A Pleistocene, pyroclastic-poor maar from central Anatolia, Turkey: influence of a local fault on a phreatomagmatic eruption

In central Anatolia, the Late Pleistocene Narkِy maar formed on a fault zone. A 5-m-thick pyroclastic succession erupted from a crater 900 m in diameter. The presence of gas fumeroles, hot springs, and hydrothermal alteration zones indicates that the area is geothermally active. The products of the maar are large blocks and lapilli to coarse ash. Planar bedding and cross-stratification are well developed within coarse ash beds. The maar deposits were generated by a single period of phreatomagmatic explosion with two episodes. The first episode produced wet eruption clouds, while the second one was relatively dry in nature. The estimate of the volume of pyroclastic ejecta compared with the dimensions of the maar demonstrates a material deficiency, which is attributed to a large volume of gas emanated during the phreatomagmatic explosion along a fault presently cross-cutting the maar. In addition, a relatively small volume of magma intruded along the fault and mixed with meteoric water in the fault zone to produce the phreatomagmatic eruption. The existence of a hydrothermal system in the fault zone is important in affecting the eruption style and evolution of Narkِy maar.