Shrinking of Ischia Island (Italy) from Long-Term Geodetic Data: Implications for the Deflation Mechanisms of Resurgent Calderas and Their Relationships with Seismicity

The identification of the mechanisms responsible for the deformation of calderas is of primary importance for our understanding of the dynamics of magmatic systems and the evaluation of volcanic hazards. We analyze twenty years (1997–2018) of geodetic measurements on Ischia Island (Italy), which include the Mt. Epomeo resurgent block, and is affected by hydrothermal manifestations and shallow seismicity. The data from the GPS Network and the leveling route show a constant subsidence with values up to −15 ± 2.0 mm/yr and a centripetal displacement rate with the largest deformations on the southern flank of Mt. Epomeo. The joint inversion of GPS and levelling data is consistent with a 4 km deep source deflating by degassing and magma cooling below the southern flank of Mt. Epomeo. The depth of the source is supported by independent geophysical data. The Ischia deformation field is not related to the instability of the resurgent block or extensive gravity or tectonic processes. The seismicity reflects the dynamics of the shallow hydrothermal system being neither temporally nor spatially related to the deflation.

Genesis of the Dawadi potassium nitrate deposit in Lop Nor, China

Nitrate deposits are rare worldwide, especially potassium nitrate deposits; furthermore, their genesis remains disputed. There is a rare salt-lake type potassium nitrate deposit in the Dawadi area of Lop Nor at the eastern margin of the Tarim Basin, and the ore bodies show coexisting solid and liquid phases. Additionally, there are large sulphate-type potash deposits in the adjoining Luobei Depression, south of the Dawadi area. To determine why there are two different types of potash deposits in adjacent depressions with similar climates, field geological surveys were conducted and samples collected. It was found that the Tertiary clastic layer at the periphery of the Dawadi deposit was rich in high-salinity brine, with nitrate contents of up to 495–16,719 mg/L, much higher than those in the Luobei Depression, 1–35 mg/L. Additionally, a type of deep hydrothermal (Ca–Cl) brine was found in the fault zones, with nitrate contents of up to 8044 mg/L, dozens of times greater than that of ordinary groundwater. Using comprehensive analysis and research, we concluded that the Dawadi and Luobei depressions belong to different hydrological systems with no connection between them; thus, the two deposits belong to different metallogenic systems. Furthermore, groundwater played an important role in the mineralization of the potassium nitrate deposit, and a deep source may have been an important source of the ore-forming materials. The fault system widely developed in Lop Nor provides favorable channels for deep hydrothermal recharge, and the groundwater and deep hydrothermal brine could provide the source for the nitrate mineralization in the Dawadi Depression through water–rock reactions.

Proportions, Timing, and Re-equilibration Progress During the 1959 Summit Eruption of Kīlauea: an Example of Magma Mixing Processes Operating During OIB Petrogenesis

Petrographic and chemical analysis of scoria samples collected during the 1959 Kīlauea summit eruption illustrate the progress of thermal and chemical homogenization of the melts, and the gradual growth and/or re-equilibration of olivine phenocrysts, over the course of the eruption. Glass compositions show that thermal equilibration was largely complete within the span of the eruption, while chemical homogenization was a work in progress. The olivine phenocryst population, known to contain conspicuous antecrystic components, is also hybrid within the euhedral population. The bulk of the olivine reached the level of the erupting magma on November 18-19, 1959. Zoning patterns in olivine phenocrysts show that initially unzoned grains developed normal zoning by the end of the eruption. Reverse zoning in relatively Fe-rich olivine phenocrysts (interpreted as cognate to the stored magma) was progressively eliminated from November 21 to December 19, 1959, by diffusive re-equilibration between crystals and melt. Toward the end of the eruption, the only olivine composition in direct contact with the melt was Fo84-86, with the original rim compositional heterogeneity gone in 4-5 weeks’ time. Activity in December 1959 differed from that in November, as high fountaining events were more closely spaced and almost all samples were picritic, with bulk MgO ≥16.5 wt %. Three different levels were in play during the 1959 eruption: a deep source for high-MgO melts and forsteritic (Fo87-89) olivines, an intermediate source for the bulk of the stored magma, and a shallower source for the most differentiated magma. This model is consistent with geophysical, petrologic and chemical observations. Comparison of the 1959 eruption with results from older explosive deposits suggest that stored and recharge melts and olivine from the deeper parts of Kīlauea’s plumbing are similar in composition to those observed or inferred in the 1959 eruption, so they behave similarly during extrusive and explosive periods alike.

