Radiogenic Heat Research Articles

Post-main sequence thermal evolution of planetesimals

ABSTRACT White dwarfs that have accreted planetary materials provide a powerful tool to probe the interiors and formation of exoplanets. In particular, the high Fe/Si ratio of some white dwarf pollutants suggests that they are fragments of bodies that were heated enough to undergo large-scale melting and iron core formation. In the Solar system, this phenomenon is associated with bodies that formed early and so had short-lived radionuclides to power their melting, and/or grew large. However, if the planetary bodies accreted by white dwarfs formed during the (pre)-main sequence lifetime of the host star, they will have potentially been exposed to a second era of heating during the star’s giant branches. This work aims to quantify the effect of stellar irradiation during the giant branches on planetary bodies by coupling stellar evolution to thermal and orbital evolution of planetesimals. We find that large-scale melting, sufficient to form an iron core, can be induced by stellar irradiation, but only in close-in small bodies: planetesimals with radii ≲ 30 km originally within ∼2 au orbiting a 1–3 M⊙ host star with solar metallicity. Most of the observed white dwarf pollutants are too massive to be explained by the accretion of these small planetesimals that are melted during the giant branches. Therefore, we conclude that those white dwarfs that have accreted large masses of materials with enhanced or reduced Fe/Si remain an indicator of planetesimal’s differentiation shortly after formation, potentially linked to radiogenic heating.

Himalayan-like Crustal Melting and Differentiation in the Southern North American Cordilleran Anatectic Belt during the Laramide Orogeny: Coyote Mountains, Arizona

Abstract The southern US and northern Mexican Cordillera experienced crustal melting during the Laramide orogeny (c. 80–40 Ma). The metamorphic sources of melt are not exposed at the surface; however, anatectic granites are present throughout the region, providing an opportunity to investigate the metamorphic processes associated with this orogeny. A detailed geochemical and petrochronological analysis of the Pan Tak Granite from the Coyote Mountains core complex in southern Arizona suggests that prograde metamorphism, melting, and melt crystallization occurred here from 62 to 42 Ma. Ti-in-zircon temperatures (TTi-zr) correlate with changes in zircon rare earth elements (REE) concentrations, and indicate prograde heating, mineral breakdown, and melt generation took place from 62 to 53 Ma. TTi-zr increases from ~650 to 850 °C during this interval. A prominent gap in zircon ages is observed from 53 to 51 Ma and is interpreted to reflect the timing of peak metamorphism and melting, which caused zircon dissolution. The age gap is an inflection point in several geochemical-temporal trends that suggest crystallization and cooling dominated afterward, from 51 to 42 Ma. Supporting this interpretation is an increase in zircon U/Th and Hf, a decrease in TTi-zr, increasing zircon (Dy/Yb)n, and textural evidence for coupled dissolution–reprecipitation processes that resulted in zircon (re)crystallization. In addition, whole rock REE, large ion lithophile elements, and major elements suggest that the Pan Tak Granite experienced advanced fractional crystallization during this time. High-silica, muscovite± garnet leucogranite dikes that crosscut two-mica granite represent more evolved residual melt compositions. The Pan Tak Granite was formed by fluid-deficient melting and biotite dehydration melting of meta-igneous protoliths, including Jurassic arc rocks and the Proterozoic Oracle Granite. The most likely causes of melting are interpreted to be a combination of (1) radiogenic heating and relaxation of isotherms associated with crustal thickening under a plateau environment, (2) heat and fluid transfer related to the Laramide continental arc, and (3) shear and viscous heating related to the deformation of the deep lithosphere. The characteristics and petrologic processes that created the Pan Tak Granite are strikingly similar to intrusive suites in the Himalayan leucogranite belt and further support the association between the North American Cordilleran anatectic belt and a major orogenic and thermal event during the Laramide orogeny.

