Publisher: Bachudo Science Co. Ltd

Partial Melting Mechanism and Mantle Peridotite Chemical Geodynamics

M. Loubet, U. A. Lar
KEYWORDS: mantle peridotite, mantle diapir, partial melting, modeling.

ABSTRACT:

Peridotite samples collected d uring ODP Leg 109 drilling on the flanks of the Mid-Atlantic Ridge (MARJ (23°10'NJ were analysed for major, trace elements and isotopic compositions. As is common of abyssal peridotite, the samples have been affected by variable degrees of serpentinizatio11. The data is in favour of the residual nature of these mantle peridotites, with compositional characteristics intermediate between slightly depleted orogenic 4herzolites and highly depleted ophiolitic harzburgites. The modeling of the conditions of partial melting of these peridotites, based on analysis of the Nd to Lu part of the REE spectra (which appears to be unaffected by the serpentinization process), supports partial melting processes operating at equilibrium at least during specific stages of the process, with moderate degrees of partial melting (9% to 14%). The degree of equilibrium attained between segregating melts and residues is sensitive to the ascent rate of the mantle diapirs. Some evaluations have shown that equilibrium can operate when spreading rates and inferred ascent of mantle diapirs are small as is the case at 23 ° on the M.A.R. The equilibrium/disequilibrium type of melting might represent another characteristic distinguishing mantle peridotites coming from different geodynamic environments (Lherzolite orogenic massifs, Harzburgite Ophiolite massif, this Leg 109 Mid oceanic ridge section), which is indicative of their different conditions of melting.


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