NNE SSW Research Articles

Gravity and magnetic field interpretation to detect deep buried paleobasinal fault lines contributing to intraplate earthquakes: a case study from Pohang Basin, SE Korea

SUMMARY Potential field interpretation is a powerful method to locate deep buried tectonic fault lines that contribute to intraplate earthquakes. A magnitude 5.4 earthquake (2017, M5.4_PO) occurred in the Middle-Miocene Pohang Basin (PB), SE of the Korean Peninsula on 15 November 2017, in the area where no fault lines appear on geological and tectonic maps. To constrain fault locations, we calculate the gravity effect of the current basin fill with a gravity stripping method and used curvature analysis to identify former geological and tectonic structures, assumed formed in the Early-Miocene. The Early-Miocene PB is divided into two subregions (northern- and southern sub-basins) by a modelled NW–SE fault line, similar to the other Early-Miocene basins (e.g. Eoil basin). Fault line trends are NE–SW in the northern sub-basin, and NNE–SSW in the southern sub-basin. 2017M5.4_PO arose from a tectonic movement along the eastern boundary of the northern sub-basin, the cross-over area from the isolated high-magnetic/low-gravity region to low-magnetic/high-gravity region. The largest aftershock of the 2017M5.4_PO occurred along the NW–SE fault line bordering the northern- and southern sub-basin.

Tectonic deformation in the Santorini volcanic complex (Greece) as inferred by joint analysis of gravity, magnetotelluric and DGPS observations

SUMMARYTectonic activity is very difficult to study in the Santorini volcanic complex (SVC) as it comprises a cluster of small/awkwardly shaped islands covered by pyroclastic deposits from which tell-tale markers are swiftly erased, while seismicity is generally absent. We address the problem by combining geophysical exploration methods to evaluate the long-term effects of tectonic deformation and time-lapse differential GPS to directly evaluate the magnitude and kinematics of present-day deformation. The former comprise 3-D gravity modelling to investigate the footprint of tectonics on the pre-volcanic Alpine basement and natural-field EM induction to map conductivity anomalies epiphenomenal to fluid circulation in faults. Our analysis identified the following principal tectonic elements:The Trans-Santorin Divide (TSD), a segmented NNW–SSE dextral strike-slip fault splitting the SVC sideways of the line joining Cape Exomytis, the Kammeni Islets and the Oia–Therassia Strait. It is collocated with a major vertical conductive zone and forms a series of dents and depressions in the basement. The Columbo Fault Zone (CFZ) is a pair of parallel NE–SW subvertical normal-sinistral faults straddling the northern SVC and terminating against the TSD; it may be associated with fluid injection into the shallow crust but appears to have limited effect on crustal conductivity (compared to TSD). The Anhydros Fault Zone (AFZ) is detected by its footprint on the basement, as a set of parallel northerly dipping NE–SW faults between the Athinios–Monolithos line and Fira. If it has any heave, it is left-lateral. It does not have distinguishable electrical signature and does not contribute to present-day horizontal deformation. The CFZ and AFZ are antithetic and form a graben containing the volcanic centre of Kammeni Islets.E–W extension was identified lengthwise of a zone stretching from Cape Exomytis to Athinios and along the east flank of the caldera to Imerovigli. N–S normal faulting confirmed therein, may have contributed to the localization of the east caldera wall. NNE–SSW compression was observed at SW Thera; this may have produced E-W failure and contributed to the localization of the south caldera wall. The footprint of the caldera on the basement is a parallelogram with N–S long and WNW–ESE short dimensions: if the east and south flanks collapsed along N–S normal and E–W inverse failures, then the west and north flanks may have formed analogously. Present-day deformation is localized on the TSD and CFZ: this can only be explained if the former is the synthetic (dextral) Riedel-R shear and the latter the antithetic (sinistral) Riedel-R′ shear, generated by N–S σ1 and E–W σ3 principal stress axes. Accordingly, NW–SE right-lateral shearing of the broader area is expected and indicated by several lines of indirect evidence. The geographic extent of this shearing and its role in the regional tectonics of the south Aegean remains to be confirmed and appraised by future research.Contemporary volcanic centres develop at the interface of the TSD with the CFZ/AFZ graben; volcanism appears to be controlled by tectonics and the SVC to be shaped by tectonic rather than volcanic activity.

