Geodynamic Effects Research Articles

Study of Grouting in the Hydraulically Activated Subfoundation Soils Using the Comprehensive Approach

Introduction. The large-scale “wet” closure of collieries had led to irreversible changes in the underworked rock mass. First of all, there took place the mine-water level rise and hydraulic activation of buildings’ subfoundation soils, which induced the new geodynamic effects and hazardous deformations of buildings. Therefore, it is necessary to carry out the reconstruction of buildings’ subfoundations on the underworked territories. Under these circumstances, the high-pressure jet grouting with viscoplastic grouts using the hydraulic fracturing is considered a highly-promising trend of soil grouting. The work aims at studying the parameters of grouting and the degree of consolidation of hydraulically activated soils on the underworked territories.Materials and Methods. The research was carried out with the rock full scale specimens, taking into account their physical-mechanical and strain-strength properties. The comprehensive approach to research implied studying the geotechnical conditions and the technological parameters of rock grouting along with the quality of stabilisation and waterproofing of hydraulically activated soils.Results. In accordance with the comprehensive research methodology, at the first stage, the geotechnical and miningengineering analysis of the underworked territories were carried out and the geostructural typification of the ShakhtinskNesvetaevsky district territories was substantiated depending on the thickness of the covering deposits. At the second stage, the grout pad formation parameters at contact with the parent rocks were analytically determined. Moreover, for dispersive decompacted rocks the consistent patterns and the degree of filtration consolidation were established in the empirically-analytical way by viscoplastic grout injection. Using the computer and physical modeling method, the consistent patterns of subfoundation soils deformation before and after grouting were obtained for three geostructural types. At the third stage, the field studies of the grouting parameters and quality were carried out during the subfoundations reconstruction of two buildings in the city of Shakhty. It was proved that grouting in the hydraulically activated soils increases their strength up to 0.4 MPa and reduces subfoundations deformation by 2–2.5 times.Discussion and Conclusions. Application of the comprehensive methodology to the study of grouting in the hydraulically activated soils of the underworked territories made it possible to substantiate the process flow schemes and parameters of consolidation and waterproofing of dispersive and fractured hard rocks. Based on the analytical, computer, laboratory and field study results, the consistent patterns and the degree of variation in the deformation-strength properties of the hydraulically activated subfoundation soils after viscoplastic grouting were established.

Ghost-arc geochemical anomaly at a spreading ridge caused by supersized flat subduction

The Southern Atlantic-Southwest Indian ridges (SASWIR) host mid-ocean ridge basalts with a residual subduction-related geochemical fingerprint (i.e., a ghost-arc signature) of unclear origin. Here, we show through an analysis of plate kinematic reconstructions and seismic tomography models that the SASWIR subduction-modified mantle source formed in the Jurassic close to the Georgia Islands slab (GI) and remained near-stationary in the mantle reference frame. In this analysis, the GI lies far inboard the Jurassic Patagonian-Antarctic Peninsula active margin. This was formerly attributed to a large-scale flat subduction event in the Late Triassic-Early Jurassic. We propose that during this flat slab stage, the subduction-modified mantle areas beneath the Mesozoic active margin and surrounding sutures zones may have been bulldozed inland by >2280 km. After the demise of the flat slab, this mantle anomaly remained near-stationary and was sampled by the Karoo mantle plume 183 Million years (Myr) ago and again since 55 Myr ago by the SASWIR. We refer to this process as asthenospheric anomaly telescoping. This study provides a hitherto unrecognized geodynamic effect of flat subduction, the viability of which we support through numerical modeling.

Geodynamic effects of the critically stressed state of the earth’s crust. Russian Mining Industry

Geodynamic effects of the critically stressed state of the earth’s crust. Russian Mining Industry

Estimating the thermal effect in gPhoneX observations

Stationary relative gravimeters are used in variety of applications, mainly due to their high sampling rate which is more suitable for study of certain geodynamic effects than absolute gravimeters. Study of weak signals is almost exclusively in the domain of superconducting gravimeters, as they possess the highest accuracy and stability of all types of relative gravimeters. Possible alternative to superconducting gravimeters are portable earth tide metal spring gravimeters. Zero-length spring gravimeters (e.g. LCR instruments) are usually considered to be the most accurate mechanical spring gravimeters. However, compared to superconducting instruments they remain too unstable for long-term gravity monitoring. Main reason supporting this statement is related to instrument's sensitivity to temperature changes and temperature induced tilts. Gravity observations from the gPhoneX #108 gravimeter stationed at Hurbanovo gravimetric observatory were tested in order to confirm the correlation between the observed gravity changes and ambient temperature changes and provide a solution for correcting the gPhone data for influence of the ambient temperature changes. Paper also aims to serve as a guide for other operators to estimate a parameters required for the calculation of ambient temperature correction.

