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Permanent link (DOI): https://doi.org/10.7939/R3707WV71

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Intracontinental Deformation Caused by Gravitational Lithosphere Removal Open Access

Descriptions

Other title
Subject/Keyword
continental deformation
Lithosphere removal
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Wang,Huilin
Supervisor and department
Currie,Claire (Department of Physics)
Examining committee member and department
Unsworth, Martyn (Department of Physics)
Pysklywec, Russell (Department of Earth Sciences)
Potter, David (Department of Physics)
Chacko, Tom (Department of Earth and Atmospheric Sciences)
Gu, Jeffrey (Department of Physics)
Currie, Claire (Department of Physics)
Department
Department of Physics
Specialization
Geophysics
Date accepted
2015-03-26T11:34:32Z
Graduation date
2015-06
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Gravitational removal of the dense lower lithosphere is proposed to be a fundamental process in continental tectonics. This has been used to explain seismological observations of an abnormally thin lithosphere beneath some regions and evidence for detached lithospheric materials at 100-200 km depth. In addition, geochemical arguments suggest that a significant portion of the lower lithosphere may have been recycled into the deeper mantle. The removal process should significantly affect the overlying crust, causing transient uplift/subsidence, crustal contraction/extension and pulses of volcanism. As removal can occur in continental plate interiors, it may provide an explanation of areas of anomalous intraplate deformation that can not be readily linked to tectonic processes. This thesis uses two-dimensional thermal-mechanical numerical models to explore the surface deflection and magmatism induced by gravitational lithosphere removal. Removal is widely believed to be associated with surface subsidence and widespread asthenospheric magmatism. However, the models show that the surface expression depends strongly on the thermal and rheological structure of the lithosphere. If the crust is weak, the descending dense lithosphere induces lateral crustal flow, leading to crustal thickening and surface uplift. Crustal flow in a mid-crustal channel will smooth the surface subsidence caused by the dense lithosphere; crustal flow in a lower-crust channel can cause the surface to invert to become a topographic high. Magmatism caused by lithosphere removal depends on the removal style and the initial thermal structure of lithosphere. During a Rayleigh-Taylor instability (drip), three types of magmas are found: (1) for a hot lithosphere (e.g., back arc), the foundering lithosphere can melt as it is descends and the asthenosphere can undergo decompression melting as it upwells to replace the removed lithosphere; (2) for a warm lithosphere (e.g., average Phanerozoic lithosphere), only asthenospheric melt is predicted; (3) for a cold and thick lithosphere (e.g., craton), no magmas are generated during removal. If removal occurs through delamination, the dense mantle lithosphere rapidly peels along the Moho and sinks into the deep mantle before it can melt. However, significant decompression melting of the asthenosphere may occur as it upwells to the base of crust. Delamination is associated with an asymmetric surface signature, where crustal deformation and magmatism migrate with the detachment hinge. In a Rayleigh-Taylor instability, the deformation and magmatism are symmetric. Observational data from a number of regions (e.g., southern Sierra Nevada in North America, Puna plateau in the central Andes, and Tibet in western China) are consistent with the numerical models, suggesting that intracontinental deformation and magmatism in these areas are related to lithosphere removal.
Language
English
DOI
doi:10.7939/R3707WV71
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Wang, H., Currie, C. A., and Zhan, Y., 2014. Surface Expressions of Rayleigh‐Taylor Instability in Continental Interiors. Acta Geologica Sinica (English Edition), 88(3), 1004-1016.Wang, H., Currie, C. A., and DeCelles, P. G., 2015. Hinterland basin formation and gravitational instabilities in the central Andes: Constraints from gravity data and geodynamic models. Geological Society of America Memoirs, 212, 387-406.

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