The dynamic of magmatic system and volcano hazard implications of the Damavand volcano (N. Iran) inferred from the textural data

Abstract

The Damavand stratovolcano (N Iran) consists mainly of lavas with trachyandesite-trachyte composition, and subordinate pyroclastic deposits. The intensity of explosive eruptions and the volume of pyroclastic deposits have increased over time, which may be related to increasing viscosity due to the development of crystal-rich magmas. This research integrates microanalytical and quantitative textural measurements to understand the textural evolutions from the old to the young lavas and their relationships with the physical processes occurred in the plumbing system. Age-constrained samples from the lavas were analyzed using crystal size distribution (CSD), the newly proposed multifractal analysis, including the Number-Length of crystals (N-LoC) and the Number-Area of crystals (N-AoC), along with mineral chemistry. Three to five populations of feldspars can be identified, which have undergone evolution and coarsening over time. We propose a textural development sequence established at mid to shallow crustal levels, involving several physicochemical processes, such as cycles of polybaric differentiation and episodic magma recharge into the crystal-rich magma chambers. This, in turn, caused disaggregation of crystal mushes and textural coarsening due to crystal aggregation and temperature cycling. The increasing population of microphenocrysts in younger lavas may be linked to pulsating groundmass crystallization resulting from degassing at a newly formed shallow chamber (0.5–1 kbar) beneath the young cone. The final stages of crystallization occurred during multi-step decompression in the conduits. The comparison of age data from lava samples and their stratigraphic positions suggests that triggering groundmass crystallization might have caused shifts in eruptive behavior.