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

Abstract

A newly discovered sedimentary accumulation of micrometeorites in the Sør Rondane Mountains of East Antarctica, close to the Widerøefjellet summit at $2750 m above sea level, is characterized in this work. The focus here lies on 2099 melted cosmic spherules larger than 200 lm, extracted from 3.2 kg of sampled sediment. Although the Widerøefjellet deposit shares similarities to the micrometeorite traps encountered in the Transantarctic Mountains, both subtle and more distinct differences in the physicochemical properties of the retrieved extraterrestrial particles and sedimentary host deposits are discernable (e.g., types of bedrock, degree of wind exposure, abundance of metal-rich particles). Unlike the Frontier Mountain and Miller Butte sedimentary traps, the size fraction below 240 lm indicates some degree of sorting at Widerøefjellet, potentially through the redistribution by wind, preferential alteration of smaller particles, or processing biases. However, the cosmic spherules larger than 300 lm appear largely unbiased following their size distribution, frequency by textural type, and bulk chemical compositions. Based on the available bedrock exposure ages for the Sør Rondane Mountains, extraterrestrial dust is estimated to have accumulated over a time span of $1-3 Ma at Widerøefjellet. Consequently, the Widerøefjellet collection reflects a substantial reservoir to sample the micrometeorite influx over this time interval. Petrographic observations and 3D microscopic CT imaging are combined with chemical and triple-oxygen isotopic analyses of silicate-rich cosmic spherules larger than 325 lm. The major element composition of 49 cosmic spherules confirms their principally chondritic parentage. For 18 glassy, 15 barred olivine, and 11 cryptocrystalline cosmic spherules, trace element concentrations are also reported on.Based on comparison with evaporation experiments reported in literature and accounting for siderophile and chalcophile element losses during high-density phase segregation and ejection, the observed compositional sequence largely reflects progressive heating and evaporation during atmospheric passage accompanied by significant redox shifts, although the influence of (refractory) chondrite mineral constituents and terrestrial alteration cannot be excluded in all cases. Twenty-eight cosmic spherules larger than 325 lm analyzed for triple-oxygen isotope ratios confirm inheritance from mostly carbonaceous chondritic precursor materials ($55% of the particles). Yet, $30% of the measured cosmic spherules and $50% of all glassy cosmic spherules are characterized by oxygen isotope ratios above the terrestrial fractionation line, implying genetic links to ordinary chondrites and parent bodies currently unsampled by meteorites. The structural, textural, chemical, and isotopic characteristics of the cosmic spherules from the Sør Rondane Mountains, and particularly the high proportion of Mg-rich glass particles contained therein, imply a well-preserved and representative new sedimentary micrometeorite collect...

Evidence for the presence of chondrule‐ and CAI‐derived material in an isotopically anomalous Antarctic micrometeorite

“…The Antarctic environment has proven to be beneficial toward the preservation of meteoritic material due to the (1) cold and dry climate, (2) prolonged accumulation ages (up to several Ma), and (3) absence of anthropogenic contamination. Although weathering conditions vary significantly among the different types of micrometeorite deposits (Van Ginneken et al 2016), the Sør Rondane Mountain collection appears to be relatively unbiased when compared to other Antarctic collections, including the well-preserved South Pole Water Well collection, and is thus representative of the contemporary cosmic dust flux to Earth (Taylor et al 2000(Taylor et al , 2007Suavet et al 2011;Goderis et al 2020). Based on cosmogenic nuclide dating of granitoid basement rocks from the Walnumfjellet mountain summit, the Sør Rondane Mountains have been deglaciated and exposed to atmospheric fallout, including volcanic ash, microtektites, and cosmic dust, for a time span of~1-3 Ma (Suganuma et al 2014), yielding a large, new collection of impact-or extraterrestrial-related materials.…”

“…2011; Goderis et al. 2020). Based on cosmogenic nuclide dating of granitoid basement rocks from the Walnumfjellet mountain summit, the Sør Rondane Mountains have been deglaciated and exposed to atmospheric fallout, including volcanic ash, microtektites, and cosmic dust, for a time span of ~1–3 Ma (Suganuma et al.…”

“…2008), the joint Belgian‐Japanese MICROMETA expedition (2012–2013) sampled similar types of sedimentary deposits from a different region on the Antarctic continent, that is, the Sør Rondane Mountains in Drønning Maud Land of East Antarctica (Goderis et al. 2020; Fig. 1).…”

“…Following the discovery of micrometeorites and -tektites in sedimentary traps from the Transantarctic Mountains (Folco et al 2008;Rochette et al 2008), the joint Belgian-Japanese MICROMETA expedition (2012-2013) sampled similar types of sedimentary deposits from a different region on the Antarctic continent, that is, the Sør Rondane Mountains in Drønning Maud Land of East Antarctica (Goderis et al 2020; Fig. 1).…”

The Extraterrestrial Dust Flux: Size Distribution and Mass Contribution Estimates Inferred From the Transantarctic Mountains (TAM) Micrometeorite Collection

“…Meanwhile petrological investigation of micrometeorites tends to conclude that asteroidal sources, from fine-grained hydrated CM, CR, and CI-like materials, are dominant (Kurat et al, 1994;Suttle et al, 2019;Taylor et al, 2012;van Ginneken et al, 2012). Finally, O-isotope data collated from multiple studies conclude that 20% of the dust flux is sourced from anhydrous inner solar system asteroids (ordinary chondrites and basaltic HED materials), while 60% are derived from primitive carbonaceous chondrite materials, including both CM/CO/CR/CI chondrites and cometary objects (Cordier & Folco, 2014;Goderis et al, 2019;Suavet et al, 2010;van Ginneken et al, 2017). The problems differentiating primitive asteroids and cometary material may reflect a possible continuum between these objects (Gounelle, 2011).…”