Date of Award
Master of Science (MS)
The Ankara volcanics comprise a small volcanic field immediately to the north of Ankara, Turkey. This volcanic field is composed of a mixture of flows, tuffs, and agglomerates, with the flows ranging in composition from high-K basaltic andesite to rhyolite. Dacitic flows are the most common. A potassium-argon date gives a Middle Eocene age of 42.0 ± 1.6 m.y. The volcanics unconformably overlie Paleozoic sediments of the "Cimmerian continent" to the south and Mesozoic rocks of the Ankara melange to the north.
Results of analyses on 25 samples for major elements and Y, Sr, Rb, Ni, Cr, V, Co, Zn, Cu, Nb, and Zr are presented. Major elements and most trace elements show well defined trends when plotted on SiO2 variation diagrams, indicating a chemical consanguinity. The processes of partial melting, fractional crystallization, and mixing/contamination are evaluated in terms of the roles they may have played in the generation of these magmas. A model based on fractional crystallization best explains the observed chemical trends; xenocrystic phases and disequilibrium phenomena in plagioclase indicate that mixing/contamination processes may have played a lesser role.
Comparison of major and trace element abundances of the Ankara rocks to those of other suites of calc-alkaline rocks reveals that these volcanic rocks most resemble those that have been produced by magmatic arcs built upon continental basement. This is consistent with the hypothesis that these rocks are related to the Eocene subduction and convergence which closed the northern branches of Neo-Tethys.
Ach, Jay A., "The Petrochemistry of the Ankara Volcanics, Central Turkey" (1982). Geology Theses and Dissertations. 1.