Browsing by Subject "magnetic anomaly"

Now showing 1 - 13 of 13

Atlas of Mesozoic/Cenozoic reconstructions (200 Ma to Present Day) (PLATES Project, Progress Report No. 01-0192)
(Institute for Geophysics, 1992) Coffin, Millard F.; Gahagan, Lisa M.; Lawver, Lawrence A.; Lee, Tung-Yi; Rosencrant, Eric.
Catalog of Cuban Gulf Oil Co. Data
(Institute for Geophysics, 1991) Rosencrantz, Eric; Ganey-Curry, Patricia; Code, Elizabeth; Lewis, Dan'l
Cenozoic Evolution of the American-Antarctic Ridge (Paleoceanographic Mapping Project Report No. 09-0286)
(Institute for Geophysics, 1986) Barker, Peter A.; Lawver, Lawrence A.
New bathymetric and magnetic anomaly data for the American-Antarctic Ridge region of the South Atlantic are compiled and presented. The magnetic anomaly data are used to produce poles of rotation and angles of opening for six stages for the Cenozoic between anomaly 5 time (9. 7 Ma) and anomaly 21 time (50.3 Ma). Synthetic spreading centers and fracture zones are generated, some of which give very close agreement with noted SEASAT derived gravity anomalies. Two large symmetrical regions of the American-Antarctic Ridge area could not have been formed at the present-day active American-Antarctic Ridge spreading centers. We conclude that the 560 kilometer long Bullard Fracture Zone was created just prior to anomaly 6 (20.4 Ma) time eliminating two or more spreading segments of the American-Antarctic Ridge. The change in spreading and direction which precipitated the realignment of transform faults was caused by the subduction of about 25% of the American-Antarctic Ridge at anomaly 6A or 6B time (21.0-23.0 Ma) at Jane Bank. An additional section of the ridge was subducted near Discovery Bank at about 7-10 Ma and about half of the remaining American-Antarctic Ridge will be subducted between 17 and 20 million years from now if present-day rates persist.
Evolution of the Southwest Indian Ridge between the Late Cretaceous and the Middle Eocene (Paleoceanographic Mapping Project Progress Report No. 13-0986)
(Institute for Geophysics, 1986) Royer, Jean-Yves
Evolution of the Southwest Indian Ridge from the Late Cretaceous (Anomaly 34) to the Middle Eocene (Anomaly 20) (Paleoceanographic Mapping Project Progress Report No. 25-0987)
(Institute for Geophysics, 1987) Royer, Jean-Yves; Patriat, Philippe; Bergh, Hugh W.; Scotese, Christopher R.
The determination of the motion of Antarctica relative to Africa is particularly important when considering the breakup of Gondwana. Two models have been proposed that describe the pattern of seafloor spreading between Africa and Antarctica during the Late Cetaceous (starting at chron 34, 84 Ma) through to the Middle Eocene (chron 20, 46 Ma). In the flrst model, the motion of Antarctica relative to Africa can be simply described by a rotation about a single pole of rotation. In the second model, which we favor, the relative motion of Antarctica and Africa is more complex, and a major change in spreading direction between chron 32 (74 Ma) and chron 24 (56 Ma) times is required. In this paper we present 10 plate tectonic reconstructions of the Southwest Indian Ridge that were produced using a new compilation of magnetic, bathymetric, and satellite altimetry data, in combination with interactive computer graphics. These reconstructions illustrate that spreading directions started to change at chron 32 time (74 Ma). Between chrons 31 and 28 (69 to 64 Ma), spreading was very slow ( <1 cm/yr) and the direction of spreading changed from NE-SW to a more N-S direction. Between chrons 26 and 24 (61 to 56 Ma) the direction of spreading shifted back to a NE-SW orientation. These changes in spreading direction suggest that the present-day fracture zones in the area of the Prince Edward fracture zone are younger features (Eocene) than their lengths might imply. Our results also provide important constraints concerning the Mesozoic reconstructions of the Indian Ocean and the motion of South America relative to Antarctica prior to the Eocene.
