Mantle Plume Research Articles

Review of morphotectonic studies in the East African Rift System: Insights from legacy research to modern advances

The East African Rift System (EARS) is a prime example of continental rifting, characterized by its iconic topographic features, which are significantly shaped by the interplay of tectonic and climatic forces. This review synthesizes past decades of morphotectonic studies (recent studies) on the plateau landscapes of the EARS, focusing particularly on their interiors and margins, and highlights their crucial role in advancing our understanding of landscape evolution. The paper revisits the legacy of geologic research in the EARS and delves into recent morphotectonic studies that quantify the rates and patterns of plateau incision, exhumation, and uplift through advanced thermochronological and topographic analyses. Additionally, the review identifies key unresolved questions, such as the origins of the plateau topography–whether from volcanic activity or mantle plume influence and explores how these plateaus maintained high elevations during the humid Oligocene Epoch without significant incision. The recent work described in this paper alongside legacy perspectives, continues to refine our geological understanding of the EARS, with broader implications for studies worldwide.

The Gulf of Suez rifting: implications from low-temperature thermochronology

ABSTRACT The Gulf of Suez is a continental rift basin that has been developed during the Oligocene-Miocene as a northern extension of the Red Sea rift system. The Oligo-Miocene rift-activated flanks are represented by exposures of the Neoproterozoic basement rocks of the Arabian-Nubian Shield. An additional thermal overprint (i.e. mantle plume) and the preceding tectono-thermal events that also affected the rifting dynamics and the uplift of its flanks remain uncertain. We here present thermochronological data for 20 basement samples collected from the Gabal Somr ElQaa area at the northwestern flank of the Gulf of Suez. The resulted zircon fission-track ages could be divided temporospatially into two groups: the Cambrian and the Silurian-Devonian with average ages of 503 ± 14 Ma and 407 ± 11 Ma, respectively. While apatite fission-track data reveal three different age groups of the Devonian-Carboniferous, the Permian-Triassic, and the Late Cretaceous, with average ages of 349 ± 10 Ma, 246 ± 6 Ma, and 81 ± 5 Ma, respectively. The modelled t-T histories indicate four cooling pulses during the Neoproterozoic, the Devonian-Carboniferous, the Cretaceous, and the Oligocene-Miocene. Integrating our findings with the regional tectonism and depositional records indicates that these cooling pulses could be attributed to synchronous activities of the post-accretion erosional event, the Variscan tectonic event, the Mid-Atlantic Ridge spreading, and the Gulf of Suez rifting. The Gulf of Suez is a passive rift, formed by a single and rapid rifting pulse within the framework of the Red Sea rift system. An additional east-southward far-field thermal overprint from the Arabian marginal plume partially affected the Suez rifting process. This thermal print affected only the rift’s southern portion of its eastern flank, causing syn-rift cooling ages, highly elevated rift flanks, and an increased heat flow. The western rift flank and the northern segment of the eastern flank are characterized by pre-rift cooling ages, modest rift flanks, and reduction in heat flow.

Mechanisms of Co enrichment in the Zhubu Ni–Co–PGE deposit in the Emeishan LIP, SW China: Constraints from mineral geochemistry and Fe–S isotopes of sulfides

The Zhubu Ni–Co–PGE sulfide deposit in the Permian Emeishan Large Igneous Province (LIP), SW China is hosted by a mafic–ultramafic intrusion that comprises two morphologically distinct ore-forming spaces: a central, layered sequence that represents a magma chamber surrounded by a marginal sub-vertical conduit zone. The marginal conduit zone contains significant Ni–Co–PGE sulfide mineralization, suggesting that high volumes of sulfide-bearing silicate melt flowed through the magma conduit system. Determining the hosts of Co is key to understanding the Co enrichment process in the Zhubu deposit, as well as in the Emeishan LIP as a whole. We assess this here using the geochemistry and Fe–S isotope compositions of sulfides in the Zhubu deposit. Cobalt is mainly concentrated in pentlandite sulfide in the websterite, with Co contents increasing in the order pyrrhotite < chalcopyrite < pyrite < pentlandite < violarite; the abundance of violarite, however, is notably lower than that of the other sulfides. The Co contents of pentlandite, pyrite, and chalcopyrite are negatively correlated with their Ni and Fe contents, suggesting that Co substitutes isomorphically for Ni and Fe in the sulfide structure. The δ56Fe values of sulfides increase in the order pyrrhotite < chalcopyrite < pentlandite < pyrite resulted from kinetic fractionation of Fe isotopes. The δ56Fe values of pentlandite and chalcopyrite in lherzolite are higher than those in websterite, implying that lherzolite and websterite formed in compositionally distinct magmas, Fe isotope compositions become heavier with crystal fractionation. The δ34S values of sulfides increase in the order pyrrhotite < pentlandite < chalcopyrite < pyrite, similar to the fractionation sequence of sulfide melts, suggesting that externally derived S was added to the magma and contributed to its sulfide saturation. The Co contents of chalcopyrite and pyrite vary positively with δ56Fe values, and negatively with δ34S values, indicating that the addition of externally derived S and resulting sulfide segregation were critical to Co enrichment.

