Mineralogy and Partial Melt Textures within an Uhramafic-Mafic Body, Greece

Ultramafic-mafic rocks from Makrirrakhi, Central Greece exhibit features of an original ophiolite sequence which contains depleted mantle material, ultramafic containing partial melt textures and possibly the marie "pluton" which resulted from the coalescing of these partial melt segregations. Considerable mineralogical variation exists: unzoned olivine crystals range in composition from FoTs_s~ (mMics) to FOss_9~ (ultramafics), plagioclases An6~_79 (mafies) to Anso_90 (ultramafics) and spinel varies from a chromian spinel (ultramafics) to a more aluminous-titaniferous spinel (mafics). Pyroxenes from the ultramafics display a limited range: Ens9_92 Fsg_ s Woo_ 2 (orthopyroxene) and En4s_5~ Fsl_lo W%s-50 (clinopyroxene). Marie rocks display a greater range being richer in ferrosilite En36 _65 Fs~ 20 W%3-sr Pyroxenes from within the partial melt segregations have chemical affinities with those from the gabbrotroctolite series. A model of partial melt within the upper mantle, and, a set of criteria to distinguish partial melt textures from cumulate textures, are developed from analytical data and textural evidence. Introduction and General Geology The ultramafic-mafic belt is si tuated around Makrirrakhi village in the Othris Mountains Greece, at an alt i tude of 800-1000met re s (Fig. 1). Geologically Greece can be sub-divided into several N . W . trending facies zones (Auboin, 1965). This body lies within the Sub-Pelagonian zone; a zone occupied mainly by a Mesozoic ophiolite-radiolarian chert sequence. This is overlain unconformably by Upper Cretaceous limestone and Eocene flysch (Hynes, 1972). The complete assemblage is thought to represent (Fig. 2) par t of a Mesozoic oceanic crust-upper mantle which was tectonically emplaced onto the cont inental margin during the Upper Jurassic-Middle Cretaceous interval. During emplacement serpentinisation occured along major thrusts and fractures. The purpose of this paper is to : (1) Present mineral da ta on the complex, essentially the pyroxenes, discuss the chemical var ia t ion and to examine the implications. (2) Repor t the presence of possible partial melt textures and tabulate the criteria used to distinguish these textures f rom pr imary cumulate magmat ic textures. Petrology and Textural Relationships The lower par t of this thrus t sheet carries a mixture of mafic-ultramafic rocks which can be sub-divided into the following units: [Photomicrographs a) to d) (Fig. 3a -d) correspond to units 1) to 4).] (1) Pillow lavas and upper dike complex (Hynes, 1972). 19 Contr. Mineral. and Petrol., Vol. 42