Maganom: A computer program for the modeling and interpretation of marine magnetic anomalies
(Institute for Geophysics, 1987) Ross, Malcolm I.
Opening of the Central North Atlantic: Revised Seafloor Spreading Isochrons and Tectonic Map from Geosat Data (Paleoceanographic Mapping Project Progress Report No. 39-0888)
(Institute for Geophysics, 1988) Mueller, R. Dietmar; Scotese, Christopher R.; Sandwell, David T.
Plate reconstructions for the opening of the Central and North Atlantic were made by combining Geosat altimetry and magnetic anomaly data. Geosat deflection of the vertical (horizontal gravity) data, which reflect the short wavelength basement topography of the ocean floor allowed us to construct a much improved map of fracture zones m the Central and North Atlantic. The fabric of prominent fracture zones, as interpreted from Geosat deflection of the vertical data, was utilized to constrain the fits of corresponding magnetic anomaly lineations by using an Evans and Sutherland 3-D graphics computer system. For example, we have used the trace of the Charlie-Gibbs Fracture Zone to better constrain the spreading history between the North American and Eurasian plate. Movements of smaller plates such as in the Canadian Arctic and the western Mediterranean were tied to the relative motion of the major plates by applying a hierarchical plate analysis technique. Our tectonic model served as a base to construct a self-consistent isochron chart of the Central and North Atlantic ocean floor.
An Overview of the Cuban Orogen, With an Assessment of Hydrocarbons Potential
(Institute for Geophysics, 1993) Rosencrantz, Eric
Reconstructions and Isochron Charts of the South Pacific (Paleoceanographic Mapping Project, Progress Report No. 24-1287)
(Institute for Geophysics, 1987) Mayes, Catherine L.; Sandwell, David T.; Lawver, Lawrence A.
Reconstructions of the South Pacific (Paleoceanographic Mapping Project Progress Report No. 15-1186)
(Institute for Geophysics, 1986) Mayes, Catherine L.
Tectonic Development of the North Atlantic: Revised Seafloor Spreading Isochrons and Tectonic Fabric Map from SEASAT Altimetry (Paleoceanographic Mapping Project, Progress Report No. 26-1287)
(Institute for Geophysics, 1987) Mueller, R. Dietmar; Scotese, Christopher R.
New plate reconstructions for the opening of the North Atlantic were made by combining recent magnetic anomaly data and Seasat altimetry data. A tectonic fabric map of the North Atlantic from interpretation of Seasat data allowed us to trace the Charlie Gibbs Fracture Zone from the North American to the European margin. Ve use fracture zone lineations as additional constraints in fitting magnetic anomaly pairs by interactively using the advanced 3-D graphics capabilities of an Evans & Sutherland PS 300 computer system. We have applied a hierarchical analysis technique (Ross & Scotese, in press) to obtain a new set of reconstruction poles of relative motion for plates around the North Atlantic. Intraplate movements in the Canadian Arctic, in NE-Greenland, and the North Sea region were included in the model to improve the fit reconstruction and better describe propagating rift tectonics. Plate reorganizations at Chron 25 and 13 resulted in major changes of the plate boundary between Eurasia and North America in eastern Siberia and between Greenland and Svalbard. For the relative motion between Eurasia and North America in the Bering Sea region we suggest a succession of 4 tectonic phases from the Aptian to present day. Sinistral transpression dominated from chron MO (118.7 Ma) to chron 25. It was followed by dextral transtension from chron 25 to chron 13. Compression/left lateral transpression prevailed after chron 13. Our plate model predicts a Tertiary tectonic development between Greenland and Svalbard in four phases. We propose extension from chron 30 (68.4 Ma) to 25 (59.2), strike slip from chron 25 to 24 (56.1) and transpression from chron 24 to 20 (46.2 Ma) followed by transtension after chron 20.
Tectonic Evolution of the South Atlantic from Late Jurassic to Present (Paleoceanographic Mapping Project Progress Report No. 27-1287)
(Institute for Geophysics, 1987) Nuernberg, Dirk; Mueller, R. Dietmar; Scotese, Christopher R.
