[meteorite-list] xenolith vs. polymict breccia?
From: Walter Branch <branchw_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:09 2004 Message-ID: <009901c3e301$b96544c0$3cebd944_at_wbranch> This is a multi-part message in MIME format. ------=_NextPart_000_0096_01C3E2D7.D02A8780 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi Aubry, Thanks very much for your comments. Yes, I was considering rocks with a matrix. I must admit, I had not = thought of rocks without a matrix - clast supported vs. matrix = supported. That is a very interesting distinction. Now I have yet = another term with which I can try to impress my wife (not an easy thing = to do after 17 years of marriage:-) Would the term xenolith apply to the individual clasts in a polymict = breccia? Could an igneous rock have a xenolithic clast of non-igneous material or could a sedimentary (e.g., = rubble pile) type host have an igneous clast, thus making both polymict = breccias? =20 I suppose given enough collisions among asteroids, any combination is = possible (e.g., chondritic monomict breccia's with exoctic igneous = clasts). >Perhaps in descriptions of meteorites the terms polymict >xenolithic breccia and monomict xenolithic breccia >should be used as oppose to just xenolithic breccia >which to me does not distinguish whether the clasts are >the same or not. It merely says that at least some of the >clasts are different to the matrix. Yes, as you have described it, this makes sense. Aubry (and everyone) I have received an email from a recently former list member who reports = that there is a paper which describes formal guidelines on the = description xenolithic inclusions in meteorites: Binns R.A. (1968) Cognate xenoliths in chondritic meteorites: Examples = in Mez=F6-Madaras and Ghubara (GCA 32, 299-317). Hope this helps. Thanks again for your comments. -Walter ------------------------------------------ www.branchmeteorites.com ----- Original Message -----=20 From: Aubrey Whymark=20 To: meteorite-list_at_meteoritecentral.com=20 Sent: Saturday, January 24, 2004 9:41 AM Subject: Re: [meteorite-list] xenolith vs. polymict breccia? Hi=20 Sorry for the length of this reply. Got carried away! Go to bottom 3 = paragraphs for summary. You are right. A polymict breccia descibes a sedimentary rock made up = of angluar clasts of different rock whilst a monomict breccia refers to = a sedimentary rock made up of angular clasts of the same rock. A breccia = can be clast supported (the clasts are touching) or matrix supported = (clasts are not touching). If clast supported, a matrix may or may not = be present. The term xenolith refers to a foreign rock or clast incorporated into = another rock. Traditionally I would tend to only use this term when = refering to igneous rocks but it could be used for exotic clasts in = sedimentary rocks (and chondrites). Ghubara is an example, being = classified as a xenolithic chondrite. If using the term xenolith you = are probably implying a matrix is present. The matrix is local, in the = case of chondrites, and the xenolith not local - it came from elsewhere. = If you were to apply the term xenolith to a matrix free polymict = breccia the xenolith would simply have to be the less abundant type of = clast. This is not satisfactory as just because it is less abundant = does not neccessarily make it the 'foreign' bit. This is my understanding of rock names: Angular clast of same composition, no matrix =3D monomict clast=20 supported breccia Angular clasts of different composition, no matrix =3D polymict clast = supported breccia Angular clasts of same composition with matrix also of same = composition =3D monomict clast or matrix supported breccia Angular clasts of same composition in a matrix of different = composition =3D monomict clast or matrix supported breccia or xenolithic = chondrite. Angular clasts of different compositions in a matrix =3D polymict = clast or matrix supported breccia or xenolithic chondrite ( but if the = matrix is the same as some of the clasts the term xenolith would only = apply to the different composition clasts) So, to summarise, in my opinion a monomict or polymict breccia can be = the same thing as a xenolithic chondrite. Xenolithic simply implies = some or all the clasts are different to the matrix of the rock. The = terms polymict and monomict do not consider the matrix. Perhaps in descriptions of meteorites the terms polymict xenolithic = breccia and monomict xenolithic breccia should be used as oppose to just = xenolithic breccia which to me does not distinguish whether the