Spilite

Spilit (Greek σπιλάς ( spilás ) - rock) is a collective term for basic igneous rocks, which are primarily caused by metasomatism of oceanic basalt. The term was introduced in 1827 by Alexandre Brongniart in the geological literature.

Rock description

Spilite resemble the basalts in appearance and shape, the differences for this can only be seen under a microscope on thin sections. They are gray-green, greenish or reddish- brown in color and have a mostly above-average levels of CaO2 and Na2O. Frequently remains of flow structures or structures pillow ( pillow lava) are obtained, the rock is traversed by veins calcitgefüllten and has cavities that are filled with minerals such as calcite.

Characteristic of Spilite are albite and chlorite, typical other minerals are actinolite, sphene, carbonate, iron oxide minerals, epidote, prehnite, laumontite and relict pyroxenes.

Formation

After the first scientific description of Spiliten over 180 years ago as a pillow lava in ophiolites long time it was believed that they were created from a special spilitischen magma due to the particular composition of these rocks. Other explanations assumed that aqueous solutions of a residual magma to convert existing minerals have led.

Because of the similarity in chemical composition between basalts and Spiliten, and the occurrence of apparently the basalts own pillow structures, however, conversion operations were in petrology increasingly preferred as an explanation for the emergence of Spiliten from basalts, especially since the Spiliten own minerals are all caused by low-grade metamorphism.

The conversion of basalts in Spilite is due to our current knowledge on mass transfer processes that occur in the vicinity of oceanic rifts such as the Mid-Atlantic Ridge as a result of the circulation of hot sea water in the rocks of the ocean floor. Some Spilitvorkommen are also explained by a low-grade regional metamorphism or hydrothermal alteration.

The parent rocks of Spilite are basalts with high water content, low metamorphic diabase or other basic igneous rocks. A Anchimetamorphose - a precursor of metamorphosis - leads to the transformation of the original mineral deposits, mainly of plagioclase, so that there is a predominance of albite and chlorite.

Occurrence

On land Spilite are to be found in Ophiolithkomplexen and originally formed in the ocean volcanic rock series. Due to the prevailing during the formation of these complexes pressure and temperature conditions Spilite may be overprinted in a complicated way. Further, Spilite find in so-called subsequenten or final magmatic series that arose towards the end of orogeny.

Spilite found in many deposits throughout the world, for example,

• In the Prague depression in the Precambrian strata of Spilitserie
• In the Lahn trough the Rhenish Slate Mountains
• In Verrucano of the Permian in the Alps
• In Motton - Spilite in Tasmania
• In the ophiolites of Oman
• In the Deccan Traps of India