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The impact of gas hydrate dissociation on submarine landslides has become an increasingly significant issue. However, previous models cannot interpret the newly discovered non-conformity between the slide surface and the base of the gas hydrate stability zone. Here, the authors design an experimental approach for visualising fluid migration during hydrate dissociation at atmospheric pressure. The results identify the lateral and vertical fluid migration pathways. Weak layers propagate nearly laterally beyond the hydrate zone, which lengthens the potential slide surface. Vertical pathways branch and deviate from their original paths, generating a shallower slide surface. Furthermore, the findings show that fluid overpressure under the overlying layer leads to steepening slopes. The lubrication effect and the underestimated inclination of slopes at failure may account for the low-angle failure of clay slopes. The results support a new conceptual model that reconciles the non-conformity between the slide surface and the base of the gas hydrate stability zone and offer a new perspective for the large-scale failure of low-angle submarine slopes. It will be interesting and important to confirm these implications in the future.

Imperfect determination of petroleum system processes coincidence, entrapment and charge timing, along with reservoir heterogeneity can considerably cause high risks throughout exploration and development phases of petroleum. Therefore, a complete subsurface visualization of the petroleum system nature, elements and processes, is badly required. To this end, we corroborated, in this study, static reservoir modeling with petroleum system analysis workflows, to better characterize the Cenomanian fluvio-marine reservoir, sandstones of Bahariya Formation, at Bed-2 Field, Abu Gharadig basin (Western Desert, Egypt). We used dataset of 2D seismic profiles and well logs of eight wells. The geometry and property of the reservoir were acquired performing static reservoir geocellular modeling approach. The geohistory, timing of charge, migration pathways, and accumulation sites were identified performing 1D and 2D basin modeling approaches. Combining both approaches was aimed at identifying new petroleum prospect areas, and estimating the hydrocarbon volumes, that are the need for such poorly-defined petroleum systems area. As indicated by the constructed, robust, reservoir and 1D-2D basin models, an additional hydrocarbon prospect, to the north central part of Bed-2 Field, is proposed to be drilled during the further oilfield development phases of the area. This prospect has all features that adequately lead to reliable inferences regarding the ultimate petroleum potential of the area.

Antina Čuka listvenite originated by hydrothermal alteration of small ophiolite mass caused by Paleogene magmatic activity. Mineralogical and petrological examination of the listvenite revealed serpentine-rich, silica-rich, and carbonate-rich varieties of the listvenite. Typical minerals are serpentine (group), carbonates (calcite, dolomite, and magnesite), pyrite, gersdorffite, Cr-spinel, barite, limonite, and native Ag. Gemological analysis revealed all serpentine varieties from Antina Čuka (serpentine-rich listvenite, serpentine-rich listvenite with magnetite and fresh serpentinite) have values of both refractive index and specific gravity in the range for serpentine group minerals. A Refractive index value of 1.54 for silica-rich variety confirms the presence of quartz. The results of lapidary processing have proven that both listvenite from Antina Čuka and serpentinite host rock are attractive gemstones. The adequate types of processing of Antina Čuka listvenite are plain cut (different-shaped cabochons) and glyptography/carving.

Reservoir quality is one of the important geological factors controlling the development of tight oil in the Honghe oilfield, Ordos Basin, northwestern China. Analyses of core, well logging, mud logging and geophysical data as well as thin sections (casting and fluorescence) were combined with testing methods (such as grain size analysis, constant-rate mercury injection, and scanning electron microscopy) to characterize the micropore–throat development in reservoirs of the eighth member of Yanchang Formation in the oilfield. From the perspective of sedimentation and diagenesis, the mechanisms causing reservoir quality difference were explored and a method for characterizing reservoir quality difference and distribution was proposed. The results show that complex and diverse pore–throat configurations and multi-scale throat development are the microscale manifestations of reservoir quality differences in the member. Three types of pore–throat combinations are recognized, including intergranular pore-wide lamellar throat, intergranular and intragranular pore-wide lamellar throat, and intergranular/clustered micropore-wide lamellar throat. Different diagenesis processes and intensities under the control of sedimentary conditions determine the differential development of the reservoirs. Diagenetic facies are the indicators of reservoir quality. Diagenetic facies with chlorite cementation-moderate dissolution indicates reservoirs with the most ideal physical properties for hydrocarbon accumulation, while that with moderate calcite and kaolinite cementations are usually observed in reservoirs with less ideal physical properties. Reservoirs with the worst physical properties often correlate with diagenetic facies with strong calcite cementation and compaction facies. A multi-level constrained method under the control of sedimentation and diagenetic facies is proposed for characterizing tight reservoir quality difference in the member. The spatial distribution of sedimentary elements is analyzed through sedimentary configurations, the diagenetic facies distribution is constrained by sedimentary elements and the reservoir quality distribution is predicted with constraint of diagenetic facies. It suggests that the high-quality reservoirs in the member occur vertically in the middle of thick channel sandstone, while poor reservoirs occur in the upper or lower parts of the channel sandstone due to intensive compaction and cementation. Laterally, the quality of reservoirs enhances along the channels with a change in shape to lens or strips along the middle and downstream sections.

Natural fractures, like tectoclases, are essential in the formation of shale gas reservoirs and have been the focus of study for shale gas development. Tectoclases provide most storage space for gas and are largely controlled by the paleo-tectonic stress field in shale reservoirs of the Niutitang Formation, northern Guizhou area, China. An accurate prediction of the development and distribution of tectoclases in the reservoirs is of great significance to exploring and developing shale gas sweet spots in the area. Based on geological structure evolution and fracture characterization, this study is focused on factors that control the fracture development in the Niutitang Formation shale reservoirs in northern Guizhou through characterization and modeling of geomechanisms and tectonic movements. A geomechanical model is formulated for the shale reservoirs against the geological background of the area. On this basis, the fractures are predicted by using the acoustic emission data. Numerical simulation results show that the development and distribution of tectoclase is controlled by fault zones, some of which have no obvious turning points with tectoclase in the middle sections being more developed and fragmented than those at the two ends. Some of these have obvious S-shaped turning points where tectoclases are the most developed and fragmented .

Tight sandstone reservoirs are widely developed in the Mesozoic Yanchang Formation of the Ordos Basin, China. There is a lack of understanding on the sedimentary setting, source-reservoir relationship and oil accumulation conditions in this area. In this study, through the comprehensive analysis of the distribution of tight oil, we evaluated the properties and petrological features of reservoir, geochemical characteristics of source rocks, the source-reservoir relationship, as well as the trapping, preservation and accumulation conditions of tight oil in the Chang 7 Member, and predicted the sweet spots of tight oil in the study area. The results show that the Chang 7 Member is a typical low-porosity and ultra-low permeability reservoir with great tightness, small pore throat and high capillary pressure, and must have been of near-source accumulation. The source rocks are mainly developed in the Chang 73 submember, and the reservoirs mainly occur in the Chang 71 and Chang 72 submembers, forming a combination mode of “lower source rock and upper reservoir”. Sandbodies with good connectivity and fractures being well developed in local areas are the main hydrocarbon transport systems. The abnormal high pressure caused by hydrocarbon generation and pressurization is the main driving force of tight oil accumulation. The mode of hydrocarbon transportation is dominated by the vertical or lateral migration from underlying source rocks or adjacent source rocks to reservoirs within a short distance. Following the integrated evaluation of lithology, physical properties and oil saturation of reservoirs and geochemical characteristics of source rocks, we grouped the sweet spots of Chang 7 Member into three types: Type I, Type II and Type III. Among others, the Type I sweet spots are the best in terms of porosity, permeability and source rock thickness and hydrocarbon enrichment which should be the focus of oilfield development. This study lays an important foundation for the economic and efficient development of tight oil in the Chang 7 Member of Heshui area, and has important implications on tight sandstone reservoirs in other regions of Ordos Basin in China.

