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We present a comprehensive petrological and geochronological study of a single granulite sample from the lithosphere-scale Beraketa shear zone in southern Madagascar to constrain the orogenic history of Gondwana assembly in this region. The studied sample provides a panoply of data constraining the prograde, retrograde, and late metasomatic history of the region via the application of Ti-in-quartz, Ti-in-zircon, Zr-in-rutile, and Al-in-orthopyroxene thermobarometry; phase-equilibrium modeling; U–Pb monazite, zircon, and rutile petrochronology; and trace element diffusion chronometry in rutile methods. Our results reveal five stages of metamorphism along a clockwise P-T path that may have begun as early as 620–600 Ma and certainly by 580–560 Ma, based on the oldest concordant zircon dates. The rock heated to >725 °C at less than 7.5 kbar (stage 1) before burial to ~8 kbar (stage 2). By c. 540 Ma, the rock had heated to ~970 °C at ~9 kbar, and lost approximately 12% melt (stage 3), before decompressing and cooling to the solidus at ~860 °C and 6.5 kbar within 10 Myr (stage 4). The vast majority of monazite and zircon dates record stage 4 cooling and exhumation. Monazite and zircon rim dates as young as c. 510 Ma record subsolidus cooling (stage 5) and associated symplectite formation around garnet. U–Pb rutile dates record partial resetting at c. 460 Ma; Zr- and Nb-in-rutile diffusion chronometry link these dates to a metasomatic event that lasted

Wildfires can change ecosystems by altering solutes in streams. We examined major cations in streams draining a chaparral-dominated watershed in the Santa Ynez Mountains (California, USA) following a wildfire that burned 75 km2 from July 8 to October 5, 2017. We identified changes in solute concentrations, and postulated a relation between these changes and ash leached by rainwater following the wildfire. Collectively, K+ leached from ash samples exceeded that of all other major cations combined. After the wildfire, the concentrations of all major cations increased in stream water sampled near the fire perimeter following the first storm of the season: K+ increased 12-fold, Na+ and Ca2+ increased 1.4-fold, and Mg2+ increased 1.6-fold. Our results suggested that the 12-fold increase in K+ in stream water resulted from K+ leached from ash in the fire scar. Both C and N were measured in the ash samples. The low N content of the ash indicated either high volatilization of N relative to C occurred, or burned material contained less N.

Magnesium carbonates have been identified within the landing site of the Perseverance rover mission. This study reviews terrestrial analog environments and textural, mineral assemblage, isotopic, and elemental analyses that have been applied to establish formation conditions of magnesium carbonates. Magnesium carbonates form in five distinct settings: ultramafic rock-hosted veins, the matrix of carbonated peridotite, nodules in soil, alkaline lake, and playa deposits, and as diagenetic replacements within lime—and dolostones. Dominant textures include fine-grained or microcrystalline veins, nodules, and crusts. Microbial influences on formation are recorded in thrombolites, stromatolites, crinkly, and pustular laminites, spheroids, and filamentous microstructures. Mineral assemblages, fluid inclusions, and carbon, oxygen, magnesium, and clumped isotopes of carbon and oxygen have been used to determine the sources of carbon, magnesium, and fluid for magnesium carbonates as well as their temperatures of formation. Isotopic signatures in ultramafic rock-hosted magnesium carbonates reveal that they form by either low-temperature meteoric water infiltration and alteration, hydrothermal alteration, or metamorphic processes. Isotopic compositions of lacustrine magnesium carbonate record precipitation from lake water, evaporation processes, and ambient formation temperatures. Assessment of these features with similar analytical techniques applied to returned Martian samples can establish whether carbonates on ancient Mars were formed at high or low temperature conditions in the surface or subsurface through abiotic or biotic processes. The timing of carbonate formation processes could be constrained by 147Sm-143Nd isochron, U-Pb concordia, 207Pb-206Pb isochron radiometric dating as well as 3He, 21Ne, 22Ne, or 36Ar surface exposure dating of returned Martian magnesium carbonate samples., Plain Language Summary Magnesium carbonate minerals rarely form large deposits on Earth and because they constitute such a small proportion of the terrestrial carbonate record in comparison to calcium-rich carbonates, they have received little attention. In contrast, the largest carbonate deposit detected on Mars has magnesium carbonate, and it has been detected at the landing site of the 2020 mission where the Perseverance rover will collect samples for return to Earth. We synthesized the field observations and laboratory experiments that pertain to magnesium carbonates formed on Earth and find that they form in five types of environments as follows: within veins or in the bulk volume of magnesium-rich rocks, soils, alkaline or salty lakes, and as replacements of previously formed calcium-rich carbonate minerals. Conceptually, these environments may be analogs for ancient Martian magnesium carbonate-forming environments. Magnesium carbonates formed in some environments are capable of preserving remnants of microbes, especially if magnesium carbonates formed characteristic large-scale clotted or vertical column shapes or microscale spherical and laminated textures. If life had ever originated on Mars, these would be key materials to investigate for biosignatures. Finally, a number of analytical techniques are discussed that can be performed on magnesium carbonate rocks collected by Perseverance when returned to Earth.

The intensive deformation along with the rheological behavior of the tectonic units in Taili, eastern North China Craton (NCC), are recognized as the manifestation of the presence of the NE–SW striking ductile shear zone in the region. The presence of two types of granitic veins (aplitic and pegmatitic) in Taili exhibit obvious strain refraction and boudinage structures. Ten samples from different rock types are collected to analyze their deformation characteristics and the rheological properties. The analysis is performed by measuring the rock competency following the methods of mainly two types of rheology gauges: (1) Pinch-and-swell structures, and (2) refraction of the veins. We conclude that two main factors control the deformation patterns in Taili, i.e., grain size and proportion of the mineral component. Grain size is found to be one of the dominant factors, controlling the deformation pattern, i.e., the larger the grain size the higher the rock viscosity is. The proportion of the mineral content is another important parameter which is critical to infer the rheological contrast along with the deformational style of the studied region. The rock viscosity of the samples is inversely proportional to the mica and feldspar content of the same. Micro-structural observation suggests that these rocks experienced strong extensional deformation at a low to middle-temperature condition (around 450–550 °C) during the Mesozoic. This event transformed the granitic veins into boudins associated with intensive strain-refraction which are also responsible for the formation of voluminous felsic rocks with high viscosity contrast in this region.