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Content archived on 2022-12-23

Crust-Mantle Interaction in the late Archaean Evolution of the Baltic and Ukrainian Shields: the sources, parental melts and magmatic evolution of the sanukitoid-lamprophyre and syenite-lamprophyre associations

Objective

Crust-Mantle Interaction in the late Archaean Evolution of the Baltic and Ukrainian Shields: the sources, parental melts and magmatic evolution of the sanukitoid-lamprophyre and syenite-lamprophyre associations.

Sanukitoids are high-silica, high magnesium granitoids found predominantly in Archaean terrains. Understanding the origin of Sanukitoids has recently been recognised as essential to the broader understanding of Archaean crust-formation (Rollinson, in press), for they provide a link between the process of crust formation and mantle processes.

Two competing hypotheses for the origin of sanukitoids emphasise, on the one hand their mantle-like character, and on the other the possibility that they are the product of mixing between slab melts and the mantle wedge. We propose to test these competing hypotheses by examining the petrology and geochemistry of sanukitoid associations in the Baltic and Ukrainian Shields.

In this project we investigate the significance of the links between
(a) sanukitoids and 'alkaline' igneous rocks; and
(b) between sanukitoids and calc-alkaline lamprophyres for the petrological links between these rock types is not well known.

The Sanukitoid-alkaline rock association is also important for in many Archaean terrains gold mineralisation is closely associated with lamprophyres and with granitoids of both sanukitoid and alkaline affinities.

In detail we intend to:
(1) determine the distribution of sanukitoid and alkaline intrusions within the Baltic and Ukrainian Shields;
(2) measure the precise time of their emplacement, using Nd isotopes and U-Pb zircon geochronology;
(3) investigate the geochemical links between sanukitoids, alkaline plutons and calc-alkaline lamprophyres;
(4) use field data, petrology, geochemical data and modelling to reconstruct the petrogenetic processes that gave rise to the sanukitoid suites. The target being to determine their source, the composition of the residue of melting and the PT conditions of fusion.
(5) investigate the extent to which the observed petrological and geochemical variations in the sanukitoid associations can be attributed to crust-mantle interactions, using Nd, Sr and Pb isotopes in whole-rock samples and the U-Pb isotopic compositions of xenocrystic zircons.

The Baltic and Ukrainian Shields are ideally suited to an investigation of this type for:
1. They show a long history of crust-mantle interaction;
2. Domains within these shields have contrasting geological histories. Sanukitoid and alkaline-granitoid associations are found throughout this region in crust which has a variable pre-history of between 150-700Ma;
3. Thus on a Nd-time plot, rocks from the eastern part of the Karelian Province show evidence of a long crustal history (3.5 to 2.7Ga) whereas rocks from the central and western parts of the province have a much shorter crustal history (2.7 to 2.9Ga);
4. This allows the sanukitoid association to be understood in terms of mixing processes with older crust;
5. The Sanukitoid and alkaline-granitoid association is found in close association in a number of multi-phase intrusions;
6. There is a close relationship between the sanukitoid intrusions of the Baltic Shield and gold mineralisation.

Our ultimate goal is to apply the results of this project to global models of crust-mantle interaction during the formation of the Earth's continental crust during the late Archaean.

Call for proposal

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Funding Scheme

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Coordinator

Cheltenham & Gloucester College of Higher Education
EU contribution
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Address
Francis Close Hall, Swindon Road
GL50 4AZ Cheltenham
United Kingdom

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Total cost
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Participants (6)