PETROLOGY FINDINGS AND FALLBACKS SURROUNDING MARTIAN METEORITES (Invited Presentation)

Martian petrologic processes —and more broadly the evolution of the martian interior— can be inferred using samples, surficial analyses via rovers and landers, and orbital remote observations. Here we focus on martian meteorites, rocks which have been directly ejected from the planet, currently making them the only samples that we have from Mars. We are in possession of a total of 246 meteorites, all of which are igneous, except one breccia (Northwest Africa [NWA] 7034), and all display mafic to ultramafic compositions.

Over the past decade, we have developed a clearer picture of the martian interior by studying meteorites in Earth-based laboratories, as the numbers of these rocks have exponentially increased, and as new analytical techniques have been developed. We now understand that Mars has been volcanically active throughout its entire geologic history. Comagmatic suites, such as the suite of nakhlites and chassignites or the suite of depleted shergottites, despite being petrologically different, originated from long-lived magmatic systems. In addition, the martian interior is more heterogeneous than previously thought. Although it differentiated very early in its history, Mars consists of various mantle sources, much like the Earth’s interior. Furthermore, assimilation and other open-system processes, as shown by isotopic systems like Re-Os and melt inclusion analyses, occurred during the formation of nakhlites and chassignites.

However, many questions remained unanswered regarding the martian interior as no meteorites between 4.1 and 2.4 Ga have been recovered. Martian meteorites also lack field context, and represent a bias of the Mars crust, as they lack compositional diversity. For example, bulk felsic compositions are not represented in the collection (except for lithic clasts in NWA 7034).

Returned samples, collected by the Mars 2020 Perseverance rover, originally planned to return to Earth by 2033, will help to develop insights into both the martian interior and surface processes. A variety of samples, including new lithologies and sample types (igneous, sedimentary, regolith, atmosphere), are being collected in the Jezero crater, representing multiple depositional environments and origins. The complementary study of meteorites and future returned samples will allow for a more comprehensive understanding of the evolution of the red planet.