Comments on: Meteor Impacts http://pulseplanet.com/sci-diaries/listener/source-of-breccia Just another WordPress weblog Sun, 14 Mar 2010 04:41:01 +0000 http://wordpress.org/?v=2.7.1 hourly 1 By: Jim Mungall http://pulseplanet.com/sci-diaries/listener/source-of-breccia/comment-page-1#comment-146 Jim Mungall Thu, 02 Aug 2007 02:44:12 +0000 http://s9515.gridserver.com/sci-diaries/listener/?p=6#comment-146 No problem. When I reread this thread I also recalled that a colleague of mine at U of Toronto recently contributed to a paper documenting the presence of fallout from the Sudbury structure in bedrock near Gunflint too. Perhaps there is a connection there. cheers Jim ...here is the title and abstract etc <blockquote> <strong>Discovery of distal ejecta from the 1850 Ma Sudbury impact event</strong> William D. Addison* R.R. 2, Kakabeka Falls, Ontario P0T 1W0, Canada Gregory R. Brumpton 211 Henry Street, Thunder Bay, Ontario P7E 4Y7, Canada Daniela A. Vallini Neal J. McNaughton Centre for Global Metallogeny, School of Earth and Geographic Sciences, University of Western Australia, Nedlands, Western Australia 6009, Australia Don W. Davis Department of Geology, Earth Sciences Centre, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1, Canada Stephen A. Kissin Philip W. Fralick Anne L. Hammond <blockquote> Department of Geology, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada ABSTRACT A 25–70-cm-thick, laterally correlative layer near the contact between the Paleoproterozoic sedimentary Gunflint Iron Formation and overlying Rove Formation and between the Biwabik Iron Formation and overlying Virginia Formation, western Lake Superior region, contains shocked quartz and feldspar grains found within accretionary lapilli, accreted grain clusters, and spherule masses, demonstrating that the layer contains hypervelocity impact ejecta. Zircon geochronologic data from tuffaceous horizons bracketing the layer reveal that it formed between ca. 1878 Ma and 1836 Ma. The Sudbury impact event, which occurred 650–875 km to the east at 1850 6 1 Ma, is therefore the likely ejecta source, making these the oldest ejecta linked to a specific impact. Shock features, particularly planar deformation features, are remarkably well preserved in localized zones within the ejecta, whereas in other zones, mineral replacement, primarily carbonate, has significantly altered or destroyed ejecta features. </blockquote> <em>published in Geology; March 2005; v. 33; no. 3; p. 193–196; doi: 10.1130/G21048.1; 4 figures; Data Repository item 2005036.</em> </blockquote> No problem. When I reread this thread I also recalled that a colleague of mine at U of Toronto recently contributed to a paper documenting the presence of fallout from the Sudbury structure in bedrock near Gunflint too. Perhaps there is a connection there.

cheers
Jim

…here is the title and abstract etc

Discovery of distal ejecta from the 1850 Ma Sudbury impact event
William D. Addison* R.R. 2, Kakabeka Falls, Ontario P0T 1W0, Canada
Gregory R. Brumpton 211 Henry Street, Thunder Bay, Ontario P7E 4Y7, Canada
Daniela A. Vallini
Neal J. McNaughton
Centre for Global Metallogeny, School of Earth and Geographic Sciences, University of Western Australia, Nedlands, Western Australia 6009, Australia
Don W. Davis Department of Geology, Earth Sciences Centre, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1, Canada
Stephen A. Kissin
Philip W. Fralick
Anne L. Hammond

Department of Geology, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada

ABSTRACT
A 25–70-cm-thick, laterally correlative layer near the contact between the Paleoproterozoic sedimentary Gunflint Iron Formation and overlying Rove Formation and between the Biwabik Iron Formation and overlying Virginia Formation, western Lake Superior region, contains shocked quartz and feldspar grains found within accretionary lapilli, accreted grain clusters, and spherule masses, demonstrating that the layer contains hypervelocity impact ejecta. Zircon geochronologic data from tuffaceous horizons bracketing the layer reveal that it formed between ca. 1878 Ma and 1836 Ma. The Sudbury impact event, which occurred 650–875 km to the east at 1850 6 1 Ma, is therefore the likely ejecta source, making these the oldest ejecta linked to a specific impact. Shock features, particularly planar deformation features, are remarkably well preserved in localized zones within the ejecta, whereas in other zones, mineral replacement, primarily carbonate, has significantly altered or destroyed ejecta features.

published in Geology; March 2005; v. 33; no. 3; p. 193–196; doi:
10.1130/G21048.1; 4 figures; Data Repository item 2005036.

]]> By: Jim Metzner http://pulseplanet.com/sci-diaries/listener/source-of-breccia/comment-page-1#comment-145 Jim Metzner Wed, 01 Aug 2007 23:35:31 +0000 http://s9515.gridserver.com/sci-diaries/listener/?p=6#comment-145 Jim: Thanks for your reply! Jim: Thanks for your reply!

]]> By: Jim Mungall http://pulseplanet.com/sci-diaries/listener/source-of-breccia/comment-page-1#comment-144 Jim Mungall Wed, 01 Aug 2007 22:58:48 +0000 http://s9515.gridserver.com/sci-diaries/listener/?p=6#comment-144 Not all breccias are impact-related, so it would be interesting to know what material constitutes the matrix to your breccia. If it is glassy or devitrified glass or if it is an igneous rock with a composition unlike ordinary terrestrial magmas, it could be related to an impact. If it is carbonate minerals or other phases deposited from percolating aqueous solutions, then an impact origin seems less likely. Other localities that I can think of off the top of my head are the Slate Islands in Lake Superior, and the Wanapitei structure immediately to the east of Sudbury. cheers Jim Mungall ps for a list of impact sites and other interesting stuff regarding impacts, check out the following two websites: http://www.unb.ca/passc/ImpactDatabase/ http://keith.aa.washington.edu/craterdata/scaling/index.htm Not all breccias are impact-related, so it would be interesting to know what material constitutes the matrix to your breccia. If it is glassy or devitrified glass or if it is an igneous rock with a composition unlike ordinary terrestrial magmas, it could be related to an impact. If it is carbonate minerals or other phases deposited from percolating aqueous solutions, then an impact origin seems less likely. Other localities that I can think of off the top of my head are the Slate Islands in Lake Superior, and the Wanapitei structure immediately to the east of Sudbury.

cheers
Jim Mungall

ps for a list of impact sites and other interesting stuff regarding impacts, check out the following two websites:
http://www.unb.ca/passc/ImpactDatabase/
http://keith.aa.washington.edu...../index.htm

]]> By: Jim Metzner http://pulseplanet.com/sci-diaries/listener/source-of-breccia/comment-page-1#comment-143 Jim Metzner Wed, 01 Aug 2007 14:22:13 +0000 http://s9515.gridserver.com/sci-diaries/listener/?p=6#comment-143 Dear Charles: Thanks for your email, which I am ccing to professor Mungall. Regards; Jim Metzner Dear Charles:
Thanks for your email, which I am ccing to professor Mungall.

Regards;
Jim Metzner

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