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Early Neogene foreland of the Zagros, implications for the initial closure of the Neo-Tethys and kinematics of crustal shortening

Pirouz, Mortaza and Avouac, Jean-Philippe and Hassanzadeh, Jamshid and Kirschvink, Joseph L. and Bahroudi, Abbas (2017) Early Neogene foreland of the Zagros, implications for the initial closure of the Neo-Tethys and kinematics of crustal shortening. Earth and Planetary Science Letters, 477 . pp. 168-182. ISSN 0012-821X. doi:10.1016/j.epsl.2017.07.046.

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We study the transition from passive margin to foreland basin sedimentation now exposed in the High Zagros belt to provide chronological constraints on the initial stage of Arabia–Eurasia collision and closure of the Neo-Tethys. We performed magnetostratigraphy and strontium isotope stratigraphy along two sections near the Zagros suture which expose the oldest preserved foreland deposits: the Shalamzar section in the west and the Dehmoord section in the east. The top of the passive margin Asmari formation has an age of 28–29 Ma in the High Zagros and is overlain by foreland deposits with a major basal unconformity representing 7 Myr of hiatus. The base of the foreland deposits has an age of 21.5 Ma at Dehmoord and ca. 26 Ma at Shalamzar. The sedimentation rate increased from 30 m/Myr in the passive margin to 247 m/Myr in the foreland. Combined with available age constraints across the Zagros, our results show that the unconformity is diachronous and records the southwestward migration of the flexural bulge within the Arabian plate at an average rate of 24 ± 2 mm/yr over the last 27 Ma. The time evolution of sediment accumulation in the Zagros foreland follows the prediction from a flexural model, as the foreland is thrust beneath the orogenic wedge and loaded by the wedge and basin fill. We detect the onset of forebulge formation within the Asmari Formation around 25 Ma. We conclude that closure of the Neo-Tethys formed the Zagros collisional wedge at 27 ± 2 Ma. Hence, the Arabia–Eurasia collision was probably not the main driver of global cooling which started near the Eocene–Oligocene boundary (ca. 33.7 Ma). We estimate 650 km of forebulge migration since the onset of the collision which consists of 350 km of shortening across the orogen, and 300 km of widening of the wedge and increasing flexural rigidity of Arabia. We conclude the average rate of shortening across the Zagros to be ca. 13 mm/yr over the last 27 Myr; a value comparable to the modern rate. Palinspastic restoration of structural cross-sections and crustal volume conservation comprise only ca. 200 km of shortening across the Zagros and metamorphic Sanandaj–Sirjan belt implying that at least 150 km of the Arabian crust was underthrust beneath Eurasia without contributing to crustal thickening, possibly due to eclogitization.

Item Type:Article
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URLURL TypeDescription
Pirouz, Mortaza0000-0002-7569-492X
Avouac, Jean-Philippe0000-0002-3060-8442
Kirschvink, Joseph L.0000-0001-9486-6689
Additional Information:© 2017 Elsevier B.V. Received 27 May 2017, Revised 23 July 2017, Accepted 25 July 2017, Available online 9 September 2017. This Research has been partially funded by Swiss National Science Foundation Grant No. P2GEP2-148801, and Grant PRF No. 53814-ND8 of the American Chemical Society. We are grateful to the people of Dehmoord and Shalamzar for assistance during the field work. Seyed Abdolnabi Abtahi and Yaser Gharakhani are thanked for hospitality. Tahmoures Yousefi, Ebrahim Khademi, and Ramin Elyaszadeh from Geological Survey of Iran–Shiraz, and Reza Monsef, Rasoul Esmaeili helped with logistics and sampling. Isaac Hilburn, Sarah Slotznick and Ross Mitchell are thanked for technical assistance with paleomagnetic measurements. We benefited from constructive comments from Brian Horton, Jonas B. Ruh and an anonymous reviewer. Associate Editor An Yin is thanked for handling the manuscript. Mark Allen and Frédéric Mouthereau provided valuable comments and suggestions.
Group:Seismological Laboratory
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)P2GEP2-148801
American Chemical Society Petroleum Research Fund53814-ND8
Subject Keywords:Neo-Tethys closure; Arabia–Eurasia collision; crustal shortening; Zagros foreland dynamics; magnetostratigraphy; strontium isotope stratigraphy
Record Number:CaltechAUTHORS:20170911-080518933
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Official Citation:Mortaza Pirouz, Jean-Philippe Avouac, Jamshid Hassanzadeh, Joseph L. Kirschvink, Abbas Bahroudi, Early Neogene foreland of the Zagros, implications for the initial closure of the Neo-Tethys and kinematics of crustal shortening, Earth and Planetary Science Letters, Volume 477, 1 November 2017, Pages 168-182, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:81281
Deposited By: Tony Diaz
Deposited On:11 Sep 2017 18:26
Last Modified:15 Nov 2021 19:42

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