Imbrassos' basin consists mainly of marble (24.7353 %), schist (27.9813 %) and marly limestone (21.1048 %). In addition to that, the south-west part is covered with alluvial deposits and old scree and talus cones (16.917 %).
Fig. 1: Geology and basin delineation of Imbrassos
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The recent formations (cd,dn) are located along the coastal zone and consist of sand and sand dunes (Coastal deposits).
The alluvial deposits (al2) that extent to the plain zone between the cities of Heraion and Pythagorion, consist of clayey-sandy material, loam, sand, pebbles, gravel. Recent material of sand and gravel can be found at torrent beds and torrent terraces, having a height of 1-3 m.
Old scree and talus cones (sc1,cs1) of strongly cemented agglomerate and red fine-grained material, at places, are located mainly to the southwestern side of Ampelos mountain. These formations are often intersected by faults (area of Mortia bay).
The lower series of the Mytilini basin formations (M.(k,m)2) extend to a NW – SE direction and fill the narrow tectonic root groove of Pagonda-Pyrgos. The groove consists of lacustrine, medium to thick-bedded, travertine-like limestones and whitish to yellowish, thin-bedded marls, generally of monotonous sedimentation, with intercalations of read loam and gray or greenish clay and beds of tuffs and tuffites. The thickness of this series is quite significant. Generally, the clastic materials are absent or scarce. The sediments of this sequence are intensely folded. They occupy the western part of the Mytilini basin as well as the areas of Pagonda and Pyrgos.The area of Pythagorion is dominated by thin and well-bedded, hard marls and marly limestones. The marls of the upper members of the series are thin-bedded to foliated (1-5 cm). Frequently, in the lower part of this series basaltic lavas are intercalated accompanied by tuffs as sills within the sediments. Sometimes, as can be seen in Pyrgos area, the lacustrine sediments are silicified in the vicinity of the lavas. Locally, the sediments of the series enclose plant relics, mainly parts of Hydrophytes. The maximum thickness of the series is estimated at about 650 m, while the age of formation is set to be in the Miocene, as concluded from the age of the overlying clastic series which include the known Pikermian fauna.
The existence of the conglomerates of the Neogene sediments base (Ng.c) is limited to the SW side of the tectonic groove of Pagonda-Pyrgos. It is of fluvial-terrestrial origin, commonly red-ruby colored, consisting totally of pebbles from metamorphic rocks, mainly from quartzites, marbles and schist. The pebbles tend to have small rounding and varying size, which reaches up to 30 cm. The matrix is clayey-sandy and participates in a small percentage. The maximum thickness is estimated to be circa 75 m.
Volcanic tuffs (tf) overly the great basalt mass, that occurs as sill within the lower series of Neogene sediments of Mytilini basin. They mainly consist of fine material, unbedded or partly bedded often mixed with sediments. Locally they are intersected by veins of Fe-oxides and have a thickness between 15 to 30 m.
The schist of Kotsikia – Psilli Ammos (mr,sp – sch3) belong to the metamorphic system and are limited to the eastern edge of Ampelos mountain. They are mainly chloritic, muscovite schists, sericite, quartz schists and calcareous schists, alternating vertically and passing laterally from the one lithological type to the other, with intercalations of quartzites. Within the schists there often occur intercalations of marbles, cipoline marbles (mr), ankerites and in one case intercalations of breccia marbles (Kotsikia area) 10 m. thick. Sometimes they are strongly folded with strike of folding axis N 65° E. Their maximum visible thickness is estimated at about 400 m. in the Psilli Ammos area.
The Vourliotes - “Syrrachos” marbles (sch.mi – mr3) are also part of the metamorphic system. They constitute, almost completely, the eastern mountainous block of the central island section and the SE area of the eastern island section, where the tectonic horn of “Syrrachos” is to be found. Their thickness exceeds 1.000 m. in the eastern part of the central section of the island, but in the “Syrrachos” area is limited to circa 400 m. (visible thickness). Precise stratigraphic correlation of the marbles between central and eastern island sections is not possible because of the intercalations of the Mytilini Neogene basin sediments. However, it is accepted that these marbles are of the same stratigraphic sequence and that “Syrrachos” marbles constitute its upper members. These marbles in the central section area are generally light-colored, usually gray-white, medium- to thick- bedded, fine-crystalline, often saccha-roidal, very commonly dolomitic, partly karstic and microfolded, with strike of folding axis N 50° E. In the eastern section area, they are whitish to gray-white, well - and medium - bedded, medium-to coarse- crystalline with local chert intercalations. In these marbles and mainly in the marbles of the island's central section there are many intercalations of schist (sch.mi), mainly mica schist, of considerable thickness.
The Ampelos marbles (mr2) occur as intercalations or great banks of various thickness, within the schists of Ampelos. They appear variously colored as whitish, light gray or dark gray, fine — and sometimes coarse — crystalline, medium-bedded, partly karstic. At Spatharei area, where their thickness exceeds 300 m., they are medium to coarse-bedded, gray-white or gray, the lower members being black-gray. Often, they are dolomitic and sometimes pure crystalline dolomites. In some cases, there are intercalations of breccia-marbles e.g. between Dendria and Platanos area. Generally, their thickness increases and decreases rapidly, with synchronous lateral passing to cipolines and calcareous schists. Commonly, they are strongly folded and faulted, and very karstic.
The schist of Ampelos (sch2) constitute the larger part of island's central section and more or less the upper extension of the Marathokampos-Kosmadei schists, in thewestern part of the island. They are of varied mineralogical composition: mica schist (where muscovite dominate in relation to biotite), muscovite schist, quartz:muscovite schists and quartz schists. Epidote amphibolites, chloritic schists, epidote-muscovite-glaucophane schists, hematite schists and phyllites, can also be found among them. Locally there are intercalations of ultramafic igneous rocks, often schistose (Myli village area). Sometimes quartz-schists and quartzites with a thickness exceeding 100 m, dominate within the schists (Western side of the Ampelos mountainous block). The total thickness of the schists of Ampelos is estimated to be greater than 2.500 m.
Οphiolitic masses (o) intercalates within Ampelos schists, being partly schistose and usually gabbro-type.
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