Owing to their abundance and relative availability on Earth's seafloor, mid-ocean ridge basalts (MORBs) have a well-defined chemical element budget, reflected by the low standard deviation associated with typical normal MORB (N-MORB) composition. However, the exact mechanisms leading to magma differentiation and MORB generation remain debated, which hinders our ability to evaluate MORB parental magma composition. In this study, we leverage the predictive power of the BDD21 numerical framework to obtain a representative trace element budget of parental MORB magma and assess its ability to fractionate into the N-MORB composition. Utilizing revised parameterizations for mineralogy, melting, and partitioning, we couple BDD21 with numerical simulations of a MOR system driven by seafloor spreading in which we track the evolution of partial melting, mineral modal abundances, and concentrations of incompatible elements. Parental magma compositions are determined once simulations reach a steady state, and magma chamber replenishment models are employed to predict the trace element budget of the erupted liquid. We explore a range of geophysical and geochemical parameters to evaluate their effect on computed trace element concentrations. Previous magma chamber replenishment models are extended to account for multiple crystallization events and melt-crystal interaction. Modeling outcomes suggest that petrologically constrained fractionation of parental magma compositions obtained through BDD21 yields glass compositions compatible with the N-MORB budget. Nevertheless, our results show a systematic underestimation of Sr concentration, indicating the presence of recycled oceanic crust in the MORB source region. Beneath Earth's oceans, tectonic plates spread apart at mid-ocean ridges, generating volcanic regions whose magmatic output forms Earth's oceanic crust. The rocks composing the oceanic crust represent the solidification of magma produced by partially melting deeper mantle rocks. Accordingly, they carry a message about the nature of Earth's interior. To decipher this message, scientists recover rock samples from the seabed and analyze their composition to infer the nature of that otherwise inaccessible deep layer. Unfortunately, the chemical inventories obtained for these rocks reveal that significant processing of the magma occurs as it ascends toward the surface. Therefore, the relationship between crustal rocks and their deep parental counterparts is indirect. Here, we address this complexity using a two-step process. First, we simulate the generation and composition of partial melts derived from mantle peridotites (archetypal upper-mantle rocks) using a mid-ocean ridge numerical model. Second, we employ models of magma chamber processes to account for the expected magmatic evolution of the generated liquid. By optimizing and extending existing magma chamber models, we obtain an accurate representation of rock compositions sampled from Earth's seabed. Our findings provide a new opportunity to decipher the nature of Earth's interior. Refined the BDD21 peridotite melting and melt chemistry framework to reproduce geochemical observations of the mid-ocean ridge system Improved calibration of peridotite melting parameterization revises solidus and yields appropriate crustal thickness for mid-ocean ridges Depleted mantle compositions underestimate Sr concentration in basalts, requiring a prevalent contribution from recycled oceanic crust

Quantifying the depths and temperatures from which igneous rocks are derived is an important step in understanding volcanic, magmatic and mantle processes. We present meltPT, a Python package that allows users to apply twelve published whole-rock thermobarometers within a consistent framework, as well as combine thermobarometric results and geothermal models to estimate mantle potential temperatures. We apply meltPT to basaltic rocks from mid-ocean ridges and the Hawaiian Islands. We find mid-ocean ridge basalts equilibrate between 1–2 GPa and 1275–1475 ℃, corresponding to an ambient mantle potential temperature of ~1400 ℃. We estimate that the Hawaiian plume has an excess temperature of ~150 ℃. Hawaiian melt-equilibration depths increase from 1–3 GPa to 2.5–5 GPa through each island's life cycle. Our results indicate that multiple lithologies are present within the plume, and that transient plume reconfiguration in response to changing plate velocity is a viable mechanism for generating Hawaiʻi's two geochemically distinct plume tracks.

