Lithological Controls Research Articles

Lithological Control on the Estimation of Uniaxial Compressive Strength by the P-Wave Velocity Using Supervised and Unsupervised Learning.

Uniaxial compressive strength (UCS) is the most fundamental physico–mechanical parameter used for any rock mass classification in geotechnical and geological engineering. However, determining UCS is a very tough, expensive, time consuming and destructive method and requires experienced workers. On the other hand, P-wave velocity (VP) determination is cheap, precise, non-destructive and easy. There are many established relationships between UCS and VP but mostly are low in range or proposed for multiple rock types of different origin. In this paper, the correlation of UCS with VP has been assessed based on the rocks' lithology. The methodology used in this analysis was centred on the previous studies database, lithology-based data disintegration and data integration to establish lithology based simple regression (SR) equations. A total of 37 previous studies databases were processed, and 12 characteristic regression equations have been determined based on the lithology. The lithological control was also determined using the principal component analysis (PCA), which categorised the data into diverse rock types. Artificial neural network (ANN) has been used as a robust predictive tool to estimate the UCS using the VP and rock type information.

Lithological control on scour hole formation in the Rhine-Meuse Estuary

River deltas commonly have a heterogeneous substratum of alternating peat, clay and sand deposits. This has important consequences for the river bed development and in particular for scour hole formation. When the substratum consists of an erosion resistant top layer, erosion is retarded. Upon breaking through a resistant top layer and reaching an underlying layer with higher erodibilty, deep scour holes may form within a short amount of time. The unpredictability and fast development of these scour holes makes them difficult to manage, particularly where the stability of dikes and infrastructure is at stake.In this paper we determine how subsurface lithology controls the bed elevation in net incising river branches, particularly focusing on scour hole initiation, growth rate, and direction. For this, the Rhine-Meuse Estuary forms an ideal study site, as over 100 scour holes have been identified in this area, and over 40 years of bed level data and thousands of core descriptions are available. It is shown that the subsurface lithology plays a crucial role in the emergence, shape, and evolution of scour holes. Although most scour holes follow the characteristic exponential development of fast initial growth and slower final growth, strong temporal variations are observed, with sudden growth rates of several meters per year in depth and tens of meters in extent. In addition, we relate the characteristic build-up of the subsurface lithology to specific geometric characteristics of scour holes, like large elongated expanding scour holes or confined scour holes with steep slopes. As river deltas commonly have a heterogeneous substratum and often face channel bed erosion, the observations likely apply to many delta rivers. These findings call for thorough knowledge of the subsurface lithology, as without it, scour hole development is hard to predict and can lead to sudden failures of nearby infrastructure and flood defence works.

Do Olivine Crystallization Temperatures Faithfully Record Mantle Temperature Variability?

AbstractCrystallization temperatures of primitive olivine crystals have been widely used as both a proxy for, or an intermediate step in calculating, mantle temperatures. The olivine‐spinel aluminum‐exchange thermometer has been applied to samples from mid‐ocean ridges and large igneous provinces, yielding considerable variability in olivine crystallization temperatures. We supplement the existing data with new crystallization temperature estimates for Hawaii, between 1282 ± 21 and 1375 ± 19°C. Magmatic temperatures may be linked to mantle temperatures if the thermal changes during melting can be quantified. The magnitude of this temperature change depends on melt fraction, itself controlled by mantle temperature, mantle composition and lithosphere thickness. Both mantle composition and lithosphere thickness vary spatially and temporally, with systematic differences between mid‐ocean ridges, ocean islands and large igneous provinces. For crystallization temperatures to provide robust evidence of mantle temperature variability, the controls of lithosphere thickness and mantle lithology on crystallization temperature must be isolated. We develop a multi‐lithology melting model for predicting crystallization temperatures of magmas in both intra‐plate volcanic provinces and mid‐ocean ridges. We find that the high crystallization temperatures seen at mantle plume localities do require high mantle temperatures. In the absence of further constraints on mantle lithology or melt productivity, we cannot robustly infer variable plume temperatures between ocean‐islands and large igneous provinces from crystallization temperatures alone; for example, the extremely high crystallization temperatures obtained for the Tortugal Phanerozoic komatiite could derive from mantle of comparable temperature to modern‐day Hawaii. This work demonstrates the limit of petrological thermometers when other geodynamic parameters are poorly known.

