Mantle Superplume Research Articles

DEFORMATION INTERACTION OF STRONG EARTHQUAKES OF 2010–2016 IN THE ZONE OF INFLUENCE OF THE HIKURANGA SUPERPLUME (NEW ZEALAND) ACCORDING TO GPS OBSERVATIONS

Between 2010 and 2016, a series of 11 strong M>6 earthquakes occurred in New Zealand. In the area covering the epicentral zones of these seismic events, the spatiotemporal characteristics of movements and deformations of the Earth’s crust were obtained based on the processing of continuous satellite GPS observations at 64 points of the geodetic network. Using these data, we have studied the evolution of horizontal movements and deformations in order to reveal the possible relationship between the observed deformational and seismic processes. Analysis has been made on the total shear deformation, since the main tectonic structures of the region are faults with a shear mechanism of displacement of their sides. The presence of a giant mantle superplume in the area was the reason for the study of the behavior of horizontal dilatation deformation, and horizontal and vertical crustal motions. Based on the obtained digital deformation models, there were created kinematic visualizations, which are synoptic animations providing direct observations of the seismic deformation process and their heuristic analysis. The study revealed that a series of the strongest earthquakes may be interconnected by a long-term single deformation process, which is caused by the occurrence of an anomalous total shear deformation. The general maximum of shear deformation, dilatation deformation, and horizontal and vertical displacements are concentrated in the center of mantle superplume activity. Prior to strong seismic events, there occur zones of deficit (minimum) displacements of the Earth’s crust in the area of future epicenters, which is of research interest in terms of predicting their locations.

Precambrian history of the Pacific Mantle Domain: New constraints from Woodsreef and Port Macquarie serpentinized spinel harzburgites of the New England Orogen, Australia

Abstract The present-day mantle is divided into the African and Pacific domains by the circum-Pacific subduction girdle. Very little is known about the mantle composition of the Pacific Domain before 120 Ma due to the scarcity of the oceanic record, having mostly been destroyed by subduction processes. Accreted oceanic lithosphere (ophiolites) in orogens along the Paleo-Pacific margins provide rare opportunities to partially fill this knowledge gap. The early Cambrian (530–505 Ma) Weraerai ophiolite mélange in the New England Orogen in Eastern Australia represents fragments of the now-consumed Paleo-Pacific oceanic plate, predecessor of the Panthalassa and Pacific oceanic plates, accreted to east Gondwana during ca. 410–277 Ma. Early work revealed the presence of an accreted volcanic island(s) of possible mantle plume origin. However, due to their heavy alteration and weathering, the geochemical signature of the mafic rocks in the Weraerai ophiolite cannot be used to certify their plume origin with confidence. Therefore, mantle rocks found in the ophiolitic belt offer an alternative way to decipher the origin of the oceanic lithospheric fragments in the Weraerai ophiolite mélange. Here we report the petrographic, major, and trace elements composition, including highly siderophile elements (HSE), and Re-Os isotope composition for 16 serpentinized spinel harzburgite samples from Woodsreef and Port Macquarie. The observed spinel-orthopyroxene symplectite intergrowth textures are interpreted as garnet-breakdown textures due to cooling from an initial high temperature of >1200°C. Silicon and Al contents and Mg# of serpentinized spinel harzburgite, as well as heavy rare earth element modelling results, suggest a high-degree of melt extraction of 20–30% in the garnet stability field and in an anhydrous environment, probably in ocean island or oceanic plateau environments. The samples in this study have HSE concentrations interpreted to have resulted from post-melting processes rather than a melt extraction feature, indicating that their Re-Os model ages need to be interpreted with caution. Nevertheless, the melt depletion ages obtained from the Woodsreef and Port Macquaries samples range between 1.4 and 1.1 Ga, consistent with previous studies on other Pacific-rim ophiolitic rocks. We argue that these ages might be related to a major depletion event during the transition between supercontinents Nuna and Rodinia. Such depletion events affected a large proportion of this section of the mantle before the incorporation of the peridotites into the oceanic lithosphere in the Paleo-Pacific associated with rapid ascent of mantle plumes. This interpretation is consistent with the occurrence of accreted volcanic islands in the Werearai ophiolite mélange, as shown by the OIB chemical signatures of some of the mafic rocks, and their association with shallow water limestones that formed in near-equatorial latitudes. The proposed ca. 530–510 Ma Paleo-Pacific Ocean mantle plume event coincides with a global peak of oceanic mantle plume events that may record the legacy of a circum-Rodinia subduction girdle driving antipodal mantle superplume episodes.