Large igneous provinces (LIPs) are formed by enormous (i.e., frequently >10 6 km 3 ) but short-lived magmatic events that have profound effects upon global geodynamic, tectonic, and environmental processes. Lithospheric structure is known to modulate mantle melting, yet its evolution during and after such dramatic periods of magmatism is poorly constrained. Using geochemical and seismological observations, we find that magmatism is associated with thin (i.e., ≲80 km) lithosphere and we reveal a striking positive correlation between the thickness of modern-day lithosphere beneath LIPs and time since eruption. Oceanic lithosphere rethickens to 125 km, while continental regions reach >190 km. Our results point to systematic destruction and subsequent regrowth of lithospheric mantle during and after LIP emplacement and recratonization of the continents following eruption. These insights have implications for the stability, age, and composition of ancient, thick, and chemically distinct lithospheric roots, the distribution of economic resources, and emissions of chemical species that force catastrophic environmental change.

We reconstruct spatial variations in grain size in the sediment routing system of the data-rich Middle Jurassic Brent Group of the northern North Sea, using published stratigraphic, thickness, palaeogeographic, provenance and age constraints combined with representative core and wireline-log data. Facies associations provide a textural proxy for gravel, sand and mud grain-size fractions, and their distributions define spatio-temporal variations in grain size within four stratigraphic intervals (J22, J24, J26, J32 genetic sequences). Sediment was sourced from the west (Shetland Platform), east (Norwegian Landmass) and south (Mid-North Sea High). The associated sediment routing systems were geographically distinct in the oldest (J22) and youngest (J32) genetic sequences, but combined to feed a large wave-dominated delta (‘Brent Delta’) in genetic sequences J24 and J26. Few of the Brent Group sediment routing systems exhibit the downsystem-fining grain-size trend predicted by sediment mass balance theory. Deviations from this reference trend reflect: (1) sparse sampling of channelised fluvial and fluvio-tidal sand bodies in upsystem locations; (2) preferential trapping of sand in underfilled antecedent and syn-depositional, half-graben depocentres in genetic sequences J22 and J32; and (3) nearshore retention of sand by shoaling waves in wave-dominated shoreface and barrier-strandplain systems. This third type of deviation reveals that spatial facies partitioning due to shallow-marine process regime distorts the simple downsystem-fining reference trend, and supports the interpretation that large volumes of predominantly muddy sediment were bypassed beyond the ‘Brent Delta’ into neighbouring basins. Our analysis demonstrates a practical approach to interpret sediment supply and sediment dispersal in the stratigraphic record.

Harrat Rahat is the largest volcanic field in Saudi Arabia and has been active from similar to 10 Ma to the present day. Due to its proximity to population centers, recent eruptions at Harrat Rahat- the Medinah lava flows (<1.7 Ma)- have been extensively studied to identify volcanic risk. However, evolution of Harrat Rahat's most extensive and oldest lava flows, known collectively as the Shawahit Basalt (>2.5 Ma), is poorly understood. In this study, we collected, dated and geochemically analyzed lavas from Harrat Rahat, primarily targeting the under-sampled Shawahit unit. We obtained dates of between 9.4 and 2.7 Ma using 40Ar/39Ar analyses of 23 Shawahit samples. Over the lifetime of Harrat Rahat, we observe a geochemical transition from predominantly subalkalic to alkalic eruptions coupled with a counter-intuitive decrease in incompatible element concentrations. We attribute these changes to a decrease in melt productivity and a reduction in contamination by enriched lithospheric melts, respectively. Thermobarometric analysis of basalts from Harrat Rahat indicates that they were generated by melting of asthenospheric mantle with a potential temperature of -1456(-32)(+50) degrees C beneath lithosphere that is 50-60 km thick. These results indicate that volcanic activity at Harrat Rahat was initiated by the arrival of a mantle plume beneath lithosphere thinned by a combination of rifting of the Red Sea and thermal erosion. Furthermore, we propose that this plume, either acting alone or in combination with a number of other plumes, is responsible for the formation of the Arabian swell, as well as much of the Neogene-recent intraplate volcanic activity observed across western Arabia. Our conclusions are consistent with a wide range of geochemical, seismologic, gravimetric, thermochronologic and geomorphic observations.

