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Absolute ages of multiple generations of brittle structures by U-Pb dating of calcite
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Number of Authors: 42018 (English)In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 46, no 3, p. 207-210Article in journal (Refereed) Published
Abstract [en]

Direct dating of brittle structures is challenging, especially absolute dating of diagenesis followed by a series of superimposed brittle deformation events. We report 22 calcite U-Pb ages from tectonites and carbonate host rocks that date 3 diagenetic and 6 brittle deformation events. Results show that U-Pb dating of calcite fibers from these structures is compatible with overprinting relationships. Ages indicate that diagenesis occurred between 147 +/- 6 Ma and 103 +/- 34 Ma, and was followed by top-to-the-south, layer-parallel shearing due to ophiolite obduction at 84 +/- 5 Ma (2 sigma errors). Sheared top-to-the- northeast, layer-parallel veins were dated as 64 +/- 4 Ma and are interpreted to have developed during postobduction exhumation. After this event, a series of strike-slip structures, which crosscut and reactivated older faults due to northwest-southeast horizontal shortening, were dated as 55 +/- 22 Ma and 43 +/- 6 Ma. Eight ages from strike-slip faults and thrusts resulting from northeast-southwest shortening range from 40.6 +/- 0.5 Ma to 16.1 +/- 0.2 Ma. The youngest ages are from minor overprinting fibers ranging in age between 7.5 +/- 0.9 Ma and 1.6 +/- 0.6 Ma. Our results show that U-Pb dating of calcite fibers can be successfully used to constrain a complicated succession of brittle deformation structures that encompasses two orogenies and an intervening extension period.

Place, publisher, year, edition, pages
2018. Vol. 46, no 3, p. 207-210
National Category
Earth and Related Environmental Sciences
Research subject
Geology
Identifiers
URN: urn:nbn:se:su:diva-154801DOI: 10.1130/G39822.1ISI: 000427129500008OAI: oai:DiVA.org:su-154801DiVA, id: diva2:1197734
Available from: 2018-04-13 Created: 2018-04-13 Last updated: 2018-06-21Bibliographically approved
In thesis
1. Cryptic Orogeny: uplift of the Al Hajar Mountains at an alleged passive margin
Open this publication in new window or tab >>Cryptic Orogeny: uplift of the Al Hajar Mountains at an alleged passive margin
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mountains evolve and grow because of the large forces that occur from the collision of tectonic plates. Plate boundaries change and move through time, and regions that were once stable, shallow-marine environments can be dragged into subduction zones and get transformed into vast mountain ranges. The Al Hajar Mountains in Oman consist of carbonate rocks which show that during most of the Mesozoic (c. 268 Ma – 95 Ma) they had not yet formed but were flat and below sea level. Following this, in the Late Cretaceous (c. 95 Ma), a major tectonic event caused oceanic crust to be obducted onto this Mesozoic carbonate platform. Then after obduction a shallow marine environment resumed, and Paleogene sedimentary rocks were deposited. Currently, the central mountains are located on the Arabian Plate and are 200 km away from the convergent plate boundary with Eurasia. Here, Arabia is being subducted. Further towards the northwest Arabia and Eurasia are colliding, forming the Zagros Mountains which initiated no earlier than the Oligocene (c. 30 Ma). At this time the mountains were even further away from the plate boundary. The problem with the Al Hajar Mountains is that they record a collision, but are not in a collisional zone. To better understand the formation of the Al Hajar Mountains, a multidiscipline approach was used to investigate the timing at which they developed. This included applying low-temperature thermochronology, U-Pb dating of brittle structures, and balanced cross-sections. Results indicate that the orogeny began in the late Eocene and had concluded by the early Miocene (40 Ma – 15 Ma). Therefore, the uplift of the Al Hajar Mountains is not related to either the older Late Cretaceous ophiolite obduction or the younger Zagros collision, and a new tectonic model is proposed. This research shows that the Cenozoic tectonic history of northern Oman is more cryptic than what has been formerly presented.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2018. p. 26
Keywords
uplift, mountains, structural, low-temperature, thermochronology, dating, fission-track, (U-Th)/He, U-Pb, calcite, structure-from-motion, photogrammetry, UAV, trishear, fault-propagation, Hafit, Al Hajar Mountains, United Arab Emirates, Oman
National Category
Geology
Research subject
Geology
Identifiers
urn:nbn:se:su:diva-157506 (URN)978-91-7797-338-6 (ISBN)978-91-7797-339-3 (ISBN)
Public defence
2018-09-07, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2018-08-15 Created: 2018-06-20 Last updated: 2018-08-15Bibliographically approved

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