Upward Penetration Research Articles

The Mooihoek Platinum Pipe, Eastern Bushveld Complex, South Africa – Geochemistry and Mineralization

Abstract The Mooihoek pipe is one of several platiniferous dunite pipes in the eastern Bushveld Complex that were discovered in 1924 and mined until 1930. It has a diameter of about 180 by 400 m and consists of magnesian dunite that crosscuts a sequence of layered leucocratic wall rocks of the lower part of the upper Critical Zone of the Bushveld Complex. The Mg-dunite pipe at Mooihoek hosts a smaller, carrot-shaped inner pipe, 13–16 m in diameter and cylindrical in shape near surface, consisting of mainly iron-rich dunite/wehrlite pegmatite, comprising the platinum-bearing orebody. Specific characteristics of the mineralization are the near absence of sulfides and Pt being the predominant platinum-group element (PGE). The present work comprises whole rock analyses, ore microscopy, scanning electron microscopy, and electron probe microanalysis. The main findings are as follows: Chondrite-normalized distribution patterns of the PGE in the Mooihoek samples demonstrate that mainly Pt is strongly enriched relative to the other PGE and Au. The shapes of the patterns are subparallel to each other and also to those of the Onverwacht pipe, indicating a similar mode of origin. Olivine of the ore zone is iron-rich and is frequently accompanied by coarse Ti-magnetite and ilmenite, whereas chromite is rare. Two major generations of platinum-group minerals (PGM) are present at Mooihoek, namely: (1) Early inclusions of mainly ferroan platinum in (magmatic) olivine, Ti-magnetite, and ilmenite, and (2) a later, more complex PGM assemblage, commonly associated with thin veinlets of magnetite, mainly found along grain boundaries of silicates and oxides. This assemblage consists of various Pt-Fe alloys and PGE-antimonides, -sulfarsenides, -arsenides, and -sulfides. Overall, and in line with the geochemical data of the mineralization, Pt-dominated PGM predominate (~70%), followed by Rh, Pd, and Ru species. Pt-Fe alloys are the most frequent PGM (∼44% by number of grains). Our hypothesis on the genesis of the Mooihoek pipe and its mineralization largely corresponds to that proposed for the Onverwacht pipe (Oberthür et al. 2021): The magnesian dunite pipe was formed by upward penetration of magmas which replaced the existing cumulates. Fractional crystallization of olivine within a deeper magma chamber and/or during ascent of the melt resulted in the formation of a consanguineous residual, more iron-rich, and PGE-enriched melt. This melt also contained highly mobile, supercritical fluids and was continuously enriched in PGE and other incompatible elements. The PGE-enriched residual melts formed and sealed the inner ore pipe. Apparently, the PGE mineralization is not related to the well-established mechanism of sulfide collection. Instead, it was introduced in the form of nanoparticles and small droplets of PGM, which coagulated to form larger grains during evolution of the mineralizing system. Concomitant supercritical magmatic to hydrothermal fluids were continuously active and caused a certain redistribution of the initial PGE inventory and possibly added further quantities of PGE from lower parts of the mineralizing system. Reactions with ligands like Sb, As, and S led to the formation of composite PGM grains and complex intergrowths in a continuous process of mineralization. The present work underlines that sulfide-poor magmas may constitute fertile potential precursors of PGE deposits and, therefore, deserve more attention in future exploration.

Brief communication: New sonde to unravel the mystery of polar subglacial lakes

Abstract. The newly developed RECoverable Autonomous Sonde (RECAS) allows sampling and analysis of subglacial water while the subglacial lake remains isolated from the surface. The sonde was successfully tested in East Antarctica during the 2021–2022 field season: it reached the ice-sheet base at a depth of 200.3 m, sampled basal meltwater and measured its pressure, temperature, pH and conductivity and returned to the ice surface. The average downward penetration rate was 1.85 m h−1, and the average upward penetration rate was 2.94 m h−1. The successful test of a self-melting, recoverable probe in Antarctica marks further progress towards the clean exploration of subglacial water bodies.

