Western Flank Research Articles

Sumian Basalts and Basaltic Andesites of the Karelian Province of the Fennoscandian Shield: Geologic Position, Composition, and Formation Conditions

Abstract —We performed a petrochemical study and determined the Sm–Nd isotope composition of the Sumian (early Paleoproterozoic) mafic metavolcanic rocks in the Vodlozero domain (Semch’, Kumsa, and Kamennye Ozera structures) and the Central Karelian domain (Lake Vottomuks and Lake Kogu structures, the western flank of the Lekhta structure) of the Karelian province of the Fennoscandian Shield and compared them with the coeval volcanic rocks of the Kola–Norwegian province and the intrusive rocks of the Karelian and Belomorian provinces. The Sumian mafic rocks intruding the rocks of the Archean domains with different crust ages (>3.1 and 2.7–2.8 Ga) have similar geochemical characteristics (SiO2 = 44–55 wt.%, MgO = 5–14 wt.%; LREE enrichment, (La/Yb)N = 5–17) and similar values of εNd(T) (from –2.7 to –0.5) and TNd(DM) (from 3.0 to 2.7 Ga), which distinguishes them from their Archean analogues and indicates a single large magma source. The crustal contamination of the primary melts did not exceed 15% and could not determine the isotope-geochemical specifics of the Sumian mafic rocks. Their specific composition is better explained by the model of the formation of primary melts through the low-pressure (2.5–3.0 GPa) melting of the Neoarchean metasomatized zones of the subcontinental lithospheric mantle, with the addition of the primitive-mantle melts. In the period 2.41–2.45 Ga, the early Paleoproterozoic mafic rocks of the Fennoscandian Shield formed in the intracontinental magma generation setting.

Rock–water interaction, chemical weathering and solute transport of two rivers draining contrasting climate gradients in Western Ghats, India

AbstractRock–water interactions and chemical weathering are critical factors that determine the quality and quantity of solute transport in river catchments. However, most studies in this field have been limited to temperate regions and data from the tropics and subtropics are scarce, particularly for small rivers that are more responsive to environmental and climate changes. In this study, we investigated chemical weathering, its causal mechanisms and controlling factors that determine changes in the quality and quantity of solutes in two small, tropical mountainous rivers‐the west‐flowing Thuthapuzha river and the east‐flowing Bhavani river‐that drain through contrasting climate and geologic gradients across the southern part of the Western Ghats, in India. This region is an elevated passive continental margin and an ecologically sensitive area. Hydrochemical analysis of river water revealed that the cationic and anionic concentrations in the samples are in descending order of importance Ca2+ > Na+ > Mg2+ > K+ and HCO3− > Cl− > SO42−. Principal component analysis (PCA) indicated that geogenic factors (geology, chemical weathering and leaching/erosion) have a significant role in determining the hydrochemical characteristics of the rivers. To discriminate the relative contributions of silicate weathering in the river basins, we performed a detailed analysis of the major ion ratios along with forward and inverse modelling. The weathering index computed from the molecular ratio of cations and silica concentrations suggested that silicate weathering leads to kaolinite formation in the soil profile. The carbon dioxide consumption rate (CCR) estimated for the Thuthapuzha river, which is draining the humid western flank of the Western Ghats, was 2.18 × 105 mol·km−2 year−1, whereas the Upper Bhavani river, which is draining the semi‐arid area of the Western Ghats was 1.39 × 105 mol·km−2 year−1. Our study highlights the interplay of climatic factors and the geologic characteristics of the terrain that significantly influence the nature and characteristics of solute transport through the rivers in the study area.

