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Late Cenozoic shortening in the west-central Alborz Mountains, northern Iran, by combined conjugate strike-slip and thin-skinned deformation

Guest, Bernard and Axen, Gary J. and Lam, Patrick S. and Hassanzadeh, Jamshid (2006) Late Cenozoic shortening in the west-central Alborz Mountains, northern Iran, by combined conjugate strike-slip and thin-skinned deformation. Geosphere, 2 (1). pp. 35-52. ISSN 1553-040X. https://resolver.caltech.edu/CaltechAUTHORS:20130821-151248726

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Abstract

The west-central Alborz Mountains of northern Iran have deformed in response to the Arabia-Eurasia collision since ca. 12 Ma and have accommodated 53 ± 3 km of shortening by a combination of range-parallel, conjugate strike-slip faulting and range-normal thrusting. By our interpretation, ∼17 km of shortening across the Alborz is accommodated by westward relative motion of a crustal wedge bounded by conjugate dextral and sinistral strike-slip fault systems. The Nusha, Barir, and Tang-e-Galu fault zones strike west-northwest, constrain the north side of the wedge, and, prior to ca. 5 Ma, accumulated a total of ∼25 km of dextral slip. The south side of the wedge is bounded by the active sinistral reverse Mosha and Taleghan faults, which merge northwest of Tehran and have a total slip estimate of 30–35 km. A restored cross section across the range indicates a minimum of 36 ± 2 km of fold-and-thrust–related, range-normal shortening. Combined, wedge motion, thrusting, and folding yield a net shortening of 53 ± 3 km across the range, which is within the error of the shortening estimate predicted by assuming that the present-day shortening rate (5 ± 2 mm/yr) has been constant since ca. 12 Ma (∼60 km of predicted shortening). A second restored cross section farther west, which includes the wedge, gives a total shortening of 15–18 km and a long-term shortening rate of 1.25–1.5 mm/yr (constant shortening rate since ca. 12 Ma). These strong along-strike finite-strain and long-term strain-rate gradients are important for our understanding of how long-term strain rates compare with instantaneous strain rates derived from global positioning system (GPS) data, and should be considered when planning mountain belt–scale GPS surveys. Finally, a 60-km-long right-hand bend in the Mosha-Taleghan fault system has driven the development of a transpressional duplex south of the fault. The southern boundary of the duplex is the active Farahzad–Karaj–North Tehran thrust system. The kinematic development of this strike-slip duplex has implications for seismic hazard assessment in the heavily populated Karaj and Tehran areas.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1130/GES00019.1 DOIArticle
http://geosphere.gsapubs.org/content/2/1/35PublisherArticle
http://geosphere.geoscienceworld.org/content/2/1/35PublisherArticle
http://geosphere.gsapubs.org/content/2/1/35.figures-onlyPublisherFigures
Additional Information:© 2006 Geological Society of America. Manuscript received by the Society 20 April 2005; Revised manuscript received 28 November 2005; Manuscript accepted 29 November 2005. This research was supported by the National Science Foundation (grant EAR-9902932 to G.J. Axen), University of California–Los Angeles (UCLA) Council on Research (G.J. Axen), the University of Tehran Research Council (grant 651/1/328 to J. Hassanzadeh), and a UCLA Department of Earth and Space Sciences Cross-Training Fellowship (B. Guest and G. Peltzer). G. Peltzer provided critical advice and assistance with the remote sensing component of the mapping presented here. Early drafts of this manuscript were improved greatly by informal reviews from Nathan Niemi and Charlie Verdel. The insightful reviews returned by Nadine McQuarrie and Mark Allen led to significant improvements in the plates and in the text. Kevin Mahan reviewed a final version of the manuscript before final submission.
Funders:
Funding AgencyGrant Number
NSFEAR-9902932
UCLA Council on ResearchUNSPECIFIED
University of Tehran Research Council651/1/328
UCLA Department of Earth and Space Sciences Cross-Training FellowshipUNSPECIFIED
Subject Keywords:Iran; shortening; collision; Alborz; seismic hazard
Issue or Number:1
Record Number:CaltechAUTHORS:20130821-151248726
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20130821-151248726
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:40765
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:23 Aug 2013 22:21
Last Modified:03 Oct 2019 05:42

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