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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. 相似文献
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Argo J
ELEHT Kalle KIRSIME Jüri PLADO Evelin VERSH Boris IVANOV 《Meteoritics & planetary science》2005,40(1):21-33
Abstract— 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. 相似文献
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Effect of meteorite impact on the biological evolution is usually considered by its catastrophic consequences. However, the impacts can create opportunity for other organisms and the structures themselves can serve as suitable ecological niches (oases) for life. In this contribution we present results of modeling of an impact-induced hydrothermal (IHT) system in a small-to-medium sized impact crater, where the development of zones habitable for primitive hydrothermal thermophilic and hypethermophilic microorganisms was studied. The impact and geothermal modeling was verified against the 4-km diameter Kärdla complex structure, Hiiumaa Island, Estonia. If there is an sufficient amount of water present in the target (e.g., sea cover, groundwater or permafrost resources) then the differential temperature fields created by the impact initiate a hydrothermal circulation system within the crater. The results of transient fluid flow and heat transfer simulations in Kärdla suggest that immediately after impact the temperatures in the central area, which contains the most hydrothermal alteration, were well above the boiling point. However, due to efficient heat loss at the groundwater vaporization front, the vapor-dominated area disappears within a few decades. In the central uplift area, the conditions favorable for thermophilic microorganisms (temperatures <100 °C) were reached in 500–1000 years after the impact. The overall cooling to ambient temperatures in the deeper parts of the central uplift lasted for thousands of years. In the crater depression and rim area the initial temperatures, suggested by the impact modeling, were much lower—from 150 °C to ambient temperatures, except locally in fracture zones and suevite pockets. Our data suggest that in small-to-medium size impact craters with insignificant melting, the suitable conditions for hydrothermal microbial communities are established shortly (tens to few hundreds of years as maximum) after the impact in most parts of the crater. In the central uplift area the microbial colonization is inhibited for about a thousand years. However, this is the area, which afterwards retains the optimum temperatures (45–120 °C) needed for hydrothermal microorganisms for the longest period. Geochemical and mineralogical data suggest, in general, neutral pH 7(±1) fluid of the IHT system, which is, when compared to volcanic hydrotherms, richer in dissolved oxygen and poor in reduced compounds. This suggests the preference for sulfur-reducing microorganisms in the possible impact-induced hydrothermal communities. 相似文献
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