Morphological features and formation conditions of The Almopia Speleopark caves (Loutra Almopias, N. Greece)

The Almopia Speleopark caves are located at the Almopia basin in northern Greece, at the foothill of Voras Mountain, and are formed in the Maestrichtian limestones of the Pelagonian zone. They are studied on the basis of their meso- and micro-scale morphology as well as their horizontal pattern, in order to investigate the character of the forming aquifer. Emphasis is given on the morphological description of the Loutra Almopias Cave. Cave morphology is dominated by the presence of cupolas, rock bridges, ridges and “windows”, abrupt terminations of fracture guided passages, pendants, rising channels, pseudonotches, false-floors and spongework. Speleogens indicate a speleogenesis due to slowly natural convecting hot water bodies. Phreatic calcite from the Varathron Cave is analyzed on the basis of the fluid inclusions in order to investigate the physicochemical conditions of the convecting water bodies. This has shown that the calcite was formed at temperatures ranging between 120 and 189 ºC, with a peak around 150 ºC. The fluids were dominated by NaCl of very low salinities (0.2-1.0 wt% NaCl equiv.), showing probably the incorporation of meteoric waters.

New paleontological and stratigraphical data on the upper - cretaceous transgression of the Pelagonian zone s.l. (Marmeiko, Ptoon Mt. NE Beotia)

This paper concerns the study of a transgressive series, which overlies the upperjurassic oolitic limestones of subpelagonian zone, as well as the lateritic deposits, resulting from the alteration of the ophiolitic and fill the karstic cavities of the above mentioned limestones in NE Beotia (Fig.l). The purpose of this study is to• elucidate the age of the transgression, that occurred on the Jurassic limestones of the pelagonian platform at this region.• Discuss about the observed diachronism of the Late Cretaceous transgression on the Pelagonian platform.It is based on the study of micro- and macrofauna occurred in a section we describe in the "Marmeiko" area, on the Ptoon mountain. NOETH (1931) was the first who defined as Upper Turonian the age of the transgressive series, based on the study of Rudists. Later, BIGNOT & GUERNET (1968) studied the microfauna and attributed an age of lower Senonian. STEUBER (1993) based on the study of Hippuritidae, defined as Turonian and later (1995) as Turonian - Coniacian the age of the transgessive series. The basal part of the series consists of marls and marly limestones alternations. An abundant micro and macrofauna is found in this part of the section, as well as the first Rudist biostrome. In the middle part of the section 2 Rudist biostroms alternate with bioclastic limestones, containing abundant microfauna. In the upper part marls alternate with cherty limestones. The determinated micro- and macrofauna (Fig. 1), precises the age of the transgressive series as Santonian. This result confirms the diachronism of the transgressive phenomenon on the Pelagonian Upper- Jurassic limestones and the overthrusted ophiolites (AUBOUIN et al. 1960, BRUNN et al. 1972, KALLERGIS & ALBANTAKIS 1970, MAVRIDIS et al. 1979, NOETH 1931, BIGNOT & GUERNET 1968, CLEMENT & FERRIERE 1973, BIGNOT et al. 1973, STEUBER 1993, 1995, SKARPELIS & ZAMBETAKIS – LEKKAS 1998)

THE EMPLACEMENT OF THE VERMION NAPPE IN THE AREA OF KATO SELI (MT VERMION, CENTRAL MACEDONIA, GREECE)

Our fieldwork in the area of Kato Seli of Mt Vermion suggests that the Vermion Nappe is not only tectonically overlying the Maastrichtian flysch of the Pelagonian Zone, but also a Jurassic melange that overlies the Triassic-Jurassic marbles of the Pelagonian Zone. Moreover, between the Vermion Nappe and the underlying melange, tectonic slivers of meta-sandstones-meta-rudites are tectonically emplaced. This calls for a reassessment of the emplacement of the Vermion Nappe and its role in the geotectonic evolution of the area.