Fluvial response to active tectonics: analysis of DEM-derived longitudinal profiles in the Rangit River Basin, Eastern Himalayas, India

The Himalayan Mountain Range has originated from the ongoing collision of the Eurasian and the Indo-Australian plates since the Paleogene. It is widely accepted that this tectonically-driven uplift is still continuing, as reflected by a large number of earthquakes in the area. Apart from the sub-surface and geophysical signatures, the surficial geomorphic markers deserve due attention. Fluvial systems, which preserve the evidence of the past and present tectonic perturbations on the surface, have often been investigated to assess the imprints of uplift in a region. Sensitive to long-term tectonic, structural and climatic regimes, the general forms of the longitudinal profile and its derivatives have been analysed across the globe for determining the varying roles of tectonics, litho-structure and climate. This article assesses the degree of tectonic and lithological control on the drainage network of the Rangit Basin in the Eastern Himalayas. One of the important characteristics of the studied basin is that the Main Central Thrust (MCT), which is located between the Greater Himalayas and the Lesser Himalayas, divides the basin into two distinct domains. Longitudinal profiles and their derivatives of 16 major tributaries of the Rangit River were extracted from the ALOS–PALSAR DEM and analysed. The controls on this Himalayan river were evaluated based on investigations of longitudinal profile shapes, stream gradient (SL) indices, longitudinal profile concavities and steepness. Prominent drainage anomalies such as above-grade conditions, exponential and linear fitting of longitudinal profiles, elevated values of SL indices, barbed drainage, over-steepened stream segments and fluvial hanging valleys imply rapid erosion rates in the basin. This is noticeable particularly in the lower domain of the Rangit Basin, especially in the areas located downstream of the MCT. A comparison of steep segments with the geological and lineament maps reveals that many of these anomalies are lineament-controlled. Furthermore, a large number of such features do not conform to lithological intersections, suggesting a possible tectonic factor behind the occurrence of such anomalies.

Lithologic Controls on Silicate Weathering Regimes of Temperate Planets

Abstract Weathering of silicate rocks at a planetary surface can draw down CO2 from the atmosphere for eventual burial and long-term storage in the planetary interior. This process is thought to provide essential negative feedback to the carbonate-silicate cycle (carbon cycle) to maintain clement climates on Earth and potentially similar temperate exoplanets. We implement thermodynamics to determine weathering rates as a function of surface lithology (rock type). These rates provide upper limits that allow the maximum rate of weathering in regulating climate to be estimated. This modeling shows that the weathering of mineral assemblages in a given rock, rather than individual minerals, is crucial to determine weathering rates at planetary surfaces. By implementing a fluid-transport-controlled approach, we further mimic chemical kinetics and thermodynamics to determine weathering rates for three types of rocks inspired by the lithologies of Earth's continental and oceanic crust, and its upper mantle. We find that thermodynamic weathering rates of a continental crust-like lithology are about one to two orders of magnitude lower than those of a lithology characteristic of the oceanic crust. We show that when the CO2 partial pressure decreases or surface temperature increases, thermodynamics rather than kinetics exerts a strong control on weathering. The kinetically and thermodynamically limited regimes of weathering depend on lithology, whereas the supply-limited weathering is independent of lithology. Our results imply that the temperature sensitivity of thermodynamically limited silicate weathering may instigate a positive feedback to the carbon cycle, in which the weathering rate decreases as the surface temperature increases.

