In situ differentiation and evolution of potassic syenites from Svidnya, Bulgaria |
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| Authors: | Momchil Dyulgerov Bernard Platevoet |
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| Institution: | 1. Department of Mineralogy, Petrology and Economic Geology, Sofia University “St. Kliment Ohridski”, 15 Tzar Osvoboditel, Sofia, 1504, Bulgaria
2. Laboratoire de Pétrologie et Volcanologie, Université de Paris-Sud, Bat. 504, 91405, Orsay, France
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| Abstract: | Potassic syenites from Svidnya, Bulgaria crop out as small isolated bodies as the primary for this intrusion liquid has basic to intermediate composition. The evolution in a closed magma chamber created plutonic rocks ranging from basic (melasyenite) to acid (granite) and from metaluminous to peralkaline. The most mafic varieties show cumulative textures typical for orthocumulates with cumulus phases clinopyroxene, biotite, apatite and potassium feldspar as gravitational settling is a viable process for separation of particles in the bottom parts of magma chamber. In the middle stratigraphic level of biggest body modal igneous layering with development of dark (clinopyroxene?+?amphibole) and light (potassium feldspar) laminas was observed. Oscillatory crystallization around eutectic point resulted in cyclic separation of mafic and felsic phases in repetitive layers. Fractionation of Ca- and Al-rich phases—clinopyroxene, biotie and potassium feldspar created peralkaline residual liquid strongly enriched in HFS elements. |
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