Sediment thickness map of the Indian region 79°E–86°E, 2°S–8°S based on satellite gravity interpretation

Satellite free air gravity anomalies over the Indian ocean region 79°E–86°E, 2°S–8°S were obtained from the website http://topex.ucsd.edu and a contour map was compiled. Five profiles of the anomaly have been interpreted in terms of two-dimensional structures in the ocean. Thickness of sediments lying on the oceanic crust determined from the interpretation of gravity profiles were used to compile an isopach map of the region 79°E–86°E, 2°S–8°S. This map in combination with one of the isopach maps compiled by previous workers, provides information regarding the thickness of sediments up to 6° S. According to this map sediment thickness varies from ～600 m over the middle part of the region to ～800 m further south, indicating that thinning of sediments in the middle part of the region is only localized. Information provided by this gravity study may be useful in planning detailed seismological studies to delimit the outer edge of the continental margin of Sri Lanka, defined according to the United Nations Convention of the Law of the Sea (UNCLOS).     

Mineral Components, Texture, and Forming Conditions of Hydrothermal Chimney on the East Pacific Rise at 9°-10°N

To characterize the hydrothermal processes of East Pacific rise at 9o-10oN, sulfide mineral compositions, textural, and geochemical features of chimney ores were studied using ore microscope, scanning electron microscope, X-ray diffraction analysis, and electron microprobe techniques. Results show that there are three mineral assemblages for the hydrothermal chimney ores, namely: (i) anhydrite marcasite pyrite, (ii) pyrite sphalerite chalcopyrite, and (iii) chalcopyrite bornite digenite covellite. Mineral assemblages, zonational features, and geochemical characteristics of the ore minerals indicate that ore fluid temperature changed from low to high then to low with a maximum temperature up to 400 ℃. The chimney is a typical black smoker. The initial structure of the chimney was formed by the precipitation of anhydrites, and later the sulfides began to precipitate in the inner wall.     

Study on the mechanism of transport of heavy metals in soil in western suburb of Beijing

1 IntroductionIncorporation of potentially toxic metals ( e.g.Cd, Cu, Cr, Pb, Hg, As, Se, Zn, Ni) into soils ei-ther through sewage-sludge irrigation or some othersources of pollution (e.g. atmospheric deposition, ap-plication of agri-chemicals) has posed…     

Study on the spatial and temporal variations of the surface albedo on Muz Taw Glacier,Sawir Mountains北大核心CSCD

冰川反照率时空变化特征研究对于评估冰川能量物质平衡及认识冰川消融过程至关重要。本文基于高空间分辨率的Landsat OLI影像和高时间分辨率的MOD10A1产品,并结合冰面反照率实测数据,开展了2011—2021年北疆萨吾尔山木斯岛冰川表面反照率的时空变化特征及其对冰川物质平衡影响的研究。结果表明:Landsat反演反照率和MOD10A1反照率与同期内冰面实测反照率的相关性分别为0.95和0.62,均显示木斯岛冰川表面反照率存在显著的时空变化特征;在空间尺度上,冰面反照率沿主流线整体随海拔升高呈增加趋势。但由于局部地形差异,反照率在海拔3 600 m以下区域随海拔升高出现下降趋势;在同一海拔处,反照率沿冰川两侧边缘向中部递增。2011—2021年,冰川年均反照率微弱增加,消融期内(5—8月)平均反照率与全年平均反照率的变化速率分别为0.0024 a-1和0.0017 a-1;逐月反照率具有显著的季节变化特征,6—8月冰面反照率较低(0.330),12月—次年2月冰面反照率较高(0.586);消融期内冰川消融区反照率下降幅度大于积累区。研究进一步表明,夏季(6—8月)平均反照率与冰川物质平衡存在显著的正相关(R=0.84,P<0.01),气温、固态降水、云量、太阳入射角、吸光性杂质等是影响冰川反照率变化的重要因素。该研究将对冰川消融过程和机理、能量物质平衡模拟等工作提供重要的基础支撑。     

