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Executive Summary Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (iMOST). The purpose of the team is to re‐evaluate and update the sample‐related science and engineering objectives of a Mars Sample Return (MSR) campaign. The iMOST team has also undertaken to define the measurements and the types of samples that can best address the objectives. Seven objectives have been defined for MSR, traceable through two decades of previously published international priorities. The first two objectives are further divided into sub‐objectives. Within the main part of the report, the importance to science and/or engineering of each objective is described, critical measurements that would address the objectives are specified, and the kinds of samples that would be most likely to carry key information are identified. These seven objectives provide a framework for demonstrating how the first set of returned Martian samples would impact future Martian science and exploration. They also have implications for how analogous investigations might be conducted for samples returned by future missions from other solar system bodies, especially those that may harbor biologically relevant or sensitive material, such as Ocean Worlds (Europa, Enceladus, Titan) and others. Summary of Objectives and Sub‐Objectives for MSR Identified by iMOST This objective is divided into five sub‐objectives that would apply at different landing sites. 1.1 Characterize the essential stratigraphic, sedimentologic, and facies variations of a sequence of Martian sedimentary rocks. 1.2 Understand an ancient Martian hydrothermal system through study of its mineralization products and morphological expression. 1.3 Understand the rocks and minerals representative of a deep subsurface groundwater environment. 1.4 Understand water/rock/atmosphere interactions at the Martian surface and how they have changed with time. 1.5 Determine the petrogenesis of Martian igneous rocks in time and space. This objective has three sub‐objectives: 2.1 Assess and characterize carbon, including possible organic and pre‐biotic chemistry. 2.2 Assay for the presence of biosignatures of past life at sites that hosted habitable environments and could have preserved any biosignatures. 2.3 Assess the possibility that any life forms detected are alive, or were recently alive. Summary of iMOST Findings Several specific findings were identified during the iMOST study. While they are not explicit recommendations, we suggest that they should serve as guidelines for future decision making regarding planning of potential future MSR missions. The samples to be collected by the Mars 2020 (M‐2020) rover will be of sufficient size and quality to address and solve a wide variety of scientific questions. Samples, by definition, are a statistical representation of a larger entity...

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15 western part of the Lepontine dome. In the central area some of the classical kyanite--40 staurolite--garnet schists directly underlying the metamorphosed Mesozoic sediments 41 contain monazite that records only a pre--Alpine, Variscan metamorphic event of upper 42 greenschist to lower amphibolite facies--conditions dated at 330 Ma. 43 The new age data provide evidence that nappe stacking at prograde amphibolite--44 facies conditions and refolding of the nappe stack occurred between 32 and 27 Ma, only 45 a few million years after eclogite--facies metamorphism in the Adula--Cima Lunga unit. 46 Amphibolite--facies metamorphism lasted for about 10 My to 22 Ma, allowing for 47 multiple ductile deformation and recrystallization events. The long lasting amphibolite--48 facies metamorphism requires fast cooling between 20 and 15 Ma in the Central Alps. 49 This fast cooling was not related to an increase in sedimentation rates in the foreland 50 basins, suggesting that tectonic exhumation was responsible for termination of 51 amphibolite--facies metamorphism in the Lepontine dome. 52 53 Keywords 54 Accessory minerals; Barrovian metamorphism; Central Alps; ion--microprobe; 55 metamorphic petrology; SHRIMP; U--Pb dating. 56 concentration of initial Pb incorporated into the mineral during crystallisation (e.g. 81 Romer and Siegesmund, 2003). The problem of initial Pb in allanite has been addressed 82 by Gregory et al. (2007) and Smye et al. (2014). It has been demonstrated that 83 regression in a Tera--Wasserburg diagram or the Th--isochron technique (Gregory et al., 84 2007) eliminates the need to assume the isotopic composition of initial Pb and allows 85 determination of geologically significant ages even for allanite with high amounts of 86 initial Pb (Janots and Rubatto, 2014). Additional issues with allanite are the relative 87 mobility of Th and U resulting in Th--U fractionation (Smye et al., 2014). Monazite and 88 allanite potentially incorporate excess of 206 Pb produced by the decay of 230 Th, which 89can compromise the 206 Pb/ 238 U ratios. Therefore, calculation of isotopic ages and their 90 interpretation for these minerals demand special attention to these complications. 91At amphibolite facies conditions, the stable Ti--bearing phase can be rutile, titanite 92 or ilmenite; their relative stability is controlled by pressure, temperature and bulk rock 93 composition. Rutile has the advantage that it generally does not incorporate initial Pb at 94 formation, but can contain very low U concentrations that render precise measurement 95 of radiogenic isotopic ratios difficult (Kooijman et al., 2010, Warren et al., 2012 Smye et 96 al., 2014). 97