Several sets of Paleozoic tight reservoirs are developed in the Central Uplift of the South Yellow Sea Basin. A qualitative analysis of the microscopic pore structure of the tight reservoir rocks was carried out through cast thin slice and scanning electron microscopic image observation. Based on reservoir petrophysical properties, thirty core samples in the Central Uplift of the South Yellow Sea Basin were selected for high-pressure mercury intrusion (HPMI) analysis, which was then combined with fractal calculation to classify and evaluate the tight reservoirs. The analysis of the HPMI curves and related parameters shows that the Paleozoic tight reservoirs can be divided into three types: Type-A, Type-B and Type-C. Type-A sandstone reservoirs contain pores with size mostly ranging between 0.01 and 0.1 μm, followed by pores with size range of 0.001–0.01 μm, and relatively fewer pores larger than 0.1 μm. The Type-B reservoirs are carbonate rocks with extremely heterogeneous pore size distribution, which is closely related to the development of dissolution pores and microfractures. Type-C sandstone reservoirs are dominated by nanopores and submicron pores that distribute more heterogeneously than pores in Type-A reservoirs. The pore distribution in sandstone reservoirs shows significant fractal characteristics and is closely related to the pore size. The heterogeneity of nanopore distribution has a negative correlation with porosity and median pressure and a relatively weak correlation with permeability. Our study has important implications for petroleum exploration in the South Yellow Sea Basin.

Analysis of reservoir sensitivity to velocity, water, salt, acid, alkali and stress is critical for reservoir protection. To study the tight sandstone reservoir sensitivity at different formation depths (effective stress) and formation water conditions (pH, salinity, and fluid velocity), a series of dynamic core flow tests under different pH, salinity, acid, and effective stress conditions were performed on samples from tight sandstone reservoirs of the Upper Triassic Yanchang 8 (T3y8) Member and conventional reservoirs of the Middle-Lower Jurassic Yan'an 9 (J1-2y9) Member in the Ordos Basin. The results indicate that, compared with the conventional reservoirs, the tight sandstone reservoirs are more sensitive to velocity and stress, less sensitive to water, alkali and salinity, and respond better to acid fracturing. In addition, the critical conditions (salinity, velocity, pH, and stress) for pumping drilling, completion, and fracturing fluids into tight sandstone reservoirs were investigated. A combination of scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS), cathodoluminescence (CL), casting thin section (CTS) and nuclear magnetic resonance (NMR) images, high-pressure mercury injection capillary pressure (MICP) measurements as well as X-ray fluorescence spectral (XRF) analyses were employed to analyze the damage mechanisms of the conventional reservoirs (J1-2y9) and tight sandstone reservoirs (T3y8) caused by fluid invasion. The results suggest that reservoir sensitivity is primarily conditioned by the composition of detrital components and interstitial fillings, petrophysical properties, pore-throat structure, and diagenetic facies. All these factors control the sensitivity types and extent of the reservoirs. Our results indicate that the poorer the reservoir physical properties, the stronger the reservoir heterogeneity and sensitivity, implying that tight sandstone reservoirs are more susceptible to changes in fluids than conventional reservoirs. This study offers insights into the reservoir damage types and helps to improve the design and implementation of protection measures for tight sandstone reservoir exploration.

Oceanic Transform Faults are major plate boundaries representing the most seismogenic part of the mid ocean ridge system. Nonetheless, their structure and deformation mechanisms at depth are largely unknown due to rare exposures of deep sections. Here we study the mineral fabric of deformed mantle peridotites - ultramafic mylonites - collected from the transpressive Atobá ridge, along the northern fault of the St. Paul transform system in the Equatorial Atlantic Ocean. We show that, at pressure and temperature conditions of the lower oceanic lithosphere, the dominant deformation mechanism is fluid-assisted dissolution-precipitation creep. Grain size reduction during deformation is enhanced by dissolution of coarser pyroxene grains in presence of fluid and contextual precipitation of small interstitial ones, leading to strain localization at lower stresses than dislocation creep. This mechanism potentially represents the dominant weakening factor in the oceanic lithosphere and a main driver for the onset and maintenance of oceanic transform faults.

Santorini je vulkanski otok, ki se nahaja na jugu Egejskega morja. Ta ima za sabo pestro zgodovino, med katero se je spremenil v veliko kaldero. Na otoku lahko opazimo bogato zbirko različnih vulkanskih kamnin. Z makroskopskim opazovanjem in mikroskopsko analizo z uporabo presevnega optičnega mikroskopa smo opravili pregled vzorcev, odvzetih z otoka Nea Kameni, ter lokacij Kokkari in Vlychada. Nekaj vzorcev smo naknadno pregledali s pomočjo vrstičnega elektronskega mikroskopa in na podlagi dobljenih rezultatov določili kemično sestavo izbranih mineralnih zrn v vzorcu. Z rentgensko praškovno difrakcijsko analizo smo določili mineralno sestavo in amorfno fazo posameznih vzorcev. Na podlagi geokemične analize smo kamnine razdelili v skupine na podlagi razmerja med vsebnostjo kremenice in deležem Zr/TiO2. Z optično mikroskopijo smo v vseh vzorcih določili hipohialinsko, afanitsko in oligofirsko strukturo. Vsi vzorci vsebujejo plagioklaze in piroksene, nekateri tudi olivine in nepresevne minerale. V vzorcih Nea Kameni in Kokkari se med plagioklazi pojavljata labradorit in bytownit, med pirokseni pa avgit, redkeje enstatit. Nekaj je olivinov, ki so bogatejši z magnezijem. Med plagioklazi v vzorcu Vlychada prevladuje andezin, med pirokseni je prisoten le enstatit. Rezultati geokemične analize so pokazali, da na otoku Nea Kameni prevladujejo rioliti ob manjši prisotnosti andezitov. Vzorci s Kokkari lokacije so pretežno rdeče-rjave barve in pripadajo andezitom in trahi-andezitom. Odvzete bele in lahke kamnine z bele plaže Vlychada smo uvrstili v skupino trahitov. Vulkanske kamnine z lokacije Nea Kameni smo pripisali najmlajši vulkanski dejavnosti, pri kateri je otok tudi nastal. Kamnine z bele plaže Vlychada so nastale med glavnima plinijskima izbruhoma, ob koncu prvega vulkanskega cikla. Andezitne kamnine z rdeče plaže Kokkari so kvartarne starosti in so nastale kot posledica začetka vulkanske dejavnosti na Santoriniju. Gre za pepelaste stožce, ki so nastali ob eksplozivnem izbruhu velikih vulkanskih bomb. Santorini is a volcanic island located in the south of the Aegean Sea. It has a varied history behind it, during which it turned into a large caldera. A rich collection of various volcanic rocks can be seen on the island. With macroscopic observation and microscopic analysis using a scanning optical microscope, we performed an examination of the samples taken from the island of Nea Kameni and the locations of Kokkari and Vlychada. Some samples were subsequently examined with the help of a line electron microscope and, based on the obtained results, the chemical composition of the selected mineral grains in the sample was determined. X-ray powder diffraction analysis was used to determine the mineral composition and amorphous phase of individual samples. Based on the geochemical analysis, the rocks were divided into groups based on the ratio between the quartz content and the Zr/TiO2 ratio. Optical microscopy was used to determine the hypohyaline, aphanitic and oligophyric structure in all samples. All samples contain plagioclase and pyroxenes, some also contain olivine and non-replaceable minerals. In the samples from Nea Kameni and Kokkari, labradorite and bytownite occur among plagioclase, and augite and less commonly enstatite among pyroxenes. There are some olivines that are richer in magnesium. Among the plagioclases in the Vlychada sample, andesine dominates, while only enstatite is present among the pyroxenes. The results of the geochemical analysis showed that the island of Nea Kameni is dominated by rhyolites with a minor presence of andesites. The samples from the Kokkari location are predominantly red-brown in color and belong to andesite and trachy-andesite. The white and light rocks taken from the white beach of Vlychada were classified as trachytes. Volcanic rocks from the Nea Kameni location were attributed to the youngest volcanic activity, during which the island was formed. The rocks from the white beach of Vlychada were formed during the main Plinian eruptions, at the end of the first volcanic cycle. The andesite rocks of Kokkari Red Beach are of Quaternary age and were formed as a result of the onset of volcanic activity on Santorini. These are cinder cones that were formed during the explosive eruption of large volcanic bombs.

