Nilgün Güleç

Helium isotope variations in Turkey: relationship to tectonics, volcanism and recent seismic activities

The distribution of helium isotope ratios in the various tectonic provinces of Turkey is examined through a synthesis of previously published data and the results of a recent survey along the North Anatolian Fault Zone (NAFZ) following the catastrophic 1999 earthquakes. The R/RA values (where R=sample 3He/4He and RA=air 3He/4He) cover a wide range from 0.05 to 7.87, and the mantle-derived helium is clearly identified in most locations. The mantle-derived component is high (>50% of total He) in (a) regions of central and eastern Anatolia, both of which are associated with historically active volcanoes, and (b) the seismically active west-to-central segment of NAFZ. While the mantle contribution reaches a maximum at Nemrut volcano in eastern Anatolia—a region of dominantly compressional tectonics and with moderate enthalpy geothermal fields, it is relatively low (<50%) in the western Anatolian extensional province even though this region has the highest geothermal potential. The average 3He/enthalpy ratios estimated for the different provinces suggest lithospheric stretching and rise of the geotherm as the major mechanism of high heat flow, yet limited intrusive activity in western Anatolia is suggested as the reason for the comparatively low He additions and consequently low (1.7×106 atoms/J) 3He/enthalpy ratios. A more extensive magmatic activity appears to be responsible for the greater input of both heat and helium in eastern and central Anatolia, with intra-province 3He/enthalpy variations (from 3.1×106 atoms/J in eastern to 0.25×106 atoms/J in central Anatolia) reflecting the ageing of hydro-magmatic systems. The relatively high 3He concentrations in low enthalpy waters of northern Anatolia (2.8×106 atoms/J) are particularly significant since there is no evidence of volcanic activity associated with the strike–slip motion along the seismically active segment of NAFZ. Continuous monitoring of He-isotope compositions along NAFZ should lead to a better understanding of this apparent anomaly, as well as the relationship (if any) between He-isotope variations and seismic activities in this region.

Tertiary volcanism of the Galatia province, north-west Central Anatolia, Turkey

Abstract Large volumes of trachyandesitic-dacitic lava flows and pyroclastics of Miocene age are associated with small volumes of alkali basalt lava flows in the Galatia volcanic province, northwest Central Anatolia, Turkey. The volcanism postdates continental collision, occurring in a transtensional tectonic setting associated with movement along the North Anatolian Fault zone. Major and trace element (including REE) and Sr-Nd isotope data and K-Ar ages for representative samples of mafic-intermediate volcanic rocks have been obtained from a series of localities within the province. The K-Ar age data indicate that alkali basalts were erupted during two distinct time periods in the Early Miocene (17–19 Ma) and Late Miocene (

Tectonomagmatic Evolution of Bimodal Plutons in the Central Anatolian Crystalline Complex, Turkey

The NW‐trending Agaçören Intrusive Suite (AIS) on the east side of the Salt Lake (Tuz Gölü), Turkey, is part of a curvilinear volcanoplutonic complex along the western edge of the central Anatolian crystalline complex (CACC). Granitoids constitute the predominant lithological group within the AIS and range in composition from monzonite through granite to alkali feldspar granite. Gabbroic rocks occur as irregular intrusive bodies with sinusoidal, irregular contacts with the granitoid plutons and vary from dioritic compositions at the contacts to cumulate amphibole gabbros in their center. These gabbroid to granitoid rocks are all subalkaline and display tholeiitic to calcalkaline affinities, respectively. Modeling of the major element and trace element chemistry of the granitoids to gabbroids, together with their field relations, suggest that these rocks formed synchronously from a melt source that involved both mantle and crustal components. Mafic magmas were likely derived from a metasomatized upper mantle source above a subduction zone and were injected into crustal‐level felsic magma chamber(s) in which incomplete mixing, commingling, and crystal fractionation processes produced the coeval granitoid to gabbroid plutons. New 40Ar/39Ar ages at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Structure of the Galatean Volcanic Province, Turkey

78.0\pm 0.3

Geochemistry of thermal waters and its relation to the volcanism in the Kizilcahamam (Ankara) area, Turkey

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Volcanostratigraphy and petrogenesis of the Nemrut stratovolcano (East Anatolian High Plateau): The most recent post-collisional volcanism in Turkey

78.8\pm 1.0