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Tectonic Reconstruction of the Ellice Basin

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Title:Tectonic Reconstruction of the Ellice Basin
Authors:Benyshek, Elizabeth Kathlene
Contributors:Wessel, Paul (advisor)
Geology and Geophysics (department)
Date Issued:Dec 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:The Ellice Basin is located in the south equatorial Pacific between the Ontong Java and Manihiki plateaus, two of the three major plateaus that were emplaced as part of the single largest oceanic plateau Ontong Java Nui (OJN). The emplacement of OJN was abruptly followed by the long normal magnetic period known as the Cretaceous Normal Superchron (CNS, 121-83 Ma). A large component of oceanic crust in the Pacific Basin was formed during the CNS and lacks magnetic reversal identifications that are usually used to constrain relative plate motion; therefore, it is necessary to adapt other reconstruction methods. Here, we describe the relict spreading system of the Ellice Basin utilizing new high-resolution bathymetric data acquired on survey KM1609 during December 2016-January 2017. Identifiable morphological spreading features are analyzed to qualitatively characterize the spreading system. Features such as multi-strand fracture zones and a dueling, overlapping spreading center support the inference that the Ellice Basin was a fast spreading (and fast slipping) spreading system, as well as the great extent and CNS age constraints of the basin. Directional analysis of the spreading fabric lineaments, specifically with respect to determining Euler poles of opening rotation, is also performed. Three main stages of spreading are identified in Ellice Basin. Spatially conjugate points symmetric about the spreading central zone are used to create pseudo-isochrons to aid in calculating rotation parameters for reconstructions. Stage 1 fracture zones trend generally E-W until a clockwise rotation of the spreading direction produced a transtensional system. Stage 2 fracture zones splayed 10-20° from Stage 1 fault strands while lengthening spreading ridges to produce zed pattern rhomboids. An offset of Stage 2 fracture zones evidences the presence of a Stage 3. Stage 3 appears to be the result of a counter-clockwise rotation of the spreading direction shortly before spreading ceased. Basaltic rocks dredged from selected locations along the survey track are to be dated and will provide tighter temporal constraints on the evolution of Ellice Basin and therefore this interpretation. Our reconstructions suggest that there was an earlier opening event prior to our three identified stages that ultimately reconstructs the Ontong Java and Manihiki plateaus.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2018.
Pages/Duration:46 pages
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Geology and Geophysics

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