The breakup of the continents around the South Atlantic was characterized by a stepwise, northward-propagating rift system, beginning in the southernmost South Atlantic. Fit reconstructions of South America and Africa that require rigid continental plates result in substantial misfits either in the southern South Atlantic or in the equatorial Atlantic. To achieve a fit without gaps, we assume a combination of complex rift and strike slip movements: 1. along the South American Parana-Andean Cochabamba deformation zone, 2. within marginal basins in South America (Salado, Colorado basins), and 3. along the Benue Trough/Niger Rift system in Africa. These faults are presumed to have been active before or during the breakup of the continents. Our model predicts a successive "unzipping" of rift zones starting in the southern South Atlantic. Between 150 Ma (Tithonian) and approximately 130 Ma (Hauterivian), rifting propagated to 38°S, causing tectonic movements within the Colorado and Salado basins. Subsequently, between 130 Ma and Chron M4 (126.5 Ma) the tip of the South Atlantic rift moved to 28°S, resulting in intracontinental deformation along the Parana-Andean Cochabamba line. Between Chron M4 and Chron MO (118.7 Ma) rifting propagated into the Benue Trough and Niger Rift, inducing rift and strike slip motion. After Chron MO (118.7 Ma), the equatorial Atlantic began to open, while rifting and strike slip motion still occurred in the Benue Trough and Niger Rift. Since Chron 34 (84 Ma), the opening of the South Atlantic is characterized by simple divergence of two rigid continental plates, as shown in our set of revised seafloor spreading isochrons.
Tectonic History and New Isochron Chart of the South Pacific (Paleoceanographic Mapping Project Progress Report No. 43-0888)
(Institute for Geophysics, 1988) Mayes, Catherine L.; Sandwell, David T.; Lawver, Lawrence A.
We have developed an internally consistent isochron chart and a tectonic history of the South Pacific using a combination of new satellite altimeter data and shipboard magnetic and bathymetric data. Highly accurate, vertical deflection profiles (1-2 µrad), derived from 22 repeat cycles of Geosat altimetry, reveal subtle lineations in the gravity field associated with the South Pacific fracture zones. These fracture zone lineations are correlated with sparse shipboard bathymetric identifications of fracture zones and thus can be used to determine paleo-spreading directions in uncharted areas. The high density of Geosat altimeter profiles reveals previously unknown details in paleo-spreading directions on all of the major plates. Magnetic anomaly identifications and magnetic lineation interpretations from published sources were combined with these fracture zone lineations to produce a tectonic fabric map. The tectonic fabric was then used to derive new plate reconstructions for twelve selected times in the Late Cretaceous and Cenozoic. This is the first time that the tectonic history of the entire South Pacific has been studied as a whole. From our reconstructions, we estimated the former location of the spreading centers in order to derive a new set of isochrons (interpreted lines of equal age on the ocean floor). We believe that the use of new Geosat altimeter data in combination with a multi-plate reconstruction has led to a major improvement in our understanding of South Pacific tectonics. There are three times of important changes in the tectonic history of the South Pacific. Just prior to Chron 34 (84.0 Ma) spreading initiated between Marie Byrd Land and the New Zealand block (the Campbell Plateau and the Chatham Rise). Spreading in the southwest Pacific was occurring along two different spreading centers between Chron 34 (84.0 Ma) and Chron 25 (58.9 Ma): the Pacific-Antarctic Spreading Center to the west and the Pacific-Bellingshausen Spreading Center· to the east at around the time of Chron 21 (49.4 Ma), the eastern and western spreading centers began spreading about a common pole of rotation. In addition, the Pacific-Antarctic Spreading Center broke through old crust to the north, transferring a piece of crust created at the Pacific-Aluk spreading center to the Antarctic plate. The next major change in the South Pacific occurred between Chron 7 (25.8 Ma) and Chron 5 (10.6 Ma) when spreading initiated at the Galapagos Spreading Center and the East Pacific Rise was reoriented from spreading in a northwesterly direction to spreading in a northeasterly direction.