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

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 degrees 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 degrees C) with precipitation of submicroscopic adularia type K-feldspar; 2) the main stage (300 to 150/100 degrees 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 degrees C) with calcite I, dolomite, quartz, calcite II, chalcopyrite/pyrite, Fe-oxyhydrate, and calcite III precipitation.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

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

The impact-induced hydrothermal system in the well-preserved, 4 km-diameter Krdla 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

Cooling of the Kärdla impact crater: II. Impact and geothermal modeling

Impact and geothermal modeling was performed to explain hydrothermal alteration in a 4 km marine complex crater at Krdla, 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

Cooling of the Kärdla impact crater: II. Impact and geothermal modeling

Impact and geothermal modeling was performed to explain hydrothermal alteration in a 4 km marine complex crater at Kärdla, 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.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Timing and origin of natural gas accumulation in the Siljan impact structure, Sweden

Fractured rocks of impact craters may be suitable hosts for deep microbial communities on Earth and potentially other terrestrial planets, yet direct evidence remains elusive. Here, we present a study of the largest crater of Europe, the Devonian Siljan structure, showing that impact structures can be important unexplored hosts for long-term deep microbial activity. Secondary carbonate minerals dated to 80 ± 5 to 22 ± 3 million years, and thus postdating the impact by more than 300 million years, have isotopic signatures revealing both microbial methanogenesis and anaerobic oxidation of methane in the bedrock. Hydrocarbons mobilized from matured shale source rocks were utilized by subsurface microorganisms, leading to accumulation of microbial methane mixed with a thermogenic and possibly a minor abiotic gas fraction beneath a sedimentary cap rock at the crater rim. These new insights into crater hosted gas accumulation and microbial activity have implications for understanding the astrobiological consequences of impacts