Journal of Petrology, Volume 39, Issue 5: May 1 1998.

Geochemical Characteristics of the Youngest Volcano (Mount Ross) in the Kerguelen Archipelago: Inferences for Magma Flux, Lithosphere Assimilation and Composition of the Kerguelen Plume

D. WEIS¹, F. A. FREY², A. GIRET³ AND J.-M. CANTAGREL⁴

¹DÉPARTEMENT DES SCIENCES DE LA TERRE ET DE L'ENVIRONNEMENT, UNIVERSITÉ LIBRE DE BRUXELLES,CP 160/02, AVE. F.D. ROOSEVELT 50, B-1050 BRUSSELS, BELGIUM ²DEPARTMENT OF EARTH, ATMOSPHERIC AND PLANETARY SCIENCES, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MA 02139, USA ³UNIVERSITÉ JEAN MONNET, FACULTÉ DES SCIENCES, DÉPARTEMENT DE GÉOLOGIE-PÉTROLOGIE-GÉOCHIMIE, CNRS-UMR 6524, 23 RUE DU DOCTEUR PAUL MICHELON, 42023 SAINT-ETIENNE, CEDEX 2, FRANCE ⁴UNIVERSITÉ DE CLERMONT-FERRAND, CNRS-UA 10, 5, RUE KESSLER, 63000 CLERMONT-FERRAND, FRANCE

Mount Ross is the youngest, ~1-0·1 Ma, volcanic edifice recognized in the Kerguelen Archipelago, which is located on the northern part of the submarine Kerguelen Plateau. Lava types range from basaltic trachyandesite to trachyte and extensive glaciation has exposed an intrusive core ranging from gabbro to syenite. Mount Ross rocks are not as silica undersaturated as the basanite to phonolite Upper Miocene lavas erupted in the Southeast Province of the archipelago; however, both lava suites are characterized by relatively high ⁸⁷Sr/⁸⁶Sr (0·7051-0·7054 and 0·7054-0·7058, respectively) and low ²⁰⁶Pb/²⁰⁴Pb (18·02-18·14 and 18·06-18·27, respectively). The abundant trachytes and phonolites in the age range from Lower Miocene to Pleistocene on the Kerguelen Archipelago indicate that the supply of basaltic magma has been low for the last 20 my. Despite the prolonged time period required for extensive mineral fractionation, there is no evidence for assimilation of geochemically distinctive lithosphere; i.e. most of the trachytes and syenites have initial isotopic ratios within the narrow range of the more mafic rocks. Volcanic and plutonic rocks of diverse composition and age (~0·1-30 Ma) in the Kerguelen Archipelago have similar initial isotopic ratios; consequently, we infer that the Kerguelen plume is characterized by ⁸⁷Sr/⁸⁶Sr = 0·7051-0·7058, ¹⁴³Nd/¹⁴⁴Nd = 0·51263-0·51249 and ²⁰⁶Pb/²⁰⁴Pb = 18·02-18·27.

Keywords: geochemistry; isotopes; Kerguelen Islands; magma flux; plume magmatism

Pages 973-994