Abstract-Impact and geothermal modeling was performed to explain hydrothermal alteration in a 4 km marine complex crater at K‰rdla, Estonia. The impact modeling was used to simulate the formation of the crater and the post-impact temperature distribution in crater environment. The geothermal modeling accounted for coupled heat transfer and multi-phase fluid flow in a variably saturated medium. The modeling results suggest that strong convective fluid flow was initiated. During the first stage, the cooling was rapid due to the effect of the latent heat of vaporization, which efficiently decreased the temperature to the boiling point. The modeling results are consistent with geological observations.

Abstract-The impact-induced hydrothermal system in the well-preserved, 4 km-diameter Kärdla impact crater on Hiiumaa Island, western Estonia, was investigated by means of mineralogical, chemical, and stable C and O isotope studies. The mineralization paragenetic sequence, with gradually decreasing temperature, reveals at least three evolutionary stages in the development of the post-impact hydrothermal system: 1) an early vapor-dominated stage (>300 °C) with precipitation of submicroscopic adularia type K-feldspar; 2) the main stage (300 to 150/100 °C) with the development of a two-phase (vapor to liquid) zone leading to precipitation of chlorite/corrensite, (idiomorphic) euhedral K-feldspar, and quartz; and 3) a late liquid-dominated stage (<100 °C) with calcite I, dolomite, quartz, calcite II, chalcopyrite/pyrite, Fe-oxyhydrate, and calcite III precipitation.

No abstract