Performance evaluation of the CDN1 altimetry Cal/Val transponder to internal and external constituents of uncertainty

A microwave range transponder has been operating at the CDN1 Cal/Val site on the mountains of Crete for about 6 years, to calibrate international satellite radar altimeters in the Ku-band. This transponder is part of the European Space Agency Permanent Facility for Altimetry Calibration, and has been producing a continuous time series of range biases for Sentinel-3A, Sentinel-3B, Jason-2, Jason-3 and CryoSat-2 since 2015. As of 18-Dec-2020, the CDN1 transponder has allowed calibration of the new operational altimeter of Sentinel-6 MF satellite as it flies in tandem with Jason-3. This work investigates range biases derived from the long time series of Jason-3 (and subsequently that of Sentinel-6 MF since both follow the same orbit) and tries to isolate systematic and random constituents in the produced calibration results of the transponder. Systematic components in the dispersion of transponder biases are identified as of internal origin, coming from irregularities in the transponder instrument itself and its setting, and of external cause arising from the altimeter, satellite orbit, Earth’s position in space, geodynamic effects and others. Draconic harmonics, principally the 58-day period, play a significant role in the transponder results and create cyclic trends of maximum amplitude of 17 mm at times in the calibration results. The attitude of the satellite body as it changes for solar panel orientation contributes an offset of about 7 mm when yaw rotation is off its central position, and the atmospheric, water mass and non-tidal ocean loadings are responsible for an annual systematic signal of 10 mm. At the time of writing, all other constituents of uncertainty seem random in nature and not significantly influential, although humidity requires further investigation in relation to the final transponder calibration results.

Study on room-temperature effect of a superconducting gravimeter prototype

PurposeThis study aims to reveal the room-temperature effect of a superconducting gravimeter prototype, which will guide its subsequent optimization to improve its gravimetric measurement accuracy.Design/methodology/approachWithout leveling, the prototype output signal, tilt data and room temperature were measured under steady operating conditions. After analyzing the correlations of the three data sets, the residuals of the prototype’s output signal were compensated using the tilt data and the geodynamic effects (ocean tide loading, atmospheric loading and the gravitational effect of polar motion) were then corrected.FindingsThe remaining residuals after correction may be caused by small tilt variations that are due to the sensor chamber temperature and radiation shield temperature changes. These small tilt variations were submerged in the tilt signal noise. Although the peak-to-peak noise of the tiltmeter does not exceed 15 µrad, it can still produce gravimetric deviations above 60 µGal when the prototype is significantly tilted.Originality/valueThis study analyzes in detail the room-temperature effect of a superconducting gravimeter prototype, introduces the tilt effect of the relative gravimeters to compensate for the gravimetric deviations and emphasizes that the improvement of fine leveling and the accuracy of the tiltmeter are key requirements for the prototype to perform high-accuracy gravity measurement tasks.

Discovery of Late Mesozoic volcanic seamounts at the ocean-continent transition zone in the Northeastern margin of South China Sea and its tectonic implication

The Northern South China Sea (SCS) margin experienced the switch from Andean-type active subduction to passive extension during late Mesozoic era. However, the mechanism of cessation of paleo-Pacific subduction in the SCS region is unclear, and the location of suture zone between paleo-Pacific plate and South China block is obscure. In this study, we report new 40Ar/39Ar ages and whole-rock Hf isotopes of basalts from two poorly studied volcanic seamounts (namely, Puyuan and Beipo) at the ocean-continent transition zone in the Northeastern SCS margin, with an emphasis on the existence of exotic, buoyant oceanic plateau and its geodynamic effect on subduction cessation. Results indicate that the OIB-type Puyuan and E-MORB-type Beipo volcanic seamounts were erupted at 154.1 Ma and 93.2 Ma, respectively. Whole-rock trace element, Sr-Nd-Pb-Hf isotopic compositions, and subduction polarity point out that these samples were oceanic intraplate basalts formed within the paleo-Pacific plate, independent of the coeval, Late Mesozoic paleo-Pacific subduction system in the region. The ages and geochemical data of the two volcanic seamounts, combined with geochemical data of Late Mesozoic Pacific oceanic plateaus and seismic data of the Northeastern SCS margin, show that there may exist a Late Mesozoic exotic, buoyant oceanic plateau in the region. The collision between the oceanic plateau and the South China block could lead to the cessation of paleo-Pacific plate subduction, and changes in tectonic regime during the Late Cretaceous era (ca. 100–65 Ma). The pre-existing, Late Mesozoic suture zone has been well constrained by the remnant oceanic plateau and continental arc, and may play a key role in the formation of Cenozoic rifting tectonic units in the region.