clasts = are the same or not. It merely says that at least some of the clasts = are different to the matrix. Does anyone know of some formal guidelines on the description of = meteorites? There must be some somewhere which give the formal = definition of a xenolithic chondrite. Regards, Aubrey Walter Branch <branchw_at_bellsouth.net> wrote: Hello Everyone, What is the difference between a xenolith and a polymict breccia? Is it that the xenolithic host is igneous, whereas the polymict = breccia is sedimentary? -Walter ------------------------------------------ www.branchmeteorites.com -------------------------------------------------------------------------= ----- Yahoo! Messenger - Communicate instantly..."Ping" your friends today! = Download Messenger Now ------=_NextPart_000_0096_01C3E2D7.D02A8780 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=3DContent-Type content=3D"text/html; = charset=3Diso-8859-1"> <META content=3D"MSHTML 6.00.2800.1276" name=3DGENERATOR></HEAD> <BODY bgColor=3D#ffffff> <DIV><FONT face=3DArial size=3D2>Hi Aubry,</FONT></DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV><FONT face=3DArial size=3D2>Thanks very much for your = comments.</FONT></DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV>Yes, I was considering rocks with a matrix. I must admit, I = had not=20 thought of rocks without a matrix - clast supported vs. matrix = supported. =20 That is a very interesting distinction. Now I have yet = another term=20 with which I can try to impress my wife (not an easy thing to do after = 17 years=20 of marriage:-)</DIV> <DIV> </DIV> <DIV>Would the term xenolith apply to the individual clasts in a = polymict=20 breccia? Could an igneous rock have a<BR>xenolithic clast of = non-igneous=20 material or could a sedimentary (e.g., rubble pile) type host have an = igneous=20 clast, thus making both polymict breccias? </DIV> <DIV> </DIV> <DIV><FONT face=3DArial size=3D2>I suppose given enough collisions among = asteroids,=20 any combination is possible (e.g., chondritic monomict breccia's with = exoctic=20 igneous clasts).</FONT></DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV>>Perhaps in descriptions of meteorites the terms polymict</DIV> <DIV>>xenolithic breccia and monomict xenolithic breccia</DIV> <DIV>>should be used as oppose to just xenolithic breccia</DIV> <DIV>>which to me does not distinguish whether the clasts are</DIV> <DIV>>the same or not. It merely says that at least some of = the</DIV> <DIV>>clasts are different to the matrix.</DIV> <DIV> </DIV> <DIV><FONT face=3DArial size=3D2>Yes, as you have described it, this = makes=20 sense.</FONT></DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV><FONT face=3DArial size=3D2>Aubry (and everyone)</FONT></DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV><FONT face=3DArial size=3D2>I have received an email from a = recently former=20 list member who reports that there is a paper which describes formal = guidelines=20 on the description xenolithic inclusions in meteorites:</FONT></DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV>Binns R.A. (1968) Cognate xenoliths in chondritic meteorites: = Examples in=20 Mez=F6-Madaras and Ghubara (GCA 32, 299-317).</DIV> <DIV> </DIV> <DIV><FONT face=3DArial size=3D2>Hope this helps.</FONT><BR></DIV> <DIV><FONT face=3DArial size=3D2>Thanks again for your = comments.</FONT></DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV><FONT face=3DArial size=3D2>-Walter</FONT></DIV> <DIV><BR></DIV> <DIV>------------------------------------------<BR><A=20 href=3D"http://www.branchmeteorites.com">www.branchmeteorites.com</A></DI= V> <BLOCKQUOTE=20 style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px"> <DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV> <DIV=20 style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black"><B>From:</B>=20 <A title=3Dtinbider_at_yahoo.co.uk = href=3D"mailto:tinbider_at_yahoo.co.uk">Aubrey=20 Whymark</A> </DIV> <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A=20 title=3Dmeteorite-list_at_meteoritecentral.com=20 = href=3D"mailto:meteorite-list_at_meteoritecentral.com">meteorite-list@meteor= itecentral.com</A>=20 </DIV> <DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Saturday, January 24, = 2004 9:41=20 AM</DIV> <DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Re: [meteorite-list] = xenolith=20 vs. polymict breccia?</DIV> <DIV><BR></DIV> <DIV>Hi </DIV> <DIV> </DIV> <DIV>Sorry for the length of this reply. Got carried away! = Go to=20 bottom 3 paragraphs for summary.