Ore composition and native gold characteristics of an ore occurrence in Eastern Transbaikalia

The article deals with the characteristics of the ores of an ore occurrence of the Munginsky cluster located on the western flank of one of the commercial fields of Eastern Transbaikalia. The ores of this promising ore occurrence are underexplored, especially in the technological aspect, which served the basis for studying their composition and characterizing native gold as their main commercial component. The composition of ores and altered rocks was studied by the following methods: atomic emission spectral quantitative analysis, X-ray fluorescence, as well as phase atomic absorption and atomic emission analysis with inductively coupled plasma ICP-AES. The mass fraction of total and organic carbon was determined in the Central Fire Assay Laboratory of JSC Pokrovsky Rudnik, Blagoveshchensk. The proportion of carbonate carbon dioxide was determined by the method of titrimetric determination of carbon dioxide. The content of gold was given according to the data of assay melting, the content of silver – according to the data of atomic absorption analysis. Petrographic and mineragraphic studies were carried out using an optical microscope Olympus BX-51. The mineral composition of the ore sample was also estimated based on the results of X-ray diffraction analysis. The quantitative mineral composition was studied on the crushed material of the original ore with a particle size of -2 mm using the microscopic study data of transparent and polished thin sections on a microscope Nikon Eclipse LV 100 POL. The content of iron hydroxides was determined from the weight difference after the sample was treated with a 10 % oxalic acid solution in a water bath. Comparison of the results obtained on the ore occurrence with the materials on the ore composition of the closest deposit located in 30 km demonstrates that on the one hand they are similar and uniform, and on the other hand they feature some differences. Their common parameters include a rather high degree of sulfide content of ores and similar chemical and mineral composition with the predominance of arsenopyrite, an increased role of bismuth as well as the predominance of fine gold and its similar morphological characteristics. This fact allows to consider the ore occurrence under investigation as an integral part of a single ore system of the closest deposit.

Insights into the Magmatic Feeding System of the 2021 Eruption at Cumbre Vieja (La Palma, Canary Islands) Inferred from Gravity Data Modeling

This study used spatiotemporal land gravity data to investigate the 2021 eruption that occurred in the Cumbre Vieja volcano (La Palma, Canary Islands). First, we produced a density model by inverting the local gravity field using data collected in July 2005 and July 2021. This model revealed a low-density body beneath the western flank of the volcano that explains a highly fractured and altered structure related to the active hydrothermal system. Then, we retrieved changes in gravity and GNSS vertical displacements from repeated measurements made in a local network before (July 2021) and after (January 2022) the eruption. After correcting the vertical surface displacements, the gravity changes produced by mass variation during the eruptive process were used to build a forward model of the magmatic feeding system consisting of dikes and sills based on an initial model defined by the paths of the earthquake hypocenters preceding the eruption. Our study provides a final model of the magma plumbing system, which establishes a spatiotemporal framework tracing the path of magma ascent from the crust–mantle boundary to the surface from 11–19 September 2021, where the shallowest magma path was strongly influenced by the low-density body identified in the inversion process.

Improving the Recovery of Hydrocarbons in a Well in the Gullfaks Field by Injecting Sequestrated CO2

The Gullfaks field was discovered in 1978 in the Tampen area of the North Sea and it is one of the largest Norwegian oil fields located in Block 34/10 along the western flank of the Viking Graben in the northern North Sea. The Gullfaks field came on stream in 1986 and reached a peak of production in 2001. After some years, a decrease in production was noticed due to the decrease in pressure in the well. The goal of this paper is to improve the production of a well located in Gullfaks field by injecting CO2 through coiled tubing. The use of the CO2 injection method is due to the fact that it is a greenhouse gas, and its production in the atmosphere contributes to global warming. It is important to reduce its emission into the atmosphere and to boost the production of oil in the well. The CO2 is injected through the coil tubing to lighten the hydrostatic column and allow the fluid to move from the tubing to the surface. The completion and PVT data are processed in Pipesim and Prosper softwares. By integrating a number of calculations by using the nodal analysis methods and gas injection methods, the results obtained show that the well is not producing and by injecting sequestrated CO2 at the flow rate of 1.482 MMScft/d with an injection pressure of 2500 psig, the oil flow rate provided by the coiled tubing gas injection is 900 Stb/d. The profitability of the project is achieved over a period of 20 years with a net present value (NPV) of $11948858.5 and a return on investment after 5 years 2 weeks.

