An example for the volcanic section of the intraoceanic subduction zone type ophiolite (Komurhan ophiolite) from the southeast anatolia (Elazig-Turkey)

Abstract

In this study, the volcanic rocks located in the South of Baskil (Elazig) town were investigated in terms of their geochemical, petrographical and geological characteristics, for pointing out the relations of this unit with the late Cretaceous Komurhan ophiolite and Andean type are magmatics (Baskil granitoid). The volcanic rocks crop out along an approximately east-west trending belt in the region. It is represented by alternations of volcanic and sedimentary rock units. The measured thickness of the volcanics in the study area is about 750 in. At the base, the volcanic section has a sharp north dipping tectonic contact with the gabbroic rocks of the Komurhan ophiolite, and is intruded by the granitic rocks of the Baskil granitoid. This volcanic section is characterized by a wide spectrum of rocks such as: basalt, basaltic-andesite, andesite, rhyodacite and dacite. Same rock association also is seen on the top of the other ophiolitic units in the region The basalts display vesicular, amygdaloidal, intersertal, hyalomicrolitic porphyritic to microlitic porphyritic textures and are dominated by plagioclase and pyroxenephyric lavas. The secondary phases are albite, chlorite, epidote, calcite and quartz. The andesites show amygdaloidal, hyalomicrolitic porphyritic to microlitic porphyritic textures and are plagioclase and amphibolephyric lavas. Epidote, chlorite calcite and sericite form the secondary phases in the rock The rhyodacites display microlitic porphyritic to microgranular porphyritic textures, and are represented by plagioclasephyric lavas. Plagioclase is seen either as phenocrysts or as microliths within the matrix. Dacites show hyalo-porphyritic to amygdaloidal textures and are dominated by zoned plagioclase and corroded quartz set in a fine-grained matrix. Kaolinization and sericitization are present in plagioclases. On the other hand the volcano-sedimentary unit includes gypsum as vein filling material and individual crystals in the upper part of the section. Volcanogenic massive sulphide deposits are seen in this section. These volcanic rocks have been previously regarded as extrusive equivalents of the Baskil intrusive body, which is calc-alkaline in composition. Both field and geochemical studies show that these volcano-sedimentary unit representing the upper levels of an intra-oceanic volcanic arc formed above of north-dipping subduction zone during Late Cretaceous time.