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Charakterystyka morfologiczna i geochemiczna kryształów cyrkonu z migmatytu ze Smreczyńskiego Wierchu (Tatry Zachodnie)

Burda J.

Przegląd Geologiczny

2005

Vol. 53, nr 2

127--133

In the Polish part of the metamorphic envelope of the granitoid Rohače pluton, migmatites are the predominant component. Migmatisation took place in the amphibolite facies conditions (T = 690–780C ; P =7.5–11 kbar). To observe the response of zircon crystals to the melt formation, zircon from the anatectic group of migmatites was investigated (both from leucosome and mesosome of stromatitic migmatite). Different generations of zircon present in leuco- and mesosome reflect different geological processes acting during the rock formation. Zircon from leucosome represent mainly the euhedral varieties, with two typological maxima: S1-2 (I generation) and S21-22 (II generation). Zircon from mesosome represents the anhedral varieties with one maximum at S1 (I gen-eration). In CL images the first generation (S1-2) comprises an inherited core surrounded by younger metamorphic and magmatic rims. The microchemical analyses showed that the inherited cores have higher Zr/Hf ratios than the overgrowing rims. The second genera-tion (S21-22) revealed only oscillatory zonation. The zones with strong luminescence are characterized by a decrease of Hf and U con-tent. Zircon showing polyphase internal structure might represent a component of mesosome which survived the dissolution in granitic melt, while zircon with oscillatory zonation might have crystallized from anatectic melt.