Plagioclase of Intrusive Rocks From the Islandarc Pervomay-Ayudag Complex (Mountain Crimea) - From Plagiolerzolites to Plagiogranites

The Middle Jurassic hypabyssal island-arc pervomay-ayudag intrusive complex includes plagiolerzolites, olivine gabbro-norites, quartz gabbro-norites, quartz gabbro-norite- diorites, quartz diorites, plagiogranites. Ultramafic and mafic rocks contain anorthite (An92-90) and bytownite (An89-73). Plagiogranites containing andesine and oligoclase, up to albite-oligoclase (An19-9). This composition of plagioclase is typical for island-arc rocks. Due to the abundance of anorthite and bytownite, which are poor in silica, many types of gabbroids of the pervomay-ayudag complex are enriched with quartz. Calcium-rich plagioclases of the complex are enriched with FeO up to 0.9 wt.%. From anorthite to oligoclase, the K2O content gradually increases up to 1.4 wt.% During the alteration process, plagioclase significantly depletes with K2O. In the gabbroids of the central parts of intrusive bodies, the elongation of plagioclase crystals from anorthite to andesine is 2-5, usually 3-4. The porphyritic gabbroids of the quenching zone contain long-prismatic plagioclase crystals with elongation up to 10, and the fine-grained matrix contains skeleton crystals.