Impact Origin of the Domaine du Meteore Crater

Small impact craters (< 300m) are rare, making proof of impact origin difficult, especially without remnants of the impactor.
The EarthImpactDatabase (EID) lists only three confirmed high-velocity impact craters in West and Central Europe:
- Rochechouart (France)
- Nördlinger Ries (Germany)
- Steinheimer Becken (Germany)
Despite the expected higher frequency of smaller impact structures, there's a lack of confirmed small crater structures.
This contribution presents mineralogical and geophysical evidence for a small crater structure (about 200m wide) in Southern France, potentially part of the Herault impact structure.
The data was collected for the "Domaine du Meteore"-crater, formally known as "le Clot".

First mentioned over 70 years ago, the 200m wide crater south of Cabrerolles in southern France was largely ignored.
Gezè and Cailleux (1950) first suggested an impact origin based on its shape and a strong magnetic anomaly.
Janssen (1951) supported this idea, noting similarities to lunar craters.
Beals (1964) rejected the impact origin based on:
- Absence of an elevated rim.
- Lack of evidence for a magnetic anomaly.
This rejection led to the crater being largely ignored for half a century, with no mineralogical or geophysical work conducted until recently.
Recent detailed fieldwork was initiated following promising preliminary findings.

The current crater is 200m wide and about 30m deep, with a circular shape crosscut by two stream beds.
Assessing the original crater size is difficult due to complex topography and erosion from the Montagne Noire.
The impact may have occurred on already shaped terrain.
The distribution of crater infall breccia suggests the original size wasn't much larger.
The size-to-depth ratio fits closely with the mean values of simple impact craters worldwide.

The geophysical study included radar (GPR), geoelectric, and geomagnetic measurements.
GPR results were inconclusive due to intensive folding of the schist-quartzite unit during regional metamorphism.
Geoelectric data processing is ongoing.
Measurements of the magnetic field within and around the crater yielded the most interesting data.

The most striking geophysical feature is the spatial distribution of geomagnetic field strength, showing a systematic decrease towards the crater bottom.
Measurements were taken along several profiles from the surrounding area, through the crater rim, and towards the center.
Data were corrected for time variations of Earth's magnetic field.
A significant magnetic low of about 100 nT was found within the crater, which is typical for small impact craters.

Impact spherules are rare in small craters.
A study of magnetic spherules in the Kamil crater in Egypt showed their potential for detecting and confirming new impact craters.

Screening of soils using high-energy magnets isolated over a hundred Fe-oxide spherules.
These spherules exhibited a variety of textures (dendritic, ashlar, smooth) and sizes (few 10s of microns to over 1 mm, mean size ~200 microns).
Compound spherules were detected, potentially indicating high-speed collisions.
Larger spherules, when broken apart, showed a core-rim structure.
A 1.2 mm-sized spherule was polished for further study.
- Rim: Si, Al-bearing Fe-oxides with remnants of Ni-rich Fe-metal.
- Core: Fragments of quartz, feldspar, mica, carbonate, TiO2, and carbonaceous material, similar to mineral phases in the target rocks.
- Micro-diamonds were detected between these minerals via Raman spectroscopy.
- Peak broadening and shift towards lower wave numbers indicate a shock origin.
- No other high-pressure polymorphs have been detected so far.

Pieces of impact breccia were found near the crater.
Quartzite fragments show a high degree of deformation, including undulatory extinction, subgrain formation, and mosaicism.
Narrow crosscutting planar features in quartz might indicate planar fractures and planar deformation features.
Melt pockets around quartzite fragments contain nano-graphite and shock diamonds.

No clear evidence of shatter cones has been found so far.
A piece of schist found near the crater center shows numerous crosscutting cataclastic to pseudotachylite veins, potentially representing shock veins.

The magnetic low inside the crater, along with impact spherules containing target fragments in a shock diamond matrix surrounded by Si, Al-containing Fe-oxide and Ni-rich Fe-metal, confirms the impact origin of the "Domaine du Meteore"-Crater.
Further evidence includes shock diamonds, mosaicism, planar fractures, and planar deformation features in quartz of impact breccia.

Thanks to Paul Jenkins, Paul Jarman, and Simon Frech for access to the vineyard.
Thanks to students for help during fieldwork.
Special thanks to C. Ogunjobi for discovering an important impact spherule.

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