气候变化领域集成服务门户(CCPortal): The Ca isotope composition of mare basalts as a probe into the heterogeneous lunar mantle

CCPortal

DOI	10.1016/j.epsl.2021.117079
	The Ca isotope composition of mare basalts as a probe into the heterogeneous lunar mantle
	Klaver M.; Luu T.-H.; Lewis J.; Jansen M.N.; Anand M.; Schwieters J.; Elliott T.
发表日期	2021
ISSN	0012821X
卷号	570
英文摘要	The Ca isotope compositions of mare basalts offer a novel insight into the heterogeneous nature of the lunar mantle. We present new high-precision Ca isotope data for a suite of low-Ti and high-Ti mare basalts obtained using our collision cell MC-ICP-MS/MS instrument, Proteus. Mare basalts were found to have a Ca isotope composition resembling terrestrial basalts (δ44/40CaSRM 915a =0.78–0.89‰) even though they are derived from a differentiated, refractory cumulate mantle source. Modelling of Ca isotope fractionation during crystallisation of a lunar magma ocean (LMO) indicates that the dominantly harzburgitic cumulates of the lunar interior should be isotopically heavier than Earth's mantle (δ44/40CaSRM 915a =1.1–1.2‰ versus 0.93‰, respectively). These are balanced by an isotopically light lunar anorthosite crust, consistent with data for lunar anorthosite and feldspathic breccia meteorites. We investigate the major element and Ca isotope composition of partial melts of various cumulate reservoirs by combining pMELTS models with equilibrium isotope fractionation mass balance calculations. The principal finding is that harzburgite cumulates alone are too refractory a source to produce low-Ti magmas. Partial melts of harzburgite cumulates have too low CaO contents, too high Al2O3/CaO and too high δ44/40CaSRM 915a to resemble low-Ti magmas. From Ca isotope constraints, we find that the addition of 10–15% of late-stage, clinopyroxenite cumulates crystallising at 95% LMO solidification is required to produce a suitable source that can generate low-Ti basalt compositions. Despite the addition of such late-stage cumulates pMELTS finds that these hybrid sources are undersaturated in clinopyroxene and are thus consistent with experimental constraints that the mantle sources of the lunar magmas are clinopyroxene-free. High-Ti basalts have slightly lower δ44/40CaSRM 915a (0.80–0.86‰) than low-Ti magmas (0.85–0.89‰) and clearly elevated TiO2/CaO. No suitable hybrid source involving ilmenite-bearing cumulates (IBC) was found that could reproduce melts with appropriate δ44/40Ca and major element systematics. Instead, we suggest that metasomatism of low-Ti mantle sources by IBC melts is the most plausible way to generate high-Ti magma sources and the rich diversity in TiO2 contents of lunar basalts and pyroclastic glasses. © 2021 Elsevier B.V.
关键词	cumulate remelting ilmenite-bearing cumulates lunar magma ocean mass-dependent Ca isotope variations Moon
英文关键词	Alumina; Aluminum oxide; Basalt; Calcium; Meteorites; Moon; Refractory materials; Cumulate remelting; Ilmenite-bearing cumulate; Isotope compositions; Isotope fractionation; Lunar magma ocean; Magma ocean; Major elements; Mantle source; Mass-dependent ca isotope variation; Partial melt; Isotopes; calcium; cumulate; heterogeneity; isotopic composition; isotopic fractionation; lunar mantle; magma; mare basalt; Moon; partial melting; probe
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/203167
作者单位	Bristol Isotope Group, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ, United Kingdom; Université de Paris, Institut de Physique du Globe de Paris, CNRS, Paris, F-75005, France; School of Earth and Environmental Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, United Kingdom; School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom; Thermo-Fisher Scientific, Hannah-Kunath Strasse, Bremen, Germany
推荐引用方式 GB/T 7714	Klaver M.,Luu T.-H.,Lewis J.,et al. The Ca isotope composition of mare basalts as a probe into the heterogeneous lunar mantle[J],2021,570.
APA	Klaver M..,Luu T.-H..,Lewis J..,Jansen M.N..,Anand M..,...&Elliott T..(2021).The Ca isotope composition of mare basalts as a probe into the heterogeneous lunar mantle.Earth and Planetary Science Letters,570.
MLA	Klaver M.,et al."The Ca isotope composition of mare basalts as a probe into the heterogeneous lunar mantle".Earth and Planetary Science Letters 570(2021).