Dissolved-recrystallized zircon from mariupolite in the Mariupol Massif, Priazovje (SE Ukraine)

Abstract

Zircon in mariupolite from the alkaline Mariupol Massif has a relatively simple, monotonous composition with only some variation in its rEE2o3 and tho2 content, i.e., 0.00–1.55 and 0.00–0.34 wt. %, respectively. it contains numerous inclusions such as albite, lepidomelane, aegirine, k-feldspars, pyrochlore, paristite and bastnäsite-(ce). the crystallization of the inclusions (except for rEE-bearing carbonates) was contemporaneous with the formation of the zircon crystals. these inclusions were enclosed by faster growing zircons. the SEM-cl images of the zircon are typical of crystals with signs of local thermal recrystallization, i.e., primary oscillatory zoning along the grain margins and secondary irregular patchy zoning in the interior. its complex internal texture most probably formed as a result of a coupled dissolution-recrystallization process during the late magmatic or post-magmatic stage of the cooling of the host rocks. the abundant micropores could have originated as a result of leaching of the zircon. the recrystallization process definitely disturbed the concentric oscillatory zoning pattern characteristic of magmatic zircon.