MELT-ROCK INTERACTIONS: INFINITE SOURCE OF NEW MANTLE LITHOLOGIES

It is generally believed that melt-peridotite interaction in the upper mantle plays an important role in melt transport. A major aspect of these interactions is the coupled dissolution of pyroxene and precipitation of olivine, or vice versa. Pyroxene dissolution and olivine precipitation increase the proportion of melt in the system and facilitate its transport by increasing the porosity and permeability of mantle rocks [1,2]. This process has also been suggested for the extraction of pyroxenite-derived melt with little interaction with the peridotite mantle [3,4]. Natural occurrences of this reaction are found, for example, in the Krivaja-Konjuh massif in Bosnia [5], in mantle xenoliths from French Polynesia [6], and in the Balmuccia massif in Italy [7]. Inversely, pyroxene crystallization at the expense of olivine would lead to a porosity reduction and increase the lithological variability of the mantle [8,9]. However, melt-peridotite interaction processes depend on many chemical and physical parameters such as the composition of the melts, and the nature of the transport mechanism (pervasive porous flow, focused flow or magma transport in dikes), and are very difficult to model in the laboratory.

First I will review the experimental and theoretical efforts that have been published to constrain the effect of melt-rock interaction on the lithological variability of the mantle as functions of the melt composition, the melt-rock ratio and the pressure-temperature conditions. Then I will discuss the conditions to reproduce the rock suite observed in the Krivaja-Konjuh massif and how they differ from the conditions in the Balmuccia massif and the French Polynesia xenoliths.

References: [1] Kelemen et al., 1990, J. Petrol. 31(1), 51-98; [2] Daines & Kohlstedt, 1994, GGG 21(2), 145-148; [3] Lundstrom et al., 2000, Chem. Geol. 162, 105–126; [4] Hirschmann et al., 2003, Geology 31(6), 481-484; [5] Faul et al., 2014, Lithos 202-203, 283-299; [6] Tommasi et al., 2004, EPSL 227, 539-556; [7] Mazzucchelli et al., 2009, J. Petrol 50(7), 1205-1233; [8] Lambart et al., 2012, J. Petrol. 53(3), 451-476; [9] Sobolev et al., 2005, Nature 434, 590-597.