부산대학교 도서관

The Wadi Muweilha muscovite pegmatite in the Central Eastern Desert (CED) of Egypt is strongly influenced by a strike-slip shearing and fault system related to the final stage of the East African Orogen (EAO) in the Arabian Nubian Shield (ANS). It intrudes the volcano-sedimentary succession, occurs in large pegmatitic plugs, and is comprised of K-feldspar, quartz, plagioclase, and muscovite as rock-forming minerals, while abundant garnet, monazite-(Ce), Nb-depleted rutile, ilmenite, zircon, xenotime-(Y), and Y–thorite represent the rare metal minerals. Most minerals show several signatures of ductile/brittle deformations. Garnets form almandine–spessartine solid solutions and exhibit Mn bell-shaped type zoning, due to temperature decrease and fractionation of Fe–Mn during crystallization. The monazite occurs in three phases: pristine (Mnz1), recrystallized (Mnz2), and hydrothermal (Mnz3). The Y–Th-enriched Mn1 was altered into Y–Th-depleted Mnz3 associated with xenotime–thorite solid solutions (Y–thorite) via dissolution–reprecipitation mechanism. The mineral reaction happened along the preexisting microfractures (resulting from the former brittle deformation) that were used as pathways for interfacial fluids. The chemical and textural characteristics of monazite, garnet, and other minerals enhance the igneous origin of pegmatite and the relation to syn-tectonic I-type granitic magma source. The 641 ± 5 Ma (2σ) age of Mnz1 indicates that the post-collisional stage began after ~ 640 Ma in the north of the ANS. The date range (584–590 Ma) of Mnz2 is simultaneous with the rare metal-bearing post-collisional A-type granite in the CED, while the 538 to 563 Ma date range of Mnz3 may suggest a prolonged period (100 Ma) of the tectonic rejuvenation in the Mubarak–Barramiya Shear Belt at ca. 640–540 Ma. [ABSTRACT FROM AUTHOR]