Probe Screening Techniques for Rapid, High-Resolution Core Analysis and Their Potential Usefulness for Energy Transition Applications

Core analysis techniques have traditionally been used mainly for hydrocarbon reservoir applications. However, the same techniques are equally applicable to reservoir issues associated with energy transition, such as geothermal prospects, carbon geosequestration, and hydrogen storage. Traditionally, much core analysis has been performed successfully using core plugs. However, this approach has certain drawbacks: (1) the selected plugs may not necessarily be representative of the full range of lithologies, (2) key features (e.g., thin naturally cemented or fractured zones) may be missed, (3) high-resolution detail at the lamina scale may be missed, (4) depth shifting to well logs may not be sufficiently accurate, and (5) this strategy may be more sensitive to missing core. In this paper, we highlight the usefulness of probe core analysis techniques on slabbed core and powdered samples. For many reservoirs relevant to energy transition, it is crucial to have a high-resolution continuous record of petrophysical properties so that key features are not missed. Probe measurements are less destructive, without the need to cut core plugs, and provide: (1) high-resolution data at the lamina scale so that key features and small-scale heterogeneities can be identified, (2) improved depth matching to well-log data, and (3) rapid, cost-effective data. We describe examples highlighting some different probe techniques. While some techniques are well known, such as probe permeability, others, such as probe acoustics, probe luminance (from linear X-ray measurements), and probe magnetics, are less familiar to core analysts but are well suited for analyzing cores from reservoirs associated with energy transition as well as hydrocarbons. For example, potential geothermal prospects involve studying igneous and metamorphic samples (where the main radiogenic heat sources reside) as well as sedimentary samples, and differences in the magnetic susceptibility signals using a small, portable magnetic probe can quickly differentiate the different rock types. Probe acoustics can be used to (1) rapidly identify anisotropy by orienting the acoustic transmitter-receiver bracket in different directions, (2) identify open microfractures via longer transit times, and (3) produce high-resolution porosity profiles after correlation of transit times with some representative plug or well-log porosity data. Probe luminance and associated linear X-ray images, which are related to density, can indicate small-scale heterogeneities that may impact permeability variation and anisotropy and may not be seen from mere visual observations of the slabbed core surface.

The inevitability of large shallow craters on Callisto and Ganymede: Implications for crater depth-diameter trends

Complex craters with diameters (D) ≥ 40 km on Callisto and Ganymede are shallower than would be expected from simply extrapolating the depth-diameter trend from smaller (D ≤ 40 km) craters. This unusual depth-diameter (d-D) trend, and associated changes in crater morphology, have been hypothesized to result from rheological transitions, including the existence of an ocean, within the moons' ice shell. Simulations of impact crater formation can reproduce the observed shallow depths but require heat fluxes roughly twice the maximum radiogenic flux to do so. Here we demonstrate that the d-D trends on Callisto and Ganymede can instead be explained as a direct consequence of viscous relaxation under radiogenic heating. We use numerical simulations of viscous relaxation to show that if craters form at the depth expected from an extrapolation of the complex crater d-D trend, they will evolve to the observed depths over timescales of 200 Myrs to 1 Gyrs. Large craters (e.g., D ≥ 80 km) younger than 200 Myrs, which would retain greater depths, should be relatively rare. If we instead assume that the craters formed at their observed depths, as proposed by previous impact modeling, they quickly become much shallower than observed. We find excellent agreement between observed crater depths on Ganymede and our simulated crater depths by assuming a pure-water ice composition and a diurnally averaged surface temperature of 120 K, but require either larger-grained or “dirty” ice with a modestly higher viscosity to match observations at Callisto, where the surface temperature is warmer (130 K). We favor the latter explanation because it is consistent with the existence of a dusty lag on Callisto's surface and the absence of a similar lag on Ganymede. Our results predict that, for a given crater diameter, post-relaxation crater depth should increase with increasing latitude, a hypothesis best tested on Callisto, whose relatively quiescent geologic history best preserves the signature of viscous relaxation under radiogenic heating.

