Ultra-refractory mantle within oceanic plateau: Petrology of the spinel harzburgites from Lac Michèle, Kerguelen Archipelago

The subantarctic lithospheric mantle

“…Like the Subantarctic mantle lithosphere associated with Kerguelen and Zealandia, Os isotopic analyses show the modern Subantarctic oceanic upper mantle must have embedded ancient peridotite fragments that have histories that long-predate the formation of the lithosphere. Grégoire, 1994;Moine, 2000;Grégoire et al, 1997;2000a-b;Moine et al, 2004;Delpech et al, 2004;Bascou et al, 2008;Wasilewski et al, 2017;Schiano et al, 1994;Hassler, 1999; this study). Ol; olivine, Cpx; clinopyroxene, Sp; spinel.…”

“…Dy/Yb) ratios and low HREE contents, can also be explained in a similar way. This idea is supported by Wasilewski et al (2017), who also interpreted the more refractory bulk compositions of the Lac Michèle harzburgites to record evidence of polybaric decompression fractional melting between 5 and 3 GPa, initiated at high pressure in the garnet stability field (Fig. 5B, 5D).…”

“…Although xenoliths were subsequently mentioned regularly in publications (Talbot et al, 1963;Nougier, 1970;McBirney and Aoki, 1973; Giret, 1983;Gautier, 1987;Leyrit, 1992), systematic study only really began in the early 90's during the Kerguelen cartographic programs initiated by André Giret and the TAAF. The results of these studies make Kerguelen one of the best studied off-craton mantle xenolith occurrences on Earth (Grégoire et al, 1992(Grégoire et al, , 1994(Grégoire et al, , 1995(Grégoire et al, , 1996(Grégoire et al, , 1997(Grégoire et al, , 1998(Grégoire et al, , 2000a(Grégoire et al, -b, 2001Mattielli et al, 1996Mattielli et al, , 1999Schiano et al, 1994;Valbracht et al, 1996;Moine et al, 2000Moine et al, , 2001Moine et al, , 2004Lorand et al, 2004;Delpech et al, 2004Delpech et al, , 2012Bascou et al, 2008;Wasilewski et al, 2017). There are at least 22 mantle xenolith localities (Fig.…”

“…The type-I xenoliths comprise spinel-bearing harzburgite (30%), dunite (10%) and associated composite rocks. These are commonly very fresh, except a group of moderately serpentinised harzburgites from Lac Michéle (Wasilewski et al, 2017). The type-II xenoliths (50%) are metacumulates (peridotites, pyroxenites and metagabbros) recrystallized in the P-T conditions of the lower crust and upper mantle.…”

“…Based on their modal and bulk major element compositions that resemble cratonic peridotites (Fig. 5A, B, D), the Lac Michèle harzburgites were also considered by Wasilewski et al (2017) in the same manner as Hassler & Shimizu (1998). However, the low Mg# in olivine (91-92) for a given Cr# in spinel (Fig.…”