Papers on five new Mars meteorites will be presented at the upcoming 33rd Lunar And Planetary Science Conference (LPSC) to be in March 2002 in Texas. Taking into account pairing, this now raises the number of Mars meteorites to 24. The new meteorites are:
Location Name Found Mass Type NWA 1068 Sahara Desert 654 grams picritic shergottite Y000593 Antarctica 13.7 kg clinopyroxenite (nakhlite) Y000749 Antarctica 1.3 kg clinopyroxenite (nakhlite) YA1075 Antarctica 55 grams peridotite (lherzolitic shergottite) Dhofar 378 Oman 15 grams shergottite GRV 9927 Antarctica 9.97 grams shergottite
The two nakhlites (Y000593 & Y000749) are assumed to be paired together. I have photos of NWA 1068 provided by the finder available here:
The two nakhlites are the first to be found in the Antarctic, and at 13.7 kg, Y000593 is the largest nakhlite ever found. Y000593 is also the second largest Mars meteorite fragment found, second only to the Zagami meteorite which fell in Nigeria in 1962. Of additional note, NWA 1068 is the first picritic shergottite because of its high olivine content. Dhofar 378 unusual in that it is composed predominantly of maskelynite, a plagioclase glass most likely formed by shock from a large impact event.
Below are excerpts from the abstracts of the papers that will be presented at LPSC. Note that the total known weight of NWA 1068 is listed as 577 grams in the abstract, but the finder has informed me that they have found additional fragments which increases the total weight to 654 grams.
THE PICRITIC SHERGOTTITE NORTH WEST AFRICA 1068 (NWA 1068 or "Louise Michel")
J. A. Barrat, et al.
LPS XXXIII #1538
Introduction: North West Africa 1068 (TKM about 577 g), a new picritic shergottite was found last April in Moroccan Sahara by meteorite hunters ("La Memoire de la Terre"). Its synonymous name of "Louise Michel" (which we have used during the Met'Soc meeting last september) is preferred to avoid confusion with the many meteorites of all types reported under the NWA nomenclature (including now 4 Martian meteorites). In this abstract, its main petrological and geochemical features will be described.
Petrography: "Louise Michel" is a greenish- brown rock totally devoid of fusion crust. It displays a porphyritic texture consisting of a fine-grained groundmass and olivine grains. Olivines with various habits occur as clusters often associated with chromite, or single crystals ranging in size from 50 \265m to 2 millimeters. The largest crystals contain magmatic inclusions, consisting of two immiscible silica-rich glasses, Ca-rich pyroxenes and Fe-sulfides.
Chemistry: The bulk composition of "Louise Michel" has been determined for 45 elements. It is an Al-poor ferroan basaltic rock, rich in MgO. Its major element abundances are similar to those reported for EETA79001A . Key element ratios such as Fe/Mn (=45), Al/Ti (=6.6), and Ga/Al (=4.4 10-4) are typical of Martian meteorites. The trace elements demonstrate unambiguously that "Louise Michel" is unpaired with any of the other hot desert finds: it is the first picritic shergottite with a REE pattern similar to those of Shergotty, Zagami, Los Angeles, and Djel Ibone (NWA 856).
THE FIRST NAKHLITE FROM ANTARCTICA.
N. Imae, et al.
LPS XXXIII #1483
Introduction: 27 meteorites from Mars have been identified adding of recent findings of 15 meteorites including paired specimen from hot deserts these five years. Most of these are classified to be shergottites, and nakhlites have been limited to be only four including one from a hot desert. Recent Japanese Antarctic Research Expedition (JARE) found the heaviest achondrite in Antarctica (Y000593) of 13.7 kg from the bare ice field around the Yamato Mountains. The petrographical studies and noble gas analyses of the specimen (Y000593) and paired specimen (Y000749) assured that these are nakhlites coming from Mars, consisting with the recent classification. The finding of nakhlites in Antarctica is for the first time and it suggests that the Yamato meteorite field potentially includes more unique meteorites. We describe the analytical results of the meteorite.
Field Occurrence: About 60 % of Y000593 is covered with black fusion crust, and the interior is greenish colored. Several days after the finding the quite similar specimen (Y000749 of 1.3 kg) was found. It is suggested that it is a paired specimen with Y000593. Two meteorites locate on a bare ice field of the north of JAREIV nunataks, and the area had insufficiently searched only by JARE-20. In the area, the heaviest meteorite in the Yamato bare ice field has been also found by the same expedition of JARE-41.
Conclusion: Our mineralogical-petrographical and noble gas studies strongly suggest that Y000593 and the paired specimen Y000749 are a Martian meteorite subclassified into nakhlites.
New Martian Meteorite Identified as a Lherzolitic Shergottite Similar to ALH-77005
LPS XXXIII #1248
A meteorite found at Antarctica, which we have given the tentative name of YA1075, has been identified as the new martian meteorite which belong to one of shergottite. The YA1075 meteorite is 55 grams in weight which nearly complete stone with dark green color and partly covered_by the shiny-black fusion crust. The interior of the stone shows grey to light grey in color, and brecciated partly. The stone looks like type A of the Yamato diogenites especially Yamato-74013 diogenite for its appearance. The YA1075 meteorite is also similar to one of Antarctic martian meteorites such as ALH-77005 lherzoritic shergottite and other shergottites.
