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

Abstract

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 (<30 cm thick) on top of a few isolated, linearly arranged hills parallel to the axis of the Hemrin South Anticline, which was previously called burnt hills by Basi (1973) and Basi and Jassim (1974). The Zarloukh Tuff exists as flat-lying beds (~3 m thick) alternating with bentonized horizons filling a few closely spaced depressions exposed on top of the Muqdadiya (Lower Bakhtiari) Formation. The aim of this work is to report the first occurrence of a prominent volcanic body in the Gercus Formation and the surrounding area and to study these basaltic rocks 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 1 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 (Ab 85 An 2 Or 13), pyroxene (Wo 49 En 40 Fs 11), olivine (Fo 87.2-Fa 12.6-Tp 0.2), 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,...

Timing of the Arabia-Eurasia continental collision—Evidence from detrital zircon U-Pb geochronology of the Red Bed Series strata of the northwest Zagros hinterland, Kurdistan region of Iraq: REPLY

“…Furthermore, the recently reported Gercus Basalt is considered to be a superficial lava flow and syndepositional in age with no crosscutting relationship (Kettanah and Bamarni, 2018). Mohammad and Karim did not provide any citation for their statement, but we assume they meant the Gercus Basalt in Kettanah and Bamarni (2018). Our results show that the youngest zircon grains from the Red Bed Series (RBS) are found in the lower Suwais unit rather than in the upper Merga unit.…”

“…Therefore, consideration of the Suwais unit as an equivalent of the Gercus Formation can not be precise. Furthermore, the recently reported Gercus Basalt is considered to be a superficial lava flow and syndepositional in age with no crosscutting relationship (Kettanah and Bamarni, 2018). Mohammad and Karim did not provide any citation for their statement, but we assume they meant the Gercus Basalt in Kettanah and Bamarni (2018).…”

Petrography and geochemistry of siliciclastic rocks of the Middle Eocene Gercus Formation, northern Iraq: Implications for provenance and tectonic setting

“…The most unusual characteristic of Gercus Formation in the study area unlike anywhere else in northern Iraq and the surrounding parts of southeastern Turkey and northwestern Iran where the formation is widely exposed, is the occurrence of a prominent basaltic body in its central part called Gercus Basalt. This basalt is 4.5 km long and 1-16 m thick, exposed in the middle of the formation within the Bekhair anticline, which was discovered and studied in detail by Kettanah and Bamarni (2018) and Kettanah (2019) (Figure 1b-d). The dolomitic limestone beds are mostly <1 m thick, micritic in texture and contain microfossils such as foraminifers, and contain sporadically distributed grains of chert, quartz, and iron oxides.…”

“…The conglomerate beds are very hard, dark grey in colour and made up dominantly of few millimetres to few centimetres coarse chert and carbonate grains cemented by silica and carbonates. Such conglomerate beds are few in number but attain considerable thickness of up to 20 m in other locations such as those near the village of Briefca to the east of the study area where it occurs within the Gercus Formation, F I G U R E 1 (a) Generalized tectonic map of Iraq showing the location of the study area (after Fouad, 2015; taken from Kettanah & Bamarni, 2018); (b and c) Google Earth map showing the Bekhair Anticline and the exposed formations in the eroded core including the Gercus Formation (taken from Kettanah & Bamarni, 2018); (d) Field view of the Gercus Formation including the Gercus Basalt at the northeastern limb of the anticline [Colour figure can be viewed at wileyonlinelibrary.com] and also near the town of Shaqlawa where it forms a 16-m-thick bed at the top of the Gercus Formation separating it from the overlying carbonates of the Pila Spi Formation.…”

Hydrogeochemical Characteristics and Genesis of the Chazi Geothermal Field Area in Tibet

“…The Na + /Cl − ratio is considerable higher than 1 (Table 3), indicating strong dissolution and filtration in groundwater [37,38]. Hot water exhibits strong dissolution for the surrounding rocks during upwelling, enabling Na + , K + , and Ca 2+ in the potash feldspar and plagioclase to migrate into the hot water [10,39]. The pH of the geothermal fluid was 7.83-7.93, a range in which the carbonic acid balance favoured HCO 3…”