The application of hydrophobic treatments as a means of protecting vulnerable stone heritage has been a topic of research for decades. The findings of previous research have shown that there are a number of factors that influence the efficiency of a treatment and that sometimes, if used incorrectly, such treatments can even accelerate stone weathering and decay. In this study, we revisit a hydrophobic treatment test area at Arbroath Abbey where the product was applied over 40 years ago, thus providing a rare opportunity to investigate the long-term efficiency of hydrophobic treatments. As well as assessing the condition of the treated area in situ by means of moisture analyses, lab-based accelerated salt weathering experiments are conducted to better understand the impact of silane-based treatments on sandstone durability. Moreover, the petrography and petrophysical properties of weathered sandstone (open porosity, capillary absorption, and vapour diffusion) before and after treatment are also characterised to provide a better understanding of how stone properties may influence the compatibility of the treatment. The field-based results show that the treated area has maintained a degree of hydrophobicity since its application over 40 years ago. Both field-based and lab-based analyses suggest that silane-based treatments can be used successfully in protecting sandstone when applied correctly, both in reducing the rate of decay and functioning over long periods of time. However, sandstone heterogeneity may mean that some individual stones are less compatible with the hydrophobic treatment tested than others. Further field-based analyses (including methods such as XRF and in situ vp) of the treated area is required in order to determine the state of conservation more accurately. These results highlight the complexity in selecting a suitable hydrophobic treatment, especially at built sites where the mineralogy and petrophysical properties of the stone may vary between blocks. However, such treatments may still be important to consider as many climates, including Scotland’s, are becoming progressively wetter, increasing the vulnerability of stone heritage to moisture ingress, accelerated decay, and eventual ruin.

The application of hydrophobic treatments as a means of protecting vulnerable stone heritage has been a topic of research for decades. The findings of previous research have shown that there are a number of factors that influence the efficiency of a treatment and that sometimes, if used incorrectly, such treatments can even accelerate stone weathering and decay. In this study, we revisit a hydrophobic treatment test area at Arbroath Abbey where the product was applied over 40 years ago, thus providing a rare opportunity to investigate the long-term efficiency of hydrophobic treatments. As well as assessing the condition of the treated area in situ by means of moisture analyses, lab-based accelerated salt weathering experiments are conducted to better understand the impact of silane-based treatments on sandstone durability. Moreover, the petrography and petrophysical properties of weathered sandstone (open porosity, capillary absorption, and vapour diffusion) before and after treatment are also characterised to provide a better understanding of how stone properties may influence the compatibility of the treatment. The field-based results show that the treated area has maintained a degree of hydrophobicity since its application over 40 years ago. Both field-based and lab-based analyses suggest that silane-based treatments can be used successfully in protecting sandstone when applied correctly, both in reducing the rate of decay and functioning over long periods of time. However, sandstone heterogeneity may mean that some individual stones are less compatible with the hydrophobic treatment tested than others. Further field-based analyses (including methods such as XRF and in situ vp) of the treated area is required in order to determine the state of conservation more accurately. These results highlight the complexity in selecting a suitable hydrophobic treatment, especially at built sites where the mineralogy and petrophysical properties of the stone may vary between blocks. However, such treatments may still be important to consider as many climates, including Scotland’s, are becoming progressively wetter, increasing the vulnerability of stone heritage to moisture ingress, accelerated decay, and eventual ruin. This research was funded by the University of Glasgow and Historic Environment Scotland as part of a fully-funded Ph.D. project (HES project number: 301140). The British Geological Survey (BGS) supported preparation and revision of the manuscript.

The Yamaat Uul mafic complex with Cu-Ni mineralization is located in the Khangai Mountains of Western Mongolia. We have received new unique data for mafic rocks of the complex: U-Pb dating (SHRIMP II), mineralogy (WDS) and geochemistry (XRF, ICP-MS), Sm-Nd and Rb-Sr isotope data and sulphur isotopes. The Yamaat Uul mafic complex consists of two intrusions: Intrusion 1 is represented by rocks of plagioclase cumulates and olivine–pyroxene cumulates; Intrusion 2 consists of monzogabbro. Intrusions 1 and 2 are different in composition of minerals such as olivine, plagioclase and biotite. The monzogabbro has higher contents of incompatible elements (REE, K, Ti, P) than rocks of Intrusion 1. Zircon U-Pb dating of the anorthosite and Bt-Am-Ol gabbronorite shows a Late Permian age (255.8 ± 2.9 Ma and 262.6 ± 3.1 Ma, respectively) for the Yamaat Uul mafic complex. All of the rocks of the complex are derived from a unified parental melt due to different amounts of trapped melts in plagioclase and olivine–pyroxene cumulates and without crustal contamination. The Cu-Ni mineralization of the complex has a low degree of evolution of the sulphide melt, similar to PGE-Cu-Ni mafic–ultramafic intrusions of the Khangai Mountains (Nomgon and Oortsog Uul). The Yamaat Uul mafic complex together with other mafic–ultramafic intrusions of the Khangai Mountains is related to the Khangai LIP and can be considered as potential for the PGE-Cu-Ni. The new geological, petrological, geochemical and isotope–geochronological data can later be used to reconstruct the geotectonics of the Khangai Mountains and the Central Asian orogenic belt as a whole.

Résumé. Les questionnements abordés dans cet article portent sur l’homogénéité et les relations spatiales entre l’ensemble belloisien et le Laborien. Nous avons pris pour cadre géographique d’étude, la (réputée) marge méridionale du Belloisien : la France centrale. Cet espace est jalonné par plusieurs gisements clés de la transition Pléistocène-Holocène, notamment Muides-sur-Loire, Champ-Chalatras et le Cuze de Sainte-Anastasie. C’est à travers l’étude de l’industrie lithique de ces trois sites que nous questionnons les réseaux de relations à l’extrême fin du Paléolithique. Cet espace est également situé à l’écart des grandes dynamiques de recherche universitaire. Il nous faut donc interroger la notion de frontière à travers l’œil du « préhistorique » ou du « préhistoriens », suivant une analyse pétrotechno-typologique. Les résultats mettent en évidence une fréquentation de gîtes communs et une gestion économique des matériaux parfois semblables entre les trois sites étudiés. Ce réseau de relations complexes met en exergue la porosité entre les appellations préhistoriennes. De plus, l’identification de savoir-faire laboriens, à partir de silicites du sud du Bassin parisien, ainsi que la circulation de grands supports laminaires au sein de sites laborien, confirme cette perméabilité. Ces premières observations alimentent l’hypothèse d’une imbrication d’un sous-système technique belloisien à une tradition plus large : le Laborien. Abstract. The aim of this paper is about discussing to the homogeneity and relationship of the Belloisian tradition with the more southern Laborian. In this regard, we choose central France, the reputed southern margin of Belloisian, to be the geographical framework of this study. It is punctuated by key sites belonging to the Pleistocene-Holocene transition: Muides-sur-Loire, Champ-Chalatras and Cuze de Sainte-Anastasie. What we are questioning in this article are the networks relationships between the Belloisian and the Laborian traditions through the study of lithic industry. This research area is on the fringes of the major dynamic’s university programs too and involves research traditions that differ regionally. We therefore also question the notion of “prehistoric” or “prehistorian” boundaries through a petro-techno-typological analysis of lithic series. In this case study, the techno-economic data shows a frequentation of common outcrops and economic management of the silicites for the three sites. This complex network of relationships between groups shows the porosity between the prehistorian designation. The identification of laborian “know-how” from silicites in the south of the Paris Basin and the circulation of large laminar supports corroborate this fact. So finally, these results lead us to propose the hypothesis of an interweaving of a Belloisian technical sub-system with a Laborian tradition, now well defined.

Nanometer-sized crystals (nanolites) play an important role in controlling eruptions by affecting the viscosity of magmas and inducing bubble nucleation. We present detailed microscopic and nanoscopic petrographic analyses of nanolite-bearing and nanolite-free pumice from the 2021 eruption of Fukutoku-Oka-no-Ba, Japan. The nanolite mineral assemblage includes biotite, which is absent from the phenocryst mineral assemblage, and magnetite and clinopyroxene, which are observed as phenocrysts. The boundary between the nanolite-bearing brown glass and nanolite-free colorless glass is either sharp or gradational, and the sharp boundaries also appear sharp under the transmitted electron microscope. X-ray absorption fine structure (XAFS) analysis of the volcanic glass revealed that the nanolite-free colorless glass records an oxygen fugacity of QFM + 0.98 (log units), whereas the nanolite-bearing brown glass records a higher apparent oxygen fugacity (~ QFM + 2). Thermodynamic modelling using MELTS indicates that higher oxygen fugacities increase the liquidus temperature and thus induced the crystallization of magnetite nanolites. The hydrous nanolite mineral assemblage and glass oxygen fugacity estimates suggest that an oxidizing fluid supplied by a hot mafic magma induced nanolite crystallization in the magma reservoir, before the magma fragmentation. The oxidation-induced nanolite crystallization then enhanced heterogeneous bubble nucleation, resulting in convection in the magma reservoir and triggering the eruption., 軽石のナノスケール岩石学から福徳岡ノ場の新しい噴火モデルを提案 --マグマの酸化が噴火の引き金に--. 京都大学プレスリリース. 2023-05-10.

