Low mantle plume component in 370 Ma old Kola...

RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 1, NO. 2, PAGES 179–222, doi:10.2205/1999ES000015, 1999

Low mantle plume component in 370 Ma old Kola ultrabasic-alkaline-carbonatite complexes: Evidences from rare gas isotopes and related trace elements

I. N. Tolstikhin, I. L. Kamensky, V. A. Nivin, V. R. Vetrin, E. G. Balaganskaya, S. V. Ikorsky, M. A. Gannibal, and Yu. M. Kirnarsky

Geological Institute, Kola Scientific Centre, Russian Academy of Sciences, Apatity, Russia

B. Marty

Centre National de la Recherche Scientifique Centre de Recherches Petrographiques et Geochimiques(C.R.P.G.), Vandoeuvre-Nancy Cedex, France

D. Weiss, A. Verhulst, and D. Demaiffe

Petrologie et Geodynamique Chimique Department des Sciences de la Terre et de l`Environnement Faculte des Sciences Universite, Bruxelles, Belgique

Abstract

[1] During Devonian pulse of alkaline magmatism (370 Ma ago) 18 ultrabasic-alkaline-carbonatite complexes were formed on the Kola Peninsula. Rare gas isotope abundances were studied in ~300 samples from 8 complexes and also from Devonian dikes. A comparison of expected from in-situ closed-system production (calc) and measured (meas) abundances has shown that ⁴He _meas ⁴He_calc whereas in some rocks and minerals ³He_meas exceeded ³He_calc up to 1,000 times indicating occurrence of a mantle fluid in a majority of samples. Gas extraction liberated fluid-related helium with as low ⁴He/³He ratios as 3 x 104. These values show a contribution of ³He-rich plume-like component. A reason for highly variable ⁴He/³He ratios is not well understood yet. Isotope composition of Ne supports the occurrence of plume component: ²⁰Ne/²²Ne ratio varies from 10.4 to 12.0 and ²⁰Ne/²²Ne versus ²¹Ne/²²Ne correlation is quite similar to that observed for Loihi hot spot, Hawaii. A comparison of these data with rare gas systematic in the mantle enable us to suggest a contribution of material from the less degassed deep mantle reservoir, source of primordial rare gases, to Devonian ultrabasic-alkaline and carbonatite rocks on the Kola Peninsula.

Received 5 December 1998; published 12 February 1999.

Keywords: mantle plume, rare gas isotopes, trace elements.

Citation: Tolstikhin, I. N., I. L. Kamensky, V. A. Nivin, V. R. Vetrin, E. G. Balaganskaya, S. V. Ikorsky, M. A. Gannibal, Yu. M. Kirnarsky, B. Marty, D. Weiss, A. Verhulst, and D. Demaiffe (1999), Low mantle plume component in 370 Ma old Kola ultrabasic-alkaline-carbonatite complexes: Evidences from rare gas isotopes and related trace elements, Russ. J. Earth Sci., 1, No.2, 179-222, doi:10.2205/1999ES000015.

Version of this paper in Russian