Characteristics of cloud properties over South America and over Andes observed using CloudSat and reanalysis data

ABSTRACT CloudSat profile of attenuated corrected radar reflectivity (Ze) and cloud mask data are used to investigate the cloud properties over South America (SA) during Austral Summer monsoon seasons. Deep convective core (DCC), deep & intense convective systems (DCSs & ICSs), and cloud clusters (CCs) are defined based on the Ze and cloud mask values. The spatial distributions of DCCs show that land-dominated areas have higher frequency of DCCs and Atlantic Ocean has less DCCs. The Pacific Ocean does not consist of DCCs, whereas eastern flank of Andes has higher frequency of DCCs compared to western flank of the Andes. North La Plata basin (Sierra de Cordoba) has a higher fraction of deeper (shallower) DCCs. Deep convection over the Sierra de Cordoba and South La Plata Basin is characterized by precipitation-size particles compared to cloud-size particles, whereas deep convection over north La Plata Basin is dominated by mostly cloud-size particles. The horizontal span of DCSs and ICSs is higher over south La Plata Basin and Atlantic Oceans compared to other SA areas. Sierra de Cordoba (Atlantic Ocean) has the highest (lowest) frequency of small DCSs and vice versa. DCSs and ICSs show the opposite characteristic, as all the selected areas consist of a higher fraction of large (small) sized DCSs (ICSs). CCs develop more in horizontal than in vertical direction over the high latitude and vice versa over lower latitude. The CCs distribution reflects the orography and moisture flow pattern at the east and west side of Andes. The higher Ze, which is the proxy for rainfall, occurs at the eastern flank/slope of the Andes, and related to easterly moisture loaded synoptic flow, transported from Amazon and upslope flow along the slope.

Genetics as a novel tool in mining impact assessment and biomonitoring of critically endangered western chimpanzees in the Nimba Mountains, Guinea

AbstractWestern chimpanzees (Pan troglodytes verus) are Critically Endangered and Guinea is a key stronghold for this subspecies. However, Guinea is also rich in minerals with some of the highest‐grade iron‐ore deposits in the world. Specifically, the Nimba Mountains, home to western chimpanzees, is one of the sites under consideration for mining activities. To assess the impact of mining activities in the area, we used non‐invasive genetic sampling to estimate chimpanzee population size, sex ratio, community composition, and range boundaries on the western flank of the massif. The level of genetic diversity and affinity between communities was estimated and recommendations for future genetic censusing provided. Between 2003 and 2018, we collected 999 fecal samples of which 663 were analyzed using a panel of 26 microsatellites. We identified a minimum of 136 chimpanzees in four communities, with evidence of migratory events, a high level of shared ancestry and genetic diversity. We assessed sampling intensities and capture rates for each community. Saturation was reached in two communities with sampling between 3.2 and 4.3 times the estimated number of chimpanzees. Our findings highlight the utility of genetic censusing for temporal monitoring of ape abundance, as well as capturing migratory events and gauging genetic diversity and population viability over time. We recommend genetic sampling, combined with camera trapping, for use in future Environmental and Social Impact Assessments, as these methods can yield robust baselines for implementing the mitigation hierarchy, future biomonitoring and conservation management.

Morphometric analysis of the large en- closed depression of the Southern East European plain

The results of morphometric analysis based on the SRTM digital elevation model of large enclosed depressions (LEDs) of controversial origin, commonly found on the loess interfluves in the Northern Black Sea region, around the Sea of Azov, at the Western flanks of Caucus Mountains and in the Lower Don basin, are presented in the paper. We have registered 312 LEDs landforms. The morphometric characteristics of landforms vary from 0.4 to 216 km2 for area, from 1 to 21 m for depth, from 0.5 to 13.3 km for width, from 0.7 to 27.5 km for length, from 1 to 4 for elongation coefficient, and from 3.3 to 103.3 m a.s.l for height. The most common depressions have the following parameters: area 24 km2; depth 23 m; width 1.01.5 km; length 2.53.0 km; elongation coefficient 1.21.4; height 1520 m a.s.l. There is a correlation between the area and depth of the depressions. The depressions' shape is mostly elongated, e. g. teardrop-shaped, eggshaped, elliptical, triangular, and rarely round. The sharp ends of the egg-shaped depressions always tend to point to the north, and the blunt ones to the south. We grouped the depressions into seven restricted sites where the differences in size and other morphological features of the LEDs are very small. Within all sites, there is a high consistency of orientation of the long axes of the depressions. The largest depressions around the Sea of Azov and the Western flanks of Caucus Mountains are characterized by longitudinal ridges confined to western side of LEDs. Comparison analysis of sites demonstrated a fan-shaped pattern in changing of the long axes orientation from the NW in the Northern Black Sea region; to the East in the Azov Sea region; to the N in the Western flanks of Caucus Mountains; and the NE in the Central flanks of Caucus Mountains. A radial-centripetal pattern of the erosion network is observed across the territories where LEDs are distributed. Small erosive forms flowing into the center of depressions are represented by very flat and wide gullies and hollows with intermitted channel flow. Such morphological characteristics suggest the relict origin of the erosional forms and, as a result, indicates the pre-Holocene age of the depressions themselves. Morphological and geological data suggests that wind erosion was probably the main factor in the formation of LEDs.