Identification of a surface layer structure and analysis of humidity data in two weather situations at Jodhpur (26°18′N, 73°04′E), India,during MONTBLEX 1990

The Monsoon Trough Boundary Layer Experiment held in 1990 was a multi-institutional effort to probe the atmospheric boundary layer over the monsoon trough over northern India. For this experiment, four micrometeorological towers were set up at four different locations along the normal position of the trough. One such tower of 30m height was located at Jodhpur (26‡18′N, 73‡04′E), Rajasthan. The fast and slow response data available during the experiment have been used in the present study to determine a suitable layer-structure of the surface layer for evaluation of sensible heat flux using the multilayer hypothesis of Kramm (1989).     

Study on rainfall variations in the middle part of Inner Mongolia,China during the past 43 years

The study area, the middle part of Inner Mongolia including Hohhot city, Baotou city, Wulanchabu city, Ordos city, Bayannaoer city and Wuhai city, is one of typical eco-geographical transition zones in China. Using monthly precipitation data (1961–2003) from 45 meteorological stations in the study area, this paper analyzes characteristics and tendencies of annual and seasonal rainfall variations, and reveals multi-time scales structures of these time series through wavelet analyses; also, the periods of annual and seasonal precipitation series are identified, and the periodical oscillations and points of abrupt change at the principal period scale are discovered. The results show that annual precipitation varies in a large range, and has an ascending tendency at an increasing rate of 1.482 mm/10a; the multi-time scales periodical oscillations are clear; differences in tendencies, ranges and decadal precipitation anomalies exist within each decade during 1961–2000. The seasonal allocation of overall annual precipitation is extremely uneven; in terms of tendencies of seasonal precipitation, winter and spring have upward trends while summer and autumn have downward tendencies; distinctions in tendencies, ranges and decadal precipitation anomalies among each seasons are in existence within each decade during 1961–2000. The periodical oscillations of each seasonal precipitation time series are also evident. The research results not only provide convincing evidence for global climate change research, but also facilitate the understanding of specific natural process and pattern to make steps to rehabilitate and reconstruct vegetation, and contribute to fulfill the sustainability of water management.     

Sodium-rich metasomatism in the upper mantle: Implications of experiments on the pyrolite-Na2O-rich fluid system at 950°C, 20 kbar

Sodium-rich metasomatism in the upper levels of the mantle has been modelled by reacting pyrolite with alkali-bearing H₂O fluids containing minor CO₂ and concentrations of Na₂O and Na₂O + K₂O (K/K + Na = 0.1 ) up to 4.0 g alkalies/10 g H₂O at 20 kbar and 950°C. With increasing alkali concentration, the amounts of amphibole (pargasite-edenite) and olivine increase as orthopyroxene and clinopyroxene decrease. Amphiboles show progressive increases in Na (and K) and Si concentrations and decreases in Al and Ca concentrations suggesting the dominant substitution mechanism is (Na, K) + SiAl + Ca. These results and least squares mass balance calculations suggest the reaction of clinopyroxene + orthopyroxene + spinel produces amphibole + olivine.In nature, upper mantle spinel lherzolite is commonly veined by a variety of rock types which may contain Ti-pargasite as a magmatic crystallization product. Pargasite-edenite occurs interstitially in spinel Iherzolite, often spatially related to Ti-pargasite and may be produced by hydrous fluids evolved during late stage crystallization of the veined rocks. This is supported by the close compositional correlation between the natural pargasite-edenite amphiboles and those produced in this study.The present study suggests that up to 43 wt.% amphibole may be accommodated in pyrolite in the presence of Na₂O-rich H₂O-CO₂ fluids. This represents 0.8 wt.% H₂O and 1.7 wt.% Na₂O in the hydrated pyrolite composition and indicates the importance of sodium in determining the extent of metasomatism. Sodium also lowers the solidus temperature of pyrolite by more than 50°C over the H₂O-saturated pyrolite system at 20 kbar.     

