Kochi University is a national university in Kōchi, Kōchi, Japan. The predecessor of the school was founded in 1922, and it was chartered as a university in 1949.Faculty of Humanities and EconomicsFaculty of EducationFaculty of ScienceMedical SchoolFaculty of AgricultureGraduate School of Kuroshio Science Doctoral CourseThe United Graduate School of Agricultural science Ehime University Wikipedia.
Santosh M.,Kochi University
Geological Society Special Publication | Year: 2012
The Indian lithospheric plate assembles the history of geological events covering almost the entire history of our planet. The proto-Indian continent was an integral part of the Palaeoproterozoic supercontinent Columbia. Global mantle warming beneath this supercontinent triggered rising plumes that led to rifting and the emplacement of mafic dyke swarms and large igneous provinces in many of the major cratons of Peninsular India. Continued rifting and separation of crustal blocks led to the formation of thick passive margin successions. The opening of ocean basins and their eventual closure are recorded in the travelogue of oceanic plates from mid-ocean ridge to the trench in the form of 'ocean plate stratigraphy' in Proterozoic belts, including the association of dismembered ophiolites, pelagic sediments and continental margin sequences that were imbricated into accretionary belts such as those in the Aravalli-Delhi domain (Western India Suture), the Central India Tectonic Zone (Central India Suture) and the eastern margin of the East Dharwar Craton (Eastern India Suture). Recent U-Pb zircon chronology from ophiolitic rocks in the eastern margin of the Dharwar Craton shows ages spanning from 1.85 to 1.33 Ga suggesting a prolonged Wilson cycle of subduction-accretion processes before the final collisional event and the extrusion of high-grade metamorphic orogens. The extruded high pressure-temperature (P-T) metamorphic belts are often associated with mafic/ultramafic units with an abyssal signature. The available geophysical information from the Indian Palaeoproterozoic belts, particularly deep seismic reflection data, provides important clues on the architecture of these orogens and the subduction polarity. Whereas the Palaeoproterozoic convergent margins in the NW and SE sectors of the Indian peninsula were characterized by the westward subduction of oceanic plates, ocean closure along the Central India Tectonic Zone probably involved a double-sided subduction. The Wilson cycle traces a continuum from Palaeoproterozoic through Mesoproterozoic to Neoproterozoic in some of these belts, with a prolonged subduction-accretion history similar to the ongoing convergent margin processes in the western Pacific region. Peninsular India thus preserves a complete record from Pacific-type accretionary tectonics along the margins of the Columbia supercontinent to Himalayan-style collisional assembly within the Neoproterozoic Rodinia supercontinent.
Ikezoe T.,Kochi University
International Journal of Hematology | Year: 2014
Acute promyelocytic leukemia (APL) is an uncommon subtype of acute myelogenous leukemia characterized by the proliferation of blasts with distinct morphology, a specific balanced reciprocal translocation t(15;17), and life-threatening hemorrhage caused mainly by enhanced fibrinolytic-type disseminated intravascular coagulation (DIC). The introduction of all-trans retinoic acid (ATRA) into anthracycline-based induction chemotherapy regimens has dramatically improved overall survival of individuals with APL, although hemorrhage-related death during the early phase of therapy remains a serious problem. Moreover, population-based studies have shown that the incidence of early death during induction chemotherapy is nearly 30 %, and the most common cause of death is associated with hemorrhage. Thus, development of a novel treatment strategy to alleviate abnormal coagulation in APL patients is urgently required. Recombinant human soluble thrombomodulin (rTM) comprises the active extracellular domain of TM, and has been used for treatment of DIC since 2008 in Japan. Use of rTM in combination with remission induction chemotherapy, including ATRA, produces potent resolution of DIC without exacerbation of bleeding tendency in individuals with APL. This review article discusses the pathogenesis and features of DIC caused by APL, as well as the possible anticoagulant and anti-leukemic action of rTM in APL patients. © 2013 The Japanese Society of Hematology.