When were the First Exocontinents?

Earth’s biosphere was able to increase as continents emerged. I assess when continents could first appear on hypothetical rocky planets of nearby stars. Radiogenic heating of the planetary mantle is evaluated through stellar abundances of iron and silicon (core and mantle proxies) and thorium and potassium (mantle heating proxies). The heat per unit mantle mass is compared to a threshold on Earth after which large-scale continents appeared. Longer delays are inferred for some exoplanets, particularly those with high thorium, but earliest continents could have arisen 2 Gyr before those on Earth, among thin disk stars. In the thick disk, continents could appear 4–5 Gyr pre-Earth. Hence, subsolar-metalicity systems could be an important focus in searching for planets where life could be more advanced than on Earth. At least ∼2 worlds with such old continents are expected to be accessible to future space telescopes, such as Habitable Worlds Observatory.

Role of crustal radiogenic heating in ultra-high temperature metamorphism of the Greater Himalayan Crystalline complex: Phase equilibrium and numerical modelling

Ultra-high temperature (UHT) metamorphism is a significant feature of the Greater Himalayan Crystalline complex (GHC), which constrains the dynamics of continental subduction and subsequent continental collision. However, the mechanism of such kind of UHT metamorphism is widely debated, including slab tearing-induced mantle upwelling, mechanical heating, radiogenic heating, and others. To better understand the UHT metamorphism and the thermal budget of collisional orogens, we first conduct a forward phase equilibrium modelling coupled with geochemical modelling to explore the variation of radiogenic heat production (RHP) of felsic melt, indicating that it may range from 4 μW/m3 to 9 μW/m3. Then, we incorporate the variable RHP into a thermo-mechanical model to study its effect on the thermal evolution of the collision zone. The numerical models reveal that a reasonably increased radiogenic heat production of 4 μW/m3 for the partially molten felsic crust contributes to UHT metamorphism after the continental collision for 30–35 million years. The model results are consistent with the structural observations, geochemical signatures, and P-T paths of the GHC. After the comparison with other mechanisms (e.g., the effects of mechanical heating and anomalous mantle heating), we propose that radiogenic heating could be a predominant heat source for the rapid UHT metamorphism of the GHC, whereas mechanical heating and heat flux from the mantle play secondary roles.

Radiogenic heat production in rocks from the Sabinas Basin (northeastern Mexico) determined by in situ gamma radiation measurements

Radiogenic heat production in rocks from the Sabinas Basin (northeastern Mexico) determined by in situ gamma radiation measurements

Early Paleozoic Tectonothermal Evolution of the Khan-Khukhay Metamorphic Complex (Northern Mongolia)

A reconstruction of metamorphic stages of Moren and Erzin metamorphic Complexes in the Khan-Khuhay block of Nothern Mongolia presented in the paper. Based on it a general geodynamic history of Sangilen terrain of Tuva-Mongolia Massif discussed. Reconstructed “clock-wise” P-T trend demonstrated two stage of metamorphism, the first of which is due to collision metamorphism with P-T parameters of 9 kbar, 740°C, the second one is due to regional magmatic episode with P-T parameters of 6-7 kbar, 860–880°C. Geochemical and petrological peculiarities of rocks in the Khan-Khuhay block demonstrates resemblance with metamorphic block of Western Sangilen in South-East Tuva. In the first time quartz monzodiorite intrusive bodies founded within Khan-Khuhay block. Their geochemical peculiarities are similar to Ordovician gabbro-monzodiorite intrusives of Western Sangilen. Quartz monzodiorite intrusives of Khan-Khuhay are likely a small apophysis of a deep-crust intermediate magma chamber and can present probable thermal source of metamorphic stage M2 in the Khan-Khuhay block. Numerical thermo-mechanical model of metamorphism in the Khan-Khuhay block explain heating in the thickening crust during collision due to higher radiogenic heat source of 1.52 μW/m3. Using computer modeling was show that the P-T parameters of second metamorphic stage can realize only by means of magmatic heat from monzodiorite intrusion. Reconstruction of P-T parameters using mineral thermobarometry, similarity of geochemical characteristics, as well as the results of thermomechanical modeling allow us to conclude that the Erzin and Moren complexes have undergone a joint tectono-metamorphic evolution.