On the construction of gravimetric geoid model on the Lviv region area

Baltic Height System 1977, currently used in Ukraine, the starting point of which is the zero of the Kronstadttide-gauge, isobsoletedue to the great distance from the zero-point of the reference height and the difficulty of adapting satellite methods of geodesy. For the successful modernization of the height system of Ukraine, it is necessary to integrate it into the United European Leveling Network (UELN). For the full functioning of any modern height system, namely to determine the gravity-depend heights by satellite methods, it is necessary to operate with a high-precision geoid model. Therefore, an important task is construction of a high-precision regional model of the geoid on the territory of our state. The rear many methods of constructing a model of the regional Earth’s gravitational field, including the geoid model, each of which has its advantages and disadvantages. The purpose of this article is to test the STHA-method for calculating the model of the regional gravitational field, in particular the gravimetric model of the geoid, on the territory of Lviv region and to assess its accuracy. Free air gravity anomalies ∆g from WGM2012 provided by the International Gravimetric Bureau (BGI) were used as initial data. The gravimetric STHA-model of the geoid was calculated with in the procedure «Remove-Compute-Restore» up to 8 degrees/order. To assess the accuracy of the model, it was compared with 213 points of GNSS leveling, as well as with the model EGM2008 up to 360 degrees/order. There are always differences between geometric and gravimetric geoid models duet or and ommeasurement errors, in consistencies in datums, different geodynamic effects etc. Respectively the parameters of the transition between gravimetric and geometric models of the geoid on the territory of Lviv region were also found. The proposed method can be used to build a high-precision model of the geoid for the entire territory of Ukraine with its subsequent coordination with the model of the European geoid EGG2015.

Phase Relations in Spinel Lherzolite KLB-1 According to Results of Thermodynamic Modeling up to 30 GPa: Peculiarities of Mineral Assemblages and Geodynamic Effects

The composition of spinel lherzolite xenolith KLB-1 from the Kilbourne Hole volcanic crater, United States, which is close to the composition of the Earth’s primitive mantle, was used for thermodynamic modeling of phase relations in the Na2O–CaO–FeO–MgO–Al2O3–SiO2 system (NCFMAS) using the Perple_X software package in the temperature range of 900–2000 °C and pressures of 0.0001–30 GPa. The calculated phase diagram is in good agreement with published thermodynamic data on KLB-1 composition and reveals the peculiarities of mantle mineral assemblages at P–T parameters on which experimental data are insufficient or absent. The results showed that the mineral assemblage of garnet wehrlite (garnet + olivine + clinopyroxene), the least common type of mantle peridotite on the Earth’s surface, prevails in the upper mantle since the Archean. Mineral assemblage of garnet lherzolite (garnet + olivine + clinopyroxene + orthopyroxene), which is a variety of mantle peridotites most widely found on the Earth’s surface, is formed in the lithospheric mantle because its temperatures are lower than those of the convecting mantle. Thermodynamic modeling reveals a ringwoodite-free field in the P–T diagram (located at the bottom of the mantle transition zone), which is crosscut by Archean adiabats and by the geotherms of Archean and the hottest Phanerozoic plumes. This area causes a change, from negative to positive, in the slope of the boundary between the lower mantle and the mantle transition zone. A positive slope of the boundary in the Archean should have stimulated the ascend of lower mantle plumes through the transition zone. Conversely, this boundary has a negative slope for most Phanerozoic plumes, rising from the lower mantle, and as a result, the plumes either slow down or stop.

