%0 Journal Article
%T Mantle transect of the Karelian Craton from margin to core based on P-T data from garnet and clinopyroxene xenocrysts in kimberlites
%A Marja Lehtonen
%A Hugh O＊Brien
%J Bulletin of the Geological Society of Finland
%D 2009
%I The Geological Society of Finland
%X Peridotitic garnet and clinopyroxene xenocrysts from the 1.2 Ga Lentiira每Kuhmo and the 760 Ma Kuusamo kimberlite fields, emplaced within the Central Karelian Craton, have been studied using major and trace element geochemistry to obtain information on the stratigraphy,compositional variability, and evolutionary history of the underlying lithospheric mantle. An earlier study on the 600 Ma Kaavi每Kuopio kimberlite field showed that near the SW margin of the craton the 230-km-thick subcontinental lithospheric mantle (SCLM) exhibitsa well-developed 3-layer structure indicative of episodic construction. New Ni in garnet thermometry on samples farther into the craton, from Kuhmo, Lentiira, and southern and northern Kuusamo, gives temperature ranges of 800每1400, 700每1450, 700每1450 and600每1300 ∼C, respectively, and when extrapolated to the geotherm determined for the Kaavi-Kuopio area, indicates sampling intervals of c. 100每240, 80每250, 80每250 and 65每210 km, respectively. The results demonstrate that the SCLM of the Karelian Craton reaches itsgreatest thickness in the Lentiira-Kuhmo and southern Kuusamo area and thins towards the North and South. The mantle stratigraphy of the craton core, compared to the craton edge, shows less compositional variation, with only two distinguishable horizons correspondinggenerally to the two deepest layers at Kaavi-Kuopio. Additionally, based on the Mg# of pyropes, the level of depletion of peridotites comprising the mantle lithosphere in the central craton is significantly higher than at the craton edge represented by Kaavi-Kuopio. Coupled with the rarity of mantle-derived chrome diopside, the implication is that this portion of the mantle either underwent high levels of partial melting to produce very refractory residua or experienced less melt-modification than average SCLM subsequent toformation. The craton core provides a wide diamond window up to 110 km thick compared to c. 40 km at the craton edge.
%K kimberlite
%K lithosphere
%K mantle
%K xenocrysts
%K pyrope
%K Finland
%U http://www.geologinenseura.fi/bulletin/Volume81/Lehtonen_OBrien.pdf