Spilit

Spilit (Greek σπιλάς (spilás) - rock) is a collective name for basic igneous rocks, which are mainly formed by metasomatosis from oceanic basalt . The term was introduced into geological literature in 1827 by Alexandre Brongniart .

Rock description

Spilite are similar to basalts in appearance and shape, the differences to this can only be seen under the microscope on the thin section . They are gray-green, greenish or reddish-brown in color and usually have an above-average content of CaO and Na ₂ O. Remnants of flow structures or pillow structures ( pillow lava ) are often preserved, the rock is criss -crossed with calcite- filled veins and has cavities that are filled with minerals like calcite.

Albite and chlorite are characteristic of Spilite, other typical minerals are actinolite , titanite , carbonates , iron oxide minerals , epidote , prehnite , laumontite and relictic pyroxene .

Emergence

After the first scientific description of spilites over 180 years ago as pillow lava in ophiolites , due to the special composition of these rocks it was assumed for a long time that they originated from a special spilitic magma. Other explanations assumed that residual aqueous solutions of a magma led to the conversion of the existing minerals.

Because of the similarity of the chemical composition between basalts and spilites, and the occurrence of pillow structures that are obviously inherent to basalts, transformation processes have increasingly been preferred in petrology as an explanation for the formation of spilites from basalts, especially since the minerals inherent in the spilites are all formed by low-grade metamorphosis .

According to the current state of knowledge, the transformation of basalts into spilite can be traced back to mass transfer processes that take place in the vicinity of oceanic rifts such as the mid-Atlantic ridge as a result of the circulation of hot seawater in the rocks of the ocean floor. Some Spilit occurrences are also explained by a low-grade regional metamorphosis or hydrothermal alteration .

The parent rocks of the Spilite are basalts with a high water content, weakly metamorphic diabase or other basic igneous rocks. Anchimetamorphosis - a preliminary stage of metamorphosis - leads to the transformation of the original mineral inventory, especially the plagioclase , so that albite and chlorite predominate.

Occurrence

On land, spilites can be found today in ophiolite complexes and volcanic rock series originally formed in the ocean . Due to the pressure and temperature conditions prevailing during the formation of these complexes, spilites can be overprinted in a complicated manner. Spilites can also be found in what are known as subsequent or final magmatic series that emerged towards the end of a mountain formation .

Spilite can be found in numerous occurrences around the world, for example

in the Prague Mulde in the Precambrian layers of the Spiliterie
in the Lahnmulde in the Rhenish Slate Mountains
in the Verrucano des Perm in the Alps
at the Motton Spilite in Tasmania
in the ophiolites of Oman
in the Dekkan-Trapp of India

literature

Myron G. Best: Igneous and Metamorphic Petrology . WH Freemann & Company, San Francisco 1982, ISBN 0-7167-1335-7 , pp. 398 .
Manfred Schidlowski : Spilite and the basaltic volcanism. In: Natural Sciences . 56, No. 10, ISSN 0028-1042 , pp. 488-493 (PDF; 1.12 MB).

Web links

Anchimetamorphic Gabbro: Comments on "Spilitization". Polarization microscopy course, Institute for Geology and Mineralogy of the University of Cologne

Individual evidence

↑ ^a ^b ^c Schidlowski 1969, p. 489f
↑ Lena Zetterström: Oklo. A review and critical evaluation of literature. Technical Report TR-00-17, Svensk Kärnbränslehantering AB, 2000 (PDF, 324 kB)
^ Hans Murawski, Wilhelm Meyer: Geological dictionary . 11th edition. Elsevier / Spektrum, Heidelberg 2004, ISBN 3-8274-1445-8 , pp. 262 .
↑ Hohl, Rudolf (ed.): The history of the development of the earth. 6th edition, Werner Dausien Verlag, Hanau 1985, 703 pp. ISBN 3-768-46526-8
↑ Suwardi Tanumihardja, Karl W. Strauss, Georg Müller: Petrology of sub-carbonic Spilite of the NE-Lahnmulde / Rheinisches Schiefergebirge. Journal of the German Society for Geosciences, Volume 137, pp. 465–487, 1986
↑ Stratigraphic Units Database: Motton Spilite. Department of Industry, Tourism & Resources, Geoscience Australia, Commonwealth of Australia
^ ^A ^b W. Wieseneder: Book Reviews: International Union of Geological Sciences , Series A. Number 4: Spilites and Spilitic Rocks . Editor: AMSTUTZ, G. C, Heidelberg. 138 ills., 13 plates, VII, 482 pp., 1974. Berlin - Heidelberg - New York: Springer Verlag. ISBN 3-540-06448-6 . Communications from the Austrian Geological Society, vol. 68 (1975), pp. 219–240, Vienna 1978 (PDF; 1.9 MB)

[Schidlowski_489-1] Schidlowski 1969, p. 489f

[2] Lena Zetterström: Oklo. A review and critical evaluation of literature. Technical Report TR-00-17, Svensk Kärnbränslehantering AB, 2000 (PDF, 324 kB)

[3] Hans Murawski, Wilhelm Meyer: Geological dictionary . 11th edition. Elsevier / Spektrum, Heidelberg 2004, ISBN 3-8274-1445-8 , pp. 262 .

[4] Hohl, Rudolf (ed.): The history of the development of the earth. 6th edition, Werner Dausien Verlag, Hanau 1985, 703 pp. ISBN 3-768-46526-8

[5] Suwardi Tanumihardja, Karl W. Strauss, Georg Müller: Petrology of sub-carbonic Spilite of the NE-Lahnmulde / Rheinisches Schiefergebirge. Journal of the German Society for Geosciences, Volume 137, pp. 465–487, 1986

[6] Stratigraphic Units Database: Motton Spilite. Department of Industry, Tourism & Resources, Geoscience Australia, Commonwealth of Australia

[oegg-7] A ^b W. Wieseneder: Book Reviews: International Union of Geological Sciences , Series A. Number 4: Spilites and Spilitic Rocks . Editor: AMSTUTZ, G. C, Heidelberg. 138 ills., 13 plates, VII, 482 pp., 1974. Berlin - Heidelberg - New York: Springer Verlag. ISBN 3-540-06448-6 . Communications from the Austrian Geological Society, vol. 68 (1975), pp. 219–240, Vienna 1978 (PDF; 1.9 MB)