Widespread magmatic provinces at the onset of the Sturtian snowball Earth

The striking coincidence of the Franklin large igneous province (LIP) and the Sturtian glaciation onset ca. 717 million years ago (Ma) has inspired the hypothesis that either basaltic weathering or stratospheric sulfate aerosol injection of the Franklin LIP plunged Earth into global glaciation. The cool background climate just before the Sturtian has been commonly invoked by such initiation models. Difficulty in definitively linking these concepts with geological evidence has precluded complete demonstration of a snowball trigger mechanism. Here, we report that Franklin-aged magmatism was not only present in Laurentia and Siberia, but also in South China, where the Hubei–Shaanxi Magmatic Province formed at 720 Ma, revealing widespread magmatic provinces immediately preceding the onset of the Sturtian snowball Earth. Geochronological and geochemical data suggest that the geographically widespread magmatic provinces were emplaced over a short duration (ca. 720–717 Ma) and likely related to a mantle superplume beneath supercontinent Rodinia. We propose that low-to-mid-latitude volcanism prior to the Sturtian by a few million years enhanced global weatherability and created the background cool climate for the superimposed shock of stratospheric sulfate aerosol injection of the terminal Franklin eruption. Such widespread 720–717 Ma volcanism on different continents may have driven the Sturtian snowball initiation.

Multisphere Tectonics of the Earth System

AbstractThe fundamental theoretical framework of the Multisphere Tectonics of the Earth System is as follows: (1) It intends to extend the geotectonic studies from the crustal and lithospheric tectonics to the multisphere tectonics of the Earth system as a whole. (2) The global dynamics driven by both the Earth system and the cosmic celestial system: solar energy, multispheric interactions of the Earth system and the combined effects of the motions of celestial bodies in the cosmos system are the driving forces of various geological processes. (3) The Continent‐Ocean transformation theory: the continent and ocean are two opposite yet unified geological units, which can be transformed into each other; neither continent nor ocean will survive forever; there is no one‐way development of continental accretion or ocean extinction; the simple theory of one‐way continental accretion is regarded as invalid. (4) The continental crust and mantle are characterized by multiple layers, with different layers liable to slide along the interfaces between them, but corroboration is needed that continents move as a whole or even drift freely. (5) The cyclic evolution theory: the development of Earth's tectonics is not a uniform change, but a spiral forward evolution, characterized by a combination of non‐uniform, non‐linear, gradual and catastrophic changes; different evolutionary stages (tectonic cycles) of Earth have distinctive global tectonic patterns and characteristics, one tectonic model should not be applied to different tectonic cycles or evolutionary stages. (6) The structure and evolution of Earth are asymmetric and heterogeneous, thus one tectonic model cannot be applied to different areas of the world. (7) The polycyclic evolution of the continental crust: the continental crust is formed by polycyclic tectonics and magmatism, rather than simply lateral or vertical accretion. (8) The role of deep faults: the deep fault zones cutting through different layers of the crust and mantle usually play important roles in tectonic evolution. For example, the present‐day mid‐ocean ridge fault zones, transform fault zones and Benioff zones outline the global tectonic framework. Different tectonic cycles and stages of Earth's evolution must have their own distinctive deep fault systems which control the global tectonic framework and evolutionary processes during different tectonic cycles and stages. Starting from the two mantle superplumes Jason (Pacific) and Tuzo (Africa), the study of the evolutionary process of the composition and structure of the crust and mantle during the great transformation and reorganization of the Meso‐Cenozoic tectonic framework in China and the other regions of Asia is a good demonstration of theory of Multisphere Tectonics of the Earth System.

Re Sulfides from Zhelos and Tokty-Oi Intrusions (East Sayan, Russia)

Re sulfides were discovered in Cu–Ni–platinum-group elements (PGE) ores of the Zhelos and Tokty-Oi intrusions. These intrusions can be considered as products of the mantle superplume responsible for Rodinia’s break-up. The mineral compositions were determined in situ in polished samples. Electron microprobe analyses were mostly consistent with a general formula of (Cu,Fe,Mo,Os,Re)5S8, (Cu,Fe,Mo,Os,Re)4S7, and (Cu,Fe,Mo,Re)S2. One of the major features of Re sulfide from the Zhelos intrusion is its high osmium content. The ΣMe/S ratio for a part of our data is consistent with that of the tarkianite. Re sulfides from the Tokty-Oi have a ΣMe/S ratio similar to those in rheniite or dzeskazganite, but differ from them by the presence of Fe and Cu and the metal-to-metal ratio. The localization of the Re sulfide within the chalcopyrite suggests its crystallization from the residual Cu-rich liquid.

