Ocean floor metamorphosis
As the ocean floor metamorphosis is already designated caused by sea water, in the true in the border area to metasomatism processes located on the ocean floor.
These processes change the still hot volcanic MORB rock as well as the underlying peridotite , which can be accessible to supercritical fluids such as H₂O and CO₂ due to transform faults .
Similar to regional metamorphosis , a distinction is made between different metamorphic facies , which are caused by the parent rock (protolith) and the prevailing temperature conditions. Differences in pressure on the ocean floor are so small for geological conditions that, in contrast to other types of metamorphosis, the pressure here can be regarded as constant.
- Zeolite facies up to approx. 200 ° C with zeolite
- Greenschist facies with chlorite and actinolite . The so-called spilitization or albitization of feldsparsalsotakes place here. Sodium contained in seawater replaces the calcium presentin the crystal lattice of plagioclase , which creates albite (sodium terminal member of the feldspar mixed series).
- Amphibolite facies from 500 ° C; amphiboles develop here,preferably hornblende due to the chemistry of the oceanic crust
Furthermore, the serpentinization of peridotite can take place, which due to its low density (2.7 g / cm³) can rise up to the crust surface like a diapir.
Individual evidence
- ^ Frisch & Meschede: Plate tectonics - continent shift and mountain formation. 5th edition Darmstadt, 2011.