In situ U-Pb dating of hydrothermal diagenesis in tectonically controlled fracturing in the Upper Cretaceous Bekhme Formation, Kurdistan Region-Iraq

This study concerns the absolute LA ICP-MS U-Pb dating of hydrothermal cementation, particularly in tectonically controlled fractures filling saddle dolomites and blocky calcites in the carbonate succession of Bekhme Formation (Campanian–Maastrichtian). Dating of multiphase hydrothermal cementation combined with δ¹⁸O and δ¹³C analyses, petrography and field observations shows two major episodes of hydrothermal fluid circulation. The first was measured at ~73.8 Ma and is associated with the Zagros folding-faulting tectonic event (Late Cretaceous) and with the depositional age of the Bekhme Formation (75.1 Ma), and the second was at 30.3 Ma and is associated with the second folding-faulting tectonic event during the Tertiary. The δ¹⁸O and δ¹³C values grouped into two populations corroborate the two episodes of hydrothermal fluid flow. Late Cretaceous folding and faulting tectonics and reactivation during the Tertiary in the study area provided conduits for the hydrothermal fluids along deeply seated faults. This work shows for the first time through U-Pb dating that the hydrothermal diagenetic processes in Upper Cretaceous Bekhme Formation are directly linked with the timings of the major regional tectonics in the Zagros Fold-Thrust Belt (ZFTB) through the flow of hot fluid fluxes in a fractured sedimentary basin.