Understanding Orogenic Theories and Geological Processes

Theories Orogeniques: 2 groups:

Theories Orogeniques Fixistes: Mountain chain formation is due to vertical terrestrial crustal efforts. Important:

• Theory of Undations: Mountain chain formation due to the emergence of a magmatic mass.
• Oceanization Theory: Basic theory suggesting that masses of magma invaded an area of continental crust.
• Geosynclinal Theory: Existence of a deep sedimentary basin in which large quantities of sediment accumulate, provoking the subsidence of the sedimentary basin.

Theories Orogeniques Mobilistes: Modern theories, utilizing recent advances.

• Theory of Continental Drift: (Alfred Wegener) The cause of the phenomena is due to orogenic compressive horizontal efforts of the terrestrial crust.
• Tectonic Plate Theory: Orogenic phenomena are produced by the displacement of tectonic plates due to magmatic convection currents.

Pangea: Supercontinent, where all the continents were together. Geographical Tests: Matching the contours of the continents. Geological Tests: Rock type coincidence. Paleoclimatic Tests: High quantity of coincidence of glacial sediments. Paleontological Tests: Existence of fossils of these organisms.

Paleomagnetism: Magnetic field change from north to south in the land.

• Magnetic Normal Polarity: North Pole matches the geological magnetic north pole (today).
• Magnetic Polarity Reverse: North pole to south pole lies in geographic magnetism.

Dorsal Oceanikes: Long chains and high mountains on the seabed.

Two Types of Lithosphere:

• Oceanic Lithosphere: Composed of basaltic crust and residual mantle, 65 km thick.
• Continental Lithosphere: Composed of granitic crust and residual mantle, with a maximum thickness of 250 km.

Tectonic Plates: Two types:

• Oceanic Plates: Oceanic lithosphere formed exclusively for mixed plates, showing oceanic lithosphere and satellite sectors.
• Continental Plates: The movements of the plates and their interactions give rise to three types of plate boundaries: constructive, passive, and destructive.

Rift: A long and narrow valley separating the dorsal oceanikes.