USGS Science⌕ Search

SEARCH · USGS Science

Results for “Earth and Planetary Science Letters”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources
USGS2023

Constraints on near-ridge magmatism using 40Ar/39Ar geochronology of enriched MORB from the 8°20' N seamount chain

Our understanding of the spatial-temporal-compositional relationships between off-axis magmatism and mid-ocean ridge spreading centers is limited. Determining the 40 Ar/ 39 Ar ages of mid-ocean ridge basalt (MORB) lavas erupting near mid-ocean ridges (MOR) has been a challenge due to the characteristically low K 2 O contents in incompatible element-depleted normal MORB (NMORB). High-precision 40 Ar/ 39 Ar geochronology is used here to determine ages of young, basaltic lavas erupted along the 8°20' N seamount chain west of the East Pacific Rise (EPR) axis that have a range of incompatible element enrichments (EMORB) suitable for 40 Ar/ 39 Ar geochronology (e.g., K 2 O contents > 0.3 wt%). 40 Ar/ 39 Ar ages were determined in 29 well-characterized basalts sampled using HOV Alvin and dredging. Detailed geochronology and geochemical analyses provide important constraints on the timing, distribution, and origins of lavas that constructed this extensive volcanic lineament relative to magmatism beneath the adjacent EPR axis. Seamount eruption ages are up to ∼1.6 Ma younger than the underlying lithosphere, supporting a model of prolonged off-axis magmatism for at least 2 Myrs at distances as great as ∼90 km from the ridge axis. Increasing geochemical heterogeneity with eruption distance reflects the diminishing effect of sub-ridge melt focusing. The range of geochemically distinct lavas erupted at given distances from the ridge highlights the dynamic nature of the near-ridge magmatic environment over Myr timescales. Linear ridge-like (EPR-parallel) morphotectonic features erupt the youngest and most incompatible element-enriched lavas of the entire seamount chain, indicating there is a recent change in the influence of mantle heterogeneity and off-axis melt metasomatism on the near-ridge lithospheric mantle. Changes in seamount morphologies are attributed to counter-clockwise rotation and southward migration of the nearby Siqueiros transform over the last few million years.

Earth and Planetary Science Letters↗
USGS2023

Ring fault creep drives volcano-tectonic seismicity during caldera collapse of Kīlauea in 2018

Basaltic caldera collapses are episodic, producing very-long-period (VLP) earthquakes up to M w 5.4, with prolific inter-collapse (between collapses) volcano-tectonic (VT) seismicity. During the 2018 caldera collapse of Kīlauea Volcano, VT seismicity ceased following each collapse, and then accelerated to a quasi-steady rate prior to the next collapse, marking a temporal pattern distinct from typical foreshock/aftershock sequences. There is currently no consensus on the mechanism(s) that generates the VT seismicity. Here we demonstrate that inter-collapse ring fault creep, induced by chamber depressurization, was the main driver of VT seismicity at Kīlauea in 2018. This is evidenced by: 1) the correlation between cumulative number of VT events and GNSS-derived ring fault creep; 2) agreement between repeating earthquake and GNSS derived creep rates; and 3) consistency between the time dependence of mechanically modeled, creep-driven seismicity and observations. We further show that, ring fault creep can be explained by velocity strengthening friction alone or in conjunction with viscous shear zone rheology. The simultaneous occurrence of creep and seismicity highlights the spatially heterogeneous velocity weakening/strengthening friction on the ring fault. If the VT seismicity-creep correlation can be replicated at other basaltic volcanoes, it would demonstrate that VT seismicity can be used as a proxy for ring fault creep in the absence of GNSS measurements on subsiding caldera block(s).

