Sand‐shale mélanges from the Kodiak accretionary complex and Shimanto belt of Japan record deformation during underthrusting along a paleosubduction interface in the range 150 to 350 °C. We use ...observations from these mélanges to construct a simple kinetic model that estimates the maximum time required to seal a single fracture as a measure of the rate of fault zone healing. Crack sealing involves diffusive redistribution of Si from mudstones with scaly fabric to undersaturated fluid‐filled cracks in sandstone blocks. Two driving forces are considered for the chemical potential gradient that drives crack sealing: (1) a transient drop in fluid pressure ∆Pf, and (2) a difference in mean stress between scaly slip surfaces in mudstones and cracks in stronger sandstone blocks. Sealing times are more sensitive to mean stress than ∆Pf, with up to four orders of magnitude faster sealing. Sealing durations are dependent on crack spacing, silica diffusion kinetics, and magnitude of the strength contrast between block and matrix, each of which is loosely constrained for conditions relevant to the seismogenic zone. We apply the model to three active subduction zones and find that sealing rates are fastest along Cascadia and several orders of magnitude slower for a given depth along Nicaragua and Tohoku slab‐top geotherms. The model provides (1) a framework for geochemical processes that influence subduction mechanics via crack sealing and shear fabric development and (2) demonstration that kinetically driven mass redistribution during the interseismic period is a plausible mechanism for creating asperities along smooth, sediment‐dominated convergent margins.
Plain Language Summary
Geophysical monitoring of active subduction zones has revealed plate boundary slip behaviors such as creep, slow slip events, and earthquakes that vary spatially and temporally for different plate boundaries and downdip along a given boundary. Fault rocks exposed on land from paleosubduction plate boundaries provide a record of the deformation processes that likely occur during slip along active boundaries, so we review the characteristics of these ancient rocks to develop insight into slip behavior in subduction zones. We find that plate boundary deformation in these cases occurs within a wide fault zone through processes that involve redistribution of silica from shearing mudstones to cracking sandstone blocks. We use a geochemical model to calculate how long it would take to seal a crack by this process and conclude that cracks seal at rates that could influence the earthquake cycle, with rates of crack healing dependent on the temperature structure and the depth where slip occurs. Our results suggest that processes of frictional failure and geochemical healing in downgoing sediments may influence the slip stability along the subduction interface.
Key Points
Microstructural observations of subduction mélange record dissolution along a scaly fabric and diffusion to cracks in sandstone blocks
A silica kinetics model depicts crack healing that is highly dependent on temperature and slab‐top geotherm
Kinetic healing of cracks could modulate fault zone strength during the interseismic period
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
•Influences of build direction/laser conditions (30-wt%-SGF specimens) were evaluated.•Fiber orientation is ordered as roller-movement, vertical, and thickness directions.•Significant influence of ...fiber orientation on various properties was observed.•Double-scan method improved mechanical and thermal properties.•Shrinkage differs in the cases of single- and double-scan scanning.
