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Třebel - geologie

The Earth crust consists of solid plates, which are permanently moving. They are driven by plastic currents in the mantle of planet Earth. The plates form prevalently ocean floor, and some of them carry continents. The most of zones, where plates draw away, lie on the ocean's floor. Along the boundary zone form huge mountain chains with up to 1500 kilometers in width and tens of thousands kilometers in length, so called mid-ocean ridges. Through their axis are passing valleys, in which magma ascent and effusions of basaltic lavas happen. By the moving of the underlying rock the valley gapes and basaltic lavas flow through here. In these places the plates are becoming more distant, and molten rocks ascend from the depth. By cooling on the sea floor the rock solidifies. In this way new Earth's crust forms. The plates affect themselves on their rims. If they are moving against each other, the thinner and heavier oceanic plate is passing under thicker and relatively lightweight continental plate. Where one plate submerges under another one, deep trenches are formed. The submerging plate is molten there. The melt penetrates locally in the overlying plate, causes arching of that and in some places volcanism. During collision of oceanic lithosphere plates submerges in the space of oceanic trench in so-called subduction zone one plate under another. The sinking plate is in the depth gradually smelted, and the magma formed rises to surface. In this way form arrays of volcanic islands, so-called island arcs. If two continental lithosphere plates are colliding, the Earth's crust makes the subduction of one plate under another not possible. In such places are created mountains with nappe- and imbricate structure and with intensively folded rock complexes. Formation of the largest mountain belts in the world is due to collisions of tectonic plates. Mountains are formed there, where a continental and an oceanic plate, or two continental plates are pushed together. The present shape of Europe is a result of gradual jointing of several continental blocks, so-called amalgamation. The Bohemian Massif, whose part is the Geopark GeoLoci too, formed by collision of continental plates. The National Geopark Geoloci represents a territory of exceptional values with a varying and interesting geological framework. The long history of the Earth was here accompanied by a number of uncommon events. More than 300 millions years ago during the younger Paleozoic the Variscan folding took a place. During orogenic processes, older rocks were metamorphosed.

subdukce.avi [785 kB]

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