#Sikhote alin meteorite series

This conclusion is based upon the similarity of microspherules both to the diagenetically altered I-type cosmic spherules and meteorite ablation spherules previously reported from modern and ancient sediments: spherical morphologies and sizes 10вЂ“150 Ојm, dendritic textures exhibiting cruciform or cellular arrangements, large sub-circular cavities representing the former position of weathered metal beads, irregular cavity networks, representing vesicles and vesicle networks of residual trapped volatile gases, and Fe-rich magnetite mineralogy. Using both in situ and destructive microanalysis techniques (micro CT, XRF, SEM, EDS, and Raman spectroscopy), we examined a range of different possibilities of their origin and concluded that studied Upper Roadian microinclusions have an extraterrestrial genesis. We studied Fe-rich microspherules and microparticles found as inclusions within a gypsum host rock, sourced from the Kamsko-Ustyinskoe gypsum field (Republic of Tatarstan, Russia). The following criteria are recommended for the conclusive identification of I-type spherules within sediments and sedimentary rocks: (i) spherical particle morphologies, (ii) dendritic crystal morphologies, (iii) the presence of wГјstite and magnetite, (iv) Ni-bearing wГјstite and magnetite, and (v) the presence of relict FeNi metal. Weathering is restricted to replacement of metal by iron hydroxides. The formation of secondary metal in the form of sub-micron Ni-rich or Pt-group nuggets and as symplectite with magnetite was also identified and suggested to occur largely due to the exsolution of metallic alloys during decomposition of non-stoichiometric wГјstite. Variations in magnetite and wГјstite crystal sizes are also suggested to relate to cooling rate allowing relative entry angle of particles to be evaluated. Non-equilibrium effects in the exchange of Ni between wГјstite and metal, and magnetite and wГјstite are suggested as proxies for the rate of oxidation and cooling rate respectively.

#Sikhote alin meteorite series

Oxidation during entry heating increases in the series MET 80 wt% Ni comprising a particle mass fraction of <0.2. Two textural types of I-type cosmic spherule are recognised: (1) metal bead-bearing (MET) spherules dominated by Ni-poor (100 and suggest that metal from H-group ordinary, CM, CR and iron meteorites may form the majority of particles. We report the results of a study of the mineralogy and petrology of 88 I-type cosmic spherules recovered from Antarctica in order to evaluate how they formed and evolved during atmospheric entry, to constrain the nature of their precursors and to establish rigorous criteria by which they may be conclusively identified within sediments and sedimentary rocks. I-types are important because they can readily be recovered from sedimentary rocks allowing study of solar system events over geological time. I-type cosmic spherules are micrometeorites that formed by melting during atmospheric entry and consist mainly of iron oxides and FeNi metal. Conceivably, the ablated material was enriched in silicates compared to the fallen material. The spherules are thought to were produced by the ablation of meteoritic material at elevations of about 12 km (in the region where disintegration starts) and below, at maximum temperatures of 1600вЂ“2180вЊ and oxygen fugacity of 10в€’14 to 10в€’1 atm. The texture, mineralogy, and chemistry (presence of P and Si) of these spherules differ from those of iron cosmic spherules (type I) that occur in the background flux of micrometeorites. The spherules can classified into two textural types: (i) fine-grained, which consist of Ni-bearing magnetite (3вЂ“6 wt % NiO) dendrites, sometimes with minor amounts of interstitial P- and Fe-rich material, and (ii) coarse-grained, which also consist of Ni-bearing magnetite dendrites or grains, sometimes with wuestite, an interstitial material, which resembles that in type (i) or has a silicate composition. Practically all of the examined spherules extracted in 1948вЂ“1949 from soil at the crater field of the 1947 Sikhote Alin meteorite shower are ablation spherules produced during this meteorite fall.