^1,2Ye Li, ^1,3Yuting Wang, ⁴Haoxuan Jiang, ^5,6Jia Liu, ^6,5Liping Qin, ⁷Qiu-Li Li, ⁷Yu Liu, ^8,9Zhenfei Wang, ^1,2Weibiao Hsu
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.11.020]
¹Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210023, China
²CAS Center for Excellence in Comparative Planetology, Hefei, China
³School of Astronomy and Space Sciences, University of Science and Technology of China, Hefei, 230026, China
⁴School of Mechanical and Electrical Engineering, Chuzhou University, Chuzhou, 239099, China
⁵Institute of Deep Space Sciences, Deep Space Exploration Laboratory, Hefei, China
⁶CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China
⁷State Key Laboratory of Lithospheric and Environmental Coevolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
⁸International Center for Isotope Effect Research, Nanjing University, Nanjing 210023, China
⁹Frontiers Science Center for Critical Earth Material Cycling, State, Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023, China
Copyright Elsevier

Type 7 chondrites, which record a higher degree of heating process than typical type 3 to type 6 chondrites, are characterized with textures and petrography of partial melting. Understanding the timing and cooling history of incipient melting event for type 7 chondrites could provide insights into the complex thermal process of the early solar system. Here, we studied two chondrites NWA 12272 and NWA 11021. Both samples display partial melting characteristics of LL chondrites, including interconnected plagioclase/high-Ca pyroxene network, zoned plagioclase and lack of chondrules, which concurs with their classification of LL7 chondrites in the Meteoritical Bulletin Database. The 53Mn-53Cr isotopic data of NWA 12272, determined by mineral separates and bulk samples, yielded an isochron with a 53Mn/55Mn ratio of (1.40 ± 0.59) × 10-6 and a corresponding absolute age of 4558.8 ± 2.3 Ma (anchored to D’Orbigny angrite). Combined with the cooling rate estimated by the integration of REE-in-two-pyroxene thermometry and two-pyroxene thermometry, Mn-Cr isochron age of 4558.8 ± 2.3 Ma and Ca-phosphate Pb-Pb age of 4517 ± 6 Ma, we suggest that NWA 12272 experienced a two-stage cooling process after the incipient melting: it exposed to a relatively cold environment with a rapid cooling rate of ∼ 30-100°C/yr at 1150–1000 °C, and soon reburied with a slower cooling rate of ∼ 13 °C/Ma at 1000–475 °C. Although the Mn-Cr isotopic study was not conducted for NWA 11021, the average Ca-phosphate Pb-Pb age of 4509 ± 7 Ma and high-temperature cooling rate (∼1-30°C/yr) of NWA 11021 are indistinguishable from or slightly lower than those of NWA 12272. Assuming NWA 11021 cooled from the same incipient melting event as NWA 12272, it could have recorded a similar two-stage cooling process. We suggest that the studied LL7 chondrites were most likely formed in the early solar system when additional impact heat overlapped on the “heated” type 5–6 chondrites. Integrated with the previous cooling rates of LL6-7 chondrites, the prevailing two-stage cooling rates of LL chondrites provide compelling evidence for the fragmentation-re-accretion process in the early history of LL chondrite parent body. This early impact event also happened in other ordinary chondrite groups and some iron meteorites.

¹M.D. Cashion, ^1,2B.C. Johnson, ³R. Deienno, ³K.A. Kretke, ³K.J. Walsh, ⁴A.N. Krot
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116400]

¹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, United States of America
²Department of Physics and Astronomy, Purdue University, West Lafayette, IN, United States of America
³Southwest Research Institute, Boulder, CO, United States of America
⁴Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI, United States of America
Copyright Elsevier

Chondrules, igneous spherules found in most meteorites, formed throughout the protoplanetary disk, but their formation is largely unexplored beyond the water snowline, in the outer disk. Combining simulations of giant planet core accretion with simulations of planetesimal collisions, we find that impact jetting can produce chondrules to distances of ~15 AU from the Sun. In our simulations, chondrule formation ceases by the time the first giant planet core exceeds isolation mass, ~10 Earth masses. The time it takes to reach this mass is sensitive to the total mass of the disk, and how the mass is distributed within planetesimals and small pebbles. Measured chondrule ages subsequently constrain the time of Jupiter’s core formation to approximately 3–4 Myr after the first solar system solids. This protracted growth indicates the separation of non‑carbonaceous and carbonaceous material reservoirs predates the formation of Jupiter’s core.