Electrical conductivity of mantle minerals beneath East Asia revealed by geomagnetic observatory data

The electrical conductivity of the earth’s mantle can provide important information about geodynamic phenomena. East Asia is associated with complex tectonics and geodynamic processes. Hence, it is necessary to better understand the deep structure beneath East Asia. In this study, geomagnetic data obtained from East Asian observatories are employed to image the conductivity structure of the mantle at depths ranging from 410 to 900 km. First, the data are processed using the modified bounded influence remote reference processing (BIRRP) method and the ratio method is used to correct for the ocean effect. Thereafter, the stable C-response curves at the 27 observatories are estimated, and 1D electrical conductivity models for these observatories are established using the L-BFGS method. The conductivity-depth profiles reveal a heterogeneous distribution of the electrical conductivity beneath East Asia. The mantle transition zone (MTZ) beneath East China and Japan is found to be more conductive, whereas the MTZ beneath central and southern regions of China is more resistive. In East China, the dehydration of the stagnant Pacific slab may lead to an increase in the conductivity of the mantle minerals. There is also the possibility of upwelling of the thermal material from the lower mantle beneath the Japanese Island arc. In Northwest China, there exists a large high-conductive body beneath the Tarim area, which could indicate an upwelling of the Tarim mantle plume. Our results provide insights into the deep structure of the earth at the mantle scale.

Anatomy of the Emeishan Mantle Plume Head: Insights From New Geochronologic, Geochemical, and Geologic Data

AbstractThe link between mantle plumes and the formation of large igneous provinces (LIPs) is well established although the anatomy of these remains equivocal. Recent experimental studies and geophysical data suggest that the mantle plume head is more likely to be irregular and asymmetric, rather than an axisymmetric flattened disk. The Emeishan large igneous province (ELIP) provides a unique opportunity to test this hypothesis. According to robust petrographic, geochronologic, and geochemical evidence from the late Permian basalts in the Sichuan Basin, and in conjunction with a comprehensive compilation of geologic maps and published geochemical data from the ELIP, we identified several giant radial “fingering” structures. Based on the shallow mantle source from the center to margin in the ELIP and relief of the lithosphere‐asthenosphere boundary, we propose a new mantle plume model to explain the evolution of the Emeishan plume periphery, where narrow finger‐like protrusions and plumelets developed outwards from the main body of the plume to the edges of the flattened plume head. Dragged fingers might have been torn apart into some plumelets, which dispersed and were trapped beneath the thinnest lithosphere relief, and eventually erupted to form small‐scale flood basalt in the Outer Zone of the ELIP.

Tectonic evolution of the Early Paleozoic proto-East Asian continental margin: Inference from Paleozoic metamorphic rocks in the South Kitakami belt, northeast Japan