Tectonic Phenomena and Supervising Underlying Geodynamic Processes

The study concerns two deep sources of tectonic processes in Late Mesozoic and Cenozoic which influence is transferred and enforced on the spheroid surface – Earth crust. The first source is mantle convection. Its upgoing branches are comprised by mantle superplumes from which the upper mantle flows spreads laterally. Downgoing convection branches are comprised by detached highly metamorphosed fragments of thickened continental lithosphere and partially by subducted slabs, submerged lower than transitional mantle layer (~410–680 km). Major of subduction zones are transformed to subhorizontal lenses at the transitional layer depth participating in upper mantle convection. Coupled with total mantle convection it defines plate tectonic processes and lithosphere density loose, bringing rise amplifying during mountain formation. The second source is outer core flows reflected in magnetic field inversions, which are more frequent during or before of major of tectonic activity phases (phases of compression and transpression deformations strengthen). Inversion frequency rises during neotectonic orogeny. It is supposed, that Earth core flows change its spheroid parameters, which brings to the appearance of volume forces, affecting almost immediately in geological time. Thus core flows contribute to global character of tectonic phases occurrences and synchronicity for superposition of modern mountain formation main phase with plate tectonic processes.

Geochemistry of black shales from the Mesoproterozoic Srisailam Formation, Cuddapah basin, India: Implications for provenance, palaeoweathering, tectonics, and timing of Columbia breakup

The Mesoproterozoic Srisailam Formation, exposed along the northern part of the Cuddapah basin, India, comprises mainly medium- to fine-grained siliciclastics, and is devoid of any carbonate sediment. Preliminary sedimentological studies helped in recognizing fifteen distinct facies (five facies associations) in Chitrial outlier of the Srisailam Formation deposited in continental half-graben basin(s). Black shales (sensu lato) are minor components of the Srisailam Formation, and inferred to have deposited in deep lacustrine and prodelta facies of the half-graben(s). The black shales show restricted thickness (up to 29.0m), and are characterized by overall high ‘black shale' to ‘total shale' ratio (>0.51). Their geochemical characteristics were studied to constrain provenance, palaeoclimate, and tectonic setting of deposition of the Srisailam Formation. Further, an attempt has been made to use the Srisailam black shales as proxy for constraining the timing of breakup of the supercontinent Columbia.The Srisailam black shales are geochemically quite distinct. At similar SiO2 contents they are considerably different from PAAS. They are characterized by considerably lower ΣREE (Av. 136.0±50.4ppm) but a more conspicuous negative Eu-anomaly (Av. 0.34±0.09) than PAAS. Al2O3/TiO2 and TiO2/Zr ratios coupled with Eu/Eu*, GdCN/YbCN, La/Sc, Th/Sc, and Th/Cr ratios suggest their derivation from granite and granodiorite. The CIA values (65–90, Av. 72±9) as a whole indicate moderate chemical weathering under semiarid climate. Discriminating geochemical parameters indicate passive margin depositional setting. The combined sedimentological and geochemical characteristics reveal deposition of the Srisailam sediments in continental rift basin(s).Thick succession of black shales (with high CIA values) that deposited with shelf carbonates proxy for mantle superplume and supercontinent breakup events. The sedimentological characteristics and geochemical data of the Srisailam black shales plausibly exclude any large-scale breakup of Columbia during the interval (1400–1327Ma) of deposition of the Srisailam Formation.

Geochronology of the Chuktukon carbonatite massif, Chadobets uplift (Krasnoyarsk Territory)

We present results of U-Pb (SHRIMP II) and Ar-Ar geochronological study of the rocks of the Chuktukon massif, which is part of the Chadobets alkaline-carbonatite complex, and of the weathering crust developed after them. Perovskite from picrites and monazite from the weathering crust were dated by the U-Pb (SHRIMP II) method, and rippite from carbonatites, by the Ar-Ar method. Rippite has first been used as a geochronometer. The estimated ages (252 ± 12 and 231 ± 2.7 Ma) testify to two magmatism pulses close in time (within the estimation error) to the stages of alkaline magmatism in the Siberian Platform (250-245 and 238-234 Ma). These pulses characterize, most likely, the processes accompanying and completing the activity of the mantle superplume that formed the Siberian Igneous Province at 250-248 Ma. The monazite-estimated age (102.6 ± 2.9 Ma) reflects the time of formation of the ore-bearing weathering crust on the massif rocks.