Convergent development of experimental landforms with differing rainfall and substrate properties

AbstractFour runs of experimental landform development, with the same uplift rate, different rainfall intensity, and the same material of different permeability adjusted by the degree of compaction, showed complicated effects of rainfall and mound‐forming material. In the run with more rainfall on less permeable material, low separated ridges developed in the uplifted area, because abundant overland flow promoted valley erosion and slope processes from early stages. In the run with less rainfall on less permeable material, valley incision proceeded mostly in major valleys where surface water converges. Canyons developed during early stages and later a high massive mountain emerged. The effect of rainfall difference, however, appeared completely opposite on more permeable material accompanied by lower shear strength. In the run with more rainfall on more permeable material, a massive mountain similar to that with less rainfall on less permeable material appeared, and low separated ridges appeared in the run with less rainfall on more permeable material as in the run with more rainfall on less permeable material. In the former case, similar amount of water available for Hortonian overland flow in early stages estimated from rainfall rate and permeability can explain the development of similar landforms. In the latter case, while abundant surface water with more rainfall on less permeable material made fluvial erosion active from early stages, the deficiency in surface water with less rainfall on more permeable material apparently attenuated fluvial erosion but possibly accentuated slope processes and slope failures by seepage water flow through more permeable material of low shear strength. The active erosion from early stages apparently resulted in the development of enduring similar low landforms later in the dynamic equilibrium stage. These experimental results indicate that similar landforms can emerge from different environmental and lithologic controls, and that process does not necessarily follow from form.

Morphotectonic analysis of the Bihar River, Madhya Pradesh, India

The river basins evolve with time; the forces may be autogenic or allogenic in nature which control their evolution. Changes in the discharge or sediment load, change the morphology of the rivers. Such changes are largely controlled by the climate change or tectonic activity. Morphometric analysis helps in quantifying various aspects of a river basin. Morphotectonic indices also provide valuable information on the tectonic activity and landscape evolution of the river basin. To evaluate the morphotectonic parameters small rivers are well suited due to their low discharge and low sediment load. Bihar river is one such river in the Central India, flowing through the sedimentary terrain of Vindhyan. The Bihar river is unique because in its upper reaches, the river runs parallel to the Sone-Narmada Lineament (SNL) and provides an opportunity to evaluate the effects of this fault in surrounding region. The SNL has been reactivated several times in the past. Several morphometric and morphotectonic parameters such as the stream order, bifurcation ratio, asymmetry factor, elongation ratio were calculated and have values of 2170, 4.47, 72.41 and 0.507 respectively. These values equivocally indicate that Bihar river basin is affected by the activities on the SNL. In addition to that stream length index have also been calculated. The value of the SL index has ranged from 5 to 3500. These variations in the lower part can be attributed to the lithological controls while, the changes in the upper part are due to the activity on the SNL. Different lineaments have been identified and plotted. The study shows that two different sets of lineament are present in the study area. The effect of activity of SNL on the Bihar river basin can also be seen in the form of paleochannels.

Major Elements in the Upstream of Three Gorges Reservoir: An Investigation of Chemical Weathering and Water Quality during Flood Events

Rivers transport terrestrial matter into the ocean, constituting a fundamental channel between inland and oceanic ecosystem and affect global climate change. To reveal chemical weathering processes and environmental health risks during flood periods, water samples were collected in the upper reaches of Three Gorges Reservoir (TGR) in 2020. HCO3− and Ca2+ were the most abundant anions and cations of the river water, respectively. The range of HCO3− concentration was between 1.81 and 3.02 mmol/L, while the mean content of Ca2+ was 1.03 mmol/L. The results of the Piper diagram and element ratios revealed that the river solutes were mainly contributed by carbonate weathering and gypsum-rich evaporite dissolution. A mass balance model indicated that the contribution order of sources to cations in the main channel (Yibin-Luzhou) was evaporites > carbonates > atmospheric input > silicates. The order in the Chongqing—Three Gorges Dam was carbonates > atmospheric input > evaporites > silicates. These results showed a lithologic control on hydrochemical characteristics. Most sampling sites were suitable for agricultural irrigation according to the water quality assessment. However, indexes sodium adsorption ratio (SAR) and soluble sodium percentage (Na%) were higher than 1.0 in Yibin-Luzhou and 30% in Yibin–Chongqing, respectively, suggesting a potential sodium hazard. In addition, except Tuojiang River and Shennong River, the risk of sodium hazard in tributaries was relatively low. High Na+ concentration in irrigation water can damage soil structure and function and ultimately affect agricultural production. Water quality in the upstream of a Piper diagram should attract enough attention.

