Supervisors info:
Δημήτριος Κωστόπουλος, Επίκ. Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, Σχολή Θετικών Επιστημών του Εθνικού και Καποδιστριακού Πανεπιστημίου Αθηνών
Original Title:
METAMORPHIC PETROLOGY OF THE ARNA (PHYLLITE- QUARTZITE) AND MANI (PLATTENKALK) UNITS, WEST LACONIA, PELOPONNESUS, GREECE
Translated title:
Metamorphic petrology of the Arna (Phyllite- Quartite) and Mani (Plattenkalk) units, west Laconia, Peloponnesus
Summary:
The main metamorphic units of the External Hellenides are the Phyllite-Quartzite s.l. (PQ) and the Plattenkalk (PK) units. They were exhumed during the second exhumation episode that took place in the Aegean, in Oligocene-Miocene times. They occupy the lowermost structural position in the External Hellenides’ nappe stack, cropping out as tectonic windows in Peloponnesus, Crete and the surrounding area of South Aegean.
The PQ unit (s.l.) is a former pelitic-sandstone sequence with basaltic intercalations that has been metamorphosed under high-pressure low-temperature conditions in the blueschist facies. Metamorphic rock types include typical phyllites, quartzites and blueschists (metamafics). Many scenarios have been put forward to explain the origin of these rocks by the scientific community based mainly on their similarity with other time and facies-equivalent rocks of the External Hellenides and their possible geotectonic position. The last few years, detrital zircon geochronology studies have shown that the rocks of the PQ Unit s.l. were derived from the northeastern margin of Gondwana, where they had been deposited during the Cambro-Ordovician. They were later transported northwards during the opening up of Neotethys in the Permo-Triassic and involved in subduction-exhumation processes in the late Cenozoic and acquired their metamorphism and deformation.
The PK unit, on the other hand, which underlies the PQ s.l. unit, is a former carbonate platform that has undergone a lower degree of metamorphism. At the base of the unit, in the Peloponnesus, the Kastania beds crop out, which is a sequence consisting of alternations of phyllites and quartzites. In the field, these beds seem to have the same characteristics as the overlying metamorphosed rocks of the PQ s.l. unit, but their degree of metamorphism is actually lower. This information, along with field observations that the transition from the metasiliciclastic rocks of Kastania to the meta-carbonates of PK is continuous, suggests that the rocks of the Kastania beds are the lowest formation of the PK unit.
In the present research, samples from both the Arna Unit (as part of the PQ s.l. unit) and the Kastania beds in W. Laconia, Peloponnesus, were collected, covering all possible lithologies. The petrographic comparison made between the phyllitic rocks of the two sequences showed that the rocks of the Kastania beds have undergone a lower degree of metamorphism, which together with the data available at the time of writing, confirm that they belong to the PK unit.
Metamafic rocks collected a few kilometers SE of Arna village revealed the paragenesis: ± amphibole ± lawsonite ± zoisite + phengite + chlorite ± actinolite + epidote ± albite + titanite + quartz. The amphiboles identified in the samples were sodic (eckermannite, glaucophane), calcic-sodic (katophorite, richterite) and calcic (actinolite, edenite) type amphiboles. These different types of amphibole reflect both the prograde and retrograde
metamorphic path of the unit in the blueschist- and greenschist-facies respectively. One of the samples has a typical geochemical signature of intra-plate oceanic island basalts (OIB), indicating magma generation possibly during the Permo-Triassic rifting and opening up of Neotethys.
Keywords:
Phyllite- Quartzite, Arna, Kastania Phyllites, petrographic research, metamafics
