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Fluid regimes at depth (lower crust, upper mantle) and during the early stage of formation of the continents (from a study of fluid/melt inclusions in rock-forming minerals, notably zircons)

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Fluids, either high-temperature melts or volatiles, can be trapped in zircon and rock-forming minerals and preserved as fluid (or melt) inclusions. The aim of this project is to compare and interpret these remnants from geologically most extreme environments: the oldest (Archean gneisses) and deepest rocks such as lower crust xenoliths in alkali basalts and kimberlites, eclogites and eclogite-like rocks from metamorphic complexes, presently occurring at the Earth's surface. Special attention will be paid to the study of zircon-hosted melt and fluid inclusions from the most ancient tonalite-trondjhemite and charnockite gneisses, which are typical of the early stages of development of the continental crust. The data obtained will give better insight into the endogenic processes active during the earliest formation of the Earth's continental crust, focusing on the fluid regime at depth and its possible implication on the global volatile earth cycle. In order to check the special features of the Archean, archean rocks will be compared to deep continental intrusions (charnockites) of more recent age (Proterozoic), for which some petrographical and geochemical data are already available.

The current research will be focused on the following four topics: firstly, the determination of the origin of protoliths (primary rocks) of Archean tonalite-trondjhemite and charnockite gneisses as well as the composition of the most ancient magmas such as crystallisation conditions, composition in which most ancient zircons occur; secondly, the determination of P-T conditions and fluid regime during the granulitic metamorphism and anatexis of the Archean primary-crustal rocks, by investigations of the fluid (and melt) inclusions in zircon and rock-forming minerals from tonalite-trondjhemite and charnockite gneisses of the Aldan and Anabar shields; thirdly, the determination of the origin (magmatic or metamorphic) and fluid regimes of the deepest rocks (kyanite granulites, eclogites and eclogite-like rocks) presently occurring at the surface of the Earth; and finally, to trace the mantle-crust interaction during the genesis of magmas at depth, the timing of rock formation and the recycling of surface material at great depth (subduction) using isotopic tracers, notably (and hopefully) through ion probe analysis on melt inclusions in zircon.

The results will be published in high-quality international journals, such as Contributions to Mineralogy and Petrology, Earth Science Planetary Letters, Journal of Geology. The first results, dealing essentially with the presentation of some examples of melt inclusions in zircons from the Anabar and Aldan shields, and the characterisation of the fluid regimes in these rocks, will be presented at meetings of the European Current Research on Fluid Inclusion and at the International Geological Congress in Beijing, China.

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Vrije Universiteit Amsterdam
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De Boelelaan 1085
1081 HV Amsterdam
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Letzte Aktualisierung: 19 September 1996

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Permalink: https://cordis.europa.eu/project/id/INTAS-94-2373/de

European Union, 2024