Overview of the thermal properties of rocks and sediments in Slovenia

The use of geothermal energy, which comes from both deep geothermal systems and the shallow underground, has been developing rapidly in the last few decades. The purpose of the paper is to present the results of measurements of the thermal properties of all rock samples and sediments that were available from boreholes, two tunnels and numerous surface locations in Slovenia in the period from 1982 to the end of 2022. In relation to the shallow geothermal potential, a special effort is needed to characterize the thermal properties of the rocks and sediments and to implement thermal energy transfer technology. In this sense, knowledge of the thermal conductivity of rocks and sediments is required to assess the possibility of low-enthalpy heat exchange in a given local area. The largest number of measurements was taken to determine thermal conductivity. Determinations of thermal diffusivity were carried out on a much smaller number of rock and sediment samples, as well as determinations of radiogenic heat production in rocks. The results of thermal conductivity measurements on 430 samples from 119 wells, 20 samples from two tunnels and 156 samples from surface locations are shown. The highest thermal conductivities are shown by samples of dolomite, quartz conglomerate and conglomerate, phyllonite, quartz phyllite and gneiss, while the lowest are measured in sediments such as clay, lignite with clay, peat and dry sand. The determined radioactive heat generation is the lowest for milonitized dolomite and highest for dark grey sandstone with shale clasts. Our results are comparable to those already published worldwide, and they could be the basis for the possible future Slovenian standard for the thermal properties of measured rocks and sediments.

Hydrothermal Systems Characterized by Crustal Thermally‐dominated Structures of Southeastern China

AbstractSoutheastern China (SE China) is located in the Pacific tectonic domain and has experienced a series of tectonomagmatic events induced by the subduction of the Paleo‐Pacific Plate since the late Mesozoic. The subduction formed a series of NE‐NNE oriented faults under a NW–SE regional stress field, along which a number of thermal springs occur. Previous studies have focused on the genesis mechanism of specific geothermal fields in SE China, but the general characteristics of hydrothermal systems in SE China remains unclear. In this study, we investigate the correlation between geothermal activity, hydrochemical type and regional faults by studying the distribution of hydrothermal activity and geochemical properties of typical hydrothermal systems in SE China. The hydrothermal systems in SE China have a crustal thermally‐dominated structural origin unique to the specific geological and tectonic conditions of the Eurasian Plate margin. The upwelling of the asthenosphere and the widespread granitoids with high radiogenic heat production in SE China provide major heat sources for regional geothermal anomalies. The NE‐oriented crustal thermally‐dominated faults are critical for the formation of geothermal anomalies and NW‐oriented extensional faults have created favorable conditions for meteoric water infiltration, transportation and the formation of thermal springs.

Lithospheric structural dynamics and geothermal modeling of the Western Arabian Shield

