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Doctoral thesis
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Magmatisme basaltique, péridotites ophiolitiques et formations associées en Eubée centrale (Grèce) : origines et implications géotectoniques

ContributorsSimantov, Joséph
Number of pages155
Imprimatur date1987-11-09
Abstract

The Central part of Euboea Island is built-up essentially by sedimentary and igneous formations of the pelagonian zone. The lower part of the sedimentary sequence is formed by thick neritic limestones of Triassic - Jurassic age. A volcanodetrital formation of Upper Malm age is found at the higher part of the sedimentary buildup, consisting in blocks and boulders of lavas and radiolarian cherts, embedded in a pelitic or siliceous matrix, together with other minor sedimentary facies like limestones, sandstones and microconglomeratic levels. The ophiolite nappe is found thrust over this sequence, the contact being marked by an important metamorphic "auréole". Basaltic lavas are locally observed in form of a distinct tectonic unit at the base of the ophiolite nappe.

The purpose of this work has been to study the mineralogical and geochemical compositions and the petrological character of the different facies of the ophiolite nappe and the associated lavas and metamorphic sequence. Detailed mapping has brought into light many occurences of lavas and metamorphic rocks, most of them observed for the first time.

The ophiolite is composed by the lower terms of the classically recognized pseudostratigraphy. Foliated feldspar lherzolites form the greatest part of the peridotitic massifs found at the southem district of the studied area. Of minor importance are the wehrlites and websteritic and gabbroic cumulates found locally associated with the lherzolites. Numerous mafic dikes cross-cut the lherzolites, without having however the importance of a sheeted-dike complex. In most cases the pristine mineralogical and geochemical features of the dikes have been obliterated by subsequent rodingitization. The missing higher parts of the ophiolite pseudostratigraphical column have been eroded during the lower cretaceous, giving rise to the thick layer of lateritic nickel-iron ore covering the lherzolites.

Remarkably homogeneous harzburgites form the ophiolitic massifs found at the northern district of Central Euboea, around the villages of Limni and Mantoudi. The stratigraphically lower part of these massifs is usually composed by massive locally chromite - bearing dunites.

A continuity has been observed between feldspar lherzolites and underlying harzburgites near Aghios Pass, the transition zone being marked by the progressive disappearance of plagioclase.

The degree of serpentinization of the peridotites varies greatly, and is apparently controlled by tectonic discontinuities within the massifs.

The refractory nature of the peridotites is inferred from the composition of the main mineral phases. Feldspar lherzolites are partially depleted residuals after a low degree of partial melting of mantle diapirs (less than 15%), whereas harzburgites represent completely impoverished material derived from high degrees of partial melting. Dunites may have been formed by progressive accumulation of refractory material ( Highly magnesian olivine and chrome spinel) during partial melting. [...]

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Citation (ISO format)
SIMANTOV, Joséph. Magmatisme basaltique, péridotites ophiolitiques et formations associées en Eubée centrale (Grèce) : origines et implications géotectoniques. 1987. doi: 10.13097/archive-ouverte/unige:174831
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