The Proto‐Zagros Foreland Basin in Lorestan, Western Iran: Insights From Multimineral Detrital Geothermochronometric and Trace Elemental Provenance Analysis

Abstract

Detrital zircon (DZ) U‐Pb geochronology is a widely used provenance tool that leverages bedrock age signatures of hinterland source terranes. However, complex sediment recycling of multicycle zircon and hinterland provinces with nondiagnostic U‐Pb ages represent possible pitfalls for provenance reconstructions. Additional biases pertain to source rock zircon fertilities and insensitivity to low‐ and medium‐grade tectonothermal events that do not result in zircon generation. To bridge these inherent biases and gaps in DZ U‐Pb provenance data sets and derive more comprehensive tectonic reconstruction, this study combined U‐Pb and trace element analyses on DZ, apatite, and rutile as well as zircon (U‐Th)/He analyses from the Proto‐Zagros foreland basin in western Iran to shed light on Late Cretaceous tectonic accretion along Arabia. Integrated multimineral, multimethod data sets record formation of a 110‐ to 85‐Ma island arc within Triassic mid‐oceanic ridge crust of the Neotethys ocean, simultaneous obduction starting in Santonian‐Early Campanian times, and inversion of the Arabian rift margin. Overall, integration of these techniques constrains provenance based on multiple independent criteria including crystallization age, cooling history, and petrogenic‐geodynamic environment. This approach not only more completely described provenance signatures but also helped avoid significant pitfalls. For example, while Triassic DZ U‐Pb ages might be mistaken as input from Eurasia, zircon trace element analysis reveals a MORB signature and attributes these DZ to Neotethyan oceanic rather than Eurasian continental origin, having fundamentally different paleogeographic/tectonic implications for the Arabia‐Eurasia collision. Moreover, detrital rutile and apatite resolve and characterize multiple Paleozoic‐Mesozoic thermotectonic events not recorded by DZ U‐Pb due to their largely amagmatic nature.

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

“…To render a unique solution, detrital zircon (U-Th)/(He-Pb) double dating method has 350 been utilized. In scenario a, as the proto-Zagros foreland basin detrital zircon spectra is a dominated by a ~100 age peak (this study) and characterized by a ~70 Ma peak exhumation age (Barber et al, 2019), the RBS deposits are expected to have a similar signature. In scenario b, because the RBS deposition involves an early stage foreland and a late stage intermontane basin a mixed U-Pb age distribution from the recycled ~100 Ma grains with a ~75 Ma ZHe age and new ~60 Ma and ~40 Ma grains with their corresponding ZHe ages are expected.…”

“…By the Maastrichtian time the proto-Zagros flexural foreland basin started to form in response to arrival of the Neotethys intraoceanic subduction zone at the Arabia plate margin, leading to the ophiolite obduction (Homke et al, 2010;Saura et al, 2011;Barber et al, 2019). This process resulted in a basin geometry where the sedimentary infill thinned toward the West with a surge of clastic input sourced mostly from NW and NE (Karim and Surdashy, 2005;Aqrawi et al, 2010;110 Çelik and Salih, 2021).…”

“…This contrast in provenance signature between the pre-Zagros and proto-Zagros deposits reflect a fundamental reversal in the sediment routing system from the West to the East as the basin started to flex due to arrival of the Neotethys ophiolitic island arc and oceanic curst terranes that are associated with numerous Upper Cretaceous intrusions (Delaloye and Desmons, 1980;Ali et al, 2012;Nouri et al, 2016;Al Humadi et al, 2019;255 Ismail et al, 2020). However along-strike toward SE, the proto-Zagros strata of the Amiran and Kashghan Formations have a ~240 Ma Triassic age mid-oceanic ridge signature (Zhang et al, 2016;Barber et al, 2019) in addition to the ~100 Ma signature, implying a different paleogeography toward NW. As zircon in mafic rocks is not a common mineral (Grimes et al, 2007), sandstone petrographic analysis on the Tanjero Formation revealed contents of limestone and chert (Aziz and Sadiq, 2020;Jones et al, 2020) that were particularly sourced from the older Qulqula radiolarite and Balambo Formations in 260 the NW (Çelik and Salih, 2021).…”

“…The new field evidence and provenance data and interpretation from this study along with the existing knowledge about the magmatic and tectonic history of the Arabian and Eurasian margins unravel the Cenozoic convergence history between the two plates (Figs. 12 and 13) After the initiation of the Neotethys interoceanic subduction zone during the Aptian, its development until the middle Late Cretaceous, including the growth of ophiolitic island arcs (Aswad and Elias, 1988;Aziz et al, 2011;Ali et al, 380 2012;Barber et al, 2019), the ophiolitic terranes obducted on the northeastern margin of Arabian plate during the Campanian (Fig. 13a) and shed sediments on the newly formed proto-Zagros foreland basin as evidenced from the detrital zircon provenance from this study and the detrital zircon ZHe from the Amiran and Kashghan Formations from Lurestan in Iran (Barber et al, 2019).…”

Late Miocene Deformation Kinematics Along the NW Zagros Fold‐Thrust Belt, Kurdistan Region of Iraq: Constraints From Apatite (U‐Th)/He Thermochronometry and Balanced Cross Sections

“…During the Maastrichtian, the intraoceanic convergent margin within the Neotethyan ocean reached the NE margin of the Arabian plate, leading to ophiolite obduction onto the Arabian continental margin, and initiation of the proto-Zagros foreland basin (Barber et al, 2018(Barber et al, , 2019Farahpour & Hessami, 2012;Homke et al, 2009;Lovelock, 1984;Saura et al, 2011). In response, a thick (locally >2 km) package of deep-marine clastic sediments (Tanjero Formation; equivalent to Amiran Formation in Iran) was deposited in a flexural basin, sourced from obducted ophiolites and older carbonate rocks to the NE (Ali & Mohmmad, 2018;Bellen et al, 1959;Çelik & Salih, 2018;Karim & Surdashy, 2005a;Koshnaw et al, 2017;Lawa, 2018).…”