Stratigraphic and paleontological investigations in Mugi Town, on the Pacific coast of Shikoku Island, revealed evidence of as many as five tsunami inundations from events along the Nankai Trough between 5581 and 3640 cal yr BP. Nine event deposits (E1-E9) were identified in cores ranging in length from 2 to 6 m, consisting of sandy and gravelly layers interbedded with organic-rich mud. Sedimentary structures in the event deposits observed by computed tomography included normal grading and sharp lower stratigraphic contacts. Event deposits E3, E6, E7, and E8 contained mainly brackish-marine diatom species, suggesting that they had been deposited during inundation by seawater. In addition, fossil diatom assemblages were markedly different above and below event deposits E3, E4, E6, and E8. For example, assemblages below event deposit E6 were dominated by a freshwater species (Ulnaria acus), whereas assemblages above it were predominantly brackish-marine (Diploneis smithii, Fallacia forcipata, and Fallacia tenera). We attributed these changes to the increase of marine influence due to coastal subsidence associated with subduction-zone earthquakes, as documented in the 1946 Showa-Nankai earthquakes. We conclude that event deposits E3, E6, and E8 and perhaps E4 and E7 were deposited by tsunamis generated by subduction zone earthquakes along the Nankai Trough. The ages of these event deposits, as constrained by ten radiocarbon ages, suggest that some of the tsunamis that impacted Mugi Town were correlated with those reported elsewhere along the Nankai Trough, thereby complementing the existing but still incomplete geological record for these events.

This study aimed to evaluate the effect of chemical exchange saturation transfer (CEST) on the ischemic regions in hypoxic-ischemic encephalopathy (HIE) in comparison with diffusion-weighted imaging (DWI) and magnetic resonance spectroscopy (MRS) using a 7T-MRI. Methods: We used neonatal rats (n = 8), aged 8 days, to clarify the progression of HIE. The rat model of HIE was developed by ligating and severing the left common carotid artery, followed by 45 minutes of recovery, and 60 minutes of hypoxia (8% O 2 /92% N 2 ; 34°C). At 0-2 and 24 hours after the onset of HIE, CEST imaging, DWI, and MRS were performed with a 7T-MRI. The magnetization transfer ratio (MTR) asymmetry curves and four MTR asymmetry maps at 0.5, 1.0, 2.0, and 3.5 ppm were calculated using the CEST images. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) maps were calculated by DWI, and brain metabolites were assessed by MRS. Results: In the ischemic regions of neonatal rats, FA was significantly increased at 0-2 hours and decreased at 24 hours after the onset of HIE. ADC in the ipsilateral side was significantly lower than that of contralateral side. All rats with HIE showed hypointense areas on MTR asymmetry maps (2.0 and 3.5 ppm), that did not correspond with the hyperintense areas on DWI. In addition, a significant increase in lactate levels was observed at 0-2 and 24 hours after the onset of HIE. Conclusion: CEST MTR maps did not correspond with the hyperintense areas on DWI at 0-2 and 24 hours after the onset of HIE. The change of multi offset CEST signal may be primarily related to the brain metabolites and pH alterations, such as that caused by lactate, after the onset of HIE.

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We report new petrological and geochronological data of garnet‐cordierite (Grt‐Crd) gneiss as well as two types of leucocratic rocks (garnet‐bearing and cordierite‐bearing leucosomes) crystallized during prograde and near‐peak metamorphisms of the Wanni Complex (WC) in Sri Lanka, and investigate the pressure–temperature–time evolution of granulite‐facies metamorphism for unravelling the timing and tectonics of the Neoproterozoic collisional processes related to Gondwana amalgamation. Grt‐Crd gneiss, garnet‐biotite (Grt‐Bt) gneiss, garnet‐bearing leucocratic rock (Grt‐L), and cordierite‐bearing leucocratic rock (Crd‐L) discussed in this study were collected from Walpita in the margin of the WC along the boundary with the Highland Complex (HC). Grt‐L occurs as thin layers parallel to the foliation of matrix Grt‐Bt and Grt‐Crd gneisses. The occurrences of porphyroblastic garnet in quartzo‐feldspathic matrix and crystallised melt inclusions within the garnet suggest that the Grt‐L could have formed by partial melting of host Grt‐Bt gneiss during prograde to peak metamorphism. Crd‐L is coarse‐grained and massive, lacks obvious foliation, and crosscuts the foliation of host Grt‐Bt gneiss. These observations suggest that the Crd‐L could have intruded after the crystallization of the Grt‐L. Application of phase equilibria modelling in the system NCKFMASHTO for the rocks yielded three discrete thermal events: 600–800°C/4.0–6.0 kbar (Stage 1 from Grt‐L), 700–840°C/5.5–7.0 kbar (Stage 2 from Grt‐Crd gneiss), and 840–880°C/4.5–5.5 kbar (Stage 3 from Crd‐L), suggesting a clockwise P–T evolution. LA‐ICP‐MS zircon U–Pb dating of the leucosomes yielded several metamorphic events: >577 Ma (partial melting of Grt‐L), ~562 Ma (crystallization of Grt‐L), 537 ± 14 Ma (peak metamorphism and crystallization of Crd‐L), and 507–503 Ma (post‐peak cooling event). The results of this study therefore confirmed prolonged (>70 Myr) high‐grade metamorphism of the WC, although the duration might be shorter than that of the HC (>100 Ma). The continuous heat supply necessary for such long‐lived high‐grade metamorphism is explained by a recent tectonic model of Sri Lanka. The model suggests double‐sided subduction and continent‐continent collision, which could have given rise to subsequent slab delamination and differential heating of lower to middle crust. Such complex subduction–collision processes possibly controlled the difference in the style of P–T path and the duration of high‐grade metamorphism between the HC and the WC.

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