New evidence for persistent impact-generated hydrothermal activity in the Miocene Ries impact structure, Germany

The Saint-Honoré carbonatite complex hosts a rare earth element (REE) deposit traditionally interpreted as being produced by late-stage hydrothermal fluids that leached REE from apatite or dolomite found in the early units and concentrated the REE in the late-stage units. New evidence from deeper units suggest that the Fe-carbonatite was mineralized by a combination of both magmatic and hydrothermal crystallization of rare earth minerals. The upper Fe-carbonatite has characteristics typical of hydrothermal mineralization—polycrystalline clusters hosting bastnäsite-(Ce), which crystallized radially from carbonate or barite crystals, as well as the presence of halite and silicification within strongly brecciated units. However, bastnäsite-(Ce) inclusions in primary magmatic barite crystals have also been identified deeper in the Fe-carbonatite (below 1000 m), suggesting that primary crystallization of rare earth minerals occurred prior to hydrothermal leaching. Based on the intensity of hydrothermal brecciation, Cl depletion at depth and greater abundance of secondary fluid inclusions in carbonates in the upper levels, it is interpreted that hydrothermal activity was weaker in this deepest portion, thereby preserving the original magmatic textures. This early magmatic crystallization of rare earth minerals could be a significant factor in generating high-volume REE deposits. Crystallization of primary barite could be an important guide for REE exploration.

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Paleomagnetism and rock magnetism of East and West Clearwater Lake impact structures

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2018-0291 ◽

2019 ◽

Vol 56 (9) ◽

pp. 983-993

Author(s):

Jérôme Gattacceca ◽

William Zylberman ◽

Adam B. Coulter ◽

François Demory ◽

Yoann Quesnel ◽

...

Keyword(s):

Rock Magnetism ◽

Drill Hole ◽

Hydrothermal Activity ◽

Radiometric Dating ◽

Impact Structure ◽

The West ◽

Impact Melt ◽

Basement Rocks ◽

East And West ◽

The Impact

The East and West Cleawater Lake impact structures (Wiyâshâkimî Lake, Québec), ∼26 and 32 km in diameter, respectively, have been proposed to represent an impact doublet. We investigated their paleomagnetism to contribute to this debate. The paleomagnetic directions of the impact melt rocks and impact melt-bearing breccias from the West Clearwater structure are compatible with the radiometric age of 280–290 Ma previously determined for this structure and indicate that the impact occurred during a reverse polarity interval of the geomagnetic field. A similar remagnetization direction is found in the basement within 10 km of the structure center, whereas basement farther away from the center has escaped remagnetization by the impact. Samples for the East Clearwater structure come from two holes drilled in 1963 and 1964. Unfortunately, the drill hole through the melt rocks is tilted by 30° from the vertical with an unknown azimuth. The paleomagnetic inclination of these melt rocks cannot be constrained to better than between −28° and +32°. This is, however, distinct from the inclination of the melt rocks of the West Clearwater Lake impact structure (−27.8° ± 3.7°), suggesting that the two structures do not represent an impact doublet, in agreement with recent radiometric dating. The basement rocks and the melt rocks within 10 km of the center of the West Clearwater Lake impact structure show a magnetic signature of titanohematite that crystallized during postimpact hydrothermal activity under oxidizing conditions. This is not observed in the basement or the melt rocks from the East Clearwater Lake impact structure.

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Late Ediacaran organic microfossils from Finland

Geological Magazine ◽

10.1017/s0016756821000753 ◽

2021 ◽

pp. 1-14

Author(s):

Sebastian Willman ◽

Ben J. Slater

Keyword(s):

Microbial Communities ◽

Microbial Mats ◽

Trace Fossils ◽

Impact Structure ◽

Meteorite Impact ◽

Fine Grained ◽

Body Fossil ◽

New Evidence ◽

Insight Into ◽

Direct Body

Abstract Here we present a detailed accounting of organic microfossils from late Ediacaran sediments of Finland, from the island of Hailuoto (northwest Finnish coast), and the Saarijärvi meteorite impact structure (~170 km northeast of Hailuoto, mainland Finland). Fossils were recovered from fine-grained thermally immature mudstones and siltstones and are preserved in exquisite detail. The majority of recovered forms are sourced from filamentous prokaryotic and protistan-grade organisms forming interwoven microbial mats. Flattened Nostoc-ball-like masses of bundled Siphonophycus filaments are abundant, alongside Rugosoopsis and Palaeolyngbya of probable cyanobacterial origin. Acritarchs include Chuaria, Leiosphaeridia, Symplassosphaeridium and Synsphaeridium. Significantly, rare spine-shaped sclerites of bilaterian origin were recovered, providing new evidence for a nascent bilaterian fauna in the terminal Ediacaran. These findings offer a direct body-fossil insight into Ediacaran mat-forming microbial communities, and demonstrate that alongside trace fossils, detection of a bilaterian fauna prior to the Cambrian might also be sought among the emerging record of small carbonaceous fossils (SCFs).