Copolymer poly(butylene terephthalate) with 30- wt% short glass fiber (SGF) added was used to evaluate the dependence of the properties of specimens manufactured by selective laser sintering (SLS) and the influence of laser-irradiation conditions on build direction. The degree of orientation of SGFs in SLS is ranked in descending order of roller-movement direction, vertical direction in the powder-bed plane, and direction of lamination-layer thickness. Moreover, the influence of fiber orientation on mechanical properties, thermal properties, and shrinkage ratio was found to be remarkable. In the case of the double-scan method, in comparison to the single-scan case, while thermal degradation was suppressed, porosity was reduced, and mechanical properties were improved. In addition, degree of crystallinity of the SLS specimens increased, and heat-deflection temperature increased slightly. Furthermore, in regard to roller-movement direction and lamination-layer thickness direction, the trends of shrinkage ratio differ in the cases of the single- and double-scan scanning methods.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The causes for forearc basin and megathrust rupture zone segmentation are controversial. The Nankai forearc, Japan, is separated into five domains based on topography: Enshu, Kumano, Muroto, Tosa, ...and Hyuga. The boundaries of these domains correspond to the rupture limits of large earthquakes. We examined the geologic structure of the boundary region between the Kumano and Muroto domains off the Kii Peninsula using multichannel seismic reflection data to evaluate the role of upper plate composition in controlling segmentation. The results suggest that thick cover sediments and underlying accretionary prism are obliquely thrust landward over the igneous basement complex rock in the region of offshore of Cape Shionomisaki and separate the forearc basin. The igneous basement complex rocks directly overlying the plate interface in the hypocentral regions of 1944 Tonankai and 1946 Nankai earthquakes. The 1944 earthquake originated at the base of the complex, and the rupture extent slipped past its basement boundary, whereas the 1946 event nucleated at the updip boundary of the basement complex. The dense igneous rocks might have worked as a heavily loaded barrier on the seismogenic megathrust and separated the rupture area of both the earthquakes. Upper plate geology may be an important factor in controlling seismogenesis in the Nankai Trough and may serve as an example for understanding the controls on megathrust slip in other subduction zones.
Plain Language Summary
The Nankai Trough, Japan is the place where quakes nucleate in the margin and tsunamis repeatedly devastated circum‐Pacific societies. When, where, why, and how the quakes were started in the trench is a central scientific question but unsolved. The historical records of earthquakes suggest that the rupture started around Cape Shionomisaki of the Kii Peninsula, where there is also a topographic segment boundary of the ∼2,000 m deep basin in the middle continental slope. Our research of the geologic structure beneath the earthquake epicenters indicates a dense and hard rock mass situated upon the hypocenters of 1944, and 1946 megaquakes off Cape Shionomisaki. The rock mass might have worked as a heavy load and barrier on the low angle dipping plate boundary fault when the fault slipped the large rupture was propagated in the Nankai Trough.
Key Points
The Nankai forearc basin is separated off the Kii Peninsula owing to the existence of middle Miocene igneous basement in the upper plate
The rupture areas of the 1944 Tonankai, 1946 Nankai, and 2016 off‐Mie earthquakes appear to be controlled by the igneous basement
The shallow distribution of very low‐frequency earthquakes and tremors are related to the geological heterogeneity of the upper plate
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We investigated the roles of osteocytes in osteoclastic bone resorption during orthodontic tooth movement using the transgenic mice in which osteocytes can be specifically ablated. Because these ...transgenic mice express the receptor for diphtheria toxin on the cell surfaces of osteocytes, the injection of diphtheria toxin can ablate their osteocytes in vivo. Injection of diphtheria toxin into the transgenic mice significantly increased the number of ablated osteocytes in alveolar bone compared with that in wild-type mice with or without diphtheria toxin injection. Increased numbers of ablated osteocytes were observed from day 4 to day 12 after the injection in alveolar bones as well as in cortical bone of the tibiae. We applied the orthodontic force 4 days after the injection of diphtheria toxin, and the distance of tooth movement on day 12 was significantly smaller in transgenic mice than that in control mice. The numbers of osteoclasts and the quantity of eroded bone surface at the compression site were significantly reduced in the transgenic mice injected with diphtheria toxin than in control mice. These results provide in vivo demonstration of osteocyte involvement in osteoclastic bone resorption during orthodontic tooth movement.
