Comparative Chemical Investigations among E3 Chondrules Mesostasis

Introduction: Enstatite chondrites have a particular minera-logical composition which consists of silicates, sulfide, metal as major phases. But, were the chondrules of EH and EL chondrites originated from the genetic context? In order to answer to this question we have started to investigate on mesostasis chemical composition of chondrules in three thin sections: one from EET90299-EL3 chondrite and two from SAH97072-EH3. Major and minor elements contents in chondrules were analyzed by the electron microprobe (CNR, Padova, Italy). Results: For all the chondrules selected for investigating on mesostasis we found that although the87wt% for EH3 chondrules these contents are comparable. The average values for the chondrules of the two chondrites classes are comparable. There is also a good correlation between Al 2 O 3 and MgO that could be explained as a function of Al decay. The average CaO content is again comparable among chondrules in these three thin sections although seem to be little more in EH chondrules (CaO up to 8,83wt%) and in the bigger, anomalous rimmed one [1] EL3 chondrule (up to 9,51wt% in some spots)[2]. We also found FeO contents with a good correlation with MgO for EH3 chondrules, but weak for the EL3 ones. On the other hand MgO in EL3 well correlates in negative way with MnO and Cr 2 O 3 but this time do not for EH3 chondrites. In all chondrules there is also high silica contents as rounded little grain inside the mesostasis, that range in composition from 91,34-98,85wt% SiO 2. Discussion: The comparable contents of sodium and aluminum oxides in both EL3 and EH3 mesostasis let us to think about a genetic context that could have been common for these chon-drules. As we read in literature [3] these high Na 2 O contents can be explained with a chondrules formation in high partial pressure context for this oxide. However the last thermal processes would have been not at so high temperature or not too longer to would results in Na 2 O loss [4]. CaO contents can be explained as belonging to pyroxene, probably as cryptocrystalline phase in mesostasis, or to mesostasis as vicariant of Na 2 O as showed by normative composition calculations. The occurences of Fe, Mn and Cr-sulfides as tiny phases in the mesostasis could explain the correlation we can observe in each of two enstatite chondrites class chondrule mesostasis. So, other mineralogical and geo-chemical investigations are in …