633 research outputs found
Impact-generated hydrothermal circulation and metasomatism of the rochechouart astrobleme: mineralogy and major and trace element distribution
The energy released during a hypervelocity
impact on Earth can generate high temperatures
in the target rock. There are currently 170 known
impact structures worldwide, of which over one-third
contain fossil hydrothermal systems [1]. Results from
the analysis of these hydrothermal systems have many
implications for the study of the origin of life on Earth
and potential thereof on Mars. Hypervelocity impacts
are also of particular economic interest as they may
produce, expose or concentrate high commodity resources
such as hydrocarbons, precious metals and ore
minerals
Evidence for Localized High Temperature Hydrothermal Fluid Flow within the Sub-Crater Environment of the Rochechouart Impact Structure: Observations from a Polymict Breccia Dike
Hypervelocity impacts into volatilebearing terrestrial targets can initiate hydrothermal circulation for a finite period of time; evidence for this is preserved in approximately one-third of impact structures on Earth [1, 2]. Hydrothermal environments can host extremophile life, and microbial communities have been found to colonize impact craters [3, 4]. The majority of impact structures on Earth have yet to be studied in great detail; many aspects of the post-impact environment such as the extent and duration hydrothermal circulation with respect to location within the structure as well as crater diameter, target composition and external influences, (paleogeography) are not fully understood. <p></p>We present evidence for high temperature hydrothermal fluid circulation within the sub-crater environment of the highly eroded, 23km diameter, Mesozoic Rochechouart impact structure located in west-central France [5]. This evidence is a new impact lithology that was found during a recent field campaign at a collection site located approximately 7.5km north-east of the structure's center. It is a highly porous, polymict lithic impact breccia dike containing carbonate mineralization found below the transient crater floor. Secondary hydrothermal mineral assemblages are diagnostic of a range of temperatures (>100°C to low temperature diagenetic).<p></p>
Impact fracturing and aqueous alteration of the CM carbonaceous chondrites
Aqueous alteration of the CM carbonaceous
chondrites has produced a suite of secondary
minerals, and differences between meteorites in
their abundance defines a progressive alteration sequence
[e.g. 1, 2]. The means by which this water
gained access to the original anhydrous constituents of
the meteorites is the subject of considerable debate.
Studies of rock texture, mineralogy and bulk chemical
composition have concluded that solutions were generated
by the melting of water ice in situ, and remained
essentially static as a consequence very low intergranular
permeabilities [e.g. 3, 4]. By contrast, results of
oxygen isotope work and modelling have suggested
that the fluids moved considerable distances within the
parent body [5, 6]. Given the intergranular permeability
of the CMs, an extensive fracture network would be
required to support such flow.
Clues to how the two very different models for
aqueous alteration of the CMs can be reconciled have
been recently provided by Rubin [7]. He recognised a
good correlation between the magnitude of impact-induced
compaction of CM meteorites and their degree
of aqueous processing, with the more highly deformed
meteorites being more altered. Here we have asked
whether compaction was accompanied by the development
of fracture networks that could have provided the
conduits for aqueous solutions that mediated all or
some of the alteration
Evidence for an impact-induced biosphere from the δ34S signature of sulphides in the Rochechouart impact structure, France
The highly eroded 23 km diameter Rochechouart impact structure, France, has extensive evidence for post-impact hydrothermal alteration and sulphide mineralization. The sulphides can be divided into four types on the basis of their mineralogy and host rock. They range from pyrites and chalcopyrite in the underlying coherent crystalline basement to pyrites hosted in the impactites. Sulphur isotopic results show that δ34S values vary over a wide range, from -35.8‰ to +0.4‰. The highest values, δ34S -3.7‰ to +0.4‰, are recorded in the coherent basement, and likely represent a primary terrestrial sulphur reservoir. Sulphides with the lowest values, δ34S -35.8‰ to -5.2‰, are hosted within locally brecciated and displaced parautochthonous and autochthonous impactites. Intermediate δ34S values of -10.7‰ to -1.2‰ are recorded in the semi-continuous monomict lithic breccia unit, differing between carbonate-hosted sulphides and intraclastic and clastic matrix-hosted sulphides. Such variable isotope values are consistent with a biological origin, via bacterial sulphate reduction, for sulphides in the parautochthonous and autochthonous units; these minerals formed in the shallow subsurface and are probably related to the post impact hydrothermal system. The source of the sulphate is likely to have been seawater, penecontemporaneous to the impact, as inferred from the marginal marine paleogeography of the structure. In other eroded impact craters that show evidence for impact-induced hydrothermal circulation, indirect evidence for life may be sought isotopically within late-stage (≤120°C) secondary sulphides and within the shocked and brecciated basement immediately beneath the transient crater floor
