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Field, petrographic and
geochemical characteristics of the alkaline magmatism in central
Anatolia (Turkey)
Yalcin M.G.*,
Ilbeyli N.*, Pearce J.A.**, Yalcin F.*
* Akdeniz University,
Faculty of Engineering, Department of Geological Sciences, 07058
Antalya, Turkey; ** Cardiff University, School of Earth & Ocean
Sciences, CF10 3AT Cardiff, United Kingdom
gurhanyalcin@akdeniz.edu.tr
The
Anatolian plate is located in an Eastern Mediterranean collision zone
between Eurasian and African-Arabian plates. This plate is a complex of
continental blocks, each of which are surrounded by the northern and
southern branches of Tethys. This complex framework shaped as the result
of two main branches of the Neo-Tethyan Ocean during the Late
Cretaceous-Eocene (Sengör and Yilmaz, 1981).
The
investigating area is placed in this complicated frame, named the
central Anatolian crystalline complex (Göncüoglu et al., 1991). It
consists of several metamorphic massifs numerous granitic to syenitic
plutons and dismembered ophiolites, and Tertiary volcanic and
sedimentary rocks that unconformably overly the crystalline rocks (Göncüoglu
et al., 1991).
In
this complex, calc-alkaline and alkaline magmatism of the latest
Cretaceous age was formed in collision-related tectonic setting (Ilbeyli
et al., 2004). This magmatism produced a wide variety of rock types,
from calk-alkaline through subalkaline and alkaline (Ilbeyli et al.,
2004). Their compositions range from feldspathoid-bearing monzosyenite
through monzonite to granite (Ilbeyli et al., 2004). They are also
metaluminous (I-type) to peralkaline (A-type).
Except for the feldspathoid-bearing rocks, these rocks have igneous
enclaves. The calc-alkaline and subalkaline rocks are cut by aplite and
pegmatites. On the other hand the feldspathoid-bearing rocks are cut by
phonolitic dykes.
The
main mineral components in the calc-alkaline-subalkaline rocks are
quartz, plagioclase (An52-25), alkali feldspar (Or95-79), amphibole (edenite,
magnesio-hornblende, magnesio-hastingsite), biotite and clinopyroxene (salite).
Accessory components include magnetite, ilmenite, zircon, apatite,
allanite and monazite.
Those in the alkaline samples are (An71-1), ortoklas (Or95-60),
amphibole (hastingsite, edenite), clinopyroxene (salite), garnet (melanite)
and biotite. Accessory components are magnetite, zircon, apatite,
xenotime, monazite, allanite and fluorite.
These rock types crystallized under a wide range of pressure (5.3-2.6
kbar) and temperatures (858-698
°C)
from highly oxidized magmas (log fO2 -17 to -12) (Ilbeyli, 2005).
The
intrusive rocks from the complex have a range from
~46
to 80 wt% SiO2. These plutonic rocks are enriched in LILE (K,
Rb, Ba, Th) relative to HFSE (Ta, Nb, Hf, Zr, Sm, Y, Yb), and also
radiogenic in terms of Sr, and unradiogenic in terms of Nd isotope
ratios (Ilbeyli et al., 2004). Moreover, these rocks have a range of
δ18O values between 6.5‰ and 14.8‰ (Ilbeyli et al., 2009).
Multi-trace element diagrams and isotope ratios indicate distinct mantle
sources with different amount of crustal components because of
subduction. In addition radiogenic (Rb, Sr) and stable isotope (O)
diagrams display that all rocks have experienced different amount of
crustal assimilation (also crust compositions).
In
central Anatolia, these heterogeneous distribution magma types may
indicate a non-uniform source(s) resulting distinct kind of rocks.
Mechanism for the different source types in central Anatolia could be
related to perturbation of metasomatized lithosphere or delamination of
the thermal boundary layer.
References:
Göncüoglu, M.C., Toprak, V., Kuscu, I., Erler, A., Olgun, E. 1991.
Geology of the western part of the Central Anatolian Massif. Part I:
Southern Section. Turkish Petroleum Corporation (TPAO) Report No.2909
(unpublished, in Turkish).
Ilbeyli, N., Pearce, J.A., Thirlwall, M.F., Mitchell, J.G. Petrogenesis
of collision-related plutonics in central Anatolia, Turkey. Lithos.
2004. Vol. 72, P. 163-182.
Ilbeyli N. Mineralogical-geochemical constraints on intrusives in
central Anatolia, Turkey: tectono-magmatic evolution and characteristics
of mantle source. Geol Mag. 2005. Vol. 142: P. 187-207.
Ilbeyli, N., Pearce, J.A., Meighan, I.G., Fallick, A.E. Contemporaneous
late Cretaceous calc-alkaline and alkaline magmatism in central
Anatolia, Turkey: oxygen isotope constraints on petrogenesis. Turkish
Journal of Earth Sciences. 2009. Vol. 18, P. 529–547.
Sengör, A.M.C., Yilmaz, Y. Tethyan evolution of Turkey: a plate tectonic
approach. Tectonophysics. 1981. Vol. 75, P.181-241. |