Hawaii↗
USGS2023

The presence of silicate melt may enhance rates of cation diffusion in olivine

Olivine is commonly used as a ‘crystal clock’ to extract timescales relevant to pre-eruptive perturbations within mafic magmatic systems. Diffusion chronometry applications require accurate calibrations for the rates at which Fe-Mg or other commonly measured elements like Ni, Mn, and Ca diffuse through the crystal lattice. In the past, these rates have been mainly characterized using solid-solid diffusion couple experiments involving olivine single crystals, thin films, or powder sources. Despite the presence of melt surrounding olivine in natural magmatic systems, very few experiments involving magma have been performed, largely because controlling interface reactions is difficult. For this study, we carried out olivine-melt diffusion experiments as a test of the diffusion chronometry method, and to determine whether the presence of melt influences the calculated timescales. To approximate a natural system, we incorporated small natural Kīlauea and San Carlos olivine seeds within a natural Kīlauea basalt and tracked diffusive re-equilibration through time. To better control interface reactions, after some equilibration period at an initial superliquidus temperature of 1290 °C, the runs were rapidly cooled to form a rim and left to dwell at various final temperatures (1200, 1220, 1240, 1255 °C) for 6–84 h. Concentration gradients for Fe-Mg, Mn, Ni, Ca were measured, and the step-wise nature of the core-rim transition was ascertained using slow diffusing elements like P or Al. When these gradients are modeled using published diffusivities, the timescales retrieved are typically 10 times longer than the actual experiment durations. Thus, measured diffusivities are an order of magnitude faster than those previously obtained in olivine-solid source experiments, but they are in excellent agreement with the only two other melt-olivine datasets. We explore reasons for why melt-bearing olivine diffusion experiments tend to yield faster rates. The possible effects of (1) growth during diffusion, (2) diffusion during any initial dissolution step, and (3) extended tube or planar defects at the interface on calculated diffusivities are all considered but found to be inconsequential. Instead, we argue that additional point defects (vacancies) are likely created at the interface by higher concentrations in elements like Al or H in the basalt melt compared to other solid couple diffusant sources. Future applications of diffusion chronometry in olivine may require a complete re-evaluation of published diffusivities using melt-bearing experimental configurations.

Earth and Planetary Science Letters↗
USGS2023

Geochemical evidence for evolving Proterozoic crustal thickness and orogenic styles in southwestern Laurentia

It has long been challenging for researchers to track the crustal thickness and mode(s) of crustal modification in ancient convergent margins, limiting evaluation of the tectonic styles and processes that modify continental crust during orogenesis. We present trace element igneous geochemical crustal thickness proxies that quantitatively track the crustal thickness evolution of the long-lived Proterozoic active margin in the southwestern U.S.A. We integrate these results with geobarometric data to constrain the mode of crustal modification. The data indicate a complex record of crustal thickness change in space and time and evolving orogenic styles. Geochemical proxies at 1.84–1.72 Ga are consistent with 20–40 km thick magmatic arcs that were locally thickened to ∼50 km during ∼1.75 Ga tectonism. During the Yavapai orogeny, 1.72–1.69 Ga, a ∼200-km-wide belt of 50-60 km thick crust extended from southern California to northern Colorado and was rapidly thinned and exhumed by ∼1.68 Ga. Crustal thickening and thinning during the Yavapai orogeny largely occurred by shortening and exhumation, respectively, in the upper 25 km of the crust. Subsequent 1.68–1.60 Ga tectonism involved crustal growth, local crustal thickening, and low-P, high-T metamorphism, consistent with extensional accretionary orogenesis. The 1.47–1.37 Ga Picuris orogeny was associated with 50–60 km thick crust across much of the Southwest and involved crustal shortening with ∼10 km of magmatic underplating. Advective heat from the emplacement of ferroan granites in the mid-crust likely contributed to elevated geothermal gradients and rheologically weakened the crust. Our results suggest evolving orogenic styles in the Southwest from 1.75–1.69 Ga short-lived crustal thickening associated with terrane accretion to 1.69–1.60 Ga largely extensional accretionary orogenesis, and regional, long-lived crustal thickening at 1.47–1.37 Ga involving extensive basaltic underplating. Contrasting with some recent hypotheses, our data document a complex middle Proterozoic record for the Southwest that was not orogenically quiescent or tectonically stagnant but involved complex mountain building styles.

