A structural and metamorphic study of the southern Menderes Massif (Western Turkey)
Loading...
Files
Date issued
Authors
Editors
Journal Title
Journal ISSN
Volume Title
Publisher
Reuse License
Abstract
P-T conditions, paragenetic studies and the relation between mineral growth, deformation and -
when possible- isograd minerals have been used to describe the type of metamorphism involved
within lower units of the southern Menderes Massif of the Anatolide Belt in western Turkey. The
study areas mainly consist of Proterozoic orthogneiss and surrounding schists of presumed Paleozoic
age. Both
units are seen as nappes in the southern study area, the Çine and the Selimiye nappe, on the
whole corresponding to Proterozoic orthogneiss and surrounding schists, respectively. The Çine and
Selimiye nappes are part of a complex geological structure within the core series of the Menderes
Massif. Their emplacement under lower greenschist facies conditions, would result from closure of the
northern Neo-Thethys branch during the Eocene. These two nappes are separated by a major tectonic
structure, the Selimiye shear zone, which records top-to-the-S shearing under greenschist facies
conditions. Amphibolite to upper amphibolite facies metamorphism is widely developed within the
metasedimentary rocks of the Çine nappe whereas no metamorphism exceeding lower amphibolite
facies has been observed in the Selimiye nappe.
In the southern margin of the Çine Massif, around Selimiye and Millas villages, detailed
sampling has been undertaken in order to map mineral isograds within the Selimiye
nappe and to
specify P-T conditions in this area. The data collected in this area reveals a global prograde normal
erosion field gradient from south to north and toward the orthogneiss. The mineralogical parageneses
and P-T estimates are correlated with Barrovian-type metamorphism. A jump of P-T conditions across
the Selimiye shear zone has been identified and estimated c. 2 kbar and 100 °C which evidences the
presence of amphibolite facies metasedimentary rocks near the orthogneiss. Metasedimentary rocks
from the overlying Selimiye nappe have maximum P-T conditions of c. 4-5 kbar and c. 525 °C near
the base of the nappe. Metasedimentary rocks from the Çine nappe underneath the Selimiye shear zone
record maximum P-T conditions of about 7 kbar and >550 °C. Kinematic indicators in both nappes
consistently show a top-S shear sense. Metamorphic grade in the Selimiye nappe decreases
structurally upwards as indicated by mineral isograds defining the garnet-chlorite zone at the base,
the
chloritoid-biotite zone and the biotite-chlorite zone at the top of the nappe. The mineral isograds in the
Selimiye nappe run parallel to the regional SR foliation. 40Ar/39Ar mica ages indicate an Eocene age of
metamorphism in the Selimiye nappe and underneath the Çine nappe in this area.
Metasedimentary rocks of the Çine nappe 20-30 km north of the Selimiye shear zone record
maximum P-T conditions of 8-11 kbar and 600-650 °C. Kinematic indicators show mainly top-N shear
sense associated with prograde amphibolite facies metamorphism. An age of about 550 Ma could be
indicated for amphibolite facies metamorphism and associated top-N shear in the orthogneiss and
metasedimentary rocks of the Çine nappe. However, there is no evidence for polymetamorphism in the
6
metasedimentary rocks of the Çine nappe, making tectonic interpretations about late Neoproterozoic to
Cambrian and Tertiary metamorphic events speculative.
In the western margin of the Çine Massif metamorphic
mineral parageneses and pressure–
temperature conditions lead to similar conclusion regarding the erosion field gradient, prograde
normal toward the orthogneiss. The contact between orthogneiss and surrounding metasedimentary
rocks is mylonitic and syn-metamorphism. P-T estimates are those already observed within the
Selimiye nappe and correlated with lower amphibolite facies parageneses.
Finally additional data in the eastern part and a general paragenetic study within the Menderes
Massif lower units, the Çine and the Selimiye nappes, strongly suggest a single Barrovian-type
metamorphism predating Eocene emplacement of the high pressure–low temperature Lycean and
Cycladic blueschist nappes. Metamorphic mineral parageneses and pressure–temperature conditions
do not support the recently proposed model of high pressure–low temperature metamorphic
overprinting, which implies burial of the lower units of the Menderes Massif up to depth of 30 km, as
a result of closure of the Neo-
Tethys.
According to the geochronological problem outlined during this thesis, there are two possible
schemes: either Barrovian-type metamorphism is Proterozoic in age and part of the sediments from
Selimiye nappe (lower amphibolite facies) has to be proterozoic of age too, or Barrovian-type
metamorphism in Eocene of age. In the first case the structure observed now in the core series would
correspond to simple exhumation of Proterozoic basement. In the latter case a possible correlation
with closure of Neo-Tethys (sensu stricto, southern branch) is envisaged.