Polyformational Agdai Massif (Verkhoyansk-Kolyma Orogenic Region)

The earliest Mesozoic granitoid formations of the Verkhoyansk-Kolyma orogenic region are derivatives of the Late Jurassic-Early Cretaceous gabbro-diorite-granodiorite formation, involvinggold and polymetallic mineralization. Late Cretaceous alkaline-feldspar or alkaline granites with associated rare-earth mineralization complete the granitoid magmatism of the region. The Agdai massif, which combines both of the mentioned groups of rocks, was the object of our research. Therefore, understanding their petrological and genetic features is of great interest. It is determined that the eastern part of the massif is composed of diorites and granodiorites and includes autoliths and xenoliths of gabbro-diorite composition. The isotopic K-Ar age of gabbro-diorites is 154Ma, diorites –148 Ma, granodiorites –117–124 Ma, and dike granites – 114 Ma. The rocks are characterized bydisequilibrium mineral assemblages: early magmatic pyroxene-Labrador, typical for the basic rocks, and late - micropegmatite granitoid. The origin of the parent melts occurred within the lower crust in amphibolite substrates at temperatures of 1000–1150°C and a pressure of 1.4-1.6 GPa under the influence of the mantle main melt and the partial mixing of the latter with the resulting crustal melt. The western part of the outcrop was formed at the beginning of the Late Cretaceous (the isotopic K-Ar age of the granites is 92+/-3 Ma) and is composed of alkaline feldspar leucogranites. According to all petro - and geochemical parameters, the rocks are defined as post-orogenic or rift-related granites of the A-type. The presence of inclusions of pyroxene-labrador composition, titanomagnetite, zircon of morphotype D and the ratio of the basic petrochemical parameters allow us to refer them to A-type granites related to continental rifting. High melt temperatures (990-1030°C) at relatively low pressures during magma generation (0.7–0.8 GPa) could be achieved only when additional heat was supplied from an external (deep) source. The presence of nonequilibrium mineral associations indicates a possible syntax of the granite and the main melt. In general, the Agdai massif is a polyformational, polygenic structure formed by the intrusion of melts through common or closely located magma conduits.

Real magnetic stripping method in unexploded ordnance detection and remediation – a case study from Rohožník military training range in SW Slovakia

In this contribution we present results from a case-study, which was performed in collaboration between geophysicists and explosive ordnance disposal technicians at the Rohožník military training range in SW Slovakia. The aim of this study was to locate a deep-penetrated unexploded Mk-82 aerial bomb using high-definition digital magnetometry. The location where this bomb had entered the ground was known but its final position needed to be determined so that a safe excavation and disposal could be conducted. However, the detection of this unexploded ordnance object was complicated by the presence of intense magnetic interference from a number of near surface ferrous items including non-explosive test bombs, fragmentation and other iron junk. These items contributed a localised, high amplitude of magnetic clutter masking any deeper source. Our strategy was to approach the problem in three stages. First, we used magnetic data to locate the near surface items. After the detection and before the excavation of the searched objects, two quantitative interpretation methods were used. These involved an optimised modelling of source bodies and the application of a 3D Euler deconvolution. Both methods yielded acceptable results, but the former was found to be more accurate. After the interpretation phase, many of the items were then safely excavated and removed individually. A second magnetic mapping was then performed and from this data which was now significantly less cluttered, we were able to identify but not quantify, two deep source items and to confirm that all remaining near surface items were significantly smaller in size than a Mk-82 bomb. As the remaining near surface sources were interpreted as being contained within the surface one metre of soil and being small they could be assured to be non-explosive, it was considered most practical to mechanically excavate and remove this soil and the remaining objects contained.

Geological controls on focused fluid flow in the Song Hong Basin, offshore Vietnam

This study uses 2D seismic lines located in the central Song Hong Basin, covering an area of c. 3900 m2, in the water depth of c. 100 m. Focused fluid flows are developed intensively and can be classified into two types: blow - out pipe and seepage pipe. They have similar seismic characteristics as a vertical zone of disturbed seismic reflections. The significant difference between them is the blow - out pipes associated with seafloor pockmarks and paleo - pockmarks which are absent in the seepage pipe. Besides, the scale of the blow - out pipe is larger, compared with the seepage pipe. The blow - out pipe is c. 500 m wide and 450÷3500 ms TWT; the seepage pipe is smaller scale, c. 200 m wide and 500 ms TWT. Blow - out pipe is rooting from the sequence just above the diapir or deformation unit or deep lacustrine mudstones from the Late Eocene to Oligocene, and marine mudstones from the Early to Middle Miocene. The seepage pipe is rooting from the sequence above the diapir. The focused fluid flow is supposed to be controlled by the overpressured deep source layers and passive diapirism. The occurrence of focused fluid flow is an indicator for the active petroleum system in the study area. Intensive development of focused fluid flow proves a great hydrocarbon potential in the Song Hong basin.