Quaternary Map, Active Faulting, Tectonic Geomorphology, and Uplift Rate of the Humboldt Range in the Basin and Range Province of Nevada, United States

ABSTRACT Fault-truncated, uplifted, and abandoned alluvial fans are frequent along the western flank of the active normal fault bounded Humboldt range. Terrestrial cosmogenic nuclide surface exposure dating of a faulted terrace at Rocky Canyon indicates that uplift of the range has averaged about 0.12 mm/yr during the last ∼160 ka. A similar uplift rate of less than about 0.07 mm/yr over the last 35 ka or more years is estimated from offset of a younger terrace at the same site. Values of extension rate across the range are 0.04–0.07 mm/yr, if it is assumed that the range-bounding fault dips at 60°, in general accord with very low values of contemporary geodetic strain reported for the area. Geomorphology at Rocky Canyon records a period leading up to about 160 ka ago that erosion and aggradation of sediment along the rangefront were dominant over fault generated uplift, at which time faulting again became dominant, leading to uplift, incision, and preservation of ∼160-ka-old alluvial terraces here and elsewhere along the rangefront.

On the nature of the Zhamanshin crater (Northern Cis-Aralian Region)

Research subject. The Zhamanshin structure is located in the northern Aral Sea region and represents the outcrops of pre-Mesozoic rocks among Paleogene deposits. This structure has been known in the literature as a young meteorite crater for more than half a century. Aim. To consider all available geological and geophysical information on the structure and material composition of rocks and explain the development features of the Zhamanshin structure in relation to its position within the Late Paleozoic suture-collision zone of the Eastern-Uralian fold system. Materials and methods. The materials of geological surveys of various scales, as well as the interpretation of geophysical data, satellite images, data on the material composition of rock samples and paleotectonic reconstructions were analysed. In addition, the published literature on the meteorite origin of the Zhamanshin structure was analysed. Results. The main structural features of the Zhamanshin structure are rather associated with the accretion-subduction processes in the Paleozoic and strike-slip movements, especially active in the Pliocene, than with an impact event. The young age of glasses (from 10 thousand to 50 Ma) remains unproven due to unreliable methods used. The composition of the glasses allows them to be attributed to Paleozoic volcanic rocks, while some samples of slags and glasses may be of technogenic origin. Conclusions. Almost all arguments in favour of the meteorite origin of the Zhamanshin structure are questioned. A more realistic conclusion is that it has formed by deep tectonic and geological processes. The Zhamanshin structure is a dissected rounded upland with a ring of Paleozoic rocks along the edges and a hollow in the middle, which is associated with an eroded Carboniferous caldera. After the collision in the middle of the Carboniferous, the entire Northern Aral Sea remained an area of denudation until the beginning of the Cretaceous. After that, terrigenous lacustrine-alluvial strata up to 300 m thick had accumulated. During the Paleogene and Miocene, this upland with the remnants located along a circular rampart tens of meters high was covered by marine and continental sediments. In the Pliocene, the area was subjected to active strikeslip movements with the formation of the Tasaran mega-anticline with the Zhamanshin, North-Zhamanshin and Tasaran uplifts. The Irgiz-Tobolsk shear-thrust had limited and uplifted the western flank of the Zhamanshin structure, while feathering faults resulted in the formation and subsidence of a rounded depression around the Paleozoic caldera in the centre of Zhamanshin.

