GEODYNAMIC PHASES OF THE ARAÇ MASSIF, WESTERN PONTIDS, KASTAMONU, TURKEY

Year 2000, Volume: 122 Issue: 122, 42 - 43, 01.03.2000

Doğan Aydal

Abstract

This paper is concerned with the
geological, mineralogical and geochemical properties of Araç massif. The Araç
massif is mainly composed of ophiolites and metamorphic rocks. The age of the
metamorphic rocks, which are dominant rock group in the study area, are ranging
from Pre-Malm to Upper Cretaceous. K-Ar age determination were performed in
hornblendes derived from amphibolites, which are previously thought to be
Precambriam age in the study area. According to the KAr age results, which
gives 130-146 ma, suggests that the amphibolites were affected by retrograde
metamorphism, which took place in Berriasian (Lower Cretaceous). These ages are
believed to represent the metamorphism age, not the occurence age of the
formation. Because of this, the occurence of the Bekirçay formation should have
taken place before this retrograde metamorphism. Some very intensely altered
metaophiolitic bloks were found as xenolits in Bekirçay metamorphic units. Therefore
the age of the metaophiolites shoud have been older than the Bekirçay
formation. Mercimekdere metaophiolites were overlain, not only by Bekirçay
formation, but also by Kavacık formation, which is represented by
graphite-garnet micaschist in the study area. The Bekirçay formation and the
other above mentioned formation is overlayed discordantly by Palaeozoic
metasediments, namely the Dumantepe formation, which consists of various low
grade schists and phyllites. The Mesozoic is represented by Yongalıdağ formation,
Pelitveren ophiolitic melange and serpentinized, carbonatized and sillicified
rocks, so called listwaenites of the Gemiköy formation. Finally, this Mesozoic
formations were transgresively superseded by biosparite and biomicrite units of
the Araç formation. The area and surroundings were then affected by post Eocene
faulting. According to the geochemical investigations, it can easily be said
that ultramafic rocks occured as mantle fractionates and all mafic rocks were
originated from subalcaline tholeiitic magma. Amphibolites are found as
metaluminous, while garnet-micaschist are peraluminous and epidoteamphibolites
show both character in different places. Carbonaceous rocks in the study area
are found to be rich in calcite rather than dolomite and other minerals.

Keywords

GEODYNAMIC, PHASES, ARAÇ MASSIF

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