To constrain the incipient Pacific-type orogeny and tectonic processes in the Early Paleozoic proto-East Asian continental margin, the Motai–Matsugadaira–Yamagami (MMY) metamorphic rocks in the South Kitakami belt, northeast Japan were investigated. They are divided into two different types: amphibolite-facies rocks associated with serpentinite and blueschist-facies rocks associated with pelitic and psammitic schists. Three geochemical groups are identified from the MMY metamorphic rocks. Groups 1 and 2 resemble geochemical characteristics of mid-ocean ridge basalt and continental arc rocks, respectively. Group 3 exhibits considerable depletion of highly incompatible elements, which is caused by the high degree of partial melting of a hot mantle plume. The zircon U–Pb ages of Group 1 indicate that the protoliths experienced amphibolite-facies metamorphism soon after their formation in the Early Ordovician. Group 2 exhibits a coeval zircon U–Pb age with Group 1. The age distribution of detrital zircons in the MMY psammitic schists shows a peak of 500–400 Ma, the presence of Archean to Neoproterozoic zircons, and the youngest Late Devonian zircon. The following model is proposed for the tectonic evolution of the proto-East Asian continental margin: (1) the formation of an arc in the eastern margin of the South China craton in the Cambrian to Ordovician; (2) the subduction of a spreading axis and an oceanic plateau at the same time as the continental arc formation; (3) the consumption and subduction of arc materials by tectonic erosion; and (4) the formation of the Carboniferous accretionary complex and high-pressure metamorphic rocks under steady oceanic plate subduction. The proposed tectonic evolution model may also be applicable to equivalent Early Paleozoic rocks in southwest Japan.

Craton deformation from flat-slab subduction and rollback

The mechanisms underlying the deformation and eventual destruction of Earth’s cratons remain enigmatic, despite proposed links to subduction and deep mantle plume processes. Here we study the deformation of the North China Craton using four-dimensional mantle flow models of the plate–mantle system since the late Mesozoic, integrating constraints from lithospheric deformation, mantle seismic tomography and the evolution of surface topography. We find that flat-slab subduction induced landward shortening and lithospheric thickening, while subsequent flat-slab rollback caused seaward extension and lithospheric thinning. Both subduction phases resulted in substantial topographic changes in basin sediments. Rapid flat-slab rollback, coupled with a viscosity jump and phase change across the 660 km mantle discontinuity, was a key ingredient in shaping a large mantle wedge. We argue that craton deformation through lithospheric extension and thinning was triggered by the subduction of a flat slab and its subsequent rollback. The integration of data into mechanical models provides insights into the four-dimensional dynamic interplay involving subduction, mantle processes, craton deformation and topography.

Is the mantle transition zone uniform beneath Precambrian shields?

In the present study, we examine the mantle transition zone (MTZ) structure below the prominent Precambrian shields on the Earth to understand its thermal and compositional properties and depth distribution of MTZ discontinuities. For this study, we used data from Canadian, Brazilian, Baltic, African and Australian Shields. We migrate the receiver functions to the depth domain using 3D tomographic models to examine the topography of MTZ discontinuities that define the upper and lower boundaries of the MTZ. The depth migration results were obtained using two different 3D tomographic velocity models, LLNL_G3D_JPS and GyPSuM. The analysis shows that both models yield similar results. The findings indicate a thinner than usual MTZ beneath all the Precambrian shields with an average thickness of ∼238 ± 8 km. Notably, the present study reveals the upper boundary of the MTZ (410 km discontinuity) displays distinctive topography; in contrast, the lower boundary of the MTZ (660 km discontinuity) is situated at shallower depths. Therefore, the main factor causing the variation in MTZ thickness is the shallowing of the 660 km discontinuity, indicating that the post-spinel transition occurred at higher temperatures with a negative Clapeyron slope, supporting the theory of whole-mantle convection. This suggests that mantle plumes have some appreciable impact on the MTZ beneath Precambrian shields, which are limited to the base of the MTZ. Alternatively, the global mantle warming explanation could be invoked, as it best explains the similar characteristics of the 660 km discontinuity beneath the Precambrian shields. However, this phenomenon needs to be tested through numerical modelling.

Deciphering the 3D density structure using gravity data in the Vitória-Trindade Ridge, South Atlantic-Brazil

The Vitória-Trindade Ridge, situated in the central South Atlantic Ocean, is the longest aseismic ridge. The ridge comprises alkaline volcanic formations, including seamounts such as Davis, Colúmbia, Congress banks, Jaseur, Montague, and Vitória. The VTR resulted from a mantle plume, making it structurally complex. A study was conducted to investigate the structure of the VTR using gravity anomalies and bathymetric data. The study revealed the 3D structure of seamounts in terms of their density, depth, and volume. The results showed that the volume of seamounts with depth of VTR ranges from 10 to 14 km. Additionally, the uneven distribution of density contrast indicates the complex structure of the VTR region.

