Mathematics – Logic
Scientific paper
Jul 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000m%26ps...35..827f&link_type=abstract
Meteoritics & Planetary Science, vol. 35, no. 4, pp. 827-839 (2000).
Mathematics
Logic
29
Scientific paper
Dar al Gani 489 (DaG 489) is a meteorite fragment of 2146 g found in the Libyan Sahara by a meteorite finder during one of his search campaigns in 1997-98. It is a porphyritic rock with mm-sized olivine crystals (Fo79-59) set in a fine-grained groundmass (avg. grain size 0.1 mm) consisting of pigeonite (En75-57 Wo5-15) crystals and interstitial feldspathic glass (An67-56 Or0-1). Minor phases include enstatite (En82-71 Wo2-4), augite (En48-52 Wo29-32), chromite, Ti-chromite, ilmenite, pyrrhotite, merrillite and secondary calcite and iron oxides. Based on mineralogical, petrographic, bulk chemical, oxygen isotope and noble gases data, DaG 489 can be classified as a highly shocked Martian meteorite (e.g., Fe/Mn(bulk) = 42.1, Ni/Mg(bulk) = 0.002; ?17O = 2.89, ?18O = 4.98 and ?17O = 0.305), belonging to the basaltic shergottite subgroup. The texture and modal composition of DaG 489 are indeed those of basalts; nonetheless, the bulk chemistry, the abundance of large olivine and chromite crystals, and enstatitic pyroxene suggest some relationship with lherzolitic shergottites. As such, DaG 489 is similar to the hybrid shergottite EETA79001 lithology A; however there are some relevant differences including a higher olivine content (20 vol. %), the lack of orthopyroxene megacrysts, a higher molar Mg/(Mg+Fe)(molar) = 0.68 and a lower REE content in the bulk sample. Therefore DaG 489 has the potential of providing us with a further petrogenetic link between basaltic and lherzolitic shergottites. Noble gases data show that DaG 489 has an ejection age of ~1.3 Ma. This young age lends support to the requirement of several ejection events to produce the current population of SNC meteorites. In terms of texture, mineral and bulk compositions, shock level and weathering features DaG 489 is essentially identical to Dar al Gani 476 (DaG 476), another basaltic shergottite independently found about 25 km due NNE of DaG 489. Since DaG 489 also has the same exposure history as DaG 476, it is very likely that both meteorites are fragments of the same fall. In addition to the existing hypotheses on the petrogenesis of the similar EETA79001 lithology A and the identical DaG 476, we propose that DaG 489 could have formed through high-degree partial melting of a lherzolite-like material.
D'Orazio Massimo
Folco Luigi
Franchi Ian A.
Rocchi Sergio
Schultz Ludolf
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