</DIV> <DIV> </DIV> <DIV>You are right. A polymict breccia descibes a sedimentary = rock made=20 up of angluar clasts of <U>different</U> rock whilst a monomict = breccia refers=20 to a sedimentary rock made up of angular clasts of the <U>same</U> = rock. A=20 breccia can be clast supported (the clasts are touching) or = matrix=20 supported (clasts are not touching). If clast supported, a = matrix may or=20 may not be present.</DIV> <DIV> </DIV> <DIV>The term xenolith refers to a foreign rock or clast incorporated = into=20 another rock. Traditionally I would tend to only use this term = when=20 refering to igneous rocks but it could be used for exotic clasts in=20 sedimentary rocks (and chondrites). Ghubara is an = example, being=20 classified as a xenolithic chondrite. If using the term xenolith = you are=20 probably implying a matrix is present. The matrix is local, in = the case=20 of chondrites, and the xenolith not local - it came from = elsewhere. If=20 you were to apply the term xenolith to a matrix free polymict breccia = the=20 xenolith would simply have to be the less abundant type of = clast. This=20 is not satisfactory as just because it is less abundant does not = neccessarily=20 make it the 'foreign' bit.</DIV> <DIV> </DIV> <DIV>This is my understanding of rock names:</DIV> <DIV> </DIV> <DIV>Angular clast of same composition, no matrix =3D monomict clast = </DIV> <DIV>supported breccia</DIV> <DIV> </DIV> <DIV>Angular clasts of different composition, no matrix =3D polymict = clast=20 supported breccia</DIV> <DIV> </DIV> <DIV>Angular clasts of same composition with matrix also of same = composition =3D=20 monomict clast or matrix supported breccia</DIV> <DIV> </DIV> <DIV>Angular clasts of same composition in a matrix of different = composition =3D=20 monomict clast or matrix supported breccia <U>or</U> xenolithic=20 chondrite.</DIV> <DIV> </DIV> <DIV>Angular clasts of different compositions in a matrix =3D polymict = clast or=20 matrix supported breccia <U>or</U> xenolithic chondrite ( but if the = matrix is=20 the same as some of the clasts the term xenolith would only apply to = the=20 different composition clasts)</DIV> <DIV> </DIV> <DIV>So, to summarise, in my opinion a monomict or polymict breccia = can be the=20 same thing as a xenolithic chondrite. Xenolithic simply implies = some or=20 all the clasts are different to the matrix of the rock. The = terms=20 polymict and monomict do not consider the matrix.</DIV> <DIV> </DIV> <DIV>Perhaps in descriptions of meteorites the terms polymict = xenolithic=20 breccia and monomict xenolithic breccia should be used as oppose to = just=20 xenolithic breccia which to me does not distinguish whether the clasts = are the=20 same or not. It merely says that at least some of the clasts are = different to the matrix.</DIV> <DIV> </DIV> <DIV>Does anyone know of some formal guidelines on the description of=20 meteorites? There must be some somewhere which give the formal=20 definition of a xenolithic chondrite.</DIV> <DIV> </DIV> <DIV>Regards,</DIV> <DIV> </DIV> <DIV>Aubrey</DIV> <DIV> </DIV> <DIV> </DIV> <DIV><BR><B><I>Walter Branch <branchw_at_bellsouth.net></I></B>=20 wrote:</DIV> <BLOCKQUOTE class=3Dreplbq=20 style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px = solid"> <META content=3D"MSHTML 6.00.2800.1276" name=3DGENERATOR> <STYLE></STYLE> <DIV><FONT face=3DArial size=3D2>Hello Everyone,</FONT></DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV><FONT face=3DArial size=3D2>What is the difference between a = xenolith and a=20 polymict breccia?</FONT></DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV><FONT face=3DArial size=3D2>Is it that the xenolithic host is = igneous,=20 whereas the polymict breccia is sedimentary?</FONT></DIV> <DIV><FONT face=3DArial size=3D2></FONT> </DIV> <DIV><FONT face=3DArial size=3D2>-Walter</FONT></DIV> <DIV><FONT face=3DArial=20 size=3D2>------------------------------------------<BR><A=20 = href=3D"http://www.branchmeteorites.com/">www.branchmeteorites.com</A></F= ONT></DIV></BLOCKQUOTE> <P> <HR SIZE=3D1> <FONT face=3DArial size=3D2><A=20 = href=3D"http://uk.rd.yahoo.com/mail/tagline_messenger/*http://uk.messenge= r.yahoo.com"><B>Yahoo!=20 Messenger</B></A> - Communicate instantly..."Ping" your friends today! = <A=20 = href=3D"http://uk.rd.yahoo.com/mail/tagline_messenger/*http://uk.messenge= r.yahoo.com/download/index.html"><STRONG>Download=20 Messenger Now</STRONG></A></FONT></BLOCKQUOTE></BODY></HTML> ------=_NextPart_000_0096_01C3E2D7.D02A8780-- Received on Sun 25 Jan 2004 12:11:43 AM PST |
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