Major and trace element geochemistry of S‐type cosmic spherules

Abstract

Abstract-Micrometeorites that pass through the Earth's atmosphere undergo changes in their chemical compositions, thereby making it difficult to understand if they are sourced from the matrix, chondrules, or calcium-aluminum-rich inclusions (CAIs). These components have the potential to provide evidence toward the understanding of the early solar nebular evolution. The variations in the major element and trace element compositions of 155 different type (scoriaceous, relict bearing, porphyritic, barred, cryptocrystalline, and glass) of S-type cosmic spherules are investigated with the intent to decipher the parent sources using electron microprobe and laser ablation inductively coupled plasma-mass spectrometry. The S-type cosmic spherules appear to show a systematic depletion in volatile element contents, but have preserved their refractory trace elements. The trends in their chemical compositions suggest that the S-type spherules comprise of components from similar parent bodies, that is, carbonaceous chondrites. Large fosteritic relict grains observed in this investigation appear to be related to the fragments of chondrules from carbonaceous chondrites. Furthermore, four spherules (two of these spherules enclose spinels and one comprised entirely of a Ca-Al-rich plagioclase) show enhanced trace element enrichment patterns that are drastically different from all the other 151 cosmic spherules. The information on the chemical composition and rare earth elements (REEs) on cosmic spherules suggest that the partially to fully melted ones can preserve evidences related to their parent bodies. The Ce, Eu, and Tm anomalies found in the cosmic spherules have similar behavior as that of chondrites. Distinct correlations observed between different REEs and types of cosmic spherules reflect the inherited properties of the precursors.

Cosmic spherules from Widerøefjellet, Sør Rondane Mountains (East Antarctica)

“…As atmospheric melting and concomitant evaporation experienced by CSs strongly affected primary textures, mineralogy and chemical compositions, precisely constraining the nature of the chondritic sources remains highly challenging (e.g., Alexander et al, 2002;Taylor et al, 2005). Most elemental concentrations and ratios are either not sufficiently discriminative or underwent too large a modification to deduce the type of precursor body (e.g., Rudraswami et al, 2016).…”

“…Due to different production mechanisms in and transportation pathways from their source regions, these microscopic particles sample parent bodies different from those of meteorites (e.g., Fredriksson and Martin, 1963;Ganapathy et al, 1978;Engrand and Maurette, 1998;Flynn et al, 2009;Gounelle et al, 2009;Dartois et al, 2013;Cordier and Folco, 2014;Rubin, 2018). Generally recovered from deep-sea sediments, seasonal lakes in Greenland, ice and snow in Greenland and Antarctica, Antarctic moraines, continental sands and soils, and more recently also urban environments (e.g., Brownlee et al, 1979;Blanchard et al, 1980;Koeberl and Hagen, 1989;Hagen et al, 1989;Engrand and Maurette, 1998;Taylor and Lever, 2001;Genge et al, 2016Genge et al, , 2017Rudraswami et al, 2016;van Ginneken et al, 2017), MMs have also been found concentrated in high-altitude sedimentary traps, i.e., a pits, fissures and cracks of glacially eroded surfaces, in the Transantarctic Mountains (TAM) (e.g., Rochette et al, 2008;Suavet et al, 2009). To concentrate MMs in numbers sufficient to be able to efficiently distinguish them from terrestrial particles in sedimentary deposits, the accumulation time of such traps is ideally of the order of millions of years, while at the same time alteration must have remained limited, with minimal background or anthropogenic contributions (Suavet et al, 2009).…”

“…While the textures and chemical compositions of extraterrestrial particles are reprocessed by alteration during their terrestrial residence, this work focuses on confirming the primary nature of the MM precursor materials and refining the processes that affected these particles during atmospheric passage. While there is convincing evidence, based on elemental compositions and oxygen isotope ratio studies (e.g., Genge et al, 1997;Noguchi et al, 2002), that a large fraction of the MMs is related to carbonaceous chondrites of various clans and groups, the ratio of MMs related to ordinary as compared to carbonaceous chondrites and their distribution per size fraction, is currently based on only a limited number of analyses, especially for the larger size fractions (e.g., Steele, 1992;Kurat et al, 1994;Brownlee et al, 1997;Engrand and Maurette, 1998;Engrand et al, 2005;Gounelle et al, 2005;Genge et al, 2008;Suavet et al, 2010;Cordier et al, 2011aCordier et al, , 2011bTaylor et al, 2012;Rudraswami et al, 2012Rudraswami et al, , 2015aRudraswami et al, , 2015bRudraswami et al, , 2016van Ginneken et al, 2012van Ginneken et al, , 2017Imae et al, 2013;Cordier and Folco, 2014). The ratio of carbonaceous chondrite relative to ordinary chondrite material decreases as CS diameters increase, from a factor of 10 for small particles (<500 lm in diameter) to a factor of 0.3 for larger particles, indicating that the contribution of ordinary chondrite material to the composition of the micrometeoroid complex increases with MM size, with a possible continuum between meteorites and MMs (Cordier and Folco, 2014).…”

A unique corundum and refractory metal‐nugget bearing micrometeorite P117

“…Cosmic spherules from deep‐sea sediments, namely AAS38‐164‐P69 and AAS62‐9‐P51, also revealed spinels contained in them (Rudraswami et al. ). Spinel is the refractory mineral that is frequently found in CAIs of CM or CV chondrites, but forms a small fraction of these meteorites: ~1.2 and ~3 area% of refractory inclusions, respectively (Hezel et al.…”

Fine‐grained volatile components ubiquitous in solar nebula: Corroboration from scoriaceous cosmic spherules

“…; Rudraswami et al. , ), in addition to oxygen isotope studies on different types of MMs (Engrand et al. , ; Yada et al.…”