Relict Olivines in Micrometeorites: Precursors and Interactions in the Earth’s Atmosphere

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%), Al 2 O 3 (0.0-0.3wt%), MnO (0.0-0.3wt%), and Cr 2 O 3 (0.1-0.7wt%). Numerical simulations carried out with the Chemical Ablation Model (CABMOD) 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.

Ablation and Chemical Alteration of Cosmic Dust Particles During Entry Into the Earth’s Atmosphere

“…Micrometeorites are the largest contributors of extra-terrestrial material; this material is recovered from the Earthʼs surface using different collection techniques that target the stratosphere, Antarctica, and deep-sea sediments (Love & Brownlee 1993;Taylor et al 1998;Peucker-Ehrenbrink & Ravizza 2000;Plane 2012;Prasad et al 2013). The micrometeorites found on the Earthʼs surface have distinct chemical compositions that show similarities and differences with respect to the precursors they originate from; however, in general, a large number of micrometeorites are related to carbonaceous chondrites (e.g., Kurat et al 1994;Brownlee et al 1997;Taylor et al 2000Taylor et al , 2012Yada et al 2005;Rudraswami et al 2011Rudraswami et al , 2012Rudraswami et al , 2014Rudraswami et al , 2015aRudraswami et al , 2015bRudraswami et al , 2016a. The deviations in the chemical compositions from the precursors are caused by modification that occurs during melting and vaporization that take place as these particles enter into the Earthʼs atmosphere.…”

“…The deviations in the chemical compositions from the precursors are caused by modification that occurs during melting and vaporization that take place as these particles enter into the Earthʼs atmosphere. These modifications are dominated by a loss of elements based on their relative volatilities, and other physical processes that are parameterized by key variables such as size, density, entry velocity, and angle of entry, in addition to others (Love & Brownlee 1991;Rudraswami et al 2015aRudraswami et al , 2016a. The origin of micrometeorites is currently debated, whether the micrometeorites are asteroidal or cometary, and to what extent the origin contributes to the micrometeorites' flux is also debated (Dermott et al 1994;Brownlee 2001;Nesvorný et al 2010Nesvorný et al , 2011.…”

Selective Disparity of Ordinary Chondritic Precursors in Micrometeorite Flux

“…According to the terrestrial meteorite records, ordinary chondrites dominate the falls frequency (∼80%) followed by achondrites (∼13%) and carbonaceous chondrites (∼4%; Keil et al 1994). In contrast, this is not the case with MMs where carbonaceous chondrites overwhelmingly dominate (∼70% to >90%) the flux with minor contribution from ordinary chondrites based on chemical and isotopic evidence (e.g., Kurat et al 1994;Brownlee et al 1997;Genge et al 1997;Engrand et al 1999Engrand et al , 2005Taylor et al 2000Taylor et al , 2012Yada et al 2005;Rudraswami et al 2012Rudraswami et al , 2014Rudraswami et al , 2015aRudraswami et al , 2015bRudraswami et al , 2016aRudraswami et al , 2016c.…”

“…The present study compiles all of our earlier studies (Rudraswami et al 2012(Rudraswami et al , 2015a(Rudraswami et al , 2015b(Rudraswami et al , 2016a(Rudraswami et al , 2016c apart from newly collected MMs from Antarctica to know the bulk chemical composition and perceives with the model results. The collection methods in the polar region allow for better preservation of the MMs compared to that of the deep-sea sediments (Taylor & Brownlee 1991;Brownlee et al 1997).…”

“…Laboratory investigation based on chemical and isotopic studies from various researchers have shown that MMs are related to chondrules, calcium-aluminium-rich inclusions, and matrix from carbonaceous chondrites (e.g., Maurette et al 1991;Steele 1992;Kurat et al 1994;Beckerling & Bischoff 1995;Engrand et al 1999;Genge et al 2005Genge et al , 2008Gounelle et al 2005;Cordier et al 2011aCordier et al , 2011bVan Ginneken et al 2012, 2016Taylor et al 2012;Imae et al 2013;Rudraswami et al 2015aRudraswami et al , 2015bRudraswami et al , 2016aRudraswami et al , 2016c. However, there is evidence for some particles that are associated with cometary and interplanetary dust particles (Bradley 1994;Rietmeijer 1998;Ishii et al 2008;Noguchi et al 2015).…”