Petrogenesis of the largest Cenozoic volcano of the Circum-Mediterranean Area: Mt. Karacadag, SE Turkey
33rd International Geological Congress, Oslo, Norway, 1 - 04 August 2008, pp.501
- Publication Type: Conference Paper / Summary Text
- Country: Norway
- Page Numbers: pp.501
- Istanbul University Affiliated: Yes
Abstract
Mt. Karacadag is the largest volcano of the Circum-Mediterranean Anorogenic Cenozoic Igneous Province (CiMACI; Lustrino and Wilson, 2007) with an area of ∼10,000 km2. Volcanic activity of Mt. Karacadag can be divided into three main stages: Early (∼11-6.6 Ma), Middle (∼6.6-1.2 Ma), and Late (0.4-0.1 Ma or less). During the Early Stage, olivine (ol) + clinopyroxene (cpx) + plagioclase (pl)-phyric lava flows with mostly subophitic texture erupted in the western sector of the volcano, creating an extensive plateau. Mantle xenoliths are occasionally present in these lavas. The Middle Stage can be divided into three units on the basis of the morphological aspects and petrography of the lavas: (a) plateau-forming ol+cpx+pl-phyric lavas (∼4-2.7 Ma); (b) ol+cpx+pl-phyric lavas comprising the main volcanic edifice (∼1.7-1.2 Ma; they also contain occasional mantle xenoliths), and (c) scoria cones extending broadly N-S at the summit of the volcanic edifice and also being scattered on its flanks (mostly ol+cpx-phyric plus rarer amphibole-bearing lavas). The Late Stage rocks are represented by young scoria cones, dykes and small volume ol+cpx-phyric lava flows.
More than 150 samples were collected, studied petrographically and analyzed for major and trace element contents. Most of the samples (>60%) are basalts (transitional to alkaline) with minor hawaiites (∼20%), basanites (∼20%) and very rare more evolved rocks (mugearites and benmoreites, <1%). Na2O/K2O ratios are all >2, while CIPW norms compositions range from SiO2-undersaturated (nepheline content ranging from ∼19 to 0.2%) to SiO2-saturated (hypersthene-ol normative). Except for a few benmoreites, no quartz-normative rocks have been found. Apart from a few MgO-rich samples (Mg# = 0.75-0.79), the whole-rock composition of the majority of the samples is compatible with magmas that experienced variable degrees of crystal fractionation of mafic phases (Mg# = 0.68-0.44; Cr = 460-40 ppm; Ni = 310-40 ppm). Positive correlation of Mg# with Cr-Ni indicates the importance of ol and cpx as fractionating phases, consistent with petrographic findings. The absence of correlation between Mg# and CaO/Al2O3 and Sr indicates the late onset of pl.
Primitive mantle-normalized patterns of most of the Karacadag rocks share some similarities with magmas emplaced in continental intra-plate settings like those belonging to the CiMACI Province (e.g. Nb-Ta and Zr-Hf peaks, and high Nb-Ta/LILE ratios). However, some of the Karacadag lavas show slightly negative anomalies at Nb-Ta, positive K and Pb anomalies, which are unusual for typical "anorogenic" or "intra-plate" magmas. These may be linked to interaction with crustal lithologies. Incompatible-incompatible trace element ratios (e.g., Zr/Nb, Zr/La, La/Ta) are rather homogeneous but the slight scatter could be again related either to heterogeneous mantle sources or to interaction with crustal lithologies at shallow depths.
Lustrino M., Wilson M., 2007. Earth-Sci. Rev., 81, 1-65