![]() When aggradation is zero or below seismic resolution, that means that the seaward displacement of the shoreline (depositional coastal break of the depositional surface) or the basin edge (which may coincide) is, practically horizontal. In this way, island and oceanic arches can be attached as new terrain to an adjacent continent. Often, an obduction occurs where a small lithospheric plate is compressed between two larger plates. It may be said that an obduction occurs when a fragment of the continental crust is stopped and raised as a result of the thrusting of the mafic and ultramafic mantle material over the continental crust. In this example, the old continental lithospheric plate of Kalimantan and Tarakan (a non-Atlantic divergent margin, that is, developed in a, globally, compressional geological context within the Meso-Cenozoic megasuture) rode the old Brunei plate, which corresponds, also, to an old non-Atlantic divergent margin, that uplifted strongly. Often, as illustrated in this geological section through the north of the island of Borneo (Indonesia), due to the total subduction of the oceanic crust under the continental crust, the upper plate can enter into obduction, i.e., it can strongly ride the descending plate. The greater the subduction angle, the closer the volcanic arc, on the overriding or ascending plate, will be from the oceanic trench. In B-type subduction zones, in the overriding plate (upper plate) a volcanic arc forms, whose distance, measured from the oceanic trench, is function, mainly, of the subduction angle. In the former, it is a cold and dense lithospheric plate, which dips under a less dense plate, whereas in the second, i.e., in the A-type subduction zones, in general, the two plates (plunging and overriding) have, roughly, the same density. The mechanism of these two subduction zones is not the same. There are two types of subduction zones: (i) B-type or Benioff subduction zones in which a volcanic lithospheric plate sinks under a continental or volcanic lithospheric plate and (ii) A-type or Ampferer subduction zones, in which a continental lithospheric plate dives beneath a plate continental or volcanic lithospheric. An obduction puts a part of the oceanic crust of the descending plate (ophiolites) in the plane of the subduction zone, that is to say, between two old lithospheric plates. Uplift of the continental material, either of the descending or plunging lithospheric plate, in association with a B-type subduction zone (Benioff). Obdução / Obducción / Obduktion (Geologie) / 逆冲 / Обду́кция / Obduzione /
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |