DBPapers
DOI: 10.5593/sgem2012/s01.v1009

GEOCHRONOLOGY AND SR-ND-PB ISOTOPE GEOCHEMISTRY OF EOCENE MAFIC VOLCANISM IN NW ANATOLIA: CONSTRAINTS ON PETROGENESIS AND MANTLE SOURCE CHARACTERISTICS

S. ALTUNKAYNAK
Wednesday 1 August 2012 by Libadmin2012

References: 12th International Multidisciplinary Scientific GeoConference, www.sgem.org, SGEM2012 Conference Proceedings/ ISSN 1314-2704, June 17-23, 2012, Vol. 1, 75 - 82 pp

ABSTRACT

Early to Late Eocene magmatic activity produced mafic to intemediate lavas, dikes,
pyroclastic rocks and coeval granitic intrusions, forming E-W trending magmatic belt
in north of Izmir-Ankara suture zone (NW Anatolia). This study reports new 40Ar/39Ar
geochronology, major-trace element geochemistry and Sr-Nd-Pb isotope data from
Eocene mafic lavas and dikes of this magmatic belt in order to constrain mantle source
charateristics and evolution of mafic volcanism beneath NW Anatolia. Ranging from
basalt, basaltic andesite to basaltic trachyandesite, mafic dikes and lavas include both
calc-alkaline and transitional (calc-alkaline to tholeiitic) affinity. They are slightlymoderately
enriched in large ion lithophile elements and light rare earth elements with
respect to high field strength elements and show negative Nb, Ta, and Ti anomalies
typical of subduction related magmatic suites. Basaltic lavas and dikes are characterized
by 87Sr/86Sr(i) compositions ranging from 0.70530 to 0.70415, positive εNd (2.7-6.6)
and restricted Pb-isotope compositions (206Pb/204Pb:18.6-18.7, 207Pb/204Pb:15.6-15.66
and 208Pb/204Pb: 38.60-38.87). The 40Ar/39Ar cooling ages (37.8-41.1 Ma) obtained from
this study combined with radiometric ages from literature indicate that mafic volcanism
was dominant between early and late Eocene.
40Ar/39Ar ages, geochemistry and Sr-Nd-Pb isotope data indicate the involment of a
depleted (MORB-like) mantle modified by earlier subduction event(s) in the genesis of
Eocene basaltic lavas and dikes. The break-off of Neotethyan slab may have caused the
rise of asthenospheric mantle below NW Anatolia, resulting in a linear zone of
asthenospheric upwelling in the study area.

Keywords: NW Anatolia, Geochronology, isotope geochemisty, mafic dikes, Eocene

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