Geochemical characterisation of the Neoarchaean newer dolerite dykes of the Bahalda region, Singhbhum craton, Odisha, India: Implication for petrogenesis

The mafic dyke swarm, newer dolerite dykes (NDDs) intrudes the Archaean Singbhum granite of the Singhbhum craton, eastern India. The present investigation focuses on the petrography and geochemistry of 19 NNE–SSW to NE–SW trending NDDs in two sectors in the northern and south-western part of Bahalda town, Odisha, Singhbhum. Chondrite normalised rare earth element (REE) patterns show light REE (LREE) enrichment among majority of the 13 dykes while the remaining six dykes show a flat REE pattern. Critical analyses of some important trace element ratios like Ba/La, La/Sm, Nb/Y, Ba/Y, Sm/La, Th/La, La/Sm, Nb/Zr, Th/Zr, Hf/Sm, Ta/La and Gd/Yb indicate that the dolerite dykes originated from a heterogeneous spinel peridotite mantle source which was modified by fluids and melts in an arc/back arc setting. REE modelling of these dolerite dykes were attempted on LREE-enriched representative of NDD which shows that these dykes might have been generated by 5–25% partial melting of a modified spinel peridotite source which subsequently suffered around 30% fractional crystallisation of olivine, orthopyroxene and clinopyroxene. The reported age of ~2.75–2.8 Ma seems to be applicable for these dykes and this magmatism appears to be contemporaneous with major scale anorogenic granitic activity in the Singhbhum craton marking a major event of magmatic activity in eastern India.

Plio-Quaternary transpressive tectonics: a key factor in the structural evolution of the outer Apennine–Adriatic system, Italy

We used data from seismic reflection profiles and well logs from both onshore and offshore locations along the Adriatic coast to investigate the structural style and recent active deformation in the external area of the northern Apennines adjoining the Po Plain. We prepared four NE–SW sub-parallel transects based on a detailed interpretation of the available subsurface data, supported by surface geological data. Through analysis of the well logs, we identified two significant seismo-stratigraphic markers, together with some unconformities within the Middle Pliocene/Quaternary succession. We propose a detailed structural scheme for the area that identifies and interprets both the outcropping and buried Apennine structures. NW/NNW–SE/SSE high-angle transpressive or flower structures, referred to the recent and actual deformation history, may be responsible for surface features and features at shallow depths, with possible implications for active tectonics. We show the continuity of some of these structures towards the Conero area to the south, suggesting a wider and more regional meaning for the proposed tectonic style. These Apenninic structures close against the active NNE–SSW Cattolica fault system in the northern offshore part of the area to form an asymmetrical arch. This study contributes to the interpretation of the deformation style of the outer northern Apennines. Supplementary material: High resolution seismic lines not interpreted are available at https://doi.org/10.6084/m9.figshare.c.4497542 Thematic collection: This article is part of the ‘Apennines and Tyrrhenian system’ collection available at: https://www.lyellcollection.org/cc/the-apennines-tyrrhenian-system

Kinematic and paleomagnetic restoration of the Semail ophiolite (Oman) reveals subduction initiation along an ancient Neotethyan fracture zone

The archetypal Semail ophiolite of Oman has inspired much thought on the dynamics of initiation of intra-oceanic subduction zones. Current models invoke subduction initiation at a mid-oceanic ridge located sufficiently close to the Arabian passive margin to allow initiation of continental subduction below the ophiolite within ∼10–15 Myr after the 96–95 Ma age of formation of supra-subduction zone crust. Here, we perform an extensive paleomagnetic analysis of sheeted dyke sections across the Semail ophiolite to restore the orientation of the supra-subduction zone ridge during spreading. Our results consistently indicate that the ridge was oriented NNE–SSW, and we infer that the associated trench, close to the modern obduction front, had the same orientation. Our data are consistent with a previously documented ∼150° clockwise rotation of the ophiolite, and we reconstruct that the original subduction zone was WNW-ward dipping and NNE–SSW striking. Initial subduction likely occurred in the ocean adjacent and parallel to a transform margin of the part of the Arabian continent now underthrust below Iran that originally underpinned the nappes of the Zagros fold-thrust belt. Subduction thus likely initiated along an ancient, continental margin-parallel fracture zone, as also recently inferred from near-coeval ophiolites from the eastern Mediterranean and NW Arabian regions. Subduction initiation was therefore likely induced by (WN)W–(ES)E contraction and this constraint may help the future identification of the dynamic triggers of Neotethyan subduction initiation in the Late Cretaceous.

