Isotope-geochemical constraints on the formation of the early Earth’ crust

Analysis of isotope-geochemical data obtained for the early crustal complexes of the Earth provided constraints on the formation time, scales of development, and geochemical features of protocrust. Most informative were isotope-geochemical and geochemical data on the oldest zircons with ages up to 4.4 Ga, short-lived ¹⁴⁶Sm/¹⁴²Nd isotope system, and lead isotope composition of the oldest rocks of Greenland. The presence of positive ¹⁴²Nd anomaly in the rocks of West Greenland and negative anomaly in the amphibolites of the oldest Nuvvuagittuq greenstone belt of the Superior province (O’Neil et al., 2008) indicates the early differentiation of the Earth material into depleted mantle and enriched (basaltic) crust (Caro et al., 2006; Benett et al., 2007a, b; O’Neil et al., 2008). Pb-Pb isotopic systematics of the oldest crustal rocks from West Greenland and Labrador testifies that high μ enriched crust (²³⁸U/²⁰⁴Pb = 10.9) of basaltic composition already existed 3.9 Ga ago (Kamber et al., 2003). Based on isotope-geochemical and geochemical features of the oldest zircons in the Late Archean greenstone belts of the Yilgarn block (Western Australia), the crust of intermediate-felsic composition and water on the Earth’s surface already existed 4.4 Ga ago (Wilde et al., 2001).     

Carbonate equilibrium in the water of the Razdol’naya River

The paper suggests an accurate approach to studying carbonate equilibrium in the water of the Razdol’naya River. The approach involves measuring pH by Pitzer’s scale, using a cell without liquid junction; measuring the total alkalinity by Bruevich’s technique; and using apparent constants of carbonate equilibrium with regard for the organic alkalinity. The Pitzer technique was employed to calculate the apparent constants of carbonate equilibrium in solution that models the riverine water: Ca(HCO₃)₂–NaCl–H₂O within the range of alkalinity of 0–0.005 mol/kg and temperatures of 0–25°C. Carbonate equilibrium in the water of the Razdol’naya River was sampled for studying at eight sites during all four seasons. Although the contents of biogenic compounds in the water are high, they can merely insignificantly affect the acid–base equilibrium, which is controlled in the riverine water by carbonate equilibrium and the concentrations of humic substances, which play the greater role, the greater the discharge of the river. In addition to the production and destruction of organic matter, carbonate equilibrium in the river is also affected by the supply of humic substances with soil waters and total alkalinity with groundwaters. The fluxes of alkalinity and humic substances annually brought by the Razdol’naya River to Amur Bay are evaluated at 1.33 × 10⁹ mol and 9.9 × 10⁶ kgC, respectively. The carbon dioxide export with the Razdol’naya River is equal to the alkalinity flux and does not depend on the weathering mechanisms.     

Lateral protrusions in the structure of the Earth’s lithosphere

The factual material and modeling results concerning the geology of specific structural elements defined as lateral protrusions, or flowing layers, are considered. The formation of such structural elements is a fundamental phenomenon that controls many features of the structural evolution and geodynamics of platform basement and foldbelts. A lateral protrusion, or flowing layer, is a spatially constrained, nearly horizontal geological body with attributes of 3D tectonic flow (rheid deformation) and lateral transport of rock masses. Flowing layers are large lateral protrusions that play important role in the structure of the continental and oceanic lithosphere. They embody the internal mobility of huge rock bodies and confirm the possibility of their lateral redistribution at different depths of the continental lithosphere. The lateral displacement of rocks within such assemblies may occur in the regime of cold deformation, heating, metamorphism, and ductile flow of rocks under subsolidus conditions or in the process of their partial melting.     

On the nature of ore-bearing fluids on the Dal’negorskoe borosilicate deposit (Primor’e)

Doklady Earth Sciences -     

Irregularities in the Earth’s rotation and the overall angular momentum of the atmosphere

Methods of celestial mechanics are used to refine a mathematical model for irregularity in the axial rotation of the Earth proposed earlier. This refinement applies corrections (residuals) introduced by perturbations of zonal tides. We examine intraday and near-diurnal variations in the Earth’s axial rotation, and a celestial-mechanical model explaining the origin of the intraday and near-diurnal oscillations in the rotational angular velocity is constructed. The correspondence between the variations of the intrayear rotational irregularity and the overall angular momentum of the atmosphere is analyzed.     

Temperature Distribution in the Earth’s Mantle

Doklady Earth Sciences - The influence of the compressibility and sphericity of the mantle on the temperature distribution in various models of mantle convection is analyzed. A model providing a...     

