The University of Arizona

A primitive dark inclusion with radiation-damaged silicates in the Ningqiang carbonaceous chondrite

M. Zolensky, K. Nakamura, M. K. Weisberg, M. Prinz, T. Nakamura, K. Ohsumi, A. Saitow, M. Mukai, M. Gounelle

Abstract


A petrologic and TEM study of a remarkable dark inclusion (DI) in the Ningqiang CV3 chondrite reveals that it is a mixture of highly primitive solar nebula materials. The DI contains two lithologies. The first, lithology A, contains micron-sized olivine and pyroxene grains rimmed by amorphous materials with compositions similar to the underlying crystalline grains. The second, lithology B, appears to preserve the mineralogy of lithology A before formation of the amorphous rims. Overall, the Ningqiang DI appears to record the following processes: 1) formation (condensation and Fe-enrichment) of olivine crystals in the nebula with compositions of Fo42­62; 2) irradiation, resulting in amorphitization of the olivine and pyroxene to varying degrees; 3) partial annealing, resulting in formation of fairly large, euhedral olivine and pyroxene grains with remnant amorphous sharply-bounded rims; 4) in some cases, prolonged annealing, resulting in the formation of microcrystalline olivine or pyroxene rims. The latter annealing would have been a natural consequence of irradiation near the critical temperature for olivine; and 5) mixture of the above materials (lithology A) with nebular condensate high-Ca pyroxene and olivine, which escaped nebular processing, to become lithology B. We suggest that the amorphous rims in lithology A formed in an energetic solar event such as a bi-polar outflow or FU-orionis flare.

Keywords


TEM;solar nebula;solar;primitive dark inclusion;olivine

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