Short time interval for condensation of high-temperature silicates in the solar accretion disk

Abstract

Chondritic meteorites are made of primitive components that record the first steps of formation of solids in our Solar System. Chondrules are the major component of chondrites, yet little is known about their formation mechanisms and history within the solar protoplanetary disk (SPD . In addition, mineral 26 Al isochrons determined on the same chondrules show that their formation (i.e., fusion of their precursors by energetic events) took place from 0 Myr to ∼2 Myr after the formation of their precursors, thus showing in some cases a clear decoupling in time between the two events. The finding of a minimum bulk chondrule 26 Al isochron is used to constrain the astrophysical settings for chondrule formation. Either the temperature of the condensation zone dropped below the condensation temperature of chondrule precursors at ∼1.5 My after the start of the Solar System or the transport of precursors from the condensation zone to potential storage sites stopped after 1.5 My, possibly due to a drop in the disk accretion rate.Mg isotope analyses | MC-SIMS | HR-MC-ICPMS | chondrule history | short-lived 26 Al P rimitive meteorites (i.e., chondrites) are rocks that escaped melting and differentiation on their parent bodies. As a result, their components preserved a record of the mineralogy, chemistry, and isotopic compositions of the solids formed in the solar protoplanetary disk (SPD) before planetesimal formation. Viscous heating in the inner regions of the SPD (1) brought presolar dust and gas to temperatures higher than the sublimation point of most minerals, producing a gas that upon cooling produced the first Solar System solids by condensation. The relative uniformity of isotope ratios among many early Solar System materials (2) is testament to this phase of homogenization. The calcium−aluminum-rich inclusions (CAIs) that are found in primitive meteorites are considered to be formed from refractory precursors condensed at temperatures in the range from ∼1,400 K to ∼1,800 K (3). Chondrules are millimeter-size once-molten silicate spherules that comprise most of the mass (70-80%) of chondrites. They have compositions indicating that their formation took place from solid precursors condensed below 1,500 K (4, 5). The exact timing (duration, chronology) of (i) the condensation processes that produced the precursors of CAIs and of chondrules, and (ii) the processes that resulted in the formation of CAIs and chondrules, is still poorly known, although it is key to a better understanding of the complex origin and evolution of solids in the solar accretion disk.

Mixing and Transport of Dust in the Early Solar Nebula as Inferred from Titanium Isotope Variations among Chondrules

“…1). The CR chondrules seem to have formed later, at ~3.7 Ma after CAI formation (Amelin et al 2002;Schrader et al 2017), than CV chondrules at ~2.2 Ma after CAI formation (Budde et al 2016b;Luu et al 2015;Nagashima et al 2017). Therefore, one explanation for the smaller 50 Ti heterogeneity among CR compared to CV chondrules is an increasing homogenization of the added 50 Ti-enriched CAI-like material over time.…”

“…Further, the two meteorite reservoirs must have remained separated for at least ~2-3 Ma, because they both contain chondrites, which accreted between ~2 and ~4 Ma after CAI formation (Budde et al 2016a;Luu et al 2015;Nagashima et al 2017;Schrader et al 2017;Ushikubo et al 2013). Thus, the dust carriers of the supernova-derived material that had been added to the carbonaceous meteorite reservoir did not infiltrate the reservoir of the non-carbonaceous meteorites for at least 2-3 Ma (Budde et al 2016a).…”

Chondrules: Ubiquitous Chondritic Solids Tracking the Evolution of the Solar Protoplanetary Disk

“…Such an age gap, however, is not apparent in the U-corrected Pb-Pb ages of individual chondrules. Luu et al (2015) recently suggested that the bulk Al-Mg systematics of a number of chondrules from the non-pristine and aqueously altered Allende carbonaceous chondrites can be used to date the timing of condensation of chondrule precursors. This is based on the observations that a number of chondrules form an array in the Al-Mg diagram that corresponds to an initial 26 Al/ 27 Al value of 1.2 10 5 , which the authors interpret as reflecting the timing of cessation of condensation of chondrule precursors 1.5 Myr after formation of the Solar System first solids.…”

The abundance of26Al-rich planetary systems in the Galaxy

“…Lower ratios observed in chondrules (millimetre-sized quenched silicate droplets ubiquitous in chondrites; Krot et al 2009) are usually attributed to their later formation relative to CAIs (e.g. Luu et al 2015). This difference can also be due to a heterogeneous distribution of 26 Al in the SPD (Gounelle & Russell 2005;Connelly et al 2012).…”