Abstract

Research Article| April 01, 2002 Secular changes in tonalite-trondhjemite-granodiorite composition as markers of the progressive cooling of Earth Hervé Martin; Hervé Martin 1Laboratoire Magmas et Volcans, Observatoire de Physique du Globe de Clermont-Ferrand, Université Blaise Pascal, Centre National de la Recherche Scientifique 5, rue Kessler 63038, Clermont-Ferrand cedex, France Search for other works by this author on: GSW Google Scholar Jean-François Moyen Jean-François Moyen 1Laboratoire Magmas et Volcans, Observatoire de Physique du Globe de Clermont-Ferrand, Université Blaise Pascal, Centre National de la Recherche Scientifique 5, rue Kessler 63038, Clermont-Ferrand cedex, France Search for other works by this author on: GSW Google Scholar Author and Article Information Hervé Martin 1Laboratoire Magmas et Volcans, Observatoire de Physique du Globe de Clermont-Ferrand, Université Blaise Pascal, Centre National de la Recherche Scientifique 5, rue Kessler 63038, Clermont-Ferrand cedex, France Jean-François Moyen 1Laboratoire Magmas et Volcans, Observatoire de Physique du Globe de Clermont-Ferrand, Université Blaise Pascal, Centre National de la Recherche Scientifique 5, rue Kessler 63038, Clermont-Ferrand cedex, France Publisher: Geological Society of America Received: 13 Sep 2001 Revision Received: 23 Nov 2001 Accepted: 27 Nov 2001 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2002) 30 (4): 319–322. https://doi.org/10.1130/0091-7613(2002)0302.0.CO;2 Article history Received: 13 Sep 2001 Revision Received: 23 Nov 2001 Accepted: 27 Nov 2001 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hervé Martin, Jean-François Moyen; Secular changes in tonalite-trondhjemite-granodiorite composition as markers of the progressive cooling of Earth. Geology 2002;; 30 (4): 319–322. doi: https://doi.org/10.1130/0091-7613(2002)0302.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Archean tonalite-trondhjemite-granodiorite associations (TTG) are classically thought to generate through partial melting of hydrous metabasalts. However, the chemical composition of the least differentiated TTG parental magmas evolved from 4.0 to 2.5 Ga. During this interval, the Mg# as well as the Ni and Cr contents increased, which is interpreted as reflecting increased interactions between felsic melts generated by metabasalt melting and mantle peridotite. Similarly, (CaO + Na2O) and Sr also increased over time, thus reflecting an increase in the abundance of plagioclase in the melt residue. The presence or absence of residual plagioclase is interpreted in terms of melting depth. The demonstrated interaction between TTG parental magmas and the mantle rules out their genesis by fusion of previously underplated metabasalt and favors the melting of subducted slab material. At 4.0 Ga, Earth's geothermal gradient was sufficiently high to allow slab melting at shallow depths where plagioclase was stable. Consequently, due to the small thickness of the overlying mantle wedge, felsic magmas interacted little with the mantle. At 2.5 Ga, however, owing to lower geothermal gradients, the melting depth was greater and plagioclase became no longer stable in the thick mantle wedge overlying the subducted slab. As a result, felsic magmas reacted strongly with the mantle peridotite. The changes of TTG composition during Archean time can be thus interpreted as reflecting the progressive cooling of Earth. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.