Features of the processed of crystallization and geochemistry of tholeiite magmas of the western end of African-Antarctic Ridge (Shpiss Ridge) in the area of Bouve triple junction

Constancy of Nb/U in the mantle revisited

“…It has been proposed that the recycling of subducted oceanic crusts, after long term residence ($1-2 Ga) in the lower mantle, is responsible to the geochemical characteristics of the OIB White, 1980, 1982;Chase, 1981;Christensen and Hofmann, 1994;Hofmann, 2003). This hypothesis is supported by seismic tomographic images, which suggest that cold subducting slabs can descend across the 660-km discontinuity and reach the coremantle boundary (van der Hilst et al, 1997), and that many OIBs can be trace down into the lower mantle (DePaolo and Manga, 2003;Burke et al, 2008). Because of the negative buoyancy of the bulk oceanic crusts in both solid (Kesson et al, 1998;Ono et al, 2001) and liquid states (Agee, 1998;Ohtani and Maeda, 2001) in the lower mantle, a controversy arises over whether the subducted slabs have been mixed back into the mantle sources of OIB (Hofmann and White, 1982;Hofmann, 1997) and MORB (Hofmann, 1997), or have been totally retained in the lower mantle (Niu and O'Hara, 2003).…”

“…Given that La is only slightly more incompatible than Ce, the good correlation also indicates that the log A B À Á versus log Nb Hf À Á diagrams are very sensitive and reliable. This also implies that the basic assumptions, C 0 and (Sushchevskaya et al, 1999(Sushchevskaya et al, , 2000(Sushchevskaya et al, , 2002Kamenetsky et al, 2000Kamenetsky et al, , 2001Kamenetsky and Maas, 2002;Sun et al, 2003b Sun, 1995), CC (Rudnick and Fountain, 1995) and estimated average of OIB (Sun and McDonough, 1989), back arc basin basalts (BABB) (Sun et al, 2003b) and island arc basalt (IAB, Eastern Manus) (Sun et al, 2003a(Sun et al, , 2004b for comparison. MORB and most BABB, OIB, and primitive mantle (PM), fall in a tightly defined array, indicating that the partition coefficients of La, Ce, Nb, Hf are fairly constantly relative to each other during the whole range of MORB and OIB magmatisms.…”

“…Detailed analytical methods can be found in previous publications (Sushchevskaya et al, 1999(Sushchevskaya et al, , 2000(Sushchevskaya et al, , 2002Kamenetsky et al, 2000Kamenetsky et al, , 2001Eggins and Shelley, 2002;Kamenetsky and Maas, 2002;Sun et al, 2003b). In brief, the system consists of a Lambda Physik LPX 120I pulsed ArF excimer laser coupled to an Agilent 7500 ICP-MS. Isotopes were measured in peakhopping mode using one point-per-peak.…”