On the cooling rate evolution of asteroid fragments

Ren, Jialong; Hesse, M. A.; Lucas, Michael P.; Dygert, Nick

doi:10.1016/j.icarus.2022.114905

Cited by 2 publications

(4 citation statements)

References 30 publications

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“…The calculations ignore the effects related to porosity, shape, atmospheric blanketing, impact-related heating, and internal heat production, which for the most part would have slowed cooling further. Ren et al (2022) present a more general treatment of these subjects. Herrin et al (2010) describe a thermal history for AhS.…”

Section: Thermal History Of Ahs and Other Polymict Ureilitesmentioning

confidence: 99%

⁴⁰Ar/³⁹Arages ofL4,H5,EL6,and feldspathic ureilitic clasts from the Almahata Sitta polymict ureilite (asteroid 2008TC₃)

Turrin

Lindsay

Delaney

et al. 2023

Meteorit & Planetary Scien

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The Almahata Sitta (AhS) meteorite consists of disaggregated clasts from the impact of the polymict asteroid 2008 TC3, including ureilitic (70%–80%) and diverse non‐ureilitic materials. We determined the 40Ar/39Ar release patterns for 16 AhS samples (3–1500 μg) taken from three chondritic clasts, AhS 100 (L4), AhS 25 (H5), and MS‐D (EL6), as well as a clast of ureilitic trachyandesite MS‐MU‐011, also known as ALM‐A, which is probably a sample of the crust of the ureilite parent body (UPB). Based on our analyses, best estimates of the 40Ar/39Ar ages (Ma) of the chondritic clasts are 4535 ± 10 (L4), 4537–4555 with a younger age preferred (H5), and 4513 ± 17 (EL6). The ages for the L4 and the H5 clasts are older than the most published 40Ar/39Ar ages for L4 and H5 meteorites, respectively. The age for the EL6 clast is typical of older EL6 chondrites. These ages indicate times of argon closure ranging up to 50 Ma after the main constituents of the host breccia, that is, the ureilitic components of AhS, reached the >800°C blocking temperatures of pyroxene and olivine thermometers. We suggest that these ages record the times at which the clasts cooled to the Ar closure temperatures on their respective parent bodies. This interpretation is consistent with the recent proposal that the majority of xenolithic materials in polymict ureilites were implanted into regolith 40–60 Ma after calcium–aluminum‐rich inclusion and is consistent with the interpretation that 2008 TC3 was a polymict ureilite. With allowance for its 10‐Ma uncertainty, the 4549‐Ma 40Ar/39Ar age of ALM‐A is consistent with closure within a few Ma of the time recorded by its Pb/Pb age either on the UPB or as part of a rapidly cooling fragment. Plots of age versus cumulative 39Ar release for 10 of 15 samples with ≥5 heating steps indicate minor losses of 40Ar over the last 4.5 Ga. The other five such samples lost some 40Ar at estimated times no earlier than 3800–4500 Ma bp. Clustering of ages in the low‐temperature data for these five samples suggests that an impact caused localized heating of the AhS progenitor ~2.7 Ga ago. In agreement with the published work, 10 estimates of cosmic‐ray exposure ages based on 38Ar concentrations average 17 ± 5 Ma but may include some early irradiation.

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Section: Thermal History Of Ahs and Other Polymict Ureilitesmentioning

confidence: 99%

⁴⁰Ar/³⁹Arages ofL4,H5,EL6,and feldspathic ureilitic clasts from the Almahata Sitta polymict ureilite (asteroid 2008TC₃)

Turrin

Lindsay

Delaney

et al. 2023

Meteorit & Planetary Scien

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“…Modeled curves for different cooling times are indicated by thick colored lines (cooling times labeled on left), while modeled curves for different depths within each fragment are normalized by % radius and are indicated by thin, black arrowed lines (% radius depths labeled on right). Monotonic cooling curve for acapulcoite‐transitional fragments (0.01% depth) at an initial temperature of 1025 °C (gray dashed curve) is essentially identical to the lodranite 0.01% depth cooling curve, demonstrating that collisional fragments cool at similar rates independent of initial temperature (Ren et al., 2022). High‐temperature (>750 °C) lodranite cooling rates are best reproduced by fragments in the size range of 300 m to 10 km, which experienced cooling times between several and ~20,000 yr. (Color figure can be viewed at wileyonlinelibrary.com.…”

