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AN OVERVIEW OF THE SHERGOTTY CONSORTIUM STUDIES; J. C. Laul, Battell e, Pacific Northwest Laboratories, Richland, Washington 99352 At the 16th Lunar and Conference (LPSC),the results of the Shergotty Consortium studies were presented in a special session on the Shergotty Consortium. The Shergotty Consortium focused on 11 scientific studies that involved 14 research groups from four countries (U-S~A*,Germany, U.K., and India). These studies ranged from chemistry, petrology, age dating, cosmogenics, tracks ---- , to stable isotopic studies. Though the main emphasis of the Shergotty Consortium was on Shergotty, the consortium extended their efforts to other shergottites, and (SNC) as well. Since the 16th LPSC, the individual research groups (20) had more time to interpret the data and have written papers for publica- tions in a special issue of Geochim. Cosmochim. Acta. (GCA)Journal. As a Consortium leader, I thought it would be worthwhile to summarize the highlights of the consortium studies at the 17th LPSC. The rationales for the SNC meteorites, as potential candidates from , are discussed in various papers.(l-13) A major point worth mentioning is that origin for the SNC is strongly favored from the evidence of trapped noble gases and nitrogen component in gl asses (1 i tho1 ogy C) of EETA 79001 meteor- ite(5~12~13),which compares well with the Martian atmosphere analysis. (I4) Shergotty has a 91 y-metamorphic (magmatic and shock) hi story. Chemical study by Laul et a1 .(IE showed that the majority of REE are concen- trated in phosphate phashich are soluble in 1M HC1 and govern the bulk REE pattern. The Shergotty leachate consists of two components; component 1 may be similar to EETA 79001 leachate (whitlockite) and component 2 (apa- tite) is enriched in LREE elements. Shergotty was an open system and compo- nent 2 was introduced after crystallization. The inferred parent magma estimated from the "core" CPX using Kd values of McKay et a1 .(IS) has an overall S-shaped REE pattern and is enriched in LREE (~mwith a subchon- dritic Nd/Sm ratio, which is consistent with the Sm/Nd isotopic constraint.(3~ 16) The SPB (Shergotty ) mantle is depleted in volatile elements and strongly depeleted in siderophile and chalcophile elements. he SPB is about 2 to 4 times richer in volatiles than the ~arth.(8,10~17T The chalco- phile elements are depleted in the SPB mantle; the core is dominate b sul ides. The SPB and Earth mantles have quite different chemical signatures .?8~!0~17f Unl i ke the Earth, the SPB probably accreted homogeneously from two chemically different om onents: a reduced refractory and a volatile-rich oxidized component. f2 YE) Stoffler et a1 .(l8) reported that Shergotty consists of about 68% pyroxene (augite, pigeonite) , 24% , 2% titanomagnetite, 0.2% ilmenite, 2% whitlockite and apatite, and 3% mesostasis. Shergotty meteorite was shocked with a single shock event at 30 GPa pressure, which apparently converted pl agiocl ase to maskelyni te. The post-shock temperature is inferred as 200 + 20°C. Shock pressures and post-shock temperature for other sher- gottites are: 31 + 2 GPa and 220 t 500C for Zagami; 34 + 2 GPa and 250 2 50°C for EETA 79001; and 43 + 2 GPa and 400-8000C for ALHA 77005.(18) Cosmogenic nuclidesug) and noble gas (3~e,21~e, 38~r)(20) data in Shergotty yield a cosmic ray exposure age of about 2.5 m.y and pre-atmos- pheric size of about 12 cm radius. Fission tracks(21) in Shergotty are well formed and show no effect of deformation, indicating that they were formed after the shock event. The cosmogenic and track data favor a simple single-stage exPosure history.(21) ALHA 77005 has an exposure age of 2.5 m.y and pre-atmospheric size of 5-6 cm radius, and EETA 79001 has an expo- sure age of 0.6 m.y and pre-atmospheric size of 15-20 cm radius.(lg) Ther-

