Cooling of the Kärdla impact crater: I. The mineral paragenetic sequence observation

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.