Study of the Behavior of Uranium,Niobium, and Tantalum in the Granite Melt–Fluoride Fluid System at 800–950°C, 2300 Bar

Geology of Ore Deposits - Experimental studies were carried out on the solubility of uranium, niobium, and tantalum in acidic melts of Li–F granites and predominantly fluoride fluids at...     

Evidence for Granitoid Magmatism and the Composition of the Silicic Melt in the Gabbroid Assemblage of the Mid-Atlantic Ridge at 13° N: New Data on Melt Inclusions

Doklady Earth Sciences - Despite the local occurrence of silicic magmatism during the formation of the oceanic crust, the nature of felsic granitoid veins (“oceanic plagiogranite”)...     

Pressure-composition relations for coexisting gases and liquids and the critical points in the system NaCl-H2O at 450, 475, and 500°C

Pressure-temperature-composition (P, T, x) relations for the co-existing vapor and liquid phases in the system NaCl-H₂O were determined experimentally at 450, 475, and 500°C. Data for each isotherm include P-x relations near the critical point and extend to the three-phase assemblage vapor-liquid-halite on the vapor side. On the liquid side the P-x data range from the critical point to the room-temperature halite saturation point (~25 wt.% NaCl). Critical pressures were calculated from measured pressures and compositions and classical theory. The results generally support the few data points of Urusova (1974, 1975) and Ölander and Liander (1950) but differ markedly from the extensive data of Sourirajan and Kennedy (1962).     

The Magmatic–Hydrothermal Transition and Origin of Brine in the Oceanic Core Complex of the Mid-Atlantic Ridge at 13° N

New data on local mineral associations and the microheterogeneity of minerals and fluid inclusions in gabbro were obtained for the gabbro–peridotite oceanic core complex with a long-lived detachment fault controlling the hydrothermal activity. It is assumed that the hydrothermal hydrogen-bearing fluid with a NaCl content of >30 wt % is formed in the seawater/harzburgite (~1/5) reaction of serpentinization. The brine residual after serpentinization interacted with gabbro at the final stages of crystallization of an intrusion and assimilated some components (K, REEs, and Ba) from the residual melt. The interaction was resulted in metamorphic transformations of gabbro at decreasing temperature below 500°C. The reaction of the decomposition of magmatic titanomagnetite with the transition of iron reduced to Fe²⁺ into newly formed chlorinebearing amphibole at 540–450°C and logf(O₂) from–20 to–24 is shown.

     

Along-strike variations of P–T conditions in accretionary wedges and syn-orogenic extension,the HP–LT Phyllite–Quartzite Nappe in Crete and the Peloponnese

Syn-orogenic detachments in accretionary wedges make the exhumation of high-pressure and low-temperature metamorphic rocks possible with little erosion. The velocity of exhumation within the subduction channel or the accretionary complex, and thus the shape of P–T paths, depend upon the kinematic boundary conditions. A component of slab retreat tends to open the channel and facilitates the exhumation. We document the effect of slab retreat on the shape of P–T paths using the example of the Phyllite–Quartzite Nappe that has been exhumed below the Cretan syn-orogenic detachment during the Miocene in Crete and the Peloponnese. Data show a clear tendency toward colder conditions at peak pressure and during exhumation where the intensity of slab retreat is larger. This spatial evolution of P–T gradient is accompanied with an evolution from a partly coaxial regime below the Peloponnese section of the detachment toward a clearly non-coaxial regime in Crete.     

Tectonic controls on the evolution of the Andean Cenozoic foreland basin: Evidence from fluvial system variations in the Payogastilla Group,in the Calchaquí, Tonco and Amblayo Valleys,NW Argentina