Harrat Rahat is the largest volcanic eld in Saudi Arabia and has been active from ~10 Ma to the present day. Due to its close proximity to important population centres, Harrat Rahat's recent eruptions, the Medinah lava flows (< 1.7 Ma), have been extensively studied to identify volcanic risk. However, the evolution of Harrat Rahat's most extensive and oldest lava flows, known collectively as the Shawahit Basalt (> 2.5 Ma), is poorly understood. In this study, we collected, dated and geochemically analyzed lava samples from Harrat Rahat, primarily targeting the under-sampled Shawahit unit. We 40Ar/39Ar dated 23 Shawahit samples that erupted between 9.4-2.7 Ma. Over the lifetime of Harrat Rahat, we observe a geochemical transition from predominantly tholeiitic to alkalic eruptions coupled with a counter-intuitive decrease in incompatible element concentrations. We attribute these changes to a decrease in melt productivity and a reduction in contamination by enriched lithospheric melts, respectively. Thermobarometric analysis of Harrat Rahat basalts indicates that these lavas were generated by melting of asthenospheric mantle with a potential temperature of ~1456 +50/-32 oC beneath lithosphere 50-60 km thick. These results indicate that volcanic activity at Harrat Rahat was initiated by the arrival of a mantle plume beneath lithosphere thinned by a combination of Red-Sea rifting and thermal erosion. Furthermore, we believe that this plume, either acting alone or in combination with a number of other plumes, is responsible for the formation of the Arabian swell, as well as much of the Neogene-recent intraplate volcanic activity observed across western Arabia. Our conclusions are consistent with a wide range of geochemical, seismologic, gravimetric, thermochronologic and geomorphologic observations.

Geodynamic simulations underpin our understanding of upper‐mantle processes, but their predictions require validation against observational data. Widely used geophysical datasets provide limited constraints on dynamic processes into the geological past, whereas under‐exploited geochemical observations from volcanic lavas at Earth's surface constitute a valuable record of mantle processes back in time. Here, we describe a new peridotite‐melting parameterization, BDD21, that can predict the incompatible‐element concentrations of melts within geodynamic simulations, thereby providing a means to validate these simulations against geochemical datasets. Here, BDD21's functionality is illustrated using the Fluidity computational modeling framework, although it is designed so that it can be integrated with other geodynamic software. To validate our melting parameterization and coupled geochemical‐geodynamic approach, we develop 2‐D single‐phase flow simulations of melting associated with passive upwelling beneath mid‐oceanic ridges and edge‐driven convection adjacent to lithospheric steps. We find that melt volumes and compositions calculated for mid‐oceanic ridges at a range of mantle temperatures and plate spreading rates closely match those observed at present‐day ridges with the same conditions. Our lithospheric step simulations predict spatial and temporal melting trends that are consistent with those recorded at intraplate volcanic provinces in similar geologic settings. Taken together, these results suggest that our coupled geochemical‐geodynamic approach can accurately predict a suite of present‐day geochemical observations. Since our results are sensitive to small changes in upper‐mantle thermal and compositional structure, this novel approach provides a means to improve our understanding of the mantle's thermo‐chemical structure and flow regime into the geological past.

To examine the effect of upper mantle compositional variations on seismic velocities, we exploit the Perple_X thermodynamic solver using the Holland and Powell database, and the mineral physics parameters of Schutt and Lesher (2010), to estimate seismic wave speeds through a wide range of mantle xenoliths.Our database includes peridotitic and eclogitic xenoliths from abyssal, forearc, cratonic, off-cratonic continental, passive margin, ophiolite, and massif settings.Initial results show that, although large compositionally modulated velocity variations occur in each setting, the mean velocities in these geologic regions are almost the same.Thus, we conclude that, on average, different settings have almost no compositional effect of seismic velocity.This finding suggests that seismic velocities vary compositionally over small scales, but that the mean seismic velocity observed on a regional scale is nearly independent of composition.Then, using these measured velocities, we estimate temperatures at the base of the crust in the U.S., China, and Australia by mapping Pn velocities to temperature.These temperatures are compared to xenolith-derived geotherms to determine spatio-temporal thermal variations in the mantle lithosphere.Our lithospheric temperatures in the U.S. (updated from Schutt et al., 2018) show patterns consistent with recent tectonism, whereas temperatures in Australia and China are more complex and show large variations.Areas that are predicted to be anomalously hot using our Pn conversion are generally consistent with Cenozoic-Recent xenolith locales where geothermometry indicates high temperatures, but these large variations also may be due to instability in derived Pn velocities.