Earth and Planetary Science Letters↗
USGS2024

Insights into magma storage depths and eruption controls at Kīlauea Volcano during explosive and effusive periods of the past 500 years based on melt and fluid inclusions

Kīlauea Volcano experiences centuries-long cycles of explosive and effusive eruptive behavior, but the relation, if any, between these eruptive styles and changing conditions in the magma plumbing system remains poorly known. We analyze olivine-hosted melt and fluid inclusions to determine magma storage depths during the explosive-era Keanakākoʻi Tephra eruptions (∼1500–1840 CE) and compare these results to modern effusive-era Kīlauea eruptions (1959 Kīlauea Iki, 1960 Kapoho, 2018 lower East Rift Zone). We find that shallow (1–3 km) magma storage has persisted for centuries at Kīlauea, spanning both explosive and effusive periods. In contrast, mid-crustal zones of magma storage shallowed over time, from 5 to 8 km during the Keanakākoʻi sequence to 3–5 km during the modern effusive period. Melt and fluid inclusions in high-forsterite olivine (Fo 86–89 ) trapped at shallow depths indicate that high-temperature magmas (1200 to ∼1300 °C) commonly reach depths of ≤3 km. CO 2 -rich fluid inclusions are present in olivine from all investigated Kīlauea eruptions but are larger and much more abundant in Keanakākoʻi units, which we interpret as indicating that a greater volume fraction of exsolved CO 2 -rich fluid was present in pre-eruptive Keanakākoʻi melts. Increased amounts of CO 2 -rich fluids in the Keanakākoʻi-era magmas would have increased magma buoyancy and driven rapid magma ascent, thereby increasing eruption energy and enhancing near-surface magma-water interactions compared to the current effusive period.

Hawaii↗
USGS2024

The evolution of a young ocean within Mimas

The fractured, young surfaces on confirmed ocean worlds such as Europa and Enceladus suggest that ocean-bearing moons with relatively thin overlying ice shells should be easy to identify. Hence, the discovery that Mimas’ rotation state is best explained by an internal ocean seems challenging to reconcile with its heavily cratered surface. Previous studies have shown that an internal ocean is compatible with Mimas’ geology as long as the ice shell has been thinning throughout the surface age. This scenario has yet to be placed into context within Mimas’ thermal-orbital history, in particular, the link between tidal dissipation and orbit circularization. Here, we model Mimas’ coupled thermal-orbital evolution, and the implications of an emerging ocean on Mimas’ geology, to determine whether a thinning ice shell is feasible. We find that the ice shell can thin – and the ocean grow – even as the eccentricity decays due to tidal dissipation as long as the ocean formed within the past 10 – 15 million years and the onset of melting occurred when Mimas’ eccentricity was between 2.5 and 3 times the present-day value. As Mimas’ eccentricity continues to decay, the ocean will likely enter an epoch of freezing, leading to fractures within the ice shell and eruptions of ocean material at the surface, before freezing completely. These results suggest that Mimas, Enceladus, and Tethys may represent three points along a continuum of ocean initiation, growth, and loss.

Earth and Planetary Science Letters↗
USGS2024

A great tsunami earthquake component of the 1957 Aleutian Islands earthquake

The great 1957 Aleutian Islands earthquake ruptured ∼1200 km of the plate boundary along the Aleutian subduction zone and produced a destructive tsunami across Hawaiʻi. Early seismic and tsunami analyses indicated that large megathrust fault slip was concentrated in the western Aleutian Islands, but tsunami waves generated by slip in the west cannot explain the large observed runup in Hawaiʻi far to the southeast. Recently mapped 1957 geologic deposits on eastern Aleutian Islands suggest occurrence of very large nearby slip. Jointly modeling tsunami runup along the eastern Aleutian and Hawaiian Islands together with tide gauge recordings across the Pacific resolves 12-26 m shallow slip along 600 km of the eastern Aleutian Islands in addition to modest, deeper western slip inferred from seismic records. The eastern near-trench slip results in an M W 8.3-8.6 tsunami earthquake component of the M W 8.6-8.8 rupture, comparable in size to the adjacent 1946 Aleutian tsunami earthquake to the east. The reexamination of the 1957 rupture confirms the tsunami hazards posed by the eastern Aleutian subduction zone to Hawaiʻi and lays the groundwork for investigation of large prehistoric earthquakes through modeling tsunami runup inferred from stratigraphic observations to constrain their rupture processes.