Mass Transfer of Base Metals in Upward Penetration of Solutions in Tailing Dumps

Mass Transfer of Base Metals in Upward Penetration of Solutions in Tailing Dumps

CFD SIMULATIONS AND ANALYSES OF ASYMPTOMATIC AND SYMPTOMATIC NASAL AIRWAY OBSTRUCTIONS

The numerical simulations of the flow in nasal airways were performed for two different clinical cases. The results comprised the distributions of scalars at five different sections and included contours of pressure, velocity magnitude, turbulent kinetic energy and vorticity magnitude. Simulations showed the air branching occurring at the inferior meatus is unaffected by the variations in the volumetric flow rate or the changes in the flow regime through the olfactory cleft. However, the contractions and the following rapid change in the cross-section of the nasopharynx preclude the upward penetration of the vacuum field set by the lungs during the inhalation process. As a result, considerably low velocities and significant cross-sectional nonuniformities are observed, which lead to the appearances of the secondary flow structures and strong unsteadiness. Increased interactions between the airflow and the walls of the nasal cavity resulted in an increase in the vorticity on the right middle meatus and upper inferior meatus. The vorticity was also very high in the nostrils, where the flow was not fully developed.

Mass Transfer of Base Metals in Upward Penetration of Solutions in Tailing Dumps

Mass Transfer of Base Metals in Upward Penetration of Solutions in Tailing Dumps

High grade ores of the Onverwacht platinum pipe, eastern Bushveld, South Africa

ABSTRACT The platiniferous dunite pipes are discordant orebodies in the Bushveld Complex. The Onverwacht pipe is a large body (>300 m in diameter) of magnesian dunite (Fo80–83) that crosscuts a sequence of cumulates in the Lower Critical Zone of the Bushveld Complex. In a pipe-in-pipe configuration, the main dunite pipe at Onverwacht hosts a carrot-shaped inner pipe of Fe-rich dunite pegmatite (Fo46–62) which comprises the platinum-bearing orebody. The latter was ca. 18 m in diameter and a mining depth of about 320 m was reached. In the present work, a variety of ore samples were studied by whole-rock geochemistry, including analyses of platinum group elements, ore microscopy, and electron probe microanalysis. Olivine of the ore zone displays considerable chemical variation (range 46–62 mol.% Fo) and may represent either a continuum, or different batches of magma, or vertical or horizontal zonation within the ore zone. Chromite is principally regarded to be a consanguineous component of the pipe magma that crystallized in situ and simultaneously with olivine. The Onverwacht mineralization is Pt-dominated (>95% of the platinum group elements) and the ore is virtually devoid of sulfides. Platinum-dominated platinum group minerals predominate, followed by Rh-, Pd-, and Ru-species. Pt-Fe alloys are most frequent, followed by Pt-Rh-Ru-arsenides and -sulfarsenides, platinum group element antimonides, and platinum group element sulfides. Our hypothesis on the genesis of the Onverwacht pipe and its mineralization is as follows: After near-consolidation of the layered series of the Critical Zone, the magnesian dunite pipe of Onverwacht was formed by upward penetration of magmas that replaced the existing cumulates initially by infiltration, followed by the development of a central channel where large volumes of magma flowed through. Fractional crystallization of olivine within the deeper magma chamber and/or during ascent of the melt resulted in the formation of a consanguineous, residual, more iron-rich melt. This melt also contained highly mobile, supercritical, water-bearing fluids and was continuously enriched in platinum group elements and other incompatible elements. In several closing pulses, the platinum group element-enriched residual melts crystallized and sealed the inner ore pipe. Crystallization of the melt resulted in the coeval formation of Fe-rich olivine, chromite, and platinum group minerals. The non-sulfide platinum group element mineralization was introduced in the form of nanoparticles and small droplets of platinum group minerals, which coagulated to form larger grains during evolution of the mineralizing system. The suspended platinum group minerals acted as collectors of other platinum group elements and incompatible elements during generation and ascent of the melt. With decreasing temperature, the platinum group mineral grains annealed and recrystallized, leading to the formation of composite platinum group mineral grains, complex intergrowths, or lamellar exsolution bodies. On further cooling, platinum group minerals overgrowing Pt-Fe alloys formed by reaction of leached elements and ligands like Sb, As, and S mobilized by supercritical magmatic/hydrothermal fluids. Redistribution of platinum group elements/platinum group minerals apparently only occurred on the scale of millimeters to centimeters. Finally, surface weathering led to the local formation of platinum group element oxides/hydroxides by oxidation of reactive precursor platinum group minerals.