Source characteristics and b-values of the Tuz Gölü Fault Zone in Central Anatolia, Turkey

We investigate significant earthquake sequences in the observation period between 2000 and 2018 along the Tuz Gölü Fault Zone in Central Anatolia. These sequences include a series of strong events with moment magnitudes (Mw) >5.0, e.g. 30 July 2005 Bala-Ankara Mw 5.2, 20 December 2007 Bala-Ankara Mw 5.7 and 26 December 2007 Mw 5.6 Afşar-Ankara earthquakes. The mainshocks are shallow focus strike-slip events with minor normal component at depths of 12–15 km. Focal depths of aftershocks range from 2 to 30 km. The focal mechanisms of the aftershocks are mainly normal faulting with variable strike-slip components. The geometry of focal mechanisms reveals a normal faulting regime with E-W and also NE-SW trending directions of T-axis in the entire activated region. A stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the Tuz Gölü Fault Zone stress field. The stress tensor inversion results display a predominant normal stress regime with a NNE–SSW oriented maximum horizontal compressive stress (SH). According to high-resolution hypocenter relocations of the Tuz Gölü Fault Zone seismic sequences, eight clusters are revealed. The aftershock activities in the observation period between 5 March 2000 and 2 June 2018 extend from NW to SE direction. Seismic cross-sections show that a complex pattern of the hypocenter distribution with the activation of Tuz Gölü Fault Zone segments. The western clusters are associated with a fault plane trending mainly N-S and dipping towards almost vertical, while the eastern clusters are related to a fault plane trending NW and dipping towards SE direction. The best constrained focal depths are mainly confined in the crust (depth < 30 km) and range from 2 to 30 km. In this study, we compare the results of an analysis of b-values from seismicity and stress tensors of focal mechanism solutions to understand their coupling in terms of faulting and earthquake hazard implications. In particular, this comparison allows to investigate the spatiotemporal correlation between b-values and stress distributions and it is therefore able to locate fault segments that have a high potential of generating large earthquakes. According to recent seismicity, b-values range from 0.5 to 1.5 along the Tuz Gölü Fault Zone in Central Anatolia. The maximum horizontal compressive stress (SH) indicates N-S and NE-SW directions while the minimum horizontal compressive stress (Sh) displays E-W. These results represent that low stress variances are correlated with high b-values. Low b-values are predominant in areas with high stress rates, consistent with a high heterogeneity of focal mechanisms.

Linking natural fractures to karst cave development: a case study combining drone imagery, a natural cave network and numerical modelling

In carbonate rocks, channelized fluid flow through fracture conduits can result in the development of large and connected karst networks. These cavity systems have been found in multiple hydrocarbon and geothermal reservoirs, and are often associated with high-permeability zones, but also pose significant challenges in drilling and reservoir management. Here, we expand on the observed interplay between fractures, fluid flow and large cave systems, using outcrop analysis, drone imagery and fluid-flow modelling. The studied carbonate rocks are heavily fractured and are part of the Salitre Formation (750–650 Ma), located in central Bahia (NE Brazil). Firstly, the fracture and cave network data show a similar geometry, and both systems depict three main orientations, namely; NNE–SSW, NW–SE and ESE–WNW. Moreover, the two datasets are dominated by the longer NNE–SSW features. These observed similarities suggest that the fractures and caves are related. The presented numerical results further acknowledge this observed correlation. These results show that open fractures act as the main fluid-flow conduits, with the aperture model defining the fracture-controlled flow contribution. Furthermore, the performed modelling highlights that geometrical features such as length, orientation and connectivity play an important role in the preferred flow orientations. Thematic collection: This article is part of the Naturally Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/naturally-fractured-reservoirs

Integrated geophysical appraisal of crustal structure and tectonic evolution of the Angria Bank, western continental margin of India