Alaska↗
USGS2024

A Bayesian age from dispersed plagioclase and zircon dates in the Los Chocoyos ash, Central America

The eruption that produced the modern Atitlán caldera in Guatemala has a Volcanic Explosivity Index (VEI) greater than 8, making it the largest of the Quaternary in the Central American Volcanic Arc (CAVA). It generated ∼1220 km 3 (730 km 3 dense rock equivalent) of dispersed rhyolitic ash and unwelded pyroclastic flow deposits known as the Los Chocoyos ash. Despite its scale, the age of the Los Chocoyos ash has been difficult to constrain. Its inferred position in marine sediment off the coast of Ecuador suggests an oxygen isotope-based age of 84 ± 5 thousand years (ka) that has been used for decades. A recent effort to determine the eruption age of the Los Chocoyos ash used U-Th/He and U/Th disequilibrium methods that both yield overdispersed sets of dates from zircon. Using U/Th disequilibrium corrected U-Th/He dates, which include some that are up to 19 ± 8 kyr younger than the youngest U/Th disequilibrium dates, an eruption age of 75 ± 4 ka has been proposed, which overlaps the eruption age of the Youngest Toba Tuff, 40 Ar/ 39 Ar dated at 73.9 ± 0.6 ka. Critically, the above findings have led to the hypothesis that this pair of sulfate-rich supereruptions may be responsible for a global cooling event ∼74 ka. To further test this supereruption doublet hypothesis we present new 40 Ar/ 39 Ar and U-Th disequilibrium data from plagioclase and zircon rim surfaces, respectively, to quantify the timing of the Los Chocoyos eruption. We apply Bayesian estimation to the overdispersed sets of 40 Ar/ 39 Ar plagioclase and U-Th disequilibrium zircon dates. This approach accounts for retention of radiogenic 40 Ar in plagioclase in a subset of crystals and for crystallization of zircon that may precede the time of eruption and yields remarkably consistent ages from two independent chronometers. The Bayesian estimate of 98 ± 6 ka calculated from 308 individual dates identifies the population nearest to the time of the Los Chocoyos eruption. Interpreted as an eruption age, this finding precludes a link between the Los Chocoyos eruption and global cooling ∼74 ka and rules out the supereruption doublet trigger.

Earth and Planetary Science Letters↗
USGS2024

An integrated perspective of paleoenvironmental change in the Western Interior Seaway before and during OAE-2 reveals how organic-rich mudstones form in dynamic environments

Organic and inorganic geochemistry was integrated with sedimentology from the Eagle Ford Group in the U.S. Geological Survey Gulf Coast-3 drill core to investigate why organic matter enrichment and anoxia predate the Cenomanian–Turonian oceanic anoxic event (OAE-2) at the southern Western Interior Seaway (WIS). The relationship between the degree of organic matter sulfurization and preservation in the southern WIS is comparable to OAE-2 sites outside of the WIS, but enhanced organic matter sulfurization and preservation predated OAE-2, distinguishing the southern WIS from other OAE-2 localities. Persistent euxinia and organic matter sulfurization before and during the mid-Cenomanian event (MCE) facilitated maximum organic matter enrichment and preservation to coincide with extensive lateral sediment transport. The new perspective detailed here reconciles geochemical evidence of depositional euxinia with sedimentological evidence of sediment transport, which informs how organic-rich mudstones form in dynamic environments. After the MCE but before OAE-2, reducing conditions weakened as relative sea-level continued to rise, resulting in an oxygen-depleted environment that was prone to transient euxinia. The extent of organic matter sulfurization, preservation, and enrichment declined as euxinia became intermittent. As maximum sea-level was established during OAE-2, boreal water masses flowed into the southern WIS and unrestricted, oxygenated marine conditions developed, which resulted in degradation of marine organic matter and less organic enrichment. The highest relative contribution of marine bacterial organic matter occurred during the persistently euxinic interval before and during the MCE. The relative input of algal organic matter increased as the depositional conditions became less reducing after the MCE but before OAE-2. Prasinophyte green algae contributed to the consistent dominance of C 28 steranes preceding OAE-2, which is becoming a widely observed feature across the southern and central WIS. A sharp drop in the C 28 sterane relative abundance reflects a decline in the abundance of prasinophytes as oxic depositional conditions developed during OAE-2. Relative abundances of 2-methylhopanes increased during OAE-2, which is a common signature of OAEs, suggesting a modified nitrogen cycle in the offshore southern WIS despite oxic depositional conditions during OAE-2.