The stratigraphic and sedimentological characteristics of the Payogastilla Group represent important tectono-sedimentary constraints on the evolution of the Andean foreland basin in northwestern Argentina. This nonmarine unit unconformably rests on top of the post-rift deposits of the middle Eocene Lumbrera Formation of the Santa Bárbara Subgroup (Salta Group). Eocene-Pliocene paleoenvironmental changes are a direct result of the tectonic settings and accommodation space. Sequential stratigraphic analysis of the paleoenvironment of the Los Colorados Formation strata indicates the presence of three third-order sequences. Each sequence comprises a low-accommodation systems tract (LAST) and a high-accommodation systems tract (HAST). Substantial tectonic activity from the middle to upper Miocene is represented by Angastaco Formation strata that contain a shallow, gravel-braided fluvial system associated with gravity flows, with thicknesses of 4550 m (Calchaquí River) to 1500 m (Tonco). This activity marked the depocenter of the Angastaco basin. The development of a basal unconformity and the erosion of the Los Colorados Formation suggest a renewed uplift of the source area. Changes in the fluvial systems indicate an increase of the accommodation space.To obtain better temporal constraints on the basin evolution, new U–Pb ages on zircons from five pyroclastic airfall and two sedimentary levels were determined. A substantial environmental change in the upper Miocene (10–5 Ma) is associated with three episodes of tectonic uplift that are reflected in variations in the sedimentation rates of the Palo Pintado Formation. A reactivated Pliocene tectonic uplift is recorded in alluvial fans that originated from the east.     

A Study of the Impacts of Freeze–Thaw on Cliff Recession at the Calvert Cliffs in Calvert County,Maryland

The Calvert Cliffs, which form much of the western coastline of the Chesapeake Bay in Calvert County, Maryland, are actively eroding and destabilizing, yielding critical situations for many homes in close proximity to the slope’s crest. Past studies have identified that waves directly interacting with the slope toe control cliff recession; however, where waves do not regularly interact with the slope toe, freeze–thaw controls recession. This study investigated the validity of this second claim by analyzing the recession rate and freeze–thaw behavior of six study sites along the Calvert Cliffs that are not directly affected by waves. While waves do remove failed material from the toe in these regions, freeze–thaw is believed to be the dominant factor driving recession at these sites. Past recession rates were calculated using historical aerial photographs and were analyzed together with a number of other variables selected to represent the freeze–thaw behavior of the Calvert Cliffs. The investigation studied sixteen independent variables and found that over 65 % of recession at these study sites can be represented by freeze–thaw through the following variables: (1) slope aspect, (2) soil freeze–thaw susceptibility, (3) the number of freeze–thaw cycles, and (4) the weighted shear strength. Future mitigation techniques at these sites should focus on addressing these variables. Unmitigated, the Calvert Cliffs will continue to recede until a stable slope angle is reached and maintained.     

Experimental Study of the Influence of Hydrous Minerals on the Melting Behaviour of Rocks at High Temperatures and Pressures

The experimental study on the melting of potassic basalt and eclogite with about 2% waterat 800-1300℃ and 1.0-3.5 GPa shows that the solidi of both rocks are significantly lower thanthose obtained from the previous experiments of the same type of rocks under dry conditions,and the former which is enriched in potassium has a lower melting point than the latter. It is con-sistent with the previous study. The melting temperature of eclogite increases with pressure,whereas potassic basalt has similar properties only at 1.5—2.5 GPa and>3.0 GPa, and at 2.5—3.0 GPa the melting temperature decreases with pressure. This can be explained as follows: (1)eclogite only has one hydrous mineral amphibole and the dehydous temperature is lower than thewet solidus of the rock. (2) Amphibole exists in potassic basalt at the pressures lower than 2.5GPa and phlogopite exists at pressures higher than 2.5 GPa, and the special compositions of bothminerals determine that amphibole has a dehydration temperature higher than or close to that ofthe wet solidus of the rocks, while phlogopite has a dehydration temperature lower than that ofthe wet solidus. On the other hand the features of the continuous solidus in the experiment ofhydrous eclogite were produced by the fact that the dehydration temperature of its amphibolelower than or close to the melting temperature of the hydrous conditions. So the melting tempera-ture lowers at higher pressures. Therefore, the composition of the rocks in the lithosphere and thetypes of hydrous minerals and their stable P-T conditions are the important factors controllingthe solidi of rocks. It can quite well explain the partial melting of rocks and the origin of the lowvelocity zone in the deep lithosphere.     

