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A preliminary study of methane inclusions in alkaline igneous rocks of the Kola igneous province, Russia; implications for the origin of methane in igneous rocks

Joanna Potter, Andrew H. Rankin, Peter J. Treloar, Valentin A. Nivin, Wupao Ting and Pei Ni
A preliminary study of methane inclusions in alkaline igneous rocks of the Kola igneous province, Russia; implications for the origin of methane in igneous rocks (in ECROFI XIV (European Current Research on Fluid Inclusions) symposium, Michel Cathelineau and Jean Dubessy)
European Journal of Mineralogy (December 1998) 10 (6): 1167-1180

Abstract

Fluid inclusions from the Kovdor, Khibina and Lovozero complexes of the Kola alkaline igneous province have been investigated using microthermometric techniques and PVTX modelling. CH (sub 4) inclusions, found in all three complexes, are always secondary in origin and frequently occur in curvilinear arrays associated with secondary H (sub 2) O-dominant inclusions and, in Khibina, CH (sub 4) -H (sub 2) O inclusions. The secondary nature of the CH (sub 4) -bearing inclusions appears to preclude a direct magmatic origin for the methane, which is supported by preliminary C-isotope data which indicate an abiogenic origin. Isochore projections for primary CO (sub 2) - and H (sub 2) O-dominant inclusions intersect the volatile-saturated, agpaitic, nepheline syenite solidus (at 700 degrees C), at pressures between 3.5 and 5.5 kbar, compatible with magmatic exsolution of these fluids at crustal depths of between 11-18 km. By contrast, fluid-phase equilibria and the shallow slopes of isochores derived from the PVTX modelling of CH (sub 4) -dominant and related inclusions are indicative of trapping conditions at pressures of 0.5 to 1.8 kbar. The close association of CH (sub 4) inclusions with magnetite and late-stage hydrated phases suggests evolution of CH (sub 4) during hydration within a reducing environment. This evolution involved subsolidus Fischer-Tropsch reactions of the type CO (sub 2) +4H (sub 2) -->CH (sub 4) +2H (sub 2) O, with the water-produced driving hydration reactions which generated magnetite and more H (sub 2) . Methane production is thus a function of vapour-mineral reactions in the C-H-O system operative during late-stage hydrothermal processes and, in particular, is due to two self-reinforcing reaction types linked through a positive feedback mechanism.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 10
Serial Issue: 6
Title: A preliminary study of methane inclusions in alkaline igneous rocks of the Kola igneous province, Russia; implications for the origin of methane in igneous rocks
Title: ECROFI XIV (European Current Research on Fluid Inclusions) symposium
Author(s): Potter, JoannaRankin, Andrew H.Treloar, Peter J.Nivin, Valentin A.Ting, WupaoNi, Pei
Author(s): Cathelineau, Michel
Author(s): Dubessy, Jean
Affiliation: Kingston University, School of Geological Sciences, Kingston, United Kingdom
Affiliation: UMR, CREGU, Vandoeuvre-les-Nancy, France
Pages: 1167-1180
Published: 199812
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
Meeting name: ECROFI XIV (European Current Research on Fluid Inclusions) symposium
Meeting location: Nancy, FRA, France
Meeting date: 19970701July 1-4, 1997
References: 54
Accession Number: 1999-018591
Categories: Igneous and metamorphic petrology
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
N67°00'00" - N68°00'00", E33°00'00" - E34°00'00"
N66°00'00" - N70°00'00", E32°00'00" - E42°00'00"
N67°34'60" - N67°34'60", E30°19'60" - E30°19'60"
Secondary Affiliation: Russian Academy of Sciences, USA, United States
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 199907
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