Here, the authors compile a global geochemical database of Neogene-Quaternary intraplate volcanism. By comparing the distribution and composition of these rocks with tomographic models they show that intraplate volcanism can be used to constrain upper-mantle structure at the time of eruption.

Abstract It has been proposed that Oligo‐Miocene regional uplift of Madagascar was generated and is maintained by mantle dynamical processes. Expressions of regional uplift include flat‐lying Upper Cretaceous‐Paleogene marine limestones that crop out at elevations of hundreds of meters along the western seaboard and emergent Quaternary coral‐rich terraces that rim the coastline. Here, we explore the history of subcrustal topographic support through a combined analysis of four sets of observational constraints. First, we exploit published receiver function estimates of crustal thickness and spectral admittance between gravity and topography. An admittance value of ∼+40 ± 10 mGal km−1 at wavelengths >500 km implies that ∼1 km of topography is supported by subcrustal processes. Secondly, new apatite fission‐track and helium measurements from 18 basement samples are inverted, constraining temperature and denudation histories. Results suggest that 0.5–1.6 km of regional uplift occurred after ∼30 Ma. Thirdly, we calculate a history of regional uplift by minimizing the misfit between observed and calculated longitudinal river profiles. Results suggest that topography was generated during Neogene times. Finally, inverse modeling of rare earth element concentrations in Neogene mafic rocks indicates that melting of the asthenospheric source occurred at depths of ≤65 km with potential temperatures of 1300–1370 °C. Melting occurred at higher temperatures beneath Réunion Island and northern Madagascar and at lower temperatures beneath the Comores and southern Madagascar. These inferences are consistent with shear wave velocities obtained from tomographic models. We conclude that Madagascar is underlain by thinned lithospheric mantle and that a thermal anomaly lies within an asthenospheric layer beneath northern Madagascar.

The thermochemical structure of lithospheric and asthenospheric mantle exert primary controls on surface topography and volcanic activity. Volcanic rock compositions and mantle seismic velocities provide indirect observations of this structure. Here, we compile and analyze a global database of the distribution and composition of Neogene-Quaternary intraplate volcanic rocks. By integrating this database with seismic tomographic models, we show that intraplate volcanism is concentrated in regions characterized by slow upper mantle shear-wave velocities and by thin lithosphere (i.e. <100 km). We observe a negative correlation between shear-wave velocities at depths of 125–175 km and melt fractions inferred from volcanic rock compositions. Furthermore, mantle temperature and lithospheric thickness estimates obtained by geochemical modeling broadly agree with values determined from tomographic models that have been converted into temperature. Intraplate volcanism often occurs in regions where uplifted (but undeformed) marine sedimentary rocks are exposed. Regional elevation of these rocks can be generated by a combination of hotter asthenosphere and lithospheric thinning. Therefore, the distribution and composition of intraplate volcanic rocks through geologic time will help to probe past mantle conditions and surface processes.

