K-Ar dating, petrography, and geochemistry of diabase dikes from Sidakan area, northeastern Iraq: Implications for petrogenesis and Neotethyan tectonics

Abstract

This study presents petrography, geochemistry, mineral chemistry and geochronology of diabase dikes from Sidakan area, northeastern Iraq. The area consists of basalts and diabase dikes alternating with sedimentary rocks, hosted by Walash Metavolcanic Group (WMG) as part of the Zagros Fold-Thrust Zone (ZFTZ). These rocks are dark grey to pale brown in color, fine to medium in grain size, and have ophitic and porphyritic textures. They consist of plagioclase and clinopyroxene as essential minerals and minor olivine as well as their alteration and low-grade metamorphism products including amphibole, albite, epidote, chlorite, serpentine, calcite and sericite, with ilmenite as an accessory mineral. The diabase dikes consist (as average wt.%) of 51.41 SiO2, 15.82 Al2O3, 9.95 FeOt, 6.58 MgO, 9.63 CaO, 3.42 Na2O, 0.87 TiO2, 0.17 MnO, 0.35 K2O, 0.09 P2O5, and 1.92 LOI. The Harker diagrams indicate that the diabases were formed from fractional crystallization of tholeiitic parent magma. The classification diagram Nb/Y vs. Zr/TiO2 indicated that the studied diabases have affinities of subalkaline basalts, while the SiO2 vs. K2O diagram showed that they are divided between the low-K basalt and basaltic andesite. The tectonic discriminant diagrams show that the diabases are oceanic island-arc tholeiites with N-MORB geochemical affinities. The K − Ar age of the diabases is Late Eocene (Bartonian-Priabonian) ranging between 34.6 ± 0.84 to 39.2 ± 1.81 Ma representing their intrusion/crystallization age and possibly the age of the formation of Oceanic Island Arc and/or the initial collision stage between the Arabian-Iranian microplates.

Keywords

• Diabase
• Walash Metavolcanic Group (WMG)
• K-Ar geochronology
• Geochemistry
• Petrography
• NE-Iraq