UPPER MANTLE CONVECTION RELATED TO SUBDUCTION ZONE AND APPLICATION OF THE MODEL TO INVESTIGATE THE CRETACEOUS-CENOZOIC GEODYNAMICS OF CENTRAL EAST ASIA AND THE ARCTIC

A geodynamic model of upper mantle convection related to the Pacific subduction zone is mathematically substantiated and applied to investigate the Cretaceous-Cenozoic evolution of Central East Asia (CEA) and the Arctic. We present a solution for the two-dimensional stationary problem of thermal convection in the upper mantle layer, considering different Rayleigh numbers and taking into account the influence of the subduction process and lithospheric movements along the upper mantle base. We describe the results of 3D modeling of nonstationary upper mantle convection in a subduction zone. Our data give grounds to propose explanations for the entire spectrum of tectonic-magmatic processes developing within CEA in the Cenozoic and the Arctic in the Upper Cretaceous and Cenozoic. We discuss the reasons why the lithosphere in CEA and the Arctic is generally shifting towards the Pacific subduction zone, considering the presence of separate magmatic provinces and rift zones. In our opinion, this is due to the existence of a large horizontally elongated convective cell, which interior is composed of smaller isometric cells. This long cell creates the effect of conveyor dragging of the lithosphere, while its internal cells produce the effect of upper mantle plumes.

Characterisation and identification of ectomycorrhizae formed by the species of Asproinocybe (Tricholomataceae) and Inocybe (Inocybaceae) with the roots of the tropical sal tree Shorea robusta (Dipterocarpaceae)

In the course of the present study, surveys on occurrence and distribution of ectomycorrhizal (EcM) fungi in tropical sal forests of foothills of the Himalayas, India, were undertaken. The species of two genera of agarics, namely Asproinocybe and Inocybe, were found organically associated with the roots of Shorea robusta (sal tree). However, prior to our study the genus Asproinocybe has not been reported from India. In this article, the morpho-anatomical details of mycorrhizal roots of Shorea robusta associated with Asproinocybe lactifera and Inocybe purpureoflavida are provided for the first time. The EcM colonized roots of the two species are distinguished by differences in the shape and colour of the roots, surface texture, size and shape of cystidia, type of mantle, as well as different chemical reactions. Asproinocybe lactifera EcM is mainly characterised by a monopodial pinnate mycorrhizal system with the dark brown to reddish brown and loose cottony surface, while in Inocybe purpureoflavida it is irregularly pinnate to coralloid, silvery grey to reddish brown, with densely woolly surface. The outer mantle layer is heterogeneous with obclavate to awl-shaped cystidia in Asproinocybe lactifera, whereas Inocybe purpureoflavida EcM have a plectenchymatous outer mantle with subcylindrical to obclavate metuloidal and non-metuloidal cystidia. The presence of lactifers in the mantle is a unique feature in Asproinocybe lactifera as compared to Inocybe purpureoflavida.

A Method for Quantitative Interpretation of Stationary Thermal Fields for Layered Media

A new method to solve thermal conjugacy problems is presented for layered models with a thermal conductivity jump at their boundaries. The purpose of this method is to approximate the inverse thermal conductivity coefficient, which has breaks, by using a combination of step functions. A generalized continuous operator is constructed in a continuous space of piecewise–homogeneous media. We obtained an analytical solution for the stationary problem of heat conjugacy in the layered model with finite thickness and with Dirichlet–Neumann conditions at the external boundaries. An algorithm was constructed for downward continuation of the heat flux to depths that correspond to the top of the mantle layer. The advantages of this method are illustrated by testing the crustal seismic, gravity and geothermal data of a study area in the Urals and neighboring regions of Russia. We examined statistical relations between density and thermal parameters and determined heat flux components for the crust and the mantle. The method enables a downward continuation of the heat flux to the base of the upper mantle and allows us to determine the thermal effects of the lateral and vertical features of deep tectonic structures.

Mantle plume dynamics at the rear of a retreating slab

SUMMARY In this paper, we present 3-D numerical simulations in which a compositional mantle plume rises through a shallow mantle layer at the rear of a retreating slab. The slab–plume buoyancy flux ratio Bs/Bp is varied from 3 to 30 over nine slab–plume simulations. The plume causes an overall decrease of the slab retreat rate from 15 to 7 % in the corresponding range $B_s/B_p=[3,30]$. The retreat rate decrease occurs in two stages: the first decrease occurs remotely when plume and slab are hundreds of kilometres apart; the second decrease is linked to the slab–plume-head impact. Continuous tracking of key positions along the plume head and conduit together with velocity profiling further shows a very close interplay between the conduit and plume head dynamics. In particular, the combination of the slab– and plume(head)–induced flows at the rear of the slab increases the advection and tilt of the conduit and causes its flaring with height in the direction parallel to the trench. As a result, the conduit source slowly drifts away from the slab by hundreds of kilometres and flares by one and a half times its original radius over 30 Myr of plume head spreading. The conduit tilt and flaring result in an increasingly unbalanced azimuthal distribution of the incoming plume flux from the feeding conduit into the head. These changes in the feeding conditions coupled with the mantle flow at the level of the plume head lead to the asymmetric spreading of plume material beneath the plate in the preferential direction that is parallel to the trench. Upon its arrival against the slab, it can be a front of buoyant material set to subduct along the slab width that has widened up to two and a half times its initial dimension. In nature, it is expected to extend from hundreds to thousands of kilometres depending on the slab–plume buoyancy flux ratio. To our knowledge, this study is the first to highlight the inter-relationships between a plume head and its feeding conditions in the plume source region.