Understanding the dynamics of suturing and cratonisation and their implications are vital in estimating the link between the lithospheric mantle architecture and geothermal resources. We propose new interpretations of the Western Arabian Shield’s geodynamic styles and geothermal anomalies. In this work, features of the crust and mantle were interpreted from geophysical modeling to unravel the structural dynamics between the Arabian Shield and the Red Sea rift, as well as the influence of these mechanisms on the uplift of the Cenozoic basalts. Estimates of the lower crust thermal properties were also achieved. Spectral properties of the potential field were used to define the Curie isotherm, heat fluxes, geothermal gradients, radiogenic heat production, Moho configuration, and lithosphere-asthenosphere boundary. Results show new structural styles, micro-sutures, and significant thermal anomalies. The defined geothermal patterns were inferred to be due to localized initiation of tectonic and asthenospheric disequilibrium during the rifting episodes within the Red Sea. Also, magma mixing is initiated by the northward migration of magma from the Afar plume towards the Western Arabian Shield which drives local mantle melts beneath the western Arabia, thereby providing the pressure field required for magma ascent. The ascendant magma flow provides the heating source of geothermal reservoirs within the Western Arabian Shield. However, there are indications that during the episodes of rifting within the Red Sea and/or ancient Pan-African activities, the mixing process may have been altered resulting in crustal thinning and creating pathways of ascendant magma flow along the MMN volcanic line. Integrating geophysical and geothermal models indicated new zones of suturing and extensional tectonics between the amalgamated terranes. The geodynamic interpretation shows a new redistribution of terranes and continuous compressional and transtentional movements within the Arabian Shield.

Low Ni and Co olivine in Chang’E-5 basalts reveals the origin of the young volcanism on the Moon

Mare basalts returned by the Chang’E-5 (CE5) mission extend the duration of lunar volcanism almost one billion years longer than previously dated. Recent studies demonstrated that the young volcanism was related neither to radiogenic heating nor to hydrous melting. These findings beg the question of how the young lunar volcanism happened. Here we perform high-precision minor element analyses of olivine in the CE5 basalts, focusing on Ni and Co. Our results reveal that the CE5 basalt olivines have overall lower Ni and Co than those in the Apollo low-Ti basalts. The distinctive olivine chemistry with recently reported bulk-rock chemistry carries evidence for more late-stage clinopyroxene-ilmenite cumulates of the lunar magma ocean (LMO) in the CE5 mantle source. The involvement of these Fe-rich cumulates could lower the mantle melting temperature and produce low MgO magma, inhibiting Ni and Co partitioning into the magma during lunar mantle melting and forming low Ni and Co olivines for the CE5 basalts. Moreover, the CE5 olivines show a continuous decrease of Ni and Co with crystallization proceeding. Fractional crystallization modeling indicates that Co decreasing with crystallization resulted from CaO and TiO2 enrichment (with MgO and SiO2 depletion) in the CE5 primary magma. This further supports the significant contribution of late-stage LMO cumulates to the CE5 volcanic formation. We suggest that adding easily melted LMO components resulting in mantle melting point depression is a key pathway for driving prolonged lunar volcanism. This study highlights the usefulness of olivine for investigating magmatic processes on the Moon.

Examining the power supplied to Earth's dynamo by magnesium precipitation and radiogenic heat production

We examine magnesium and potassium solubility in liquid Fe mixtures, representative of Earth's core composition, in equilibrium with liquid silicate mixtures representative of an early magma ocean. Our study is based on the calculation of the chemical potentials of MgO and K2O in both phases, using density functional theory. For MgO, we also study stability against precipitation of the solid phase. We use thermal evolution models of the core and mantle to assess whether either radiogenic heating from 40K decay or Mg precipitation from the liquid core can resolve the new core paradox by powering the geodynamo prior to inner core formation. Our results for K show that concentrations in the core are likely to be small and the effect of 40K decay on the thermal evolution of the core is minimal, making it incapable of sustaining the early geodynamo alone. Our results also predict small concentrations of Mg in the core which might be sufficient to power the geodynamo prior to inner core formation, depending on the process by which it is transported across the core mantle boundary.

Is the most recently active volcano in the Carpathian-Pannonian Region capable of further eruptions?