Paleoclimatic and paleolatitude settings of accumulation of radiolarian siliceous–volcanogenic sequences in the middle Mesozoic Pacific: Evidence from allochthons of East Asia

Jurassic–Cretaceous siliceous–volcanogenic rocks from nappes of tectonostratigraphic sequences of the East Asia Middle Cretaceous Okhotsk–Koryak orogenic belt are represented by a wide range of geodynamic sedimentation settings: oceanic (near-spreading zones, seamounts, and deep-water basins), marginal seas, and island arcs. The taxonomic compositions of radiolarian communities are used as paleolatitude indicators in the Northern Pacific. In addition, a tendency toward climate change in the Mesozoic is revealed based on these communities: from the warm Triassic to the cold Jurassic with intense warming from the Late Jurassic to the Early Cretaceous. Cretaceous warming led to heating of ocean waters even at moderately high latitudes and to the development of Tethyan radiolarians there. These data are confirmed by a global Cretaceous temperature peak coinciding with a high-activity pulse of the planetary mantle superplume system, which created thermal anomalies and the greenhouse effect. In addition, the Pacific superplume attributed to this system caused accelerated movement of oceanic plates, which resulted in a compression setting on the periphery of the Pacific and the formation of the Okhotsk–Koryak orogenic belt on its northwestern framing in the Middle Cretaceous, where Mesozoic rocks of different geodynamic and latitudinal–climate settings were juxtaposed into allochthonous units.

Neoproterozoic magmatic complexes of the Songino block (Mongolia): A problem of formation and correlation of Precambrian terranes in the Central-Asian Orogenic Belt

An important role of the early Neoproterozoic juvenile crustal growth in the formation of the Khangai group of Precambrian terranes in the Central Asian Orogenic Belt was demonstrated by the example of the Holbo Nur Zone of the Songin Block. Magmatic complexes of this zone correspond to different settings of the Early Neoproterozoic ocean: oceanic islands, mid-ocean ridges, intraoceanic island arcs, and turbidite basins. Obtained data on volcanic rocks and associated granitoids constrain a timing of the island-arc magmatic complexes, at least within the interval of 888–859 Ma. The comparison of structures of the Songino and Tarbagatai blocks of the Khangai group of terranes showed that they share many common features in their geology and evolution and may be united into the single Songino–Tarbagatai terrane. This terrane was formed owing to the Early Neoproterozoic (~800 Ma) accretion of the ocean island, spreading, island-arc, and turbidite complexes of the oceanic plate to a stable continental massif represented by the Early Neoproterozoic Ider Complex of the Tarbagatai Block. The involvement of the Dzabkhan terrane into a Khangai collage of terranes is constrained between the formation of the volcanic rocks of the Dzabkhan Formation (~770–755 Ma), which are unknown in the Songino–Tarbagatai terrane, and the Tsagaan-Olom carbonate cover (~630 Ma), overlying both the Dzabkhan and Songino–Tarbagatai terranes. It was proposed that the formation of the Precambrian terranes of the Central Asian Orogenic Belt began from the Early Neoproterozoic accretion to the Rodinia supercontinent. The fragmentation of the latter above a mantle superplume at the end of the Early Neoproterozoic spanned also the newly formed fold area. This led to the formation of terranes, which included both fragments of the Paleoproterozoic craton and Early Neoproterozoic structures. Subsequent amalgamation of these Precambrian crustal fragments into composite terranes possibly occurred at the end of the early Baikalian tectonic phase.

Neoproterozoic granitic gneiss offshore the Shandong Peninsula of Eastern China: the eastward extension of the Sulu Orogenic Belt

