NW Flank Research Articles

Porosity–permeability characteristics and mineralization–alteration zones of the Maoping germanium-rich lead–zinc deposit in SW China

The Maoping superlarge germanium-rich lead–zinc deposit is a typical nonmagmatic hydrothermal deposit that is structurally controlled in the Sichuan–Yunnan–Guizhou lead–zinc polymetallic metallogenic area. The orebodies are distributed in several formations. This paper is based on large-scale alteration mapping combined with porosity and permeability measurements. We delineated the mineralization–alteration zones of different ore-bearing formations, explored the geological significance of porosity and permeability, and proposed prospecting directions. The research results indicate that during the mineralization period, the ore-forming metal fluids migrated from the deep part of the SSW region to the shallow part of the NNE region along the ore-guiding structure (Maoping Fault). Through the ore distribution structure, depressurization boiling occurred in the open space of the NE-trending interlayered sinistral compressive–torsional faults in several ore-bearing formations, resulting in fluid precipitation and the formation of different brecciated hot-melt dolomite lead–zinc mineralization zones. From the orebody to the wallrock, the C2w Formation and D3zg Formation are divided into four different mineralization–alteration zones. Tectonic activity affects the properties, migration, and precipitation of fluids, thereby controlling the alteration characteristics generated during fluid migration and thus changing the porosity and permeability. The porosity and permeability of strata on the NW flank of the anticline are greater than those of strata on the SE flank. On the NW flank, the greater the degree of mineralization–alteration is, the greater the porosity and permeability are, and the porosity of the orebody is lower than that during dolomitization. Finally, we believe that the NW flank of the anticline is an important area for prospecting. The pyrite + striped altered dolomite zone (Zones II–III) in the C2w limestone and the pyrite + strong dolomite zone (Zones II–III) in the D3zg dolomite are important prospecting indicators.

Twenty years of explosive-effusive activity at El Reventador volcano (Ecuador) recorded in its geomorphology

Shifts in activity at long-active, open-vent volcanoes are difficult to forecast because precursory signals are enigmatic and can be lost in and amongst daily activity. Here, we propose that crater and vent morphologies, along with summit height, can help us bring some insights into future activity at one of Ecuador’s most active volcanoes El Reventador. On 3 November 2002, El Reventador volcano experienced the largest eruption in Ecuador in the last 140 years and has been continuously active ever since with transitions between and coexistence of explosive and effusive activity, characterized by Strombolian and Vulcanian behavior. Based on the analysis of a large dataset of thermal and visual images, we determined that in the last 20 years of activity, the volcano faced three destructive events: A. Destruction of the upper part of the summit leaving a north-south breached crater (3 November 2002), B. NE border crater collapse (2017), and C. NW flank collapse (2018), with two periods of reconstruction of the edifice: Period 1. Refill of the crater (2002-early 2018) and Period 2. Refill of the 2018 scar (April 2018–December 2022). Through photogrammetric analysis of visual and thermal images acquired in 11 overflights of the volcano, we created a time-series of digital elevation models (DEMs) to determine the maximum height of the volcano at each date, quantify the volume changes between successive dates, and characterize the morphological changes in the summit region. We estimate that approximately 34.1x106 m3 of volcanic material was removed from the volcano due to destructive events, whereas 64.1x106 m3 was added by constructive processes. The pre-2002 summit height was 3,560 m and due to the 2002 eruption it decreased to 3,527 m; it regained its previous height between 2014 and 2015 and the summit crater was completely filled by early April 2018. Event A resulted from an intrusion of magma that erupted violently; we proposed that Events B and C could be a result of an intrusion as well but may also be due to a lack of stability of the volcano summit which occurs when it reaches its maximum height of approximately 3,590 and 3,600 m.

Scenario-based probabilistic hazard assessment for explosive events at the San Salvador volcanic complex, El Salvador