The thermochemical structure of lithospheric and asthenospheric mantle exert primary controls on surface topography and volcanic activity. Volcanic rock compositions and mantle seismic velocities provide indirect observations of this structure. Here, we compile and analyze a global database of the distribution and composition of Neogene-Quaternary intraplate volcanic rocks. By integrating this database with seismic tomographic models, we show that intraplate volcanism is concentrated in regions characterized by slow upper mantle shear-wave velocities and by thin lithosphere (i.e. < 100 km). We observe a negative correlation between shear-wave velocities at depths of 125-175 km and melt fractions inferred from volcanic rock compositions. Furthermore, mantle temperature and lithospheric thickness estimates obtained by geochemical modeling broadly agree with values determined from tomographic models that have been converted into temperature. Intraplate volcanism often occurs in regions where uplifted (but undeformed) marine sedimentary rocks are exposed. Regional elevation of these rocks can be generated by a combination of hotter asthenosphere and lithospheric thinning. Therefore, the distribution and composition of intraplate volcanic rocks through geologic time will help to probe past mantle conditions and surface processes.

Abstract Spatio‐temporal changes of upper mantle structure play a significant role in generating and maintaining surface topography. Although geophysical models of upper mantle structure have become increasingly refined, there is a paucity of geologic constraints with respect to its present‐day state and temporal evolution. Cenozoic intraplate volcanic rocks that crop out across eastern Australia provide a significant opportunity to quantify mantle conditions at the time of emplacement and to independently validate geophysical estimates. This volcanic activity is divided into two categories: age‐progressive provinces that are generated by the sub‐plate passage of mantle plumes and age‐independent provinces that could be generated by convective upwelling at lithospheric steps. In this study, we acquired and analyzed 78 samples from both types of provinces across Queensland. These samples were incorporated into a comprehensive database of Australian Cenozoic volcanism assembled from legacy analyses. We use geochemical modeling techniques to estimate mantle temperature and lithospheric thickness beneath each province. Our results suggest that melting occurred at depths ≤80 km across eastern Australia. Prior to, or coincident with, onset of volcanism, lithospheric thinning as well as dynamic support from shallow convective processes could have triggered uplift of the Eastern Highlands. Mantle temperatures are inferred to be ∼50–100°C hotter beneath age‐progressive provinces that demarcate passage of the Cosgrove mantle plume than beneath age‐independent provinces. Even though this plume initiated as one of the hottest recorded during Cenozoic times, it appears to have thermally waned with time. These results are consistent with xenolith thermobarometric and geophysical studies.

The database published as part of this paper was collected and analyzed over a ten year period by the authors. It is a compilation of three individual suites of XRF, ICP-MS and Sr-Nd-Pb-He isotopic analyses. Samples that were analyzed using different protocols and procedures are identified by names of authors who carried out the analyses (ie Ball, Nixon, Masoud).

19 African basin-and-swell morphology is often attributed to the planform of sub-plate 20 mantle convection. Across North Africa, the coincidence of Neogene and Quaternary (i.e. 21 < 23 Ma) magmatism, topographic swells, long wavelength gravity anomalies, and slow 22 shear wave velocity anomalies within the asthenosphere provides observational constraints 23 for this hypothesis. Admittance analysis of topographic and gravity fields corroborates the 24 existence of sub-plate support. To investigate quantitative relationships between intraplate 25 magmatism, shear wave velocity, and asthenospheric temperature, we collected and an26 alyzed a suite of 224 lava samples from Tibesti, Jabal Eghei, Haruj, Sawda/Hasawinah 27 and Gharyan volcanic centers of Libya and Chad. Forward and inverse modeling of ma28 jor, trace, and Rare Earth elements were used for thermobarometric studies and to deter29 mine melt fraction as a function of depth. At each center, mafic magmatism is modeled 30 by assuming adiabatic decompression of dry peridotite with asthenospheric potential tem31 peratures of 1300–1360◦C. Surprisingly, the highest temperatures are associated with the 32 low-lying Haruj volcanic center rather than with the more prominent Tibesti swell. Our 33 results are consistent with earthquake tomographic models which show that the slowest 34 shear wave anomalies within the upper mantle occur directly beneath the Haruj center. 35 This inference is corroborated by converting observed velocities into potential tempera36 tures, which are in good agreement with those determined by geochemical inverse mod37 eling. Our results suggest that North African volcanic swells are primarily generated by 38 thermal anomalies located beneath thinned lithosphere. 39

