Magnesite (MgCO3) is a magnesium carbonate mineral that records the aqueous environmental conditions of its formation. On Earth, magnesite forms in metamorphic, diagenetic or pedogenic environments, and distinguishing between these environments is critical for understanding the nature of fluid chemistry during magnesite precipitation. Magnesite has been identified across the Nili Fossae region on Mars and in Jezero crater by orbital spectroscopic observations and in-situ instrument observations acquired with the Perseverance rover. Core samples with magnesite may provide constraints on the chemical conditions of the ancient aqueous environments of Jezero crater, and may also be an important phase to target for the preservation of potential biosignatures. This work explores pedogenic magnesite phases found in Vertisols of the Kunwarara Mine, Australia, as a potential analog environment for magnesite identified within Jezero crater, Mars. We document the principal microtextures and investigate the processes involved in the formation and diagenesis of magnesite nodules and magnecretes. Kunwarara magnesite nodules show complex textural relationships at the outcrop scale, and these relationships extend to the nanoscale in samples that were collected along a depth profile. By characterizing textural and chemical variations in magnesite at different scales, this work reveals a continuum between diagenetic and pedogenic magnesites. It illustrates that diagenetic reactions produce magnesite from ascending Mg²⁺-rich groundwater interacting with detrital phases; groundwater interaction with descending meteoric solutions result in the conversion of magnesite into authigenic dolomite. Overall, this work shows how the superposition of textures and elemental compositions permits reconstruction of pedogenic processes leading to magnesite authigenesis.

This work integrates spatiotemporal datasets in California over a twenty-year period (2003–2023) to identify links between anomalies in fecal indicator bacteria (FIB) — Escherichia coli , total coliforms, fecal coliforms, and Enterococcus — in coastal areas and the occurrence of recent wildfires. Average FIB concentrations, land cover, precipitation, and burn histories are quantified for every month across all watersheds flowing into the California Coast. Monthly non-burn background FIB concentrations are calibrated in coastal areas and define local baselines. FIB anomalies are identified relative to local baselines for both burn periods (>10% of the watershed burned within a two-year window) and non-burn periods and are reported as the anomalous FIB concentrations normalized by the local baseline concentrations. Correlations between FIB anomalies and monthly precipitation and land cover fractions are identified by comparing data from all watersheds impacted by large fires. During burn periods, anomalous total coliform concentrations relative to baseline values (anomalies) exhibit a negative correlation with urban and positive correlations with coastal oak woodland, mixed chaparral, and redwood land cover fraction and monthly precipitation. Burn-period fecal coliform anomalies exhibited a positive correlation with urban land cover fraction. Positive correlations between burn-period total coliform anomalies and monthly precipitation and coastal oak woodland land cover, negative correlations between burn-period total coliform anomalies and urban land cover, positive correlations between burn-period Escherichia coli anomalies and mixed chaparral land cover, and negative correlations between burn-period Escherichia coli anomalies and redwood land cover survive the Benjamini–Hochberg false discovery rate correction. Results indicate prominent post-fire export of total coliform bacteria (perhaps from decaying plant material and soils) in watersheds with less urbanization, and prominent export of fecal coliform bacteria from humans and animals in urbanized watersheds to coastal waters. This is the first effort to generalize post-fire FIB responses in coastal waters. Results may inform future risk assessments.

Magnesium carbonates in surficial environments act as CO2 sinks and can record aspects of the palaeohydrological cycles on Earth and Mars. In natural environments, magnesium carbonates can be intimately intermixed at the micrometer scale with complex assemblages of other non-carbonate minerals. To better determine magnesium carbonate composition in complex samples and minimize contamination from secondary Fe/Mn-oxides/hydroxides, we developed and assessed methods for sample cleaning, selective digestion, and quadrupole inductively coupled plasma mass spectrometry to measure the trace and minor elemental composition. By pre-cleaning and selectively digesting carbonate, we identified previously unrecognized geochemical trends in magnesite +/- dolomite nodules and their host fluvial sediments collected along a depth profile at the Kunwarara magnesite mine, Queensland, Australia. In particular, Ce anomalies in magnesite diminishes with depth coincident with decreasing abundances of authigenic Fe/Mn-oxides/hydroxide minerals in the host sediments. These results reveal how the magnesium carbonates capture interactions between the ascending groundwaters and descending surface waters. We further demonstrate the value of magnesium carbonate-specific trace element data with reanalysis of previously published ion microprobe data from Martian meteorite ALH84001, which also shows Ce fractionation. Accurate mineral-specific trace and minor element measurements in Earth and Martian magnesium carbonate samples improve our understanding of the timing and identities of carbonate mineral-forming reactions that occurred on both planets.

