Assessing Crustal Contributions in Enriched Shergottite Magmas of Mars using Petrology, Geochemistry and Radiogenic Isotope Systematics



Journal Title

Journal ISSN

Volume Title



Shergottites are the most abundant type of meteorite we have from Mars and their study is invaluable to understand the geological evolution of that planet. For over three decades, a debate about the source of incompatible trace elements (ITE)-enriched shergottites has focused on two contradicting scenarios and remains unsolved. One scenario explains their Sr-Nd-Hf isotopic compositions as a result of mantle heterogeneity. This implies that the enriched shergottite magma is derived from enriched late-stage residual melts in the Mars mantle that resulted from early magma ocean crystallization. The second scenario states that depleted mantle-derived magmas assimilated highly enriched old Martian crust in variable amounts to form enriched shergottites. In my research, I have addressed this dispute to understand the origin and evolution history of enriched shergottite magmas and by extension, the origin of basaltic volcanism on Mars. My study is segmented into three projects: 1) evaluating crustal contributions in enriched shergottite magma by a comprehensive geochemical analysis and Sr-Nd isotope systematics of an enriched basaltic shergottite, NWA 856; 2) testing the potential crustal link in enriched shergottite magma from their early-formed olivine-hosted melt inclusions in two enriched poikilitic shergottites, NWA 7397 and RBT 04262; and 3) determining the crystallization age of NWA 7397 using Sm-Nd isotope systematics. The results of the NWA 856 study indicate that no successful crustal contamination model can explain the restricted εNdI of -6.8 ± 0.2 over the wide range of Mg# (0.65–0.25), and corresponding trace element variations from enriched shergottites to depleted shergottites. Thus, the origin of the enriched signatures observed in enriched shergottites are likely not the result of crustal contamination but instead reflect ancient mantle heterogeneity. The findings derived from the analyses of olivine-hosted melt inclusions in NWA 7397 and RBT 04262 suggest that the melt inclusions are highly evolved, and have compositions overlapping with basaltic shergottites and Martian crustal rocks. They were trapped in a closed-system progressive crystallization, without any crustal involvement which implies that Martian crust is directly related to shergottite magma differentiation. The Sm-Nd crystallization age of NWA 7397 is 182±28 Ma with an initial εNdI of ~ -7.0, consistent with those of other enriched shergottites, suggesting that the source regions of all the enriched shergottites share a similar melting history.



Mars, Shergottites, Petrology, Geochemistry, Isotopes


Portions of this document appear in: Ferdous, J., A. D. Brandon, A. H. Peslier, and Z. Pirotte. "Evaluating crustal contributions to enriched shergottites from the petrology, trace elements, and Rb-Sr and Sm-Nd isotope systematics of Northwest Africa 856." Geochimica et Cosmochimica Acta 211 (2017): 280-306.