Morphology and tectonics of Icelandic rifts western branch

Iceland is a unique example of a place, where rift zone of Mid-Atlantic Ridge appears onshore. Its morphological and tectonic features considerably differ from typical mid-oceanic ridge rift zones. The morphology and geodynamics of Icelandic rift western branch are formed by Iceland plume thermal influence that generated the North Atlantic Large Igneous Province. Icelandic rift western branch is characterized by ceasing tectonic and magmatic activity. Overlapping with the Eastern Rift Zone it forms rotating block of Hreppar Microplate that leads to tectono-magmatic activity decline northwards. Based on morphometric analysis of normal faults, the relative activity degree of individual parts of volcanic systems was revealed. For some parts, the activity changes in late Quaternary were traced. Obtained inferences demonstrate explicit differences in contemporary tectonic structure and dynamics of the rift zones and volcanic systems within them. For instance, transtensive Reykjanes Rift Zone, the southernmost one, has decreasing eastwards tectono-magmatic activity, which is connected with influence decrease of Reykjanes Ridge adjoining from the south-west. Its gradual southward shifting is observed that is explained by similar southward propagation of the most active Eastern Rift Zone and by the formation of new transtensive zone aggregating contemporary Reykjanes Rift Zone and South-Iceland Seismic Zone. In contrast, the Western Rift Zone develops independently from Reykjanes Rift Zone. It has the largest extension center in the area of Thingvallavatn Lake. In its northern part as within the Central Rift Zone, Holocene tectono-magmatic activity is very faint and is linked to glacioisostatic reactivation of more ancient structures. Revealed structural heterogeneities are traced in rift zone morphology as well. For example, within Western and Central Rift Zones, well-developed shield volcanoes are common. They consist of hyaloclasts predominantly. Within fissure swarms, individual lava shields are observed. In contrast, Reykjanes Rift Zone is characterized by absence of topographically expressed central volcanoes, and within fissure swarms, the chains of volcanic cones are present.