A subduction-dismembered Neoproterozoic large igneous province in the Qinling Orogenic Belt, China: Implications for 850 Ma–initiated mantle plume activity in the greater Yangtze Block

Large igneous provinces (LIP) provide invaluable clues for recognizing the growth, breakup, and cycles of supercontinents and constraining the activity of ancient mantle plumes (or superplumes). The widespread intraplate magmatism is considered as a possible fingerprint of ancient plume activities and LIPs. Here, we present the results of an integrated study on protoliths of eclogites and amphibolite-facies bimodal volcanic rocks from North Qinling Ultrahigh-pressure Metamorphic (UHPM) Terrane, Qinling Orogen, and identify a dismembered Neoproterozoic LIP. These rocks share similar protolith ages of ca. 850–800 Ma and experienced high- to ultrahigh-pressure metamorphism at ca. 500–480 Ma. The mafic rocks are mainly tholeiitic and display enrichment of LILEs and HFSEs, similar to the E-MORB/OIB characters. They also have typical features of continental flood basalts (CFBs) with low CaO/Al2O3 (0.68–0.87), Lu/Yb (0.14–0.15), Zr/Nb (8–13), high Nb/La (0.87–1.24, mean 1.07), La/Nb (0.80–1.15), La/Ta (11–20), Nb/Yb (3.0–6.2) ratios, and positive εNd(t) (+4.3 to + 5.4). Their occurrence, geochemical features, age data, and high mantle potential temperature (1500–1550 °C) suggest that they are remnants of Neoproterozoic CFBs with mantle plume origin. Based on the lateral distribution length (ca. 300 km) of meta-basaltic rocks and the maximum subduction depths (ca. 100–200 km) recorded by UHP eclogites, the identified ca. 850 Ma-initiated CFBs in the North Qinling terrane should represent an LIP, covering more than 100,000 km2. This Neoproterozoic LIP, together with the coeval volcanic sequences in the South Qinling terrane and the northern Yangtze, would have occupied a maximum landmass of 300,000 km2, which lends support for the onset of a mantle plume at ca. 850 Ma within the Rodinia supercontinent. We conclude that the Qinling Block is one of the fragments of the Rodinia supercontinent with a passive margin covered by CFBs, which was subducted to mantle depths in the Early Paleozoic.

Discovery of mafic dikes in northeastern Tibet plateau belonging to the Emeishan large igneous province: Implications for paleocontinental reconstruction and mineral exploration

Due to the lack of paleomagnetic data and paleoclimatic records, the paleocontinental belonging of the Yidun terrane in northeastern Tibet plateau is debated. In this paper, we use the distribution of the Emeishan large igneous province (ELIP) to put the issue to rest. The ELIP is the product of mantle plume activity, which took place at 260 ± 3 Ma in the western margin of the Yangtze craton. The Yangtze craton is the northern part of the South China paleocontinental block. Our new discovery of four mafic dikes in the Yidun terrane with ages and chemistry like the ELIP strongly supports a new interpretation that this terrane was an integral part of the Yangtze craton during the ELIP magmatic event. Baddeleyites from these mafic dikes yield the U–Pb ages of 257.1 ± 4.8, 259.8 ± 8.5, 260.2 ± 4.5 and 261.5 ± 6.8 Ma for each of these dikes, which are similar to the zircon U-Pb ages of the mafic–ultramafic intrusions of the ELIP within the Yangtze craton. The Yidun mafic dikes and some high-Ti basalts of the ELIP within the Yangtze craton have similar Sr-Nd isotope compositions and mantle-normalized incompatible trace element distribution patterns, indicating similar mantle source compositions. Mixing calculation using Sr-Nd isotope compositions shows that the parental magmas for the Yidun mafic dikes experienced only 2–3 % crustal contamination. Partial melting modelling shows that the primary magmas for the Yidun mafic dikes were produced by 5–6 % mantle partial melting at the depths > 85 km below surface, consistent with mantle plume-related magmatism in a continental setting. The Yidun terrane is a new exploration frontier for magmatic Fe-Ti-V oxide deposits that are present elsewhere in the ELIP.