The effect of seamount chain subduction and accretion

Seamount chains (oceanic plateaus, submarine ridges) are unique morphologic features on the seafloor, which resulted from the motion of the lithosphere over a convective plume. Seamount chains are being carried along by plate motions, which are eventually subducted beneath continental/oceanic plates or accreted in the accretionary complex, thus causing a series of effects in the convergent margin. In this paper, we briefly review the distribution and features of the typical modern seamount chains, including Hawaiian‐Emperor and Louisville seamount chains, Cocos, Ninetyeast and Caroline ridges, and Ogasawara Plateau, and mainly focus on the effects of seamount chains subduction and accretion. The geological effects mainly include the following: (1) deformation and tectonic erosion of the overriding plate; (2) flat‐slab subduction in the convergent margin; (3) growth of continental crust through time; (4) subduction initiation of plate tectonics; (5) generation of large earthquakes; (6) magmatism of the volcanic arc; and (7) formation of porphyry copper and gold deposits. The subduction of seamount chains resulted in similar effects in the Central Asian Orogenic Belt (CAOB) which is one of the largest and longest‐lived accretionary orogens on Earth. However, there are still many aspects that need further improvements, such as identification of the seamounts in the geological record, and geodynamic effects of subducted seamount chains. A detailed study on these sides of the seamount chains will enable us to further understand the tectonic evolution and metallogenesis of the CAOB, especially in accretionary orogenesis, continental crust growth, and subduction initiation dynamics.

Neoproterozoic Metabasalts of the Tyya Complex of the Olokit Rift Trough (Baikal–Muya Belt): Composition, U–Pb Age, Isotope-Geochemical Characteristics, and Geodynamic Effects

Abstract—We present results of new mineralogical, geochemical, geochronological, and isotope (Sm–Nd, Rb–Sr, and O) studies of the volcanic rocks of the Tyya complex in the Olokit trough. These are normal tholeiitic basalts and scarcer basaltic andesites forming a fractionated series with mg# = 45–65, medium TiO2 contents (0.73–1.62 wt.%), low P2O5 contents (0.04–0.25 wt.%), and a significant domination of Na over K (Na2O/K2O = 2.1–50.0). The rocks are metamorphosed to greenschists, which are composed of chlorite, actinolite, epidote, and albite with quartz, titanite, ilmenite, and magnetite impurity. The metabasalts have is an age of 915 ± 5 Ma (zircon U–Pb dating) and are characterized by wide variations in εNd(T) (–3.5 to –11.9) and 87Sr/86Sr (0.70602–0.70732) and high δ18O values (9.0–15.2‰) as compared to the mantle ones. According to the isotope-geochemical characteristics, the studied metabasalts have features of both IAB and E-MORB. The Tyya metabasalts might have resulted from the melting of the lithospheric mantle with a subductional component. Comparison of the studied rocks with volcanic rocks of recent geodynamic settings shows their similarity to basalts of back-arc basins. The Tyya metabasalts might belong to a back-arc basin of the late Mesoproterozoic Nyurundukan island arc system.

Анализ влияния геодинамических факторов на релятивистское смещение частоты атомных стандартов

The impact of geodynamic factors on the relativistic frequency shift of atomic standards is analyzed. The results of frequency shift calculations caused by various geodynamic phenomena are presented, and the significance of these shifts for modern optical frequency standards is estimated. Based on the results of the assessment, it was concluded that for the relativistic frequency shift at the level of 10-18, the most significant factors are tides in the solid Earth and oceans, which are well taken into account using modern global tidal models. Nontidal phenomena in the oceans, which cause a change in the geopotential at the level of 0.2 m2/s2 (frequency shift of the order of 2·10-18), do not have much effect on the course of stationary atomic standards located on the continents. The postglacial uplift has a secular character and is well modeled at the present time. It is recommended to pay special attention to the complexly modeled potential changes caused by fluctuations in the water level in reservoirs (for stations located near reservoirs) and the groundwater level. The rest of the considered geodynamic ef-fects have practically no effect on the course of the optical clock.