ABSTRACTThe Sulu Orogenic Belt in eastern China has experienced a multistage tectonic evolutionary history. However, its geological evolution has not yet been corroborated by sufficient direct evidence from basement rocks. Chaolian Island on the Qianliyan Uplift provides an opportunity to study the formation and evolution of the Sulu Orogenic Belt using direct geochronological and geochemical evidence. We determined that the characteristic mineral assemblage in the study region is quartz + K-feldspar + perthite + biotite + muscovite. The samples are silica- (SiO2 = 72.8%–75.8%) and alkali-rich (ALK(Na2O+K2O) = 8.7%–9.3%), with high iron-magnesium ratios (FeO*/(FeO*+MgO) = 0.92–0.96) and low CaO and MgO concentrations. Furthermore, they are rich in large-ion lithophile elements K, Rb, Ba, and U, but depleted in high field strength elements Nb, Ta, and Zr. They exhibit high Ga/Al values (Ga × 104/Al = 3.33–3.74) and significant fractionation between light and heavy rare earth elements. The samples are A-type granites. In the discrimination diagrams for granite genesis types, the samples plotted in the post-orogenic A2-type granite region. Secondary ion mass spectrometer (SIMS) zircon U–Pb dating results indicated that the granitic gneiss formed ~782.6–802.3 Ma (Middle Neoproterozoic), consistent with the timing of the breakup of the Rodinia supercontinent on the northeastern margin of the Yangtze Plate. Comparing geochemical characteristics and zircon U–Pb ages of the A-type granitic gneisses of the Sulu Orogenic Belt, the Qianliyan Uplift appears to be an extension of the belt across the ocean and is affiliated with the Yangtze Plate. The granitic gneiss on Chaolian Island is related to the formation of a mantle superplume during the breakup of Rodinia, and the northeastern margin of the Yangtze Plate during the Middle Neoproterozoic was located in a back-arc extension setting induced by the subduction of oceanic plates.

Mid-late neoproterozoic to early paleozoic volcanism and tectonic evolution of the Qilianshan, NW China

Mid-Late Neoproterozoic to Early Paleozoic volcanism in the Qilianshan area, which shows systematic variations in space and time, is the volcanic response to the tectonic evolution of the Qilianshan. The volcanism gradually changed from continental rift-related and continental flood basaltic through MORB-type, island-arc and back-arc to post-collisional rift-related eruptions along with the tectonic evolution of the Qilianshan shifting from rifting and break-up of Rodinia through opening, spreading, subducting and closing of the Early Paleozoic oceans to arc-continent and continent-continent collision. The continental rift-related and flood lavas with ages of 850–604Ma distribute mainly on the Qilian and Qiadam Blocks. The widespread MORB-type and “island-arc-backarc”-type lavas were generated from ∼550 to 446Ma in both the North Qilian and the South Qilian ocean-trench-arc-basin systems. In the meantime the intracontinental rift-related volcanism occurred in the central Qilian Block between ∼522 and 442Ma. The Early Paleozoic oceanic basins were closed at the end of Ordovician (∼446Ma). Subsequent post-collisional vocanism occurred on the northern margin of the Qilian Block from ∼445 to ∼428Ma. Such spatial-temporal variations provide important constraints on the geodynamic processes that evolved at depth to form the Qilianshan. These processes involve: (1) upwelling of mantle plumes or a mantle superplume and subsequent rifting and break-up of Rodinia and subsequent opening, spreading and subduction of Early Paleozoic oceans followed by island-arc formation, (2) roll-back of the subducted oceanic slabs followed by back-arc extension and back-arc basin formation, (3) ocean closure and slab break-off followed by upwelling of asthenosphere and post-collisional volcanism. Intensive orogenic activities occurred in the Late Silurian and Early Devonian (∼420 - ∼400Ma) in response to the exhumation of the subducted crustal materials. Mountain collapse and lithosphere extension happened in the priod of ∼400–360Ma and formed post-collisional granitic intrusions, which marked the end of a complete orogenic cycle.

Mantle control of the geodynamo: Consequences of top‐down regulation

The mantle global circulation, including deep subduction and lower mantle superplumes, exerts first-order controls on the evolution of the core, the history of the geodynamo, and the structure of the geomagnetic field. Mantle global circulation models that include realistic plate motions, deep subduction, and compositional heterogeneity similar to the observed large low seismic velocity provinces in the lower mantle predict that the present-day global average heat flux at the core-mantle boundary (CMB) exceeds 85 mW m−2. This is sufficient to drive the present-day geodynamo by thermochemical convection and implies a very young inner core, with inner core nucleation between 400 and 1100 Ma. The mantle global circulation also generates spatially heterogeneous heat flux at the CMB, with peak-to-peak lateral variations exceeding 100 mW m−2. Such extreme lateral variability in CMB heat flux, in conjunction with the high thermal conductivity of the core, implies that the liquid outer core is thermally unstable beneath the high seismic velocity regions in the lower mantle but thermally stable beneath the large low seismic velocity provinces. Numerical dynamo simulations show how this pattern of heterogeneous boundary heat flux affects flow in the outer core, producing localized circulation patterns beneath the CMB tied to the mantle heterogeneity and long-lived deviations from axial symmetry in the geomagnetic field.

