1. Vishnevsky S.A. (2001). Andorra Basin: a possiable heavily eroded impact site?. Meteorit. and Planet. Sci., Vol.36, No.9, P. A215
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A rounded basin of 16 - 18 km in diameter, with center co-ordinates 1 33'E and 42 31'N is present in the Eastern Pyrenees; a major part of the Andorra State is localized within this basin. It is surrounded by mountain ridges of up to +2,700-3,000 m a.s.l. along its western, northern, eastern and south-eastern sides. To south-west, the basin is opened along the Valira river valley. In spite of the numerous river valley downcuttings and a complex topography, the basin, in a whole, has a relatively flat bottom but step slopes; these slopes turn gradually into surrounding mountains. The river net (Valira-river and its tributaries) forms a radial centripetal system within the basin. Owing to this pattern, this net differs from other river systems of the Eastern Pyrenees. Commonly, other rivers of the region have a plume- or wing-like branching pattern, which is a typical feature for the eroding highlands.
In a geological respect, the region described is made up of a broad number of formations of various age. Like the Eastern Pyrenees in a whole, these formations include old crystalline rocks (gneisses and mica gneisses), Paleozoic (Cambrian, Silurian, Devonian, Carboniferous and Permian members) and Mesozoic (Triassic and Jurassic members) rocks. All the supracrustal formations are folded up into a complex system of anticlinal and synclinal srtuctures of sublatitudal extent. Blocks of crystalline rocks and intrusions of alkaline and amphibole granites take also part in geologic structure of the area. Loose Cenozoic sediments of various ages (Oligocene to Pleistocene) are also present within intermountain depressions and river valleys. The Andorra Basin has a clear superimposing origin in respect to the regional geologic structures. Its shape does not correlate with the sublatitudal extent of these structures. Together with its morphology, there is another feature of the Basin, which can attract attention. Being the erosionresistant bodies, the granite massifs of the Pyrenees usually play an important relief-forming role and form the highest points of the given mountain ridge. However, an offshoot of a large granite massif, which extends into a central part of the Basin from the east, exhibits anomalous low resistance to erosion and occupies the part of the Basins bottom.
An isometric shape of the Andorra Basin and its clear superimposing position in respect to the regional geologic structures, as well as a radial centripetal pattern of the river net within, are of a special interest. Author paid attention to this structure still in 1990, when a spatial analyses of some regions of the globe was performed in order to search for the possible impact structures. Anomalous low erosional strength of granites inside the Basin is another point of the interest. Based upon these features, there is a possibility to suppose, that the Andorra Basin may be a heavily eroded impact structure of ~16-18 km in diameter. Within such a supposition, a low resistance of granites within the Basin can be explained as a result of shock brecciation. Based upon stratigraphic and tectonic data, the age of the supposed impact structure can be estimated as Mesozoic or Cenozoic.
(Vishnevsky S.A., 2001).

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