The Lower Unit of the ophiolitic sequence of Northern Argolis comprises turbiditic sediments and olistostromes. both containing ophiolitic clasts. mainly crystal fragments (clinopyroxene. plagioclase. Cr-spinel, amphibole) in the turbidites and cumulitic intrusives (quartz noritic amphibole-bearing gabbros). subvolcanic rocks (dolerites) and various effusive lithologies (mainly Si-rich basalts to basaltic andesites) in the olistostromes. The volcanic rocks belong to three groups. In rare cases the lavas are niineralogically and chemically comparable with MORB; most of them. and the subvolcanic rocks, contain primary quartz and amphibole, orthopyroxene, Ca-rich plagioclase and clino-pyroxene_+ Cr-spinels. All rocks are Si-and Mg-rich and have high concentrations of 'compatible' and very low concentrations of 'incompatible' elements. The REE profiles are characteristically U-shaped. Many of the observed features are comparable with those of suhduction-related lavas and, in particular, with present day boninites and ophiolitic boninitic rocks. The gabbroic rocks have mineralogical and chemical analogies with the dolerites and lavas, thus it may be argued that the gabbros represent the intrusive counterparts of the 'boninitic' volcanic clasts. The mineral clasts occurring in the turbidites are chemically comparable with those analysed in the ophiolitic clasts of the overlying olistostrome. It may be concluded that the ophiolitic clasts of both olistostromes and turbidites were derived from a subduction-related sequence. An island arc back-arc system might explain the occurrence of both boninitic and MORB-type lithologies in the olistostrome of Angelokastron. This may support the hypothesis of the onset of compressive tectonics along the Pindos Ocean during the Jurassic. X; 1996 No. of Tables: 6 . No. of Refs: fvl 3-4 vol.%) intergranular phase of most samples, whereas biotite forms rare intergranular flakes. The opaque minerals are rare accessories crystallizing both as early phases included in the cumulus pyroxenes and in the intercumulus.
Dolerites and granophjwsThe dolerites (samples 1495, 1503, 1512 and A33a) are non-cumulus. ophitic to subophitic or intergranular in texture; most samples are porphyritic, with orthopyroxene, clinopyroxene, plagioclase and opaque minerals as possible phenocrysts. Orthopyroxene and/or plagioclase were the first minerals to separate, followed by clinopyroxene. The same phases compose the matrix of the porphyritic rocks and the aphyric samples, in addition to the following minerals: light green --light brown amphibole (up to 30% modal content), frequently poikilitic with pyroxenes and plagioclase; primary interstitial quartz, variable from a few vol.% up to 20 vol.%; very rare biotite; opaque minerals locally abundant; and rare apatite. Sample 1499 is a medium-grained quartz-rich differentiate, resembling granophyre, which contains 70% modal granophyric intergrowths of primary quartz and andesine, in addition to green amphibole, apatite and ores.
Group I effusivesThe rocks of this gr...
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