File:Shatter-cone from Slate Islands impact crater (40163660442).jpg

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Stored in the rock and drillcore archive of the Ontario Geological Survey, Thunder Bay office is this excellent shatter-cone. These uniquely shaped fractures are evidence of extremely high pressure events in hard rock delivered by asteroid impacts.

The 32 km wide Slate Islands impact structure of Ordovician age (some 450 million years old) was identified as a crater even though the hole itself has since been erased from the face of the Earth. The compression-hardened Precambrian rocks in the crater's sub-basement, however, form a circular set of islands near the north shore of Lake Superior.

A deeply eroded impact site will have the 'footprint of the elephant', even after the crater has been eroded away. A circular area of inward-facing shatter-cones are evidence that the Earth backstop'd an asteroid moving at uber-velocity speed. The tip of the "V" in this shatter-cone most likely pointed upwards and towards the centre of the now eroded impact. The Slate Islands group has a vertical 9 m tall shatter-cone, which Wikipedia says is one of the world's largest; it can be seen by following this link_

<a href="https://en.wikipedia.org/wiki/Slate_Islands_" rel="noreferrer nofollow">en.wikipedia.org/wiki/Slate_Islands_</a>(Ontario) note: Wikipedia glitch (via Slate Islands, Scotland)

All shatter-cones in the near-vicinity of an impact crater point towards the centre of a extremely concentrated burst of kinetic energy. The impacted crust takes a hard enough smack to form a suite of high pressure impact indicator 'shock minerals'. Meanwhile ground-central is momentarily transformed into sun-equivalent plasma energy. The impact flash-melts all rock within the confines of a semi-hemisphere as outlined by its circular crater.

Please investigate my Rocks From Space set if you like this sort of thing. My thanks to geologist Dorothy Campbell who is holding the specimen and providing scale. The OGS archives behind 435 James Street, Thunder Bay is geotagged.
Date
Source shatter-cone from Slate Islands impact crater
Author Mike Beauregard from Canada
Camera location48° 22′ 47.33″ N, 89° 17′ 33.45″ W Kartographer map based on OpenStreetMap.View this and other nearby images on: OpenStreetMapinfo

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This image was originally posted to Flickr by subarcticmike at https://flickr.com/photos/31856336@N03/40163660442. It was reviewed on 13 June 2022 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

13 June 2022

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current22:54, 13 June 2022Thumbnail for version as of 22:54, 13 June 20223,200 × 2,019 (2.17 MB)Geo Swan (talk | contribs)Transferred from Flickr via #flickr2commons

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