Santosh M.,Kochi University
Journal of Geodynamics | Year: 2010
A synthesis of some of the recent conceptual models suggests that mantle dynamics exerted a significant control on the assembly and breakup of supercontinents through the history of the Earth. During the amalgamation of continental fragments, the subducted oceanic lithosphere of intervening oceans either moves down to the deep mantle or gets horizontally flattened as stagnant slabs in the mantle transition zone. Blobs of these stagnant slabs sink down into the deep mantle and accumulate as slab graveyards at the core-mantle boundary. The recycled oceanic lithosphere at the core-mantle boundary is thought to contribute potential fuel for generating superplumes which rise from the core-mantle interface to the uppermost mantle, penetrating the mantle transition zone and eventually giving rise to hot spots. Multiple subduction zones promote the rapid amalgamation of continental fragments into supercontinents and also act as major zones of material flux into the deep mantle transporting substantial volume of trench sediments and arc crust through sediment subduction and tectonic erosion. Due to buoyancy, the subducted TTG (tonalite-trondhjemite-granite) material is stacked in the mid mantle region and may not sink down to deeper levels. Thus, continents and supercontinents can be speculated to occur as three layers: on the surface of the globe, at the mid mantle region and on the core-mantle boundary, with material transfer on a whole earth scale controlled by plate, plume and 'anti-plate' tectonics. Whereas mantle tomography opens windows into the deep Earth, the imbricated remnants of 'ocean plate stratigraphy' preserved in accretionary orogens constitute useful geological tools to study subduction-accretion-collision history, particularly in relation to the assembly of older supercontinents on the surface of the globe. The dynamics of supercontinents also impact the origin and extinction of life as well as surface environmental changes. Large scale flow of material and energy through mantle downwelling and upwelling associated with supercontinent assembly and breakup is thought to affect the Earth's dynamo which would lead to catastrophic environmental changes, sometimes even triggering mass extinction. When a rising plume impinges the base of a supercontinent, the resultant continental rifting, formation of large igneous provinces and volcanic emissions might lead to the initiation of a plume winter, the aftermath of which would be mass extinction and long-term oceanic anoxia. Supercontinent tectonics in relation to mantle dynamics thus provides a key to evaluate the history of evolution and destruction of the continental crust, to understand the history of life, and to trace the major surface environmental changes of our planet. © 2010 Elsevier Ltd.
Santosh M.,Kochi University
Precambrian Research | Year: 2010
An evaluation of recent S-wave receiver functions, S-wave velocities and two versions of P-wave tomographic images along various transects in the North China Craton provides some clues on the subduction-collision history of the different crustal blocks and their final amalgamation within the Paleoproterozoic Columbia supercontinent. Interpretation of a N-S seismic section of the craton suggests thick slab debris sinking to various depths in the mantle. The W-E seismic corridors show the preservation of a thick (>200 km) lithospheric root (tectosphere) beneath the Ordos Block and its variable and extensive erosion towards the Yanliao Block (Eastern Block). This zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted Paleoproterozoic oceanic lithosphere. The present day lithosphere-asthenosphere boundary beneath this region probably marks the 'erosional plane' along which decratonization occurred through subduction-erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east. Within the asthenosphere below the Yanliao Block, younger and thinner slabs predominate, in the absence of any prominent thick high velocity layers. These younger slabs define a westward polarity and constitute a mega-scale duplex formed by underplating through Phanerozoic subduction process, particularly the Pacific plate subduction from the east. The lithologic associations within the Inner Mongolia Suture Zone dividing the Yinshan Block to the north and Ordos Block to the south correspond to an accreted ocean plate stratigraphic sequence, with the tonalite-trondhjemite-granodiorite (TTG) gneisses, charnockites and calc-alkaline granites representing a continental arc built up through subduction from the north. The seismic transects bring out a contrasting polarity in the subduction regime with an oblique east- to southward subduction of the Yinshan Block and a westward subduction of the Yanliao Block. Here I propose a double-sided subduction history for the NCC, similar to the ongoing subduction process in the Western Pacific. Such double-sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of NCC are therefore considered to be critical in evaluating the final assembly of the Paleoproterozoic supercontinent Columbia. © 2010 Elsevier B.V. All rights reserved.
