Transition from phreatomagmatic to strombolian eruptions in the Sahand volcano; constrain from pyroclastic studies
|Location||The 25 Symposium of Geosciences|
|Holding Date||01 July 2007|
The Sahand volcano is a young volcano in northern part of Urumieh-Dokhtar magmatic belt which from late-Miocene to Pleistocene alternatively had been explosion and lava extrusion activities. Composition of Sahand lavas varies from andesite to dacite and rhyodacite which dacites are predominant. The Sahand pyroclastic sequence composed of volcanic sands, clays with lapilli, pumice, and unconsolidated conglomerate with volcanic rocks pebbles, armored lapillus, ignimbrite and lahar which accidental, cogenetic and juvenile materials form components of them. Studies on clay layers of pyroclastic sequence based on XRD method and oriented sections after necessary treatments indicate existing of montmorilonite, illite, chlorite and kaolinite minerals in studied samples. Abundance of kaolinite increases toward upper level of sequence. Increasing of fine grained volcanic ashes and accidental materials in lower part of sequence could be a result of phreatomagmatic explosion eruptions which occurred due to interaction of magma with groundwater or waters of lacustrine environments and subsequently strombolian activities is governed.
Key words: Sahand, pyroclastic, phreatomagmatic, stromboly, armored lapilli