Jurassic granitic magmatism in the lesser Xing’an-Zhangguangcai ranges of NE China: the Dong’an example

ABSTRACT

The ~100,000 km² granitoid belt in the Lesser Xing’an-Zhangguangcai Ranges (LXZR) is an important component of the Phanerozoic granitic provinces (known as the ‘granitoid ocean’) in NE China. To reveal the mechanisms of Mesozoic magmatism and crustal growth in the LXZR, we present systematic geologic data, lithofacies information, zircon U-Pb ages, Hf isotopic, and element geochemical data for the Dong’an granites in the northern LXZR. The results show the following: (1) the Dong’an granites can be subdivided into three lithofacies, namely, medium- to coarse-grained alkali-feldspar granite, fine-grained alkali-feldspar granite, and granitic aplite, which were emplaced during the Early Jurassic (187–178 Ma); (2) the Dong’an granites are characterized by high SiO₂ and total alkali contents and low Fe₂O₃^t contents and Mg# values, and they are enriched in LILEs (e.g., Rb and K) and depleted in HFSEs (e.g., Nb and Ta); and (3) the zircons from these granites yield ε_Hf(t) values of ?2.4 to +5.7 and two-stage model ages of 772–1542 Ma. These results indicate that the Dong’an granites were emplaced during the Early Jurassic, are highly fractionated I-type (HFI) granites and were likely derived from partial melting of the thickened lower crust. Regionally, the Dong’an granites and the Early-Middle Jurassic intrusive rocks (201–163 Ma; 90,000 km²) in the LXZR show a trend of comagmatic evolution controlled by fractional crystallization, and they were successively emplaced during magma evolution. The HFI granites that are geochemically similar to the Dong’an granites formed in the later stage of magma evolution. Combined with regional geological observations, we conclude that the granitic rocks in the LXZR formed in an active continental margin setting related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent. This process may record an important episode of crustal accretion in the LXZR.     

Campanian-Maastrichtian radiolarians from the Malokuril’skaya Formation,the Shikotan Island

The results of radiolarian analysis confirm the Campanian-Maastrichtian age of the Malokuril’skaya Formation in the Shikotan Island. The Campanian-Maastrichtian age of the formation is implied simultaneously by radiolarians and inoceramids. The studied Campanian and Campanian-Maastrichtian radiolarian assemblages include abundant specimens representing genus Prunobrachium, characteristic of which was bipolar distribution in cold-water to temperate basins. The new occurrence site of prunobrachids is established at the latitude of 43°N, the Far East of Russia.     

Supercontinental cyclicity in the Earth’s evolution

The Earth’s evolution is determined by supercontinental cyclicity with a period of 400 Ma. A supercycle consists of a supercontinental proper and an inter-supercontinental stage, each of which includes two phases, respectively: integration-destruction and fragmentation-convergence. The worldwide analysis of geologic-historic and isotope-geochronologic data supports the existence of such cyclicity. In all, ten supercontinental cycles of supercontinents have been identified; in this case, the most ancient proto-supercontinent was recognized tentatively, Supercontinents identified previously by other researchers fit into this cyclicity. An association between magmatism from mantle plumes and certain phases of supercontinental cyclicity was revealed. Amalgamation and breakup of supercontinents occurred against the background of disymmetry of the Northern and Southern hemispheres of the Earth, which changed its polarity between the cycles.     

Parker’s dynamo near the excitation threshold

A method of constructing asymptotic solutions for nonlinear mean-field dynamo equations near the excitation threshold is developed and applied to equations describing the solar dynamo in a Parker model. The form of solution obtained corresponds to the eigensolution for a kinematic dynamo, for the intensity of the generation sources at which self-excitation of the magnetic field begins (the so-called marginally stable eigenfunction). The wave amplitude is calculated.     

What is the ‘Just Transition’?

The ‘just transition’ is a concept receiving more attention in the literature to-date. This critical review discusses this and how there are overlaps with literature on energy, environmental and climate justice. Within the separate energy, environment and climate change scholar communities, there is too much distortion of what the ‘transition’ means and what ‘justice’ means, and they all should be understood within the just transition concept. To increase public understanding and public acceptance of a just transition, these research communities need to unite rather than continue alone.     

Gold Deposits in the Earth’s History

Geology of Ore Deposits - The distribution of major gold deposits in the Earth’s history is discussed. The primary heterogeneity of the Archean crust in terms of gold mineralization is...     

Intrayear irregularities of the Earth’s rotation

The methods of celestial mechanics can be used to construct a mathematical model for the perturbed rotational motions of the deformable Earth that can adequately describe the astrometric measurements of the International Earth Rotation Service (IERS). This model describes the gravitational and tidal influences of the Sun and Moon. Fine resonant interactions of long-period zonal tides (annual, semiannual, monthly, and biweekly) with the diurnal and semidiurnal tides are revealed. These interactions can be reliably confirmed via a spectral analysis of the IERS data. Numerical modeling of tidal irregularities of the Earth’s axial rotation was carried out, focusing on the analysis and forecasting of variations of the day length occurring within short time intervals of a year or shorter (intrayear variations).     

Shear Wave Velocity in the Top of the Earth’s Inner Core

Doklady Earth Sciences - Analysis of PKIIKP waves reflected off the inner surface of the solid core boundary and recorded close to the antipode indicates that the shear wave velocity at its top can...