The Muria-Peninsula is a Quaternary volcano located in the northern Sunda arc. Its activity was controlled under high potassic and very high potassic magma series resulting in leucite-rich trachyte and pyroxene-rich basaltic-andesite. It is a strato-type volcano that is composed of lava, breccia, and tuff layers, and some dikes have some volcanic craters and maars varying in age and composition. The study area is covering the volcanoes of Muria, Genuk, and Patiayam. This paper aims to describe the petrology, mineralogy, and volcano-stratigraphy of the different volcanic materials. The data and materials were sourced from the primary and secondary data. The methods are field mapping, stratigraphy measurements, collecting samples, thin section analyses, and major element geochemistry using X-Ray fluorescence (XRF). The results describe two groups of volcanic rocks consisting of pyroxene-rich andesitic-basaltic volcanic materials and leucite-rich trachytic volcanic materials. Augite presents in the andesitic basalt together with small grains of olivine and a few anorthite and foid minerals. Aegirine (Na-Pyroxene) is present in the leucite-rich trachyte that is often associated with biotite and hornblende. Na-Ca Plagioclase such as labradorite-andesine is often present in the basaltic-trachy-andesite that is usually rarely leucite. The major elements show high-K volcanic rocks with % K2O is 4-5.9% and very high-K volcanic rocks (with % K2O is between 6-8.24%) and low-K volcanic rocks that contain % K2O is 2-3,9%. There are two groups of high-K to very high-K volcanic materials consisting of silicic-rich volcanic materials (~57-64% of SiO2) and low-silicic volcanic materials (~46-50%). The TAS diagram identifies tephrite, phonolite, and trachyte. Stratigraphic data identifies calcareous sediments of the Bulu Formation as the basement rocks of the Muria trachyandesite. Beds of pumice-rich volcanic breccia of the Ujungwatu Formation are the basement rocks of the basanite-tephrite of the Genuk Volcano, and the tuff of the Ujungwatu is also exposed consisting of the basanite-tephritic-phonolite of the Patiayam Volcano. The leucite-like feldspars are very common in the andesite lava and dikes that compose the crater of Muria. Most of the Muria volcanic materials are rarely in leucite, while some maars contain pumice-rich pyroclastic flows and basaltic lava. The results of the major elemental analysis of the Muria materials indicate that the rock tends to be of medium to high K affinity (~2% K2O). The Genuk and older Muria are consisting of leucite-rich tephrite-phonolite. It was two periods of magmatic series developed in the Muria-Peninsula that was resulting in the high-K to very high-K magmatism and the medium K Kalk-alkaline magmatism.

Tectonism often plays an important role in the mineralization process, which is generally thought to be the main controlling factor in the accumulation of economic materials (e.g., gold, coal, oil and gas) through deformation. However, numerous experimental and theoretical studies have suggested that tectonic stress not only causes deformation (physical changes) in rocks and minerals but also promotes their chemical changes by acting directly on chemical bonds and causing bond scission or regeneration, called tectonic stress chemistry (TSC). In recent years, TSC actions caused by tectonic activities have provided new ideas and evidence for explaining the chemical structural evolution of coal, hydrocarbon formation, organic (coal-derived) and inorganic graphitization and hydrothermal mineralization under shear stress. These background studies have provided incentives and insights into how tectonic stress affects the chemical structures of minerals, rocks and even ore-forming fluids in the process of mineralization. In this paper, we briefly review: (1) the concept of TSC; (2) the TSC process in the formation of shear zone type gold deposits from stress concentration, brittle fracturing, sudden reduction of fluid pressure, and flash vaporization to gold precipitation; (3) mechanisms of the macromolecular structural evolution of coal and gas generation under shear stress from deformation experiments and molecular dynamic simulations; (4) coal-derived graphitization caused by preferred orientation and extension of the basic structural units (BSUs) under shear stress; and (5) some preliminary experimental explorations on inorganic graphitization in carbonate-hosted shear zones. In addition, some existing problems and possible solutions for these processes are also discussed. Finally, we propose additional potential TSC processes in extensive geological processes, e.g., the relationship between deformation and metamorphism and trigger mechanisms of slow-slip earthquakes. To further explore these processes, a combination of experiments and molecular dynamic simulations should be undertaken by researchers.

Anisotropy is a crucial characteristic of metamorphic rocks whereby minerals oriented in a preferential direction can originate mineral foliation. Inherent anisotropy can affect the rock behaviour significantly. Transverse isotropy is a particular case of anisotropy where foliation planes are distributed in the rock mass. Therefore, in this study the anisotropy effect on the elastic properties of a foliated phyllite is considered. To this end, a series of laboratory tests was programmed. Triaxial tests were carried out under confining pressures up to 20 MPa. Elastic parameters such as elasticity modulus, E, and Poisson's ratio, ν, are assessed from triaxial test results as well as from ultrasonic tests, where compression and shear wave velocities are determined. Empirical relationships for elastic parameters are suggested as a function of foliation angle, β, and confinement. In addition, anisotropy indexes are adopted to evaluate results, comparing when possible with those of previous works. It was found that E increases with confinement; however, the effect of anisotropy on E reduces with confinement. It was also found that ν is affected by β but not by confinement.

In marine continental margins, high saturations of natural gas hydrate are observed within the gas hydrate stability zone, but the gas migration pathways to the hydrate reservoir are not often clear. We focus on a site in Green Canyon Block 955 (GC 955) in the Gulf of Mexico, where gas hydrate occurs in a 35 m-thick reservoir with saturations of 79-93% in numerous centimeter- to decimeter-thick sandy silt layers and little to no gas hydrate in the interbedded cm to decimeter-thick clayey silt layers. Different datasets (well logging, coring, and seismic data) suggest different types of potential methane migration mechanisms. For example, relatively high particulate organic carbon content in the reservoir and the microbial methane source indicated by gas chromatography and methane isotopes suggest gas might be made locally and migration could occur through dissolved methane sources or water advection. In contrast, the visible deeply rooted faults intersecting the gas hydrate reservoir and the gas pockets adjacent to the faults on seismic data suggest that free gas may migrate directly into the reservoir. We tested three different mechanisms to form gas hydrate at GC 955: short-range methane diffusion, short-range methane diffusion coupled with upward water advection, and free gas flow. The 1-D and 2-D numerical models show that both the short-range migration and the upward water advection are not enough to form high saturations gas hydrate at GC 955, and that free gas flow is required to form the high saturations of gas hydrate observed at GC 955.

The Qinling Complex is the only continental nucleus that outcrops in the North Qinling Orogenic Belt (NQOB) and preserves valuable evolutionary information of NQOB during the early Paleozoic. There are many high-pressure (HP)–ultrahigh-pressure (UHP) metamorphic rocks distributed in the northern and southern parts of the Qinling Complex. Whether the central part (namely the Qihe tectonic slab) underwent a similar HP–UHP metamorphism and what the relationship among different tectonic slabs of Qinling Complex is, are the key to revealing the formation and exhumation process of these HP–UHP rocks. Four episodes of deformation (D1–4) have been recognized in the Qinling Complex. The metamorphic pressure‐temperature conditions of syn-D3 amphibolite in the Qihe tectonic slab are limited to 3.3–6.4 Kbar and 479–538 ℃ based on equilibrium modeling, corresponding to an extensional tectonic setting. The U-Pb dating of the amphibolite yielded a protolith age of 714 ± 46 Ma, an eclogite-facies metamorphic age of 514 ± 4 Ma, and two stages of retrograde metamorphism at 462 ± 3 Ma and 418 ± 5 Ma. The parametamorphic rocks of different tectonic slabs have similar detrital zircon age spectra, which is a very different pattern from adjacent areas of the Qinling Complex. The consistency in the protolith ages, peak metamorphic ages, two stages of retrograde metamorphism, and detrital zircon age from different tectonic slabs in the Qinling Complex indicate that HP–UHP metamorphic rocks from Qinling Complex formed during the same tectonic event. Therefore, the Qinling Complex evolved in deep subduction and underwent eclogite facies metamorphism, followed by superimposed deformation structures and retrograde metamorphism during the two stages of exhumation.

