¹Tarryn Aucamp,¹Geoffrey H. Howarth,¹Chad J. Peel,²Gelu Costin,³James M. D. Day,¹Petrus le Roux,⁴James M. Scott,⁵Ansgar Greshake,⁶Rainer Bartoschewitz
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14090]
¹Department of Geological Sciences, University of Cape Town, Rondebosch, South Africa
²Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, Texas, USA
³Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
⁴Department of Geology, University of Otago, Dunedin, New Zealand
⁵Institut für Mineralogie, Museum für Naturkunde, Humboldt-Universität zu Berlin, Berlin, Germany
⁶Bartoschewitz Meteorite Laboratory, Gifhorn, Germany
Published by arrangement with John Wiley & Sons

The Dar al Gani (DaG) olivine-phyric shergottites share mineralogical and geochemical characteristics, which confirm that these meteorites are derived from a single source. Bulk trace elements (La/Yb—0.12), in situ maskelynite 87Sr/86Sr (~0.7014) and redox estimates (FMQ ~ −2) indicate derivation from a depleted, reduced mantle reservoir; identical to all ~470 Ma shergottites ejected at 1.1 Ma. The DaG shergottites have been variably affected by terrestrial alteration, which precipitated carbonate along fractures and modified bulk-rock fluid mobile (e.g., Ba) elements. Nonetheless, sufficient data are available to construct a multi-stage formation model for the DaG shergottites and other 1.1 Ma ejection-paired shergottites that erupted at ~470 Ma. First, partial melting of a depleted mantle source occurred at 1540 ± 20°C and 1.2 ± 0.1 GPa, equivalent to > ~100 km depth. Then, initial crystallization in a staging chamber at ~85 km depth at the crust–mantle boundary took place, followed by magma evolution and variable incorporation of antecrystic olivine ± orthopyroxene. Subsequently, crystallization of olivine phenocrysts and re-equilibration of olivine antecrysts occurred within an ascending magma. Finally, magmas with variable crystal loads erupted at the surface, where varied cooling rates produced a range of groundmass textures. This model is similar to picritic flood basalt magmas erupted on Earth.