The Characteristics of Laser Welding of a Thin Aluminum Tab and Steel Battery Case for Lithium-Ion Battery

During lithium-ion battery packing, joining between battery cases and tabs is challenging for manufacturers due to dissimilar materials of the battery case and the tab, as well as their thicknesses. Laser welding, which has proven to produce a good weld with high productivity and low electrical resistance, is introduced to weld these materials. The weld was conducted with nanosecond-pulsed fiber laser and the effect of laser powers on mechanical and electrical properties as well as microstructure of the joint is investigated. The weld bead at the low laser power exhibited several blowholes on the surface, while the formation of voids including centerline and root cavities was observed through the cross-section. Moreover, the phenomenon of upward penetration (UP) was observed in all laser powers and recoil pressure which was generated by metal evaporation was supposed to cause the formation of an upward flow of the lower material. A hardness test was performed on both horizontal and vertical directions through the fusion zone. Additionally, the increase of upward penetration (UP) resulted in higher strength and lower electrical resistance of the weld.

Spawning superplumes from the midmantle: The impact of spin transitions in the mantle

AbstractThe formation of large‐scale upwellings with lateral extents of several hundreds of kilometers, reaching up to ∼10,000 km or more, still remains a hotly debated topic. Some seismic imaging studies based on high‐resolution data suggest that the main superplumes underneath Africa and South‐central Pacific are clusters, composed of several individual plumes rather than being a single large mantle upwelling. The iron spin transition in the lower mantle minerals may present a new idea on the origin and the formation of such superplumes, notably sourcing such features in the midmantle. Stagnation of both cold sinking slabs and hot rising plumes can be caused by density and viscosity variation due to the spin transition in iron in ferropericlase (Fp) and a possible spin‐dependent bulk modulus hardening in bridgmanite silicate perovskite (Pv). This process produces intermittent downward spin transition‐induced midmantle avalanches (SIMMA) of the cold sinking flow as well as upward spin transition‐induced midmantle superplume avalanches (SIMMSA) of the rising hot plumes, triggered at the spin transition‐induced thermal boundary layer at around 1600 km depth. Our high‐resolution axi‐symmetric models reveal that the hot upwellings, trapped below ∼1600 km depth, can suddenly penetrate into the upper levels in the mantle and spread laterally for hundreds of kilometres. Owing to the upward penetration of the midmantle‐rooted superplumes, as broad as ∼1500 km across, a large amount of heat can be delivered to the upper mantle and base of the lithosphere with implications for large volcanic episodes.

Experience of LU Zhi-zheng to apply tenuifolia

Professor LU Zhi-zheng, one of the first traditional Chinese medicine masters, is good at using tenuifoliain clinical practice, which often brings unexpected surprises. Lu said, tenuifolia is a mild herbal medicine with the nature of upward dispersion and outward penetration but not dryness. Tenuifolia has the following functions: making people conscious, relieving sore throat, diverging incubated diseases, regulating functional activities of qi, sending up Yang, dispelling wind evil and eliminating dampness, and activating collaterals to relieve pain. When well used, it will not only enhance the effect of monarch drug, but also restrict the impetuosity nature in a prescription, achieving better efficacy.

