Polyphase magmatic pulses along the Northern Gondwana margin: U-Pb zircon geochronology from gneiss domes of the Pyrenees |
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| Institution: | 1. Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, Prague, 12843, Czech Republic;2. Institute of Geology of the Czech Academy of Sciences, Rozvojová 269, Prague, 16500, Czech Republic;1. Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland;2. Dipartimento di Geoscienze, University of Padova, 35131 Padova, Italy;3. ENSER srl, viale Baccarini 29, 48018 Faenza, RA, Italy;4. Italferr S.p.A., via V. G. Galati, 71, 00155 Roma, Italy;5. Alma Mater Studiorum, University of Bologna, School of Engineering and Architecture, Viale del Risorgimento 2, Bologna, Italy;1. Department of Research and Cooperation, Mongolian University of Science and Technology, 8th khoroo, Baga toiruu 34, Sukhbaatar district, Ulaanbaatar 14191, Mongolia;2. Department of Earth Sciences and Astronomy, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan;3. Department of Biosphere-Geosphere Science, Faculty of Biosphere-Geosphere Science, Okayama University of Science, 1-1 Ridaicho, Kita-ku, Okayama-shi 700-0005, Japan;4. Department of Chemistry, Gakushuin University, 1-5-1, Mejiro, Toshima-ku, Tokyo 171-8588, Japan;5. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8550, Japan |
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| Abstract: | Alkaline granitic dikes intruding the metasedimentary mantle and orthogneiss cores of the Aston and Hospitalet domes of the Axial Zone of the Pyrenees are subjects of a laser ablation ICP-MS U-Pb zircon geochronology study. The age spectra recorded by detrital, magmatic xenocrystic and inherited zircons reveal a more complex, nearly continuous Paleozoic magmatic history of the Variscan basement of the Pyrenees than previously known. Inherited and detrital zircons of Mesoarchean, Paleoproterozoic to Ediacaran ages attest to the Peri-Gondwana location of the Cambrian sediments that later form the metamorphic core of the Variscan Pyrenees. The youngest magmatic zircon ages fall into the late Carboniferous and earliest Permian, ranging from ca. 306–297 Ma, and represent the emplacement ages of the dikes and small granite intrusions. The age spectra of magmatic xenocrystic zircons contain several maxima, middle (475–465 Ma) and late Ordovician (455–445 Ma), early (415–402 Ma) and late Devonian (385–383 Ma), early (356–351 Ma) and middle Carboniferous (ca. 328 Ma). Middle Ordovician and middle Carboniferous ages are obtained from xenocrystic zircons that were assimilated from the rocks the dikes intruded, the Aston and Hospitalet orthogneisses and the Soulcem granite. The presence of early-mid Carboniferous magmatic zircons in several samples lends further support to a wide-spread early Variscan magmatic activity in the central Pyrenees. The other age peaks do not have equivalent igneous or metaigneous rocks in the central Axial Zone, but are thought to be present in the Pyrenean crust, not exposed and yet to be identified. The diversity of Ordovician, Devonian and Carboniferous up to Permian magmatic ages indicates polyphase emplacement of intrusive bodies during pre-Variscan and Variscan orogenies. The source of the heat for the Devonian to early-mid Carboniferous magmatic activity remains elusive and may involve intracontinental subduction zone, lithospheric-scale shearing or a mantle plume (TUZO). |
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