Stable Isotope Studies of the Rochechouart Impact Structure: Sources of Secondary Carbonates and Sulphides within Allochthonous and Parautochthonous Impactites
Hypervelocity impacts are among the most ubiquitous processes to affect solid bodies within our solar system [1, 2]. Although they are notoriously devastating, citing responsibility for mass extinction events and global climate perturbations, impacts can also create temporary environments which are favorable for life to thrive, if there is enough water present in the target, and sufficient energy is released as heat [1, 2]. One-third of impact structures on Earth contain fossil impact-initiated hydrothermal systems, and they are therefore being explored as potential “cradles of life” on other solid planets and satellites in our solar system [1].<p></p> We are presenting a case for the evaluation of the Mesozoic Rochechouart impact structure in France as a once-habitable environment. Initial δ 13C, δ18O and δ 34S isotope data collected in 2014 from hydrothermal carbonates and sulphides within monomict lithic impact breccia, collected from a site located 7.5km from the center of the structure at Champagnac quarry, supports our hypothesis of a warm, wet environment; we also found evidence for metabolically reduced sulphate [3]. Similar mineral assemblages can be found throughout the structure, including allochthonous breccias and low to unshocked target material. In order to explore our hypothesis further, a larger sample set was collected from various lithologies within the Champagnac site containing sulphide and carbonate mineralization for δ 13C, δ18O and δ34S isotope analysis in January 2015. These results will allow us to determine the relationships between the many hydrothermal mineral assemblages within this area of the structure, and ask whether the isotopic compositions recorded in secondary sulphides and carbonates of the impactites are inherited from the target, or possibly represent colonization by thermophilic microbes during the post-impact hydrothermal period.<p></p>
Impact fracturing and aqueous alteration of the CM carbonaceous chondrites
Aqueous alteration of the CM carbonaceous
chondrites has produced a suite of secondary
minerals, and differences between meteorites in
their abundance defines a progressive alteration sequence
[e.g. 1, 2]. The means by which this water
gained access to the original anhydrous constituents of
the meteorites is the subject of considerable debate.
Studies of rock texture, mineralogy and bulk chemical
composition have concluded that solutions were generated
by the melting of water ice in situ, and remained
essentially static as a consequence very low intergranular
permeabilities [e.g. 3, 4]. By contrast, results of
oxygen isotope work and modelling have suggested
that the fluids moved considerable distances within the
parent body [5, 6]. Given the intergranular permeability
of the CMs, an extensive fracture network would be
required to support such flow.
Clues to how the two very different models for
aqueous alteration of the CMs can be reconciled have
been recently provided by Rubin [7]. He recognised a
good correlation between the magnitude of impact-induced
compaction of CM meteorites and their degree
of aqueous processing, with the more highly deformed
meteorites being more altered. Here we have asked
whether compaction was accompanied by the development
of fracture networks that could have provided the
conduits for aqueous solutions that mediated all or
some of the alteration
Impact-generated hydrothermal circulation and metasomatism of the rochechouart astrobleme: mineralogy and major and trace element distribution
The energy released during a hypervelocity
impact on Earth can generate high temperatures
in the target rock. There are currently 170 known
impact structures worldwide, of which over one-third
contain fossil hydrothermal systems [1]. Results from
the analysis of these hydrothermal systems have many
implications for the study of the origin of life on Earth
and potential thereof on Mars. Hypervelocity impacts
are also of particular economic interest as they may
produce, expose or concentrate high commodity resources
such as hydrocarbons, precious metals and ore
minerals
Stable isotope studies of post impact hydrothermal deposits within the sub-crater environment of the Rochechouart structure
No abstract available
Stable isotope studies of post impact hydrothermal deposits within the sub-crater environment of the Rochechouart structure
No abstract available
Spatial-temporal variation in Greenland shark (Somniosus microcephalus) bycatch in the NAFO Regulatory Area
Spatial and temporal variation in Greenland shark (Somniosus microcephalus) bycatch occurrence was investigated using At-Sea Fisheries Observer data and MaxEnt, a maximum entropy species distribution model. Within the Northwest Atlantic Fisheries Organization Regulatory Area (NRA), the Flemish Pass, the slopes of the Flemish cap, and the shelf edge of Divisions 3NO contained areas of suitable habitat where Greenland shark bycatch is expected to occur. However, it should be noted that there are major areas of Greenland shark bycatch outside the NRA, in the Canadian and Greenland Exclusive Economic Zones (EEZ).En prens
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