Petrology, Geochronology and Tectonic Setting of Early Triassic Alkaline Metagabbros From the Eastern Pontide Orogenic Belt (NE Turkey): Implications for the Geodynamic Evolution of Gondwana's Early Mesozoic Northern Margin


EYÜBOĞLU Y. , Dudas F. O. , Chatterjee N., Santosh M., BILLOR M. Z. , Yuva S.

TECTONICS, vol.37, no.9, pp.3174-3206, 2018 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 37 Issue: 9
  • Publication Date: 2018
  • Doi Number: 10.1029/2017tc004837
  • Title of Journal : TECTONICS
  • Page Numbers: pp.3174-3206
  • Keywords: alkaline, Triassic, riebeckite, Gondwana, rifting, Karakaya, PB ZIRCON CHRONOLOGY, KARAKAYA COMPLEX, CONTINENTAL-MARGIN, MAGMATIC ARC, SUBDUCTION, GEOCHEMISTRY, PETROGENESIS, TEMPERATURE, BASIN, INTRUSIONS

Abstract

The Triassic geodynamic evolution of the Pontides Belt, which geographically corresponds to northern Anatolia, is still a matter of debate. We present and interpret geological, petrographical, geochemical, and geochronological data from small, discordant, metagabbroic rocks exposed in the Tokat Massif. Field and petrographic characteristics distinguish four subgroups: (i) medium-grained, slightly lineated, clinopyroxene-rich metagabbros; (ii) fine-grained, nonlineated, clinopyroxene-rich metagabbros; (iii) medium-grained, nonlineated, brown amphibole-rich metagabbros; and (iv) medium-grained, slightly lineated, brown and blue amphibole-rich metagabbros. Magmatic kaersutites give Ar-39/Ar-40 plateau ages of 244.60.5 and 243.160.92Ma and overlap the U-Pb age of titanite from a clinopyroxene-rich sample. Inherited zircons (similar to 460, similar to 880, and similar to 2600Ma) in fine-grained clinopyroxene-rich metagabbros indicate interaction with a range of crustal rocks during the intrusion. The blue amphiboles are magnesioriebeckites that formed during metamorphism or late-stage crystallization. Geochemical data, including whole rock major and trace element concentrations, and Sr-Nd-Pb isotope compositions reveal that both clinopyroxene- and amphibole-rich metagabbros are alkaline in composition but derived from distinct mantle sources. They are compositionally distinct from mafic igneous rocks in the contemporaneous Permo-Triassic Karakaya Complex that is well exposed in the western part of the Pontides Belt. Considering all data, we suggest that the Pontides Belt was shaped above a south dipping subduction zone during Permo-Triassic and the alkaline gabbros that were emplaced into crustal rocks during Early Triassic back-arc rifting of the northern margin of Gondwana.