1] Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Mānoa, Pacific Ocean Science &Technology (POST) Building, 1680 East-West Road, Honolulu, Hawai'i 96822, USA [2] University of Hawai'i NASA Astrobiology Institute, Honolulu, Hawai'i 96822, USA.
Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Mānoa, Pacific Ocean Science &Technology (POST) Building, 1680 East-West Road, Honolulu, Hawai'i 96822, USA.
Nat Commun. 2015 Jun 23;6:7444. doi: 10.1038/ncomms8444.
Chronology of aqueous activity on chondrite parent bodies constrains their accretion times and thermal histories. Radiometric (53)Mn-(53)Cr dating has been successfully applied to aqueously formed carbonates in CM carbonaceous chondrites. Owing to the absence of carbonates in ordinary (H, L and LL), and CV and CO carbonaceous chondrites, and the lack of proper standards, there are no reliable ages of aqueous activity on their parent bodies. Here we report the first (53)Mn-(53)Cr ages of aqueously formed fayalite in the L3 chondrite Elephant Moraine 90161 as Myr after calcium-aluminium-rich inclusions (CAIs), the oldest Solar System solids. In addition, measurements using our synthesized fayalite standard show that fayalite in the CV3 chondrite Asuka 881317 and CO3-like chondrite MacAlpine Hills 88107 formed and Myr after CAIs, respectively. Thermal modelling, combined with the inferred conditions (temperature and water/rock ratio) and (53)Mn-(53)Cr ages of aqueous alteration, suggests accretion of the L, CV and CO parent bodies ∼1.8-2.5 Myr after CAIs.
球粒陨石母体上水活动的时间进程约束了它们的形成时间和热历史。放射性 (53)Mn-(53)Cr 测年法已成功应用于 CM 碳质球粒陨石中形成于水相的碳酸盐。由于普通（H、L 和 LL）、CV 和 CO 碳质球粒陨石中不存在碳酸盐，且缺乏合适的标准，因此它们的母体上水活动的可靠年龄尚未确定。在这里，我们报告了 L3 球粒陨石 Elephant Moraine 90161 中首次利用 (53)Mn-(53)Cr 测年法测定的水合形成的镁铁尖晶石的年龄，其形成于钙铝富包裹体 (CAI) 之后 Myr，为太阳系中最古老的固体。此外，使用我们合成的镁铁尖晶石标准进行的测量表明，CV3 球粒陨石 Asuka 881317 和 CO3 型球粒陨石 MacAlpine Hills 88107 中的镁铁尖晶石分别形成于 CAI 之后 Myr。热模拟，结合推断的条件（温度和水/岩石比）以及水蚀变的 (53)Mn-(53)Cr 年龄，表明 L、CV 和 CO 母体的形成时间分别为 CAI 之后 1.8-2.5 Myr。