20 July 2017 Bodrum-Kos Earthquake (Mw:6.6) in southwestern Anatolia, Turkey

In the Aegean Sea, the western part of Gökova Gulf, Kos and Bodrum were struck by a 6.6 (Mw) earthquake on July 20, 2017. The fault plane solution for the main shock shows an E-W striking normal type fault with approximately N-S (N4°E) tensional axis (T-axis). Fault plane solutions of 33 aftershocks show two groups of normal type fault with E-W and NE-SW to ENE-WSW orientations. The inversion of the focal mechanisms of the aftershocks yields two different normal faulting stress regimes: one is characterized by an approximately N-S (N5°E) σ3 axis (minimum horizontal stress axis). This extension is obtained from 13 focal mechanisms of aftershocks with approximately E-W direction. The other is characterized by approximately NW-SE (N330°E) σ3 axis. The latter is calculated from 21 seismic faults of aftershocks with approximately NE-SW direction. These aftershocks occurred on relatively small-scale faults that were directed from NE-SW to ENE-WSW, and possibly contributed to expansion of the basin in the west. The 24 focal mechanisms of earthquakes which occurred since 1933 in and around Gökova Basin are introduced into the inversion analysis to obtain the stress state effective in a wider region. The inversion yields an extensional stress regime characterized by an approximately N-S (N355°E) σ3 axis. The E-W directional metric faults, measured in the central part of Gökova Fault Zone bordering the Gökova Gulf in the north, also indicate N-S extension. The NE-SW extension obtained from NE-SW aftershocks appears to be more local and is responsible for the expansion of the western part of the asymmetric Gökova Basin. This N-S extension which appears to act on a regional-scale may be attributed to the geodynamic effects related to the combined forces of the southwestward extrusion of Anatolia and the roll-back process of African subduction beneath Anatolia.

Sedimentary response to a collision orogeny recorded in detrital zircon provenance of Greater Caucasus foreland basin sediments

AbstractThe Greater Caucasus orogen on the southern margin of Eurasia is hypothesized to be a young collisional system and may present an opportunity to probe the structural, sedimentary and geodynamic effects of continental collision. We present detrital zircon U‐Pb age data from the Caucasus region that constrain changes in sediment routing and source exposure during the late Cenozoic convergence and collision between the Greater Caucasus orogen and the Lesser Caucasus, an arc terrane on the lower plate of the system. During Oligocene to Middle Miocene time, following the initiation of deformation within the Greater Caucasus, marine sandstones and shales were deposited between the Greater and Lesser Caucasus, and detrital zircon age data suggest no mixing of Greater Caucasus and Lesser Caucasus detritus. During Middle to Late Miocene time, Greater Caucasus detritus was deposited onto the Lesser Caucasus basin margin, and terrestrial, largely conglomeratic, sedimentation began between the Greater and Lesser Caucasus. Around 5.3 Ma, upper plate exhumation rates increased and shortening migrated to pro‐ and retro‐wedge fold‐thrust belts, coinciding with the initiation of foreland basin erosion. Sediment composition, provenance and structural data from the orogen together suggest the existence of a wide (230–280 km) marine basin that was progressively closed during Oligocene to Late Miocene time, probably by subduction/lithospheric underthrusting beneath the Greater Caucasus, followed by initiation of collision between the Lesser Caucasus arc terrane and the Greater Caucasus in Late Miocene to Pliocene time. The pace of the transition from hypothesized subduction to collision in the Caucasus is consistent with predictions from numerical modeling for a system with moderate convergence rates (<13 mm/yr) and hot lower plate continental lithosphere. Basement crystallization histories implied by our detrital zircon age data suggest the presence of two pre‐Jurassic sutures between stable Eurasia and the Lesser Caucasus, which likely guided later deformation.

