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Journal of Petrology | Volume 43 | Number 7 | Pages 1341-1366 | 2002
© Oxford University Press 2002
The Depleted Mantle Component in Kerguelen Archipelago Basalts: Petrogenesis of Tholeiitic–Transitional Basalts From the Loranchet Peninsula
1DÉPARTEMENT DES SCIENCES DE LA TERRE ET DE L’ENVIRONNEMENT, UNIVERSITÉ LIBRE DE BRUXELLES, B-1050 BRUSSELS, BELGIUM
2DEPARTMENT OF EARTH, ATMOSPHERIC AND PLANETARY SCIENCES, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MA 02139, USA
3LABORATOIRE DE GÉOLOGIE–PÉTROLOGIE, CNRS–UMR 6524, UNIVERSITÉ JEAN MONNET, 42023 SAINT-ETIENNE, FRANCE
A geochemical study of 28 Ma tholeiitic to transitional basalts from the Kerguelen Archipelago (Mont des Ruches and Mont Fontaine) indicates that three distinct magma types erupted within 
1 Myr. Low-MgO basalts (4–6 wt %) in both sections are overlain by high-MgO basalts (7–13 wt %), mostly present in Mont Fontaine. Both high- and low-MgO basalts have nearly identical low 87Sr/86Sr and high 143Nd/144Nd and formed from similar parental magmas that represent mixtures between a depleted mantle component and the Kerguelen plume. The third magma type, predominant in Mont des Ruches, is represented by high-MgO basalts that are isotopically heterogeneous with isotopic ratios that are intermediate between those of the stratigraphically lower basalts and the Kerguelen plume compositions; this third magma type may have formed by mixing of similar material, but with a higher contribution from the Kerguelen plume. The depleted component involved in all three magma types is similar to the source for Southeast Indian Ridge basalts and is present in Kerguelen Archipelago basalts older than 26 Ma, which erupted when the ridge axis was <500 km away from the Kerguelen hotspot. Depleted heterogeneities intrinsic to the plume and entrainment of depleted mantle during plume ascent do not explain the marked cut-off in the presence of a depleted component in the archipelago basalts within a time interval of 1 Myr after 26 Ma. Mixing of depleted asthenosphere with the plume in sublithospheric channels during migration of the Southeast Indian Ridge axis away from the Kerguelen hotspot is proposed as a suitable explanation to account for the temporal distribution of the depleted component in basalts from the Northern Kerguelen Plateau and the >26 Ma Kerguelen Archipelago flood basalts; cessation of plume–ridge interactions may explain the absence of depleted basalts in the youngest sections that erupted further away from the ridge axis.
KEY WORDS: Kerguelen Archipelago; basalt; geochemistry; depleted component; Kerguelen plume; mixing
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