We investigate the anisotropic nature of the mantle in a part of the Arabia-Eurasia collision zone where several of the constituent tectonic blocks of Iran come into contact. Our aim is to identify the dominant source of anisotropy in order to infer the pattern of mantle deformation as it responds to the forces of continental convergence. The broadband seismic data used in this study were recorded by 68 seismic stations in three temporary arrays in NW Iran (between 45º00'E - 51º00'E and 35º00'N - 39º00'N) installed and operated non-concurrently between 2008 and 2016 by the Institute for Advanced Studies in Basic Sciences (IASBS) and the University of Cambridge, and one permanent station of the Iranian National Seismic Network (INSN). The stations were repositioned during deployment and the recording span at individual stations varied between 4 and 31 months. The temporary arrays were mainly linear profiles that traversed the Talesh and western Alborz Mountains, NW Iran, and parts of the central Iran Plateau to the vicinity of the UDMA. Our dataset includes seismic records of S and SK(K)S phases. For the SK(K)S splitting measurements we used teleseismic earthquakes with magnitudes greater than 5.5 and epicentral distances between 90º and 130º, and for the direct S phase analysis we considered events larger than magnitude 5.5 in the distance range of 40º to 80º.