Armalcolite-Bearing Island Arc Plagiolherzolites and Olivine Gabbro–Norite–Dolerites of the Balaklava Area (Crimea)

Armalcolite (Mg,Fe)Ti₂O₅ is a characteristic mineral of lunar titaniferous basalts that occurs widely in island-arc low-alkaline plagiolherzolites and olivine gabbro–norite–dolerites of the Early Bajocian Pervomaiskoe–Ayu-Dag complex of mesozoids in Crimea, especially in Balaklava sea cliffs near Sevastopol. Cumulose Mg-olivine contains inclusions of chromium spinels. Chromium spinels I are moderately chromic and ferruginous (f = 45–55) containing 8–14 and up to 1.2 wt % of Fe₂O₃ and TiO₂, respectively; they are distinguished clearly in this way from chromium spinels of alpinotype ultrabasites. Chromium spinels II are more ferruginous (f = 58–75) and contain up to 26, 2.5–9, and up to 1.8 wt % of Fe₂O₃, TiO₂, and V₂O₃, respectively. The typical basic trend from ferruginous aluminomagnesiochromite to chromium titanomagnetite is characteristic for Balaklava chromium spinels. Tabular armalcolite crystals of approximately 0.6–0.2 mm are included in intercumulus magnesium bronzite and augite, as well as in anorthite and bytownite. The treated armalcolite contains (wt %) TiO₂, 63–66; MgO, 6.9–8.4; FeO, 9.9–11.7; Fe₂O₃, 13–18; Al₂O₃ and V₂O₃, up to 1.5 each, and Cr₂O₃, up to 0.7. The armalcolite formula is (Mg_0.38–0.45\({\text{Fe}}_{{0.30 - 0.34}}^{{2 + }}\)\({\text{Fe}}_{{0.36 - 0.49}}^{{3 + }}\)V_0.04–0.05Al_0–0.06Cr_0–0.02Ti_1.73–1.77)₃O₅; minals contain (mol %): MgTi₂O₅, 38–45; Fe²⁺Ti₂O₅, 31–36; and Fe³⁺₂TiO₅, 23–27. Baddeleyite and zirconolite are associated with armalcolite. The composition of zirconolite is (Ca_0.7Y_0.2REE_0.1)Zr(Ti_1.6\({\text{Fe}}_{{0.3}}^{{2 + }}{\text{Fe}}_{{0.1}}^{{3 + }}\))₂O₇. The more recent minerals are ilmenite I, which contains 5–8 wt % MgO and 0.3–0.6 wt % MnO, as well as Mg-deficient and Mn-enriched ilmenite II replacing armalcolite. The occurrence and preservation of armalcolite and zirconolite within the near-surface basic intrusions of the Crimean Mountains is probably caused by poor development of late magmatic processes.