CENOZOIC VOLCANO-STRATIGRAPHY AND PETROLOGICAL EVOLUTION OF POST-COLLISIONAL VOLCANIC ROCKS IN EASTERN BIGA PENINSULA, NW ANATOLIA, TURKEY
11th International Multidisciplinary Scientific GeoConference SGEM2011, www.sgem.org, SGEM2011 Conference Proceedings/ ISSN 1314-2704, June 20-25, 2011, Vol. 1, 19-26 pp
Post collisional volcanic rocks cover large areas in the east of the Biga peninsula, which
is located in the NW Anatolian magmatic belt along the southern margin of Marmara
Sea. These volcanic units span a compositional range from calc-akaline (i.e. andesite,
dacite, and rhyodacite to rhyolite), to alkaline (olivine basalts) lavas. All rock units
display coherent variation trends on the major and trace element Harker diagrams.
Cenozoic volcanic sequences exposed in the east of Biga are divided into three volcanostratigraphic
formations in this study: (1) the Işıkeli and (2) Arabaalan volcanics, and
(3) the Taştepe basalt. The first two units are calc-alkaline in character (these are named
in this study as the calc-alkaline suite) in contrast to the Taştepe basalt which is alkaline.
The Işıkeli volcanics are composed of rhyodacitic and rhyolitic tuffs and lavas of Upper
Oligocene age (new K-Ar age for this formation is 28.3±1.3 Ma). The Arabaalan
volcanics consist of andesitic and dacitic lavas and is Upper Oligocene to Lower
Miocene in age (26.3±1.0 - 18.4±1.3 Ma). The Taştepe basalt is made up of alkali
olivine basaltic dykes and lavas that were erupted along the zones of local extension
during a period from Upper Miocene to Pliocene (12.7±0.6 Ma).
Our analytical results indicate that the SiO2 content of the Işıkeli volcanics varies
between 59.88% and 67.26%, while that of the Arabaalan volcanics varies between
54.24% and 64.88%. Alkaline basaltic dyke from the Taştepe unit has the lowest SiO2
content by 49.4%. Except for K2O, all major elements gradually decrease with
increasing SiO2 in e linear fashion.
The calc-akaline suit (i.e. the Işıkeli and the Arabaalan volcanics) is characterized by a
distinct enrichment in the large ion lithophile elements (LILEs), and also in light rare
earth elements (LREEs) and depletion in the high field strength elements (HFSEs). This
can be interpreted as a reflection of either hydrous melting of mantle wedge in a
subduction zone or enrichment of the magma sources with an inherited component from
an ancient subduction plate. Our geochemical data also indicate that a number of
magma chamber processes involving magma mixing, fractional crystallization (FC) and
assimilation with fractional crystallization (AFC) might have been operational with
together. The Taştepe alkali olivine basalt is characterized by the enrichment of LILE,
HFSEs, LREEs and MREEs, and a slight depletion in HREEs, implying a
metasomatized mantle source.
Keywords: Post collisional volcanism, Biga Peninsula, NW Anatolia.
PAPER 2011/s01.103: CENOZOIC VOLCANO-STRATIGRAPHY AND PETROLOGICAL EVOLUTION OF POST-COLLISIONAL VOLCANIC ROCKS IN EASTERN BIGA PENINSULA, NW ANATOLIA, TURKEY
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