Seismic evidence for catastrophic slab loss beneath Kamchatka

Thermal remote sensing reveals communication between volcanoes of the Klyuchevskoy Volcanic Group

Volcanoes are traditionally considered isolated with an activity that is mostly independent of the surrounding, with few eruptions only (< 2%) associated with a tectonic earthquake trigger. Evidence is now increasing that volcanoes forming clusters of eruptive centers may simultaneously erupt, show unrest, or even shut-down activity. Using infrared satellite data, we detail 20 years of eruptive activity (2000-2020) at Klyuchevskoy, Bezymianny, and Tolbachik, the three active volcanoes of the Klyuchevskoy Volcanic Group (KVG), Kamchatka. We show that the neighboring volcanoes exhibit multiple and reciprocal interactions on different timescales that unravel the magmatic system's complexity below the KVG. Klyuchevskoy and Bezymianny volcanoes show correlated activity with time-predictable and quasiperiodic behaviors, respectively. This is consistent with magma accumulation and discharge dynamics at both volcanoes, typical of steady-state volcanism. However, Tolbachik volcano can interrupt this steady-state regime and modify the magma output rate of its neighbors for several years. We suggest that below the KVG the transfer of magma at crustal level is modulated by the presence of three distinct but hydraulically connected plumbing systems. Similar complex interactions may occur at other volcanic groups and must be considered to evaluate the hazard of grouped volcanoes.

Surface and mantle records reveal an ancient slab tear beneath Gondwana

Vertical slab-tearing has been widely reported in modern convergent settings profoundly influencing subduction and mantle dynamics. However, evaluating a similar impact in ancient convergent settings, where oceanic plates have been subducted and the geological record is limited, remains challenging. In this study, we correlate the lower mantle structure, which retained the past subduction configuration, with the upper-plate geological record to show a deep slab rupture interpreted as a large-scale tearing event in the early Mesozoic beneath southwestern Gondwana. For this purpose, we integrated geochronological and geological datasets with P-wave global seismic tomography and plate-kinematic reconstructions. The development of a Late Triassic-Early Jurassic slab-tearing episode supports (i) a slab gap at lower mantle depths, (ii) a contrasting spatiotemporal magmatic evolution, (iii) a lull in arc activity, and (iv) intraplate extension and magmatism in the Neuquén and Colorado basins. This finding not only has implications for identifying past examples of a fundamental process that shapes subduction zones, but also illustrates an additional mechanism to trigger slab-tearing in which plate rupture is caused by opposite rotation of slab segments.

Hepatocellular Carcinoma in the Cirrhotic Liver: Evaluation Using Computed Tomography and Magnetic Resonance Imaging

Hepatocellular carcinoma is the fifth most common tumor in patients worldwide and the third most common cause of cancer-related death, after lung and stomach cancer. Cirrhosis of the liver is the strongest predisposing factor for hepatocellular carcinoma, with approximately 80% of cases of hepatocellular carcinoma developing in a cirrhotic liver. The annual incidence of hepatocellular carcinoma is 2.0% to 6.6% in patients with cirrhosis compared with 0.4% in patients without cirrhosis. The 5-year survival rates of patients undergoing curative therapies for hepatocellular carcinoma, including liver transplant, hepatic resection, and percutaneous ablative techniques, range between 40% and 75%. Orthotropic liver transplant offers the prima facie cure for both hepatocellular carcinoma and liver cirrhosis. In hepatocellular carcinoma confined to the liver without macrovascular invasion, patients with a single tumor ≤ 5 cm or up to 3 tumors ≤ 3 cm each had a 5-year survival rate of 75% and a disease-free survival rate of 83%. In the adult population, liver transplant for hepatocellular carcinoma yields good results for patients whose tumor masses do not exceed the Milan criteria. The diagnosis of hepatocellular carcinoma using imaging tests has had a substantial impact on transplant decisions. Radiologists should be aware of this responsibility and exercise the utmost scrutiny before making a diagnosis of hepatocellular carcinoma. Erroneous diagnosis of hepatocellular carcinoma based on imaging tests could deny deserving patients the opportunity of a life-saving liver transplant and result in unnecessary liver transplants for others. Contrast-enhanced magnetic resonance imaging and helical computed tomography are the best imaging techniques currently available for the noninvasive diagnosis of hepatocellular carcinoma. With technological advances in hardware and software, diffusion-weighted imaging can be readily applied to the liver with resulting improved image quality.

Numerical modelling of spontaneous slab breakoff dynamics during continental collision

Slab detachment or breakoff is directly associated with phenomena like morphological orogenesis, occurrence of earthquakes and magmatism. At depth the detachment process is slow and characterized by viscous rheolgy, whereas closer to the surface the process is relatively fast and plastic. Using a 2D mantle model 1500 km deep and 4000 km wide we investigated, with finite-difference and marker-in-cell numerical techniques, the impact of slab age, convergence rate and phase transitions on the viscous mode of slab detachment. In contrast to previous studies exploring simplified breakoff models in which the blockage responsible for inducing breakoff is kinematically prescribed, we constructed a fully dynamic coupled petrological–thermomechanical model of viscous slab breakoff. In this model, forced subduction of a 700 km-long oceanic plate was followed by collision of two continental plates and spontaneous slab blocking resulting from the buoyancy of the continental crust once it had been subducted to a depth of 100–124 km. Typically, five phases of model development can be distinguished: (a) oceanic slab subduction and bending; (b) continental collision initiation followed by the spontaneous slab blocking, thermal relaxation and unbending – in experiments with old oceanic plates in this phase slab roll-back occurs; (c) slab stretching and necking; (d) slab breakoff and accelerated sinking; and (e) post-breakoff relaxation.

Our experiments confirm a correlation between slab age and the time of spontaneous viscous breakoff as previously identified in simplified breakoff models. The results also demonstrate a non-linear dependence of the duration of the breakoff event on slab age: a positive correlation being characteristic of young (<50 Ma) slabs while for older slabs the correlation is negative. The increasing duration of the breakoff with slab age in young slabs is attributed to the slab thermal thickness, which increases both the slab thermal relaxation time and duration of the necking process. In older slabs this tendency is counteracted by negative slab buoyancy, which generate higher stresses that facilitate slab necking and breakoff. A prediction from our breakoff models is that the olivine–wadsleyite transition plays an important role in localizing viscous slab breakoff at depths of 410–510 km due to the buoyancy effects of the transition.

Geophysics. Slabs do not go gently

High-resolution seismic tomography reveals an active vertical tear in a descending ocean plate off the coast of Japan.