We present a scenario-based, probabilistic hazard assessment for the San Salvador volcanic complex (SSVC), a volcanic field located in the vicinity of San Salvador that includes the El Boquerón stratovolcano and 25 monogenetic vents. We define a set of likely eruption scenarios for tephra fallout and pyroclastic density currents (PDCs). The eruption scenarios range from violent Strombolian eruptions with a significant uncertainty in source position to sub-Plinian and Plinian activity fed from the central cone. The adopted methodology is mainly based on numerical modeling using Tephra2 (adopting the software TephraProb) to study tephra fallout and the branching box model and the branching energy cone model (adopting the programs BoxMapProb 2.0 and ECMapProb 2.0) to describe inertial and frictional PDCs, respectively. Despite the dominant W-WSW-trending winds, numerical results show that Plinian eruptions at El Boquerón volcano are able to deposit thick tephra layers in the metropolitan area of San Salvador city, likely reaching mass loads of the order of 100 kg/m2 (conditional probability of 50%). The simulated sub-Plinian events highlight the seasonal influence of wind patterns. In fact, the conditional probability of significant tephra sedimentation in San Salvador city is strongly reduced when eruptions occur during the rainy season. Numerical modeling of violent Strombolian eruptions is performed considering uncertainty in vent position. Results show that the conditional probability of depositing tephra mass loads higher than 10 kg/m2 at a given point reaches a maximum value of ∼7% on the NW flank of the volcano, at about 8 km from the central crater. On the other hand, very low conditional probabilities (<1%) are obtained for San Salvador city for any relevant threshold (10 kg/m2 or more) of tephra mass load during violent Strombolian events. Regarding PDCs, results show that those produced during large-scale Plinian eruptions are able to invade significant areas of the volcano surroundings, including San Salvador city. PDCs generated from the partial collapse of a sub-Plinian eruption column exhibit maximum inundation probabilities on the N, W and S flanks of the volcano. Cerro El Picacho exerts a significant shield effect on the propagation of these PDCs, with low inundation probabilities for San Salvador city (<3%). Finally, coupling published vent opening probability maps and numerical modeling of small-scale PDCs yields maximum inundation probabilities on the NW flank of the volcano, reaching maximum conditional probabilities of the order of ∼10% and values of about 5% near the village of Nuevo Sitio del Niño.

Multi-parametric study of an eruptive phase comprising unrest, major explosions, crater failure, pyroclastic density currents and lava flows: Stromboli volcano, 1 December 2020–30 June 2021

Open conduit volcanoes like Stromboli can display elusive changes in activity before major eruptive events. Starting on December 2020, Stromboli volcano displayed an increasing eruptive activity, that on 19 May 2021 led to a crater-rim collapse, with pyroclastic density currents (PDCs) that spread along the barren NW flank, entered the sea and ran across it for more than 1 km. This episode was followed by lava flow output from the crater rim lasting a few hours, followed by another phase of lava flow in June 2021. These episodes are potentially very dangerous on island volcanoes since a landslide of hot material that turns into a pyroclastic density current and spreads on the sea surface can threaten mariners and coastal communities, as happened at Stromboli on 3 July and 28 August 2019. In addition, on entering the sea, if their volume is large enough, landslides may trigger tsunamis, as occurred at Stromboli on 30 December 2002. In this paper, we present an integration of multidisciplinary monitoring data, including thermal and visible camera images, ground deformation data gathered from GNSS, tilt, strainmeter and GBInSAR, seismicity, SO2 plume and CO2 ground fluxes and thermal data from the ground and satellite imagery, together with petrological analyses of the erupted products compared with samples from previous similar events. We aim at characterizing the preparatory phase of the volcano that began on December 2020 and led to the May–June 2021 eruptive activity, distinguishing this small intrusion of magma from the much greater 2019 eruptive phase, which was fed by gas-rich magma responsible for the paroxysmal explosive and effusive phases of July–August 2019. These complex eruption scenarios have important implications for hazard assessment and the lessons learned at Stromboli volcano may prove useful for other open conduit active basaltic volcanoes.

Changes in the Eruptive Style of Stromboli Volcano before the 2019 Paroxysmal Phase Discovered through SOM Clustering of Seismo-Acoustic Features Compared with Camera Images and GBInSAR Data

Two paroxysmal explosions occurred at Stromboli on 3 July and 28 August 2019, the first of which caused the death of a young tourist. After the first paroxysm an effusive activity began from the summit vents and affected the NW flank of the island for the entire period between the two paroxysms. We carried out an unsupervised analysis of seismic and infrasonic data of Strombolian explosions over 10 months (15 November 2018–15 September 2019) using a Self-Organizing Map (SOM) neural network to recognize changes in the eruptive patterns of Stromboli that preceded the paroxysms. We used a dataset of 14,289 events. The SOM analysis identified three main clusters that showed different occurrences with time indicating a clear change in Stromboli’s eruptive style before the paroxysm of 3 July 2019. We compared the main clusters with the recordings of the fixed monitoring cameras and with the Ground-Based Interferometric Synthetic Aperture Radar measurements, and found that the clusters are associated with different types of Strombolian explosions and different deformation patterns of the summit area. Our findings provide new insights into Strombolian eruptive mechanisms and new perspectives to improve the monitoring of Stromboli and other open conduit volcanoes.