Understanding the dominant physical processes that cause fault reactivation due to fluid injection is vital to develop strategies to avoid and mitigate injection-induced seismicity. Injection-induced seismicity is a risk for several industries, including hydraulic fracturing, geothermal stimulation, oilfield waste disposal and carbon capture and storage, with hydraulic fracturing having been associated with some of the highest magnitude induced earthquakes (M > 5). As such, strict regulatory schemes have been implemented globally to limit the felt seismicity associated with operations. In the UK, a very strict “traffic light” system is currently in place. These procedures were employed several times during injection at the PNR-1z well at Preston New Road, Lancashire, UK, from October to December 2018. As injection proceeded, it became apparent to the operator that stages were interacting with a seismogenic planar structure, interpreted as a fault zone, with several ML > 0.5 events occurring. Microseismicity was clustered along this planar structure in a fashion that could not readily be explained through pore pressure diffusion or hydraulic fracture growth. Instead, we investigate the role of static elastic stress transfer created by the tensile opening of hydraulic fractures. We find that the spatial distributions of microseismicity are strongly correlated with areas that receive positive Mohr-Coulomb stress changes from the tensile fracture opening, while areas that receive negative Mohr-Coulomb stress change are quiescent. We conclude that the stressing due to tensile hydraulic fracture opening plays a significant role in controlling the spatiotemporal distribution of induced seismicity.

The Campos Basin (SE Brazil) hosts significant hydrocarbon accumulations in reservoirs above and below a layer of evaporites. The rift to post-rift lacustrine carbonates that constitutes the Pre-Salt reservoirs have been the object of several studies focused on the depositional and diagenetic characteristics of these Barremian to Aptian carbonates. Nevertheless, the basement geology, tectono-stratigraphic evolution and geochronologic constraints for the hydrothermal diagenesis are yet to be established. This thesis presents a novel integrated geological study of the entire presalt sequence utilizing 2D and 3D seismic surveys and sidewall cores from a hydrocarbon accumulation in the northern Campos Basin. The basement is constituted by anisotropic, high-grade supracrustal rocks in the East and relatively isotropic granitic rocks in the West. Lithologies, structural style and age suggest a correlation with the onshore Cabo Frio Tectonic Domain. The overall rift evolution probably started during the Berriasian with a peak of rift-related faulting from the Hauterivian to Barremian, followed by a rift transition and post-rift stages (Barremian to Aptian). The pre-existing metamorphic fabric was selectively reactivated whenever its orientation was favourable. Petrography and geochemistry show diagenetic phases composed predominantly of quartz, calcite and dolomite to ankerite series, and secondarily pyrite, Sr-barite and svanbergite. Additional studies of stable isotopes, fluid inclusion microthermometry and LA-ICP-MS U-Pb geochronology in the diagenetic minerals provide evidence for three tectono-diagenetic events that occurred under distinct diagenetic settings during the Barremian to Aptian, the Albo-Cenomanian and the Campanian to Maastrichtian stages. The diagenetic conditions were initially hydrothermal and progressively attained geothermal equilibrium under deep-burial conditions towards the Late Cretaceous. These diagenetic episodes were not necessarily coeval with magmatic events were are always coeval with basin-scale tectonic events described previously using balanced cross-sections in the post salt section.

The problem of heat–mass transfer in the permeable areas above the asthenosphere zones was numerically studied based on an examination of the inclusion content in the minerals (olivine and clinopyroxenes) of igneous and metamorphic rocks of the lithospheric mantle and the Earth’s crust; evaluations of thermodynamic conditions of the inclusion formation; and experimental modeling of the influence of hot reduced gases on rocks in the mantle beneath the Siberian craton. The flow of fluids of a certain composition from the upper-mantle magma chambers leads to the formation of zonal metasomatic columns in the ultrabasic mantle lithosphere in the permeable zones of deep faults (starting from the lithosphere base at 6–7 GPa). When petrogenic components enter from the magma pocket, depleted ultrabasic lithospheric mantle rocks change to substrates, which can be considered as the deep counterparts of crustal rodingites. Other fluid compositions result in strong calcination and pronounced salinization of the metasomatized substrates or an increase in the garnet content of the primary ultrabasic matrix. A region of alkaline rocks forms above these areas, which changes to pyroxenes, amphiboles, and biotites. The heat–mass transfer modeling for the two-velocity hydrodynamic model shows that gas–fluid and melt percolation lead to an increase in the thermal front velocity under convective heating and a pressure drop in flow. It is also shown that grospidites are considered to be eclogites, are found in the permeable zones of the lithospheric mantle columns serving as conduits for the melt/fluids and represent the products of the carbonated metasomatic columns. The carbonization caused by proto-kimberlite melts may essentially decrease the diamond grade of kimberlites due to carbon oxidation.

The Istituto Nazionale di Geofisica e Vulcanologia ­ Osservatorio Etneo (INGV ­ OE) hosts a collection of thin sections – thin slices of rock made for petrographic observation and chemical characterization under the microscope. Thin sections are from eruptive products of Etna, collected over the last 30 years for monitoring purposes. This collection is a resource that can be utilized by the INGV staff to support volcano monitoring as well as by researchers for investigating petrological processes and contributing to the understanding of the genesis of recent Etna magmas. To facilitate and encourage these activities we created a database, in the form of a Microsoft Excel™ spreadsheet with defined fields, designed to describe the key petrographic properties of samples cut into thin sections, in a consistent way. The freely available database, which includes linked images of the thin sections, allows researchers interested in studying Etna volcanism to gain an overview of the main petrographic features of the rocks, which can help them to select the most appropriate samples for their research project(s). The information included in the database can also be utilized for monitoring purposes via comparison with samples from ongoing eruptive events. The database currently contains the description of 33 thin sections from the 2007­2008 eruptions of Etna, with the remaining thin sections in the INGV ­ OE collection to be added in future. This work has been designed to be incorporated, in the future, into the TSDSystem (Time Series Database), a resource developed over many years by the INGV ­ OE Information Technology (IT) staff, the purpose of which is to archive, update and distribute data from INGV ­ OE monitoring activities. It is hoped that this resource, once available for the scientific community, will both inspire and facilitate research projects involving Etna eruption products, making full use of this extensive but otherwise scarcely studied sample collection, with the ultimate aim of improving understanding of volcanic activity at Etna.

Core, thin section, conventional and image logs are used to provide insights into distribution of fractures in fine grained sedimentary rocks of Permian Lucaogou Formation in Jimusar Sag. Bedding parallel fractures are common in fine grained sedimentary rocks which are characterized by layered structures. Core and thin section analysis reveal that fractures in Lucaogou Formation include tectonic inclined fracture, bedding parallel fracture, and abnormal high pressure fracture. Bedding parallel fractures are abundant, but only minor amounts of them remain open, and most of them are partly to fully sealed by carbonate minerals (calcite) and bitumen. Bedding parallel fractures result in a rapid decrease in resistivity, and they are recognized on image logs to extend along bedding planes and have discontinuous surfaces due to partly-fully filled resistive carbonate minerals as well as late stage dissolution. A comprehensive interpretation of distribution of bedding parallel fractures is performed with green line, red line, yellow line and blue line representing bedding planes, induced fractures, resistive fractures, and open (bedding and inclined) fractures, respectively. The strike of bedding parallel fractures is coinciding with bedding planes. Bedding parallel fractures are closely associated with the amounts of bedding planes, and high density of bedding planes favor the formation of bedding parallel fractures. Alternating dark and bright layers have the most abundant bedding parallel fractures on the image logs, and the bedding parallel fractures are always associated with low resistivity zones. The results above may help optimize sweet spots in fine grained sedimentary rocks, and improve future fracturing design and optimize well spacing.

