Komsomolskaya diamondiferous eclogites: evidence for oceanic crustal protoliths

Subduction-related origin of eclogite xenoliths from the Wajrakarur kimberlite field, Eastern Dharwar craton, Southern India: Constraints from petrology and geochemistry

“…d 18 O values higher than 5.5& as the range observed here are typical for zeolite facies seafloor alteration and many cratonic eclogite xenoliths from kimberlites share this signature (e.g. Jacob, 2004;Spetsius et al, 2008;Pernet-Fisher et al, 2014).…”

“…Jacob and Foley, 1999;Jacob et al, 2003;Pernet-Fisher et al, 2014) whose protoliths were altered at high water/rock ratios by colder water closer to the ocean crust surface under zeolite facies conditions (Gregory and Taylor, 1981;Bach et al, 2001). These rocks are typically ocean floor basalts, but may sometimes also comprise oceanic gabbros exposed to seawater alteration along fractures or shear zones.…”

“…5a, b). Abundances are typical for eclogite xenoliths worldwide (Jacob, 2004;Tappe et al, 2011;Pernet-Fisher et al, 2014;Smart et al, 2014;Smit et al, 2014) except for sample KL2-33, which has anomalously high HREE abundances for an eclogite (ca. 350 times chondritic; Fig.…”

“…Eclogite xenoliths are usually interpreted either as fragments of subducted oceanic crust representing gabbroic or basaltic protoliths or oceanic crustal cumulates emplaced tectonically into the lithospheric mantle (Shervais et al, 1988;Taylor and Neal, 1989;Neal et al, 1990;Jerde et al, 1993;Jacob et al, 1994;Viljoen et al, 1996;Snyder et al, 1997;Jacob and Foley, 1999;Barth et al, 2001;Shirey et al, 2001;Jacob, 2004;Usui et al, 2006;Nikitina et al, 2014), or as high-pressure, magmatic cumulates (MacGregor and Carter, 1970;Hatton, 1978;Smyth et al, 1989;Viljoen et al, 1996;Snyder et al, 1997;Barth et al, 2002;Taylor et al, 2003;Heaman et al, 2006;Appleyard et al, 2009;Jacob et al, 2009). Some eclogites have been linked to partial melting and melt-mantle reaction processes associated with subduction, representing residues of tonalite melt extraction from basaltic crust (Ireland et al, 1994;Rollinson, 1997;Jacob and Foley, 1999;Barth et al, 2002;Rapp et al, 2003;Smart et al, 2009;Tappe et al, 2011;Pernet-Fisher et al, 2014;Smit et al, 2014).…”

Probing the Earth’s Deep Interior Through Geochemistry

“…Furthermore, oxygen isotope ratios that are both well above and well below the mantle value (~+5.5 ‰) have been found in eclogite xenoliths from kimberlites (e.g., MacGregor and Manton, 1986;Pernet-Fisher et al, 2014;Smart et al, 2014). Eclogitic diamonds also show highly variable carbon (Mattey, 1987) and nitrogen (Marty and Dauphas, 2003) isotopic compositions.…”