Magmatic systems of large continental igneous provinces

Large igneous provinces (LIPs) formed by mantle superplume events have irreversibly changed their composition in the geological evolution of the Earth from high-Mg melts (during Archean and early Paleoproterozoic) to Phanerozoic-type geochemically enriched Fe-Ti basalts and picrites at 2.3 Ga. We propose that this upheaval could be related to the change in the source and nature of the mantle superplumes of different generations. The first generation plumes were derived from the depleted mantle, whereas the second generation (thermochemical) originated from the core-mantle boundary (CMB). This study mainly focuses on the second (Phanerozoic) type of LIPs, as exemplified by the mid-Paleoproterozoic Jatulian–Ludicovian LIP in the Fennoscandian Shield, the Permian–Triassic Siberian LIP, and the late Cenozoic flood basalts of Syria. The latter LIP contains mantle xenoliths represented by green and black series. These xenoliths are fragments of cooled upper margins of the mantle plume heads, above zones of adiabatic melting, and provide information about composition of the plume material and processes in the plume head. Based on the previous studies on the composition of the mantle xenoliths in within-plate basalts around the world, it is inferred that the heads of the mantle (thermochemical) plumes are made up of moderately depleted spinel peridotites (mainly lherzolites) and geochemically-enriched intergranular fluid/melt. Further, it is presumed that the plume heads intrude the mafic lower crust and reach up to the bottom of the upper crust at depths ∼20 km. The generation of two major types of mantle-derived magmas (alkali and tholeiitic basalts) was previously attributed to the processes related to different PT-parameters in the adiabatic melting zone whereas this study relates to the fluid regime in the plume heads. It is also suggested that a newly-formed melt can occur on different sides of a critical plane of silica undersaturation and can acquire either alkalic or tholeiitic composition depending on the concentration and composition of the fluids. The presence of melt-pockets in the peridotite matrix indicates fluid migration to the rocks of cooled upper margin of the plume head from the lower portion. This process causes secondary melting in this zone and the generation of melts of the black series and differentiated trachytic magmas.

Petrogenesis and tectonic implications of the Neoproterozoic Datian mafic–ultramafic dykes in the Panzhihua area, western Yangtze Block, SW China

Mafic–ultramafic dykes are important geological markers that can punctuate the onset of crustal extension during the breakup of a continent and provide valuable information on the mantle source. This study reports secondary ion mass spectroscopy zircon and baddeleyite U–Pb ages, elemental and Nd isotopic data for the Datian mafic–ultramafic dykes in the Panzhihua area, western Yangtze Block, SW China. Two kinds of rocks are confirmed: the picritic rock and the dolerite. Based on petrographic and geochemical features, the dolerite dykes are further subdivided into two groups: Group I mafic and Group II mafic dykes, which emplaced at ~760 Ma (zircon U–Pb) and ~800 Ma (zircon and baddeleyite U–Pb), respectively. All samples from the picritic rocks and the Group I mafic rocks show the features of high-Ti and alkaline basaltic magma in composition as well as “humped” trace element patterns, which are similar to those of typical alkaline basalts associated with continental rifts except for the slightly negative Nb–Ta anomalies. The Group II mafic rocks display the features of low-Ti and tholeiitic magma, moderately enriched in LILE and LREE, and characterized by distinctively negative Nb–Ta anomalies. The primary magmas of the picritic rocks and the Group I mafic rocks were generated from ca 25 % partial melting of an OIB-like, Nd isotopically depleted but incompatible elements relatively enriched mantle source within a garnet stable field. The Group II mafic rocks crystallized from crustal contaminated mafic magmas that were derived from a spinel-bearing sub-continental lithospheric mantle source, because of low ratios of La/Yb, Ti/Y and Sm/Yb. Geochemical features suggest that these groups of mafic–ultramafic dykes were formed in a continental rift setting, but derived from different mantle sources. In combination with other Neoproterozoic igneous rocks in the western margin of Yangtze Block, it is suggested that the Datian mafic–ultramafic dykes in the Panzhihua area could have been formed in a multistage continental rift system, most likely related to the proposed mantle superplume, which centered beneath South China at ca. 820 Ma and may have finally triggered the breakup of the supercontinent Rodinia.

