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We present new zircon U/Pb provenance data using laser ablation induced coupled plasma mass spectroscopy (LA‐ICP‐MS) for eight samples of mature quartz arenites and subarkosic sandstones of the Lower Ordovician Khabour Formation, northern Iraq, to establish their depositional age and provenance. The samples were collected from thin‐ to medium‐bedded sandstones along profiles of the Chalky Nasara and Ora sections. Most analysed detrital zircon analyses are concordant within 100 ± 10% and include a prevalence of Proterozoic over Archean ages. Collectively, the data can be divided into four main age groups: (a) Neoproterozoic ages, 570–1,000 Ma (58%); (b) Mesoproterozoic ages, 1,000–1,500 Ma (10%); (c) Palaeoproterozoic ages, 1,620–2,480 Ma (21%); and (d) Archean ages, 2,500–3,300 Ma (11%). The predominance of Cryogenian–Ediacaran ages (850–550 Ma) reflects major magmatic events associated with the assembly of northern Gondwana. The major age group at ~600 Ma likely represents the unroofing of late‐stage granitic rocks from the Arabian‐Nubian Shield. The lack of zircons younger than 490 Ma suggests that Lower Ordovician sandstones in northern Iraq were probably deposited on the distal shelf of the northern Gondwana passive margin and were not influenced by rifting and magmatism in northern Gondwana caused by the opening of Palaeo‐Tethys. Diagenetic xenotime overgrowths are common on detrital zircon grains, but radiometric dating of these was not possible. [ABSTRACT FROM AUTHOR]

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Quartz cements of the quartz arenitic sandstones from the Chalky Nasara and Ora sections of the (Devonian-Carboniferous) Ora Formation in northern Iraq have been studied. A combination of hot cathodoluminescence, LA-ICP-MS, and fluid inclusion microthermometry revealed three syntaxial quartz cement generations (Q1, Q2, and Q3). The early Q1 cementation has gray to slightly brown luminescences, postdated compaction, and reduced intergranular porosity associated with illite formed during eogenesis. Q2 is characterized by dark brown luminescence overgrowths and is more voluminous in the thinly bedded sandstones than in the thickly bedded sandstones filling most of the remaining pore space during mesogenesis. Q3 was formed during the early telogenesis stage fully cementing the sandstones and the fractures were filled by hydrothermal chlorite and sulfides. Significant amounts of trace elements Al, Li, Ge, and Fe have been detected in quartz overgrowths. Al varies consistently between each cement with averages of 7125, 4044, and 2036 ppm for the Q1, Q2, and Q3 generations, respectively. A strong linear correlation between Al and Li in the three quartz cements with an average Li/Al of ~0.02 in Q1 and Q2 indicates sufficient availability of both Al and Li where Li is most likely to be found in highsaline pore waters. Illite is the most probable origin of Li since high salinities favor the mobilization of Li during diagenesis. Germanium concentrations in quartz cements are slightly less than that in the detrital quartz of the Ora Formation, indicating that the pressure dissolutions of quartz and feldspar are the dominant sources of cementation in the Ora Formation. Homogenization temperatures of fluid inclusions indicate precipitation of the Q1, Q2, and Q3 cement generations at temperature ranges of 155-160 °C, 160-166 °C, and 168-178 °C, respectively, with salinities ranging between 5.0 and 6.4 wt.% NaCl equiv., as an indication of hydrothermal burial conditions for Q3 cement, which was affected by the major Zagros Thrust Zone faulting. [ABSTRACT FROM AUTHOR]