Silurian A-type metaquartz-syenite to -granite in the Eastern Anatolia: Implications for Late Ordovician-Silurian rifting at the northern margin of Gondwana


Topuz G. , CANDAN O., Wang J., Li Q., Wu F., YILMAZ A.

GONDWANA RESEARCH, cilt.91, ss.1-17, 2021 (SCI İndekslerine Giren Dergi) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 91
  • Basım Tarihi: 2021
  • Doi Numarası: 10.1016/j.gr.2020.12.005
  • Dergi Adı: GONDWANA RESEARCH
  • Sayfa Sayıları: ss.1-17

Özet

The Anatolide-Tauride block in the Tethyan belt represented passive northern continental margin of Gondwana throughout Paleozoic time. In this paper, we report on a relatively large amphibolite-facies metaquartz-syenite to -granite complex (similar to 60 km(2)) in the Eastern Anatolia, the easternmost part of the Anatolide-Tauride block. Igneous textures in the metaintrusive complex are variably preserved. The preserved igneous minerals include mesoperthite + quartz +/- aegirine-augite +/- sodic amphibole +/- calcic amphibole +/- biotite and +/- allanite. Mesoperthite is the sole feldspar in well-preserved igneous textures, suggesting hypersolvus nature of the original quartz syenite to granite. In the well-recrystallized samples, mesoperthite is partially or totally replaced by discrete grains of plagioclase and K-feldspar. U-Pb dating on igneous zircons from three samples yielded Silurian igneous crystallization ages (430-440 Ma). All rock types have typical geochemical characteristics of A-type syenite to granite with relatively high abundances of FeO*, Na2O, K2O, Nb, Ga, Zr, Ce, and Zn, and low abundances of MgO, CaO and Sr, resulting in high ratios of Fe/Mg and Ga/Al. Geochemical features such as (i) the absence of negative Nb-Ta anomalies on multielement variation diagrams, (ii) the enrichment of Nb and Ce relative to Y, and (iii) Y/Nb, Yb/Ta and Ce/Nb ratios similar to those in ocean island basalts point to A(1)-type syenite and granite which are thought to be differentiates of ocean island basaltic magmas. Estimated magma temperatures based on zirconium saturation range from 850 to 990 degrees C, indicating derivation of the original quartz syenite and granite from high-temperature juvenile magmas. Initial epsilon Hf values of the igneous zircons from two samples are 2.59 +/- 1.14 and 2.30 +/- 1.29, while delta O-18 values of the zircons range from 5.41 to 7.32 parts per thousand with a median of 6.50 +/- 0.48 parts per thousand. All these isotopic characteristics suggest that the quartz syenite to granite were derived from high-temperature mantle magmas with insignificant crustal assimilation. The Late Ordovician-Silurian A-type igneous rocks in the northern part of the Anatolide-Tauride block were probably related to a rifting event at the northern margin of Gondwana, leading to the opening of the Paleo-Tethys. This interpretation is also supported from (i) regional geological features of the Early Paleozoic sedimentary successions suggestive of extensional setting during the Late Ordovician-Silurian, (ii) the presence of Silurian anorogenic magmatism in continental blocks detached from Gondwana during Early Paleozoic time, and (iii) the presence of Silurian deep sea sedimentary blocks in Paleo-Tethyan accretionary complexes. (C) 2020 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.