Dear John, I think, for chondrites, regolith breccias (monomict or genomict) are quite more abundant than polymict breccias. The opposite is true for achondrites. Polymict breccias, especially eucrites (howardites are polymict by definition!) are quite often polymict (there is an unusual high fraction of polymict eucrites from Antarctica), whereas regolith breccias are rather common only for lunaites (e.g. anorthositic highland breccias), which are - by definition - achondrites. A nice example for another regolithic achondrite is the howardite Kapoeta (higly solar-gas-rich material).
Regarding the H/Ls (Bremervoerde, NWA 1955, Tieschitz...): these aren't polymict breccias containing H and L lithologies, but members of a group intermediate between H and L chondrite in terms of composition and isotopic signatures. They likely come from a parent body (PB) distinct from the PBs of both, the L and H chondrites. Though they are breccias, they are not mixing products of L and H material. Best wishes, Joern _______________________________________________________________________________ Joern Koblitz MetBase Editor The MetBase Library of Meteoritics and Planetary Sciences Benquestrasse 27 D-28209 Bremen, Germany phone: +49 421 24 100 24 fax: +49 421 24 100 99 email: [EMAIL PROTECTED] _______________________________________________________________________________ > -----Urspr�ngliche Nachricht----- > Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Gesendet: Dienstag, 16. M�rz 2004 19:44 > An: J�rn Koblitz > Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED] > Betreff: Re: AW: [meteorite-list] Amgala, Tsarev and Zag > > > Joern, > > Thanx for the clarification on regolith versus the basic > breccia types. > > As far as chondrites go...is a genomict breccia with a > regolith history like Zag more or less unusual when compared > to a polymict breccia for chondrites, as in the supposed case > for Amgala? I ask this since you did point out that > achondrites are the ones that usually have the polymict > breccias, and not chondrites. > > Does this make NWA 1955 (H/L 3-4) a polymict breccia also? Or > does its classification as being unequilibrated chondrite > make it different than a breccia per say? > > John > > > Tsarev noble gas data data: > > > > he_3 he_4 ne_20 ne_21 ne_22 ar_36 ar_38 ar_40 > > 1,58 121 0,54 0,54 0,60 0,42 0,11 575 > > 2,07 108 0,78 0,82 0,88 0,83 0,20 1635 > > all values: x 10E-8 cc STP/g > > > > Reference: Herzog G. F., Vogt S., Albrecht A., Xue S., Fink > D., Klein J., > > Middleton R., Weber H. W. and Schultz L. (1997) Complex > exposure histories for > > meteorites with "short" exposure ages. Meteoritics 32, 413-422. > > > > According to this, Tsarev isn't a regolith breccia. > > > > BTW: A regolith breccia can be either polymict (different > source types of > > clasts, e.g., H3 + L6), xenolithic (some minor exotic > (non-host type) clasts, > > e.g. CM clasts in L6 host), genomict (same material type > but different > > petrologic grades, e.g. H3 + H5), or monomict (e.g. light > H3 + dark H3 > > (irradiated) lithologies). Usually, regolith breccias are > monomict or genomict > > breccias. Achondrites are often polymict breccias (e.g. > howardites, eucrites, > > diogenits, ureilites, lunaites). > > > > Regards, > > Joern > > > > > ______________________________________________________________ > _________________ > > Joern Koblitz > > MetBase Editor > > The MetBase Library of Meteoritics and Planetary Sciences > > Benquestrasse 27 > > D-28209 Bremen, Germany > > phone: +49 421 24 100 24 > > fax: +49 421 24 100 99 > > email: [EMAIL PROTECTED] > > > ______________________________________________________________ > _________________ > > > > > > > > > -----Urspr�ngliche Nachricht----- > > > Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > > > Gesendet: Montag, 15. M�rz 2004 21:20 > > > An: [EMAIL PROTECTED] > > > Betreff: [meteorite-list] Amgala, Tsarev and Zag > > > > > > > > > Adam wrote: > > > > > > > I do not believe it is going to classify as a > > > > regolith breccia but rather a polymict breccia. > > > > > > Adam also wrote: > > > > > > > I thought one distinction made for a regolith breccia is that > > > > there are signs of crystal damage caused by the solar wind > > > > > > Martin A. chirped: > > > > > > > Tsarev which is brecciated but not polymict > > > > is also altered by solar winds, isn't it? > > > > > > Hello Adam, Martin, and List, > > > > > > There are 3 types of inert and/or noble gases in some meteorites: > > > > > > (1) those produced by cosmic ray bombardment (cosmogenic); > > > (2) those resulting from radioactive decay of elements > (radiogenic) > > > in the meteorite; > > > (3) those present originally (= trapped or primordial gases). > > > > > > No. (3) is what we are interested in to find out if Amgala, Tsarev > > > and Zag have or have not been altered by solar wind particles. > > > > > > These gases are 4^He, 20^Ne, 36^Ar, 84^Kr, 132^Xe. > > > > > > There are two different sources for these inert/noble gases: > > > > > > (a) solar-type gas > > > (b) planetary-type gas > > > > > > To find out "what is what" and "which is which", meteoriticists > > > consider the relative amounts and, above all, ratios of a number > > > of isotopes. > > > > > > J.T. Wasson proposed the following arbitrary > > > definition of a solar gas-rich meteorite: > > > > > > - The 20^Ne/22^Ne ratio should be greater than 2.5 > > > - Ne isotopic data should plot above the dashed line > > > you find on p. 102 and on p. 111 of Wasson's and > > > Sears' books (see: Reference) > > > - The 4^He content should exceed 2 x 10^-5 cm^3 g^-1 > > > - The 20^Ne / 36^Ar ratio should be greater than 0.3 > > > > > > Unfortunately, I don't have any of these isotope data handy for > > > Tsarev :-( What I do have are some 3^He and 21^Ne data from > > > the MPI Mainz but they are of little help at the moment). > > > > > > There is an abstract paper by Honda et al. but they only discuss > > > cosmogenic nuclides (see: Reference) - again of little help. > > > > > > Anyway, Tsarev is a special case and as such mentioned in a > > > research article by S.K. Vogt et al. The authors group Tsarev > > > with a number of other H and L chondrites that underwent a > > > complex "two-stage exposure history": > > > > > > t1 = 8 million years, radius ca. 200 cm > > > t2 = ca. 0.3 million years, radius ca. 140 cm > > > > > > > > > Best wishes, > > > > > > Bernd > > > > > > > > > References: > > > > > > VOGT S.K. et al. (1993) On the Bur Ghelulai H5 chondrite and other > > > meteorites with complex exposure histories (Meteoritics 28, > > > 1993, 71-85). > > > > > > HONDA M. et al. (1992) Cosmogenic nuclides in the > > > Tsarev chondrite (Meteoritics 27-3, 1992, 234-235). > > > > > > WASSON J.T. (1974) Meteorites Classification and Properties > > > (Springer-Verlag, Berlin, Heidelberg, New York, pp. 97-109). > > > > > > SEARS D.W. (1978) The Nature and Origin of > > > Meteorites (Adam Hilger Ltd. Bristol, pp. 110-115). > > > > > > McSWEEN H.Y. (1999) Meteorites and Their Parent Planets > > > (Cambridge University Press, Glossary, pp. 41-44, > 111-112, 244-248). > > > > > > > > > ______________________________________________ > > > 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 mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