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CMK, NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
In order to constrain deformation processes close to the brittle-ductile transition in seismogenic zone, we have carried out a microstructural study in the Shimanto accretionary complex (Japan), the ...fossil equivalent of modern Nankai accretionary prisms. The Hyuga Tectonic Mélange was sheared along the plate interface at mean temperatures of 245°C±30°C, as estimated by Raman spectroscopy of carbonaceous material (RSCM). It contains strongly elongated quartz ribbons, characterized by very high fluid inclusions density, as well as micro-veins of quartz. Both fluid inclusion planes and micro-veins are preferentially developed orthogonal to the stretching direction. Furthermore, crystallographic preferred orientation (CPO) of quartz c-axes in the ribbons has maxima parallel to the stretching direction. Recrystallization to a small grain size is restricted to rare deformation bands cutting across the ribbons. In such recrystallized quartz domains, CPO of quartz c-axes are orthogonal to foliation plane. The evolution of deformation micro-processes with increasing temperature can be further analyzed using the Foliated Morotsuka, a slightly higher-grade metamorphic unit (342±30°C by RSCM) from the Shimanto accretionary complex. In this unit, in contrast to Hyuga Tectonic Mélange, recrystallization of quartz veins is penetrative. CPO of quartz c-axes is concentrated perpendicularly to foliation plane. These variations in microstructures and quartz crystallographic fabric reflect a change in the dominant deformation mechanism with increasing temperatures: above ~300°C, dislocation creep is dominant and results in intense quartz dynamic recrystallization. In contrast, below ~300°C, quartz plasticity is not totally activated and pressure solution is the major deformation process responsible for quartz ribbons growth. In addition, the geometry of the quartz ribbons with respect to the phyllosilicate-rich shear zones shows that bulk rheology is controlled by quartz behavior. Consequently, below 300°C, the application of quartz pressure-solution laws, based on realistic geometry derived from Hyuga microstructures, results in strongly lowering the overall strength of the plate interface with respect to the classical brittle envelop.
•Foliation planes (dissolution sites) and ribbons (precipitation sites) are associated to pressure solution mechanism.•Shear stress values estimated for pressure solution creep are strongly lower than the classical Byerlee's law.•The brittle-ductile transition in subduction zones needs to be accounted of the effect of pressure-solution improved by large water amount.•Below ~300°C pressure solution creep is the dominant deformation process for quartz.•Bulk rheology in the Hyuga Tectonic Mélange is controlled by quartz.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In Arabidopsis, several genetic pathways controlling the floral transition (flowering) are integrated at the transcriptional regulation of FT, LFY and SOC1. TSF is the closest homolog of FT in ...Arabidopsis. TSF expression was induced rapidly upon activation of CONSTANS (CO). The mRNA levels of TSF and FT showed similar patterns of diurnal oscillation and response to photoperiods: an evening peak, higher levels in long day (LD) than in short day (SD) conditions, and immediate up-regulation upon day-length extension. These observations suggest that TSF is a direct regulatory target of CO. tsf mutation delayed flowering in SD conditions and enhanced the phenotype of ft in both LD and SD conditions. TSF and FT also shared similar modes of regulation by FLC, an integrator of autonomous and vernalization pathways, and other factors such as EBS and PHYB. Consistently, TSF overexpression caused a precocious flowering phenotype independent of photoperiods or CO, or FLC. These observations suggest that TSF is a new member of the floral pathway integrators and promotes flowering largely redundantly with FT but makes a distinct contribution in SD conditions. TSF and FT seem to act independently of each other and of LFY, and partially upstream of SOC1. Interestingly, the expression patterns of TSF and FT in seedlings did not overlap, although both were expressed in the phloem tissues. Our work revealed additional complexity and spatial aspects of the regulatory network at the pathway integration level. We propose that the phloem is the site where multiple regulatory pathways are integrated at the transcriptional regulation of FT and TSF.