Collisions and compositional variability in chondrule-forming events

Abstract

Compound chondrules, i.e. chondrules fused together, make a powerful probe of the density and compositional diversity in chondrule-forming environments, but their abundance among the dominating porphyritic textures may have been drastically underestimated. I report herein microscopic observations and LA-ICP-MS analyses of lobate chondrules in the CO3 chondrites Miller Range 07193 and 07342. Lobes in a given chondrule show correlated volatile and moderately volatile element abundances but refractory element concentrations are essentially independent. This indicates that they formed by the collision of preexisting droplets whose refractory elements behaved in closed system, while their more volatile elements were buffered by the same gaseous medium. The presence of lobes would otherwise be difficult to explain, as surface tension should have rapidly imposed a spherical shape at the temperature peak. In fact, since most chondrules across chondrite groups are nonspherical, a majority are probably compounds variously relaxed toward sphericity. The lack of correlation of refractory elements between conjoined compound chondrule components is inconsistent with derivation of chondrules from the disruption of homogenized melt bodies as in impact scenarios and evokes rather the melting of independent mm-size nebular aggregates. Yet a "nebular" setting for chondrule formation would need to involve not only increased solid concentration, e.g. by settling to the midplane, but also a boost in relative velocities between droplets during chondrule-forming events to account for observed compound chondrule frequencies .

arXiv comment50 pages, 12 figures

References in corpus (27)

• Dynamics of Solids in the Midplane of Protoplanetary Disks: Implications for Planetesimal Formation
• Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics
• Dust evolution in protoplanetary discs and the formation of planetesimals. What have we learned from laboratory experiments?
• Abundance, Major Element Composition and Size of Components and Matrix in CV, CO and Acfer 094 Chondrites
• Transport and Accretion in Planet-Forming Disks
• Impact splash chondrule formation during planetesimal recycling
• Mixing and transport of dust in the early solar nebula as inferred from titanium isotope variations among chondrules
• Thulium anomalies and rare earth element patterns in meteorites and Earth: Nebular fractionation and the nugget effect
• On the aerodynamic redistribution of chondrite components in protoplanetary disks
• On the coexistence of the streaming instability and the vertical shear instability in protoplanetary disks
• Magmatic sulfides in the porphyritic chondrules of EH enstatite chondrites
• Northwest Africa 5958: a weakly altered CM-related ungrouped chondrite, not a CI3
• Origin of isolated olivine grains in carbonaceous chondrites
• Trace element geochemistry of ordinary chondrite chondrules: the type I/type II chondrule dichotomy
• Chondrule heritage and thermal histories from trace element and oxygen isotope analyses of chondrules and amoeboid olivine aggregates
• Chondrule trace element geochemistry at the mineral scale
• Trace element geochemistry of CR chondrite metal
• The formation conditions of enstatite chondrites: Insights from trace element geochemistry of olivine-bearing chondrules in Sahara 97096 (EH3)
• Viscous coalescence of droplets: a Lattice Boltzmann study
• The quasi-universality of chondrule size as a constraint for chondrule formation models
• Harvesting the decay energy of ${}^{26}$Al to drive lightning discharge in protoplanetary discs
• On vertical variations of gas flow in protoplanetary disks and their impact on the transport of solids
• Chondrule destruction in nebular shocks
• Compound Chondrules fused Cold
• Compound chondrule formation via collision of supercooled droplets
• Compound chondrule formation in optically thin shock waves
• Dust concentration and chondrule formation

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• Chondrule Formation During Low-Speed Collisions of Planetesimals: A Hybrid Splash-Flyby Framework