Modeling long-term volcanic deformations at the Kusatsu-Shirane and Asama volcanoes, Japan using the GNSS coordinate time series

Long-term deformations of the Kusatsu-Shirane and Asama volcanoes in central Japan were investigated using Global Navigation Satellite System (GNSS) measurements. Large postseismic deformations caused by the 2011 Tohoku earthquake — which obscure the long-term volcanic deformations — were effectively removed by approximating the postseismic and other recent tectonic deformations in terms of quadrature of the geographical eastings/northings. Subsequently, deformation source parameters were estimated by the Markov Chain Monte-Carlo (MCMC) method and linear inversion. The deformation source of the Kusatsu-Shirane volcano was found to be a sill-like oblate spheroid located a few kilometers northwest of the Yugama crater at a depth of approximately five km, while that of Asama was also estimated to be a sill-like oblate spheroid located at the western flank of the edifice at a depth of approximately 13 km, along with the previously reported shallow east-west striking dike at a depth of approximately 1 km. It was revealed that 1) volume changes of the Kusatsu-Shirane deformation source and the shallow deformation source of Asama were correlated with the volcanic activities of the corresponding volcanoes, and 2) the Asama deep source has been steadily losing volume, which may indicate that the volcano will experience less eruptions in the near future.

The use of simultaneous stereo-electroencephalography and magnetoencephalography in localising the epileptogenic focus in refractory focal epilepsy

Both magnetoencephalography and stereo-electroencephalography are used in presurgical epilepsy assessment, with contrasting advantages and limitations. It is not known whether simultaneous stereo-electroencephalography-magnetoencephalography recording confers an advantage over both individual modalities, in particular whether magnetoencephalography can provide spatial context to epileptiform activity seen on stereo-electroencephalography. 24 adult and paediatric patients who underwent stereo-electroencephalography study for pre-surgical evaluation of drug-resistant focal epilepsy, were recorded using simultaneous stereo-electroencephalography-magnetoencephalography, of which 14 had abnormal interictal activity during recording. The 14 patients were divided into two groups; those with detected superficial (n = 7) and deep (n = 7) brain interictal activity. Interictal spikes were independently identified in stereo-electroencephalography and magnetoencephalography. Magnetoencephalography dipoles were derived using a distributed inverse method. There was no significant difference between stereo-electroencephalography and magnetoencephalography in detecting superficial spikes (p = 0.135) and stereo-electroencephalography was significantly better at detecting deep spikes (p = 0.002). Mean distance across patients between stereo-electroencephalography channel with highest average spike amplitude and magnetoencephalography dipole was 20.7+/- 4.4 mm. for superficial sources, and 17.8 +/- 3.7 mm. for deep sources, even though for some of the latter (n = 4) no magnetoencephalography spikes were detected and magnetoencephalography dipole was fitted to a stereo-electroencephalography interictal activity triggered average. Removal of magnetoencephalography dipole was associated with 1 year seizure freedom in 6/7 patients with superficial source, and 5/6 patients with deep source. Although stereo-electroencephalography has greater sensitivity in identifying interictal activity from deeper sources, a magnetoencephalography source can be localised using stereo-electroencephalography information, thereby providing useful whole brain context to stereo-electroencephalography and potential role in epilepsy surgery planning.In the largest case series to date, Vivekananda et al. perform simultaneous magnetoencephalography and stereo-electroencephalography in refractory focal epilepsy patients. They demonstrate that for deep brain epileptogenic foci, magnetoencephalography dipoles could be derived from average stereo-electroencephalography data, thereby overcoming a traditional limitation of magnetoencephalography of reduced sensitivity for deep sources.

Epithermal Fluorite Deposits in Transbaikalia (Geochemical Features, Sources of Matter and Fluids, and Genesis)

—We consider the isotope-geochemical features of epithermal fluorite deposits in Transbaikalia, including the REE compositions, Sr isotope ratios, Sm–Nd systems, and isotope compositions of oxygen, carbon, hydrogen, and sulfur. The 87Sr/86Sr ratios in fluorites are within 0.706–0.708, and the εNd values are negative. Oxygen in quartz, the main mineral of the deposits, has a light isotope composition (δ18O = –3.4 to +2.6‰), and the calculated isotope composition of oxygen in the fluid in equilibrium with quartz (δ18O = –9 to –16‰) indicates the presence of meteoric water. The latter is confirmed by analysis of the isotope compositions of oxygen and hydrogen in gas–liquid inclusions in fluorites from three deposits. These isotope compositions are due to recycling caused by the impact of shallow basic plutons. The isotope composition of sulfur indicates its deep source. During ascent, sulfur became enriched in its light isotope (δ34S = –1.8 to –7.7‰). We assess the association of fluorite ores with basaltoids widespread in the study area. The isotope and geochemical parameters suggest their spatial proximity. Probably, the basaltoids were responsible for the recycling of meteoric water. It is shown that the epithermal fluorite deposits formed by the same mechanism as fissure–vein thermal waters in western Transbaikalia.