January 18 @ 4:00 pm - 5:00 pm CST
EEPS Seminar: Valérie Payré, GeoRessources laboratory, University of Lorraine, Nancy, France
Trace Element Distributions in Gale Crater, Mars: Understanding the Early Martian Crust and its AlterationProcesses
Trace elements provide essential information about ancient geological processes such as
magmatism, hydrothermalism and/or aqueous alteration. In order to investigate martian
petrogenetic processes, the Alpha Particle X-ray Spectrometer (APXS) and Chemistry
Camera (ChemCam) instruments onboard the Curiosity rover in Gale crater, located on the
border of the North-South dichotomy, have analyzed a large number of trace element
compositions along with major element concentrations. A part of this work aims to quantify
Li, Rb, Sr, Ba and Cu within all materials analyzed by ChemCam since the beginning of the
mission (>1500 sols, > 6000 targets) . By providing the distributions of these elements
along the Curiosity traverse, several magmatic and alteration processes have been highlighted.
Although the martian crust was seen until recently as a “mostly basaltic” world [e.g., 2],
the unexpected discovery of Rb-Ba-rich evolved igneous rocks, likely from the crater rim of
Noachian origin (> 3.8 Gyr), provided evidence for an evolved ancient magmatism [3,4].
Evidence from 4.43 Gyr felsic igneous clasts (e.g., monzonite) within a martian brecciated
meteorite reinforced the idea of an unexpected differentiated ancient magmatism . A
comparison between these igneous clasts and Gale felsic igneous rocks reveals at least two
distinct K/Rb ratios (108 and 298) that could reflect several differentiated reservoirs. In
addition, the orbital compositional maps of the gamma ray spectrometer (GRS) onboard the
Mars Odyssey spacecraft show the occurrence of sparse Noachian terrains that are Si- K- and
Th-rich and Fe-poor in comparison with most regions. Several of them correspond to
Noachian areas displaying feldspar-rich rocks , suggesting an ancient evolved magmatism.
All these observations could suggest that the felsic terrains may be the remaining exposures of
a differentiated early crust. If so, the absence of Ca-feldspars in felsic igneous rocks and clasts
from Gale and the martian breccia [3-5] highlights that this crust would not be anorthositic
and thus would not have been formed according to the lunar ocean magma model .
Concurrently, Cu distribution along the rover traverse revealed anomalously high Cu
contents in a K-rich sedimentary region named Kimberley that was apparently formed from
detrital igneous minerals . This region is located at the end of the Peace Vallis alluvial fan,
which extends below a channel that dissects the northern crater rim . According to
ChemCam analyses, Cu-phases are associated with detrital alkali silicates coming from a
potassic igneous source (likely trachytic); these silicates were likely transported to the fan by
fluvial activity. Hydrothermal circulation within this potassic igneous source suggested by 
would thus have favored the concentration of metals like Cu within the melt, forming a Cu
deposit upstream of Gale crater.
The investigation of igneous materials within Gale crater mostly provides evidence for
evolved melting, potentially with a variety of source(s), but the formation processes
explaining such differentiated magmas remain controversial (e. g., low partial melting?
Fractional crystallization? Mantle metasomatism? ). I propose with this postdoctoral position
to better constrain these processes in an innovative way: combining numerical modeling with
various pressure-temperature experiments on starting materials with distinct compositions.