U-Pb ZIRCON DATING OF MIDDLE EOCENE CLASTIC ROCKS FROM THE GERCUS MOLASSE, NE IRAQ: NEW CONSTRAINTS ON THEIR PROVENANCE, AND TECTONIC EVOLUTION

Abstract

The provenance of Middle Eocene clastic rock from the Gercus Molasse, NE Iraq was determined by detrital zircon (DZ) U-Pb geochronology. The Gercus Molasse in the Iraqi segment of the north-eastern Zagros Thrust Zone provides an ideal example of foreland system evolution with respect to the transition from passive margin to the accretionary complex terrene-flexural foreland basins. The DZ U-Pb age spectra from the Gercus Molasse suggest that the foreland sediments either influx from multiple provenances or are the result of recycling from the accretionary complex terrane. During pre-accretion, however, the radiolarite basin (Qulqula Radiolarite, 221 Ma) located along Arabian passive margin likely acted as an intermediate sediment repository for most or all of the DZ. Representative DZ U-Pb measurements revealed that the Gercus clastic rocks fall into several separable age population ranges of 92-102 (Albian-Cenomanian), 221 (Upper Triassic), 395-511 (Cambrian), 570- 645 (Neoproterozoic), 1111 (Mesoproterozoic), and lesser numbers of Paleoproterozoic (1622-1991 Ma) ages. The source of Proterozoic detrital Zircons is enigmatic; the age peaks at 1.1, 1.5, 1.6, and 1.9 Ga (Proterozoic) does not correspond to any known outcrops of Precambrian rocks in Iraq, and it may be useful to continue to search for such basement. The detrital zircons with age populations at 0.63–0.86 Ga probably originated from the Arabian-Nubian Shield. The age peak at 0.55 Ga correlates with Cadomian Magmatism reported from north Gondwana. The age peaks at ~0.4 Ga is interpreted to represent Gondwana rifting and the opening of Paleotethys. The youngest ages populations at 93 Ma indicate that fraction of DZ were transported directly from the contemporaneously active magmatic arc (Zagros Ophiolite segments). The paleogeography and tectonic evolution of the Neogene Zagros foreland basin were reconstructed and divided into two tectonic stages. The early stage is defined by the Campanian accreted terranes (i.e. orogenic wedge) form loads sufficient to produce flexural basin with a deepest part is situated next to the tip of the loads. This flexural basin is filled by the flysch clastics of the Maastrichtian– Early Eocene (i.e. referred to by the Tanjero-Kolosh flysch sequence). The late stage is marked by a synchronized modification of the clastics fill of the basin and changes in dip directions to compensate for the reduction of the load by both erosion and extension and the basin, therefore, was sealed by a shallowing upwards depositional sequence ending with the terrestrial Gercus Formation.

Detrital zircon provenance record of the Zagros mountain building from the Neotethys obduction to the Arabia–Eurasia collision, NW Zagros fold–thrust belt, Kurdistan region of Iraq

“…The ∼ 240 Ma Triassic age signature in the detrital zircon records of the Amiran and Kashghan formations has been attributed to the mid-oceanic ridge based on the trace element data measured in zircon grains (Barber et al, 2019). Additionally, sandstone petrographic analysis on the Tanjero Formation revealed the occurrence of limestone and chert grains that were particularly sourced from the older Qulqula radiolarite and Balambo formations in the NW (Aziz and Sadiq, 2020;Jones et al, 2020;Çelik and Salih, 2021). Such variation in the sediment source for the proto-Zagros foreland basin is in line with (i) the destruction of the Gotnia Basin architecture, (ii) an input of carbonate material into the new flexural basin, and (iii) the occurrence of some recycled Paleozoic and older zircon grains in the Tanjero Formation (Aqrawi et al, 2010;English et al, 2015;Aziz and Sadiq, 2020;Jones et al, 2020).…”

“…Additionally, sandstone petrographic analysis on the Tanjero Formation revealed the occurrence of limestone and chert grains that were particularly sourced from the older Qulqula radiolarite and Balambo formations in the NW (Aziz and Sadiq, 2020;Jones et al, 2020;Çelik and Salih, 2021). Such variation in the sediment source for the proto-Zagros foreland basin is in line with (i) the destruction of the Gotnia Basin architecture, (ii) an input of carbonate material into the new flexural basin, and (iii) the occurrence of some recycled Paleozoic and older zircon grains in the Tanjero Formation (Aqrawi et al, 2010;English et al, 2015;Aziz and Sadiq, 2020;Jones et al, 2020). The younger Neogene Zagros foreland basin strata also have distinct U-Pb age spectra that are dissimilar to the proto-Zagros and the pre-Zagros U-Pb age distributions.…”

Neo-Tectonism and Quantitative Morphotectonic Analysis of Roste Valley at Imbricated-Suture Zones, Kurdistan Region, Iraq

“…During Paleocene and Eocene, the sheet thrusting continued toward the foreland onto the Arabian margin. Development of volcanic arc of Naopurdan Group and back-arc basins of the Walash group in (Paleogene) Paleocene and Eocene epoch (Aziz et al, 2021), with the magmatic activity which intrudes volcanic component and ashes into the existing deposits (Fig. 3d).…”

Sedimentary and mineralogy characteristics of late quaternary sediments, Garmian area, Kurdistan Region, NE Iraq

“…These minerals grains as occur angular to subrounded. Aziz & Sadiq (2020) stated that the presence of opaque grains, pyroxene, amphibole and, epidotes that derived from mafic to ultramafic igneous rocks and zircon grains are indicator of derivation from metamorphic and earlier igneous source. The variety of heavy minerals in quaternary sediment reflects the multiple sources of rock types, represented by the igneous, metamorphic and sedimentary rocks.…”