Delta-Notch Signaling: The Long and The Short of a Neuron’s Influence on Progenitor Fates

Maintenance of the neural progenitor pool during embryonic development is essential to promote growth of the central nervous system (CNS). The CNS is initially formed by tightly compacted proliferative neuroepithelial cells that later acquire radial glial characteristics and continue to divide at the ventricular (apical) and pial (basal) surface of the neuroepithelium to generate neurons. While neural progenitors such as neuroepithelial cells and apical radial glia form strong connections with their neighbours at the apical and basal surfaces of the neuroepithelium, neurons usually form the mantle layer at the basal surface. This review will discuss the existing evidence that supports a role for neurons, from early stages of differentiation, in promoting progenitor cell fates in the vertebrates CNS, maintaining tissue homeostasis and regulating spatiotemporal patterning of neuronal differentiation through Delta-Notch signalling.

Permian plume beneath Tarim from receiver functions

Receiver functions for the central Tien Shan and northern Tarim in central Asia reveal a pronounced depression on the 410 km discontinuity beneath the Permian basalts in Tarim. The depression may be caused by elevated temperature. The striking spatial correlation between the anomaly of the MTZ and the Permian basalts suggests that both may be effects of the same plume. This relation can be reconciled with the possible motion of Tarim on the order of 1000 km by assuming that the mantle layer, which has moved coherently with the plate since the Permian, extends to a depth of 410 km or more. Alternatively, the lithosphere and underlying mantle are decoupled at a depth of ∼ 200 km, but a cumulative effect of the Tarim plate motion since the Permian is less by an order of magnitude. A similar explanation is applicable to the Siberian traps.

MeHg Causes Ultrastructural Changes in Mitochondria and Autophagy in the Spinal Cord Cells of Chicken Embryo

Methylmercury (MeHg) is a known neurodevelopmental toxicant, which causes changes in various structures of the central nervous system (CNS). However, ultrastructural studies of its effects on the developing CNS are still scarce. Here, we investigated the effect of MeHg on the ultrastructure of the cells in spinal cord layers. Chicken embryos at E3 were treated in ovo with 0.1 μg MeHg/50 μL saline solution and analyzed at E10. Then, we used transmission electron microscopy (TEM) to identify possible damage caused by MeHg to the structures and organelles of the spinal cord cells. After MeHg treatment, we observed, in the spinal cord mantle layer, a significant number of altered mitochondria with external membrane disruptions, crest disorganization, swelling in the mitochondrial matrix, and vacuole formation between the internal and external mitochondrial membranes. We also observed dilations in the Golgi complex and endoplasmic reticulum cisterns and the appearance of myelin-like cytoplasmic inclusions. We observed no difference in the total mitochondria number between the control and MeHg-treated groups. However, the MeHg-treated embryos showed an increased number of altered mitochondria and a decreased number of mitochondrial fusion profiles. Additionally, unusual mitochondrial shapes were found in MeHg-treated embryos as well as autophagic vacuoles similar to mitophagic profiles. In addition, we observed autophagic vacuoles with amorphous, homogeneous, and electron-dense contents, similar to the autophagy. Our results showed, for the first time, the neurotoxic effect of MeHg on the ultrastructure of the developing spinal cord. Using TEM we demonstrate that changes in the endomembrane system, mitochondrial damage, disturbance in mitochondrial dynamics, and increase in mitophagy were caused by MeHg exposure.

Permian plume beneath Tarim from receiver functions

Receiver functions for the central Tien Shan and northern Tarim in central Asia reveal a pronounced depression on the 410-km discontinuity beneath the Permian basalts in Tarim. The depression may most likely be caused by elevated temperature. The striking spatial coherence between the anomaly of the MTZ and the Permian basalts suggests that both may be effects of the same plume. This relation can be reconciled with reconstructed positions of paleo-continents since the Permian by assuming that the mantle layer which translated coherently with the Tarim plate extended to a depth of 410 km or more. Alternatively, lithosphere and the underlying mantle are decoupled at a depth of ~ 200 km, but a cumulative effect of the Tarim plate motions since the Permian is by an order of magnitude less than predicted by the paleo-reconstructions. A similar explanation is applicable to the Siberian traps.

Cervical vagal nerve ganglioneuroma: a rare case report

<p class="abstract"><span lang="EN-IN">Ganglioneuromas occurring in the neck are uncommon. Schumacker and Lawrence (1939) stated that cervical ganglioneuroma is a rarest neck tumor. These tumors arise from cells of mantle layer of primitive neural tube and from the neural crest which migrate to a station or intermediate point in the autonomic paraganglionic nervous system. They have thus been described in neck arising elsewhere than from the cervical sympathetic chain e.g. larynx, pharynx and from nodus ganglion of vagus nerve. They may also spread or arise intraspinally. It doesn’t show sex predilection. Both sexes almost equally affected. Most often present as painless, slow growing lateral neck mass. At time of presentation they present with Vocal cord paralysis. Family history may be present. Definite preoperative diagnosis may be difficult and investigations not usually helpful. We are presenting a unique case of management of left cervical vagal nerve ganglioneuroma who presented to us left side neck swelling and hoarseness of voice.</span></p>