Historical Development of the Present Day Lineaments of the Western Zagros Fold Thrust Belt A Case Study from Northeastern Iraq, Kurdistan Region

Abstract

The part of the Zagros within the Iraqi border occupies an area less than quarter of the country. It includes three tectonic zones which can be clearly identified in the field. These are the Low and High Folded, Imbricated and Thrusted Zones. The main lineaments are the axes of the anticlines; transverse and longitudinal faults; lines of distribution of ophiolite and metamorphic rocks; drainage direction discharge and line of distribution of conglomerates. The direction of axes of the anticlines are trending nearly N38W which normal to the direction of the imposed stress by the Iranian plate front. Due to differences in thicknesses and physical properties of the sedimentary rocks, the axes of these anticlines are not continuous they plunge more or less in an en echelon pattern and in some cases are bend. The lengths of most of these anticlines are around 10-30km. The first appearance of the anticlines in the High Folded Zone possibly started at the Eocene while those of the Thrust Zone initiated at Maastrichtian. Some of these anticlines are cut by transverse faults whose ages are not known. These faults trend nearly normal to the axis of anticlines. Other kinds of lineaments are the distribution of ophiolites and metamorphic rocks. Historically the first appearance of trace of ophiolites (as pebbles in sedimentary rocks) has an age of Lower Maastrichtian. The direction of drainage discharge is nearly towards the south and southwest, which is inherited from that of the Upper Cretaceous and Tertiary paleocurrent directions (sediment transport direction). This direction is related to uplift of the extreme northwestern part of the studied area during Maastrichtian. Evidence for these suggestions is the occurrence of thicknesses of 500m of conglomerates as valley fillings during Late Cretaceous. The depositional axes of the successions was migrated for about 50kms during Cretaceous and Tertiary and becomes younger from northeast towards the southwest as recorded by four narrow belts. The line of migration is nearly coinciding with both directions of present regional slope and the Cretaceous sediment transport.