The Troodos Terrane or the Troodos Ophiolite complex dominates the central part of the island, constitutes the geological core of Cyprus, appears in two regions (main mass of the Troodos mountain range and in the Limassol and Akapnou Forests south of the range) having a characteristic elongated domal structure. Minor outcrops appear in the Akamas peninsula and in the area of Troulloi village. It was formed in the Upper Cretaceous (90 Ma) on the Tethys sea floor, which then extended from the Pyrenees through the Alps to the Himalayas. It is regarded as the most complete, intact and studied ophiolite in the world. It is a fragment of a fully developed oceanic crust, consisting of plutonic, intrusive and volcanic rocks and chemical sediments. The stratigraphic completeness of the ophiolite makes it unique. It was created during the complex process of sea-floor spreading and formation of oceanic crust and was emerged and placed in its present position through complicated tectonic processes related to the collision of the Eurasian plate to the north and the African plate to the south. The stratigraphy of the ophiolite shows a topographic inversion, with the stratigraphically lower suites of rocks outcropping in the highest points of the range, while the higher units appear on the periphery of the ophiolite. This apparent inversion is related to the way the ophiolite was uplifted (diapirically) and later eroded. The uplift of the island took place during episodes of abrupt uplift up to the Pleistocene (2 Ma).
The Troodos Ophiolite consists of the following stratigraphic units, in ascending order: Plutonics (mantle sequence and cumulates), Intrusives, Volcanics and Chemical sediments.
The mantle sequence is thus termed because the rocks that form this suite are considered to be the residuals after the partial melting of the upper mantle and the formation of basaltic magma, from which the remaining rocks of the ophiolite have been derived. It is mainly composed of harzburgite and dunite with 50-80% of the original minerals altered to serpentine, and serpentinite (with or without concentrations of asbestos) where alteration is almost complete.
The cumulate rocks are the products of crystallisation and concentration of crystals at the floor of the magma chamber, beneath the zone of sea floor spreading. The main cumulate rocks include dunite with or without chromite concentrations, wehrlite, pyroxenite, gabbro and plagiogranites, which are observed in small discontinued occurrences.
The intrusive rocks (Sheeted Dyke Complex - Diabase) have a basaltic to doleritic composition and were formed by the solidification of the magma in the channels, through which it intruded from the magma chambers at the bottom of the oceanic crust feeding at the same time the submarine extrusion of lava on to the sea floor.
The Sheeted Dyke Complex is followed by a suite of volcanic rocks that consist of two series of pillow lavas and lava flows, mainly of basaltic composition. The pillow lavas have a characteristic spherical to ellipsoidal pillow shape, 30-70 cm in diameter, which were formed as a result of submarine volcanic activity. Between the intrusive rocks and the pillow lavas a transitional zone known as the Basal Group occurs. Dykes dominate the Basal Group while pillows are less common.
The Perapedhi Formation is composed of umber (chemical sediment), radiolarites and radiolaritic shales. These were the first sediments deposited over the ophiolite rocks as a result of hydrothermal activity (hot solutions rich in Fe and Mn) and sedimentation on the sea floor.
Directly associated with the Troodos Ophiolite are the massive sulphides, chromite and asbestos mineral deposits. These ore deposits were formed in different stratigraphic units of the ophiolite (lavas, dunite and harzburgite, respectively) and becameexposed as a result of its uplift. The exposure of the ore bodies to the surface, and especially that of massive sulphides and amiantos, resulted in the discovery and exploitation of copper since antiquity.
The Troodos Ophiolite has a very significant role for the water budget of the island. Most of the rocks, especially the gabbros and the sheeted dykes are good aquifers due to fracturing. The perennial rivers running radially are feeding the main aquifers in the periphery of the Troodos and the plains.