Enrichment Characteristics and Mechanisms of Lithium, Gallium, and Rare Earth Elements (REY) within Late Permian Coal-Bearing Strata in Wanfu Mine, Xian’an Coalfield, Guangxi Province, Southwest China

The study of lithium (Li), gallium (Ga), and rare earth elements (REY) within coal-bearing strata represents a cutting-edge concern in coal geology, ore deposit studies, and metallurgy research. With the rapid advancement of technology and emerging industries, the global demand for Li-Ga-REY has significantly escalated. Several countries worldwide are facing immense pressure due to shortages in Li-Ga-REY resources. Coal-associated Li-Ga-REY depositions have emerged as a pivotal direction for augmenting Li-Ga-REY reserves. To ascertain the enrichment distribution patterns and genetic mechanisms of Li-Ga-REY within the coal-bearing strata of the late Permian Heshan Formation in Wanfu mine, Xian’an Coalfield, Guangxi Province, this study carried out comprehensive testing and analysis on Li-Ga-REY enriched in the mineralized layers within the strata. The Heshan Formation in Wanfu mine presents four layers of Li-Ga-REY-enriched mineralization, labeled from bottom to top as mineralized layers I, II, III, and IV, corresponding to coal seams K5, K4, K3, and K2. These critical metals are predominantly hosted within clay minerals (kaolinite, illite/smectite, and chlorite). The enrichment of critical metals within the Heshan Formation is closely related to terrigenous detrital materials from the Daxin paleocontinent, volcanic detrital materials induced by the Emeishan mantle plume and the Yuenan magmatic arc. The accumulation of Li-Ga-REY and other critical elements within the mineralized layers is the result of inputs from terrestrial and volcanic detrital sources, interactions between peatification and diagenesis stages, and occasionally the input of metal-enriched fluids. In the mineralized layers I, II, and III, the content of lithium oxide (Li2O) surpasses the boundary grade, and the levels of REY, Ga, and (Nb,Ta)2O5 are close to boundary grades, indicating promising exploration prospects. The Wanfu mine in the Xian’an Coalfield can be considered a primary target zone for the exploration and development of coal-associated critical metal resources in Guangxi.

Pan-African and Early Paleozoic Orogenic Events in Southern Tibet: Evidence from Geochronology and Geochemistry of the Kangbuzhenri Gneissic Granite in the Zhegu Area

The Zhegu area in southern Tibet is situated in the central and eastern part of the Tethys Himalayan tectonic belt, with the Kangbuzhenri area being abundant in gneissic granites. This study examines the petrology, chronology, and geochemistry of the Kangbuzhenri gneissic granite, providing insights into its Pan-African and Early Paleozoic geological evolution. The zircon U-Pb chronology indicates an upper intercept age of ~539 Ma, reflecting Pan-African orogenic events in the eastern part of the Tethys Himalayan tectonic belt, and a lower intercept age of ~144 Ma, representing a late tectonic–thermal event. Geochemically, the gneissic granites are calc-alkaline peraluminous rocks with high SiO2 and Al2O3 contents and low TiO2, P2O5, MgO, and FeOT contents. The gneissic granites are enriched in LREE and LILEs (Rb, Pb, Th, U, etc.), but relatively depleted in HREE and HFSEs (Nb, Ti, P, etc.). Most of them show a weak negative δEu anomaly, except for two samples which show a significant negative δEu anomaly due to the crystallization of plagioclase. Based on the above study, most of the gneissic granites exhibited the characteristics of an I-type granite, while two of the samples were a highly differentiated I-type granite with S-type affinities. All the above characteristics indicate that the gneissic granite likely originated from the partial melting of crustal materials and sediments with a minor involvement of mantle-derived materials. Combined with the previous chronological studies, the Kangbuzhenri gneissic granites were formed in an extensional tectonic environment during post-collision orogeny and then they were influenced by the Kerguelen mantle plume tectonic–thermal event around ~144 Ma and the subsequent Southern Tibet Detachment System (STDS).