The geochemical evolution of the Logan Igneous Suite, Ontario, Canada: new insights from the Logan Basin and implications for the genesis of the Mesoproterozoic Midcontinent Rift System

Abstract The 1.1 Ga Midcontinent Rift System (MRS) of North America comprises a series of Mesoproterozoic flood basalts and intrusive rocks emplaced in the Lake Superior region. The mafic rocks preserved on the NW flank of Lake Superior offer insights into the early development of the rift. New geochemical data collected from intrusive rocks in the Logan Basin, coupled with improved constraints on timing relationships between units, allow for a better understanding of the geochemical evolution of intrusive rocks therein. The extensive dataset suggests many previously unrecognized relationships between MRS intrusive rocks, indicating multiple, distinct mantle-source characteristics with highly variable crustal contamination histories, implying a complicated magma plumbing system. The data presented here suggest that five geochemically distinct mantle source regions were involved in the emplacement of the Logan Igneous Suite, each with its own distinct contamination history and perhaps different degrees of partial melting. The geochemical variations could suggest either a progressive, relative depletion in the mantle source over time or heterogeneity of the source region. However, based on the model for MRS magmatism presented here, we suggest that units related to the Logan Igneous Suite were tapping a heterogeneous mantle source that varied over time.

TECTONIC AND EROSION FEATURES, AND THEIR INFLUENCE ON ZONAL DISTRIBUTION OF THE UPPER TRIASSIC AND THE LOWER CRETACEOUS SEDIMENTS IN THE EUPHRATES GRABEN AREA, SYRIA

We have investigated the tectonic and erosion features of the Upper Triassic (Mulussa F Formation) and Lower Cretaceous (Rutbah Formation) sediments in the Euphrates graben area and analysed their influence on changes in the thickness and zonal distribution patterns of these sediments. In this study, the geological modeling software of Petrel Schlumberger is used to model the regional geological structure and stratigraphy from the available geological and geophysical data.The Upper Triassic and Lower Cretaceous sediments (in total, almost 800 m thick) are the major hydrocarbon reservoirs in the Euphrates graben, which contain approximately 80 to 90 % of the total hydrocarbon reserve in this area. These sedimentary zones experienced variable changes in thickness and zonal distribution due to erosion processes caused by the two major regional unconformities, the Base Upper Cretaceous (BKU) and Base Lower Cretaceous (BKL) unconformities. The maximum thickness of the Upper Triassic sediments amounts to 480 m in the central parts of the Euphrates graben and along the NW-SE trend, i.e. in the dip direction of the Upper Triassic Mulussa F Formation. Towards the NE flank of the graben near the Khleissia uplift and the SW flank near to the Rutbah uplift, the thickness of the Upper Triassic sediments is gradually decreased due to their partial or total erosion caused by the BKL unconformity, and also due to a less space for sediment accumulation near the uplifts. The thickness of the Lower Cretaceous sediments increases in the northern, NW and NE flanks of the graben. Their maximum thickness is about 320 m. The BKL unconformity is the major cause of erosion of the Lower Cretaceous sediments along the southern, SE and SW flanks of the graben. In the Jora and Palmyra areas towards the NW flank of the Euphrates graben, the Upper Triassic and Lower Cretaceous sediments show no changes in thickness. In these areas, there was more space for sediment accumulation, and the sediments were less influenced by the BKL and BKU unconformities and thus less eroded.