African basin‐and‐swell morphology is often attributed to the planform of subplate mantle convection. Across North Africa, the coincidence of Neogene and Quaternary (i.e., <23 Ma) magmatism, topographic swells, long wavelength gravity anomalies, and slow shear wave velocity anomalies within the asthenosphere provides observational constraints for this hypothesis. Admittance analysis of topographic and gravity fields corroborates the existence of subplate support. To investigate quantitative relationships between intraplate magmatism, shear wave velocity, and asthenospheric temperature, we collected and analyzed a suite of 224 lava samples from Tibesti, Jabal Eghei, Haruj, Sawda/Hasawinah, and Gharyan volcanic centers of Libya and Chad. Forward and inverse modeling of major, trace, and rare Earth elements was used for thermobarometric studies and to determine melt fraction as a function of depth. At each center, mafic magmatism is modeled by assuming adiabatic decompression of dry peridotite with asthenospheric potential temperatures of 1300‐1360 °C. Surprisingly, the highest temperatures are associated with the low‐lying Haruj volcanic center rather than with the more prominent Tibesti swell. Our results are consistent with earthquake tomographic models which show that the slowest shear wave anomalies within the upper mantle occur directly beneath the Haruj center. This inference is corroborated by converting observed velocities into potential temperatures, which are in good agreement with those determined by geochemical inverse modeling. Our results suggest that North African volcanic swells are primarily generated by thermal anomalies located beneath thinned lithosphere.

It is agreed that mantle dynamics have played a role in generating and maintaining the elevated topography of Anatolia during Neogene times. However, there is debate about the relative importance of subduction zone and asthenospheric processes. Key issues concern onset and cause of regional uplift, thickness of the lithospheric plate, and the presence/absence of temperature and/or compositional anomalies within the convecting mantle. Here, we tackle these interlinked issues by analyzing and modeling two disparate suites of observations. First, a drainage inventory of 1,844 longitudinal river profiles is assembled. This database is inverted to calculate the variation of Neogene regional uplift through time and space by minimizing the misfit between observed and calculated river profiles subject to independent calibration. Our results suggest that regional uplift commenced at 20 Ma in the east and propagated westward. Second, we have assembled a database of geochemical analyses of basaltic rocks. Two different approaches have been used to quantitatively model this database with a view to determining the depth and degree of asthenospheric melting across Anatolia. Our results suggest that melting occurs at depths as shallow as 60 km in the presence of mantle potential temperatures as high as 1400°C. There is evidence that temperatures are higher in the east, consistent with the pattern of subplate shear wave velocity anomalies. Our combined results are consistent with isostatic and admittance analyses and suggest that elevated asthenospheric temperatures beneath thinned Anatolian lithosphere have played a first‐order role in generating and maintaining regional dynamic topography and basaltic magmatism.

Crustal thickness, drainage inventory and igneous geochemical data for Anatolia. Dataset S1 is compilation of published receiver function estimates of Anatolian crustal thickness. Station names and locations, number of receiver functions modeled, estimated Moho depth, and technique employed are all given where available. Note that elevations are extracted from topographic grid that is low-pass filtered for wavelengths> 30 km. Dataset S2 is drainage inventory as a multi-segment. csv file. Format is: latitude (◦), longitude (◦), elevation (m), longitudinal distance (m) and upstream drainage area (m^ 2). River profiles were extracted from SRTM digital elevation model of using Arc-GIS flow-routing algorithms. Dataset S3 is compilation of all available geochemical analyses for Neogene magmatic rocks from Anatolia. Ages are assigned either by radiometric dating or by stratigraphic relationships. Although only samples with MgO> 5 wt% were used in this study, samples with MgO> 4 wt% are included for completeness. Major elements are normalized so that the sum of weights= 100 wt%. We also provide estimates of melt equilibration pressure and temperature.