Mantle superplumes induce geomagnetic superchrons

We use polarity reversal systematics from numerical dynamos to quantify the hypothesis that the modulation of geomagnetic reversal frequency, including geomagnetic superchrons, results from changes in core heat flux related to growth and collapse of lower mantle superplumes. We parameterize the reversal frequency sensitivity from numerical dynamos in terms of average core heat flux normalized by the difference between the present-day core heat flux and the core heat flux at geomagnetic superchron onset. A low-order polynomial fit to the 0-300 Ma Geomagnetic Polarity Time Scale (GPTS) reveals that a decrease in core heat flux relative to present-day of approximately 30% can account for the Cretaceous Normal Polarity and Kiaman Reverse Polarity Superchrons, whereas the hyper-reversing periods in the Jurassic require a core heat flux equal to or higher than present-day. Possible links between GPTS transitions, large igneous provinces (LIPs), and the two lower mantle superplumes are explored. Lower mantle superplume growth and collapse induce GPTS transitions by increasing and decreasing core heat flux, respectively. Age clusters of major LIPs postdate transitions from hyper-reversing to superchron geodynamo states by 30-60 Myr, suggesting that superchron onset may be contemporaneous with LIP-forming instabilities produced during collapses of lower mantle superplumes.

“Roots” of magmatic systems in the large continental igneous provinces

Large igneous provinces (LIPs) are known from theArchean and were widely abundant in the Phanerozoic, when they formed large fields of flood basalts(traps) on the continents and in the oceans [10].According to the data available, the evolution of thePhanerozoic LIPs in most cases started from the continental riftogenesis accompanied by eruptions of midalkaline Fe–Ti basalt and picrobasalt, which are replacedby tholeiitic basalt at the second stage [5, 10, 11].The appearance of a LIP results from the rise ofmantle superplumes formed at the liquid core–mantleboundary [3, 10, 14]. However, the concrete state oftheir material and the conditions of its adiabatic melting are not clear. The main source of objective information may be provided by the mantle xenoliths inbasalt and basanite, which are fragments of the material of the front part of the plume above the zone ofadiabatic melting, where the primary magmas areformed. Our study is mainly aimed at concretizationof the ideas on the structure of the front parts of mantleplumes, their material, the level of penetration into thelithosphere, and the conditions of magma generationfrom an example of mantle xenoliths in basalt of theQuaternary TellDanun Volcano, Harrat Ash Samahvolcanic plateau adiabatic, South Syria [8].STRUCTURE OF THE FRONT PART OF THE PLUMEAs is evident from the data available on the structure of Phanerozoic LIPs, melting was localized in thefront parts of secondary plumes, “protuberances” onthe surface of the mantle superplume. Most likely, theirrise resulted from the local accumulation of fluid components providing additional floatage of the material.According to the data of [7], the diffluent plumehead should have a triangular crosssectional shapewith the appearance of a chamber of adiabatic meltingin its upper part (Fig. 1). The intruding newly formedmagma mostly removes fragments of the upper, cooledmarginal part of the plume. These are mantle xenolithsobserved in alkaline (subalkaline) Fe–Ti basalt andbasanite in the modern rift systems [6]. This materialdoes not come from the melting zone, but carriesimportant information on the material of mantleplumes, its phase composition, and components participating in melting. Most populations do not containxenoliths of the lower crustal rocks, which distinguishes these rocks from kimberlite pipes [6] and mayshow that the frontal parts of the local (secondary)mantle plumes reached the base of the sialic uppercrust.MANTLE XENOLITHS IN BASALT AND BASANITE OF SOUTH SYRIAThe populations of mantle xenoliths in basalt arecharacterized by surprising sameness and are dividedinto two major types: (1) the most abundant rocks ofthe “green, or Crdiopside” series and (2) more occasional rocks of the “black, or Al–Tiaugite” series,which often form veins in rocks of the “green” series[6]. The composition of these populations practicallydoes not depend on a concrete region [6], which provides evidence for the uniform nature of melting mantle substrates across the Earth. Most likely, this is thematerial of the mantle thermochemical plumes risingfrom the liquid core–mantle boundary and formed bythe silicate mantle material, as well as by fluid components of the core [1, 3, 14]. We studied these xenolithsin the example of the abovementioned QuaternaryTellDanun Volcano [8].Xenoliths of the “green” series are characterized bythe presence of Crdiopside and a very constant highMg composition of olivine and pyroxenes (Mg# =88–92). They are mostly represented by spinel peridotite with cataclastic, rarely protogranular texturewith the composition varying from predominant spinellherzolite to depleted spinel harzburgite and occasional spinel pyroxenite (mostly websterite). The latterforms veins in the peridotite matrix and is often characterized by the presence of thin kelyphytic rims of

