Alkaline-rich quartz syenite intrusions of the Western Karelia subprovince
Esa Heilimo, Perttu Mikkola, Hannu Huhma, Jaana Halla, 2017. "Alkaline-rich quartz syenite intrusions of the Western Karelia subprovince", Crust–Mantle Interactions and Granitoid Diversification: Insights from Archaean Cratons, J. Halla, M. J. Whitehouse, T. Ahmad, Z. Bagai
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We have studied a group of granitoids from the Western Karelia subprovince of the Fennoscandian Shield. This group is referred to as quartz syenites, but shows compositional variation from syenites to quartz monzonites, with a small number of monzonites and granites. Compositionally studied rocks are alkali and alkali-calcic, and magnesian, mostly metaluminous. Characteristically, they have a high content of alkaline (Na, K), large ion lithophile elements (LILE) (Ba, Sr), high-field strength elements (HFSE) (TiO2, Zr, Ce), as well as a low content of Mg, Ni and Cr, by which they can be distinguished from sanukitoid and quartz diorite suites of the Karelia Province. These quartz syenites were emplaced between 2.74 and 2.66 Ga, representing late-phase intrusions overlapping in age with the sanukitoids, the quartz diorites and the leucogranitoids. Initial whole-rock εNd values of quartz syenites vary from 1.8 to −1.8, and do not indicate a significant contribution of considerably older crust. Oxygen-isotope data for zircon indicate a varying mantle source (δ18O 5.35–7.15‰), with a contribution from source(s) with elevated δ18O values. Our data provide constraints on compositionally diverse Neoarchaean magmatism in the Archaean Karelia Province. The late Archaean evolution of the Western Karelia subprovince resembles that of the Neoarchean domains worldwide with respect to granitoid composition and temporal distribution.
Supplementary material: Tables detailing geochemical analyses, analytical data for the five age samples and oxygen-isotope analyses from this study are available at https://doi.org/10.6084/m9.figshare.c.3459771
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Crust–Mantle Interactions and Granitoid Diversification: Insights from Archaean Cratons
This Special Publication sheds light on crust formation and tectonic processes in early Earth by focusing on Archaean granitoids and related rocks from West Greenland in the North Atlantic Craton, Karelia Province of the Fennoscandian Shield, Eastern Dharwar and Bundelkhand cratons in the Indian Shield and Bug Complex of the Ukrainian Shield. Resulting from the IGCP-SIDA 599 project ‘The Changing Early Earth’, this compilation of papers provides explanations on the nomenclature of Archaean granitoids and explores the petrology, element and isotope geochemistry, geochronology and metamorphism of granitoids and supracrustal rocks of variable metamorphic grade. This volume provides information on the increase and timing of crust-mantle interactions and granitoid diversification from early Archaean protoliths of island arc origin to the emergence of multi-source high-K calc-alkaline granitoid batholiths at convergent continental margins. The formation of abundant granitoid batholiths suggests a significant change in mantle dynamics and plate tectonics towards the end of the Archaean.