The crustal structure and tectonic evolution of oceanic crust off Morocco /
| Main Author: | |
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| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1990.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | Analysis of extensive multichannel seismic (MCS) and sonobuoy reflection and refraction data show that a region within the Jurassic Quiet Zone off Morocco underwent dramatic changes as a result of the passage of the lithosphere over the Canary hotspot commencing approximately 60 Ma. A seismic unit (UCF), interpreted as volcanic in origin, is observed within the sediments in a region characterized by a broad bathymetric swell. It shows diffractions from its upper surface, an internally chaotic seismic facies, and pinches out between sedimentary units of continuous, subparallel facies. A velocity inversion is noted between the UCF (4.2 km/sec) and the underlying sediment (3.1 km/sec). The UCF is time transgressive; it lies near the Cretaceous/Tertiary boundary in the northern portion of the study area and is younger to the south. Kinematic studies of the movement of the Canary hotspot relative to Africa show that the hotspot first appeared off NW Africa about 60 Ma and was located beneath oceanic crust in the region where the UCF is observed. Depth-to-basement measurements in areas not affected by the Depth-to-basement measurements in areas not affected by the hotspot show a consistent linear trend of increased depth with age. In areas affected by the hotspot, thermal rejuvenation is evident, as basement depths shoal with increased proximity to the hotspot's present location. Subsidence curves of the reheated crust off Morocco correlate well with subsidence curves of other reheated oceanic crust on a global basis. A zone characterized by high crustal velocities (7.1 - 7.4 km/sec) and greater crustal thicknesses is observed in an area that corresponds to the bathymetric swell, the region of the UCF, and re-elevated basement. The high velocities and increased crustal thickness are interpreted to be the result of underplating and assimilation of existing oceanic crust caused by the Canary thermal anomaly. Two reflections are observed on the MCS profiles delineating a lenticular shaped body which could represent this deep unit. Gravity models suggest that a higher density is associated with this unit of anomalously high velocity. The presence of high crustal velocities, coupled with a thickened crustal section, has also been noted on various passive margins around the world. They have generally been attributed to thermal processes associated with continental rifting. Off Morocco, similar, thermally-induced phenomena have occurred, but must instead be related to mid-plate volcanism associated with the Canary hotspot. |
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| Item Description: | Typescript (photocopy). Two line graphs inside pocket of back cover. Vita. "Major subject: Oceanography." |
| Physical Description: | xiv, 185 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |