Provenance of northern Gondwana Lower Ordovician sandstones (Khabour Formation, northern Iraq) revealed by detrital zircon using LA-ICP-MS dating

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 similar to 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.

Automated summary

Zircon U/Pb provenance data from mature quartz arenites and subarkosic sandstones of the Lower Ordovician Khabour Formation in northern Iraq show predominant Neoproterozoic, Mesoproterozoic, Palaeoproterozoic, and Archean ages, indicating major magmatic events associated with the assembly of northern Gondwana. Additionally, the presence of Cryogenian-Ediacaran ages suggests the unroofing of late-stage granitic rocks from the Arabian-Nubian Shield, while the absence of zircons younger than 490 Ma indicates deposition on the distal shelf of the northern Gondwana passive margin.