Underlying riparian lithology controls redox dynamics during stage-driven mixing

The interactions between surface water-groundwater (hyporheic) exchange and sediment lithology influence oxidation–reduction (redox) conditions near river-aquifer interfaces. Redox dynamics have implications for subsurface nutrient transformations, but are difficult to assess spatially and temporally using traditional geochemical observations. This study applied continuous, three-dimensional monitoring of redox potential in a shallow riparian aquifer to assess the geochemical response to sediment lithology and hydrogeologic variables. We mapped a series of cross-sectional redox contour plots from throughout the aquifer over a storm event, which captured the dynamics of redox conditions during stage-driven mixing. Results show that redox potential increased by over 400 mV at some locations following river water infiltration during the storm, while persistent zones of high potential endured along preferential, high-conductivity flow paths. Conditions within high-conductivity (>1 cm/s) sediments took longer to recover (up to 30 days) following storms than those within finer, low-conductivity (6.9 × 10−5 cm/s) sediments (days to hours), however, attributed to less organic matter driving nutrient transformations. Dynamic surface water-groundwater interactions intermittently perturb redox conditions, but the underlying sediment lithology ultimately governs the spatial and temporal dynamics of aquifer redox conditions. These novel observations provide fundamental insights into hyporheic exchange and riparian geochemical dynamics broadly applicable to hydrogeology and biogeochemistry.

Morphometric Analysis of Parvati Basin, NW Himalaya: A Remote Sensing and GIS Based Approach

Abstract Morphometry is a quantitative approach of analysing linear, areal and relief parameters to understand the role of neotectonic activity in geomorphologic evolution of a river basin. In the present study multi-disciplinary integrated approach using morphometric parameters along with remote sensing and GIS technique have been applied for determining the quantitative parameters indicative of neotectonic activity in the Parvati basin, Higher Himalaya. The lineament pattern observed in the basin shows major trend in NE-SW followed by NW-SE and NNE-SSW directions. The basin is a 6th order drainage basin with dominating dendratic – trellis drainage pattern having very strong structural/tectonic control and is in its late youth stage of geomorphic development. Parvati basin shows coarse drainage density with fine texture suggesting more surface runoff and less infiltration in the area. The basin is highly elongated in shape tapering towards the south-west with high susceptibility to erosion with lower peak flow for longer duration. The above observations clearly indicate a tectonic and lithological control over the evolution of drainage pattern of Parvati basin.

Integration of regional gravity modeling, subsidence analysis, and source rock maturity data to understand the tectonic and hydrocarbon evolution of the Permian Basin, West Texas

The Permian Basin of West Texas and southeast New Mexico is currently the most prolific oil-producing basin in the United States. This region experienced deformation and extreme rates of subsidence (up to 500 m/my), especially during the Late Paleozoic. To investigate the larger scale crustal geometry of the Permian Basin, its tectonic evolution, and the distribution of its most productive late Paleozoic source rocks, we have created regional 2D and 3D gravity models that incorporate density and lithologic controls from wireline logs, published seismic refractions, and regional cross sections. These gravity models better define a regional northeast-trending gravity low called the Abilene gravity minimum (AGM) that underlies the northern Permian Basin. We infer this feature to be underlain by a low-density assemblage of Precambrian granitic and metasedimentary rocks. Structural inversion from the gravity model shows that the top of the lower crust and the Moho is presently depressed beneath the AGM. Subsidence analysis defines five tectonic phases from Cambrian to recent with maximum subsidence during the main, late Paleozoic deformational phase resulting in deposition of sediments up to 2.4 km thick. We have determined that the geobody under the AGM acted as a zone of preferential weakness in a “broken foreland basin” setting that accommodated regional shortening related to the Marathon orogeny and to other coeval orogenies along the Sonoran margin and Nevadan margin. Our new regional map of the top basement defines the limits of deep basinal areas that may host the most productive and thermally mature, late Paleozoic source rock kitchens — some of which are localized in depocenters controlled in part by syncollisional, left-lateral strike-slip faults that align with the edges of the AGM. Our results show a deeper basement ranging from 5.5 to 6.2 km in the Delaware basin that predicts a broader zone of source rock thermal maturity.