Arkansas, Louisiana, Oklahoma, Texas↗
USGS2024

Global variability of the composition and temperature at the 410-km discontinuity from receiver function analysis of dense arrays

Seismic boundaries caused by phase transitions between olivine polymorphs in Earth's mantle provide thermal and compositional markers that inform mantle dynamics. Seismic studies of the mantle transition zone often use either global averaging with sparse arrays or regional sampling from a single dense array. The intermediate approach of this study utilizes many densely spaced seismic arrays distributed around the globe. We systematically compute teleseismic P-to-S receiver functions for each seismic array and invert for the 1-D seismic velocity structure of the mantle transition zone beneath each array to facilitate a comparison between densely sampled regions. We stack 3,600 receiver functions on average at 67 arrays in total. The stack is used in a probabilistic inversion to estimate the mantle transition zone interface depths and velocities beneath each array. We focus on the 410-km discontinuity (410) because it is a prominent seismic interface that is clearly linked to a single mineral phase transition between olivine and wadsleyite. The depths and velocity contrasts of the 410 are mapped to temperatures and compositions using mineral physics constraints. The depth of the 410 ranges from ∼405–440 km, which is consistent with a ∼360 K temperature range in a dry mantle and a ∼260 K temperature range in a wet mantle (2 wt. % water). The Vs contrast across the 410 ranges from ∼2.5–8 %, which is consistent with ∼20–70 vol. % olivine composition in a dry mantle and ∼25–80 vol. % in a wet mantle. The bulk composition of the upper mantle near the 410-km discontinuity is typically considered to be well-mixed because there is no thermodynamic impediment to convection at the olivine to wadsleyite phase transition. However, the wide range of inferred olivine content from our study suggests that there are large lateral variations in the bulk composition of the upper mantle near the 410-km discontinuity.

Earth and Planetary Science Letters↗
USGS2024

Arctic Alaska deepwater organic carbon burial and environmental changes during the late Albian–early Campanian (103–82 Ma)

