Geochemistry of mafic Anatolian lavas: Geochemical insight on ancient continental assembly and break-up

Open Access
Author:
Pickard, Megan
Graduate Program:
Geosciences
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
September 14, 2015
Committee Members:
  • Tanya Furman, Dissertation Advisor
  • Tanya Furman, Committee Chair
  • Maureen Feineman, Committee Member
  • Kevin Patrick Furlong, Committee Member
  • Robert George Crane, Committee Member
Keywords:
  • basalt petrogenesis
  • Anatolian geodynamics
  • trace element geochemistry
  • radiogenic isotope geochemistry
Abstract:
This dissertation provides in-depth analysis of major and trace element and Sr-Nd-Pb-Hf isotope compositions of mafic lavas in the Anatolian province. I combine incompatible and fluid-mobile trace elements and radiogenic lithophile isotope compositions to interpret the genesis of Sivas, Central Anatolia mafic lavas and the source components for mafic lavas throughout the Anatolian-circum-Mediterranean region. The data provide insight into the long-term (~1.8 Ga) geologic and tectonic history of the area. I use major and trace element compositions of Sivas mafic lavas to define two groups with contrasting petrogenetic histories. The first group is comprised of basalts and basaltic trachyandesites. Their low Ba/Nb, La/Nb, and Th/Nb values are similar to those observed in mantle-derived basalts and suggest they are derived from an asthenospheric mantle-dominated source. The second group are basanites that are enriched in incompatible trace elements relative to mid-ocean ridge basalts and have high Ba/Nb, La/Nb, and Th/Nb values indicative of a source in metasomatized sub-continental lithosphere containing hydrous phases such as amphibole. I also use the major element compositions of clinopyroxene phenecrysts in the mafic lavas to constrain the pressures of melting and differentiation for Sivas mafic lavas. Specifically clinopyroxene Al contents of the basaltic group suggest crystallization both at lower crustal depths (~10 kb) and at near-surface pressures. In contrast, basanite clinopyroxene indicate only one stage of crystal growth at around 5-8 kb prior to eruption. Sr-Nd-Hf-Pb isotope compositions of Sivas mafic lavas support and expand on the trace element findings. As seen in trace element compositions, the basaltic group consistently records higher asthenospheric contributions while the basanites with more radiogenic Sr and Pb low Nd isotope values originate from magmas with higher contributions from metasomatized sub-continental lithosphere. The Pb isotope signatures also record pseudo-binary mixing between shallow depleted asthenosphere, a regionally heterogeneous lithosphere, and a common mantle source with the isotopic characteristics of the C component or the circum-Mediterranean asthenosphere to form Sivas magmas. Calculated Nd model ages relative to depleted mantle indicate the incorporated lithosphere stabilized from the mantle between 1.8 and 1.2 Ga corresponding to assembly of Rodinia and Columbia supercontinents. Variations in source contributions and lithosphere stabilization ages appear to correlate with the geographic location of a modern strike-slip fault along the Kızılırmak River in the Sivas Basin, suggesting that Sivas mafic lavas record contributions from distinct lithospheric packages that are juxtaposed across a major crustal suture. One important implication of this result is that the oft-invoked subduction modification of mantle source regions contributing to Anatolian volcanism is not related to the more recent Miocene closure of Africa and Eurasia, but rather is an ancient inherited feature that has been present for an extended period of time. This dissertation also gives insight on science education and focuses on evidence for progression of knowledge with age and importance of targeted teaching. Science concepts for each grade level are intended to build on content learned in previous grades with the idea that students transition from a very simple to a very complex understanding of Earth and Space science by high school graduation.