O Lunar and Planetary Institute Provided by the NASA Data System AN OVERVIEW OF THE SHERGOTTY CONSORTIUM STUDIES LAULy J. C. moluminescence (TL) sensitivit in shergottites is very low and is attributed to severe shock effects. (21,22f The TL sensitivity among the shergottites 10-fold and is related to post-shock cooling rates. Hasan and varies~ears(22 listed the shergottites in the order of increasing cooling rate; Shergotty, ALHA 77005, Zagami, and EETA 79001. Crystallization age of S ergotty on pyroxenes by the Sm-Nd method is reported as 343 k 17 m.y.(16! The Rb-Sr ages of Sher ott is reported as 166 m.y(16) and is also valid for other shergottites .?3,23) Pb-U a es are reported at about 200 m.y for Shergotty, Zagami , and EETA 79001. (2%) Jagoutz and ~inke(l6)claim the pyroxene isochron as the reliable crystal 1i zation age for Shergotty and point out that young ages noted by Rb-Sr and Pb-U systematics are the result of mobilization and redistribution of Rb and Pb by the shock event. ones (25) suggests 180 m.y as the igneous crystal liza- tion age for shergottites. Chen and ~asserbur~(24)point out that primary crystallization ages of shergottites are not well known. Shih et a1. (3) reported 1 0 .y age as the maskelynization event; whereas Chen and Wasserbur g724T and other evidences favor 2.5 m.y as the maskelynization event. It is clear that interpretations of age-dating and exposure scenarios are controversial and thus, may require further studies. In spite of age controversy, the overall general agreement that the ages are young, make the Martian hypothesis more attractive and further suggests that Mars was volcanicallyacti nthepast,andlikeEarth,maystill beactive. Wright et al. Yq6i reported that Shergotty and EETA 79001 at hi h emper- atures showevidence of a C02 trapped component. Becker and Pepin ?20j re- ported N2 data in Shergotty and th ir N2 data do not indicate the presence of any significant amount of high r5N component seen in EETA 79001 glass. The oxygen isotope data for Shergotty major minerals show evidence of igneous ion and the temperature of last equilibration is estimated at \rllOOoC.crystalli~iff Shergotty and other SNC meteorites indicate a low magnetic field pp&jenvironment, consistent with either a Marti an or asteroidal origin. Two scenarios(5) for the ejection of SNC meteorites are possible: 1) ejection as a large body (>6 m size) by a single impact on Mars and then multiple breakup in the asteroidal belt at about 11 m.y for Chassigny and nakhlites, at 2.5 m.y for Shergotty, Zagami and ALHA 77005, and at 0.6 m.y for EETA 79001; and 2) ejection of small objects (<0.5 m size) by mu1 tiple impacts on the Martian terrain at 11, 2.5 and 0.6 m.y with no breakup in space. Documentation of four small size (<0.2m) lunar meteorites make scenario two a favorable possibility. REFERENCES: (1 ) Wood and Ashwal (1981), PLPSC 12th, 1357. (2) Dreibus gt- -'my LPSC XIII, 186. (3) Shih et myGCA, 46, 2323. (4) Smith et a1 .T~~),PLPSC14th, B612.m Bogard ety. n984), GCA, 48, 1723. (6)~ecker and Pepin (1984), EPSL, 69, 225. (f)~yquist etx. n979), -GCAy 43, 1057. (8) Drei bus and Wanke98q, Proc. 7th Int. Geological Con ress, 11, 1-20. (9) McSween, Jr. (1985), Review of Geophysics, smfro)~aul,J. C. et a1 . (1986), in GCA. (11) Laul (19861, in $!A. et a1 . (1986), in GC~ 4- (15) McKay et1. (1986), (17) Treiman et m1986), (19) Nishi izum et a1 . (1986), (21) Bhandari 8-8.(1986), (23) Wooden et m1982), --LPSCII, 879. (24) Chen and Wasserburg (1986), in GCA. (25)ones (1986), in GCA. (26) Wright et al. m. (27) clayton and Mayeda (1986), in . (28) Cisowsk-86

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