Dating of lithospheric buckling: 40Ar/39Ar ages of syn-orocline strike–slip shear zones in northwestern Iberia



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Gutiérrez Alonso, Gabriel and Collins, Alan S. and Fernández Suárez, Javier and Pastor Galán, Daniel and González Clavijo, Emilio and Jourdan, Fred and Weil, Arlo B. and Johnston, Stephen T. (2015) Dating of lithospheric buckling: 40Ar/39Ar ages of syn-orocline strike–slip shear zones in northwestern Iberia. Tectonophysics, 643 . pp. 44-54. ISSN 0040-1951 ; 1879-3266

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Abstract Orogenic curvature is a ubiquitous feature of mountain belts, and the plate tectonic and geodynamic setting responsible for the development of curved orogens is a subject of debate. In order to distinguish between different models of orocline formation it is necessary to tightly constrain the absolute timing of oroclinal development. However, determining the absolute (isotopic) timing of oroclinal bending is challenging. The most direct method available to constrain the time interval during which an orocline formed is to obtain absolute age constraints on fabrics generated within syn-orocline strike–slip shear zones that accommodated rotations around a vertical axis during the development of crustal or lithospheric scale orogenic curvature. Here we present a data set of 40Ar/39Ar ages obtained from five shear-zones, some of which display curved traces parallel to the Cantabrian Orocline structural grain in NW Iberia and are interpreted to have been generated coevally to it. The 40Ar/39Ar ages were obtained by laser-rastering induced step-heating on single muscovite crystals that grew synkinematically during shearing. All five samples yielded ages that cluster tightly at 308 ± 3 Ma providing direct evidence for the age of oroclinal bending. This age is consistent with the age constraints obtained from paleomagnetic and structural data that place the onset of oroclinal bending in Moscovian times. Our 40Ar/39Ar age determinations therefore provide a reliable absolute constraint on the age of buckling of the Variscan orogen around a vertical axis and provide further evidence that oroclinal bending is unrelated to Variscan convergence/collision or the subsequent extensional collapse of the mountain belt.

Item Type:Article
Uncontrolled Keywords:Ar–Ar geochronology; Orocline; Iberia; Shear zones
Subjects:Sciences > Geology > Stratigraphic geology
Sciences > Geology > Petrology
ID Code:62593
Deposited On:19 Oct 2020 13:32
Last Modified:21 Jan 2022 07:58

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