The middle Cretaceous greenhouse period experienced profound environmental change including episodes of enhanced global burial of organic carbon marked by carbon isotopic excursions (CIEs). However, the role and response of polar regions like the newly formed, partially enclosed Arctic Ocean Basin during middle Cretaceous carbon burial remains enigmatic. We present the first Arctic deepwater CIE record that characterizes conditions offshore of the Alaska margin north of 75°N paleolatitude. Organic carbon isotopes (δ 13 C org ) and 103–82 Ma ash zircon U-Pb dates from the distal Hue Shale record multiple Albian–Campanian CIEs during slow ∼3–15 m/Myr sediment accumulation rates. Average total organic carbon (TOC) increased substantially during large 2–3 ‰ CIEs of the ∼101 Ma Albian-Cenomanian boundary event (from 7 to 18 % TOC) and ∼94 Ma Cenomanian-Turonian boundary event (5 to 10 % TOC). Turonian TOC remained elevated (8–13 %) during high global sea levels and temperatures of the Cretaceous Thermal Maximum, followed by an increase from 7 to 11 % TOC during the ∼90 Ma late Turonian event 1.5 ‰ CIE. Average TOC subsequently decreased in the Coniacian–Campanian, but relative maxima occurred during subtle 0.5–1 ‰ CIEs interpreted as the ∼87 Ma late Coniacian event (increase from 4 to 7 % TOC), ∼85 Ma Horseshoe Bay event (3.5 to 4.5 % TOC), and ∼84 Ma Santonian-Campanian boundary event (3.5 to 5 % TOC). Increases in hydrogen index and productivity proxies (P, Ba, Nd) that accompanied each CIE episode with enhanced TOC suggest a strong link between marine productivity and organic carbon burial at short-term CIE timescales. However, long-term (>5–8 Myr) changes in trace metal redox (Mo, Fe, V) and salinity (B/Ga) proxies suggest shifts in prevailing environmental conditions at timescales longer than the CIEs. Late Albian–middle Turonian marine salinity occurred during euxinic (103–98 Ma) and suboxic (98–90 Ma) conditions with deposition interpreted to have occurred within and beneath an oxygen minimum zone, respectively. In contrast, late Turonian–early Campanian (90–82 Ma) freshening and restricted euxinic basin conditions may signal the start of widespread restriction known to characterize the Paleogene Arctic. Overall, these results highlight that middle Cretaceous Arctic deepwater remained a productive marine carbon sink coupled to the global carbon cycle despite evolving Arctic greenhouse conditions.

Alaska↗
USGS2024

Revised timing of rapid exhumation in the West Qinling: Implications for geodynamics of Oligocene-Miocene Tibetan plateau outward expansion

Two contrasting age models for initial mountain building in the northeastern (NE) Tibetan Plateau (Paleocene-early Eocene versus late Oligocene-early Miocene) have led to the debate on how the deformed continental lithosphere absorbs plate convergence in general. The initial compressional deformation in the West Qinling (WQL) of the NE Tibetan Plateau figures prominently in this ongoing debate. Here, apatite (U-Th)/He (AHe) thermochronology combined with geomorphological analysis are used to refine the onset of compressional deformation in the WQL. New AHe ages from two vertical transects and an updated reconstruction of an obliquely-tilted erosion surface document the accelerated exhumation in the northern WQL at 23-22 Ma, interpreted as the onset of north-vergent thrusting. The AHe results, together with sedimentary records in the intermontane and foreland basins, suggest that the entire WQL began experiencing compressional deformation in the late Oligocene-early Miocene. When integrated with previous studies, our findings show that the northern plateau boundary has not remained stationary since the collision, but has instead experienced ∼750 km of outward expansion during the late Oligocene to middle Miocene. This phase of rapid plateau growth is coeval with the ∼30–50 % reduction of the India-Eurasia convergence rate, which suggests that the increased gravitational potential energy of orogenic belts played a key role in plate motion changes.

Tibetan plateau↗
USGS2024

Anomalously high relief on Denali, Alaska, caused by tectonic, lithologic, and climatic drivers

We assess the growth of anomalously high relief on Denali, located in the Alaska Range, Alaska, and the tallest mountain in North America (6190 masl). Denali is 3000 m taller than most surrounding peaks. It lies inside a 19° restraining bend in the active Denali fault system that is moving at about 7 mm/yr, and thus there is a tectonic and structural driver for ongoing rock uplift. High relief around Denali is also due, in part, to its granitic rock type and low fracture density relative to adjacent metasediments. Here we show that unique climatic conditions at high elevations also contribute to the growth of relief. We examine 10Be concentrations in 1) three new gravel samples between 3500 and 5200 m elevation from sites unaffected by recent glacial erosion, 2) previously published samples from a sidewall of the Kahiltna Glacier from 2400 to 2800 masl, 3) previously published samples from medial moraines along the length of the Kahiltna Glacier from 1400 to ~500 masl, and 4) previously published alluvial samples along the Kahiltna River at an elevation of ~200 masl. These samples constitute a transect extending more than 5000 vertical meters, and the data establish that erosion rates decrease with elevation and contribute to the growth of relief. Erosion rates for the three new high-elevation samples are calculated to 4.6±0.6 mm/ka at 5.2 km, 28.6±3.7 mm/ka at 4.0 km, and 38±5 mm/ka at 3.5 km. Erosion rates at intermediate elevations, on the sidewall of the Kahiltna Glacier, range between 160-327 mm/ka. Along the medial moraines inferred erosion rates range between 140-537 mm/ka, and basin-wide erosion rates calculated from sediments in the river below the glacier range between 450-896 mm/ka. These differences in erosion rates can create relief of 3 km within 1-10 Ma, well within the estimated period of increase in rock uplift and exhumation on Denali over the last ~6 Ma. Meteorological data from 2130 to 5550 masl at 5 sites show it rarely gets above freezing above 4 km elevation, indicating that frost weathering currently plays a diminished role in erosion at high elevations. The immediate implication of this temperature and erosional correlation is an increase in relief. This is the first study to directly measure a significant decrease in erosion rates at high elevations in the relative absence of frost weathering. The results highlight the combined influence of rock type, glacial erosion, and permanent sub-zero temperatures on erosion rates. In combination with active faulting, the data explain the resultant increase in relief along the southern side of the Alaska Range over the past 100 ka.