Due to the high density at mantle depths, subducted oceanic crust rarely exhumes to the surface of Earth, making it challenging to determine the evolution and dynamic behavior of oceanic crust. The Sumdo eclogite-bearing metamorphic belt, located between the north and south Lhasa terranes in Tibet, is a natural laboratory for studying the metamorphic evolution of oceanic eclogites. We combined phase equilibrium modeling with detailed petrological investigations for the newly discovered Xilang eclogite from this belt and obtained near-peak metamorphic conditions of 539 °C at 1.84 GPa and a steep exhumation P–T path. These values are much lower than published for the other areas of this belt. Quartz inclusions sealed in garnet from high-pressure rocks are known to preserve residual pressures during exhumation, which can be used to reexamine the peak metamorphic conditions of eclogites in the Sumdo metamorphic belt. We analyzed quartz from three different areas in the belt, including Xilang, Jilang, and Xindaduo, with laser Raman micro spectroscopy. Xilang eclogite preserved the highest residual pressure of 0.53 ± 0.07 GPa in the quartz stability field. A systematic comparison of the residual pressures of different eclogites revealed that not only the peak metamorphic conditions but also the exhumation rate of the host rocks controlled the residual pressure. Hence, the Xilang eclogite may record lower peak P–T conditions, because it exhumed differently than the eclogites from the other areas in the Sumdo metamorphic belt. Combined with numerical modeling, the residual pressures obtained by Raman spectroscopy may be a new way to compare the metamorphic conditions of eclogites and to obtain geochronological information in addition to isotopic investigations.

The dissociation of gas hydrates can increase pore pressures greatly, thereby causing the shallow layers of submarine slopes to fail. Given the high failure risk of shallow subsea soils, it is important to understand the stratum response mechanisms after hydrate dissociation. In this paper, submarine slope failure triggered by overpressure fluid associated with gas hydrate dissociation is investigated in laboratory experiments. A two-layer geological model is built based on actual geological data, and pressurised air is injected into the model to simulate the overpressure fluid. The pore pressures, surface displacements and internal deformations of soils are measured and compared under different conditions, and their evolution processes are analysed for various parameter values. The results show that the accumulation of pore pressure increases with the thickness of the soil layer and leads to layered fractures. The failure pattern can be generalised into two types: (a) disc-shaped failure and (b) penetration failure. In disc-shaped failure, a major failure occurs when the shear stress reaches the shear strength, whereas tensile fracturing is a major effect in penetration failure. This achievement is very important for a deep understanding of submarine landslides induced by overpressure fluid, as well as for risk assessments of ocean engineering sites.

The decomposition of natural gas hydrate will reduce the cementation effect of hydrate and produce ultra-static pore pressure, which will change the mechanical characteristics of the reservoir. Eventually, a series of geological disasters could be triggered, of which the submarine landslide is a typical example. In order to analyze the stability of hydrate-bearing submarine slopes and to explore the internal relationship between hydrate decomposition and submarine landslides, a “two-step reduction method” was described in this paper. This method was based on a strength reduction approach, which can be used to assess the effects of the initial geostress balance and hydrate decomposition on substrate strength reduction. This method was used to reveal the essence of hydrate decomposition and then a joint operation mode of multi-well was proposed. The internal relationship between hydrate decomposition and submarine landslides were analyzed in detail. And the development process and mechanism of submarine landslide were deeply discussed. The results showed that hydrate decomposition is a dynamic process of stress release and displacement, where the “stress inhomogeneity” distributed along the slope is transformed into “displacement inhomogeneity”. We concluded that hydrate decomposition could trigger a submarine landslide, especially along a sliding surface. The formation of submarine landslide is a gradual development process, and presents the dual characteristics of time and space.

The horizontal distribution and periodic accumulation of hydrocarbon in reservoirs are well understood. However, our understanding on the vertical distribution of hydrocarbon accumulation in reservoirs is not clear and remains mysterious to some extent. We proposed a concept of hydrocarbon accumulation depth limit (HADL) to characterize the hydrocarbon’s vertical distribution in petroliferous basins, which is determined by statistical analyses of the variation trends of reservoir layers’ essential properties, including hydrocarbon saturations (So), movable hydrocarbon ratios (Mo) and dry layer ratio (Ko), when the depth is increased. A total of 80,762 drilling results from 12,237 exploration wells in six representative petroliferous basins in China were collected and analyzed. The reservoir layers’ essential properties So, Mo and Ko and their correlations with porosity, permeability, pore throat radius and thermal evolution degree were investigated. The critical values of So, Mo and Ko that define HADL were quantified to be So=0, Mo=0 and Ko=100. Our study indicates that the HADL in petroliferous basins varies from less than 3,000 m to more than 13,000 m deep, depending on the hydrocarbon composition, reservoir lithology, reservoir age, geothermal gradient, tectonic movement, etc. Two factors play an essential role in the formation and variation of HADL: 1) the depletion of hydrocarbon generation potential of source rocks which cuts off hydrocarbon contribution for reservoirs formation and 2) the termination of differential compaction which eliminates capillary pressure difference between the outer surrounding rocks and inner reservoir layers, ending the dominant driven force for hydrocarbon migration and accumulation in deep and tight reservoir layers. All proven oil reserves of 33.95 billion tons equivalent in China, as well as world’s discovered 52,926 oil and gas reservoirs and their unproved potential resources, are distributed above the HADL we defined.

The continental collision-induced far-field intraplate deformation may be topographically separated from or coherent with the collision front, the mechanism of which is poorly constrained. Here, we build a series of 2D thermo–mechanical models to explore the controlling factors of distal orogenesis in the framework of a composite terrane sandwiched between two strong continental blocks. The model results suggest that the development of distal orogenesis requires a strong rheological heterogeneity in the overriding lithosphere. Two types of far-field collisional effects with distinct patterns of topographic evolution are identified, characterized by (I) a delayed and discrete distal orogenesis separated from the collision front by a low-relief, less-deformed terrane interior, and (II) an instant distal orogenesis subsequently integrated into a progressively growing plateau. These two types of far-field orogenesis are revealed to be analogous to the development of the Kopet Dagh and northern Tibet. The comparisons between model results and geological observations provide significant constraints on the dynamics of crustal-scale deformation propagation and the formation of distinct lithospheric architectures.

International audience; We present a new numerical modelling study of subduction initiation at (hyper-extended) magma-poor and magma-rich continental passive margins. In particular, we test how the structure and rheological stratification of these two end-member types control the formation and thermo-mechanical evolution of subduction zones. The serpentinization of mantle lithosphere in a magma-poor continental rifted margin leads to rheological decoupling at the base of the continental crust, which induces shear localization during subsequent shortening. Under these conditions, a shear zone propagates into the mantle lithosphere and leads to subduction initiation at the transition between ocean and passive margin. In contrast, a magma-rich rifted continental margin is rheologically coupled, which creates a buttressing effect and transfer of deformation into the oceanic domain during shortening, where the subduction zone initiates. These results are quantitatively compared and in agreement with the geological record of subduction initiation in the Alps and Dinarides – Hellenides, where the relics of end-member types of continental rifted margins of the same Adriatic micro-continent bordering the Alpine Tethys and Neotethys oceans, respectively, are observed.

3D geocellular modeling is increasingly essential in the petroleum industry; it brings together all petroleum disciplines, and it is commonly used in simulation and production forecast. However, modeling slope and deep-water turbidite reservoirs using conventional modeling methods pose a significant challenge due to the structural complexity and thin-beds associated with these reservoirs. Through the innovative modeling technology of PaleoScan, the reservoirs in Sub member 3 of the third member of the Shahejie Formation are modeled to understand the structural framework. The resulting model is populated with petrophysical properties i.e., porosity and permeability to predict their lateral and vertical distribution within these sandstone reservoirs. The study suggests that the reservoir in the highstand system tract (HST) is characterized by the clinoforms configuration framework. The reservoir is highly faulted mainly in the northern and southeastern parts of the depression. The sedimentary layers are deposited across the slope and downlapping, thinning, and terminating toward to the west. The two isochore surface maps reveal sediment thickness variation and depositional trends within each individual depositional layer. The zones or areas that corresponds to low values on the thickness maps suggest minor uplifts associated with intensive faulting in the Eocene period. These topographical highs played a fundamental role in distributing the sediments delivered to the basin from distant sources. The maps reveal that sediments that filled the basin appear to come from different source points, primarily delivered from the north, southeast, and northeast of the basin with varying depositional trends. The modeled porosity and permeability indicate that the delta fed turbidite reservoirs are characterized by medium to high porosity values of 10–20% and low to medium permeability values of 30-410mD, respectively. The porosity values increase to the southeast and toward the basinwards (west) while permeability varies within the individual sedimentary layers. The distribution of porosity and permeability is not uniform vertically. This suggests the presence of mixed none-reservoir layers with locally and periodically deposited sandstone reservoirs within the stratigraphic during rapid delta progradation. The HST is characterized by six different delta progradation cycles; each phase produced locally deposited lacustrine turbidite sandstones in the basin, which are essential reservoirs in this Formation. The innovative PaleoScan interpretation technology has successfully created a high-resolution 3D reservoir model of this complex geology-such innovative technology is vital to similar complex geology globally.