Angria Bank, a submerged plateau with coral reefs, is located off the central-west coast of India. Biologically, the bank attracts scientific community for its coral formations. But geologically, origin and tectonic setting of this feature are not established yet due to scarcity of geological and geophysical data. Newly acquired bathymetry and magnetic data along with existing geophysical data have allowed us to determine crustal structure and tectonic evolution of the Angria Bank. The entire geological setup of the bank consists of 34 km long water plateau (average water depth ~ 20 m), and two prominent spurs extending to its western side. The area of water plateau and entire geological setup are 365 km2 and 1460 km2, respectively. The bank is characterized by two prominent magnetic low with a relative high in the middle. Integrated gravity and magnetic models revealed that flood basalt has carpeted the entire geological structure which later acted as a foundation for coral growth. The crust below the bank is continental in nature and underplated by high-density magmatic material. Moho is almost flat and lies at a depth of ~ 27 km. The results of 3D Euler deconvolution suggest that the study area is characterized by two types of linear trend viz. NE–SW to NNE–SSW and NW–SE. These trends are interpreted mostly as basement faults but at few places, they might be associated with sills/dykes. The geological setup of the bank is fault-bounded and comprised of two horst structure (interpreted as spurs) trending NE–SW to NNE–SSW. Integrated interpretation of the geophysical data revealed that the Angria Bank is an isolated feature, evolved during rifting between India and Seychelles-Laxmi Ridge in the Late Cretaceous.

Study of the Relationship between Recently Induced Earthquakes and Water Level at the Northwestern Side of Lake Nasser in Aswan Region, Egypt

Lake Nasser is situated in an area with a very non-recurring earthquake, and revealed the history of Egypt registered 5000 years ago. After seventeen years of filling the Aswan High Dam reservoir began a long series of earthquakes caused. The main shock, Ms. = 5.6, occurred on November 14, 1981, preceded by several factions, followed by a large number of aftershocks. Thirty-three years later, seismic activity remains, but is much lower in frequency and volume. The aim of this paper is to study the effect of the reservoir on the induced seismic and determine the coordination mechanism of some earthquakes that occurred in the northwestern part of High Dam reservoir. These investigations indicate that seismic activity occurred mainly along the Kalabsha fault and small parallel sectors, and there is a range of activities in the Khor al-Ramla area, about 40 km southwest of the High Dam. From 1982 to the end of 2017, seventy-five earthquakes with a magnitude of 3.5 ≤ M < 4.0 and 13 earthquakes of magnitude greater than or equal to 4.0 have occurred. It also shows that these earthquakes occurred during loading and unloading periods. This shows that the effect of the reservoir itself does not produce earthquakes, and there is no direct relationship between changing the daily rate and the magnitude of earthquakes. So it can’t be used as a predictor in the case of the Aswan reservoir, which is a unique reservoir in its behavior. The focused coordination mechanism of four different seismic zones in the west of Lake Nasser shows errors in striking the strike with a simple natural element. The P (pressure) and T (tension) stress axes are trending ESE–WNW and NNE–SSW, respectively.

Fold interference patterns in Meso-Proterozoic Champaner fold belt (CFB) Gujarat, western India

This paper documents three phases of folding within the Meso-Proterozoic Champaner Fold Belt (CFB) located at the eastern part of Gujarat, western India. The first phase ( $$\hbox {F}_{1})$$ displays WNW plunging $$\hbox {F}_{1}$$ fold of moderately inclined nature in the schists of the Khandia Formation. The second phase ( $$\hbox {F}_{2})$$ refolded $$\hbox {F}_{1}$$ along a similar trend to produce folds of tight isoclinal nature in the Khandia and Narukot quartzites. Additionally, these $$\hbox {F}_{1}$$ folds depict second-order tight, and $$\hbox {F}_{2}$$ folds as first-order open type in the younger sequences of the CFB with varying amplitude vs. wavelength ratio. The ratio for $$\hbox {F}_{1}$$ folds ranges from 2:1 to 3:1, obtained along 3–4 m length across 3–6 $$\hbox {m}^{2}$$ area, whereas for $$\hbox {F}_{2}$$ folds the ratio ranges from 1:4 to 1:5 and is obtained along 1–2.5 km length across 0.5–1.5 km $$^{2}$$ area. The fold interference pattern developed on account of $$\hbox {F}_{1}$$ and $$\hbox {F}_{2 }$$ folds has resulted into Type-III or hook-shaped geometry regionally. The last phase of folding is characterised by N–S trending $$\hbox {F}_{3}$$ folds of open type over kilometre long limbs of $$\hbox {F}_{1}$$ and $$\hbox {F}_{2}$$ folds. The superposition of $$\hbox {F}_{1-3 }$$ folds developed map scale Type-I or Dome and Basin geometry over Type-III superposed folds. The overall compressional direction for $$\hbox {F}_{1}$$ and $$\hbox {F}_{2}$$ folds ranges from N–S to NNE–SSW and for $$\hbox {F}_{3}$$ ranges from E–W to ESE–WNW.

