www.elsevier.com/locate/rgg “Spherulite-like” jadeite growth in shock-melt veins of the Novosibirsk H5/6 chondrite I.S. Bazhan a, * , Shin Ozawa b , M. Miyahara c , E. Ohtani a,b , K.D. Litasov a,d a V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia b Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan c Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan d Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia Received 3 December 2015; accepted 26 April 2016 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 (Ab 78 An 14 Or 7 ) 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 sodium–potassium 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. © 2016, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. Keywords: Novosibirsk H5/6 chondrite; jadeite; plagioclase melt; shock metamorphism; spherulite-like microtexture Introduction Jadeite is one of the most common high-pressure minerals in the metamorphic, impacted rocks, and shocked ordinary chondrites. James (1969) reported a shock-induced jadeite in the impact rocks of Ries crater, Germany. Kimura et al. (2000) first described an extraterrestrial jadeite formed from albitic feldspar in the shocked Yamato 75100 H6 chondrite. Later, jadeites have been identified in many shocked chondrites (Acosta-Maeda et al., 2013; Kimura et al., 2001; Miyahara et al., 2011, 2013; Ohtani et al., 2004; Ozawa et al., 2009, 2014; Zhang et al., 2006). High-pressure and high-temperature static experiments indicate that jadeite forms as a result of albite dissociation reaction: albite = jadeite + silica at pressures above 3 GPa and temperature >1000 °C (Bell and Roseboom, 1969; Birch and LeComte, 1960; Holland, 1980; Liu, 1978). Although a silica phase should accompany jadeite accord- ing to the stoichiometry of feldspar, only jadeite can be identified in the originally plagioclase grains in the shock-melt veins (SMVs) of the chondrites. The issue of missing silica has been repeatedly discussed in several papers (James, 1969; Kimura et al., 2000; Kubo et al., 2010, Miyahara et al., 2013; Ozawa et al., 2009, 2014; Zhang et al., 2006). In addition, jadeite-bearing albitic feldspar grains in the natural shocked samples show a variety of microtextures such as “particle-like”, “stringer-like”, and “needle-like” (Ozawa et al., 2009, 2014) that suggest individual PT-histories for each microtexture formation. A pressure and temperature induced by a planetesimal collision depends on size, density and relative speed of individual asteroid. The differences in these parameters would induce formation and variety of crystal habits of high-pressure minerals including jadeite. The Novosibirsk meteorite is an ordinary H5/6 chondrite found on the eastern outskirts of the city of Novosibirsk in 1978. The first detailed study of the Novosibirsk meteorite was made by M.I. Petaev (Petaev, 1990; Petaev et al., 1990), who investigated petrology, mineralogy and chemistry of the meteorite in detail. Evidences of the shock metamorphism were reported, i.e., presence of melt pockets and shock veins, strong fracturing of minerals, wavy and block extinction of Russian Geology and Geophysics 58 (2017) 12–19 * Corresponding author. E-mail address: ibazhan@gmail.com (I.S. Bazhan) Available online at www.sciencedirect.com ScienceDirect ed. 1068-7971/$ - see front matter D 201 IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserv V S. . S bolev o , http://dx.doi.org/10.1016/j.rgg.201 .0 .0 6 4 12 6