Effects of Monsoon Trough Intraseasonal Oscillation on Tropical Cyclogenesis over the Western North Pacific*

Abstract The effects of intraseasonal oscillation (ISO) of the western North Pacific (WNP) monsoon trough on tropical cyclone (TC) formation were investigated using the Advanced Research Weather Research and Forecasting (ARW) Model. A weak vortex was specified initially and inserted into the background fields containing climatological-mean anomalies associated with active and inactive phases of monsoon trough ISOs. The diagnosis of simulations showed that monsoon trough ISO can modulate TC development through both dynamic and thermodynamic processes. The dynamic impact is attributed to the lower–midtropospheric large-scale vorticity associated with monsoon trough ISO. Interactions between cyclonic vorticity in the lower middle troposphere during the active ISO phase and a vortex lead to the generation of vortex-scale outflow at the midlevel, which promotes the upward penetration of friction-induced ascending motion and thus upward moisture transport. In addition, the low-level convergence associated with active ISO also helps the upward moisture transport. Both processes contribute to stronger diabatic heating and thus promote a positive convection–circulation–moisture feedback. On the other hand, the large-scale flow associated with inactive ISO suppresses upward motion near the core by inducing the midlevel inflow and the divergence forcing within the boundary layer, both inhibiting TC development. The thermodynamic impact comes from greater background specific humidity associated with active ISO that allows a stronger diabatic heating. Experiments that separated the dynamic and thermodynamic impacts of the ISO showed that the thermodynamic anomaly from active ISO contributes more to TC development, while the dynamic anomalies from inactive ISO can inhibit vortex development completely.

Calculation of Pile-soil Stress Ratio of Rigid Pile Composite Foundation with Consideration of Upward Penetration of Piles

Deformation performance of rigid pile composite foundation under vertical loading was discussed, and the relationship between the pile lateral friction and the relative deformation of piles and soi...

Upward penetration of grains through a granular medium

We study experimentally the creeping penetration of guest (percolating) grains through densely packed granular media in two dimensions. The evolution of the system of the guest grains during the penetration is studied by image analysis. To quantify the changes in the internal structure of the packing, we use Voronoï tessellation and a certain shape factor which is a clear indicator of the presence of different underlying substructures (domains). We first consider the impact of the effective gravitational acceleration on upward penetration of grains. It is found that the higher effective gravity increases the resistance to upward penetration and enhances structural organization in the system of the percolating grains. We also focus our attention on the dependence of the structural rearrangements of percolating grains on some parameters like polydispersity and the initial packing fraction of the host granular system. It is found that the anisotropy of penetration is larger in the monodisperse case than in the bidisperse one, for the same value of the packing fraction of the host medium. Compaction of initial host granular packing also increases anisotropy of penetration of guest grains. When a binary mixture of large and small guest grains is penetrated into the host granular medium, we observe size segregation patterns.

Turbulent compressible convection with rotation—penetration above a convection zone

We perform Large eddy simulations of turbulent compressible convection in stellar-type convection zones by solving the Naviér-Stokes equations in three dimensions. We estimate the extent of penetration into the stable layer above a stellar-type convection zone by varying the rotation rate (Ω), the inclination of the rotation vector (θ) and the relative stability (S) of the upper stable layer The computational domain is a rectangular box in an f-plane configuration and is divided into two regions of unstable and stable stratification with the stable layer placed above the convectively unstable layer. Several models have been computed and the penetration distance into the stable layer above the convection zone is estimated by determining the position where time averaged kinetic energy flux has the first zero in the upper stable layer. The vertical grid spacing in all the model is non-uniform, and is less in the upper region so that the flows are better resolved in the region of interest. We find that the penetration distance increases as the rotation rate increases for the case when the rotation vector is aligned with the vertical axis. However, with the increase in the stability of the upper stable layer, the upward penetration distance decreases. Since we are not able to afford computations with finer resolution for all the models, we compute a number of models to see the effect of increased resolution on the upward penetration. In addition, we estimate the upper limit on the upward convective penetration from stellar convective cores.