Submarine and Subaerial Morphological Changes Associated with the 2014 Eruption at Stromboli Island

Stromboli is an active insular volcano located in the Southern Tyrrhenian Sea and its recent volcanic activity is mostly confined within the Sciara del Fuoco (SdF, hereafter), a 2-km wide subaerial–submarine collapse scar, which morphologically dominates the NW flank of the edifice. In August-November 2014, an effusive eruption occurred along the steep SdF slope, with multiple lava flows reaching the sea. The integration of multisensor remote sensing data, including lidar, photogrammetric, bathymetric surveys coupled with SAR amplitude images collected before and after the 2014 eruption enabled to reconstruct the dynamics of the lava flows through the main morphological changes of the whole SdF slope. Well-defined and steep-sided ridges were created by lava flows during the early stages of the eruption, when effusion rates were high, favoring the penetration into the sea of lava flows as coherent bodies. Differently, fan-shaped features were emplaced during the declining stage of the eruption or in relation to lava overflows and associated gravel flows, suggesting the prevalence of volcaniclastic breccias with respect to coherent lava flows. The estimated volume of eruptive products emplaced on the SdF slope during the 2014 eruption, accounts for about 3.7 × 106 m3, 18% of which is in the submarine setting. This figure is different with respect to the previous 2007 eruption at Stromboli, when a large lava submarine delta formed. This discrepancy can be mainly related to the different elevation of the main vents feeding lava flows during the 2007 eruption (around 400 m) and the 2014 eruption (around 650 m). Besides slope accretion, instability processes were detected both in the subaerial and submarine SdF slope. Submarine slope failure mobilized at least 6 × 105 m3 of volcaniclastic material, representing the largest instability event detected since the 2007 lava delta emplacement.

SUBMARINE TECTONIC GEOMORPHOLOGY OF THE PLINY AND HELLENIC TRENCHES REFLECTING THE GEOLOGICAL EVOLUTION OF SOUTHERN GREECE

Mapping seafloor geomorphology is a complex task requiring the integration of advanced cartographic technologies and high-resolution spatial data. This paper provides a comparative geomorphological analysis of the Hellenic Trench (HT) and the Pliny Trench (PT) located in the Eastern Mediterranean Sea, southern Greece. These trenches were formed as a result of the tectonic plate subduction in the Eastern Mediterranean Sea: the northward motion of the African and Arabian plates, complicated by the regional geological settings, such as active faults and earthquakes, which resulted in their different geomorphological forms and bathymetric shapes. Technically, this paper presents an example of the advanced scripting mapping by scripting the cartographic toolset of Generic Mapping Tools (GMT), which performs mapping through shell scripts. The maps are based on the high-quality topographic, geological and geophysical data: GEBCO, EGM96, geoid, and marine free-air gravity fields. The GMT builds upon the modules used for data processing. The region was subsetted by ‘grdcut’, analysed by the Geospatial Data Abstraction Library (GDAL) (gdalinfo utility), and visualized by ‘grdimage’. Two segments of the trenches formed in a condition of varying geological and geophysical settings, have been modelled, visualized and compared, as representative cross-sections. As a result of the automated digitizing, spatial interpolation and sequential aggregating of GMT codes, the segments of the cross-sections were represented. The HT (Ionian segment) has an asymmetric one-sided shape; a steepness of 56.8° on the NE side and 7° on the SW flank. The PT has a more symmetric view; a steepness of 42.14° on its NW flank and 26.66° on its SE flank. The PT has a clear peak of the depths at -2600 to -2800 m and the most representative data range at -5000 to -6000 m. The HT has a bimodal data distribution with two peaks. The most frequent data for HT is -3200 m to -3400 m. Compared to PT, the HT is deeper. The histogram shows the peak of data for HT in the interval between -3200 to -3400 m (135 samples) while the PT shows the peak of data in the interval at -2600 to -2800 m (310 samples). Besides, 105 samples of the HT have depths exceeding 4000 m, while only 20 samples were recorded for PT in the same interval. This paper contributes to the geomorphological studies of the general Eastern Mediterranean Sea region, particularly relating to regional seafloor mapping of the Hellenic and Pliny trenches.

Small-scale slope instability on the submarine flanks of insular volcanoes: the case-study of the Sciara del Fuoco slope (Stromboli)

Small-scale landslides affecting insular and coastal volcanoes are a relevant geohazard for the surrounding infrastructures and communities, because they can directly impact them or generate local but devastating tsunamis, as demonstrated by several historical accounts. Here, a review of such landslides and associated predisposing/triggering mechanisms is presented, with particular reference to the submarine volcanic flanks. We take into account, as a case study, the instability phenomena occurring on the Sciara del Fuoco (SdF, hereafter), a 2-km wide subaerial-submarine collapse scar filled by volcaniclastic products, which form the NW flank of the Stromboli volcano. Because of its steepness (> 30°) and the high amount of loose volcanic material funneled from the summit crater towards the sea, the submarine part of the SdF is prone to instability phenomena recurring at different spatial and temporal scale. Particularly, landsides with a volume of some millions of cubic meters, as the 2002 tsunamigenic landslide, can repeatedly affect the submarine slope. Based on the integration of 11 years (2002–2013) of morpho-bathymetric monitoring of the SdF with geotechnical characterization of volcaniclastic and lava flow materials, stability analyses of the subaerial and submarine slope and previous literature studies, we analyze the role of different triggering mechanisms in controlling the occurrence and size of submarine slope failures at the SdF, such as dykes intrusion as occurred in 2002 or the emplacement of a large delta as occurred in 2007.