International audience; A leucogranite sill in the footwall of the extensional Pilat shear zone (PSZ) Eastern French Massif Central was emplaced and sheared in a short time interval, between 301.8–3.1 and 303.0–1.6 Ma (zircon U–Pb and mica 40 Ar/ 39 Ar ages, respectively). Extension ended at 298.5–1.5 Ma ( 40Ar/ 39 Ar on mica) as shown by a non deformed dike cross cutting the sheared zone. On the hanging wall of the fault, the opening of the St. Etienne Basin filled by coarse clastic sedimentation confirms the existence of a relief south of the PSZ. U-Pb dating of a lithic-rich ignimbrite at the bottom of the basin and of a volcanic layer at the top delivred ages of 310.5–3.4 Ma and 299.3–1.3 Ma, respectively. Close U-Pb and 40 Ar/ 39 Ar ages from syn- to post-tectonic granites indicate very fast cooling (150°C/Myr) and exhumation rate (6 mm/yr) corresponding to the emplacement of granites in the middle crust immediately followed by their fast tectonic exhumation and cooling into the upper crust. The development of the Pilat fault in the thermally softened crust is responsible for the rapid exhumation of the Velay dome, a Metamorphic Core Complex localized in the footwall of the sheared zone. Here we propose that its rapid exhumation was due to localized sub crustal lithospheric mantle dripping. These new data show that there was only one extensional phase in the PSZ coeval with the opening of the St. Etienne coal Basin. Finally, the new chronology obtained in this study is challenging previous ages suggesting 20 Ma activity for the Pilat shear zone.

The Qinling Orogenic Belt (QOB) is an important tectonic belt in eastern Asia, which is believed to have been formed by the intracontinental collision between the North China Craton and South China Block. By analyzing radial P-wave receiver functions recorded by 239 broadband stations, we investigate the crustal thickness and Vp/Vs ratio maps under the QOB and its adjacent regions using the H-k and common-conversion-point (CCP) stacking methods. The crustal thickness (H) and Vp/Vs ratios (k) showed significant lateral variations. The assessment of crustal isostatic compensation reveals that the topography of the Dabashan and central QOB are compensated by crustal thickness, although the later may not be fully compensated. The crust of the western and eastern QOB are possibly in a non-Airy-type isostasy state, and the low-density uppermost mantle may play an important role in compensating their elevations. The Dabashan and the region to the south have thick crustal thickness and high Vp/Vs ratios, while the east QOB have thin crustal thickness and low Vp/Vs ratios. The CCP images reveal two strong positive amplitudes at depths consistent with the Moho interface near the Ankang fault. These observations indicate complex lower crustal structure and suggest the existence of eclogitized lower crust beneath Dabashan and lower crust delamination beneath east QOB. We also observe a continuous area with thick crust and high Vp/Vs ratios that covers the Dabashan, Hannan–Micang Dome, Shennong–Huangling Dome and their surrounding regions. This area shows consistency in location with a rapidly uplifted area since approximately 15 Ma, which—with other geological studies—implies the asthenospheric flux from the Tibetan Plateau. The asthenosphere flow may have eroded the lithosphere beneath the Dabashan and promoted the lower crustal eclogization.

Regarding high drilling costs, an effort should be made to substantially reduce the drilling operation. To achieve this goal, exploration and development stages should be carried out precisely with maximum information acquired from the reservoir. The use of multi-attribute matching technology to predict sedimentary system has always been a very important but challenging task. To resolve the challenges, we utilized a quantitative analysis method of seismic attributes based on geological models involving high resolution 3D seismic data for sedimentary facies. We developed a workflow that includes core data, seismic attribute analysis, and well logging to highlight the benefit of understanding the facies distribution in the 3rd Member of the Lower Jurassic Badaowan Formation, Hongshanzui area. 1) Data preprocessing. 2) Cluster analysis. 3) RMS attribute based on a normal distribution constrains facies boundary. 4) Mapping the sedimentary facies by using MRA prediction model combined with the lithofacies assemblages and logging facies assemblages. The confident level presented in this research is 0.745, which suggests that the methods and data-mining techniques are practical and efficient, and also be used to map facies in other similar geological settings.

The sedimentary basin is a basic geological unit in the Earth system: its formation and evolution are controlled mainly by plate tectonics and geodynamics, which have produced a variety of basin types. The development and evolution of various basins depend not only on the tectonic effect of lithospheric plate but also on sublithospheric, and Earth surface actions. Basin classification schemes based on the theories of platform–geosyncline or plate tectonics could neither include all basin types nor reflect the complex processes of basin formation and evolution. From the viewpoint of Earth system, we proposed a new basin classification scheme based on geodynamic mechanism—that is, lithospheric plate, sublithospheric, and Earth surface actions. In our geodynamic classification, we employed a series of geodynamic settings of basin formation and evolution, including the lithospheric plate, sublithospheric, and Earth surface environments, the dynamic regimes of basin formation and evolution, such as tectonic setting (extension, compression and shearing), the thermal processes and gravity effects, the various natures of basin basement and crustal types (continental, oceanic, or transitional crust), and the history of basin sedimentary filling and tectonic paleogeography successively, as the controlling factors for basin classification. This new geodynamic classification scheme highlights both the role of the lithosphere and the effects of the sublithospheric and the Earth surface actions on controlling the basin formation and evolution. The basic dynamic types of basin classification include the prototype basin forming under a single tectonic, thermal, or gravity regime and the superimposed basin as well as residual basin forming under multistage thermal and/or tectonic regimes. Thus, this classification scheme could provide an evolving understanding of lithosphere, crust–mantle interaction, and geodynamic processes as well as of hydrocarbon accumulation and metallogenic mechanisms in sedimentary basins and would help in the synthetic exploration of various resources.

The eruptive history of Pantelleria has been marked by the eruption of nine peralkaline ignimbrites, with inter-ignimbrite episodes from small, local volcanic centres. New whole-rock geochemical data are presented for seven ignimbrites and used with published data for younger units to track compositional changes with time. From»190 ka, silicicmagmatismwas dominated by comenditic trachyte to comendite compositions, evolving along generally similar liquid lines of descent (LLOD). The final ignimbrite, the Green Tuff (»46 ka), was tapped from a compositionally zoned pantelleritic upper reservoir to a trachytic mush zone. Younger (20–7 ka) silicic magmatism has been relatively small scale, with compositions similar to the earliest pre-Green Tuff pantelleritic ignimbrite (Zinedi). These data suggest that the comenditic reservoirs may have been emplaced at deeper levels than the pantelleritic reservoirs. While both types of series evolved along similar LLOD dominated by fractionation of alkali feldspar, it is the fractionation of iron that determines whether comendite or pantellerite is produced. The deeper reservoirs were more oxidizing and wetter, thus leading to the crystallization of magnetite and therefore the fractionation of iron.

The propagating margins of igneous sills (and other sheet intrusions) may divide into laterally and/or vertically separated sections, which later inflate and coalesce. These components elongate parallel to and thus record the magma flow direction, and they can form either due to fracture segmentation (i.e., “segments”) or brittle and/or non-brittle deformation of the host rock (i.e., “magma fingers”). Seismic reflection data can image entire sills or sill-complexes in 3-D, and their resolution is often sufficient to allow us to identify these distinct elongate components and thereby map magma flow patterns over entire intrusion networks. However, seismic resolution is limited, so we typically cannot discern the centimeter- to meter-scale host rock deformation structures that would allow the origin of these components to be interpreted. Here, we introduce a new term that defines the components (i.e., “elements”) of sheet-like igneous intrusions without linking their description to emplacement mechanisms. Using 3-D seismic reflection data from offshore NW Australia, we quantify the 3-D geometry of these elements and their connectors within two sills and discuss how their shape may relate to emplacement processes. Based on seismic attribute analyses and our measurements of their 3-D geometry, we conclude that the mapped elements likely formed through non-elastic-brittle and/or non-brittle deformation ahead of the advancing sill tip, which implies they are magma fingers. We show that thickness varies across sills, and across distinct elements, which we infer to represent flow localization and subsequent thickening of restricted areas. The quantification of element geometries is useful for comparisons between different subsurface and field-based data sets that span a range of host rock types and tectonic settings. This, in turn, facilitates the testing of magma emplacement mechanisms and predictions from numerical and physical analogue experiments.

