В«SPHERULITE-LIKE» JADEITE GROWTH IN SHOCK-MELT VEINS OF THE NOVOSIBIRSK H5/6 CHONDRITE
I.S. Bazhan1, S. Ozawa2, M. Miyahara3, E. Ohtani1,2, K.D. Litasov1,4
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
3Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
4Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Novosibirsk H5/6 chondrite, jadeite, plagioclase melt, shock metamorphism, spherulite-like microtexture
Abstract
The Novosibirsk H5/6 ordinary chondrite has signs of shock metamorphism, such as dark shock-melt veins (SMVs) crossing the chondrite host rock. The plagioclase composition grains (Ab78An14Or7) with jadeite were found in the host-rock fragments inside the SMVs. Jadeite has an unusual radial-concentric spherulite-like microtexture. The spherulite-like jadeite formed from the molten plagioclase grain under high-pressure and high-temperature conditions during an impact event. The crystallization was accompanied by Na-K differentiation between coexisting jadeite and residual melt. The PT -conditions of jadeite formation were estimated to be 3-14 GPa and 1400-2150 ºC. Jadeite crystallization, Na-K differentiation, and the pressure-temperature estimates of jadeite formation in the Novosibirsk chondrite are very close to those in the Chelyabinsk LL5 chondrite. The spherulite-like microtexture and jadeite-glass coexistence, most likely, point to a high cooling rate of the SMVs at the pressure release stage of the metamorphic process.
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