The Blane Field, Block 30/3a, UK North Sea

Abstract The Blane Field is located in the central North Sea in Block 30/3a (Licence P.111), approximately 130 km SE of the Forties Field, in a water depth of 75 m (246 ft). It straddles the UK/Norway median line with 82% of the field in the UK and 18% in Norway. Blane produces undersaturated oil from the Upper Forties Sandstone Member of the Sele Formation and contains good quality light oil within a four-way structural closure; it has a hydrodynamically tilted original oil–water contact. The field stock-tank oil initially in place estimate is 93 MMbbl with an expected ultimate recovery of 33 MMbbl. Blane first oil was achieved in September 2007. The field has been developed by two horizontal producers located on the central crest of the field supported by a water injector drilled on the NW flank. Oil production peaked at c. 17 000 bopd in 2007 and the field is currently in decline. By the end of 2018 production was c. 3000 bopd with 55% water-cut. Cumulative oil production to the end of 2018 was 26.6 MMbbl.

Magma storage and diking revealed by GPS and InSAR geodesy at Pacaya volcano, Guatemala

GPS measurements from a campaign network at Pacaya volcano, Guatemala, occupied from 2009 to 2015 were combined with InSAR data from 2013 to 2014 to model deformation sources for two eruptive time periods: 2009–2011 and 2013–2014. The GPS data for both of these time periods show downward vertical and outward horizontal deformation greater than 25 cm at several stations surrounding the volcano, while InSAR data shows up to 15-cm line-of-sight displacement. To better understand the dynamics of the magma storage system and sources of deformation, we inverted available geodetic data for these two periods. Our analytical modeling suggests that horizontal deformation was dominated by inflation of a shallow, subvertical dike, high within the volcanic edifice, while deflation of a deeper, spherical source embedded below the NW flank of the volcano occurred during at least part of the observation period. The source parameters for the dike feature are in good agreement with the observed alignment of recent eruptive vents, while parameters for the deeper, spherical source accommodate the downward vertical deformation observed at stations on and around the volcano.

Modelling the instability phenomena on the NW flank of Stromboli Volcano (Italy) due to lateral dyke intrusion

The aim of the paper is to provide quantitative elements on the mechanisms that controlled the slope instabilities occurred after two major recent eruptions at Stromboli volcano (i.e. 2002–2003 and 2007). After a brief description of the geological setting and of the largest well documented instability phenomena on volcano flanks, the main objective is pursued using three-dimensional stress-strain analyses for modelling the effects of the magma intrusion on the stability of the volcano flank. Modelling is based on the results of an extensive geotechnical characterization of the volcaniclastic and lava materials. The numerical analyses investigate the influence of different paths and geometry of magma intrusion as well as the spatial variation of mechanical properties. As a result, favourable conditions for specific failure modes are identified. The stress-strain analyses show that magma intrusion can cause both a local failure of a wedge immediately downslope from the dyke or deep-seated movement involving large part of the slope; these two mechanisms were consistent with the deformative patterns observed during the 2007 and 2002–2003 eruptions, respectively. The magma thrust induces shear strains up to levels associated to appreciable grain crushing even below the sea level, where flow liquefaction can be invoked to explain the occurrence of past submarine slides. The submarine landslide is analysed by a combined finite element – limit equilibrium approach that demonstrates that instability conditions can develop if the loading exerted by the upper portion of the slope is sufficiently fast to produce undrained conditions. The analyses also support the hypothesis that at the 2002 subaerial failure occurred, due to combined effects of a magma mild thrust and the removal of the toe support caused by the preceding submarine slide.