A test of the influence of tidal stream polarity on the structure of turbulent dissipation

Vertical mixing by the tides plays a key role in controlling water column structure over the seasonal cycle in shelf seas. The influence of tidal stirring is generally well represented as a competition between surface buoyancy input and the production of turbulent kinetic energy (TKE) by frictional stresses, a competition which is encapsulated in the Qh/ u 3 criterion. An alternative control mechanism arises from the limitation of the thickness of the bottom boundary layer due to the effects of rotation and the oscillation of the flow. Model studies indicate that, for conditions typical of the European shelf seas, the energy constraint exerts the dominant control but that for tidal streams with large positive polarisation (i.e. anti-clockwise rotation of velocity vector), some influence of rotation in limiting mixing should be detectable. We report here measurements of flow structure (with ADCPs) and turbulent dissipation (FLY Profiler) made at two similar locations in the Celtic Sea which differ principally in that the tidal currents rotate in opposite senses with approximately equal magnitude (polarity P=±0.6). A clear contrast was observed between the two sites in the vertical structure of the currents, the density profile and the rate of dissipation of TKE. At the positive polarity (PP) site ( P≈+0.6), the bottom boundary layer in the tidal flow was limited to ∼20 mab (metre above the bed) and significant dissipation from bottom boundary friction was constrained within this layer. At the negative polarity (NP) site ( P≈−0.6), the dominant clockwise rotary current component exhibited a velocity defect (i.e. reduction relative to the free stream) extending into the upper half of the water column while significant dissipation was observed to penetrate much further up the water column with dissipation levels ∼10 −4.5 W m −3 reaching to the base of the pycnocline at 70–80 mab. These contrasting features of the vertical distribution of dissipation are well reproduced by a 1-D model when run with windstress and tidal forcing and using the observed density profile. Model runs with reversed polarity at the two sites, support the conclusion that the observed contrast in the structure of tidal velocity, dissipation and stratification is due to the influence of tidal stream polarity. Increased positive polarity reduces the upward penetration of mixing which allows the development of stronger seasonal stratification, which, in turn, further inhibits vertical mixing.

Turbulent compressible convection with rotation–penetration below a convection zone

We perform Large eddy simulations of turbulent compressible convection in stellar-type convection zones by solving the Navier-Stokes equations in three dimensions. We estimate the extent of penetration into the stable layer above a stellar-type convection zone by varying the rotation rate (Ω), the inclination of the rotation vector (θ) and the relative stability (S) of the upper stable layer The computational domain is a rectangular box in an f-plane configuration and is divided into two regions of unstable and stable stratification with the stable layer placed above the convectively unstable layer. Several models have been computed and the penetration distance into the stable layer above the convection zone is estimated by determining the position where time averaged kinetic energy flux has the first zero in the upper stable layer. The vertical grid spacing in all the model is non-uniform, and is less in the upper region so that the flows are better resolved in the region of interest. We find that the penetration distance increases as the rotation rate increases for the case when the rotation vector is aligned with the vertical axis. However, with the increase in the stability of the upper stable layer, the upward penetration distance decreases. Since we are not able to afford computations with finer resolution for all the models, we compute a number of models to see the effect of increased resolution on the upward penetration. In addition, we estimate the upper limit on the upward convective penetration from stellar convective cores.

The coupling of long-term trace metal trends to internal trace metal fluxes at the oxic–anoxic interface in the Gotland Basin (57°19,20′N; 20°03,00′E) Baltic Sea

