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 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 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 1998Natur.392..899T; Prasad+ 2013JGRE..118.2381P 2013JGRE..118.2381P).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 127 420 Relict olivine grain in Antartica micrometeorites
and Deep sea cosmic spherules
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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
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Bytes Format Units Label Explanations
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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
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Note (1): Some of the particles are not spherical in that case they are
presented as longest length of the particles.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 14-Feb-2017