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Mineralogical and geochemical specificity of carbonaceous rocks from the area of Ust'-Kara astrobleme (Pay-Khoy)

Vestnik of Geosciences ◽

10.19110/geov.2021.11.1 ◽

2021 ◽

Vol 11 ◽

pp. 3-15

Author(s):

N. S. Kovalchuk ◽

◽

B. A. Makeev ◽

S. A. Svetov ◽

◽

...

Keyword(s):

Hydrothermal Activity ◽

Rare Metal ◽

Impact Structure ◽

Hydrothermal Processes ◽

Upper Paleozoic ◽

Modern Methods ◽

Rare Earth Minerals ◽

Carbonaceous Shales ◽

Post Impact ◽

Carbonaceous Rocks

We studied Upper Paleozoic (P1pt-ng) carbonaceous shales and siltstones from the area of the Ust'-Kara astrobleme (PayKhoy). We analyzed mineralogical and geochemical features of carbonaceous rocks of the target in the vicinity of the Ust'-Kara astrobleme event using a complex of modern methods to identify possible mobilization, redeposition and concentration of ore substance under intensive post-impact hydrothermal activity. Geochemical features of carbon deposits, altered by post-impact hydrothermal processes in the vicinity of the Ust'-Kara impact structure, have been determined. We found anomalous contents of Ti, Mn, Cr, Zr, Ni, Li, Co, Sc and REE. Inherent rare metal and rare earth minerals (monazite, florensite), sulfides (pyrite, chalcopyrite, marcasite, sphalerite), apatite, barite, anatase, chrome spinels were diagnosed.

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The Effect of Arc Proximity on Hydrothermal Activity Along Spreading Centers: New Evidence From the Mariana Back Arc (12.7°N–18.3°N)

Geochemistry Geophysics Geosystems ◽

10.1002/2017gc007234 ◽

2017 ◽

Vol 18 (11) ◽

pp. 4211-4228 ◽

Cited By ~ 6

Author(s):

Edward T. Baker ◽

Sharon L. Walker ◽

Joseph A. Resing ◽

William W. Chadwick ◽

Susan G. Merle ◽

...

Keyword(s):

Hydrothermal Activity ◽

Spreading Centers ◽

Back Arc ◽

New Evidence

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A case study of impact-induced hydrothermal activity: The Haughton impact structure, Devon Island, Canadian High Arctic

Meteoritics and Planetary Science ◽

10.1111/j.1945-5100.2005.tb00150.x ◽

2005 ◽

Vol 40 (12) ◽

pp. 1859-1877 ◽

Cited By ~ 66

Author(s):

Gordon R. Osinski ◽

Pascal Lee ◽

John Parnell ◽

John G. Spray ◽

Martin Baron

Keyword(s):

Hydrothermal Activity ◽

High Arctic ◽

Impact Structure ◽

Canadian High Arctic ◽

Devon Island

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40Ar/39Ar age evidence for an impact-generated hydrothermal system in the Devonian Siljan crater, Sweden

Large Meteorite Impacts and Planetary Evolution VI ◽

10.1130/2021.2550(26) ◽

2021 ◽

Author(s):

Maria Herrmann ◽

Carl Alwmark ◽

Michael Storey

Keyword(s):

Hydrothermal System ◽

Rapid Heating ◽

Hydrothermal Activity ◽

Hydrothermal Systems ◽

Impact Structure ◽

Near Surface ◽

Central Uplift ◽

Target Rock ◽

Step Heating ◽

Pressure Regime

ABSTRACT Crater-forming events are generally followed by the development of hydrothermal systems due to the rapid heating of the target rock. Such hydrothermal systems are a feature of nearly all large terrestrial impact structures. For the Siljan impact structure in Sweden, there is evidence for such a fossil hydrothermal system, possibly triggered by the impact event ca. 380 Ma. To investigate the thermal regime of the near-surface hydrothermal activity of the Siljan crater, biotite and amphibole grains extracted from samples collected in a transect across the high-pressure regime recorded by the central uplift, as well as from distal localities outside the central uplift of the crater, were dated using the 40Ar/39Ar laser step-heating technique. Our results show that biotite from inside the central uplift, which was strongly altered to chlorite by low-temperature (200–340 °C) hydrothermal reactions, yields strongly disturbed age spectra. The first and second (low laser power) step ages range from ca. 1300 to 190 Ma. In contrast, biotite from outside the central uplift and amphibole, irrespective of location inside or outside of the central uplift, are much less altered, which is reflected in less disturbed, near-flat age spectra. This result indicates that the hydrothermal temperatures inside the central uplift were >200 °C, sufficient to disturb the K-Ar system of biotite during its chloritization, but too low to affect the amphibole (closure temperature of 480–580 °C). In contrast, the temperature of the hydrothermal system outside of the central uplift was <200 °C, as no significant reset of the K-Ar system can be observed in either biotite or amphibole. Our results are consistent with estimated trapping temperatures from fluid inclusion studies, which show a decrease from 327–342 °C within the central uplift to 40–225 °C toward outside the central uplift. We conclude that the near-surface hydrothermal system in the Siljan impact structure was an impact-triggered system. This system was strongly active, with its highest temperature inside the central uplift and decreasing rapidly toward the outlying part of the crater.

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