Boninites as windows into trace element mobility in subduction zones

New Occurrence of Pyroxenites in the Veria-Naousa Ophiolite (North Greece): Implications on Their Origin and Petrogenetic Evolution

“…This hypothesis is in agreement with the enrichments in LREE and HREE in the REE patterns of the Ol-orthopyroxenites, as boninitic melts, which are typically known to fractionate MREE, may have imprinted their REE signature on the investigated rocks ( Figure 7). Similar U-shaped REE patterns have been reported and modelled describing the nature of melt/rock interactions in Greek and other ophiolites [73][74][75][76][77]. Several authors have attributed LREE enrichments in ultramafic rocks to secondary events and particularly to serpentinisation (for a review see [78]), however such a hypothesis is less likely, as the Ol-orthopyroxenites are the least altered and no striking LREE enrichments are observed in any of the pyroxenites.…”

Neoarchean siliceous high-Mg basalt (SHMB) from the Taishan granite–greenstone terrane, Eastern North China Craton: Petrogenesis and tectonic implications

“…This clearly demonstrates that a greater proportion of sedimentary-and/or basaltic-derived slab melts have been involved in their generation Pearce and Peate, 1995;Bédard, 1999). Several studies have established that the enriched nature of most Cenozoic high-Mg rocks, including high-Mg andesites and boninites, can be attributed to a contribution from slab-derived melts (Kay, 1978;Cameron et al, 1983;Pearce et al, 1992;Yogodzinski et al, 1994;Shimoda et al, 1998;Tatsumi, 2001;Bindeman et al, 2005;König et al, 2010). Furthermore, the coeval occurrence of boninites with high-Mg andesite and slab melt-related rocks (e.g., adakites) has been recognized in some present-day arcs (e.g., Tonga, Falloon et al, 2008;IzuBonin-Mariana Fore-arc, Pearce et al, 1992), providing evidence of slab melt-related enrichment.…”

“…On the other hand, their siliceous, strong LILE and LREE enrichment and HFSE depletion may be ascribed to melting of metasomatically enriched lithospheric mantle (Weaver and Tarney, 1981;Fisk, 1986;Falloon and Danyushevsky, 2000;Smithies et al, 2004a). Hence, their petrogenesis is most likely comparable to that of typical Phanerozoic and Archean boninites (e.g., Crawford et al, 1989;Falloon and Danyushevsky, 2000;Smithies et al, 2004a), being especially similar to the Late Paleocene boninites from the Cape Vogel peninsula of Papua New Guinea (i.e., PNG boninites; König et al, 2010) and the Mesoarchean Whundo boninite-like rocks from the Pilbara Craton in northwestern Australia as shown in Fig. 5a and b.…”

“…For the Taishan SHMBs, the enriched LREE patterns ((La/Yb) cn = 6.29-15.64) and fractionated HREE ((Gd/Yb) cn = 2.61-3.12) imply deep melting in equilibrium with residual garnet in the source (König et al, 2010), rather than a residue of amphibole which is generally invoked to interpret the U-type REE patterns and positive Zr anomalies in Phanerozoic boninites (e.g., Sun and Nesbitt, 1978;Hickey and Frey, 1982;Crawford et al, 1989;Falloon and Danyushevsky, 2000). In addition, the Zr depletion relative to Sm and Ti depletion relative to Eu also supports the above interpretation, which is likely related to the breakdown of amphibole at depth, similar to the features of the Adola and Tasmania boninites (Brown and Jenner, 1989;Crawford and Berry, 1992).…”

“…However, concluded that some main differences are evident between SHMB and Phanerozoic boninites, such as the absence of U-shaped REE patterns and positive Zr spikes in the former. In fact, recent studies have shown that not all Phanerozoic boninites possess such signatures, for example the Tonga (Falloon et al, 2008) and Papua New Guinea (PNG) boninites (König et al, 2010). Therefore, whether their genesis is the same as Phanerozoic boninites or is related to komatiitic magmatism has been an issue of debate.…”