The ‘pargasosphere’ hypothesis: Looking at global plate tectonics from a new perspective
Kovács, I.J.; Liptai, N.; Koptev, A.; Cloetingh, S.A.P.L.; Lange, T.P.; Matenco, L.; Szakács, A.; Radulian, M.; Berkesi, M.; Patkó, L.; Molnár, G.; Novák, A.; Wesztergom, V.; Szabó, C.; Fancsik, T.
(2021) Global and Planetary Change, volume 204, pp. 1 - 20
(Article)
Abstract
Apart from the lithosphere-asthenosphere boundary (LAB), mid-lithospheric discontinuities (MLDs) in thick and old continental lithospheres appear to play an important role in global plate tectonics. Initiation of intra-continental subduction, delamination of the lower continental lithospheric mantle and removal of cratonic roots are likely to occur along MLDs. Here we introduce
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the ‘pargasosphere’ hypothesis which could account for the origin of both boundaries. The observation that pargasitic amphibole is stable even at very low bulk ‘water’ concentration (~a few hundreds ppm wt.) implies that the solidus of the shallow upper mantle (<3 GPa) is usually the pargasite dehydration solidus at ~1100 °C. In young continental and oceanic lithosphere (<70 Ma) this solidus defines the LAB. The LAB separates the deeper, partial melt bearing asthenosphere from the shallower melt barren lithosphere, explaining their contrasting rheology. In old continents pargasite breaks down at the sub-solidus pargasite dehydration boundary at ~3 GPa and liberates ‘water’-rich fluids. This latter process may be responsible for the formation of MLDs. The occurrence of partial melts or fluids beyond the pargasite stability field can explain commonly observed geophysical anomalies associated with the LAB and MLDs. We present forward modelled variations of shear wave velocity and resistivity at the LAB and MLDs for idealised lithospheric columns. These columns are constructed based on the ‘pargasosphere’ hypothesis and geotherms corresponding to continental lithospheres with various tectono-thermal ages. The ‘pargasosphere’ hypothesis offers a number of other empirically testable implications. For instance, cooling asthenosphere beneath young extensional continental and oceanic lithosphere settings can be the source of surface CO2 emanations even at locations distant from areas with active volcanoes. The Vrancea zone (Eastern Europe) appears to be a suitable site for testing the ‘pargasosphere’ hypothesis for elucidating the origin of intermediate-depth earthquakes (70–300 km) and to explain the delamination of the lower continental lithospheric mantle.
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Keywords: Asthenosphere, Lithosphere, Mid-lithospheric discontinuities, Pargasite, Plate tectonics, Water, Global and Planetary Change, Oceanography
ISSN: 0921-8181
Publisher: Elsevier
Note: Funding Information: We dedicate this article to the late Frank Horváth, who was a source of inspiration to all authors to integrate geological, geophysical and geochemical observations for better understanding of tectonic processes. We acknowledge the constructive and thoughtful comments of two anonymous reviewers. The time and attention of Zhengtang Guo for editorial handling is also acknowledged. We are greatly indebted to the TOPO-TRANSYLVANIA, TOPO-EUROPE and ILP community without whom this article could not have been realised. We thank the Editors of this special volume of GPC for inviting this article. The authors acknowledge the support of the MTA EK Lendület Pannon LitH 2 Oscope grant, and the NKFIH NN128629 (TOPO-TRANSYLVANIA) grant. I.K. expresses his special thanks to David H. Green for sharing his vast body of knowledge on experimental petrology and melting relations of the upper mantle. Without the motivation by his pioneering ideas and discoveries this hypothesis could have been developed. Constructive discussions on geophysics and geodynamics with Antal Ádám, Szabolcs Harangi, László Fodor, Attila Balázs, Zoltán Erdős, Zsanett Pintér and Ylona van Dinther helped us to further develop our hypothesis. L. Patkó’s and Cs. Szabó’s work was funded by the Eötvös Loránd University (ELTE) Institutional Excellence Program ( 1783-3/2018/FEKUTSRAT ) supported by the Hungarian Ministry of Human Capacities . S.A.P.L. Cloetingh was supported by the Distinguished Guest Scientist Fellowship Program of the Hungarian Academy of Sciences . T.P. Lange was supported by the GINOP-2.3.2-15-2016-00009 research program. This study is co-funded by an Alexander von Humboldt Foundation Fellowship to A. Koptev. Funding Information: We dedicate this article to the late Frank Horv?th, who was a source of inspiration to all authors to integrate geological, geophysical and geochemical observations for better understanding of tectonic processes. We acknowledge the constructive and thoughtful comments of two anonymous reviewers. The time and attention of Zhengtang Guo for editorial handling is also acknowledged. We are greatly indebted to the TOPO-TRANSYLVANIA, TOPO-EUROPE and ILP community without whom this article could not have been realised. We thank the Editors of this special volume of GPC for inviting this article. The authors acknowledge the support of the MTA EK Lend?let Pannon LitH2Oscope grant, and the NKFIH NN128629 (TOPO-TRANSYLVANIA) grant. I.K. expresses his special thanks to David H. Green for sharing his vast body of knowledge on experimental petrology and melting relations of the upper mantle. Without the motivation by his pioneering ideas and discoveries this hypothesis could have been developed. Constructive discussions on geophysics and geodynamics with Antal ?d?m, Szabolcs Harangi, L?szl? Fodor, Attila Bal?zs, Zolt?n Erd?s, Zsanett Pint?r and Ylona van Dinther helped us to further develop our hypothesis. L. Patk??s and Cs. Szab??s work was funded by the E?tv?s Lor?nd University (ELTE) Institutional Excellence Program (1783-3/2018/FEKUTSRAT) supported by the Hungarian Ministry of Human Capacities. S.A.P.L. Cloetingh was supported by the Distinguished Guest Scientist Fellowship Program of the Hungarian Academy of Sciences. T.P. Lange was supported by the GINOP-2.3.2-15-2016-00009 research program. This study is co-funded by an Alexander von Humboldt Foundation Fellowship to A. Koptev. Publisher Copyright: © 2021
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