Risk of Exposure to Coccidioides spp. in the Temblor Special Recreation Management Area (SRMA), Kern County, CA

The Temblor Mountain Special Recreation Area (SRMA) on the western flank of the San Joaquin Valley, CA, is located in the endemic area of Coccidioides, a fungal pathogen responsible for the increasing incidence of coccidioidomycosis (Valley fever). Recreationists in the SRMA, such as off-highway vehicle (OHV) drivers and mountain bikers who disturb the soils, are at risk of being exposed to airborne arthroconidia (asexual spores) of the pathogen. To reduce the risk of pathogen exposure for visitors, the Bureau of Land Management (BLM) plans to limit recreational activities to areas with a reduced pathogen presence. They envision an official OHV park in the future, by also restricting access to areas with ongoing restoration efforts and by limiting soil erosion in sensitive areas. To investigate which soils in the Temblor SRMA are most likely to support the growth of Coccidioides spp., soil samples were collected over a 3-year period from dominant soil types in a northern and a southern sampling area and analyzed for the pathogen using a culture-independent PCR-based method. In addition, soil pH and electrical conductivity were determined. The results of this study revealed slight genetic variance in the Coccidioides sequences obtained from the soils of the Temblor SRMA. An analysis of variance (ANOVA) could not confirm differences in soil pH and electrical conductivity (EC) between the different soil types investigated and between sites where the pathogen was detected compared to sites where it could not be found. However, the year of sampling appeared to have an influence on observed soil pH and EC, and the presence of the pathogen. Of all dominant soil types investigated, those belonging to the Littlesignal-Cochora association were the least likely to contain the pathogen, whereas soils of the Beam-Panoza-Hillbrick association appeared more supportive. In addition to pointing out OHV areas with lower pathogen exposure risk in the Temblor SRMA, recommendations were made to educate visitors and BLM workers about the risk of contracting Valley fever.

Causes of the Extreme Drought in Late Summer–Autumn 2019 in Eastern China and Its Future Risk

Abstract Eastern China (EC) suffered an extreme drought with long-lasting duration and record-breaking intensity in late summer–autumn 2019. Our diagnosed results show that the central Pacific (CP) El Niño, in tandem with warm sea surface temperature anomalies (SSTAs) over the Kuroshio Extension (KE) region, induces the meridionally elongated cyclonic circulation anomalies stretching from the western North Pacific (WNP) to the Yellow Sea. Its western flank corresponds to overwhelming low-level northerly wind anomalies over EC, which result in deficient moisture and anomalous descent over EC and hence cause the extreme drought in 2019. To investigate the relative contributions of SSTAs over different regions, we performed sensitivity experiments, and analyzed the relationship between extreme drought like what occurred in 2019 (a 2019Drought-like event) and the SSTAs in CMIP6 historical simulations. Modeling evidences reveal that both warm SSTAs over the central equatorial Pacific and the KE region are indispensable for shaping the meridionally elongated cyclone anomaly. Specifically, the cyclone anomaly over the WNP induced by CP El Niño aligns with the cyclone anomaly over the Yellow Sea induced by the warm SSTAs over the KE region, merging into a meridionally stretched cyclone anomaly to the east of EC. Consequently, the northerly anomalies stretch across EC, leading to unfavorable atmospheric conditions and the rainfall deficit there. Projection results show that the occurrence probability of a 2019Drought-like event will increase by 20% (decrease by 40%–50%) under a high (medium-low) emission scenario compared to present-day climate, indicating the nonlinear response of extreme drought to different emission scenarios and the urgency of carbon emission reduction. Significance Statement An extreme drought hit the Eastern China (EC) region in 2019 and caused tremendous losses. This study proposed that both the 2019 CP El Niño and the warm SST anomalies over the Kuroshio Extension (KE) region induce the meridionally elongated circulation anomalies and the resultant extreme drought. We showed that the typical circulation anomalies induced by central Pacific (CP) El Niño cannot totally explain the meridionally elongated circulation anomalies in 2019. Our modeling evidences confirmed the indispensable role of warm SST anomalies over KE region in the 2019 extreme drought’s formation. The projection results show that extreme drought like that in 2019 will occur more (less) frequently under a high (medium-low) emission scenario compared to modern-day level, indicating the urgency of carbon emission reduction.

