New Noble Gas Data of Four Enstatite Chondrites and Zaklodzie

Introduction: In two recent studies, the noble gas records of 57 enstatite chondrites (E-chondrites) are presented [1,2]. Here, we report the rare gas content of one new (SAH00225) and three so far undetermined Echondrites recovered in Antarctica (ALHA81260, MAC88180, MAC88184) (tab. 1). Both meteorites from the Mac Alpine Hills are EL3s and have been considered to be paired with MAC88136 [3,4]. In accordance with those findings, all the three of them show the same mineralogical type [5] and also reveal clear Cr excesses [6]. However, another work concluded on the basis of textural differences that they are not paired [7]. An additional well-established parameter to prove pairing is the noble gas record of meteorites. The noble gas concentrations and isotopic ratios of MAC88136 have been reported in [1,2]. Here, we present the rare gas content of MAC88180 and 88184. The other two E-chondrites investigated in this study are ALHA81260 and SAH00225, both EL6s. Additionally, we determined the noble gas record of Zaklodzie, an unusual enstatite meteorite that was found in Poland recently [8]. We will compare it with our rare gas results for Itqiy to be presented at this conference as well [9]. Itqiy is also classified as an unusual enstatite meteorite and was recovered from the Sahara in 2000 [10]. Results and discussion: MAC88180+88184. MAC88180 clearly exhibits solar noble gases and all isotopic ratios closely resemble those of MAC88136. Its Ne cosmic-ray exposure age (T21) is 2.8 Ma, compared to 3.7 Ma of MAC88136. MAC88184 reveals a similarly low T21 of 2.7 Ma. The noble gases of this meteorite, however, are not dominated by the solar component. He and Ar are basically radiogenic or trapped whereas the isotopic composition of Ne plots on a mixing line of the cosmogenic and solar signature. ALHA81260 and SAH00225. These two meteorites contain no solar rare gases but show a subsolar component. T21 are 30.6 Ma and 34.6 Ma, respectively. According to [2], the noble gas content of Echondrites leads to two different patterns of trapped heavy noble gases depending on the petrologic type (1). All E-chondrites of type 4 to 6 contain a mixture of trapped planetary rare gases (Q) and a subsolar component (average elemental ratios for EL6s are Ar/Xe = 990 ± 58 and Ar/Kr = 368 ± 16). In contrast to that, E3-chondrites, if solar gas free, show a mixture of Q and a so-called sub-Q signature with lower elemental ratios (Ar/Xe = 23.1 ± 4.1 and Ar/Kr = 34 ± 17). Trapped solar noble gases only occur in type 3 E-chondrites. These data are supported by the new results with a subsolar component in ALHA81260 and SAH00225, a solar signature in MAC88180 and a sub-Q pattern in MAC88184, which is mainly solar gas free. Zaklodzie. Unlike Itqiy, Zaklodzie exhibits radiogenic He and Ar as well as essentially Q-type trapped noble gases. Its T21 of about 77 Ma as well as its Xe concentration are considerably higher than the corresponding values of Itqiy. The only similarity between Zaklodzie and Itqiy is the cosmogenic Ne signature.