The Menderes Massif is a metamorphic complex cropping out on a large region in the Alpine
orogenic belt in Western Anatolia. The massif mainly, is made up of a Precambrian basement and the overlying
Palaeozoic-Early Tertiary cover series. The basement comprises Late Proterozoic metaclastics composed of
paragneiss and high grade micaschists, syn to post-tectonical Pan-African orthogneisses that have intruded into
them, and metagabbros which have partly turned into eclogitic form. Cover series unconformably overlying the
basement are divided into two units, in Palaeozoic and Mesozoic-Early Tertiary ages. The basement and cover
series were influenced by an effective Alpine contractional deformation and a regional metamorphism in Tertiary
time. Geological and geochronological data in the Menderes Massif, indicate the presence of three acidic
magmatic activities of i) Pan-African, ii) Triassic and iii) Miocene in ages. The acidic magmatics forming the
protolithes of Pan-African orthogneisses can be divided into three main types according to their textural and
mineralogical compositions as; 1) Biotite orthogneiss, 2) Tourmaline leucocratic orhogneiss and 3) Amphibole
orthogneiss. The relations of primary granites of these orthogneisses present a clear intrusive contact relationship
among them and with the metaclastics of Late Proterozoic age. The contact relationships show that these
orthogneiss types can be ordered as biotite orthogneisses, tourmaline leucocratic orthogneisses and amphibole
orthogneisses ranging from old to young, with respect to relative aging. Although there has been some problems
originating from the definition of samples dated in previous studies, it is noted that radiometric data mainly show
a consistency with this relative relationship (biotite orthogneiss: 550-570 Ma; tourmaline leucocratic orthogneiss:
541-547 Ma and amphibole orthogneiss: 531 Ma). These radiometric data indicate that different orthogneiss types
in the Massif are differentiated products of the same Late Proterozoic - Early Cambrian acidic magmatic activity.
When the paleogeographical position of the Massif in Early Cambrian and the close temporal relation of the metamorphic
stage of cover series and the acidic magmatism are assessed with the geochemical character of
orthogneisses, this widespread magmatic activity with an average age of about 550 Ma which is related to the
Pan-African orogenesis can be attributed to proccesses of closure of the Mozambique Ocean, collision of East
and West Gondwanaland, crustal thickening and partial melting of the lower crust. Triassic leucocratic
orthogneisses constitutes the second effective acidic magmatic activity in the Menderes Massif with dimensions
of 6-7 km. These plutonic leucocratic orthogneisses in 6-7 km dimensions are exposed in Ödemiþ-Kiraz and
Demirci-Gördes submassifs. They show well-preserved intrusive contact relationships with Late Proterozoic
metaclastics of the Pan-African basement and with metasediments of Late Palaeozoic cover series. Geochemical
data show that protolithes of leucocratic orthogneisses are in calc alkaline and S type in character. Based on
single zircon Pb/Pb evaporation method, these were radiometrically dated as ranging from 227 to 246 Ma. These
ages are interpreted as the age of emplacement of protolithes of orthogneisses in Middle Triassic. The existence
of Early-Middle Triassic magmatic activity is widely known not only in the Massif but also at the tectonical zones
of the Anatolides, at the Karaburun peninsula, in Cyclades and at the inner Hellenides. When the regional
character of Triassic magmatic activities is considered, it is suggested that there is a close genetical relationship
between these leucocratic orthogneisses and Triassic magmatics. It is also considered that it can be attributed to
the opening of Neothethys Ocean.
Primary Language | English |
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Subjects | Engineering |
Journal Section | Articles |
Authors | |
Publication Date | November 1, 2011 |
Published in Issue | Year 2011 Volume: 142 Issue: 142 |
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