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Determining relative age of out-of-sequence faults: integration of foreland basin deposits to a flexural thrust belt evolution and a case study in Western Nepal

Olsen, Joshua E S (2018) Determining relative age of out-of-sequence faults: integration of foreland basin deposits to a flexural thrust belt evolution and a case study in Western Nepal. Master's Thesis, University of Pittsburgh. (Unpublished)

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Abstract

Forward modeled, balanced cross sections, accounting for both flexural loading and erosional unloading have the potential to verify and refine the kinematic sequence of deformation in fold and thrust belts. Insight into the relative order of events is particularly apparent for out-of-sequence faults that have the ability to either vertically exhume deeper strata in the case of thrusts, or normal faults which create basins that may or may not be preserved in the mapped geology. Strata exhumed by thrusts (either in- or out-of-sequence) may leave a distinct provenance or detrital age signature in the foreland basin. The foreland basin evolution can be predicted with the isostatic modeling, allowing correlation between modeled and measured stratigraphic sections near the cross section. Incremental modeling in short displacement steps creates “pseudostratigraphy” in the foreland which predicts the location and magnitude of preserved sediment, and identifies the location and amount of material eroded in the incremental thrust event, i.e. the provenance of the sediments within the pseudostratigraphy. We present a case study for this method using two cross sections through the Himalayas of Far-Western Nepal (Api and Simikot) and assess the validity of the resulting dated kinematic histories, displacement rates, flexural wave response, section geometry, and matches to provenance for both sections. We also compare flexural forward models with and without an additional sediment loading modeling step, and find that while sediment loading does not have a large effect on the kinematic orders inferred from flexural modeling, it does affect precision in correlating model steps to paleomagnetic ages (±1 Ma). In order to reproduce the foreland provenance we argue that OOS thrust and normal faults in the Api section occurred between 11-4 Ma. In addition, we propose that shortening estimates for the Simikot cross section are too high (> 50 km) which causes unrealistic deformation rates up to 80 mm/yr between 25-20 Ma. We conclude that the flexural forward modeling method has a vast potential for revising the kinematics of fold-and-thrust belt cross sections when the full foreland basin evolution is considered.


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Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Olsen, Joshua E SJEO36@pitt.eduJEO36
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairMcQuarrie, Nadinenmcq@pitt.edunmcq
Committee MemberJones, Charlescejones@pitt.educejones
Committee MemberShelef, Eitanshelef@pitt.edushelef
Date: 30 January 2018
Date Type: Publication
Defense Date: 28 September 2017
Approval Date: 30 January 2018
Submission Date: 29 November 2017
Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
Number of Pages: 76
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Geology and Planetary Science
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Nepal Himalayas Mountain Building Orogeny Thrust faulting fault out-of-sequence
Date Deposited: 30 Jan 2018 16:23
Last Modified: 30 Jan 2018 16:23
URI: http://d-scholarship.pitt.edu/id/eprint/33497

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