Browsing by Subject "Passive margin"
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Item Geophysical investigation of the post Grenville Orogen lithosphere: Texas Gulf Coast(2013-05) Harrington, Tom; Gurrola, Harold; Nagihara, Seiichi; Asquith, George B.Receiver function and Pn tomography were used in conjunction to characterize the seismic velocity structure of the lower crust and upper mantle of the Laurentian Margin of Texas. The velocity interfaces modeled are the Mohoroviçiç Discontinuity (Moho), and the Hales Discontinuity. Observations resulted in crustal thicknesses from 26 to46 kilometers, and a Hales Discontinuity depth from 60to 88 kilometers. Pn tomography provided differential velocity variations of ±0.24 km/s, with the average velocity approximately 8.1 km/s. The Sabine and San Marcos Arches were not imaged in the upper mantle indicating they are crustal features only. A northwest-southeast trending anomaly was observed in observed in receiver function shallow Moho depths, Pn tomography low Moho velocity, and low aeromagnetic data was interpreted to be a relic of strike-slip motion attributed to the Ouachita Rift System. The anomaly crosses the Ouachita Orogenic Front without truncation or offset, inferring that the younger Ouachita Front was a, “thin-skinned,” collision along the Laurentian MarginItem Mechanics of lithospheric delamination in extensional settings.(2015-03-23) Jex, Jeffrey A. 1988-; Dunbar, John A., 1955-Delamination, the foundering of the lower crust and sub-crustal lithosphere, is one of the most important geodynamic processes that is still poorly understood. Geodynamic modeling has constrained conditions and likely outcomes of delamination in orogenically-thickened crust. In this study, I do the same for delamination in extensional settings by using finite element models of young passive margins. Delamination in these models may occur as melt beneath oceanic crust intrudes between the lower continental crust and sub-crustal lithosphere, driven by buoyancy. When sufficient melt is available and the lower crust is weak, the melt wedges between the lower crust and sub-crustal lithosphere, initiating delamination of the sub-crustal lithosphere. The speed of delamination is strongly dependent on weakness of the lower crust followed by the amount of melt present.