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Geodesy, crustal deformation and neotectonic segmentation of the eastern Central Andes

Heck, Jacob
http://rave.ohiolink.edu/etdc/view?acc_num=osu154644714256979

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Geodetic Science.
The Central Andean Plateau (CAP) is an unusually high and wide part of the second largest orogenic belt in the world. The Andes to the north and south of the CAP are much narrower and have been subject to smaller amounts of shortening. In map view the first-order morphology of the CAP is near bilaterally symmetric about a great circle running though the Santa Cruz Bend (SCB) in Bolivia. It has been suggested that the longitudinal extent of the CAP was controlled by the extent of the Paleozoic sedimentary basins found in the continental foreland. Paleozoic shales provide nearly all of the detachment horizons within and beneath the Subandes, allowing massive underthrusting of the South American craton beneath the east flank of the CAP. The approximate map view symmetry of the CAP as a whole does not apply to the active tectonic wedges (i.e. the modern foreland fold and thrust belts) either side of the SCB. The wedge south of the SCB is wider and less steep than the wedges northwest of the SCB, a situation often explained by the remarkable differences in precipitation (and therefore erosion) on either side of the SCB. Higher erosion rates promote narrower and steeper tectonic wedges. The along-strike differences in precipitation rates on either side of the SCB do not explain why the steep wedge northwest of the SCB, i.e. the Northern Subandes, is broken into two distinct segments in which the steepest slopes are laterally offset by ~100 km. We refine previous suggestions concerning the enabling role of Paleozoic sediments by examining what has happened in a small segment of the east flank of the CAP where the Chapare Basement High prevented the deposition of Paleozoic sediments. We propose that this has strongly suppressed underthrusting of the craton, essentially locking the shallow portion of the decollement, driving what might be characterized as collisional deformation in the frontal parts of the wedge. Sheffels (1995) suggested that the Cochabamba valleys are pull-apart basins produced in a left-lateral shear zone that occurs near the southeast portion of the Chapare Basement High. We extend this model by suggesting that the `collisional’ processes associated with the basement high also causes massive out-of-sequence thrusting to the west, driving a pop-up of the Cochabamba Promontory as well as the formation of the Cochabamba Shear Zone (CSZ). Using crustal velocity estimates inferred from a network of survey GPS (SGPS) and continuous GPS (CGPS) stations throughout the eastern flank of the Central Andes, interseismic surface motion within and adjacent to the east flank of the Central Andean Plateau is measured in three areas: 1) in the Southern Subandes (SSA) south of the SCB, 2) on either side of the Cochabamba pull-apart basin near where the foreland Chapare Basement High `collides’ with the edge of the CAP and 3) in the Northern Subandes (NSA) to the northwest of the Chapare Basement High. Observations at adjacent SGPS stations that act similar to one another are averaged spatially in an effort to reduce noise in the observations and extract the overall motion of a region, since extra repeat observations on the same marks was not feasible between the mark being initially set and the 2014 Pisagua earthquake that produced a coseismic jump and postseismic transient in all parts of the study area. We show that minor rotations south of the collision zone are present as the collision area is approached. In the northern part of the SSA we do not see a clear, strong velocity gradient that was apparent in two transects further south in the SSA (Brooks et al., 2011; Weiss et al., 2016). Across the CSZ, there is a statistically significant change in the surface velocity, consistent with 2.91 ± 0.46 mm/yr of left lateral shear across the zone of the pull-apart basin. In the NSA the change in motion is much less dramatic between segments. The difference in motion between the northern and southern sides of the Santa Cruz Bend provides considerable support to the Sheffels (1995) model for the development of the Cochabamba valleys and the idea that the CSZ is still active.
Michael Bevis (Advisor)
Alan Saalfeld (Committee Member)
C.K. Shum (Committee Member)
118 p.
Geophysics
Geodesy; GPS; neotectonics; Central Andes

Recommended Citations

Citations

  • Heck, J. (2019). Geodesy, crustal deformation and neotectonic segmentation of the eastern Central Andes [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu154644714256979

    APA Style (7th edition)

  • Heck, Jacob. Geodesy, crustal deformation and neotectonic segmentation of the eastern Central Andes. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu154644714256979.

    MLA Style (8th edition)

  • Heck, Jacob. "Geodesy, crustal deformation and neotectonic segmentation of the eastern Central Andes." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu154644714256979

    Chicago Manual of Style (17th edition)

osu154644714256979
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This open access ETD is published by The Ohio State University and OhioLINK.