Facies Relations and Emplacement Styles of Magmatic Bodies in N-Qazvin, Western Alborz

Lat-Blukan district situated on N-Qazvin and western Alborz zone contains various extrusive and intrusive bodies with Eocene age. They are divided into three main facies that are volcaniclastic deposits (including tuff, lapilli tuff, agglomerate, tuffaceous sandstone and shale and also the carbonate intercalations), the trachyandesitic lava flows and subvolcanic bodies (including dioritic bodies, dacitic domes and parallel dyke swarms). Because of many sedimentary structures, such as layering and graded bedding together with middle Eocene microfauna in the tuffaceous deposits, a shallow-depth sedimentary basin interrupted by the explosive volcanic eruptions is concluded. On the other hand, the overlying lava flows were formed by the subaerial effusive eruptions through vertical fractures (i.e., feeder dykes) that is verified by the columnar jointing and soil horizons under many lava flows. Finally, the intrusive facies, including the dacitic domes and dioritic bodies are the latest stage of the magmatic cycle in the region that their intrusions were controlled by the geologic structures. The main NW-SE trend of the parallel dyke swarms provide a NE-SW local extensional environment controlled the intrusion of dyke swarms (s3) with prominent NW-SE trend parallel to s1. Moreover, it seems that the microdiorite intrusion and dacitic dome in Lat area were emplaced in the local tensional curved spaces of the Lat strike-slip fault and also the NE-SW sinistral strike-slip faults. On the other hand, the dacitic dome of the Bolukan area was likely intruded in the tensional spaces of two reverse strike-slip faults. Thus, it seems that the dyke swarms had been emplaced forcefully; whereas the microdiorite bodies and dacitic domes were intruded by the ballooning and passive mechanism.