Geology and genesis of the Shalipayco evaporite-related Mississippi Valley-type Zn–Pb deposit, Central Peru: 3D geological modeling and C–O–S–Sr isotope constraints

The Shalipayco Zn–Pb deposit, in central Peru, is composed of several stratabound orebodies, the largest of which are the Resurgidora and Intermedios, contained in carbonate rocks of the Upper Triassic Chambara Formation, Pucara group. Petrography suggests that a single ore-forming episode formed sphalerite and galena within vugs, open spaces, and fractures. Three-dimensional (3D) geological modeling has allowed division of the Chambara Formation into four members (Chambara I, II, III, and IV) that better define lithological controls on sulfide formation. Diagenetic replacement of evaporite minerals with the organic matter (OM) presence likely generated secondary porosity and H2S accumulation by bacterial sulfate reduction (BSR), providing ground preparation for the later Zn–Pb mineralizing event. The least-altered host rocks have C–O isotope compositions of 1.8 ± 0.1‰ (VPDB) and 29.9 ± 2.1‰ (VSMOW), respectively, within the Triassic marine carbonate ranges. Early dolomite contains lighter C–O composition (1.1 ± 0.9 and 23.8 ± 2.9‰, respectively) consistent with OM decomposition during burial diagenesis. Post-mineralization calcite has still lighter C–O composition (− 5.1 and 13.3‰, respectively), suggesting meteoric water that had migrated through organic-rich strata. The strontium isotopes of Mitu group basalts (0.709654–0.719669) indicate it as a possible, but not the unique source of strontium and probably of other metals. Highly negative sulfide sulfur isotope values (− 23.3 to − 6.2‰ (VCDT)) indicate a major component of the ore sulfur derived ultimately from BSR. However, multiple lines of evidence suggest that preexisting H2S underwent thermochemical redox cycling prior to ore formation. The influx of hot metalliferous brines to dolomitized zones containing trapped H2S is the preferred model for ore deposition at Shalipayco.

Polyphased brittle deformation around a crustal fault: A multi-scale approach based on remote sensing and field data on the mountains surrounding the Têt hydrothermal system (Eastern Pyrénées, France)

Studying hydrothermal systems in basement environments requires knowledge of fault and fracture network distributions. This study addresses this through multi-scale structural analysis of the Têt fault and its surrounding fracture systems (Eastern Pyrénées) using remote sensing and field data. This study aims to achieve this through: 1) precisely mapping and describing the brittle fault network, 2) analysing the distribution of lineaments and outcrop-scale fractures related to these faults, 3) making comparisons to fault-kinematic evidence combined in a new regional review, 4) examining the relations between fractures features and lithology, 5) applying statistical analysis to highlight relations between different scales of deformation. The complex fault network is inherited from consecutive tectonic stages (Hercynian, Pyrenean compression, Neogene extension) and has been reactivated since the middle-Miocene. NE–SW secondary faults are abundant at the regional scale, even away from the Têt fault. Major NW–SE faults are constituted by 10s-m wide brittle core zones, and NW–SE secondary faults are concentrated around the Têt fault, attesting that they had formed at shallow crust levels after the Oligo-Miocene extension. N–S fractures, formed during Pyrenean compression, are part of the background fracturing and are scattered throughout the study area. Intersections of fault and fracture networks provide efficient permeable pathways for meteoric and hydrothermal fluids. Finally, a dislocation model reveals a lithological control on fracture apertures in crystalline rocks, which appears more preserved at depth than in metasediments. All of these elements are integrated in a global model of the hydrothermal system establishment in accordance with the faulting sequence, with the damage distribution and with the lithology. This distributed fault system could represent the surface expression of the crustal thinning revealed by recent geophysical data. The realized identification of the lithological and structural characteristics of the surrounding mountains, allowing hydrothermal circulation to establish itself, provides a better understanding of the orogenic-belt related hydrothermal systems necessary to the geothermal exploration.

