Detrital zircon U-Pb and (U-Th)/He double-dating of Upper Cretaceous-Cenozoic Zagros foreland basin strata in the Kurdistan Region of northern Iraq

Tuesday, 16 December 2014
Douglas Edward Barber, University of Texas at Austin, Department of Geological Sciences, Austin, TX, United States, Daniel F Stockli, University of Texas, Austin, TX, United States, Renas I Koshnaw, University of Texas at Austin, Austin, TX, United States, Brian K Horton, University of Texas at Austin, Department of Geological Sciences and Institute for Geophysics, Austin, TX, United States, Mazin Y Tamar-Agha, University of Baghdad, Baghdad, Iraq and Jerry J Kendall, ExxonMobil Exploration Company, Houston, TX, United States
The NW Zagros orogen is the result of the multistage collisional history associated with Late Cretaceous-Cenozoic convergence of the Arabian and Eurasian continents and final closure of Neotethys. Siliciclastic strata preserved within a ~400 km segment of the NW Zagros fold-thrust belt and foreland basin in the Iraqi Kurdistan Region (IKR) provide a widespread record of exhumation and sedimentation. As a means of assessing NW Zagros foreland basin evolution and chronostratigraphy, we present coupled detrital zircon (DZ) U-Pb and (U-Th)/He geo-thermochronometric data of Upper Cretaceous to Pliocene siliciclastic strata from the Duhok, Erbil, and Suleimaniyah provinces of IKR. LA-ICP-MS U-Pb age analyses reveal that the foreland basin fill in IKR in general was dominantly derived from Pan-African/Arabian-Nubian, Peri-Gondwandan, Eurasian, and Cretaceous volcanic arc terrenes. However, the provenance of these strata varies systematically along strike and through time, with an overall increase in complexity upsection. DZ age distribution of Paleocene-Eocene strata is dominated by a ~95 Ma grain age population, likely sourced from the Late Cretaceous Hassanbag-Bitlis volcanic arc complex along the northern margin of Arabia. In contrast, DZ U-Pb age distributions of Neogene strata show a major contribution derived from various Eurasian (e.g., Iranian, Tauride, Pontide; ~45, 150, 300 Ma) and Pan-African (~550, 950 Ma) sources. The introduction of Eurasian DZ ages at the Paleogene-Neogene transition likely records the onset of Arabian-Eurasian collision. Along strike to the southeast, the DZ U-Pb spectra of Neogene strata show a decreased percentage of Pan-African, Peri-Gondwandan, Tauride, and Ordovician ages, coupled with a dramatic increase in 40-50 Ma DZ ages that correspond to Urumieh-Dokhtar magmatic rocks in Iran. Combined with paleocurrent data, this suggests that Neogene sediments were transported longitudinally southeastward through an unbroken foreland basin system and progressively diluted downstream by detritus shed from the Iranian Plateau. Combined (U-Th)/He dating of DZ grains derived from the Hassanbag-Bitlis complex documents a major tectonothermal event at ~75 Ma, corresponding to the timing of proto-Zagros uplift and initial basin development in IKR.