Subsurface structural trends in Central-Western India: Inferences from magnetotelluric data using the complex MT apparent resistivity tensor

The central-western part of the Indian subcontinent exhibits significant geological diversity and possesses a rich record of different tectonothermal events in the earth's evolutionary history, spanning from the Archean to the present. Precambrian geology in the region is mostly obscured by Cretaceous-Tertiary/Paleocene volcanic eruptions and Proterozoic to Quaternary/recent sedimentary cover. Magnetotelluric (MT) impedance and tipper responses from 146 stations, covering central-western India in a grid fashion with a spacing of ∼55 km, were analyzed to evaluate the subsurface structural trends, dimensionalities, and qualitative characteristics of the electric lithosphere in the region. An advanced Complex Apparent Resistivity Tensor (CART) approach, along with the popular Phase Tensor (PT) approach and induction arrows are utilized to achieve the above goals. The analysis revealed a high degree of 3D induction effects in the data at almost every station and period. The directionality information retrieved from the tensor properties showed that the structural trends in the deep crust and upper mantle of the major geologic domains correlate with the known surface tectonic trend of the respective geologic domain. This study provides vital evidence to support the suspected bifurcation of the Precambrian Aravalli-Delhi Mobile Belt (ADMB) tectonic trend and its extensions into neighboring Kutch, Saurashtra, and Central Indian Tectonic Zone (CITZ) domains. The analysis results indicate a lithospheric scale enhanced conductivity beneath the Malwa plateau, which marks the first major phase of the Reunion mantle plume eruption in India. A critical finding of this study is that the Resistivity Phase Tensor better defines the subsurface resistivity structure and provides much clearer structural information than the conventional Phase Tensor.

The role of deformation on the early crystallization and rheology of basaltic liquids

This study highlights the rheological variation of magmatic systems during the early crystallization stage, which undergoes very different shear stress. Etna basaltic glass, made from natural rock powder, was used as a starting material. Nine shear rate-controlled experiments were conducted at 1150 °C (below liquidus temperature and undercooling degree ΔT ∼ 40 °C) with shear rates (γ˙) of 0.1, 1 and 10 s−1 using wide-gap concentric cylinder viscometry. Three additional experiments were conducted without spinning the melts (no shear, γ˙= 0 s−1). Run-products were collected after 3, 6 and 9 h. The experiment with the highest shear rate (γ˙=10s−1) showed a brittle failure when viscosity reached the value of 2.90 log (Pa·s) and after ca. 1150s. The measured viscosity matches the shear stress at 7244 Pa, corresponding to the brittle failure in our partly crystallised system at these conditions. After 9 h, the response of the partly crystallised Etna basalt to different deformation rates results in decreasing viscosity from 4.89 to 3.83 and 2.90 (log Pa s) as the γ˙ increases from 0.1 to 1 and 10 s−1, respectively. The main outcome of this study relates to the nucleation and growth of minerals with shear deformation. The deformation-free (γ˙ = 0 s−1) runs show the presence of only two phases: glass and Fe-oxides (Fe-ox) with only a few vol% (1–3) of oxides crystals after 3, 6 and 9 h. The deformation-bearing (γ˙ = 0.1, 1 and 10 s−1) runs show different scenarios: after 3 h, we observed only Fe-ox for a γ˙ of 0.1 s−1 (similar to deformation-free ones). As the shear rate increases to 1 s−1 and 10 s−1, solid phases after 3 h experiments are Fe-ox, plagioclase and clinopyroxene. Crystal growth rate depends on the applied shear rate: the highest rate is 1.1 × 10−6 cm/s and was measured for plagioclase after a 3 h experiment for γ˙ = 10 s−1. At γ˙ = 0.1 s−1, the plagioclase growth rate decreases to 2.70 and 1.35 × 10−6 cm/s as experimental time increases from 6 to 9 h, respectively. The vast range of shear stress and the systematic data obtained in this study are fundamental to deciphering crystallization dynamics suffered by magmas in volcanic reservoirs, dikes, conduits and lavas.