Yoshida M.,Japan Agency for Marine - Earth Science and Technology |
Santosh M.,Kochi University
Earth-Science Reviews | Year: 2011
The periodic assembly and dispersal of supercontinents through the history of the Earth had considerable impact on mantle dynamics and surface processes. Here we synthesize some of the conceptual models on supercontinent amalgamation and disruption and combine it with recent information from numerical studies to provide a unified approach in understanding Wilson Cycle and supercontinent cycle. Plate tectonic models predict that superdownwelling along multiple subduction zones might provide an effective mechanism to pull together dispersed continental fragments into a closely packed assembly. The recycled subducted material that accumulates at the mantle transition zone and sinks down into the core-mantle boundary (CMB) provides the potential fuel for the generation of plumes and superplumes which ultimately fragment the supercontinent. Geological evidence related to the disruption of two major supercontinents (Columbia and Gondwana) attest to the involvement of plumes. The re-assembly of dispersed continental fragments after the breakup of a supercontinent occurs through complex processes involving 'introversion', 'extroversion' or a combination of both, with the closure of the intervening ocean occurring through Pacific-type or Atlantic-type processes. The timescales of the assembly and dispersion of supercontinents have varied through the Earth history, and appear to be closely linked with the processes and duration of superplume genesis. The widely held view that the volume of continental crust has increased over time has been challenged in recent works and current models propose that plate tectonics creates and destroys Earth's continental crust with more crust being destroyed than created. The creation-destruction balance changes over a supercontinent cycle, with a higher crustal growth through magmatic influx during supercontinent break-up as compared to the tectonic erosion and sediment-trapped subduction in convergent margins associated with supercontinent assembly which erodes the continental crust. Ongoing subduction erosion also occurs at the leading edges of dispersing plates, which also contributes to crustal destruction, although this is only a temporary process. The previous numerical studies of mantle convection suggested that there is a significant feedback between mantle convection and continental drift. The process of assembly of supercontinents induces a temperature increase beneath the supercontinent due to the thermal insulating effect. Such thermal insulation leads to a planetary-scale reorganization of mantle flow and results in longest-wavelength thermal heterogeneity in the mantle, i.e., degree-one convection in three-dimensional spherical geometry. The formation of degree-one convection seems to be integral to the emergence of periodic supercontinent cycles. The rifting and breakup of supercontinental assemblies may be caused by either tensional stress due to the thermal insulating effect, or large-scale partial melting resulting from the flow reorganization and consequent temperature increase beneath the supercontinent. Supercontinent breakup has also been correlated with the temperature increase due to upwelling plumes originating from the deeper lower mantle or CMB as a return flow of plate subduction occurring at supercontinental margins. The active mantle plumes from the CMB may disrupt the regularity of supercontinent cycles. Two end-member scenarios can be envisaged for the mantle convection cycle. One is that mantle convection with dispersing continental blocks has a short-wavelength structure, or close to degree-two structure as the present Earth, and when a supercontinent forms, mantle convection evolves into degree-one structure. Another is that mantle convection with dispersing continental blocks has a degree-one structure, and when a supercontinent forms, mantle convection evolves into degree-two structure. In the case of the former model, it would take longer time to form a supercontinent, because continental blocks would be trapped by different downwellings thus inhibiting collision. Although most of the numerical studies have assumed the continent/supercontinent to be rigid or nondeformable body mainly because of numerical limitations as well as a simplification of models, a more recent numerical study allows the modeling of mobile, deformable continents, including oceanic plates, and successfully reproduces continental drift similar to the processes and timescales envisaged in Wilson Cycle. © 2010 Elsevier B.V.