[meteorite-list] Black inclusions in NWA R-Chondrites?
From: Jeff Kuyken <info_at_meteoritecentral.com>
Date: Tue Jul 25 07:15:12 2006 Message-ID: <002001c6afdb$9721ef40$6501a8c0_at_mandin4f89ypwu> Thanks to everyone who replied both on and off-list regarding the Rumuruti chondrites and their black inclusions. I will update the my page over the next week or two with the info. Thanks again, Jeff ----- Original Message ----- From: bernd.pauli_at_paulinet.de To: Meteorite-list_at_meteoritecentral.com Sent: Tuesday, July 25, 2006 4:25 AM Subject: [meteorite-list] Black inclusions in NWA R-Chondrites? Hi Jeff and List, "I'm hoping someone may know of an abstract/personal/web info on the black (xenolithic?) inclusions found in some of the NWA R-Chondrites? Any info would be appreciated either on or off-list." Here is an example: http://www.meteorites.com.au/features/nwa2921.html Beautiful specimen with a very conspicuous, large, dark clast and another equally large but light greyish-brown clast set in a medium-gray matrix (this light-dark structure is typical of regolith breccias). As for the black inclusion, I don't think it is xenolithic. It represents unequilibrated material of low(er) petrologic type. Hence all those tiny chondrules set in a dark matrix that resembles that of carbonaceous chon- drites. The light- to medium-colored matrix areas show only few chondrules and/or chondrule relics and thus correspond to petrologic types 5 or 6. The dark, chondrule-rich clasts are unequilibrated and correspond to type 3.x (about 3.8 some sources say). But: the dark clasts are NOT carbonaceous but are due to the dispersion of tiny grains of sulfides and Cr-spinels, which causes silicate darkening. My beautiful NWA 3098 (R5) and my latest addition, NWA 2943 (R3-6), which is still in San Diego with Cap'n Blood, also show these dark, unequilibrated clasts. But, whereas my NWA 3098 from Stefan clearly shows chondrule-poor, light clasts and a few small but chondrule-rich dark clasts (see JPEGs in my private mail to you), the NWA 2943 from Michael Blood has an overall higher abundance of chondrules - the chondrules are more evenly distributed. throughout the busy matrix. Best wishes, Bernd Here are some useful references: BLAND P. et al. (1992a) A unique type 4 chondrite from the Sahara - Acfer 217 (abs. Meteoritics 27, 1992, 204-205). BISCHOFF A. et al. (1994a) Acfer 217 - a new member of the Rumuruti chondrite group (Meteoritics 29, 264-274). DIXON E.T. et al. (2003) 39Ar-40Ar chronology of R chondrites (MAPS 38-3, 2003, pp. 341-355). JACKEL A. et al. (1996) DaG 013 - A new Saharan Rumuruti- chondrite (R3-6) with highly unequilibrated (Type 3) fragments (abs. Lun.Plan. Sci. 27, 595-596). BISCHOFF A. (2000) Mineralogical characterization of primitive, type-3 lithologies in Rumuruti chondrites (MAPS 35-4, 200, pp. 699-706). BISCHOFF A. et al. (2001) Mineralogy, Chemistry, and noble gases of the unpaired Rumuruti chondrites NWA 753 and NWA 755 (MAPS 36-9, 2001, A021). LINGEMANN C.M. et al. (2000) Rumuruti chondrites: Origin and evolution of primitive components (MAPS 35-5, 2000, A098). ______________________________________________ Meteorite-list mailing list Meteorite-list_at_meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list Received on Tue 25 Jul 2006 07:15:05 AM PDT |
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