Akademik Veri Yönetim Sistemi
24th Colloquium of African Geology (CAG 24), Addis Ababa, Etiyopya, 8 - 14 Ocak 2013, ss.43
The Pan-African basement
of the Menderes Massif consists of partially migmatized metasediments, i.e.
paragneisses and metapelites, which were intruded by numerous poly-metamorphic
Precambrian gabbros and syn-to post-metamorphic Pan-African metagranites /
orthogneisses. The relict phases and assemblages attributed to the Pan-African
metamorphic evolution at granulite- and eclogite-facies conditions have been
recognized in the basement. The relicts of granulite facies metamorphism are
represented by orthopyroxene bearing-orthogneisses and paragneisses, pelitic
granulites and metatonalites. In addition to granulite facies metamorphism,
widespread migmatization and anatectic granite generation occur in the basement.
In this study, SHRIMP and LA-ICP-MS were applied to provide timing
constraints on the granulite facies metamorphism and overprinting migmatization,
which affected the Pan-African basement of the Menderes Massif. Cathodoluminescence imaging of zircons separated from pelitic granulites occurring in
the southern part of middle submassif (SE of Tire) reveals that many of the grains contain unzoned
and/or planar zoned overgrowth textures on inherited cores. Textural relationships
clearly reveal that unzoned zircon overgrowths indicate granulite facies metamorphism
and must have occurred prior to planar zoned overgrowth reflecting
crystallization from anatectic melts. SHRIMP analyses yield concordia ages of 582.0 ± 5.3 Ma
and 565.0 ± 5.4 Ma from unzoned and planar zoned zircon
overgrowths, respectively. Additionally, LA-ICP-MS analyses of unzoned
overgrowths give similar concordia age of 586.0 ± 15.0 Ma. Furthermore,
unzoned zircon overgrowths from ortopyroxene bearing orthogneiss yield concordia age of 578.7 ± 8.1 Ma. The zircons from metatonalite of middle submassif
(northeast of Birgi area) show
that many of the grains contain magmatic crystallization texture and unzoned overgrowths representing the high temperature metamorphism. Magmatic
cores showing oscillatory zoning and unzoned overgrowths yield
concordia ages of 591.0 ± 6.9 Ma and 578.4 ± 8.2 Ma
by LA-ICP-MS U-Pb analyses, respectively. Thus, ca. 590 Ma is interpreted the
crystallization age of the protolith of metatonalite. An age of 580-585 Ma is
interpreted the age of granulite facies metamorphism and 565 Ma can be accepted
as the age of migmatization affected the basement series. All ages coincide
with assembly processes resulting in the formation of the Gondwana super
continent as a consequence of the closure of the Mozambique Ocean during Late
Neoproterozoic.