Ancient orogens eroded to midcrustal levels provide insight into strain accommodation, metamorphism and melting in Himalaya-type continent-continent collisions. This study focuses on the Neoproterozoic-Cambrian Eastern Africa-Kuunga orogen exposed in Madagascar, where uncertainty about the terrane correlations, and therefore structural framework, of the orogen persists. We present a comprehensive dataset of monazite petrochronology and thermobarometry across the southern Madagascar basement to quantify the regional and temporal variability of metamorphism. We argue that the ultrahigh-temperature Anosyen domain and associated Androyen domain have a shared geological history, recording two successive tectonic events at 630-600 and 580-500 Ma. Other Madagascar domains record primarily the former (Vohibory domain to the west) or latter (all other domains to the NE) event. From this inference, we discuss terrane correlations with Africa and India, then present a structural framework for the orogen in which the Anosyen-Androyen domain was structurally confined in a central, lithosphere-scale transpressional shear system between divergent, diachronous thrust belts. By limiting exhumation, extrusion and collapse, the structural trapping of the Androyen-Anosyen domain facilitated longer-lasting, higher-T metamorphism than associated rocks in the adjacent nappe systems. Such structural trapping may be an important control on high-T metamorphism in the cores of Himalaya-type orogens in general.

Magnesium carbonates record information on water-rock interactions during and after mineral precipitation. The Marlborough Terrane in central Queensland, Australia, contains magnesite-bearing serpentinite highlands surrounded by low-lying sedimentary basins that host authigenic magnesite (MgCO3). Open pit mines in both settings provide exposures of serpentinites (Gumigil) and Cenozoic sediments and overlying black soils (Yaamba) that host the magnesite and other authigenic phases. The Gumigil mine contains deeply weathered serpentinite hosting metamorphic magnesite veins that formed syn-tectonically; both serpentinite and magnesite are now partially dissolving, silicifying, and ferruginizing. Aqueous Mg2+ is being exported into the basins surrounding the serpentinite ridges. The Yaamba magnesite mine in the surrounding plains exposes diagenetic magnesite formation within unlithified alluvial sediments, where ascending magnesium-rich groundwaters replace arkosic sands and silts by magnesite cements, nodules, and pinnacles. Late-stage pedogenic processes at Gumigil and Yaamba drive retrograde transformation of magnesite into geochemically distinct exterior regions of secondgeneration cryptocrystalline magnesite recording interactions with Fe/Mn-oxides/hydroxides via cerium anomalies, yttrium anomalies and manganese concentrations in zoned magnesites from Yaamba. The complex history of mineral precipitation, dissolution, diagenetic replacement, and supergene alteration is recorded in the major, minor and trace element compositions of magnesites at each site. Serpentinite ridges and magnesitebearing valley floors in Central Queensland provide a useful analog to the processes that might occur in the ultramafic highlands and carbonated lowlands at Jezero crater, Mars.

We measured He and Ar in fresh peridotites from the Twin Sisters massif, Washington USA. 3He/4He ratios measured on >35 samples are highly variable (-0.8 to-6 times the atmospheric ratio, RA). Step-heating of a subset of these samples in every case reveals a low 3He/4He component (-1 RA) released at <1000 degrees C and a high 3He/4He component (>3 RA) above that temperature, but these components are not effectively isolated by crushing and powder fusion analysis. He-Ar systematics indicate an intimate association of two fluid-inclusion hosted components in the peridotites. The first is a-6 RA mantle component that is released at higher tem-peratures during step heating and is more abundant in dunite bands than surrounding harzburgites. The second component, released at low temperatures, has a 3He/4He ratio of 1.0 +/- 0.5 RA, atmospheric 40Ar/36Ar, and 4He/40Ar far above atmospheric. It appears to be a mixture of mantle and radiogenic He sources introduced during obduction-related serpentinization, sometimes invisible, by surface-derived waters enriched with deeply-sourced helium.These data indicate that mantle noble gas signatures can be retained in lithospheric peridotites against both diffusive loss and radiogenic ingrowth over at least 108 year timescales, likely due to concentration and immobilization of He in fluid inclusions. However, the mantle signature can be greatly modified by pervasive and potentially cryptic fluid alteration during emplacement.

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 modelling; U-Pb monazite, zircon, and rutile petrochronology; and trace element diffusion chronometry in rutile. Our results reveal five stages of metamorphism along a narrow 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 was heated to >725 degrees C at less than 7.5 kbar (Stage 1) before burial to similar to 8 kbar (Stage 2). By c. 540Ma, the rock had heated to similar to 970 degrees C at similar to 9 kbar, and lost approximately 12% melt (Stage 3), before decompressing and cooling to the solidus at similar to 860 degrees C and 6.5 kbar within 10 Ma (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 <1 Ma at similar to 600 degrees C. In addition to chronicling a near-complete cycle of metamorphism in southern Madagascar, this study constrains the rates of heating and cooling. We estimate that heating (7-14 degrees C/Ma) outpaced reasonable radiogenic heating rates with modest mantle heat conduction. Therefore, we conclude that elevated mantle heat conduction or injection of mantlederived magmas likely contributed to regional ultrahigh-temperature metamorphism (UHTM). Exhumation and cooling from peak metamorphic conditions to the solidus occurred at rates greater than 0.45 km/Ma and 14 degrees C/Ma.

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 147 Sm‐ 143 Nd isochron, U‐Pb concordia, 207 Pb‐ 206 Pb isochron radiometric dating as well as 3 He, 21 Ne, 22 Ne, or 36 Ar surface exposure dating of returned Martian magnesium carbonate samples.

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.

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, Le., grain size and proportion of the mineral component. Grain size is found to be one of the dominant factors, controlling the deformation pattern, Le., 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 degrees 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.