Magnetic fabric constraints for syn-magmatic doming of the laccolithic Brocken granite pluton (Harz Mountains, northern Germany)

Hyper-solidus fabrics of the early Permian Brocken granite pluton, exposed over an area of c. 160 km² and elongated in NNE–SSW direction, were determined by measuring the anisotropy of magnetic susceptibility (AMS). The Brocken granite pluton consists of five petrographically distinguishable and mappable granitic varieties characterized by a generally paramagnetic behavior with primary biotite, partly altered to chlorite, and secondary tourmaline as the major carrier of the susceptibility. Whereas biotite modal content isolines roughly follow petrographic trends, the tourmaline modal contents do not, hence implying secondary, post-emplacement processes that controlled tourmaline distribution. A few samples with primary and secondary magnetite show ferrimagnetic behavior and are co-axial with the paramagnetic fabrics. The generally low magnetic anisotropies in all granitic varieties are a distinct and challenging feature for determining magmatic flow directions. AMS data indicate the predominance of sub-horizontal fabrics outlining an NNE–SSW trending dome axis interpreted to have resulted from granite sheets stacked syn-magmatically in a high crustal level building up a laccolithic pluton. AMS fabrics together with age data and geophysical indications suggest that the emplacement and distribution of the Brocken granite pluton is structurally controlled by NNE–SSW striking deep fault structures, and only weakly influenced by WNW/NW-trending structures. Late Carboniferous-to-early Permian plutonism in the Harz Mountains evolved in an E–W directed extensional regime, and was accompanied by volcanic activity and development of NW- and NE-trending sedimentary basins.

The development of divergent margins: Insights from the North Volcanic Zone, Iceland

Iceland is a natural laboratory where plate separation and mid-ocean ridge formation can be studied directly in the field. In this setting, it is not fully understood how magma interacts with faulting and fissuring, and how rift zones propagate. In order to improve the understanding of how these processes operate, we conducted a detailed field study about the kinematics and propagation of 33 Holocene faults along the N–S Theistareykir rift (North Volcanic Zone) and mapped all tension fractures. This rift hosts the Holocene Theistareykir central volcano, for which ground deformation data (InSAR and GPS) indicate an inflating shallow magma chamber throughout 2006–2008. Analyses of the cumulative fault slip distribution at 696 sites show two opposite directions of fault/rift propagation: The first, more developed, is directed northwards and affects the area located north of Theistareykir volcano, whereas south of the volcano, the rift propagates southwards. Tension fractures increase in frequency, with respect to faults, outwards from the volcano, along a N–S to NNE–SSW direction. The presence of aligned vents, dykes and topographic bulging along some of the N–S structures, and the active magma chamber below Theistareykir volcano, suggest that faults and tension fractures propagate following repeated dyke intrusions from the magma chamber outward along the plate margin. The fact that the rift is more developed north of the volcano than south of it, is interpreted as the effect of buttressing from another, coterminous magma chamber sitting below a neighbouring central volcano. Other causes for the general observed pattern such as tectonic stresses, mechanical interaction of faults, and changes in the rheological characteristics of rocks, are discussed as well.

Quaternary negative tectonic inversion along the Sibillini Mts. thrust zone: the Arquata del Tronto case history (Central Italy)

