An abnormally odd and rare occurrence of a basaltic body has been discovered in the middle of the Gercus Formation within the large, double-plunging NW-SE trending Bekhair Anticline to the north of Duhok city, northern Iraq. This is the first discovery of such a volcanic body within the widely exposed Gercus Formation in northern Iraq, southeastern Turkey, and western Iran.
Turkish Journal of Earth Sciences Turkish J Earth Sci (2018) 27: 460-491 © TÜBİTAK doi:10.3906/yer-1803-11 http://journals.tubitak.gov.tr/earth/ Research Article Petrogenesis, geochemistry, and tectonic setting of a basaltic body within the Gercus Formation of northern Iraq: first record for Eocene anorogenic volcanic activity in the region 1,2, Yawooz A KETTANAH *, Adnan H BAMARNI Department of Applied Geosciences, Faculty of Spatial Planning & Applied Science, University of Duhok, Duhok, Iraq Department of Earth Sciences, Faculty of Graduate Studies, Dalhousie University, Halifax, Nova Scotia, Canada Received: 10.03.2018 Accepted/Published Online: 09.08.2018 Final Version: 30.11.2018 Abstract: An abnormally odd and rare occurrence of a basaltic body has been discovered in the middle of the Gercus Formation within the large, double-plunging NW-SE trending Bekhair Anticline to the north of Duhok city, northern Iraq This is the first discovery of such a volcanic body within the widely exposed Gercus Formation in northern Iraq, southeastern Turkey, and western Iran This volcanic body, named by the authors the Gercus Basalt, has a long tabular/lenticular shape with a total length of ~4.5 km and a thickness ranging between to 16 m It is exposed on both limbs of the anticline and has a conformable relation with the terrigenous beds of the Gercus Formation The basalt is greenish to grayish black in color, vesicular, amygdaloidal and porphyritic in texture, and consists of feldspar (Ab85An2Or13), pyroxene (Wo49En40Fs11), olivine (Fo87.2–Fa12.6–Tp0.2), and their alteration products Postemplacement hydrothermal fluids resulted in pervasive alteration of the Gercus Basalt and introduction of copper mineralization filling joints, fractures, and adjacent vesicles The alteration processes are dominated by calcitization, zeolitization, serpentinization, chloritization, silicification, iddingsitization, and copper mineralization Seventeen basalts have been analyzed for 63 major and trace elements including REEs and PGEs The Gercus Basalt has very similar geochemical compositions to that of OIB Excluding Cr, Co, Ni, and PGEs, it is enriched in all other analyzed major and trace elements relative to primitive mantle The chondrite-normalized distribution of REEs shows a smooth pattern, high La/Yb(N) ratio of 23, and LREE enrichment relative to HREE, indicating alkaline magmatic origin The studied rocks are basanites, alkaline basalts, melanephelinites, and picrites with an OIB-like anorogenic geochemical signature The Gercus Basalt was derived from amphibole-bearing garnet-lherzolite subcontinental asthenospheric mantle, enriched with silicate metasomatism Key words: Gercus Formation, petrology, geochemistry, anorogenic volcanism, basanite Introduction Volcanic activities have not been previously reported in the area where the currently studied basaltic body is described in this study The studied area is characterized by sedimentary formations ranging in age between Late Campanian and Recent The newly discovered basaltic body has been named the Gercus Basalt, referring to its location within the Gercus Formation (Middle Late Eocene), which is one of the widely exposed formations in N‒NE Iraq and neighboring Turkey and Iran The volcanic units closest to the studied basalt, are located some 150– 250 km to the east on the border of Iraq and Iran, which is part of the Paleogene ophiolites (Figure 1a) of the Iraqi Zagros Suture Zone (Ismail et al., 2014) For this reason, the Gercus Basalt is considered here as a rare and odd occurrence Other than the ophiolites of northeastern Iraq bordering Iran, there are only two other small-scale volcanic occurrences, some ~300–320 km southeast of the study area and ~100 km northeast of Baghdad, within the southern part of Hemrin South Mountain, which is part of the low-folded zone of Iraq (Figure 1a) These are the Hemrin Basalt and Zarloukh Tuff studied by Abdulrahman (2016) and El-Khafaji (1989), respectively The Hemrin Basalt occurs as very thin cap (0.1 and Ba/Rb of