AW: [meteorite-list] NWA 2058 and pseudotachylite
> Shock stage: S6 plus ... S7, S8...? The problem with further increasing shock pressures is that the rock is extremely heated up to melting by the energy of the shock wave and the compression and shear friction involved. This will vanish all signs of shock the material experienced before the subsequent annealing and healing of shock features happened. That's why impact melt rocks doesn't show the typical features of heavy shock which are necessary to properly classify the shock stage. Observed shock features in impact melt rocks or IMBs originated from secondary (later) shock events (imagine heavily bombardment of the chondrite parent body and further processing of the material). So, I think S6 is the limit. Beyond that, nobody can tell for sure. Joern > -Ursprüngliche Nachricht- > Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Gesendet: Mittwoch, 24. März 2004 21:44 > An: [EMAIL PROTECTED] > Betreff: [meteorite-list] NWA 2058 and pseudotachylite > > > > It is the most shocked chondrite yet discovered with no chondritic > > features that can be measured for metamorphism meaning ... > > So the Yanzhuang (H6, S6) chondrite that fell 1990, Oct 31, and is > one of the most severely reheated and the most severely shocked > H chondrites has got a new "brother". > > > Shock stage: S6 plus ... > > According to Stöffler, S6 means: very strongly shocked, > recrystallization > of olivine and phase transformations of olivine (ringwoodite). > > I wonder if this will lead to an extension of the shock stage > scale to S7 ?! > > > this meteorite was formed by a hypervelocity impact on the > surface of an > > asteroid and cooled within milliseconds as it was ejected > out into space. > > Fast cooling and complete melting also happened to Yanzhuang. > F. Begemann > et al. write: "The metal in the FeNi-FeS blobs shows the > distinct dentritic > structure characteristic of fast cooling. Indeed, the typical > dentrite width > of some 30 micrometers is comparable to that observed in a > metal regulus of > vacuum-melted H-chondrite Pantar that was cooled down to 800°C within > approximately 3 minutes." > > Adam, do NWA 2058 FeNi-FeS blobs also show this dentritic structure? > > > NWA 2058 is an H (Pseudotachylite) ... > > According to Rubin, the Elbert LL6 chondrite contains narrow > glassy pseudo- > tachylite-like veins. If these veinlets are "type-A", they > may be coesite- > and stishovite-bearing. > > Adam, any reports of these high-pressure polymorphs in NWA 2058? > > Here on Earth, The Vredefort Dome and Sudbury (Sudbury > breccia) structures > are the type areas for this unusual rock type called > pseudotachylite but it has > also been observed in other impact structures (Rochechouart, > Manicouagan, > Slate Islands). > > > Best wishes, > > Bernd > > > References: > > STÖFFLER D. et al. (1991) Proposal for a revised petrographic shock > classification of chondrites (Meteoritics 26-4, 1981, A398-A399). > > BEGEMANN F. et al. (1992) On the thermal history of heavily shocked > Yanzhuang H-chondrite (Meteoritics 27-2, 1992, 174-178). > > XIANDE X. et al. (1991) The new meteorite fall of Yanzhuang, > a severely > shocked H6 chondrite with black molten materials (Meteoritics > 26-4, 1991, A411). > > FRENCH B.M. (1998) Traces of Catastrophe (LPI Contribution > 954, pp. 65-69). > > RUBIN A.E. (2003) Post-shock annealing and post-annealing > shock: implications > for the thermal and shock histories of ordinary-chondrite > parent bodies (Lunar and > Planetary Science XXXIV (2003), 1263.pdf). > > To: [EMAIL PROTECTED] > Cc: [EMAIL PROTECTED] > > > __ > Meteorite-list mailing list > [EMAIL PROTECTED] > http://www.pairlist.net/mailman/listinfo/meteorite-list > __ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] NWA 2058 and pseudotachylite
[EMAIL PROTECTED] wrote: Here on Earth, The Vredefort Dome and Sudbury (Sudbury breccia) structures are the type areas for this unusual rock type called pseudotachylite but it has also been observed in other impact structures (Rochechouart, Manicouagan, Slate Islands). Pseudotachylites are not *just* impact-specific fault melts. They may also form along TECTONIC fault planes here on earth and I have heard of them associated with mass-wasting deposits. Matt Best wishes, Bernd References: STÖFFLER D. et al. (1991) Proposal for a revised petrographic shock classification of chondrites (Meteoritics 26-4, 1981, A398-A399). BEGEMANN F. et al. (1992) On the thermal history of heavily shocked Yanzhuang H-chondrite (Meteoritics 27-2, 1992, 174-178). XIANDE X. et al. (1991) The new meteorite fall of Yanzhuang, a severely shocked H6 chondrite with black molten materials (Meteoritics 26-4, 1991, A411). FRENCH B.M. (1998) Traces of Catastrophe (LPI Contribution 954, pp. 65-69). RUBIN A.E. (2003) Post-shock annealing and post-annealing shock: implications for the thermal and shock histories of ordinary-chondrite parent bodies (Lunar and Planetary Science XXXIV (2003), 1263.pdf). To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] __ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list __ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
