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NATURE ET REPARTITION DES FILONS BASIQUES DANS LA SECTION MANTELLAIRE DE L'OPHIOLITE D'OMAN : Implications pour la genèse des MORBs Implications pour la genèse des MORBs

Abstract : The Oman ophiolite is an ocean ridge fragment which was obducted on the Arabic margin. The mantle dykes are considered as fossilized melt migration structures that fed the gabbroic crust. Petrographical studies and microprobe analyses of a thousand dyke samples lead to the discrimination of about forty lithological facies showing the diversity of petrogenetic conditions in the mantle. These lithologies belong to two main differentiation series that exhibit distinct petrographical and chemical characteristics. The first one is similar to a N-MORB tholeiitic suite. It appears in only a few well defined regions which represent at most 25~\% of the mantle outcropping surface, the main one being a 60 km band parallel to the paleo-ridge axis and centered on the Maqsad diapiric area. The supply to the omanese crust, presenting mainly N-MORB-like characters, was probably focused by those few regions. A large part of the heterogeneity in incompatible elements of that kind of dyke is not related to fractional crystallization. It likely reflects poor mixing of the incremental melt fractions produced in the melting regime. The second suite derives from a more silicic and depleted melt, similar to a more andesitic liquid. It outcrops on the majority of the ophiolitic surface but is missing in the areas where tholeiitic dykes are numerous. Field and petrographical characteristics show that the wall rock temperature was significantly cooler than the melt temperature leading to a rapid cooling and crystallization of liquid. This can make the extraction difficult and explain the scarcity of ``andesitic'' cumulates in the crust. The depletion in some minor elements and the existence of highly depleted and magnesian lithologies may corroborate the hypothesis of the remelting of an hydrothermaly altered mantle.
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https://tel.archives-ouvertes.fr/tel-00010212
Contributor : Python Marie <>
Submitted on : Tuesday, September 20, 2005 - 12:38:07 PM
Last modification on : Monday, April 5, 2021 - 2:26:09 PM
Long-term archiving on: : Friday, April 2, 2010 - 10:07:39 PM

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Marie Python. NATURE ET REPARTITION DES FILONS BASIQUES DANS LA SECTION MANTELLAIRE DE L'OPHIOLITE D'OMAN : Implications pour la genèse des MORBs Implications pour la genèse des MORBs. Géologie appliquée. Université Paul Sabatier - Toulouse III, 2002. Français. ⟨tel-00010212⟩

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