Debate on the future eruptive capability of Ciomadul (Csomád) volcano in the East Carpathians, Romania, has recently gained a new impetus and prompted wide media attention. A tentative of numerical thermal modeling claimed that the amount of magma currently present beneath the volcano is of 20–58 km3 in volume. However, these results can be challenged because the model applied considers unrealistic initial conditions and input parameters related to crustal structure and radiogenic heat production in the local area. Instead, we propose a geologically more plausible alternative hypothesis invoking the presence of relatively small amounts of fluids percolating from the upper mantle towards the surface which may explain the conducting anomalies pointed out beneath the volcano.

Temporal and spatial radiogenic heat production rate of granitic plutons from the Eastern Pontides Orogenic Belt, NE Turkey: Constraints for the geothermal resources

The evaluation of the geothermal potential of the granitic rocks is important in long-term sustainable renewable energy projects due to increasing energy demand. The Eastern Pontides Orogenic Belt in NE Turkey contains a variety of granitic plutons changing in age, size, and composition. In this paper, we discussed the temporal and spatial distribution of radiogenic heat production by using the contents of heat-producing elements (U, Th, K) of the granitic plutons. The average U, Th, and K concentrations for the granitic plutons are 2.97 ± 0.95 ppm, 13.48 ± 3.48 ppm and 2.69 ± 0.47 wt% for Paleozoic plutons, 1.83 ± 0.98 ppm, 8.58 ± 5.10 ppm and 1.77 ± 0.80 wt% for Jurassic plutons, 5.24 ± 1.64 ppm, 26.02 ± 6.43 ppm and 3.17 ± 0.49 wt% for Cretaceous plutons, and 3.82 ± 0.90 ppm, 15.79 ± 4.27 ppm and 2.88 ± 0.40 wt% for Eocene plutons, respectively. Radiogenic heat production rates are 1.43–2.73 µW/m3 for Paleozoic plutons, 0.74–1.70 µW/m3 for Jurassic plutons, 0.66–6.28 µW/m3 for Cretaceous plutons and 1.15–5.22 µW/m3 for Eocene plutons. The studied plutons were classified as low- to moderate heat-producing granitoids. However, some Cretaceous and Eocene granitic plutons with radiogenic heat production values of 5.22–6.28 µW/m3 are considered as high heat-producing granitoids. The thermal indications in the region can be related to radiogenic heat generation and the neotectonic activity of the region. Considering the large volume of the Cretaceous- and Eocene- aged granitic plutons in the Eastern Pontides Orogenic Belt, the moderate to high radiogenic heat production of the granitic plutons in some areas has a significant geothermal impact and can be considered as the potential of enhanced geothermal systems for the future energy demand of the region.

Estimation of radiogenic heat production of the Adamawa region in Cameroon, Central Africa: an insight from spectral analysis of EMAG2 data

Estimation of radiogenic heat production of the Adamawa region in Cameroon, Central Africa: an insight from spectral analysis of EMAG2 data

Crustal remelting origin of highly silicic magmatism on the Moon

Orbital observations of non-mare, highly silicic volcanic constructs on the Moon challenge the conventional view of the formation of silicic crusts in the presence of water and plate tectonics—the former the Moon has in very short supply and the latter it likely never ever had. Revealing the silica-rich magma origin may reshape our understanding of early planetary crust formation. However, the cause of lunar silicic magmatism remains enigmatic. Here we conduct phase equilibrium simulations for potential lunar igneous lithologies that demonstrate that the compositions of silicic volcanic constructs can be produced by partial melting of KREEP (potassium, rare earth elements, and phosphorus) basalts. Either internal radiogenic heating or external impact bombardment can provide the heat needed for KREEP basalt melting. Combined with silica-rich materials identified on other rocky planets, we suggest that highly evolved crusts might be more prevalent in the early solar system than anticipated as they can originate from crustal remelting in the absence of water and plate tectonics.