Geological and geophysical investigations have been carried out in the surroundings of the villages of Pretare and Piedilama, in the Central Apennines. This area, located at the footwall of the prominent NNE–SSW oriented Sibillini thrust front, was struck by the August 24th 2016 Mw 6 earthquake. The results of the geological field survey combined with geological and geophysical subsurface investigations are here illustrated by a detailed geological map and by two significant cross-sections. The studied area is crossed by the Fosso di Morricone valley that, entrenched within the Messinian pelitic-arenaceous succession of the Laga formation, hosts a Late Pleistocene palaeo-landslide. The study evidences the occurrence of a N 10° oriented west dipping normal fault, here named Pretare–Piedilama fault, that controlled the left side of the Fosso di Morricone valley, producing a vertical displacement of the palaeo-landslide deposits of about 50 m. The geological, geomorphological and geophysical data indicate that the fault was active during the Late Pleistocene and part of the Holocene thus constraining a minimum vertical displacement-rate of 0.4 mm/a in the last 125 ka. The geometry of the deformed Laga formation cut by the fault suggests to relate it to the Late Quaternary negative tectonic inversion of a previous thrust plane located in the footwall of the Sibillini thrust front. The Pretare–Piedilama fault would represent the easternmost tectonic expression of this main potentially active structure. Future researches could be addressed to detail the age and the actual motion-rate of the structure and to define its seismic hazard assessment.

Electrical Structure of the Lithosphere From Rio de la Plata Craton to Paraná Basin: Amalgamation of Cratonic and Refertilized Lithospheres in SW Gondwanaland

AbstractWe conducted a magnetotelluric (MT) study from Paleoproterozoic Rio de la Plata Craton, in Uruguay, toward Paleozoic‐Mesozoic Paraná Basin, in Brazil. The 850‐km‐long MT transect comprises 35 evenly spaced broadband electromagnetic soundings sites. In the Paraná Basin, 11 additional long‐period measurements were acquired to extend the maximum depth of investigation. All data were inverted using two‐ and three‐dimensional approaches obtaining the electrical resistivity structure from the surface down to 200 km. The Rio de la Plata Craton is &gt;200‐km thick and resistive (~2,000 Ωm). Its northern limit is electrically defined by a lithosphere scale lateral transition and lower crust conductive anomalies (1–10 Ωm) interpreted as a Paleoproterozoic suture at the southern edge of Rivera‐Taquarembó Block. The latter is characterized by an approximately 100‐km thick and moderate resistive (&gt;500 Ωm) upper mantle. The Ibaré shear zone is another suture where an ocean‐ocean subduction generated the 120‐km thick and resistive (&gt;1,000 Ωm) São Gabriel juvenile arc. Proceeding northward, a 70‐ to 80‐km thick, 150‐km wide, and inclined resistive zone is imaged. This zone could be remnant of an oceanic lithosphere or island arcs accreted at the southern border of Paraná Basin. The MT transect terminates within the southern Paraná Basin where a 150‐ to 200‐km‐thick less resistive lithosphere (&lt;1,000 Ωm) may indicate refertilization processes during plate subduction and ocean closure in Neoproterozoic‐Cambrian time. Our MT data support a tectonic model of NNE–SSW convergence for this segment of SW Gondwanaland.

Dynamics of shallow hydrothermal eruptions: new insights from Vulcano’s Breccia di Commenda eruption

Understanding the dynamics and effects of hydrothermal eruptions is crucial to the hazard assessment in both volcanic and geothermal areas. Eruptions from hydrothermal centres may occur associated with magmatic phases, but also as isolated events without magmatic input, with the most recent examples being those of Te Maari (Tongariro, New Zealand) in 2012 and Ontake (Japan) in 2014. The most recent caldera of the Island of Vulcano (southern Italy) hosts in its centre the La Fossa cone, active since 5.5 ka and now characterised by continuous fumarolic degassing. In historical times, La Fossa cone has experienced several hydrothermal eruptions, with the most violent event being the Breccia di Commenda eruption that occurred during the thirteenth century ad. Based on analysis of 170 stratigraphic logs, we show that the Breccia di Commenda eruption occurred in three main phases. After an opening, low-intensity ash emission phase (phase 1), the eruption energy climaxed during phase 2, when a series of violent explosions produced an asymmetric shower of ballistic blocks and the contemporaneous emplacement of highly dispersed, lithic-rich, blast-like pyroclastic density currents (PDCs). The tephra units emplaced during phase 2, ranging in volume from 0.2 to 2.7 × 105 m3, were covered in turn by thin ash fall deposits (phase 3). The dynamics of the most violent and intense stage of the eruption (phase 2) was investigated by numerical simulations. A three-dimensional numerical model was applied, describing the eruptive mixture as a Eulerian–Eulerian, two-phase, non-equilibrium gas-particle fluid (plus a one-way coupled Lagrangian ballistic block fraction). At the initial simulation time, a mass of about 109 kg, with initial overpressure above 10 MPa, and a temperature of 250 °C, was suddenly ejected from a 200-m-long, eastward inclined, NNE–SSW trending fissure. The mass release formed blast-like PDCs on both sides of the fissure and launched ballistic blocks eastwards. Field investigations and numerical simulations confirm that hydrothermal explosions at La Fossa cone include intense ballistic fallout of blocks, emission of PDCs potentially travelling beyond the La Fossa caldera and significant ash fallout. The hazard associated with both ballistic impact and PDC ingress, as associated with hydrothermal eruption, is significantly larger with respect to that associated with Vulcanian-type events of La Fossa.