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Shock‐induced features are abundantly observed in meteorites. Especially, shock veins, including high‐pressure minerals, characterize many kinds of heavily shocked meteorite. On the other hand, no ...high‐pressure phases have been yet reported from enstatite chondrites. We studied a heavily shocked EH3 chondrite, Asuka 10164, containing a vein, which comprises fragments of fine‐grained silicate and opaque minerals, and chondrules. In this vein, we found a silica polymorph, coesite. This is the first discovery of a high‐pressure phase in enstatite chondrites. Other high‐pressure polymorphs were not observed in the vein. The assemblages and chemical compositions of minerals, and the occurrence of coesite indicate that the vein was subjected to the high‐pressure and temperature condition at about 3–10 GPa and 1000 °C. The host also experienced heating for a short time under lower temperature conditions, from ~700 to ~1000 °C, based on the opaque minerals typical of EH chondrites and textural features. Although the pressure condition of the vein in this chondrite is much lower than those in the other meteorites, our results suggest that all major meteorite groups contain high‐pressure polymorphs. Heavy shock events commonly took place in the solar system.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this study, hydrogen boride films are fabricated by ion-exchange treatment on magnesium diboride (MgB2) films under ambient temperature and pressure. We prepared oriented MgB2 films on strontium ...titanate (SrTiO3) substrates using pulsed laser deposition (PLD). Subsequently, these films were treated with ion exchangers in acetonitrile solution. TOF-SIMS analysis evidenced that hydrogen species were introduced into the MgB2 films by using two types of ion exchangers: proton exchange resin and formic acid. According to the HAXPES analysis, negatively charged boron species were preserved in the films after the ion-exchange treatment. In addition, the FT-IR analysis suggested that B-H bonds were formed in the MgB2 films following the ion-exchange treatment. The ion-exchange treatment using formic acid was more efficient compared to the resin treatment; with respect to the amount of hydrogen species introduced into the MgB2 films. These ion-exchanged films exhibited photoinduced hydrogen release as observed in a powder sample. Based on the present study, we expect to be able to control the morphology and hydrogen content of hydrogen boride thin films by optimising the ion-exchange treatment process, which will be useful for further studies and device applications.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Fatty and fibrous connective tissue formation is a hallmark of diseased skeletal muscle and deteriorates muscle function. We previously identified non-myogenic mesenchymal progenitors that contribute ...to adipogenesis and fibrogenesis in mouse skeletal muscle. In this study, we report the identification and characterization of a human counterpart to these progenitors. By using PDGFRα as a specific marker, mesenchymal progenitors can be identified in the interstitium and isolated from human skeletal muscle. PDGFRα(+) cells represent a cell population distinct from CD56(+) myogenic cells, and adipogenic and fibrogenic potentials were highly enriched in the PDGFRα(+) population. Activation of PDGFRα stimulates proliferation of PDGFRα(+) cells through PI3K-Akt and MEK2-MAPK signaling pathways, and aberrant accumulation of PDGFRα(+) cells was conspicuous in muscles of patients with both genetic and non-genetic muscle diseases. Our results revealed the pathological relevance of PDGFRα(+) mesenchymal progenitors to human muscle diseases and provide a basis for developing therapeutic strategy to treat muscle diseases.
With proportion of short-glass-fiber (SGF) addition (15, 30, 45, and 60 wt%) taken as a parameter, the powder properties of composite-copolymer poly(butylene terephthalate) (cPBT) powder and various ...properties of the cPBT-SGF specimens manufactured by selective laser sintering (SLS) were evaluated. Even in the case that SGF was added, the flowability of the powder was dramatically improved by adding silica to it. Moreover, as the proportion of added SGF was increased, the flowability was degraded. In the case proportion of SGF addition was taken as a parameter, tensile strength and flexural strength of the SLS specimen were maximized by SGF addition of 30 wt%; however, impact strength was maximized by SGF addition of 45 wt%. As the proportion of added SGF was increased, the amount of SGF “debonding” also increased, while the amount of resin that adheres to the SGFs decreased and porosity increased. In addition, the average glass-fiber length of the SLS specimens decreased with the addition of 45-wt% SGF, whereas it did not decrease with addition of 30-wt% SGF. Furthermore, in contrast to long fibers easily aligning and remaining in the direction of the roller, SGFs did not align in the direction of layer-thickness. Compared to SGF addition having an insignificant effect on mechanical properties, it significantly improved thermal properties (i.e., heat deflection temperature and linear-expansion coefficient) and reduced shrinkage. Moreover, even if SGF was added, it had little effect on the crystallization properties of the powder and SLS-formed specimen.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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