The study aims to find out the formation period of fault traps near faults in petroliferous basins, based on an analysis of the formation period of fault lateral sealing and related influential factors. A method to calculate the formation period of fault lateral sealing (i.e. the time when displacement pressure of fault rock is equal to that of reservoir rock in fault wall with hydrocarbon migration) is established by comparing the relationship between displacement pressure and time for fault rock and reservoir rock. This method is then applied to the study on reservoirs in the 1st, 2nd, and 3rd members of Dongying Formation (E3d1, E3d2 and E3d3) in terms of formation period of lateral sealing of F3 fault crossing the three reservoirs in the No.5 structure of Nanpu Sag in Bohai Bay Basin. The results indicate that the formation period of the lateral sealing in the studied reservoirs can date from 7.1 Ma, 7.4 Ma and 9.2 Ma respectively, all prior to the hydrocarbon accumulation period (about 2.58 Ma). Hence, it can be concluded that these reservoirs are favorable for the accumulation and preservation of hydrocarbons generated from the underlying source rock E3s3, and the method proposed is feasible in calculating the formation period of fault lateral sealing.

Strike-slip faults, proven to be closely linked to hydrocarbon migration and accumulation, are widespread in the Tarim Basin Craton. Deformation patterns in the eastern part of the Central Uplift Belt of the Tarim Basin are analyzed in detail to understand the deformation model and genetic mechanism of strike-slip faults, how their patterns impact reservoir formation and influence oil and gas potential. Regional tectonic events are taken into consideration to identify the primary factors that controlled the development of strike-slip faults in the region. The Tazhong Uplift in the eastern part of Central Uplift Belt is believed to be a complex anticlinal uplift formed by compression-and-torsion acting on the Cambrian – Middle Ordovician platform during the middle–late Caledonian period. Multi-stage development of this north-trending fault–fold belt and the NE-trending strike-slip faults make it structurally complex. The NE-trending Paleozoic strike-slip faults were formed jointly by the differential thrusting of the Tazhong Uplift along Fault No. I and the NE-trending shear sliding of the basal fault blocks during the middle–late Caledonian – early Hercynian. Based on the distribution of effective source rocks, the tectonic setting during the period critical to hydrocarbon accumulation, and the distribution of conductive faults, the northern slope of the Tazhong Uplift— especially its west-central part where the NE-trending faults are developed is not only located close to the northern hydrocarbon source rock area but also possesses conditions suitable for the development of carbonate reservoirs. In addition, the NE-trending faults provide passage for initial development of the reservoir and the subsequent migration of oil and gas from the Aman area to the uplifted zone, making the Tazhong Uplift an extremely favorable area for oil and gas accumulation with substantial potential for exploration.

Reservoir characteristics of beach-bar sandstone reservoirs in the 2nd member of the Shahejie Formation in Banqiao Sag are studied by means of well logging interpretation, thin section observation and physical property analysis. Further, the influence of deposition, diagenesis and internal architecture interface on reservoir quality are quantitatively analyzed. On this basis, the geneses of reservoir heterogeneity of beach-bar sandstone reservoirs are summarized. The following results are obtained. (1) Primary pores, secondary pores and micro-fractures are the main types of reservoir space in the study area, and the primary intergranular pore is the main pore type; the microscopic heterogeneity of reservoirs is strong, and the physical properties of beach-bar reservoirs in different regions vary widely. (2) Tectonic-deposition, diagenesis and reservoir internal architecture work in unison to cause the heterogeneity of beach-bar reservoir quality in the 2nd member of the Shahejie Formation in Banqiao Sag; the locations and scales of beach-bar sand bodies are obviously different in different fault blocks in the study area, determining the macroscopic distribution of beach-bar reservoirs; differential diagenesis intensifies the degree of reservoir heterogeneity; the fine-grained argillaceous deposits between different architecture units of beach-bar reservoirs are critical to the quality of reservoirs. (3) The differential distribution of beach-bar reservoir quality parameters in the study area affects the spatial heterogeneity of reservoirs, which not only controls the original oil/gas distribution, but also has a significant influence on the effect of waterflooding and leads to the local enrichment of remaining oil.

Oceanic lithosphere worldwide is younger than ca. 200 Myr, suggesting that it must have been globally recycled by the recurrent formation of new subduction zones since the existence of subduction on Earth. However, postulated subduction zone initiation processes remain difficult to explain in many cases, and the specific geodynamic conditions under which these might occur are still largely unknown. We here use numerical models driven by the internal force balance of a subduction system to better understand the (geo)dynamics governing (intra-oceanic) polarity-reversal subduction zone initiation. This initiation mode assumes that the birth of a new subduction zone could be triggered by buoyant plateau-obstruction of a pre-existent one dipping in the opposite direction. Our work provides a new insight on the key geodynamic conditions governing this type of subduction zone initiation and discusses their general compliance with known natural examples.

Active/recent volcanism indicates the presence of high-enthalpy resources at depth, but sometimes there is not any evidence of endogenous fluids manifestations at surface, that confirms the presence of an active geothermal system. In this study we present an extensive study of published and new diffuse 4He and 3He emission and thermal energy released data from fifteen volcanic systems, confirming a direct relationship between diffuse helium emissions and thermal energy released associated with the rise of mantle fluids. The results are useful to infer the existence of deep and/or hidden geothermal resources and to estimate roughly its potential at those areas without obvious geothermal manifestations at the surface, but with measureable anomalous emissions of 4He and 3He. Tracing diffuse He emission anomalies at the surface environment of volcanic systems provides very important information for the exploration and discovery of geothermal resources at those areas where the resources are either hidden or lie at great depth.

Determining the parameters that control fissure-fed lava morphologies is critical for reconstructing the complex emplacement histories of eruptions on Earth and other planetary bodies. We used a geomorphological map of the 2014–2015 Holuhraun lava flow field, in combination with new constraints on lava emplacement chronology and two independently derived time-averaged discharge rate (TADR) data sets, to analyze correlations between lava morphology and effusion rate. Results show that lava morphologies are dominantly controlled by effusion rate at the vent during the early phases of the eruption and by lava transport processes as the system evolves. Initially, TADR and its variance, which reflect pulsation in the lava supply rate from the vent, directly affect lava emplacement styles. However, as the eruption progresses, the lava transport system exerts a stronger control with channels and ponds that can either dampen variation in local effusion rate or create surges during sudden drainage events. The Holuhraun eruption predominantly produced rubbly lava in its earlier eruption phases and transitioned into the production of spiny lava toward the end of the eruption. However, a drop of TADR during the first phase of the eruption correlates with a decrease in rubbly lava formation and an increase in spiny lava production. This suggests that a change in effusion rate caused the observed transition in lava type. Our findings show that rubbly lava is formed under relatively high local effusion rates with pulsating supply conditions, whereas spiny lava is formed under lower local effusion rates and steadier supply.

Rock salt has high thermal conductivity (>6 W m−1 K−1 at 20 °C) compared to most overlying and adjacent sedimentary rocks, resulting in a thermal blanket effect and a favorable play for low enthalpy geothermal resources. However, the effect of temperature on rock salt thermal conductivity is greater than most other rocks. The result can be a reduction in this contrast between rock types, which has implications for geothermal exploration. The temperature dependence of rock salt thermal conductivity was shown to be a critical factor in our geothermal potential assessment of the Magdalen Islands (Canada). We evaluated the subsurface temperature of this archipelago using numerical simulations of conductive heat transfer, specifying a bulk thermal conductivity of rocks that varies with temperature and porosity, and the latter varying with pressure. A steep geothermal gradient, locally exceeding 40 °C km−1, was found in layers overlying shallow salt domes at depths of ∼1 km but not over a deeper dome due to low thermal conductivity contrasts. This finding highlights the effect of temperature on rock salt thermal conductivity, which should be considered when assessing the geothermal potential of salt domes, intrusions or diapirs, to avoid overestimating the subsurface temperature.