Subsurface structural features of the basement complex and mineralization zone investigation in the Barramiya area, Eastern Desert of Egypt, using magnetic and gravity data analysis

In the Barramiya area, the majority of gold deposits are generally related with the quartz veins that associated with shear zones cutting the crystalline basement rocks. The quartz vein system is controlled by shear zone and general faults. The present study is to delineate the general faults, shear zones, geological limits, and basement rock relief, using airborne magnetic and gravity data analysis at the Barramiya gold mine and surrounding area, Eastern Desert of Egypt. To achieve our goal, we have applied on magnetic and gravity data the following techniques: reduction to pole (RTP), analytical signal, tilt derivative, total horizontal derivative, 3D Euler deconvolution, downward continuation, and source parameter imagining power spectrum techniques. The analytical signal used to map the types of rock boundaries. Tilt derivative and total horizontal derivative filters helped to delineate fractures and the contact zones of the formations that host the main Barramiya shear zone. 3D Euler deconvolution techniques helped to delineate the fault trends which represented at the following direction: NNE–SSW and NNW–SSE. The average depths of both regional and residual causes have been estimated by applying downward continuation, source parameter imagining, and power spectrum techniques. According to the results of the present study, the depth of the basement rocks is relatively high (~ 80-m depth) in the western part of the study area and the basement rocks cropped out in the surface at the rest of the area. Our results are coinciding with the previous geological studies.

Basin Evolution Palispatic Model of Bonaparte Basin, Australia Northwest Shelf

This research area is located on the Australian NW Shelf close to the westernedge of the Sahul Platform. This research is aimed to generate the palispatic basin model of Bonaparte Basin, Australian Northwest Shelf. It is to predict the impact of Neogene collision on the petroleum system distribution on Australian Northwest Shelf. The main data used in this research are seismic data using qualitative method analysis. The well data is used to well-seismic tied. After data acquisition, the seismic data are interpreted based on the horizon and structure interpretation. These interpretation are to reconstruct the basin evolution thorough geologic time. According to data analysis, the basin evolution palispatic model are divided into Paleo-proterozoic, Paleozoic, Triassic, Early Jurassic, Middle Jurassic, Late Jurassic, Early Cretaceous, Late Cretaceous, Early Eocene, Late Miocene and Recent condition. Regional tectonically there are at least three important events in NW Shelf: Middle Triassic-Jurassic NNE–SSW extension phase, Late Jurassic NE–SW extension phase and the Neogen collision phase; the Neogen collision effects on Northwest Shelf Australia. These three events contributed in forming and disturbing the Paleozoic and Mesozoic petroleum system in Bonaparte basin especially.

Cenozoic structural evolution on northern Banks Island, N.W.T. Canada

The onshore structural architecture and evolution of large segments of the Arctic continental margin are poorly known because of the generally poor outcrop of pre-Neogene rocks, the remoteness of the area and extent of Neogene cover. Fieldwork on Banks Island during the summer of 2016 has shown that the Devonian, Cretaceous and Paleogene deposits on northern Banks Island are characterized by a number of local, restricted deformation zones, which we interpret to indicate both dextral and subordinate sinistral strike-slip deformation along NNE–SSW striking structures parallel to the continental margin of Banks Island. The presence of Cenozoic strike-slip deformation on Banks Island extends the area of known Cenozoic strike-slip along the continental margin southwestward from where it has been previously documented on northern Ellesmere Island. In addition, field and seismic data indicate that the sedimentary rocks on Banks Island have been affected by extensional movements before and after the strike-slip deformation. The observation of strike-slip motion on Banks Island may imply a component of strike slip over the whole Paleogene North American margin.

