^1,2Le Zhang,^1,2Ya-Nan Yang,^1,2Zhi-Ming Chen,^1,2Jintuan Wang,^1,2Cheng-Yuan Wang,^1,2Ze-Xian Cui,^1,2Yan-Qiang Zhang,^1,2Yi-Gang Xu
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116002]
¹State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China
Copyright Elsevier

Plagioclase is the most abundant mineral in lunar crustal rocks, and its elemental and Sr isotopic compositions vary among different lunar surface rock types, implying that plagioclase fragments in lunar regolith can be used to trace source-rock types. In this study, we measured major- and trace-elemental and Rbsingle bondSr isotopic compositions of plagioclase fragments from lunar soil returned by the Chang’e 5 (5CE) mission. Correlation between Sr and An contents allows the 5CE plagioclase fragments to be divided into three groups: normal-Sr (group A), high-Sr (group B), and low-Sr (group C). The similarity of elemental and Rbsingle bondSr isotopic compositions between plagioclase in groups A and B and plagioclase from 5CE basalt clasts indicates that plagioclase from groups A and B originated from the comminution of local 5CE basalt. Only two of the eighty-two analyzed plagioclases (~2.4%) are classified as group C and have Sr isotopes that are distinct from those of groups A and B plagioclases, indicating an exotic origin. One group C plagioclase has a high 87Sr/86Sr ratio (0.70242) and content of rare earth elements and might have been derived from the Sharp B or Aristarchus craters, which are enriched in the KREEP component. The other group C plagioclase has much lower 87Sr/86Sr (0.69908) and a moderately high content of An (92.3) indicating an Mg-suite source rock and possible derivation from the Pythagoras crater. This study highlights the applicability of using elemental and Sr isotopic compositions of plagioclase fragments to trace the origin of lunar regolith.

^1,2S. Benaroya,^1,3,4,5J. Gross,¹P. Burger,⁶M. Righter,⁶T.J. Lapen,⁷S. Eckley
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.02.004]
¹Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ, USA
²Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton Alberta, Canada
³Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY, USA
⁴Lunar and Planetary Institute, Houston, TX, USA
⁵Astromaterials Research and Exploration Science Division, NASA JSC, Houston, TX, USA
⁶Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA
⁷Jacobs – JETS, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX, USA
Copyright Elsevier

Petrologic investigations of martian meteorite Northwest Africa (NWA) 13227 indicate it is an olivine-gabbroic shergottite, a relatively new shergottite group, which differs from previously described gabbroic shergottites due to relatively high quantities of olivine. NWA 13227 is comprised of phenocrystic, oscillatory-zoned pyroxene and olivine, set in a matrix of maskelynite, Fe-Cr-Ti oxides, phosphates, and sulfides. It displays gabbroic and poikilitic textures in 2D from back-scattered electron images, and in 3D from X-ray Computed Tomography (XCT) imaging, suggesting affinities to both poikilitic and gabbroic shergottites. Measured εHf and εNd values of bulk rock (-19.7 and −5.9, respectively) and its chondrite-normalized La/Yb ratio of 1.13 indicate the specimen is derived from a mantle reservoir relatively enriched in incompatible trace elements and is similar to that which produced most ‘enriched shergottites.’ Based on the Ti/Al ratio of pyroxene, phosphorous zoning in olivine, and minor components in phosphates and oxides, we infer that NWA 13227 began crystallizing under reducing conditions of QFM–2.6 and temperatures of ∼ 1100 °C, consistent with conditions in Mars’ lower crust/upper mantle. The sample finished crystallizing at or near the surface under redox conditions between QFM–0.5 to QFM–0.1 and temperatures of ∼ 850 °C. The volatile element compositions in apatite indicate that NWA 13227 experienced degassing during the last stages of crystallization. The timing of crystallization is estimated at 225 Ma ± 50 Ma using a Lu-Hf and Sm-Nd source versus age model.