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D-poor hydrogen in lunar mare basalts assimilated from lunar regolith

Allan H. Treiman, Jeremy W. Boyce, James P. Greenwood, John M. Eiler, Juliane Gross, Yunbin Guan, Chi Ma and Edward M. Stolper
D-poor hydrogen in lunar mare basalts assimilated from lunar regolith
American Mineralogist (July 2016) 101 (7): 1596-1603


Apatite grains in lunar mare basalts contain hydrogen that ranges in D/H ratio by more than a factor of two. For most of these basalts, the D/H ratios in their apatite grains decrease with measures of the host basalts' time spent at elevated temperature, specifically the Fe-Mg homogenization of their pyroxenes. Most basalts with homogeneous pyroxenes (i.e., with constant Fe/Mg ratio) have apatite grains with low D/H (delta D nearly equal -100 ppm), whereas most basalts with heterogeneous pyroxenes (i.e., varying or zoned Fe/Mg) have apatite with high D/H (delta D up to approximately +1100 ppm). This relationship suggests that low D/H values were acquired during thermal processing, i.e., during Fe-Mg chemical equilibration, during or after emplacement. This light hydrogen is likely derived from solar wind implanted into the lunar regolith (with delta D from -125 ppm to -800 ppm), and could enter basalts either by assimilation of regolith or by vapor transport from regolith heated by the flow. If a basalt could not interact with regolith rich in solar wind (e.g., it was emplaced onto other fresh basalts), its apatite could retain a magmatic D/H signature. The high D/H component (in the apatites of unequilibrated basalts) is most reasonably that indigenous magmatic hydrogen, i.e., representing hydrogen in the basalt's source mantles, or magmatic hydrogen that was residual after partial degassing of H (sub 2) .

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 101
Serial Issue: 7
Title: D-poor hydrogen in lunar mare basalts assimilated from lunar regolith
Affiliation: Lunar and Planetary Institute, Houston, TX, United States
Pages: 1596-1603
Published: 201607
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 62
Accession Number: 2016-079220
Categories: Isotope geochemistryExtraterrestrial geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: California Institute of Technology, USA, United StatesUniversity of California at Los Angeles, USA, United StatesWesleyan University, USA, United StatesRutgers University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201638
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