Timing of deformation and location of the eastern Liaoyuan Terrane, NE China: Constraints on the final closure time of the Paleo-Asian Ocean

The Liaoyuan Terrane (LT) in NE China formed as a result of accretion during the final closure of the Paleo-Asian Ocean between the North China and Siberian cratons. However, the timing of the deformation and the location of the eastern LT remain controversial. Here we present structural data, zircon U–Pb age dating, and Hf isotopic data to constrain the kinematics and timing of deformation, and the southern boundary of the eastern LT in relation to the NE–SW-striking Yilan–Yitong Fault (YYF), one of two branches of the continental-scale Tan–Lu Fault Zone in NE China. Pre-Jurassic rocks in the eastern LT were widely involved in ductile deformation within WNW–ESE-striking thrust belts. The microstructures in these shear zones indicate a top-to-the-SSW sense of shear and deformation temperatures of 450–500 °C. The northern margin of the North China Craton (NCC) was also affected by the NNE–SSW contraction, as shown by similar ductile deformation in the Archean gneisses and WNW–ESE trending folds in the Mesoproterozoic sedimentary cover. The ages of crystallization in deformed and undeformed igneous rocks in the LT constrain the deformation to an interval between 241 and 193 Ma. U–Pb dating of zircons in syn-kinematic migmatitic rocks indicates an age of 234–229 Ma for the deformation. We consider this Middle Triassic age to represent the final closure time of the Paleo-Asian Ocean along the eastern LT, and this timing is consistent with the eastwards scissor-style closure model. Lithological variations, zircon age spectra, εHf(t) values, and model ages confirm the eastward extension of the LT across the YYF. The data constrain the boundary between the LT and NCC to be roughly along the Liao River to the west of the YYF, and along the northern edge of the exposed Archean gneisses to the east. The boundary follows the Bayan Obo–Chifeng–Kaiyuan Fault, which was active as a thrust (thrusting of material to the SSW) during the Middle Triassic orogeny. The newly determined boundary location indicates a 35 km sinistral displacement along the YYF.

Oriented graptolites in the Uppermost Ordovician Wufeng black shale in southern China

Graptolites are elongated fossils that can be used to decipher the current direction to evaluate paleocurrent conditions. Abundant graptolite fossils are well-preserved and clearly exhibit strong alignment in the black shales of the Upper Ordovician Wufeng Formation on the southern edge of the Upper Yangtze Sea, South China. The orientations of these graptolites indicate that the remains of graptolites were deposited on the seafloor under the influence of currents, instead of under calm water conditions. Based on the measurements of the long-axis directions of graptolites, the distributions of graptolites preserved on the bedding planes display discernable orientations and exhibit systematic changes throughout the stratigraphic section. In the western region of the study area, the paleocurrent directions in the stratigraphic sections gradually change from NE–SW in the Dicellograptus complexus biozone to N–S in the Paraorthograptus pacificus and Normalograptus extraordinarius–N. ojsuensis biozones. However, in the eastern region of the study area, the paleocurrent directions are more variable, ranging from multi-directional (NNE–SSW and NNW–SSE) in the P. pacificus biozone to NW–SE in the N. extraordinarius–N. ojsuensis biozone. The changes in the orientations of graptolites in the D. complexus and the P. pacificus biozones are consistent with the southern configuration of the Upper Yangtze Sea and indicate that a coastal current existed. In addition, some of the contemporaneous deformation structures were caused by tectonic forces observed in the lower Graptolite Shale Member of the Wufeng Formation in the eastern region of the study area. Some of the changes in the orientations of graptolites in the N. extraordinarius–N. ojsuensis biozone can be interpreted to have resulted from a change in tectonic activity (the Caledonian orogeny) before the N. extraordinarius–N. ojsuensis biozone. Furthermore, Lingula brachiopods, which live on the seafloor in shallow water, have been reported in the black shale of the Wufeng Formation, which indicates that the paleoenvironment was at least partially oxic; this supported the growth, development and reproduction of planktonic graptolites and other organisms. These results support the interpretation that the remains of organisms were quickly buried and that the amount of exchange between pore water and the water column gradually decreased. H2S gas generated by the decay of organisms during deposition consequently generated a strongly reducing environment in these sediments, which resulted in the formation of black shales.