FORMING OF VOLCANIC, METAVOLCANIC AND EPIVOLCANIC LANDSCAPES OF THE MADEIRA ISLAND

The Madeira Island geographically belongs to the archipelago with the same name. It is separated from the Morocco continental shelf  by the uneven oceanic bottom with depths varying between 3 and 4  km. The island itself is an above-water part of the complex partly  eroded shield volcano about 6 km high above the surrounding ocean  bottom. Such relative elevation is comparable with highest volcanic  mountains of the continents. Madeira is situated on a crest of the  submerged volcanic ridge at distal part of the seamountain massif to the southwest from the Pyrenean Peninsula. During the late Cenosoic  the Madeira experienced dramatic endogenic activity  followed by tectonic uplift with seismic and exogenic reworking  during the Quaternary. It is commonly accepted that during the  Neogene, the Madeira volcano was located above one of the hotspots associated with the Earth mantle roof bulge. The main  volume of volcano – its foundation part – was formed before the  Pliocene. Relics of the Miocene volcanic relief represented by gradual submerged lower slopes of the shield volcano may have partly  remained uneroded at its peripheral sectors, which did not  experience large scale gravitation-tectonic movements. During the  following 5 million years, large above-water shield volcano was  formed on top of the Madeira island surface as a result of  accumulation of alternated lava and tephra layers. Younger lava and  pyroclastic flows buried the older volcanic materials composed of  basic and sub-alcaline rocks. Later the volcano became subject to  erosion with radial feather-planform pattern of fluvial incisions exposing ancient volcanic rock formations buried under  younger layers of the shield central part. The modern volcano  planform differs from the ideal shield volcano shape, especially at its  eastern part – severely eroded half of the island dominated by  epivolcanic relief. Macro-scale landforms of unmodified volcanic  origin are prominent only locally along the water divide parts of the  island outer slopes and, more clearly, in the zone of moderate  elevation mountains formed by young plateau basalts at the western part of the island. Presently inactive Madeira volcanic island  represents a model of early stages of the newly formed oceanic land  masses development. Such mode of development can at present be  attributed to several volcanic archipelagos only (for example, the  Hawaii to the northwest from the Main island). However, it can be  considered as the generalized scenario of the Earth surface evolution at transition stage from Hadean (Katararchean) to Eoarchean about 3.8 billion years ago.

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