Topographic, lithospheric and lithologic controls on the transient landscape evolution after the opening of internally-drained basins. Modelling the North Iberian Neogene drainage

The opening of internally-drained (endorheic) sedimentary basins often leads to a major drainage change, re-excavation of the basin sedimentary infill, and transient landscape. The timing of such basin openings can be dated only in exceptional cases in which the youngest sedimentary infill remains preserved. For this reason, the processes and timing involved in their transient landscape evolution are poorly known. We explore the role of erodibility, basin geometry and flexural isostasy during the capture of internally-drained basins by means of numerical modelling techniques constrained by recent terrace cosmogenic dating and geomorphological analysis, addressing the issue as to why the Duero and Ebro rivers, draining two Cenozoic sedimentary basins in N Iberia with similar geographical dimensions and drainage histories, have undergone a markedly different erosion evolution leading to distinctly different present morphology. To evaluate how these intrinsic parameters affect the transient landscape evolution, we design a synthetic scenario inspired by those basins. The results show that, once a basin becomes externally drained, its drainage integration and erosion rates are strongly dependent on (1) the basin elevation above the base level; (2) the width of the topographic barrier, (3) its erodibility; and (4) the rigidity of the lithosphere. The results show that transient landscape evolution can last for tens of millions of years even in absence of tectonic activity and changes in base level or climate. Basins isolated by wide and resistant barriers such as the Duero Basin may undergo a multi-million-year time lag between drainage opening and basin-wide incision. In the case of the Duero Basin, this delay may explain the paradoxical time lag between the last lacustrine bulk sedimentation dated at 9.6 Ma and the onset of widespread basin incision variously estimated at 3.7 to 1 Ma.

Impact Of Lithology and Regional Climate Variability on Spring Characteristics Between Uttarkashi and Harsil, Garhwal Himalaya, India

Spring characteristics are dependent upon the nature of lithology and precipitation in the region. The area is divided into two zones based on their lithological characters, viz: lesser Himalayan zone and Central Crystalline Zone for the hydrogeological study. Forty-five springs and four hot springs under different lithological controls were studied to understand spring discharges' response to regional climate variability. Four types of springs, fracture jointrelated springs, colluvial springs, Karst and seepages, and contact springs identified, which emanates from two geohydrological zones with in the study area. Colluvial springs yield are higher in comparison to the fracture jointrelated springs. The study revealed that the regional climatic pattern and precipitation pattern has a direct impact on spring hydrology.

Soil formation, nutrient supply and ecosystem productivity on basaltic lava vs rhyolitic pumice on Alcedo Volcano, Galápagos

Context Rock type may exert strong control on pedogenesis and resulting soil characteristics. Little is known on how different volcanic lithologies influence soil formation and nutrient supply and thereby affect ecosystem productivity in volcanic landscapes. Aims The aim of this study was to investigate lithologic control on the mentioned properties and processes. Methods We conducted a side-by-side comparison of two contrasting sites in close proximity on Alcedo Volcano, Galápagos, one on basaltic lava and the other on rhyolitic pumice. Key results The lava site was covered by lush, stratified woodland, whereas the pumice site was covered by grassland with only few plant species. The soil on lava was a Leptosol, whereas on pumice, an Andosol had formed. Both soils had similar pH (6.0–6.5 in H2O), but the soil organic carbon stocks at the lava site were almost twice as high as at the pumice site (13.1 ± 1.6 vs 7.6 ± 1.3 kg m−2 to 25 cm depth). The soil at the pumice site had considerably lower levels of Mehlich-3-extractable P, Ca, Mg, Cu, Zn and B. Soil microbes at the pumice site had lower biomass P (and a higher C:P ratio) and excreted more phosphatase. The grass biomass here also showed lower (and deficient) levels of P and other nutrients compared to the lava site. Conclusions and implications The contrasting lithologies and their bearings on soil formation and nutrient availability diversify the aboveground and belowground ecosystems and favour the development of distinct ecological niches in close proximity.

