In the region around the sea of
Marmara, limited by the boundaries of the 1:500 000 scale Istanbul Quadrangle, the
volcanism starting in Upper Cretaceous and intermittently continuing through
the end of Upper Miocene has been differentiated into five different stages,
namely Upper Cretaceous, Eocene, Oligocene, Lower-Middle Miocene and Upper
Miocene, and the volcanic outcrops situated in the region have been dated.
Together with the detailed petrographic studies, nine samples from different
areas and stages have been dated by K/Ar method, resulting in that the oldest
and the youngest lava is of 74.3 ± 1.0 million years old (Upper Cretaceous) and
8.9±0.2 years old (Upper Miocene), respectively. Of these, belonging to the
first four stages are mostly calcalkaline (some of the Eocene aged samples are
tholeiitic) and are of basalt, basaltic andesite, trachyandesite, andesite,
dacite, rhyolite type, whereas that of belonging to the fifth stage are
alkaline and of basanite, basalt and trachybasalt types. The pyroclastics of
various size and the tuffs of the first four volcanism stages crop out in a
wide area. The Upper Cretaceous volcanics have completely formed beneath the
sea. On the other hand, some of Eocene volcanics have formed beneath the sea
which are seen intercalated with sediments while the others have formed on
land. The lavas of Oligocene, Lower-Middle Miocene and Upper Miocene age have
formed on land and are observed to be intercalated with lacustrine sediments,
in places. Of the lavas stranded along the Black sea coast, the Upper
Cretaceous aged ones have formed in a group of island arc volcanics and have
been produced in a subduction zone and the Eocene, Oligocene and Lower-Middle
Miocene aged ones have formed in an environment of compression during and after
the collision and have been produced from a material of crust and mantle
mixture. It is proposed that the Upper Miocene aged alcaline basaltic volcanics
have formed in an environment of extension by the uplift of mantle after the
change of tectonic regime in Middle Miocene.
Birincil Dil | İngilizce |
---|---|
Konular | Mühendislik |
Bölüm | Makaleler |
Yazarlar | |
Yayımlanma Tarihi | 1 Ocak 1998 |
Yayımlandığı Sayı | Yıl 1998 Cilt: 120 Sayı: 120 |
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