Morphological characteristics and spectral reflectivity of some degraded soils west Fold Makhoul

The study aim to determine the status and the types of degradation in different sites, depending on the interest of the morphological characteristics Evaluation of the selected Soils and using the Remote Sensing Thechniques as a modern and efficient technologies in monitoring and controlling changes as a result of soil degradation and vegetation and knowledge of the spectral behavior of these soils using a measuring device reflectivity spectral Spectroradiometer. The study was conducted in the province of Salah Alddin in the area between the city of Baiji, and Sharqat that represent the western flank of Makhoul fold, the Total area was to 402.20 km2. It has been identified types of Degradation of soils study, which varied between physical degradation District Representative Degradation at Soil Structure build soils and chemical Representative high content of salts and gypsum content and biological Representative down the organic matter content and lack of vegetation. The study also demonstrated through the use of Spectral Reflectance dvice (Spectroradiometer) to show properties of Spectral reflectance curves of degraded Soil, and characterized by a high degree of gypsum soils with situations of deterioration as a result of high gypsum content by distinguished absorb moisture packs at wavelengths (1400-1450) nm. A reflectance spectral increases with the color value of the Value and increases with higher content of Gypsum, which increases with depth, The results showed a linear relationship was positive and strong, a factor determining R2 value of 0.93 between the percentage of reflectivity and spectral values​​, linear relationship positive between reflectance and spectral content of gypsum, a factor determining R2 worth 0.77 Pan Pedons soils study area. And the existence of a relationship between the third-degree reflectivity ratio of the spectral content of organic matter by a factor of determining R2 value of 0.52

Deep ocean circulation in the subpolar North Atlantic observed by acoustically-tracked floats

The deep circulation in the subpolar North Atlantic determines the spread and mixing of high latitude climate signals to lower latitudes. However, our current understanding of the subpolar deep circulation has been limited due to relatively sparse observational data. To improve that understanding, we construct gridded fields of mean velocity and eddy kinetic energy (EKE) in the deep (1800–2800 dbar) subpolar North Atlantic using direct velocity measurements from 122 subsurface acoustically-tracked floats that drifted during June 2014–January 2019. The mean velocity field reveals a relatively strong deep boundary current around Greenland and in the Labrador Sea, with a weaker deep boundary current over the eastern flank of the Reykjanes Ridge, and near-zero mean flow over the western flank, implying a discontinuous deep boundary current across the subpolar basin. The deep EKE, albeit with smaller magnitudes, generally resembles the EKE pattern at the ocean surface, including relatively high values along pathways of the North Atlantic Current and west of Greenland where the Irminger Rings are formed. A surprising finding about deep EKE is an elevated band east of Greenland that parallels the coast and is not present in the surface EKE field. This high EKE band is possibly attributed to the combined influence from propagating Denmark Strait Overflow Cyclones, variability of the wind-driven recirculation offshore of southeast Greenland, and/or topographic waves. The float-based flow fields constructed in this study provide an unprecedented quantitative view of the kinematic properties of the large-scale deep circulation in the subpolar North Atlantic. Combined with cross-basin Eulerian measurements, we believe these recent observations provide a benchmark for testing and improving numerical simulations of deep ocean circulation and the Meridional Overturning Circulation, which are urgently needed for climate change predictions.

Useing of Remote SensingTtechnologies in Assessing Degradation of Soil and Vegetation Cover West Fold Makhoul

This study aimed to assess the state of deterioration (Degradation Status) to different sites of the soil, depending on the possibility of the use of remote sensing as one of modern technologies, and effective monitoring and control of the changes that you get the natural resources of soil degradation and vegetation operations as well as the risk of wind erosion study was conducted in the province Salah al-Din in an area between the city of Baiji, Sharqat south and the north, which represents the western flank of the fold Makhoul total area amounted to 402.20 km2. And was able to study with the help of technologies for remote sensing of determining the status and degree of deterioration of the soils study, which varied between moderate deterioration region, and severe deterioration, very severe degradation. The study confirmed that there is a decline in soils degraded area deteriorated moderate and actress soils untapped cultivation of grain crops increased by 33.64% of the study area space while soils degraded area recorded a severely degraded and actress soils affected by salts untapped increase of 24.55% of the area of ​​the region, while the soils degraded area deteriorated very strong and actress soils affected by salts untapped fragile dunes was registered an increase of about 9.08% of the study area, depending on the area of ​​the space visuals captured for the years 1976 and 2014 .

