Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

Abstract. To evaluate changes in water distribution generated bydynamic recrystallization of quartz, we performed infrared (IR) spectroscopymapping of quartz in deformed granite from the Wariyama uplift zone in NEJapan. We analyzed three granite samples with different degrees ofdeformation: almost undeformed, weakly deformed, and strongly deformed.Dynamically recrystallized quartz grains with a grain size of∼10 µm are found in these three samples, but thepercentages of recrystallized grains and the recrystallization processes aredifferent. Quartz in the almost-undeformed sample shows wavy grainboundaries, with a few bulged quartz grains. In the weakly deformed sample,bulging of quartz, which consumed adjacent host quartz grains, forms regionsof a few hundred micrometers. In the strongly deformed sample, almost allquartz grains are recrystallized by subgrain rotation. IR spectra of quartzin the three samples commonly show a broad water band owing to H2Ofluid at 2800–3750 cm−1, with no structural OH bands. Water contents inhost quartz grains in the almost-undeformed sample are in the range of40–1750 wt ppm, with a mean of 500±280 wt ppm H2O. On theother hand, water contents in regions of recrystallized grains, regardlessof the recrystallization processes involved, are in the range of 100–510 wt ppm, with a mean of 220±70 wt ppm; these values are low andhomogeneous compared with the contents in host quartz grains. These low watercontents in recrystallized regions also contrast with those of up to 1540 wt ppm in adjacent host grains in the weakly deformed sample. Watercontents in regions of subgrains are intermediate between those in host andrecrystallized grains. These results for water distribution in quartz implythat water was released by dynamic recrystallization.

DOI： 10.5194/se-14-409-2023

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.5194/egusphere-2022-1487

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jsg.2022.104547

DOI： 10.14863/geosocabst.2022.0_50

Publishing type：Research paper (scientific journal)  

<title>Abstract</title>Terrestrial records of the last geomagnetic reversal often have few age constraints. Chronostratigraphy using suborbital-scale paleoceanic events during marine isotope stage 19 may contribute to solving this problem. We applied the method to an 8 m long, high-resolution paleomagnetic record from a loess sequence in China and revealed millennial-to-sub-centennial scale features of the Matuyama–Brunhes (MB) transition. All samples were subjected to progressive thermal demagnetization with 14–15 steps up to 650–680 °C. As a result, 96% of the samples yielded a high-quality remanent magnetization. The MB transition terminated with a 75 cm thick zone with nine polarity flips. The polarity flip zone, dated at about 779–777 ka, began between the warm events “I” and “J” and terminated at the end of the cooling event coincident with the lowest axial-dipole strength interval. Most polarity flips occurred within 70 years. The virtual geomagnetic poles (VGPs) in the upper polarity flip zone clustered in the SW Pacific region, where the MB transitional VGPs from lavas of the Hawaiian and Canary Islands and lacustrine deposits of Java also clustered. These sites were probably dominated by dipolar fields. The absence of transitional fields across polarity flips implies a short time span for averaging fields due to a thin loess-magnetization lock-in zone. The reverse-to-normal polarity reversal dated at about 778 ka in Lingtai occurred at the end of the SW Pacific VGP zone, an important key bed for MB transition stratigraphy. The reversal is a good candidate for the main MB boundary. We found an excursion at about 766 ka spanning about 1 ka.

DOI： 10.1186/s40645-020-00337-z

Other URL： https://link.springer.com/article/10.1186/s40645-020-00337-z/fulltext.html