Alaska↗
USGS2024

Seismicity zoning at Coso geothermal field and stress changes from fluid production and migration

The Coso geothermal field is a major geothermal power production site in the western United States. It has been observed that low-magnitude seismic events ( M < 3.71) are unevenly distributed in three distinct zones, namely, nearfield (<3 km), midfield (3–6 km), and farfield (> 6 km) from the Coso geothermal plant. These zones exhibit distinct changes in earthquake location before and during geothermal production episodes that began in 1986. After 1986, the midfield region of the main flank experiences a significantly lower seismicity rate than the surrounding areas before production episodes. During 2014–2019, the farfield earthquakes cluster in the eastern and western parts of the greater Coso area, which is discernably different from how those pre-production earthquake events were distributed along the conjugate NW-SE and SW-NW trending structures across the main flank. Here, we analyze the stage of stress with finite-element-based poroelastic simulations to illustrate how the spatiotemporal evolution of the seismicity is associated with the pattern of stress perturbations caused by fluid migration amid the operations of geothermal power plants. Generally, ∼70% of co-production seismicity is found in zones of increased Coulomb stress between 2014 and 2019 at >99% confidence. Meanwhile, the midfield zone of seismic paucity overlaps with the zone of decreasing pore-fluid pressure. Overall, the results provide a physical explanation of how decadal geothermal operations at Coso have perturbed stress-field changes and contributed to the evolving characteristic seismic pattern, shedding insights into assessing the seismic hazard in other geothermal settings.

California↗
USGS2024

The chlorine evolution of arc magmas and the crustal water filter

Degassing of water from magmatic systems is key to transporting metals from magmas to form ore deposits, but elements like chlorine, through the formation of anion complexes, can be important in solubilizing and mobilizing these metals into water-rich fluids. Reconstructing the Cl systematics of evolving magmas is thus an important step towards understanding the origins of ore deposits, but the magmatic record is not well preserved because Cl can be lost during degassing. Here, we reconstruct the pre-degassing history of Cl in subduction zone (arc) magmas through amphiboles, which incorporate Cl directly into their crystal structures, preserving pre-eruptive magmatic signatures. Amphibole-reconstructed Cl contents indicate that magmatic differentiation can lead to a 4-fold increase in concentration due to Cl's incompatible behavior. The amphibole-reconstructed Cl contents of arc magmas are also significantly higher than values reported from melt inclusions, suggesting that many melt inclusions may have been trapped after magmas had already lost some Cl. We show that such Cl loss is likely associated with preferential partitioning of Cl into hydrous fluids degassed from the magma during crustal storage or ascent. The extent of Cl depletion can thus be used to estimate how much water was lost during early degassing. If Cl is important to certain ore deposits, magmatic water content may play an indirect role. Magmas too rich in water will lose water and hence Cl at greater depths, rendering such magmas less able to transport metals to the upper crust. By contrast, drier magmas may not produce enough Cl-rich fluids to mobilize metals. Thus, magmas with intermediate water contents may produce enough Cl-rich fluids at the right depths for certain types of ore deposits.