Moho topography and crustal properties in the UAE and northern Oman mountain belt from teleseismic receiver functions

SUMMARYThe United Arab Emirates (UAE)-Oman mountain belt exposes a large intact ophiolite thrust sheet that was obducted onto a rifted continental margin during the Late Cretaceous. Crustal properties of the mountain belt and the foreland region are important to better understand the mechanism of crustal deformation during the obduction process. In this study, we analysed P-wave receiver functions across the UAE and northern Oman mountain belt to determine the Moho depths, crustal properties and velocity structure beneath 53 broad-band seismic stations. Crustal thickness varies from 30.0 km in the western UAE to 46.6 km in the UAE-Oman mountain belt. The deeper Moho depth beneath the UAE-Oman mountain belt is the outcome of crustal thickening and flexure of the lithosphere during the obduction process. The eastern flank of the UAE-Oman mountain belt has relatively high-Vp/Vs ratios of 1.76–1.89. On the contrary, comparatively low-Vp/Vs ratios (1.61–1.67) are estimated in the western flank. Moreover, relatively low-Vp/Vs ratios (1.61–1.70) are observed in the foreland basin and western UAE. The high-Vp/Vs ratios and thick crust are indication of a thick ophiolite thrust sheet, while low-Vp/Vs ratios suggest that the crust is more felsic/intermediate in nature. The Vs-depth profiles in the mountain belt reveal a low-Vs zone beneath a remarkably high-Vs top layer. There is no such high-Vs top layer in the foreland area and western UAE. The high-Vs layer is correlated to a ∼10–15-km thick sequence of Semail crust and mantle ophiolite. Common Conversion Point imaging across the UAE-Oman mountain belt imaged the Moho boundary, which agrees with H-k stacking results, and intra-crustal discontinuities.

CAGE14-1 Cruise Report: CAGE research school in Arctic Marine Geology and Geophysics

Cruise CAGE 14-1 is one of several cruises in 2014 that will be carried out to collect cross-disciplinary data for addressing the objectives of the Norwegian Centre for Arctic Gas Hydrate, Environment and Climate, CAGE. The Norwegian Research Council funds CAGE for a period of 10 years to addressee main scientific questions about gas hydrate environments in Arctic regions. Cruise CAGE 14-1 was also hosting this year’s AMGG research school cruise with 14 PhD students participating, most of them from CAGE. The cruise focused on acquisition of seismic, oceanographic, atmospheric, geochemical and sediment and benthic fauna sampling data from three target areas: the shallow shelf and shelf edge methane seepage sites at Prins Karls Forelanda sediment drift on the western flank of the Knipovich Ridgethe Vestnesa Ridge Research objectives were planned long the goals of CAGE and its individual work packages, and the teaching would be organized along these goals. Scientific problems that are to be addressed in these two key target areas include the periodicity of seepage (i.e. time scales of active, inactive and reactivated systems), quantification of methane concentrations in surface sediments, water column and above the sea surface, gas and hydrates, the nature of gas sources, and the benthic communities occurring at the seep sites. Specific objectives of cruise CAGE 14-1 were as follows: Hydro-acoustic mapping of methane bubble plumes above shallow and deep-water vent fields.Seismic surveying and multibeam mapping across the contours of the Svyatogor Rise.Sediment sampling using gravity, box and multi-corer for sediment and pore-water geochemical analysesSampling of benthic fauna at several seep sites and reference stations in all three target areas.Acquisition of oceanographic data for measuring oceanographic conditions and methane concentrations in the water column, particularly at the shallow shelf sites. The cruise may be known as: CAGE14_1

Large landslide of the hyperarid Central Western Andes triggered during a humid period of the Late Pleistocene (ca. 19°S; northern Chile)

