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J/ApJ/831/197   Mg-rich olivines with electron microscopy   (Rudraswami+, 2016)

Relict olivines in micrometeorites: precursors and interactions in the Earth's atmosphere. Rudraswami N.G., Shyam Prasad M., Dey S., Fernandes D., Plane J.M.C., Feng W., Taylor S., Carrillo-Sanchez J.D. <Astrophys. J., 831, 197-197 (2016)> =2016ApJ...831..197R (SIMBAD/NED BibCode)
ADC_Keywords: Minor planets Keywords: atmospheric effects; Earth; interplanetary medium; minor planets, asteroids: general; Sun: general Abstract: Antarctica micrometeorites (∼1200) and cosmic spherules (∼5000) from deep sea sediments are studied using electron microscopy to identify Mg-rich olivine grains in order to determine the nature of the particle precursors. Mg-rich olivine (FeO<5wt%) in micrometeorites suffers insignificant chemical modification during its history and is a well-preserved phase. We examine 420 forsterite grains enclosed in 162 micrometeorites of different types-unmelted, scoriaceous, and porphyritic-in this study. Forsterites in micrometeorites of different types are crystallized during their formation in solar nebula; their closest analogues are chondrule components of CV-type chondrites or volatile rich CM chondrites. The forsteritic olivines are suggested to have originated from a cluster of closely related carbonaceous asteroids that have Mg-rich olivines in the narrow range of CaO (0.1-0.3wt%), Al2O3 (0.0-0.3wt%), MnO (0.0-0.3wt%), and Cr2O3 (0.1-0.7wt%). Numerical simulations carried out with the Chemical Ablation Model (CABMOD; Vondrak+ 2008ACP.....8.7015V) enable us to define the physical conditions of atmospheric entry that preserve the original compositions of the Mg-rich olivines in these particles. The chemical compositions of relict olivines affirm the role of heating at peak temperatures and the cooling rates of the micrometeorites. This modeling approach provides a foundation for understanding the ablation of the particles and the circumstances in which the relict grains tend to survive. Description: The samples were collected from Antarctica and deep sea sediments using different collection techniques. The Antarctica micrometeorites (AMM) were collected from the South Pole Water Well (SPWW), which has a diameter of ∼24m at a depth of ∼100m below the snow surface, with a total water volume of ∼5000m3. The cosmic spherules from deep sea sediments (CS-DSS) were collected at water depths of ∼5200m using an Okean grab sampler with a seafloor penetration depth of ∼15cm. The AMM and CS-DSS have been dated at ∼900 years BP and 0-50000 years BP, respectively (Taylor+ 1998Natur.392..899T; Prasad+ 2013JGRE..118.2381P). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 127 420 Relict olivine grain in Antartica micrometeorites and Deep sea cosmic spherules
See also: J/MNRAS/406/460 : IR absorbance spectra of olivine (Pitman+, 2010) J/A+A/449/583 : Temperature effects on spectra of olivine particles (Koike+, 2006) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 3 A3 --- Type Micrometeorite type (AMM = Antarctica micrometeorite (182 instances) or DSS = deep sea sediments (238 instances)) 5- 18 A14 --- ID Micrometeorite identifier 20- 22 I3 um Diam [41/426] Micrometeorite diameter (1) 24- 26 I3 um Len [5/227] Length of relict grain 28- 30 I3 um Bre [4/170] Breadth of relict grain 32- 33 I2 % Point [1/40] Point / 1 35- 37 A3 --- --- [/ 1] 39- 42 F4.2 % Na2O [0/0.6] Percent Na2O in micrometeorite composition 44- 48 F5.2 % MgO [45/60] Percent MgO in micrometeorite composition 50- 53 F4.2 % Al2O3 [0/1.2] Percent Al2O3 in micrometeorite composition 55- 59 F5.2 % SiO2 [33.7/46] Percent SiO2 in micrometeorite composition 61- 64 F4.2 % P2O5 [0/0.3] Percent P2O5 in micrometeorite composition 66- 69 F4.2 % SO2 [0/0.5] Percent SO2 in micrometeorite composition 71- 74 F4.2 % K2O [0/0.05] Percent K2O in micrometeorite composition 76- 79 F4.2 % CaO [0.02/3.1] Percent CaO in micrometeorite composition 81- 84 F4.2 % TiO2 [0/0.3] Percent TiO2 in micrometeorite composition 86- 89 F4.2 % Cr2O3 [0.04/0.8] Percent Cr2O3 in micrometeorite composition 91- 94 F4.2 % MnO [0/0.9] Percent MnO in micrometeorite composition 96- 99 F4.2 % FeO [0.4/5.1] Percent FeO in micrometeorite composition 101-104 F4.2 % CoO [0/0.2] Percent CoO in micrometeorite composition 106-109 F4.2 % NiO [0/0.6] Percent NiO in micrometeorite composition 111-116 F6.2 % Total [97/102] Previous columns in total composition 118-122 F5.2 % Mg2SiO4 [94.8/99.6] Percent Mg2SiO4 in micrometeorite composition 124-127 F4.2 % Fe2Si4 [0.4/5.2] Percent Fe2Si4 in micrometeorite composition
Note (1): Some of the particles are not spherical in that case they are presented as longest length of the particles.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 14-Feb-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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