THE CALLOVIAN UNCONFORMITY AND THE OPHIOLITE OBDUCTION ONTO THE PELAGONIAN CARBONATE PLATFORM OF THE INTERNAL HELLENIDES

The carbonate-platform-complex and the oceanic formations of the central Pelagonian zone of the Hellenides evolved in response to a sequence of plate tectonic episodes of ocean spreading, plate convergence and ophiolite obduction. The biostratigraphies of the carbonate platform and the oceanic successions, show that the Triassic-Early Jurassic platform was coeval with an ocean where pillow basalts and radiolarian cherts were being deposited. After convergence began during late Early- Jurassic - Middle Jurassic time, the oceanic leading edge of the Pelagonian plate was subducted beneath the leading edge of the oceanic, overriding plate. The platform subsided while a supra-subduction, volcanic-island-arc evolved. Biostratigraphic and geochemical evidence shows that the platform and the oceanic floor, temporarily became subaerially exposed during Callovian time. This “Callovian event” is suggested to have taken place as oceanic lithosphere first made compressional, tectonic contact with the carbonate platform, initiating a basal detachment fault, along which the platform was thrust upwards. The central Pelagonian zone became an extensive land area that was supplied with laterite from an ophiolite highland. A similar emergence of Vardar ophiolite most likely took place in the Guevgueli area. The Callovian emergence shows that the initial ophiolite obduction onto the platform took place about 25 million years before the final emplacement of the ophiolite during Valanginian time.

Polyphase evolution of Pelagonia (northern Greece) revealed by geological and fission-track data

The Pelagonian zone, situated between the External Hellenides/Cyclades to the west and the Axios/Vardar/Almopias zone (AVAZ) and the Rhodope to the east, was involved in late Early Cretaceous and in Late Cretaceous–Eocene orogenic events whose duration and extent are still controversial. This paper constrains their late thermal imprints. New and previously published zircon (ZFT) and apatite (AFT) fission-track ages show cooling below 240 °C of the metamorphic western AVAZ imbricates between 102 and 93–90 Ma, of northern Pelagonia between 86 and 68 Ma, of the eastern AVAZ at 80 Ma and of the western Rhodope at 72 Ma. At the regional scale, this heterogeneous cooling is coeval with subsidence of Late Cretaceous marine basin(s) that unconformably covered the Early Cretaceous (130–110 Ma) thrust system from 100 Ma. Thrusting resumed at 70 Ma in the AVAZ and migrated across Pelagonia to reach the External Hellenides at 40–38 Ma. Renewed thrusting in Pelagonia is attested at 68 Ma by abrupt and rapid cooling below 240 °C and erosion of the gneissic rocks. ZFT and AFT in western and eastern Pelagonia, respectively, testify at ~40 Ma to the latest thermal imprint related to thrusting. Central-eastern Pelagonia cooled rapidly and uniformly from 240 to 80 °C between 24 and 16 Ma in the footwall of a major extensional fault. Extension started even earlier, at ~33 Ma in the western AVAZ. Post-7 Ma rapid cooling is inferred from inverse modeling of AFT lengths. It occurred while E–W normal faults were cutting Pliocene-to-recent sediment.

Coupled phengite 40Ar–39Ar geochronology and thermobarometry: P-T-t evolution of Andros Island (Cyclades, Greece)

Andros is a key island for understanding both the timing of high-pressure–low-temperature (HP-LT) metamorphism and the dynamics of crustal-scale detachment systems exhuming high-grade units in the Cyclades (Greece). Using phengite 40Ar–39Ar geochronology coupled with thermobarometry, as well as data from literature, we constrain the pressure–temperature–time (P-T-t) paths of the Makrotantalon and Attic–Cycladic Blueschist units on Andros. Peak conditions of the HP-LT episode in the Makrotantalon unit are 550°C and 18.5 kbar, dated at 116 Ma. We correlate this episode with Early Cretaceous blueschist facies metamorphism recognized in the Pelagonian zone of continental Greece. This is a new argument favouring a Pelagonian origin for the Makrotantalon unit. In the Attic–Cycladic Blueschist unit, the P-T-t path is characterized by: (1) exhumation after peak conditions in HP-LT conditions between 55 and 35 Ma; (2) isobaric heating at 7 kbar until 30 Ma; and (3) isothermal decompression until 21 Ma. This thermal evolution and timing are similar to those of the neighbouring Tinos Island, emphasizing major thermal re-equilibration at the transition between stable and retreating subduction. Modifications of the crustal thermal state played a major role in the evolution of the North Cycladic Detachment System, below which Andros HP-LT units were exhumed.