The Lherz spinel lherzolite: Refertilized rather than pristine mantle

Abstract

Differentiation of the Earth's mantle and formation of continental and oceanic crust occur principally through partial melting and extraction of basaltic melt. Among the mantle rocks occurring at the Earth's surface, as tectonically-emplaced massifs, abyssal peridotites or xenoliths, the harzburgites (b 5% clinopyroxene) are widely considered as refractory mantle residues left after extraction of a basaltic component. In contrast, the most fertile lherzolites (15% clinopyroxene) are generally regarded as pristine mantle, only weakly affected by partial melting. In this paper we present new convergent structural and geochemical data from the Lherz massif, the type-locality of lherzolite, indicating that the lherzolites from Lherz do not represent pristine mantle. Detailed structural mapping clearly shows that the lherzolites are secondary rocks formed at the expense of the harzburgites. Variations of major, minor and trace elements through the harzburgite-lherzolite contacts indicate that the lherzolites were formed through a refertilization process involving interaction of refractory, lithospheric mantle with upwelling asthenospheric partial melts. Combined with previously published indications of refertilization in orogenic peridotites, our new observations in Lherz suggest that most lherzolite massifs represent secondary (refertilized) rather than pristine mantle. Together with geochemical data on mantle xenoliths, this indicates that melt transport and melt-rock reaction play a key role on the rejuvenation and erosion of the lithospheric mantle.

The blueschist-associated perovskite-andradite-bearing serpentinized harzburgite from Dobšiná (the Meliata Unit), Slovakia

“…Brunelli et al 2006;Le Roux et al 2007;Jean et al 2010) was not found in the studied Cpx harzburgite. Most of the Cpx 1 should have undergone the batch partial melting during the E2 event and, on this basis, we speculate that the Cpx 1 contents of our residual harzburgites were originally higher.…”

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

“…The above reactions commonly involve the formation of an Al-rich phase, which, in the case of the Veria-Naousa pyroxenites, is spinel and have been described in Archean cratons [29,50] or subcontinental mantle regions such as the Lherz Mountains [51], Ronda [11,52,53] and Cabo Ortegal [45,54]. However, quite recently, it was documented that such reactions producing two pyroxenes after dissolution of olivine can also occur in abyssal pyroxenites [55].…”

Köpenyeredetű kőzetek felismerésének története és szerepe a geológiai gondolkodás fejlődésében

“…Nagy meglepetést okozott azonban, hogy az orogén övekhez kapcsolódó, alpi típusú perido titok ban ez fordítva is történhet, azaz a korábban kimerült harz burgitból, bazaltos olvadékkal történt reakció révén újra termé keny lherzolit lesz. Ezt legrészletesebben LE ROUX et al (2007) demonstrálták a francia Pireneusok Lherz (a lherzolit típuslelőhelye!) nevű tava közelében található peri dotitmasszívum vizsgálata során.…”