钙长辉长无球粒陨石NWA 11586稀有气体及其年代学

Noble gas and its chronology of the eucrite NWA 11586

HED族陨石来自灶神星,是研究太阳系和类地行星形成及演化的重要窗口,而研究稀有气体是了解HED族陨石和灶神星撞击历史与热事件的主要途径。本文对非角砾岩化钙长辉长无球粒陨石NWA 11586开展了稀有气体、宇宙暴露(CRE)年龄和气体保存年龄研究。稀有气体同位素表明,NWA 11586陨石He、Ne和Ar气体主要是宇宙射线成因和放射性衰变成因的;该陨石CRE年龄(38.5±4.1 Ma)与HED族陨石35~41 Ma的主要撞击溅射事件年龄相一致,故其可能在~40 Ma前从灶神星或V型小行星溅离;陨石U、Th-^(4)He(T_(4))及^(40)K-^(40)Ar(T_(40))气体保存年龄分别为1019±41 Ma和3041±77 Ma,已受到后期热事件影响而发生了重置。

Howardite-Eucrite-Diogenite(HED)clan meteorites come from Vesta,and are the important window for studying the formation and evolution of the solar system and terrestrial planets.The noble gases are the key means to understand the impact and thermal history of HED meteorites and Vesta.This research work presents a detail study of the noble gas isotopes,cosmic-ray exposure(CRE)age and nominal gas retention age for the unbrecciated eucrite NWA 11586.The noble gas isotopes indicate that the He,Ne and Ar of NWA 11586 are mainly cosmogenic and radiogenic.The CRE age of this meteorite(38.5±4.1 Ma)is consistent with the ages of major impact events(35-41 Ma)of HEDs,indicating that it may be launched from Vesta or V-type asteroids at-40 Ma.The U,Th-^(4)He(T_(4))and^(40)K-^(40)Ar(T_(40))gas retention ages of NWA 11586 are 1019±41 Ma and 3041±77 Ma respectively,the reset may be caused by late thermal events.