The study of the Taftan- Bazman volcanic area, South-eastern Iran and its relation with Makran-Chagai Volcanic Arc.

Abstract

The Makran-Chagai volcanic arc transcends the Pakistan-Iran border and contains numerous strato-volcanoes prominent being the Kuh-e-Sultan, Kuh-e-Taftan, Kuh-i-Bazman and the Shahsavaran volcanic fields. Volcanism in this region dates from 6.95 Ma to 0.71 Ma. Our study relates to the Taftan-Bazman volcanic region of Sistan and Baluchestan province, Iran. We undertook a two pronged approach during this dissertation. One was to use field mapping and petrogeochemistry to evaluate the nature of the volcanism, their products and understand their petrogenesis. The second was to collect and collate seismic data and model the same to prepare cross sections along and across the magmatic arc so as to decipher the structure of below and comment on the status (dormant/extinct) of the arc volcanism.

The stratovolcanoes of Taftan and Bazman have widespread pyroclastic ash, pumice and ignimbrites with fewer but thicker lava flows. Based on already published geochemical datasets and our own analyses suggest that the volcanism is represented by a calc-alkaline basaltic andesite-dacite-rhyolite volcanism for the Taftan-Bazman stratovolcanoes. Based on this it is clear that the Taftan-Bazman volcanic fields are related to the older (2.5 Ma to present) Makran-Chagai volcanic are related to the subduction of the Oman plate below the Lut-Afghan block.

Modelling of real time seismic data from IRIS and EHB produced several cross section profiles along and cross the Makran-Chagai volcanic arc. A band of high velocity zone extends from the edge of the Oman Sea and beyond the Taftan volcano at depths of 70 to 100 km bgl. The traverse along the Makran-Chagai volcanic arc show similar patterns of the high velocity zone, but the zone diminishes towards the west and a feeble signature is seen below Bazman. Evidence if present day fumarolic activity and the shallowing of the high velocity zone below Taftan suggest that volcano is rather dormant than extinct. Dormancy of stratovolcanoes in Island arc settings can exists from 100 to 300 years and any eruption in the near future could at least be of Vulcanian to sub- pilinian type.