Structural analysis and evolution of large Venusian coronae: Insights from low-angle faults at coronae rims

We analyzed topography, fracture patterns, and faults of the asymmetric Atahensik Corona (700 × 900 km diameter), formerly known as Latona Corona, and their surrounding troughs using Magellan SAR imagery, and compare the results with the smaller, ovoid Didilia (400 × 450 km diameter) and Pavlova coronae (550 × 650 km diameter) to get insights on corona formation on Venus. Atahensik contains a high density of radial, oblique, and concentric fractures, the latter are inferred to be the youngest fractures. A high density of concentric fractures particularly occurs along the outer rise and indicates elastic downward bending of this part of the lithosphere in the later stage of corona formation. Along the steep inner slopes of Atahensik's arcuate troughs, large-scale faults are exposed that dip gently towards the corona center and crosscut all fractures. We propose that these low-angle faults were initially formed as thrust planes but subsequently became reactivated as low-angle normal faults, thereby exposing parts of their fault surfaces. Such faults have been identified not only along the arcuate troughs of Atahensik but also occur in Dali Chasma, northwest of Atahensik Corona.A phenomenological formation model of large coronae is presented: corona initiation starts with radial fracturing, which is caused by the dike emplacement and thermal uplift of the corona center due to the rise of a hot asthenospheric mantle plume. Uplift and lateral plume spreading steepen the outer rim of the uplift and cause intense radial fracturing of a central volcanic edifice and the corona's outer rim. This intermediate stage is preserved in several less-evolved coronae such as Didilia and Pavlova Coronae. The fractured ridge thrusts outward onto an intact and cooler lithosphere along strongly localized thrust planes. The overthrusted, cooler lithosphere is elastically bent downward and forms arcuate troughs and associated outer rises with numerous concentric fractures along their crest line. The fractured ridge annulus of the corona is supported by the intact and thickened lithosphere surrounding the corona. The present morphology of Atahensik Corona indicates subsequent subsidence in its central part due to declining plume activity and reduced thermal buoyancy. Reactivation of the thrusts as low-angle normal faults results from the subsidence of the corona interior, a gravitational instability of the elevated corona annulus, and a lack of shortening. The evolutionary sequence derived on the basis of structural data is in agreement with geodynamic models on corona formation involving a bending lithosphere at the plume margin.

Early terrestrial and lunar anorthosites: Comparative geochemistry and evolutionary processes

In a paper in 1970, Brian Windley first recognised that early terrestrial and lunar anorthosites both have calcic plagioclase, and low TiO2and high CaO and Al2O3contents. Despite these similarities, the geochemistry of early terrestrial and lunar anorthosites has not been rigorously compared and contrasted. To this end, we compiled 425 analyses from 212 early terrestrial anorthosite occurrences and 306 analyses from 16 lunar anorthosite occurrences. This was supplemented by a compilation of plagioclase anorthite (An) contents and pyroxene Mg# from early terrestrial and lunar anorthosites. Early terrestrial anorthosites have lower whole-rock An contents but similar Mg# to lunar anorthosites. The CaO contents of lunar anorthosites are higher than those of early terrestrial anorthosites for a given MgO and Al2O3content, early terrestrial anorthosites have higher SiO2contents than lunar anorthosites at a given MgO content, and lunar anorthosites have higher Eu/Eu* anomaly ratios yet broadly similar La/Yb and Nd/Sm ratios than early terrestrial anorthosites. Some early terrestrial anorthosites have less fractionated chondrite-normalised rare earth element (REE) patterns and less prominent positive Eu anomalies than lunar anorthosites. Lunar anorthosites have higher plagioclase An contents, yet a similar range of pyroxene Mg# compared to their early terrestrial counterparts. Some early terrestrial anorthositesare more fractionated than some lunar anorthosites. Our interpretations imply that most early terrestrial anorthosites crystallised from basaltic parental magmas that were generated by high-degree partial melting of sub-arc asthenosphere mantle wedge sources that were hydrated by slab-derived fluids, with the remainder being associated with mid-ocean ridge and mantle plume settings. Some of the arc-related early terrestrial anorthosites were influenced by crustal contamination. In addition, early terrestrial anorthosites originated from partial melting of the mantle at various depths with variable garnet residua, whereas lunar anorthosites formed without any significant garnet residua. Lower plagioclase CaO contents and pyroxene Mg# in early terrestrial anorthosites can be explained by higher proportions of clinopyroxene and olivine fractionation in terrestrial magma chambers than in the lunar magma ocean where orthopyroxene and olivine fractionation occurred. Low TiO2contents in both terrestrial and lunar anorthosites reflect rutile and/or ilmenite fractionation.

