spreading was ~138Ma (Valanginian) in the south (southern Newfoundland Basin) to ~125Ma (Barremian-Aptian boundary) in the north (Flemish Cap), comparable to those proposed for the conjugate margins.This work was funded by NSF grants OCE-9819053 and OCE-0326714 to
Woods Hole Oceanographic Institution, NSERC (Canada) and the Danish Research Council.
B. Tucholke also acknowledges support from the Henry Bryant Bigelow Chair in
Oceanography at Woods Hole Oceanographic Institution
A deep seismic investigation of the Flemish Cap margin: implications for the origin of deep reflectivity and evidence for asymmetric break-up between Newfoundland and Iberia
Author Posting. © Blacwell, 2006. This article is posted here by permission of Blackwell for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 164 (2006): 501–515, doi:10.1111/j.1365-246X.2006.02800.x.Seismic reflection and refraction data were acquired along the southeast margin of Flemish Cap at a position conjugate to drilling and geophysical surveys across the Galicia Bank margin. The data document first-order asymmetry during final break-up between Newfoundland and Iberia. An abrupt necking profile of continental crust observed off Flemish Cap contrasts strongly with gradual tapering on the conjugate margin. There is no evidence beneath Flemish Cap for a final phase of continental extension that resulted in thin continental crust underlain by a strong 'S'-like reflection, which indicates that this mode of extension occurred only on the Galicia Bank margin. Compelling evidence for a broad zone of exhumed mantle or for peridotite ridges is also lacking along the Flemish Cap margin. Instead, anomalously thin, 3–4-km-thick oceanic crust is observed. This crust is highly tectonized and broken up by high-angle normal faulting. The thin crust and rift structures that resemble the abandoned spreading centre in the Labrador sea suggest that initial seafloor spreading was affected by processes observed in present-day ultra-slow spreading environments. Landwards, Flemish Cap is underlain by a highly reflective lower crust. The reflectivity most likely originates from older Palaeozoic orogenic structures that are unrelated to extension and break-up tectonics.This work was supported by the Danish National Research Foundation, U.S. National Science Foundation grants OCE-9819053 and OCE-0326714, and the Natural Science and Engineering Research Council of Canada. Additional support for Hopper was provided by the German Research Foundation grant MO-961/4-1. Tucholke also acknowledges support from Henry Bryant Bigelow Chair in Oceanography at Woods Hole Oceanographic Institution
Crustal structure across the Grand Banks–Newfoundland Basin Continental Margin – I. Results from a seismic refraction profile
Author Posting. © Blackwell, 2006. This is the author's version of the work. It is posted here by permission of Blackwell for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 167 (2006): 127-156, doi:10.1111/j.1365-246X.2006.02988.x.A P-wave velocity model along a 565-km-long profile across the Grand
Banks/Newfoundland basin rifted margin is presented. Continental crust ~36-kmthick
beneath the Grand Banks is divided into upper (5.8-6.25 km/s), middle (6.3-
6.53 km/s) and lower crust (6.77-6.9 km/s), consistent with velocity structure of
Avalon zone Appalachian crust. Syn-rift sediment sequences 6-7-km thick occur in
two primary layers within the Jeanne d’Arc and the Carson basins (~3 km/s in upper
layer; ~5 km/s in lower layer). Abrupt crustal thinning (Moho dip ~ 35º) beneath the
Carson basin and more gradual thinning seaward forms a 170-km-wide zone of rifted
continental crust. Within this zone, lower and middle continental crust thin
preferentially seaward until they are completely removed, while very thin (<3 km)
upper crust continues ~60 km farther seaward. Adjacent to the continental crust, high
velocity gradients (0.5-1.5 s-1) define an 80-km-wide zone of transitional basement
that can be interpreted as exhumed, serpentinized mantle or anomalously thin
oceanic crust, based on its velocity model alone. We prefer the exhumed-mantle
interpretation after considering the non-reflective character of the basement and the
low amplitude of associated magnetic anomalies, which are atypical of oceanic crust.
Beneath both the transitional basement and thin (<6 km) continental crust, a 200-kmwide
zone with reduced mantle velocities (7.6-7.9 km/s) is observed, which is
interpreted as partially (<10%) serpentinized mantle. Seaward of the transitional
basement, 2- to 6-km-thick crust with layer 2 (4.5-6.3 km/s) and layer 3 (6.3-7.2
km/s) velocities is interpreted as oceanic crust. Comparison of our crustal model
with profile IAM-9 across the Iberia Abyssal Plain on the conjugate Iberia margin
suggests asymmetrical continental breakup in which a wider zone of extended
continental crust has been left on the Newfoundland side.This research was supported by National Science Foundation (NSF)
grants OCE-9819053 and OCE-0326714, by the National Sciences and Engineering
Research Council of Canada (NSERC), and by the Danish National Research
Foundation. B. Tucholke also acknowledges support from the Henry Bryant Bigelow
Chair in Oceanography from Woods Hole Oceanographic Institution
Greenland Geothermal Heat Flow Database and Map (Version 1)
We compile and analyze all available geothermal heat flow measurements collected in and around Greenland into a new database of 419 sites and generate an accompanying spatial map. This database includes 290 sites previously reported by the International Heat Flow Commission (IHFC), for which we now standardize measurement and metadata quality. This database also includes 129 new sites, which have not been previously reported by the IHFC. These new sites consist of 88 offshore measurements and 41 onshore measurements, of which 24 are subglacial. We employ machine learning to synthesize these in situ measurements into a gridded geothermal heat flow model that is consistent across both continental and marine areas in and around Greenland. This model has a native horizontal resolution of 55ĝ€¯km. In comparison to five existing Greenland geothermal heat flow models, our model has the lowest mean geothermal heat flow for Greenland onshore areas. Our modeled heat flow in central North Greenland is highly sensitive to whether the NGRIP (North GReenland Ice core Project) elevated heat flow anomaly is included in the training dataset. Our model's most distinctive spatial feature is pronounced low geothermal heat flow (<ĝ€¯40ĝ€¯mWĝ€¯m-2) across the North Atlantic Craton of southern Greenland. Crucially, our model does not show an area of elevated heat flow that might be interpreted as remnant from the Icelandic plume track. Finally, we discuss the substantial influence of paleoclimatic and other corrections on geothermal heat flow measurements in Greenland. The in situ measurement database and gridded heat flow model, as well as other supporting materials, are freely available from the GEUS Dataverse (10.22008/FK2/F9P03L; Colgan and Wansing, 2021).publishedVersionPeer reviewe
Managing at the top : roles and responsibilities of the chief executive/ Louden
ix, 159 hal.; 22 c