Early solar materials bear a variety of isotopic anomalies that reflect compositional differences deriving from distinct stellar nucleosynthetic processes. As shown in previous studies, the stepwise dissolution with increasing acid strengths of bulk rock carbonaceous chondrites liberates Cr with both excesses and deficits in 53 Cr and 54 Cr relative to the terrestrial standard. The magnitude of the 54 Cr variations within a meteorite decreases in the sequence CI1 > CR2 > CM2 > CV3 > CO3 > CK4 and correlates with the degree of metamorphism of each carbonaceous chondrite class. This study shows that the Tagish Lake meteorite presents the highest excesses in 54 Cr ever measured in a bulk silicate phase. According to this study, the Tagish Lake meteorite is composed of the least re-equilibrated material known at this time. The magnitude of 54 Cr variation decreases now in the following sequence: Tagish Lake (ungrouped CI2) > Orgueil (CI1) > Murchison (CM2) > Allende (CV2). Moreover, this study shows that excesses in 53 Cr relative to Earth can be interpreted as representing the extent of aqueous alteration on meteorite parent bodies. Finally, the high 54 Cr anomalies measured in this meteorite make Tagish Lake one of the major targets to decipher the host of these anomalies.
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.
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