AbstractThe western flank of the Central Andes offers a unique geomorphological record of large paleolandslides that are well preserved on long time‐scales (i.e. ≥Pleistocene) due to the long‐lasting aridity of this region. However, the lack of chronological constraints on those landslides limits our understanding of the respective role of tectonics and climate on their triggering. Here, we report new 10Be surface exposure dating obtained on one of those giant slope‐failures: the Limaxina landslide (northern Chile, 19°S). Five tightly grouped exposure‐ages (one outlier discarded) point to a single landslide failure at 80 ± 4 ka. This timing being consistent with others local records of a wet episode in the Atacama Desert, it suggests a primary role of climate‐forcing on landslide activity in this region, calling to further slope failures dating in the arid Central western Andes to explore landscapes responses to Quaternary climate oscillations and extreme events.

Estimation of soil overburden thickness/depth of rock strata using geo-physical survey at Himalayan region


 
 
 Estimation of soil overburden and depth of competent strata for construction of infrastructures in hilly terrain is a challenging job for engineers. Modern technologies like Electrical Resistivity Survey (ERS) techniques with site geological mapping have been carried out at the ridge area near Palace, Gangtok. Two independent 2D-electrical resistivity surveys profile sections using hybrid Schlumberger-Wenner method were conducted along the ridge line trending in the North-South direction. The ERS profile sections were taken on both the slopes of the ridge along its eastern and western flanks. With the collective information from field and geo-technical data, a comparatively stable slope has been identified with respect to geological conditions in the present work, which focuses on the vulnerable slope failure with respect to slope direction, local geological condition, depth of competent strata, thickness of soil overburden, water saturation zones and resistivity of the materials. Diamond core drilling of 15meters each was carried out at both the flanks of the slope to understand the sub-surface strata and correlate it with resistivity data generated by ERS survey. The result indicates that Sandy/silty soil with flakes of mica having resistivity of 107 ohm-m and weathered mica schist having resistivity more than 300 ohm-m in the present study area. Geological mapping in 1:3000 scale was carried in the area demarcation with various litho-units and rock type. The area is characterized by medium grade metamorphic rock sequence represented in the area by mica schist having dip of foliations towards NE direction and three sets of joint planes. The geometry of the rock orientation and slope direction plays a vital role for determining the overall stability condition of the area. The present study will provide technical input for structural engineers to design the structures in such geological conditions. Further, the thickness of overburden estimated from ERS has been validated by drilling data.
 
 

A contribution to the quantification of crustal shortening and kinematics of deformation across the Western Andes ( ∼ 20–22° S)

Abstract. The Andes are an emblematic active Cordilleran orogen. Mountain building in the Central Andes (∼20∘ S) started by the Late Cretaceous to early Cenozoic along the subduction margin and propagated eastward. In general, the structures sustaining the uplift of the western flank of the Andes are dismissed, and their contribution to mountain building remains poorly constrained. Here, we focus on two sites along the Western Andes at ∼20–22∘ S in the Atacama desert, where structures are well exposed. We combine mapping from high-resolution satellite images with field observations and numerical trishear forward modeling to provide quantitative constraints on the kinematic evolution of the investigated field sites. When upscaling our local field interpretations to the regional scale, we identify two main structures: (1) the Andean Basement Thrust, a west-vergent thrust system placing Andean Paleozoic basement over Mesozoic strata, and (2) a series of west-vergent thrusts pertaining to the West Andean Thrust System, deforming primarily Mesozoic units. From our interpreted sections, we estimate that both structures together accommodate at least ∼6–9 km of shortening across the sole investigated ∼7–17 km wide field sites. This multi-kilometric shortening represents only a fraction of the total shortening accommodated across the whole Western Andes. The timing of the main deformation recorded in the folded Mesozoic series can be bracketed between ∼68 and ∼29 Ma – and possibly between ∼68 and ∼44 Ma – from dated deformed geological layers, with a subsequent significant slowing-down of shortening rates. Even though the structures forming the Western Andes only absorbed a small fraction of the total shortening across the whole orogen, their contribution was relatively significant at the earliest stages of Andean mountain building before deformation proceeded eastward.