In situ evidence for continental crust on early Mars

Abstract

Gale crater, geological context of the rover traverse and samples studiedThe Curiosity rover landing site is located at -4.59° S, 137.44° E). Fig. S1a shows a portion of the THEMIS IR nighttime mosaic of Bradbury Rise. The landing site is marked by a black cross within the landing ellipse. It is located at a distal portion of the alluvial fan stretching below Peace Vallis on the northern rim of Gale crater.Mafic and light-toned igneous float rocks were initially observed by the Curiosity rover close to the Bradbury landing site from sol 1 to 55 in the Hummocky plain unit. After Curiosity left the fluvio-lacustrine deposit of Yellow Knife Bay (sol 55-326), it traversed back across the hummocky unit (Fig. S1b). An increasing number of light-toned rocks dominated by feldspars (porphyritic, felsic coarse-grained, felsic fine-grained) together with three groups of mafic rocks were observed along the traverse from sol 326 to sol 550. The mafic rocks are described in detail in Cousin et al. (2015) 43 and Sautter et al. (2014) 45 . The rocks selected for the present study are summarized in Table S1. Laser-Induced Breakdown Spectrometer (LIBS) spectraChemCam's laser-induced breakdown spectrometer (LIBS) uses a pulsed laser to ablate targets up to ≈ 7 m from the rover. The size of the laser interaction varies with distance, ranging from 350 µm at 1.5 m to 550 µm at 7 m 36 . The light emitted by the ablated plasma spark is collected by the same telescope used to transmit the laser beam, and is analyzed by three spectrometers which record the atomic emission spectrum over the ultraviolet (UV: 240.1-342.2nm), violet (VIO: 382.1-469.3 nm), and visible to near-infrared (VNIR: 474.0-906.5 nm) ranges 21, 22 . The ChemCam LIBS spectra consist of 6144 channels covering the above wavelength range in wavelength with typically several hundred emission peaks covering all of the major elements and many minor and trace elements.A typical ChemCam LIBS observation involves the analysis of multiple locations on the target: common geometries for LIBS observations are square grids (e.g. 3×3, 4×4) and

ChemCam activities and discoveries during the nominal mission of the Mars Science Laboratory in Gale crater, Mars

“…52 The latter rock-type (ii) is unlike anything proposed in the literature for Mars but has similarities to the TTG Archean rock suites encountered on the Earth that are related to the building of continental crust. 40 The bulk composition of igneous rocks observed at Gale, with SiO 2 reaching 67 wt% and Na 2 O + K 2 O reaching 14 wt%, greatly extends the magmatic diversity that was observed by previous landers and rovers. Mars Exploration Rover Spirit found alkalirich compositions in the Noachian terrain at Columbia Hills, but those rocks were basaltic (tephrite and trachy basalts) and they did not exhibit visible feldspar phenocrysts.…”

“…Sautter et al 40 argued that such felsic rocks are a likely feature of a major fraction of the southern highlands. If so, Gale's felsic rocks would solve the density paradox raised recently 54 between relatively high values for the crust predicted from SNC meteorites and the vast majority of orbital observation, and a lower crustal density deduced by geophysics (geoid to topography ratio).…”

“…17 The highest values of barium were found in Martian K-feldspars. 39,40 Chromium is quite difficult to quantify in geological materials with LIBS, because its peaks between 424 and 430 nm interfere with Fe. The accuracy is around 710 ppm.…”

“…39,40,49,50 Igneous rocks observed to the west of the Yellowknife Bay (YKB) sedimentary formation are oat rocks or clasts in conglomerates. ChemCam textural and compositional analyses led to the identication of 53 massive (non-layered) igneous targets, 39,40 both intrusive and effusive, with mac or felsic samples, the latter dominated by feldspar minerals.…”

“…ChemCam textural and compositional analyses led to the identication of 53 massive (non-layered) igneous targets, 39,40 both intrusive and effusive, with mac or felsic samples, the latter dominated by feldspar minerals. From the morphology, color, grain size, patina and chemistry, at least ve different groups have been identied, which t in general into two distinct geochemical series: 40,51 (i) an alkali-suite: basanite, gabbro trachy-andesite and trachyte, including porphyritic and aphyric members; (ii) quartz-normative intrusives close to granodioritic composition. All of these observations are geochemically consistent with differentiation of liquids produced by low degrees of partial melting of the primitive Martian mantle.…”