[meteorite-list] NWA 2058 and pseudotachylite
> It is the most shocked chondrite yet discovered with no chondritic > features that can be measured for metamorphism meaning ... So the Yanzhuang (H6, S6) chondrite that fell 1990, Oct 31, and is one of the most severely reheated and the most severely shocked H chondrites has got a new "brother". > Shock stage: S6 plus ... According to Stöffler, S6 means: very strongly shocked, recrystallization of olivine and phase transformations of olivine (ringwoodite). I wonder if this will lead to an extension of the shock stage scale to S7 ?! > this meteorite was formed by a hypervelocity impact on the surface of an > asteroid and cooled within milliseconds as it was ejected out into space. Fast cooling and complete melting also happened to Yanzhuang. F. Begemann et al. write: "The metal in the FeNi-FeS blobs shows the distinct dentritic structure characteristic of fast cooling. Indeed, the typical dentrite width of some 30 micrometers is comparable to that observed in a metal regulus of vacuum-melted H-chondrite Pantar that was cooled down to 800°C within approximately 3 minutes." Adam, do NWA 2058 FeNi-FeS blobs also show this dentritic structure? > NWA 2058 is an H (Pseudotachylite) ... According to Rubin, the Elbert LL6 chondrite contains narrow glassy pseudo- tachylite-like veins. If these veinlets are "type-A", they may be coesite- and stishovite-bearing. Adam, any reports of these high-pressure polymorphs in NWA 2058? Here on Earth, The Vredefort Dome and Sudbury (Sudbury breccia) structures are the type areas for this unusual rock type called pseudotachylite but it has also been observed in other impact structures (Rochechouart, Manicouagan, Slate Islands). Best wishes, Bernd References: STÖFFLER D. et al. (1991) Proposal for a revised petrographic shock classification of chondrites (Meteoritics 26-4, 1981, A398-A399). BEGEMANN F. et al. (1992) On the thermal history of heavily shocked Yanzhuang H-chondrite (Meteoritics 27-2, 1992, 174-178). XIANDE X. et al. (1991) The new meteorite fall of Yanzhuang, a severely shocked H6 chondrite with black molten materials (Meteoritics 26-4, 1991, A411). FRENCH B.M. (1998) Traces of Catastrophe (LPI Contribution 954, pp. 65-69). RUBIN A.E. (2003) Post-shock annealing and post-annealing shock: implications for the thermal and shock histories of ordinary-chondrite parent bodies (Lunar and Planetary Science XXXIV (2003), 1263.pdf). To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] __ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
[meteorite-list] NWA 2058 and pseudotachylite
> It is the most shocked chondrite yet discovered with no chondritic > features that can be measured for metamorphism meaning ... So the Yanzhuang (H6, S6) chondrite that fell 1990, Oct 31, and is one of the most severely reheated and the most severely shocked H chondrites has got a new "brother". > Shock stage: S6 plus ... According to Stöffler, S6 means: very strongly shocked, recrystallization of olivine and phase transformations of olivine (ringwoodite). I wonder if this will lead to an extension of the shock stage scale to S7 ?! > this meteorite was formed by a hypervelocity impact on the surface of an > asteroid and cooled within milliseconds as it was ejected out into space. Fast cooling and complete melting also happened to Yanzhuang. F. Begemann et al. write: "The metal in the FeNi-FeS blobs shows the distinct dentritic structure characteristic of fast cooling. Indeed, the typical dentrite width of some 30 micrometers is comparable to that observed in a metal regulus of vacuum-melted H-chondrite Pantar that was cooled down to 800°C within approximately 3 minutes." Adam, do NWA 2058 FeNi-FeS blobs also show this dentritic structure? > NWA 2058 is an H (Pseudotachylite) ... According to Rubin, the Elbert LL6 chondrite contains narrow glassy pseudo- tachylite-like veins. If these veinlets are "type-A", they may be coesite- and stishovite-bearing. Adam, any reports of these high-pressure polymorphs in NWA 2058? Here on Earth, The Vredefort Dome and Sudbury (Sudbury breccia) structures are the type areas for this unusual rock type called pseudotachylite but it has also been observed in other impact structures (Rochechouart, Manicouagan, Slate Islands). Best wishes, Bernd References: STÖFFLER D. et al. (1991) Proposal for a revised petrographic shock classification of chondrites (Meteoritics 26-4, 1981, A398-A399). BEGEMANN F. et al. (1992) On the thermal history of heavily shocked Yanzhuang H-chondrite (Meteoritics 27-2, 1992, 174-178). XIANDE X. et al. (1991) The new meteorite fall of Yanzhuang, a severely shocked H6 chondrite with black molten materials (Meteoritics 26-4, 1991, A411). FRENCH B.M. (1998) Traces of Catastrophe (LPI Contribution 954, pp. 65-69). RUBIN A.E. (2003) Post-shock annealing and post-annealing shock: implications for the thermal and shock histories of ordinary-chondrite parent bodies (Lunar and Planetary Science XXXIV (2003), 1263.pdf). To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] __ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