Lower mantle superplume growth excites geomagnetic reversals

Seismic images of the lower mantle reveal two large-scale, low shear wave velocity provinces beneath Africa and the Pacific that are variously interpreted as superplumes, plume clusters or piles of dense mantle material associated with the D″ layer. Here we show that time variations in the height of these structures produce variations in heat flux across the core–mantle boundary that can control the rate at which geomagnetic polarity reversals occur. Superplume growth increases the mean core–mantle boundary heat flux and its lateral heterogeneity, thereby stimulating polarity reversals, whereas superplume collapse decreases the mean core–mantle boundary heat flux and its lateral heterogeneity, inhibiting polarity reversals. Our results suggest that the long, stable polarity geomagnetic superchrons such as occurred in the Cretaceous, Permian, and earlier in the geologic record were initiated and terminated by the collapse and growth of lower mantle superplumes, respectively.

Tectonics and geodynamics of granulite-gneiss complexes in the East European Craton

The Neoarchean and Paleoproterozoic granulite-gneiss complexes of the northern East European Craton, including their tectonic setting, accompanying igneous and sedimentary rocks, character of metamorphism and deep structure are considered in this paper. A similar approach was applied to the description and interpretation of the granulite-gneiss complexes of the Grenville-Sveconorwegian Orogen localized in the present-day structure of the European and North American continents. One of the most important results of this study is the recognition of a new type of tectonic structures called intracontinental oval orogens. These orogens were formed in the inner domain of the Neoarchean-Proterozoic supercontinent (2.8–0.85 Ga), which is called Lauroscandia. The extensional setting, which was initiated by a series of mantle plumes, locally passing to spreading but did not lead to the eventual breakup of the supercontinent and was followed by intracontinental collisional compression accompanied by closure of short-lived local oceans, subduction, and obduction. The Neoarchean and Proterozoic granulite-gneiss belts and areas of the East European Craton are components of the Karelian-Belomorian, Kola, Volgo-Uralia, Lauro-Russian, and Grenville-Sveconorwegian intracontinental oval orogens formed in the inner domain of Lauroscandia as a result of mantle-plume and plate-tectonic processes initiated by mantle superplumes. The geodynamic settings and tectonic processes in the Neoarchean-Proterozoic supercontinent differed markedly from both the Archean tectonics of miniplates and the Phanerozoic plate tectonics.

Ulkan-Dzhugdzhur ore-bearing anorthosite-rapakivi granite-peralkaline granite association, Siberian Craton: Age, tectonic setting, sources, and metallogeny

The paper systematizes and integrates the results of geological, isotopic geochronological, and geochemical studies of the igneous rocks that make up the Ulkan-Dzhugdzhur anorthosite-rapakivi granite-peralkaline granite association and related mineralization. This association is a typical example of anorogenic igneous rocks that formed in the within-plate geodynamic setting most likely under effect of the mantle superplume, which was active in the territory of the Siberian Craton 1.75–1.70 Ga ago. The igneous rock association formed in a discrete regime that reflected the pulsatory evolution of a sublithospheric mantle source. The prerift (1736–1727 Ma) and rift proper (1722–1705 Ma) stages and a number of substages are distinguished. All igneous rocks pertaining to this association have mixed mantle-crustal origin. Basic rocks crystallized from the OIB-type basaltic magma, which underwent crustal contamination at various depths. Felsic rocks are products of mantle and crustal magma mixing. The contribution of mantle component progressively increased in a time-dependent sequence: moderately alkaline subsolvus granite → moderately alkaline and alkaline hypersolvus granites → peralkaline hypersolvus granite. All endogenic deposits in the studied district are related to a single source represented by the mantle plume and its derivatives. The Fe-Ti-apatite deposits hosted in anorthosite formed as a result of intense lower crustal contamination of basaltic magma near the Moho discontinuity and two stages of fractional crystallization at lower and upper crustal depth levels. The rare-metal deposits are genetically related to peralkaline granite. Formation of uranium deposits was most likely caused by Middle Riphean rejuvenation of the region, which also involved rocks of the Ulkan-Dzhugdzhur association.