The Gotland Basin is a well-stratified water body with lower saline surface waters and a halocline between 70 and 90 m. Since 1996, a continuous oxygen depletion started in the deep water of the Gotland Basin after the major saltwater inflow 1993/1994. Since 1996, the deep water became anoxic during periodical intervals below 150 m up to the bottom (238 m), and since 1999, a permanent redox interface developed in the range of the 150 m depth horizon. This paper presents results on the trace metal speciation between dissolved and particulate phases during long-term changes, which will be explained in relation to the upward penetration and the seasonal movement of the redox interface. Trace metal trends for surface and deep waters were observed between 1993 and 2002. In the water body “Below Halocline”, a decrease of the dissolved concentrations of Cd diss (−7.6% year −1), Cu diss (−8.3% year −1), Zn diss (−15.9% year −1) and Pb diss (−7.6% year −1) were observed since 1995, due to the formation of sulfide species and their burial in the surface sediments. “Above Halocline”, slightly increasing concentrations were observed for Cd diss (+6% year −1) between 1994 and 1999 and for Zn diss between 1994 and 1997, which has been attributed to the enrichment from riverine and atmospheric input in surface waters. Since 1999, the system is controlled and dominated by the vertical fluxes due to the establishing stagnant anoxic deep water body influencing the removal of trace metals from surface waters by time delay. Significant negative trends for Cd diss (−11% year −1) and Zn diss (−10% year −1) were observed “Above Halocline” since 1999 and 1997, respectively. Pb diss shows a negative trend of −6% year −1 “Above Halocline” between 1993 and 2002. Additional to the decrease of Pb use in gasoline, this result is attributed to the specific geochemistry and short residence time of Pb in connection with the strong affinity and export by particles of mainly lithogenic origin. For Cu diss, no trend was observed for surface waters. In this context, the relation of trace metal export through the redox interface and the linkage of trace metal dynamic due to eutrophication (movement of the redox interface) has been investigated on a seasonal scale. Highly resolved vertical profiles of trace metals (Pb, Cd, Zn, Cu, Co, Fe, Mn) have been carried out between December 1999 and February 2001 on a seasonal base. Calculations of dissolved trace metal fluxes using the vertical turbulent mixing coefficient according to the seasonal movement of the redoxcline gave information about the diffusive flux and quantitative transport of trace metals into the anoxic water body. For Cd diss, Cu diss and Zn diss, elevated downward fluxes were observed during winter season, and by a factor 1.5–2 reduced fluxes during summer. Co diss, Fe diss and Mn diss show no seasonal flux variations. About 25% of Cd, 12% of Cu and 8% of Zn which has been supplied by rivers and by the atmosphere are eliminated by diffusive exchange, due to sulfide precipitation, across the oxic–anoxic interface in the Gotland Basin. For dissolved lead, the diffusive exchange is negligible.

Experiments to study baroclinic waves penetrating into a stratified layer by a quasi-geostrophic potential vorticity equation

The upward penetration of the mid-latitude baroclinic waves has been well known to influence the air motion in the stratosphere. To study this in the laboratory, we present a new type of rotating fluid annulus experiment where a radial temperature difference is imposed on water near the flat bottom to produce a baroclinic wave in a lower layer and the water surface is heated to create a stratified upper layer. To test this model, we carried out experiments to study baroclinic waves penetrating into the stratified layer by a quasi-geostrophic potential vorticity equation in the atmospheric dynamics. The baroclinic waves produced in the lower fluid layer were observed to penetrate into the stratified upper layer. As expected from the equation, the vorticities of the flows for wavenumbers 3, 4 and 5 decayed exponentially with height and showed a weaker decay for lower wavenumbers.

Geothermal heating and its influence on the meridional overturning circulation

The effect of geothermal heating on the meridional overturning circulation is examined using an idealized, coarse‐resolution ocean general circulation model. This heating is parameterized as a spatially uniform heat flux of 50 m W m−2 through the (flat) ocean floor, in contrast with previous studies that have considered regional circulation changes caused by an isolated hot spot or a series of plumes along the Mid‐Atlantic Ridge. In our model results the equilibrated response is largely advective: a deep perturbation of the meridional overturning cell on the order of several sverdrups is produced, connecting with an upper level circulation at high latitudes, allowing the additional heat to be released to the atmosphere. Rising motion in the perturbation deep cell is concentrated near the equator. The upward penetration of this cell is limited by the thermocline, analogous to the role of the stratosphere in limiting the upward penetration of convective plumes in the atmosphere. The magnitude of the advective response is inversely proportional to the deep stratification; with a weaker background meridional overturning circulation and a less stratified abyss the overturning maximum of the perturbation deep cell is increased. This advective response also cools the low‐latitude thermocline. The qualitative behavior is similar in both a single‐hemisphere and a double‐hemisphere configuration. In summary, the anomalous circulation driven by geothermal fluxes is more substantial than previously thought. We are able to understand the structure and strength of the response in the idealized geometry and further extend these ideas to explain the results of Adcroft et al. [2001], where the impact of geothermal heating was examined using a global configuration.