ОЦЕНКА ВЛИЯНИЯ ГЕОДИНАМИЧЕСКИХ ЗОН, ПЕРЕСЕКАЮЩИХ МАГИСТРАЛЬНЫЕ ГАЗОПРОВОДЫ, НА ИХ НАПРЯЖЕННО-ДЕФОРМИРОВАННОЕ СОСТОЯНИЕ

Актуальность. Одной из причин, способной разрушать газопроводы, являются геодинамические воздействия, так как по мере длительной эксплуатации газопроводов, расположенных, например, на тектонических разломах, происходит накопление повреждающего фактора, связанного с изгибными напряжениями. Анализ фактического положения газопроводов по данным внутритрубного технического диагностирования показал наличие потенциально-опасных участков, на которых кривизна не соответствует проектной, а значит изгибные напряжения также могут значительно отличаться по абсолютной величине в большую сторону от проектных. Следовательно, необходимо своевременно выявлять такие потенциально-опасные участки, и в зависимости от уровня фактических напряжений проводить восстановительные мероприятия. Цель: провести оценку влияния геодинамических зон, пересекающих магистральные газопроводы на их напряженно-деформированное состояние с использованием данных внутритрубного технического диагностирования, в т. ч. с учетом их длительной эксплуатации. Объект: участок четырехниточного коридора магистрального газопровода, расположенного на территории западного Урала, где по данным Российской Академии Наук в настоящее время наблюдаются надвиги. Методы: аналитические методы исследования напряженно-деформированного состояния магистральных газопроводов по данным о пространственном положении его оси, полученных методами общепринятой технологии и данными внутритрубной диагностики. Результаты. Проведен анализ основных этапов общепринятой технологии выявления геодинамических зон и определения его основных параметров, оценки напряженно-деформированного состояния . Показана возможность выявления потенциально-опасных участков магистральных газопроводов на пересечениях с геодинамическими зонами, по данным внутритрубной диагностики. Установлено, что с увеличением сроков эксплуатации магистральных газопроводов возрастает количество потенциально-опасных участков, на которых радиус кривизны не соответствует требованиям нормативной документации по минимально допустимому, равному 1000 D. По результатам обработки данных внутритрубной диагностики приведены примеры определения величин изгибных напряжений, превышающих нормативные значения. В связи с невозможностью полной переукладки магистральных газопроводов, предлагается привести нормативные требования к уровню напряжений. Кроме того, показана возможность выявления активных геодинамических зон и их параметров, по данным внутритрубной диагностики.

Geodynamic effects of subducted seamount at the Manila Trench: Insights from numerical modeling

We used numerical modeling to investigate the geodynamic effects of subducted seamounts at the Manila Trench. A series of numerical modeling experiments were conducted with variable parameters, including the activation volume (Vact) and cohesion (C), which influence lithospheric rheology, the plate convergence velocity, and the age of subducting slab. Modeling results indicate that varying the Vact and C within an appropriate range have limited effects on the geodynamic process of subduction. A lower Vact allows the slab to sink more easily and results in a steeper dip angle. A slab break-off is more likely to occur under subduction at depths of 100–300 km, while the existence of a seamount further promotes the break-off process. The convergence rate is a key parameter affecting the break-off timing and depth. In contrast, under subduction where subducted oceanic plate move faster upper plate, the model results exhibit non-break-off, steady subduction. Slab age is another factor controlling break-off, where break-off time extends with slab age. A subduction without seamount will cause a ~2 Myr delay in break-off timing. We suggest that the low-velocity zone under the Manila Trench at 17o N is the result of a break-off event due to subduction of the Zhenbei-Huangyan Seamount Chain. Further to the north, such as the location at 19o N, the absence of seamount and an older oceanic crust would favor a delay in break-off timing during subduction.

Some Lessons Learned from On-Site Observations on High Concrete Dams

Some results of generalizing and analyzing long-term on-site observations of the construction and operation of high-head concrete dams with consideration of geodynamic effect and imperfection of the designs of dams in tectonically unstable regions are briefly presented.

Formation time of the big mantle wedge beneath eastern China and a new lithospheric thinning mechanism of the North China craton—Geodynamic effects of deep recycled carbon