Geochemical Anomalies in the NW Flank of Gedabek Mine (Lesser Caucasus, Azerbaijan)

Geochemical Anomalies in the NW Flank of Gedabek Mine (Lesser Caucasus, Azerbaijan)

Distribution of Rare Metals and REEs in Brown Coal Deposits of the Upper and Middle Amur Region

The distribution of REEs and rare metals in the Paleocene and Lower–Middle Miocene brown coals of the Zeya–Bureya Basin is analyzed. The migration of minor elements on the NW flank of the basin (the Sergeevskoe deposit), in the mode of the static state of orogens in the Paleocene and Miocene, in the course of active expansion of the sedimentation area occurred with uniform development of denudation plains and with the steady processes of peat accumulation. The high dynamic activity of the region on the SE margin of the Zeya–Bureya Basin (the Yerkovetskoe deposit) provided contrasting forms of coupling in the flexure–uplift system and an uneven character of localization of ore components. It is shown that coals of the Sergeevskoye deposit are enriched in Be, Sc, V, Ga, Rb, Nb, Ta, and REE + Y and may be considered as a promising complex rare-metal raw material.

Imbabura volcano (Ecuador): The influence of dipping-substrata on the structural development of composite volcanoes during strike-slip faulting

The geology and long-term structural development of Imbabura volcano (Ecuador) have been discerned from field surveys, as well as petrographical and geochemical studies. The volcano is composed of an ancient edifice (Imbabura I), which has experienced one major volcanic landslide directed N 330–340°. After the emplacement of that debris-avalanche deposit, the petrographically and geochemically different edifices Imbabura II-1 and Imbabura II-2 developed on the N and NE flank of Imbabura I, as well as in its summit zone. Finally the smaller Imbabura II-3 edifice, a dome-complex locally known as Huarmi Imbabura, was emplaced in the SSW flank of Imbabura I. The relatively complex structure of the edifice (i.e. flank collapse direction and spatial distribution of the major stratigraphical units) cannot be explained solely by volcano-tectonic interactions with the regional left-lateral Río Ambi strike-slip fault, which traverses the edifice from NNE to SSW. Instead, the fact that the whole Imbabura edifice stands on a substratum dipping to the NW (i.e. the NW flank of the neighbor Cubilche volcano) is proposed to be the main factor influencing the departure of Imbabura structure from previously known models of volcanic edifices interacting with strike-slip faults. This hypothesis was tested with scaled experiments, during which the dip-direction of the substratum was systematically changed with respect to the strike of the fault. The structures developed by the experimental prototypes are highly coherent with those observed at Imbabura volcano.

The interplay of magmatism and tectonics: An example based on the satellite scoria cones at Llaima volcano, Chile

We present a geochemical and mineralogical study of the satellite scoria cones at Llaima volcano, Chile, providing insights on magmatic processes and how these are affected by the local and regional tectonics. At Llaima, we identify two different and distinctive groups of satellite scoria cones with a common magmatic source but different petrological evolutions. Cones from group 1 (the “glomeroporphyritic group”), predominantly occur in the NE flank of the volcano, are characterized by basaltic to basaltic andesitic compositions (51–55 wt% SiO2) and have glomeroporphyritic textures. We have interpreted these cones as the product of magma replenishment, followed by an unimpeded propagation of their feeder dikes controlled mainly by the regional stress. As a result, dikes are emplaced parallel to the regional σ1, and perpendicular to the axis of local crustal extension. Cones from the group 2 (the “pilotaxitic group”), appear at the NE, NW and SW flanks of the volcano, they have more evolved compositions (55–60 wt% SiO2) and textures lacking glomerocrysts. Their location and morphometric parameters suggest that their feeder dike emplacement is mainly controlled by the stress exerted by the load of the volcanic edifice, where the compressional stress hinders magma ascent, allowing fractionation and volatile overpressure buildup. The characteristic texture of these cones is interpreted as fractionation, followed by a single crystallization event upon eruption. The lack of scoria cones at the SE flank is attributed to the local horizontal compressional stress caused by the local tectonic deformation associated to the Liquiñe-Ofqui Fault Zone.

