Petrology and Geochemistry of the nakhlite meteorites : Tracking complex igneous and aqueous processes on Mars during the Amazonian

• The overarching science question being addressed by this research project was the geological history of the nakhlite group of Martian meteorites as representative of a young Amazonian Martian crust. This included the magmatic processes and mechanism of emplacement at the origin of the meteorites but also the nature of a young Amazonian Martian aquifer that circulated throughout the nakhlites bedrock from its chemistry, origin and longevity. Answering these questions are fundamental to understand the physical and chemical properties and chronological evolution of Mars sub-surface environment over the last billion year with implication for astrobiology and current and future Mars exploration. For this project, a large set of nakhlite meteorites (probably the most comprehensible) have been assembled. It included NWA 5790, NWA 817, NWA 998, MIL 03346, Y 000593/000749, Lafayette and Nakhla. The mineralogy and mineral texture and chemistry of each meteorite have been fully characterized at the μm- and nm-scale using Electron Microscopy techniques (SEM and TEM) and Raman Spectroscopy at the University of Glasgow and Mass Spectroscopy (LA ICP-MS) at the University of Durham. The nakhlites are differentiated basaltic rocks formed by accumulation of augite in a sub-surface environment. The chemical composition of both cumulus augites (the liquidus phase) and their multiphase and glass inclusions representing trapped magma during augite growth indicate that the parent magmas at the origin of the meteorites were not primitive but residua of progenitors that experienced cryptic fractional crystallization processes in the deep basaltic plumbing system. The nakhlites have similar mineralogy but each meteorite has mineral phases with distinct properties which indicates that the rocks experienced each their own crystallization history. The nakhlites probably crystallized within separate igneous bodies/batches. Compositional variability of the nakhlites' parent magmas cannot be explained by a differentiation of a single pulse of magma that solidified through continuous fractional crystallization of augite and olivine alone in a shallow magma chamber. Aqueous alteration of the nakhlites is limited but the presence of small quantities of clay minerals from the smectite family with carbonate, sulphate, halite and Fe-oxide demonstrate the existence of briny crustal water in the young Martian basaltic crust at least at the site sampled by the nakhlites. Variations in mineral assemblages provide evidences for contrasting conditions in the aqueous environments ranging from neutral-to-acidic (with a deposition of sulfate and halite) to near neutral-to-alkaline (with a precipitation of carbonate) apparently associated with a temporal evolution of the brines' property. The texture and chemistry of the secondary mineral assemblages are consistent with a deposition from discreteaqueous events fading away over time.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

Mars

Nakhlites

Geovetenskap med inriktning mot mineralogi, petrologi och tektonik

Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics

Publikations- och innehållstyp

vet (ämneskategori)

dok (ämneskategori)