High-resolution P wave tomography shows that the subducting Pacific slab is stagnant in the mantle transition zone and forms a big mantle wedge beneath eastern China. The Mg isotopic investigation of large numbers of mantle-derived volcanic rocks from eastern China has revealed that carbonates carried by the subducted slab have been recycled into the upper mantle and formed carbonated peridotite overlying the mantle transition zone, which becomes the sources of various basalts. These basalts display light Mg isotopic compositions ( δ 26Mg = –0.60‰ to –0.30‰) and relatively low 87Sr/86Sr ratios (0.70314–0.70564) with ages ranging from 106 Ma to Quaternary, suggesting that their mantle source had been hybridized by recycled magnesite with minor dolomite and their initial melting occurred at 300−360 km in depth. Therefore, the carbonate metasomatism of their mantle source should have occurred at the depth larger than 360 km, which means that the subducted slab should be stagnant in the mantle transition zone forming the big mantle wedge before 106 Ma. This timing supports the rollback model of subducting slab to form the big mantle wedge. Based on high P-T experiment results, when carbonated silicate melts produced by partial melting of carbonated peridotite was raising and reached the bottom (180–120 km in depth) of cratonic lithosphere in North China, the carbonated silicate melts should have 25–18 wt% CO2 contents, with lower SiO2 and Al2O3 contents, and higher CaO/Al2O3 values, similar to those of nephelinites and basanites, and have higher e Nd values (2 to 6). The carbonatited silicate melts migrated upward and metasomatized the overlying lithospheric mantle, resulting in carbonated peridotite in the bottom of continental lithosphere beneath eastern China. As the craton lithospheric geotherm intersects the solidus of carbonated peridotite at 130 km in depth, the carbonated peridotite in the bottom of cratonic lithosphere should be partially melted, thus its physical characters are similar to the asthenosphere and it could be easily replaced by convective mantle. The newly formed carbonated silicate melts will migrate upward and metasomatize the overlying lithospheric mantle. Similarly, such metasomatism and partial melting processes repeat, and as a result the cratonic lithosphere in North China would be thinning and the carbonated silicate partial melts will be transformed to high-SiO2 alkali basalts with lower e Nd values (to −2). As the lithospheric thinning goes on, initial melting depth of carbonated peridotite must decrease from 130 km to close 70 km, because the craton geotherm changed to approach oceanic lithosphere geotherm along with lithospheric thinning of the North China craton. Consequently, the interaction between carbonated silicate melt and cratonic lithosphere is a possible mechanism for lithosphere thinning of the North China craton during the late Cretaceous and Cenozoic. Based on the age statistics of low δ 26Mg basalts in eastern China, the lithospheric thinning processes caused by carbonated metasomatism and partial melting in eastern China are limited in a timespan from 106 to 25 Ma, but increased quickly after 25 Ma. Therefore, there are two peak times for the lithospheric thinning of the North China craton: the first peak in 135−115 Ma simultaneously with the cratonic destruction, and the second peak caused by interaction between carbonated silicate melt and lithosphere mainly after 25 Ma. The later decreased the lithospheric thickness to about 70 km in the eastern part of North China craton.

A Non-Extensive Statistical Mechanics View on Easter Island Seamounts Volume Distribution

In the volcanic complex processes, inherent long-range interactions exist suggesting that Non-Extensive Statistical mechanics could be used to describe fundamental properties of the system. Based on the non-extensive Tsallis entropy a frequency-volume distribution function is suggested for the Easter Island-Salas y Gomez seamounts chain. Our results demonstrate the applicability of fundamental principles of Tsallis entropy to derive the cumulative distribution of seamounts volumes. The work suggests that the processes responsible for hotspot seamount formation are complex and the cumulative frequency-volume distribution of seamounts in the Easter Island/Salas y Gomez Chain (ESC) are well-described by a q-exponential function. The analysis leads to a non-extensive index q = 1.54 in agreement with that presented in other geodynamic or laboratory scale effects.

Variability of orogenic magmatism during Mediterranean-style continental collisions: A numerical modelling approach

The relationship between magma generation and the tectonic evolution of orogens during subduction and subsequent collision requires self-consistent numerical modelling approaches predicting volumes and compositions of the produced magmatic rocks. Here, we use a 2D magmatic-thermomechanical numerical modelling procedure to analyse rapid subduction of a narrow ocean, followed by Mediterranean style collision, which is characterized by the gradual accretion of lower plate material and slab migration towards the orogenic foreland. Our results suggest that magmatism has a large-scale geodynamic effect by focusing deformation throughout the entire subduction and collision process. The rheological structure and compositional layering of the crust impose a key control on the distribution of magmatic rocks within the orogen. Compared to previous simplified homogeneous crustal models, a compositionally layered crust causes an increase in felsic material influx during continental collision and results in shallower magmatic sources that migrate with time towards the foreland. Changes in the deformation style may be locally driven by magma emplacement rather than by slab movement. Our modelling also demonstrates that the migration pattern of the deformation front and the magmatic arc relative to the location of the suture zone may be driven by lower crustal indentation in the overriding plate during early stages of collision. The modelling predicts a gradual change in magma source composition with time from typical calc-alkaline to ones associated with relamination and eduction during subduction, collision and slab detachment. This transition explains the compositional changes of magma their temporal and spatial migration, as well as the observed link with deformation in the Dinarides orogen of Central Europe selected as a case study.