Parâmetros de densidade de falhas e bandas de deformação em rochas siliciclásticas pouco consolidadas da Formação Resende, Eoceno, Bacia de Volta Redonda, estado do Rio de Janeiro

O presente estudo propôs-se a analisar parâmetros de densidade de falhas e bandas de deformação em rochas siliciclásticas da Formação Resende, tomadas como geomaterial análogo a reservatórios areníticos pouco consolidados e fraturados. O estudo foi iniciado pela confecção de uma seção geológico-estrutural (escala 1:50) de um afloramento na Bacia de Volta Redonda. Essa etapa foi realizada com o auxílio de uma malha 2 × 2 m fixada sobre o afloramento. Baseado na seção geológico-estrutural, foi confeccionado um mapa de densidade de estruturas. Posteriormente, foram realizados levantamentos de parâmetros de densidade das estruturas de deformação por meio dos métodos de scanlines lineares e de amostragem em janela retangular. O afloramento é constituído de camadas lenticulares de arenitos e conglomerados estratificados, intercaladas a camadas tabulares e lenticulares de lutitos maciços, com espessuras decimétricas, havendo ainda intervalos de brechas intraformacionais. Duas falhas principais (F1 e F2) foram reconhecidas, de caráter normal, com orientação NE-SW e mergulhos para sentidos opostos, formando um gráben. Associadas a essas falhas encontram-se zonas de elevada concentração de bandas de deformação e falhas sintéticas e antitéticas. Os parâmetros de densidade revelaram um controle litológico na distribuição das estruturas. Os maiores valores de densidade são encontrados nos arenitos médios a grossos, enquanto os menores valores estão associados aos litotipos ricos em argila, como os lutitos, os arenitos lamosos e as brechas intraformacionais. Os parâmetros de densidade mostraram maior deformação do bloco abatido (gráben), associada a uma densidade de estruturas mais contínua nessa região.

Research on Failure Characteristics and Zoning Control Technology of Thick-Soft Surrounding Rock for Deep Gob-Side Entry Retaining

Controlling the large deformation caused by bed separation failure of thick and soft surrounding rock in gob-side entry retaining is difficult. The deformation and failure modes of thick and soft surrounding rock are summarized and classified based on field research, theoretical analysis, laboratory tests, and actual measurements. Systematic research is conducted on the lithologic characteristics, failure characteristics, and control methods of the surrounding rock. The research findings are as follows: (1) The low strength, softening, and water swelling of thick mudstone, as well as its cataclasis, dilatancy, and long-term creep under strong mining and high stress are the objective reasons for large deformation of the surrounding rock. (2) Due to the weak stability of the surrounding rock-support structure and low collaborative roof side bearing capacity, no complete supporting structure is formed with the supporting system, causing the support body in each area to be crushed one by one, which is the subjective reason for the deformation and failure of the surrounding rock. (3) The deformation and failure characteristics of thick and soft surrounding rock in gob-side entry retaining are primarily divided into eight types: roof bending and sinking type, roof cutting along filling body, rib spalling type, roof fall type, filling body rotation type, filling body crushing type, roof step type, and roof cutting along the coal side. The initial points and key points for a chain reaction of each failure type are determined. (4) The surrounding rock is divided into 10 support zones at four levels, and control technology for “zonal support and overall reinforcement” is put forward. The mechanical effect of the support body in each zone and its role in maintaining the stability of surrounding rock are analyzed. This technology can ensure the integrity of the surrounding rock structure and improve the roof side collaborative bearing capacity.

