The Kaidun Breccia Material Variety: New Clasts and Updated Hypothesis on a Space Trawl Origin

The Kaidun meteorite is a breccia containing a wide variety of different material types [1-5]. It contains lithologies of CI, CM1 and CM2, CR chondrites [6], CAIs of Types A and B [7, 8], enstatite chondrite materials (EH and EL) [3, 4], including altered enstatite clasts [9], ordinary chondrites [10], and possible R chondrite \nmaterial [11] as well as glass fragments and altered shock melt veins [4]. It also contains different achondritic clasts (including alkaline rocks) with unusual oxygen isotopic compositions representing unknown differentiated parent bodies [2, 12]. Based on Fe/Mn and Fe/Mg ratios these clasts correspond to the SNC and HED meteorites and confirm their origin from differentiated parent bodies that experienced impact events and aqueous alteration, and not represented by known meteorites. We continue studying Kaidun and report results on investigation of newly discovered objects and discuss processes of their formation, and the origin of the Kaidun microbreccia as a whole. \n \nResults and Discussion: Clast #d7.2-68 was found in Kaidun section #7.2d. It consists of pyroxene and SiO_(2-)phases. Pyroxene is pigeonite (Fs_(63-67), Wo_(10-14), Fe/Mn – 40.1) with augite lamellae (Fs_(44-57), Wo_(20-34), Fe/Mn – 40.4) (up to 10 µm width). Equilibrium temperature of coexisting pyroxenes is close to 900°C at 5 Kbar [13]. The observed smooth shape of the CaO profile across the pyroxene lamellae could correspond to mild metamorphism after exsolution. On a plot of Fe/Mn vs. Fe/Mg, the clast falls at the far Fe-rich end of the HED pyroxenes cluster. The SiO_(2)-phase \nis enriched in Al_2O_3 and FeO and possibly is tridymite. The exsolution textures of pyroxenes require annealing for a long period of time and are typical features of achondrites, especially eucrites. This clast could represent a fragment of differentiated material of a body size of which is similar to the HED parent body.