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Our ability to reconstruct the crystallization history of a given accessory mineral (i.e., geochronometers such as zircon, titanite, monazite, etc.)—and thus the geologic processes of its host—has increased severalfold over the past few decades; primarily through advances in precision, concurrent chemical analysis, throughput, and spatial resolution. In this contribution, we present a methodology that takes these advances a step further through the rapid characterization of a large number of accessory minerals at micron-scale resolution via laser-ablation inductively coupled plasma mass spectrometry. Our analytical setup employs an ultrafast washout laser (~1 ms; Element Scientific Laser) that can send individual, <5um ablation pulses to either one or both of two instruments: a Nu Plasma 3D mulitcollector ICP-MS and a Nu Vitesse time-of-flight ICP-MS. Because either ICP-MS can measure at the sub-ms timescale, every pulse can be analyzed at 100’s of Hz; 1D, 2D, or 3D analysis is possible, and data can be processed in a matter of minutes and hours, instead of days or weeks. We highlight the advantages of this methodology through examples of accessory phases in complex plutonic rocks and high-grade metamorphic terranes. 

Abstract Salt marshes of the northern Gulf of Mexico provide many ecosystem services, including supporting some of the USA’s most productive fisheries. Early work identified links between salt marsh area and commercial shrimp landings, while more recent research highlighted the importance of marsh edge. Many species appear to be restricted to the outer few meters of the vegetated marsh even when large areas are flooded for extended periods. We hypothesized that low dissolved oxygen (DO), driven by high respiration rates, may limit more extensive use of flooded marsh. To evaluate this, we continuously logged DO 5 cm above the substrate along transects at 10, 5, and 1 m into open water adjacent to the marsh edge and at 1, 5, and 10 m into the flooded marsh, for 48+ h periods at 10 sites in Mississippi Sound, AL, during the summer of 2024. DO levels 10 and 5 m into the flooded marsh regularly dropped to stressful levels (< 4 mg/L), often becoming hypoxic (< 2 mg/L) for periods of several hours. In addition to predictable diurnal DO cycles, we identified precipitous drops in DO on the flooded marsh surface around midday at some sites, coinciding with the beginning of the ebb tide. This suggests that even during bright sunny conditions, respiration can exceed aquatic photosynthesis in the shallow flooded marsh. Our findings suggest that much of the flooded marsh may be physiologically stressful for many aquatic species. Increasing temperatures and nutrient loads in our coastal waters will further exacerbate poor DO conditions and may degrade the suitability of this essential fish habitat. 

Evidence of metamorphism at ultrahigh‐pressure (UHP) conditions is documented by the presence of coesite, diamond and/or majoritic garnet. However, the growth of UHP‐stable phases such as majoritic garnet is often volumetrically low, and overprinting during exhumation can obscure evidence of UHP growth, making it difficult to positively identify UHP rocks. In this study, we selected garnet‐kyanite schists from three microdiamond‐bearing localities within the Rhodope Metamorphic Complex, located in eastern Greece. Samples from Xanthi, Sidironero, and Kimi have similar bulk rock compositions, but the pressure–temperature (P–T) paths differ. Because the major phases record vanishingly little evidence of metamorphism at UHP conditions, we analyzed zircon grains with complex textures to evaluate if zircon preserves a record of UHP metamorphism. Zircon grains from all localities have cores and rims separated by a characteristic interface domain, as revealed by cathodoluminescence (CL) imaging. The detrital igneous cores range in age from c. 2.5 Ga to 220 Ma and exhibit a negative Eu* anomaly, a Yb/Gd of 10–100, and variable Th/U (0–1.2). Rims yield dates of 150–125 Ma with Yb/Gd of 0.1–10 and Th/U of 0–0.2. Interface domains yield dates 165–145 Ma with Yb/Gd ranging between 0–1000 and Th/U < 0.2. We interpret the distinctive CL textures and Yb/Gd of the interface domains as evidence of zircon that reacted at UHP. The interface domain in zircon from all petrographic contexts yields variable Yb/Gd ratios that are significantly higher than both cores and rims. We therefore interpret that zircon recrystallized via interface‐coupled dissolution–reprecipitation reaction; this process preferentially partitioned heavy rare earth elements within the interface domain, which explains the higher Yb/Gd ratios. The rim domains equilibrated with the matrix, producing a relatively homogeneous and low Yb/Gd ratio in these domains. The spatial extent and degree of preservation of interface domains are interpreted as a function of the P–T path and minor variations in bulk composition. Interface domains are best preserved in rocks from Xanthi and Sidironero; in these samples, thin, homogeneous, garnet‐stable rims only partially overprint and crosscut the interface domain. In contrast, rocks from Kimi followed a higher‐temperature trajectory and the zircon grains grew large rim domains that overprinted much of the interface domain and the detrital core. Zircon grains from plagioclase‐rich versus quartz‐rich domains within samples from Sidironero show differences in texture, which indicates that local bulk composition can affect what evidence of UHP metamorphism is preserved. Collectively, these samples provide a new, durable marker of metamorphism in UHP rocks and yield new insight about which factors affect the preservation of UHP textures.