Deformational structures in the Iskur Carbonate Group (Lower - Upper Triassic) from the Western Balkanides

The deformational structures in the rocks of the Iskur Carbonate Group (Lower - Upper Triassic) frоm the Western Balkanides аrе concentrated mainly in three lithostratigraphic units (Mogila Formation, Lyubash Formation and Вabinо Formation) which cover а chronostratigraphic interval frоm the Spathian to Ladinian age. The structures оссur mostly in limestones and to а lesserextent in sandstones. The subparallel shear surfaces are observed оnlу in the lowermost levels of the Mogila Formation (Opletnya Member) and are interpreted as formed during а periodiсаl paleoseismic activity. Four morphological subtypes аrе differentiated (arcuate, sigmoidal, serpentine and subvertical). The convolute lamination (Mogila Formation) and wavy to crumpled bedding (Ваbinо Formation) emerged as а direct result frоm the primary instability of а non-homogeneous system built uр of purer carbonate and marly laminae without excluding the participation of external factors. The slump structure (Ваbinо Formation) was predetermined bу the small dip of the Middle Triassic carbonate ramp and generated through gravitational mass movements in lateral direction. The load structure (Моgilа Formation) was formed bу means of downward penetration of coarser carbonate material into underlying hydroplastic carbonate mud due to overloading. The flame structure (Ваbinо Formation) is interpreted in а similar way, but as а result from upward penetration of carbonate mud into later deposited carbonate sand. The оnlу structure that is established in sandstones is ball-and-pillow (Lyubash Formation). Its interpretation is related with а comparativelу rapid and irregular collapse of clastic material into unlithified carbonate-clayey sediments. The correlation of the stratigraphic levels with subparаllеl shear surfaces shows highest vertical density in some cross sections from the Iskur river valley (between Lacatnic railway station and hamlet of Sfrazhen). The supposed major epicentre zone of the ancient earthquakes was situated in this region. The whole seismic activity in the study area from the end of the Lower Triassic epoch resembles the paleoseismic manifestations known from the German Lower Muschelkalk. As earthquakes must have bееn at least partially а controlling factor for some of the other described structures it is quite probable that the seismic activity in the area has continued through Anisian times. The presence of typical seismites in the Lower Triassic sediments is а prerequisite for further investigations aiming at а more regional correlation with isochronic rocks.

Petrogenesis of Cenozoic Basalts from Vietnam: Implication for Origins of a `Diffuse Igneous Province'

Basalt magmatism occurred throughout east and southeast Asia after the early Tertiary India–Asia collision. This activity does not conform to the ‘Large Igneous Province’ model in view of lower eruption and melt production rates, wide dispersal of centres and the apparent absence of deep mantle upwelling. Age data for Vietnamese plateau basalts reflect spatial–temporal patterns consistent with a rotating stress field rather than supra-hotspot lithosphere migration. For most of the volcanic centres there are two eruptive episodes: an early series formed by high-SiO2, low-FeO* quartz and olivine tholeiites—large melt fractions of refractory (lithosphere-like) mantle—and a later series made up of low-SiO2, high-FeO* olivine tholeiites, alkali basalts and basanites—smaller melt fractions of more fertile (asthenosphere-like) mantle. Comparison of Mg-15 normalized basalt compositions with parameterized anhydrous and hydrous experimental melt compositions allowed calculation of melt segregation pressures and temperatures. Computed for anhydrous conditions these range from <4 GPa and ∼1470°C (for alkali basalts) to <0.5 GPa and ∼1400°C (quartz tholeiites), and for H2O-undersaturated conditions, from <3.5 GPa and ∼1450°C to ∼1.5 GPa and 1350–1400°C, respectively. Hydrous conditions are more realistic in view of high measured basalt H2O+ contents, pressure estimates consistent with melting below a thinned mechanical boundary layer (MBL) and interpolated mantle adiabats of 2–3°C/km (compared with <1°C/km for anhydrous conditions), consistent with fluid dynamic constraints and a 1440°C potential temperature. After collision-induced ‘extrusion’ of east and southeast Asia, the lithosphere was probably thinned during heating and transtension; this converted refractory MBL into a low-viscosity thermal boundary layer (TBL), and caused upward penetration and polybaric melting of TBL–asthenosphere columns.