The constant oxidation state of Earth’s mantle since the Hadean

Determining the evolutionary history of mantle oxygen fugacity (fo2) is crucial, as it controls the fo2 of mantle-derived melts and regulates atmospheric composition through volcanic outgassing. However, the evolution of mantle fo2 remains controversial. Here, we present a comprehensive dataset of plume-derived komatiites, picrites, and ambient mantle-derived (meta)basalts, spanning from ~3.8 Ga to the present, to investigate mantle thermal and redox states evolution. Our results indicate that fo2 of both mantle plume-derived and ambient mantle-derived melts was lower during the Archean compared to the post-Archean period. This increase in the fo2 of mantle-derived melts over time correlates with decreases in mantle potential temperature and melting depth. By normalizing fo2 to a constant reference pressure (potential oxygen fugacity), we show that the fo2 of both the mantle plume and ambient upper mantle has remained constant since the Hadean. These findings suggest that secular mantle cooling reduced melting depth, increasing the fo2 of mantle-derived melts and contributing to atmospheric oxygenation.

Yampi Peninsula felsic Hart Dolerite: re-evaluating the Nellie Tonalite using evidence from whole rock, petrography and geochronology

The Nellie Tonalite forms a discontinuous 20 km elongate northwest-trending felsic intrusion at the far-western end of the Western Zone of the Lamboo Province, in the Wunaamin Miliwundi Orogen, Western Australia. This intrusion is poorly understood with previous interpretations assigning it to the ca 1860 Ma Paperbark Supersuite. We present the first geochronological results for the Nellie Tonalite, which have a weighted mean laser ablation, inductively coupled plasma, mass spectrometry (LA-ICP-MS) U–Pb zircon age of 1794 ± 4 Ma. This date is coincident with the age for felsic granophyres of the Hart Dolerite, which have previously been described from the Kimberley Basin overlying the Halls Creek Orogen and central parts of the Wunaamin Miliwundi Orogen. Other similarities of the Nellie Tonalite with the felsic Hart Dolerite are micrographic and granophyric intergrowths of quartz and K-feldspar, and a distinct geochemical depletion of V. This V depletion is interpreted to be the result of closed-system, in situ fractional crystallisation of titanomagnetite from a basaltic composition. The fractional residue from this process can be found at several locations across the Halls Creek Orogen and Wunaamin Miliwundi Orogen and at Speewah Dome in the east Kimberley where magnetite gabbros within the Hart Dolerite also host a large Ti–V mineral resource. It is proposed that the Nellie Tonalite is a western correlate of the felsic Hart Dolerite. This demonstrates that the magmatic processes required for Speewah-style Ti–V mineralisation are extensive across the entire Lamboo Province. Additionally, the scale, constancy of the composition, texture and age of the felsic Hart Dolerite encompassing the entire inland margin of the Kimberley Region, and the rapid emplacement time of <3 m.y., support the interpretation of a mantle plume model for the emplacement of the Hart Dolerite.

Lamprophyres from the Chhota Udaipur alkaline–carbonatite sub-province, Deccan Large Igneous Province, India: implication for petrogenesis and crustal structure

This paper discusses the petrogenesis of lamprophyre dykes occurring in the Chhota Udaipur Alkaline–Carbonatite Sub-province (CUACS). Both calc-alkaline as well as alkaline varieties occur in the area. The major and trace elements geochemistry of the CUACS lamprophyres display good correlation with each other and other Deccan-related lamprophyres. Trace element ratios reveal a minor role of crustal contamination and support their derivation from partial melting of a lithospheric mantle source that is significantly modified by interaction with asthenosphere-derived melts emanating from an impinging mantle plume. The restricted initial 87 Sr/ 86 Sr (0.70599–0.70658) and 143 Nd/ 144 Nd (0.512501–0.512513) ratios of the CUACS lamprophyres further attest to their derivation from an ocean island basalts (OIB)-type parental melt. Their negative εNdi values (−1 to −6) are comparable with other lamprophyres of the Deccan Large Igneous Province (LIP). The lamprophyres from the present study share similar geochemical characteristics to Mt Girnar lamprophyres, which are derived from the spinel–garnet transition zone at a depth of ∼85 km, distinct from the previously considered depth (∼100 km) of the post-Deccan lithosphere–asthenosphere boundary (LAB) beneath NW India. Such geochemical characteristics of the Chhota Udaipur lamprophyres indicate a vital role of plume–lithosphere interaction at the thermal boundary layer at about ∼66 Ma.