Earth and Planetary Science Letters↗
USGS2025

From hydrated silica to quartz: Potential hydrothermal precipitates found in Jezero crater, Mars

On Earth, silica-rich phases from opal to quartz are important indicators and tracers of geological processes. Hydrated silica, such as opal, is a particularly good matrix for the preservation of molecular and macroscopic biosignatures. Cherts, a type of silica-dominated rocks, provide a unique archive of ancient terrestrial life while quartz is the emblematic mineral of the Earth's continental crust. On Mars, hydrated silica has been detected in several locations based on remote sensing and rover-based studies. In the present article we report on the detection of cobbles made of hydrated silica (opal or chalcedony), as well as well-crystallized quartz. These detections were made with the SuperCam instrument onboard Perseverance (Mars 2020 mission), using a combination of LIBS, infrared and Raman spectroscopy. Quartz-dominated stones are detected unambiguously for the first time on the Martian surface, and based on grain size and crystallinity are proposed to be of hydrothermal origin. Although these rocks were all found as float, we propose that these detections are part of a common hydrothermal system, and represent different depths / temperatures of precipitation. This attests that hydrothermal processes were active in and around Jezero crater, possibly triggered by the Jezero crater-forming impact. These silica-rich rocks, in particular opaline silica, are very promising targets for sampling and return to Earth given their high biosignature preservation potential.

Earth and Planetary Science Letters↗
USGS2025

Volcanic gases reflect magma stalling and launching depths

Many open-vent arc volcanoes display two modes in their continuous gas emissions, one with a characteristic CO 2 / S T ratio typical of periods of quiescent degassing and another punctuated by high CO 2 / S T gas emitted in the weeks before eruption, a recently recognized eruption precursor. In this study we explore the origin of the two modes of degassing revealed by time-series gas data at Turrialba volcano (Costa Rica) in the context of new melt inclusion (MI) data. To reconstruct the c[CO 2 ] of undegassed magma, we developed a rapid-quench piston-cylinder assembly to rehomogenize the vapor bubble commonly contained in MIs. We focus on olivine-hosted MIs from a mafic scoria sample erupted from Turrialba in 1864–1866. The reconstructed CO 2 contents in MIs decrease from ∼4000 to <1000 ppmw as S contents decrease from 3500 to <1000 ppmw. The highest reconstructed S and CO 2 in the MIs resulted in an initial magmatic CO 2 / S T ratio (molar) of 0.83. Informed by the MI data, we modeled the decompression degassing of Turrialba magma and vapor composition using the Sulfur_X and EVo models. Instead of being controlled by initial magmatic CO 2 /S T ratio as suggested by previous studies, we find that the quiescent gas emitted from Turrialba during 2014–2018 (CO 2 / S T = 2.3 ± 0.8, molar) appears to reflectequilibrium with magmas stored at 4–8 km (Sulfur_X) or 2 km (EVo) depth, when H 2 O is degassing extensively from the magma. A magma storage region at 4–8 km is also supported by seismic tomography. The second gas mode is noted by spikes in CO 2 / S T ∼ 7.9 ± 2 in the weeks prior to eruption. This gas reflects equilibrium with a magma at 12–18 km (Sulfur_X) or 4–8 km (EVo), where the ascending magma is saturated with a CO 2 -rich vapor. Thus, there are two important trans crustal depths beneath the volcano: one where the rate of H 2 O loss from the magma and thus magma viscosity increases, and one at greater depths where high CO 2 /S T vapor forms and may facilitate dike propagation. We interpret the shallower, H 2 O-loss region as the main site of magma stalling and storage, where quiescent gas is generated continuously. We interpret the greater depth (12–18 km) as the source of the precursory gas that precedes eruption, and where the mafic melt lastly equilibrated with a mush zone before ascending and triggering eruption weeks later. This hypothesis is ripe for testing at other volcanoes that exhibit two modes in gas geochemistry.

Turrialba volcano↗