Crustal structure and nature of emplacement of the 85°E Ridge in the Mahanadi offshore based on constrained potential field modeling: Implications for intraplate plume emplaced volcanism

An integrated interpretation of multi-channel seismic reflection, gravity and magnetic datasets belonging to northern most part of the 85°E Ridge in the Mahanadi offshore is carried out to study the crustal structure and mode of its emplacement. The basement structure map of the ridge reveals that it is 130–150 km wide and is composed of an eastern high which appears as a continuous, broad and smooth topographyand the western high characterized by several steep isolated highs. The seismic velocities reported for the first time over the ridge indicate several sedimentary sequences ranging in velocities between 1.6 and 4.0 km/s above the acoustic basement top. The salient aspects of the sedimentary velocities are; a low velocity layer (2.6–3.2 km/s) within the Cretaceous sequence in the intervening depressions encompassing the flank region, and a regionally widespread higher velocity layer (3.5–3.8 km/s) belonging to the Eocene–Oligocene section overlying the ridge. A layer having a velocity of 4.2–4.7 km/s probably made of volcanoclastic rocks is observed immediately below the acoustic basement. The sediment isopach maps presented here for three major horizons are used to compute the 3-D sediment gravity effect to obtain a crustal Bouguer anomaly map of the region. Detailed analysis of the gravity and magnetic anomaly maps clearly demonstrates the continuity of ridge up to the Mahanadi coast at Chilka Lake. Seismically constrained gravity and magnetic models indicate that the ridge is composed of volcanic material that was emplaced on continental crust in the shelf-slope areas and over the oceanic crust in the deep offshore areas. The modeled crustal structure below the ridge further indicates volcanic emplacement of the ridge on a relatively younger lithosphere. We propose two alternative models for the emplacement of the ridge.     

Formation of N–С–О–Н molecules and complexes in the basalt–basaltic andesite melts at 1.5 Gpa and 1400°C in the presence of liquid iron alloys

The contents and speciation of nitrogen, carbon, and hydrogen were determined in basalt–basaltic andesite melts in equilibrium with liquid Fe alloys at 1.5 Gpa, 1400°C, and oxygen fugacity (fO₂) 1.4–1.9 log units below that of the Fe–FeO buffer (ΔlogfO₂(IW) =–1.4 …–1.9). Experiments were carried out on a piston- cylinder type apparatus using welded Pt capsules in the presence of excess С (graphite). Starting mixture consisted of natural ferrobasaltic glass and silicon nitride (Si₃N₄) as nitrogen source in the system. Experimental quench products representing glasses with spherical inclusions of iron alloy were analyzed using electron microprobe, Raman, and IR spectroscopy. With increase of Si₃N₄ in the starting mixture and, respectively, decrease of fO₂, silicate melt forming during experiments became depleted in FeO and enriched in SiO₂. It was established that the nitrogen content in the glasses increases from 0.13 to 0.44 wt % with decrease of ΔlogfO₂(IW) from–1.4 to–1.9, whereas C content in the first approximation remains constant within 1.18–1.13 wt %, while the total water content (ОН^– + Н₂О) determined by IR spectroscopy decreases from 4.91 to 1.20 wt %. The N (0.13–0.48 wt %) and C (0.75–2.26 wt %) contents determined in the Fe alloy show no clear correlation with fO₂. The IR and Raman spectroscopic study of the glasses indicates the formation of molecules and complexes with bonds N–H (NH₃, NH₂ ^?, NH₂ ⁺, NH₄ ⁺), Н–О (Н₂О, OH^–), С–Н (СН₄) as well as N₂ and Н₂ molecules in silicate melts. IR spectra also reveal the presence of complexes with С=О, С–N bonds and СО₂ molecules. Obtained data are compared with results of previous studies on the solubility and speciation of N, С, and Н in the model FeO–Na₂O–SiO₂–Al₂O₃ melts in equilibrium with liquid iron alloys at 1.5 GPa (1400°C) and 4 GPa (1550°C) (Kadik et al., 2011, 2015).