Conditions and timing of incorporation of ophiolite into orogenic crust during oblique convergence, Central Anatolia
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ORIGINAL PAPER
Conditions and timing of incorporation of ophiolite into orogenic crust during oblique convergence, Central Anatolia Molly Radwany1,2 · Leah E. Morgan3 · Donna L. Whitney1 Received: 9 December 2019 / Accepted: 8 July 2020 © Geologische Vereinigung e.V. (GV) 2020
Abstract Ophiolitic fragments scattered over a wide area of Central Anatolia exhibit varying degrees of metamorphism, from unmetamorphosed to upper amphibolite facies, although geochemical similarities suggest they are all part of the Central Anatolian Ophiolite (CAO). Magmatic crystallization of oceanic crust in the CAO at ~ 91 Ma coincided with high-grade metamorphism of rocks that underlie the southern, highest grade part of the CAO, raising questions about the tectonic relationship of the ophiolite to underlying metasedimentary and plutonic rocks. New geochronology results show that the 40Ar/39Ar hornblende age of amphibolite-facies metagabbro in the high-grade metamorphic part of the CAO is ~ 87 Ma, similar to hornblende ages from amphibolite in the underlying Niğde metamorphic/plutonic massif. Biotite in a deformed quartzofeldspathic rock associated with high-grade meta-ophiolitic rocks yielded an 40Ar–39Ar age of ~ 78 Ma, similar to biotite ages from the Niğde Massif. Hornblende in gabbro from unmetamorphosed CAO yielded an older 40Ar/39Ar age of ~ 90 Ma, similar to the previously determined crystallization age of the ophiolite. These data indicate that the southern part of the ophiolite was incorporated into and therefore metamorphosed and deformed with the orogenic mid-crust now exposed in the Niğde metamorphic–plutonic complex, whereas the northern, unmetamorphosed part of the ophiolite was obducted onto the continent. This distinct difference in different parts of the ophiolite may indicate oblique collision or irregularities in the continental margin, resulting in part of the ophiolite being incorporated into the orogenic crust and subsequently exhumed and cooled with it, and another part being obducted. Keywords Metaophiolite · Central Anatolia · Nigde Massif
Introduction Most gabbro bodies that occur throughout Central Anatolia are fragments of ophiolites, including many of Late Cretaceous age that formed in a supra-subduction setting in Neo-Tethyan seaways that were then obducted or incorporated into suture zones (e.g., Floyd et al. 2000; Yalınız Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00531-020-01908-7) contains supplementary material, which is available to authorized users. * Molly Radwany [email protected] 1
Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455, USA
2
Department of Mining and Geological Engineering, University of Arizona, Tucson, AZ 85721, USA
3
U.S. Geological Survey, Denver, CO, USA
2008). Most of these gabbro bodies are unmetamorphosed or record seafloor hydrothermal metamorphism (subgreenschist facies) and lack ductile deformation features (e.g., van Hinsbergen et al. 2016). A signi
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