The YA1075 meteorite consists mostly of pyroxenes including many olivine grains poikiliticaly with maskelynized plagioclase interstitially, and traced some opaques. The specimen have been identified as one of the martian meteorite for its mineral assemblages and mineral compositions, especialy its maskelynized plagioclase and their compositions(~An50). Clayton analyzed this meteorite on oxygen isotopic compositions and he suggested that he YA1075 meteorite is one of the martian meteorites based on following oxygen istopes: 3.95 \245 18O,2.23 \245 17O and +0.18 \24517O. Oxygen isotope data strongly supported to authors conclusion.
Plagioclase of the YA1075 meteorite has a very unique compositons as same as those of the martian meteorites especially those of shergottites for example ALH-77005 lherzolitic shergottites and other shergottites. However the YA1075 meteorite is quite differed from those of all known other achondrites, particularly all of diogenictic achondrites and all eucrites, and all of the lunar meteorites. So author concluded that the YA1075 meteorite is a martian meteorite belong to one of lherzolitic shergottite.
A NEW SHERGOTTITE FROM OMAN, Dhofar 378.
Y. Ikeda, et al.
LPS XXXIII #1434
Introduction: The new shergottite Dhofar 378 was recently recovered from the Oman desert with fresh black fusion crust. It has a doleritic or micro-gabbroic texture, and the grain sizes of the main minerals are about 1 mm in length and a few hundreds of microns in width. Dhofar 378 is one of the most ferroan shergottite and may represent a late stage fractional crystallization product of a Martian magma.
Petrology: Dhofar 378 consists mainly of ferroan clinopyroxenes (augite and pigeonite) and plagioclase glass with minor minerals of hedenbergite, pyrox-ferroite, fayalite, silica, titanomagnetite, ilmenite, sulfide, phosphate, and rhyolitic glass. The modal composition of the stone is; clinopyroxenes (49 vol.%), plagioclase glass (47 vol.%), titanomagnetite including ilmenite (3 vol.%) and phosphates (1 vol.%).
Oxygen isotopes; The oxygen isotopic composition of the stone was obtained by T.K.Mayeda and R.N.Clayton. The result is: delta O 18 = +4.46 permil, and delta O 17 = +2.52 permil, indicating that this stone is within the range of previously analyzed Martian meteorites.
Pairing; Dhofar 378 was recovered from an area near the Dhofar 019 basaltic shergottite. Dhofar 019 is doleritic, but it may not be a pair with the new shergottite. It is because Dhofar 019 contains olivine grains with Fe/(Mg+Fe) ratios of 0.4-0.75 , although Dhofar 378 does not contain such magnesian olivine except for fayalite. Pyroxenes in Dhofar 019 are more magnesian than those in the new shergottite. Dhofar 378 is rather similar in lithology to Northwest Africa 480, but the latter has a homogeneous maskelynite (An46-50) and lacks in pyroxferroite.
ANTARCTIC GRV9927: A NEW MEMBER OF SNC METEORITES.
Cheng-Yi LIN, et al.
LPS XXXIII #1562
The GRV9927 meteorite was collected from the ice sheet in the vicinity of the Grove Hill by Xiao-Han LIU and Yi-Tai JU from the Academy Sinica during the 16th Antarctic expedition in 1999. Based on the observations under polarizing microscope, scanning electron microscope and electron probe microanalyses the GRV9927 meteorite is considered as an ultramafic achondrite. Its mineral and chemical compositions are quite similar to those of the ALHA77005 meteorite. It implies that the GRV9927 meteorite can be recognized as a member of SNC clan.
The GRV9927 meteorite looks like a rounded triangular cone. It is 9.97g in weight and partially covered by dark fusion crust. This meteorite consists predominantly of olivine and pyroxene. The olivine crystals have a distinctive brown colour and the pyroxenes are colourless in thin sections. The structure and texture are heterogeneous on a centimeter scale. Both cumulate and poikilitic textures can be seen under the polarizing microscope. Some euhedral and pyroxens in certain areas and some euhedral olivine crystals are enclosed by pyroxenes in other areas. A small amount of maskelynite, kamacite, troilite and chromite can be found in the interstices between olivines and pyroxenes. The mineral composition of the GRV9927 is intermediate between pyroxene-rich nakhlites and olivine-rich Chassigny. In addition, the pyroxene in GRV9927 is mainly orthopyroxene. It is distinguish from any other SNC meteorites.
The chemical composition of GRV9927 has been analyzed using EDS method. The following features can be recognized in comparison with the SNC meteorites.
1. The major element abundance in GRV9927 is similar to those in SNC meteorites. The SiO2 contents in GRV9927 are close to those in shergottites and the Al2O3 contents are close to those in ALHA77005. The FeO, MgO, CaO contents are close to ALHA77005 as well and they are intermediate between those in nakhlite and Chassigny.
2. Just like other SNC meteorites the high ratio of Fe/(Fe+Mg) in GRV9927 indicates that it also formed from differentiated parent magmas.
3. As Ma et al. (1982) reported the compositions of major and some minor elements among shergotties have certain colinearities and ALHA77005 and EETA79001B can be combined in various proportions to produce the approximate compositions of the other shergottites [1, 3] . The major element concentrations in GRV9927 can be projected on this plot. They just fall into the range and close to the composition of ALHA77005.
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