Tracing a Neoproterozoic subduction to collision magmatism in the eastern Pernambuco–Alagoas domain, northeastern Brazil

The Pernambuco–Alagoas (PEAL) Domain, southern Borborema Province, northeastern Brazil, bears the most voluminous Cryogenian–Ediacaran granitic rocks in this province, which was formed during the convergence of the São Francisco Craton and the Borborem Province, during the western Gondwana amalgamation. New geochemical and isotopic data along those from the literature, for one of the largest intrusions, the Correntes composite batholith, at the southern part of this domain, indicate that the granitic rocks are intermediate to acid, oxidized, metaluminous to peraluminous, magnesian, and are high-K calc alkalic to shoshonitic with I-type signature. They are enriched in large-ion lithophile elements, exhibit lightly negative Eu in rare-earth element patterns and negative Ta–Nb, P, and Ti anomalies in spidergrams. Average initial 87Sr/86Sr is 0.7055 and rocks present values of whole-rock εNd (0.6 Ga) that fall into two groups. The pre-to syn-collisional, 635–628 Ma plutons present εNd (0.6 Ga) values from +1.3 to −2.5, with Nd model ages varying from 1.29 to 0.92 Ga, while the late-to post-collisional, 602–580 Ma, plutons show more negative values (−8.2 to −9.5), and older Nd model ages from 1.95 to 1.81 Ga. This Nd-isotope pattern is also observed in other plutons of the southern PEAL Domain and indicates a change in the lower crust source rock with time, with larger contributions of crustal components in the late-to post-collisional rocks. The chemical and isotopic characteristics of the studied granitic rocks and other granitic batholiths in the southern PEAL Domain are compatible with modern magmatic arcs of continental active margins. We propose that in earlier stages of convergence, melting has further affected the younger (Stenian –Tonian), likely less refractory rocks associated with abundance of volatiles, whose segregation would have differentiated to form the oldest plutons. Slow cooling allowed the accumulation of heat from mantle-derived magma in the pre-collisional period, which, together with radiogenic heat from thickened crust, led to partial melting of older crustal rocks, and the formation of magmas whose segregation and differentiation of the melt would originate the younger plutons in this part of the PEAL Domain. Older plutons formed during a Cryogenian-Ediacaran flare-up event that occurred in the southern PEAL Domain.

Mantle fragmentation and incomplete core merging of colliding planetesimals as evidenced by pallasites

Main group pallasites were likely formed by the collision of their parent body with a smaller impactor that caused a mixing of mantle and core material from the target and impactor, respectively. In order to better constrain the collision, we present particle size distribution (PSD) analyses of olivines in seven main group pallasites and of the Eagle station pallasite. The PSDs of two fragmental pallasites (Admire and Huckitta) contain linear segments in bi-logarithmic particle number versus size diagrams that are similar to terrestrial cataclasites or impact-related rocks. On the other hand, the PSDs of four angular pallasites only display linear segments above their respective average grain sizes. We argue that fragmental pallasites record brittle rock deformation close to the impact site of the collision, while angular pallasites represent deeper-lying mantle rocks of the target body that were disintegrated by the downward percolation of core metal from the impactor. High strain-rate deformation experiments with the system olivine – FeS melt ± Au melt produced microstructures and PSDs that are broadly similar to these two textural groups. The experiments also suggest that de-localized metal melt percolation and concomitant mantle disintegration as evidenced in angular pallasites is facilitated by weak grain boundaries caused by a small fraction of previously present metal melt in the mantle as opposed to localized diking that is dominant in a melt-free mantle. The former mechanism is expected to prevent efficient core-merging and instead causes mantle-impregnation with metal melt, which could be active when planetesimal mantles were still warm due to short-lived radiogenic heating. In addition to the parent body of the PMG, asteroid 16 Psyche may be an example of this inefficient core-merging mechanism.

Radiogenic heat production drives Cambrian–Ordovician metamorphism of the Curnamona Province, south-central Australia: Insights from petrochronology and thermal modelling

Radiogenic heat production drives Cambrian–Ordovician metamorphism of the Curnamona Province, south-central Australia: Insights from petrochronology and thermal modelling