Determining melt productivity of mantle sources from 238U–230Th and 235U–231Pa disequilibria; an example from Pico Island, Azores

Combined 238U–230Th and 235U–231Pa constraints on the transport of slab-derived material beneath the Mariana Islands

“…New 238 U-230 Th and 235 U-231 Pa disequilibria (Table 1) were measured on a suite of 16 recent, mafic volcanic rocks from the Mariana arc , using established techniques in the Bristol Isotope Group (BIG) at the University of Bristol (see full details in Regelous et al, 2004;Hoffmann et al, 2007;Prytulak et al, 2008;Prytulak and Elliott, 2009). In the Electronic Annex we additionally report some measurements of 235 U-231 Pa disequilibrium made by thermal ionisation mass-spectrometry at the Vrije Universiteit Amsterdam (Elliott and Koetsier, 1999).…”

Understanding melt generation beneath the slow-spreading Kolbeinsey Ridge using 238U, 230Th, and 231Pa excesses

“…87 Sr/ 86 Sr = 0.70306) (Haase et al, 2003) and trace element ratios (U/Th = 0.26; La/Sm N = 1.95), has the lowest ( 231 Pa/ 235 U) = 1.22. The other three samples were collected further south on the Kolbeinsey Ridge and are more depleted (e Nd = +8.9 to +10.0 (Schilling et al, 1999) (Goldstein et al, 1989(Goldstein et al, , 1992(Goldstein et al, , 1993Sims et al, 1995Sims et al, , 2002Bourdon et al, 1996b;Lundstrom et al, 1999;Sturm et al, 2000;Peate et al, 2001;Tepley et al, 2004;Kokfelt et al, 2005;Russo et al, 2009;Standish and Sims, 2010), global ocean island basalt (OIB) data (except for Iceland) (Sims et al, 1995(Sims et al, , 1999(Sims et al, , 2008bTurner et al, 1997;Widom et al, 1997;Bourdon et al, 1998;Claude-Ivanaj et al, 1998;Sigmarsson et al, 1998;Claude-Ivanaj et al, 2001;Pietruszka et al, 2001Pietruszka et al, , 2009Sims and Hart, 2006;Prytulak and Elliott, 2009), and Icelandic data (Kokfelt et al, 2003;Stracke et al, 2003a,b (Pickett and Murrell, 1997;Stracke et al, 2006), global OIB (Sims et al, 1995(Sims et al, , 1999(Sims et al, , 2008bPickett and Murrell, 1997;Turner et al, 1997;…”

Genesis of 230Th excess in basalts from mid-ocean ridges and ocean islands: Constraints from the global U-series isotope database and major and rare earth element geochemistry

“…For 230 Th-238 U disequilibrium data of MORBs, 84 groups were measured by mass specrometry and 31 groups were measured by α-specrometry, whilst all 230 Th-238 U disequilibrium data of OIBs were measured by mass specrometry. Excess 230 Th and excess 226 Ra data of MORBs and OIBs are 58 and 63 pairs respectively, in which MORBs are from the East Pacific Rise [3, 35,36], Garrett Ridge [37], Gorda Ridge [38] and Juan De Fuka Ridge [36], OIBs are from the Azores islands [19,31,39], Canary island [33], Iceland [40], Hawaii [41] and Comore island [42]. REEs data of MORBs from the mid-Atlantic ridge and East Pacific Rise and OIBs are all from PetDB database.…”

“…Most studies [35,36] suggest that the presence of excess 226 Ra confines the magma transportation time to be within 8000 years (5 times of 226 Ra half-life). This conside- [35][36][37], Gorda ridge [36,38]); OIB data are from Azore island [19,31,33,[39][40][41][42].…”

“…Recently, Elkins et al [16] and Pertermann et al [17] showed by partition experiments of natural garnet and clinopyroxene that only melting with the participation of garnet can produce excess 230 Th. However, some geologists still consider excess 230 Th as an indicator of mantle plume sources (garnet stability field) [18], and usually assume the presence of garnet in the mantle melting process [19,20]. It should be noted that the current researches that use excess 230 Th to discuss the mid-ocean ridge and ocean island mantle melting process still tend to adopt a garnet-lherzolite model.…”