Transform Faults, Fracture Zones, and the Kinematics of Horizontal Thermal Contraction of Oceanic Lithosphere

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dc.contributor.advisorGordon, Richard Gen_US
dc.contributor.committeeMemberLenardic, Adrianen_US
dc.contributor.committeeMemberSawyer, Dale Sen_US
dc.contributor.committeeMemberAkin, John Een_US
dc.creatorMishra, Jay Kumaren_US
dc.date.accessioned2016-01-27T22:48:02Zen_US
dc.date.available2016-01-27T22:48:02Zen_US
dc.date.created2015-12en_US
dc.date.issued2015-12-04en_US
dc.date.submittedDecember 2015en_US
dc.date.updated2016-01-27T22:48:02Zen_US
dc.description.abstractPlate rigidity is a key assumption of the plate tectonics theory. The assumption allows us to study plate motion on Earth with great simplicity. However, recent developments in understanding plate cooling have put the assumption of plate rigidity to test. Kumar and Gordon [2009] advance the theory of horizontal thermal contraction of oceanic lithosphere as the ultimate test of plate rigidity and predict that relative intraplate velocities due to horizontal thermal contraction within the oceanic lithosphere of a tectonic plate can be as high as 3 – 10 mm a-1. Contractional strains have been predicted to vary inversely with age and hence most of the strains related with horizontal thermal contraction should be accumulated and dissipated by young oceanic lithosphere. Transform faults provide the necessary free boundaries across which most of the contractional stresses can be dissipated by ridge-parallel contraction of the oceanic lithosphere. The strike of the transform faults, earlier predicted to be parallel to the relative plate motion direction, thus, should be biased as a result of transform fault perpendicular contraction of oceanic lithosphere. I first improve the global transform fault dataset used in MORVEL [DeMets et al., 2010] and then calculate residuals between the observed transform fault azimuths and those predicted for the rigid oceanic plates. I find that on an average, for the six plate pairs with both left-lateral and right-lateral slipping transform faults, azimuths are biased by about 0.75°±0.36° clockwise for left-lateral slipping and by −0.73°±0.22° (= ±1 standard error) counter-clockwise for the right-lateral slipping. I, then investigate if this observed bias can be caused by horizontal thermal contraction. For the six selected pairs with both right-lateral and left-lateral slipping transform faults, the mean bias is predicted to be only 0.38° for only right-lateral slipping faults and −0.46° for only left-slipping transform faults. Thus the magnitudes of bias predicted by horizontal thermal contraction are ≈60% as large as the observed residual between the observed strikes of transform faults and the strikes observed for the assumption of plate rigidity. Thus we cannot exclude some normal faulting in transform fault valleys. A global analysis of plate motion based on the transform fault azimuths corrected for the predicted bias due to horizontal thermal contraction shows that the hypothesis of no horizontal thermal contraction can be rejected with at least 40% of the contractional strains causing the rotation of strikes of transform faults and the remaining being accommodated by normal faulting in transform fault valleys. Thus we conclude that plates are not rigid. Based on the predictions of horizontal thermal contraction, I further test its effect on intraplate velocities and build a 2D kinematic model of the Pacific lithosphere between the Rivera and the Heezen fracture zones to calculate the predicted intraplate relative velocity field due to horizontal thermal contraction. For the kinematic assumption that balances net contraction and extension across the fracture zones, young oceanic lithosphere along the Rivera fracture zone is predicted to have a contractional velocity of 2.6 mm a-1 in the South-Southeast direction. This is big enough to account for the misfit of 5±3 mm a-1 in the PA-NA-NB-AN plate circuit and not big enough to explain the misfit of 14±5 mm a-1 for the CO-PA-NZ plate circuit.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.citationMishra, Jay Kumar. "Transform Faults, Fracture Zones, and the Kinematics of Horizontal Thermal Contraction of Oceanic Lithosphere." (2015) Diss., Rice University. <a href="https://hdl.handle.net/1911/88214">https://hdl.handle.net/1911/88214</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/88214en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjectPlate tectonicsen_US
dc.subjecttransform faulten_US
dc.subjectfracture zoneen_US
dc.subjecthorizontal thermal contractionen_US
dc.subjectoceanic lithosphereen_US
dc.subjectthermal stressen_US
dc.subjectthermal strainen_US
dc.subjectplate rigidityen_US
dc.subjectglobal plate motionen_US
dc.subjecttransform fault azimuthen_US
dc.subjectPacific plateen_US
dc.subjectplate circuit closureen_US
dc.subjectplate motionen_US
dc.titleTransform Faults, Fracture Zones, and the Kinematics of Horizontal Thermal Contraction of Oceanic Lithosphereen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentEarth Scienceen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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