Section: Discussionmentioning

confidence: 90%

“…In the planar solution, the temperature profile is self‐similar in the Boltzmann variable

η = x / 2 \sqrt kt

, where x is the depth below the surface. Conversely, η is a constant for a given temperature, which shows that the cooling rate at a given temperature declines proportional to 1/ t (Ren et al., 2022; see their equation 6). Therefore, the cooling rate of fragments after collisional disruption, but before reassembly, at any fixed temperature decays at 1/ t so that cooling rates measured at a given closure temperature provide a constraint on both fragment radius and reassembly time scales.…”

Section: Discussionmentioning

confidence: 99%

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Thermochemical evolution of the acapulcoite–lodranite parent body: Evidence for fragmentation‐disrupted partial differentiation

Lucas

Dygert

Ren

et al. 2022

Meteorit & Planetary Scien

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Primitive achondrites of the acapulcoite–lodranite clan (ALC) are residues of partial melting that displays a continuum of thermal metamorphism and partial melting most likely set by burial depth within an internally heated, primordial acapulcoite–lodranite parent body (ALPB). New major and trace element data from eight ALC meteorites and the application of several thermometric methods suggest that the ALPB was affected by partial differentiation disrupted by rapid cooling from peak, magmatic temperatures. Application of rare earth element‐in‐two‐pyroxene thermometry recovers temperatures of 1125–1250 °C for lodranites, while two‐pyroxene solvus and Ca‐in‐olivine thermometry recover lower temperatures for ALC meteorites (941–1114 °C and 686–850 °C, respectively). Major and trace element disequilibrium in acapulcoite and transitional groups provides evidence for cryptic melt infiltration and melt rock reaction within these layers of the ALPB. From lodranites, we determined rapid cooling rates of ~1 to ~26 °C yr−1 from peak temperatures, consistent with collisional fragmentation of the parent body during differentiation. After this initial period of rapid cooling, cooling rates decreased by two to four orders of magnitude through Ca‐in‐olivine closure temperatures (~750 °C). We hypothesize that the primordial ALPB possessed an onion shell‐type layered structure that was disrupted by collisional breakup during partial differentiation. Thermal modeling suggests that ALC samples originate from ~300 m to ~10 km radius collisional fragments that cooled rapidly over time scales of several to ~20,000 yr, then reaccreted to form a slower cooling, second‐generation rubble‐pile asteroid. The source of ALC meteorites is a second‐generation (or later) rubble‐pile body of S‐type spectral class located near the Jupiter 3:1 mean motion resonance in the Main Belt of asteroids.

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On the cooling rate evolution of asteroid fragments

Cited by 2 publications

References 30 publications

⁴⁰Ar/³⁹Arages ofL4,H5,EL6,and feldspathic ureilitic clasts from the Almahata Sitta polymict ureilite (asteroid 2008TC₃)

⁴⁰Ar/³⁹Arages ofL4,H5,EL6,and feldspathic ureilitic clasts from the Almahata Sitta polymict ureilite (asteroid 2008TC₃)

Thermochemical evolution of the acapulcoite–lodranite parent body: Evidence for fragmentation‐disrupted partial differentiation

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On the cooling rate evolution of asteroid fragments

Cited by 2 publications

References 30 publications

40Ar/39Arages ofL4,H5,EL6,and feldspathic ureilitic clasts from the Almahata Sitta polymict ureilite (asteroid 2008TC3)

40Ar/39Arages ofL4,H5,EL6,and feldspathic ureilitic clasts from the Almahata Sitta polymict ureilite (asteroid 2008TC3)

Thermochemical evolution of the acapulcoite–lodranite parent body: Evidence for fragmentation‐disrupted partial differentiation

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⁴⁰Ar/³⁹Arages ofL4,H5,EL6,and feldspathic ureilitic clasts from the Almahata Sitta polymict ureilite (asteroid 2008TC₃)

⁴⁰Ar/³⁹Arages ofL4,H5,EL6,and feldspathic ureilitic clasts from the Almahata Sitta polymict ureilite (asteroid 2008TC₃)