The (?) mid Triassic volcanic rocks of Lakonia, Greece

Abstract

Thick subaerial volcanic sequences of probable mid Triassic age rest unconformably on Permo-Carboniferous limestones in the 'Phyllite Series' within the Gavrovo-Tripolitsa zone of the external Hellenide nappes. The volcanic rocks are varied in character. Pyroclastic rocks (often reddened) predominate, but minor basalt or andesite and rhyolitic hypabyssal intrusions and flows are also found. The rocks have experienced low-grade metamorphism and the only relict primary minerals are pyroxene and rare plagioclase in basic rocks and potash feldspar in acid rocks. The most important metamorphic phases are albite, chlorite, potassium mica, epidote, hematite, quartz and pumpellyite. Twenty-seven whole-rock major-element analyses suggest that there has been some exchange of Na 2 O and K 2 O for CaO during metamorphism, but that other elements have been relatively stable. A genetic interpretation of the rocks is attempted using published geochemical discriminator diagrams. The basic rocks are tholeiitic in major element chemistry and pyroxene composition. Trace element (Hf, Ta, Th, Ce, Yb) distribution suggests magma generation at a destructive plate margin.

Mineralogical, Petrological and Geochemical Features of the Unique Lapis Lacedaemonius (Krokeatis Lithos) From Laconia, Greece: Approach on Petrogenetic Processes Within the Triassic Volcanic Context

“…These rocks are regarded by many authors (e.g. Pe-Piper et al, 1982;Zezza and Lazzarini, 2002) as porphyritic andesites. However, this classification has been based upon their silica and alkali contents that were affected by metamorphic and metasomatic processes.…”

“…These volcanic occurrences, which mostly include pillow lavas and massive flows, are associated with the rift/drift phase within the Pindos oceanic realm. In the past, several studies were conducted focusing mostly to the entire Triassic volcanism of the area (Panagos, 1979;Thiebault, 1982;Pe-Piper et al, 1982;Gerolymatos, 1994;Pe-Piper and Piper, 2002). The current study aims to characterize mineralogically and geochemically the Lapis Lacedaemonius (Krokeatis lithos), in an attempt to interpret from a geological scope the reasons for its uniqueness and its absence in other Triassic volcanic localities.…”