Evolution of Icelandic rift zones geometry as result of MOR-plume interaction
Authors: Bogoliubskii Viacheslav , Dubinin Evgeny , Grokholsky Andrey 
Published: February 2023

Rift zones of Iceland large igneous province (LIP) have complicated interior geometric pattern expressing in several parallel extension centers. It significantly differs from adjacent Reykjanes (RR) and Kolbeinsey (KR) mid-oceanic ridges (MOR) that only have small overlappings between separate neovolcanic centers. At small scale, rift zones connect with each other by broad transform zones with distributed strain pattern instead of typical narrow transform faults. Those transform zones have very different structure varying from simple book-shelf fault zones of South Iceland seismic zone to sophisticated system of magmatic and amagmatic structures of Tj&#246;rnes transform zone. The whole system drastically differs from typical structure and geometry of ultra-slow MOR. Iceland rift zone evolution commenced at 25 Ma and strongly influenced by thermal pulses of Iceland plume each 6-7 My and slightly asymmetric spreading. Another challenge of this region lies in asymmetric thermal influence of Icelandic plume. RR is affected by plume at distance of at least 800 km, whereas Kolbeinsey ridge at distance of ca. 600 km. To reveal the ridge-plume interaction through Iceland evolution and possible causes of Icelandic plume influence asymmetry we used a method of physical modelling. The extending setting comprises mineral oils mixture that have numerical resemblance with oceanic crust in density, shear modulus and thickness. Two-layered model have elastic bottom layer, brittle top one and local heating source (LHS) corresponding to Icelandic plume pulses. The first experiment type configuration includes two sections corresponding to RR and KR. At their joint, the LHS melts the modelling lithosphere creating analogue of LIP. The LHS periodically switched on and transported to another position, which is similar to plume pulses in asymmetric spreading conditions. The general pattern of each cycle is as following. Initially within LIP two rift branches propagate to each other forming an overlapping. A block between two rift branches rotates as horizontally as vertically. These blocks express in Iceland topography as uplifted peninsulas of its northwestern part. In some time, overlapping transforms to oblique transfer zone and rift zones change their structure of several extension centers to one-axis structure and have direct connection. Then new plume pulse rejuvenates the cycle. If incipient offset between rift branches is quite small, then overlapping structure passes to oblique transform zone with several extension centers and small overlappings. Thermal pulses of less volumes have considerable influence as well, but current data cannot permit to correctly them. As a result, we created a conceptual model of Iceland rift zones evolution also using data of other researchers. The second model had the same initial configuration, but thermal pulses extend downward to modelling Reykjanes ridge. This migration caused by density heterogeneities of upper layers due to deep thermal differences. The resulting geometry is very similar to natural one. There are different segmentation pattern at both spreading ridges and some rift zones. Developed transform zones confine rotating blocks and have structure varying from book-shelf fault zone to overlapping as in nature. We infer that modeled asymmetry and origination can reflect the natural ones.