Cenozoic volcanism, tectonics and mineralisation of Woodlark Island (Muyuw), eastern Papua

Cenozoic geology of Woodlark Island was influenced by events prior to the onset of continental rifting at ca 8 Ma and the slightly later commencement of seafloor spreading in the eastern Woodlark Basin between ca 6 and 3.6 Ma. The embryonic Woodlark Island consisted of latest Paleocene(?)–Eocene shallow marine, deep-water shelf and turbidite deposits (Loluai Formation) and small submarine and emergent mafic volcanic centres (Utavai Basalt Member). Platform carbonates extended across the Woodlark Basin in the late Oligocene–middle Miocene (Nasai Limestone). Onset of middle Miocene eruptions in the north-northeast-trending Okiduse Volcanic Zone (OVZ) was localised in the similarly trending Kulumadau Horst and Graben Zone (KHGZ). Volcanic centres flanked major structures in the 12.5 km wide horst and graben zone, suggesting a link between volcanism and extensional tectonics. It was not an island arc settling, and there are neither andesites nor an obvious subduction zone. Offshore the KHGZ is connected with the similarly trending Nubara Fault, the plate boundary between the Solomon Sea Plate and Woodlark Plate. Contrasting volcanic deposits were erupted from volcanoes of the OVZ, viz. Mt Kabat Eruptive Centre, Uvarakoi Caldera, Watou Mountain Eruptive Centre and Suloga Harbour Tuff Cone. The epithermal Busai and Kulumadau gold deposits are located in the KHGZ. They are hosted by porous and permeable crystal lithic lapilli tuff beds in the Monasiy Tuff (Uvarakoi Caldera). Emplacement of thick dolerite sills (Auyed Dolerite) occurred post-middle Miocene. Sill emplacement coincided with the ca 6–3.6 Ma commencement of seafloor spreading in the eastern Woodlark Basin. A major phase of extensional tectonics along the KHGZ commenced post-middle Miocene and has persisted to the Holocene. Uplift was accompanied by rapid erosion and the widespread deposition of poorly to chaotically sorted gravels (Na’ku’iel Conglomerate). KEY POINTS Middle Miocene volcanism occurred from four volcanic centres in the north-northeast-trending Okiduse Volcanic Zone. Volcanism was confined to the similarly north-northeast-trending Kulumadau Horst and Graben Zone. Volcanism was not located in an island arc setting, as there are neither andesites nor an obvious subduction zone. A major phase of extensional tectonics along the horst and graben zone commenced post-middle Miocene and has persisted to the Holocene. Both the epithermal Busai and Kulumadau gold deposits exhibit lithological controls (porosity and permeability) on ore deposition.

Mapping hydrothermal alteration zone through aster data in Gadag Schist Belt of Western Dharwar Craton of Karnataka, India

Alteration zones are developed in a wide range of geological milieus such as volcano-plutonic rocks. Hydrothermal alteration zones are considered an important guide for mineral exploration and can act as a potential zone of mineralization. The minerals in alteration zones have very diagnostic absorption features in visible–near infrared (VNIR) and shortwave infrared (SWIR) regions of the electromagnetic spectrum. The Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) data have the potential to identify mineral assemblages in different hydrothermal alteration zones because of its 14 spectral bands which cover a wide spectral range. In the present article, FCC, band ratio, and SPCA techniques were applied to map the hydrothermal alteration zones in Gadag Schist Belt (GSB) of Western Dharwar Craton (WDC) of Karnataka. FCC has highlighted lithology, alteration zones, and given a fair idea about the lithological control and alteration occurrences in the area. Band ratio technique for muscovite, kaolinite, chlorite, iron oxide gossan, and silica alteration have yielded promising results. SPCA analysis successfully mapped hydrothermal alteration and delineated phyllic, argillic, and propylitic zones in the area. These results were verified through the existing geological map and by geological fieldwork in the area and these results are satisfactory. The total area, altered by different alteration process, was also calculated. In the GSB, iron alteration zone, phyllic, argillic, propylitic, and silica alteration zones were effectively mapped with the help of ASTER data.