DOI: 10.1016/j.epsl.2020.116219
论文题名: The timing of lunar solidification and mantle overturn recorded in ferroan anorthosite 62237
作者: Sio C.K. ; Borg L.E. ; Cassata W.S.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 538 语种: 英语
中文关键词: Ar-Ar
; ferroan anorthosite
; lunar magma ocean
; overturn
; Rb-Sr
; Sm-Nd
英文关键词: Basalt
; Binary alloys
; Isotopes
; Magnesium alloys
; Minerals
; Moon
; Rubidium alloys
; Samarium alloys
; Solidification
; Strontium alloys
; Timing circuits
; Crystallization products
; ferroan anorthosite
; Isotopic systematics
; Isotopic systems
; Magma ocean
; overturn
; Sm-Nd isotopic systematics
; Thermal events
; Neodymium alloys
; anorthosite
; argon-argon dating
; lunar crust
; magma chamber
; overturn
; rubidium-strontium dating
英文摘要: Ferroan anorthosite suite (FAS) rocks are widely interpreted to represent primordial lunar crust. Despite their importance in pinpointing the timing of lunar crust formation, robust chronological investigations for this rock type are scarce. Here, we report the Ar-Ar, Rb-Sr, and Sm-Nd isotopic systematics for the FAS troctolitic anorthosite 62237. The Ar-Ar isotopic system has been reset by a thermal event at 3710 ± 48 Ma, and the Rb-Sr isotopic systematics has been disturbed such that a Rb-Sr isochron age cannot be determined. However, an internal isochron for the Sm-Nd isotopic system has yielded an age of 4350 ± 73 Ma (MSWD = 2.0) with an initial ϵ143NdCHUR of −0.53 ± 0.26. The mineral and whole-rock fractions of 62237 plot on the same internal isochron as FAS sample 60025. The combined datasets define an age of 4372 ± 35 Ma (MSWD = 4.0) with an initial ϵ143NdCHUR of −0.17 ± 0.22. Literature Sm-Nd data for FAS and Mg-suite whole-rocks also plot on the 60025-62237 isochron. The coherence of data from both FAS and Mg-suite rocks examined thus far suggests that both rock suites formed contemporaneously from identical, or nearly identical, sources. In addition, the concordance of FAS and Mg-suite ages suggests that primordial crust solidification either involved both magmatic suites, or that Mg-suite magmatism was contemporaneous with FAS magmatism within resolution of the Sm-Nd chronometer. The ages for FAS and Mg-suite also coincide with the formation ages of the mare basalt source regions and urKREEP. Ferroan anorthosite suite rocks and urKREEP are thought to represent primordial LMO solidification products, whereas Mg-suite and the mare basalt source regions are argued to represent mixtures of various LMO crystallization products that were formed during density-driven overturn of the LMO. The concordance of ages implies that the 4372 ± 35 Ma Sm-Nd isochron records the age of mantle overturn, and that overturn occurred during, or shortly after, solidification of the LMO. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165269
Appears in Collections: 气候变化与战略
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作者单位: Lawrence Livermore National Laboratory, 7000 East Ave. L-231, Livermore, CA 94550, United States
Recommended Citation:
Sio C.K.,Borg L.E.,Cassata W.S.. The timing of lunar solidification and mantle overturn recorded in ferroan anorthosite 62237[J]. Earth and Planetary Science Letters,2020-01-01,538