Lateral fold growth and linkage in the Zagros fold and thrust belt (Kurdistan, NE Iraq)

摘要

The Zagros fold and thrust belt is a seismically active orogen that has accommodated the N-S shortening between the Arabian and Eurasian plates since the Miocene. Whereas the southeast parts of the belt have been studied in detail, the northwest extent has received considerably less attention, being part of the Republic of Iraq. In this study, we investigate fold growth in the area NE of Erbil (Kurdistan, Iraq). In particular, we focus on the interaction of the transient development of drainage patterns along growing antiforms, as this directly reflects the kinematics of progressive fold growth. Detailed geomorphological studies of the Bana Bawi-, Permam- and Safeen-fold trains show that these anticlines did not develop from a single embryonic fold but by lateral linkage of several different fold segments. These segments, with length between 5 and 25km, have been detected by mapping ancient and modern river courses; these initially cut the nose of growing folds until eventually defeated, leaving curved wind gaps behind. Depending on the alignment of the initial embryonic folds, the segments can either record a linear- or an en-echelon linkage. Comparison of natural examples from the Zagros fold and thrust belt in Iraq with published numerically modelled fold growth suggests that both linear-linkage and en-echelon linkage are mechanically feasible and are common processes during progressive shortening and fold growth.