Late Eocene-Early Oligocene two-mica granites in NW Turkey (the Uludag Massif): Water-fluxed melting products of a mafic metagreywacke


Topuz G., Okay A.

LITHOS, vol.268, pp.334-350, 2017 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 268
  • Publication Date: 2017
  • Doi Number: 10.1016/j.lithos.2016.11.010
  • Journal Name: LITHOS
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.334-350
  • Keywords: Two-mica granite, Adakitic signature, Mafic metagreywacke, Sr-Nd-Pb isotopy, Strike-slip setting, NW Turkey, S-TYPE GRANITES, METAMORPHIC CORE COMPLEX, LACHLAN FOLD BELT, SOUTHWESTERN NORTH-AMERICA, HIGH-PRESSURE METAMORPHISM, ALKALINE VOLCANIC-ROCKS, SOURCE MATERIAL RESTITE, ISOTOPIC MIXING MODEL, WESTERN ANATOLIA, I-TYPE
  • Istanbul Technical University Affiliated: Yes

Abstract

This paper deals with the petrogenesis of two-mica granites within the amphibolite-facies metamorphic rocks in the Uludag Massif (NW Turkey). The two-mica granites are represented by three different types (i) a similar to 17 km long and similar to 1.5 km-wide strongly foliated and lineated metagranite, (ii) a relatively younger circular granite, similar to 11 km by similar to 6.5 km, free of any penetrative fabric, and (iii) up to 5 m thick dikes of unfoliated granite porphyries. Mineral constituents include quartz, plagioclase, microcline, biotite, muscovite and minor apatite, zircon, ilmenite and monazite. U-Pb zircon dating indicates that the metagranite was emplaced at 35 +/- 1 Ma (2 sigma, latest Eocene) and the unfoliated granite at 28 +/- 1 Ma (2 sigma) (Early-Late Oligocene boundary). Overall, the two-mica granites are characterized by (i) a restricted bulk composition (SiO2 similar to 70-76 wt.%), (ii) near-linear to linear inter-element variations, (iii) high concentrations of Al2O3, Sr, Ba, LREEs, and low abundances of Rb, Y, Sc and HREEs, comparable with adakitic rocks, (iv) variably pronounced concave-upward shape of HREEs and absent to feeble Eu anomaly, (v) relatively high Na2O, CaO and Sr, and lower K2O and Rb contents at identical silica contents relative to the classical S-type granites. Sr-87/Sr-86((i)) and epsilon Nd-(i) values range from 0.7052 to 0.7080, and 0.7 to -3.6, respectively. The Pb-206/Pb-204((i)) values range from 18.23 to 18.69, Pb-207/Pb-204((i)) from 15.63 to 15.70 and Pb-208/Pb-204((i)) from 38.48 to 38.77. Sr-87/Sr-86((i)) and epsilon Nd-(i), and epsilon Nd-(i) and Pb-207/Pb-204((i)) values are negatively correlated. Isotopic variation and negative correlations can best be explained by a heterogeneous source, including an older crustal component and a more juvenile basic component. Magma temperatures are estimated as 754-790 degrees C based on zircon and monazite saturation. All these features such as (i) relatively Na-, Ca- and Sr rich compositions, (ii) isotopically heterogeneous source with inferred residual phases such as garnet and hornblende, (iii) occurrence in a ductile strike-slip zone, and (iv) relatively low magma temperatures can be accounted for by water-fluxed-melting of a metagreywacke source with substantial mafic component at middle to lower crustal depths. (C) 2016 Elsevier B.V. All rights reserved.