Geological Setting and Ore Perspective of the New Discovered Gadir Low Sulfidation Epithermal Deposit, Gedabek NW Flank, Lesser Caucasus, Azerbaijan

Gadir deposit is located in the East of Yogundag, near Gedabek deposit, also, Shamkir uplift of the Lok-Karabakh structural-formation zone in the Lesser Caucasus Mega-anticlinorium of Azerbaijan. The deposit has complicated geological structure, and consists of different age and different composite intrusive bulks and fracture structure consisted of complicated with Middle and Upper Jurassic sediments. A structural position of Yogundag area (also, Gadir) predetermined a set of magmatic complexes and a character of magmatism occurrence for Gedabek-Bittibulag deeper fault direction as a whole including the investigated area where are widely developed a set of volcano-pluton formations and volcanism of central character. Gadir was first suggested as a low sulfidation epithermal deposit type by Gedabek Exploration Geologists (2014) following field work and geological interpretation. The Gadir deposit is belong to Pb-Zn-Cu-Ag-Au vein deposit which is characteristic to Low Sulfidation epithermal deposit. The main ore minerals are sulfides. Sulfides consist of pyrite, sphalerite, galena, and trace amounts of chalcopyrite.

Complex structure of Piton de la Fournaise and its underlying lithosphere revealed by magnetotelluric 3D inversion

La Réunion is a large volcanic construction resting on Paleocene oceanic crust. Through the 3D inversion of a large set of magnetotelluric (MT) soundings, our results reveal the general resistivity structure of the western part of Piton de la Fournaise volcano down to its base and the first 10km or so of the underlying lithosphere. The resistivity pattern shows a general stratification of the resistivity values. An upper resistive layer corresponds to unsaturated and water-saturated lava flows. This layer is thinner (a few hundred meters) in the Enclos and Plaine des Sables/Fond de la Rivière de l'Est areas than on the NW flank where it reaches 2000m. Below, the rest of the edifice is distinctly more conductive and shows highly conductive patches. The origin of the globally weak resistivity of the lower part of the construction is not established but can be tentatively attributed to a higher degree of alteration. The case of the highly conductive patches is different. Resistivity values of a few Ω·m imply the presence of highly conductive fluids and/or minerals that, in this context, are generally associated with hydrothermal phenomena. In the Enclos, highly conductive patches are unambiguously attributed to the presently active hydrothermal system. Beneath the Plaine des Sables/Fond de la Rivière de l'Est, they may be associated with hydrothermal alteration developed by the ancient volcanic center. The larger highly conductive patches are found below sea level and above the crust beneath the NW flank, at depths significantly larger than the others. This area coincides with the path of the N120 rift zone, with a deep (~10–20km) seismicity and with diffuse CO2 degassing. A relationship may therefore be inferred between deep magmatic activity, eruptive activity and postulated highly conductive hydrothermal zone. In the globally weak resistivity of the lower part of the edifice, a dome of moderate resistivity (>1kΩ·m) is centered beneath the Plaine des Sables. It is wider than a dense intrusive complex inferred from gravity models in the same area. The present resolution of both MT and gravity models cannot exclude a same nature for both structures. Beneath 4kmb.s.l., an increase of the resistivity values underlines an interface in good agreement with the inferred location of the transition between the edifice and the oceanic crust at this depth. The upper lithosphere shows resistivity values above 250Ω·m. This study therefore demonstrates the capability of the method to image major shallow structures such as the hydrothermally altered zones, and deeper ones such as the heterogeneity of the crust.

Hazard assessment of volcanic ballistic impacts at Mt Chihshin, Tatun Volcano Group, northern Taiwan

This study investigates the hazard posed by Volcanic Ballistic Projectiles (VBPs) in the area surrounding Mt Chihshin, Tatun Volcano Group, northern Taiwan. Based on the volcano’s current evolutionary stage, we consider two types of volcanic activity during which VBPs can be generated, namely hydrothermal and vulcanian eruptions. Hydrothermal eruptions may occur after a sudden decompression of water in the hydrothermal system of the volcano, typically due to mass removal processes, while vulcanian eruptions are caused by solidified magma that plugs the eruptive vent and gets blasted when this caprock is no longer able to withstand the pressure in the volcanic conduit. Initial velocities of ejected VBPs were estimated for each type of activity based on physical models and inserted as initial conditions to the equations that describe their motion. A hydrothermal eruption is assumed to occur at the NW flank of Mt Chihshin near the Hsiaoyiokeng fumarole, which is a place prone to flank instability, while a vulcanian eruption is assumed to originate from a central vent at the peak of Mt Chihshin. Modeling results suggest that the radii of the areas impacted by VBPs vary between 0.1 and 1.1 km for a hydrothermal eruption, while they become 1.4–5.1 km for a vulcanian eruption. Within these areas, roads, hiking trails, and public buildings lie within the impact areas; therefore, VBPs may potentially cause damage, injury, and even casualties.