Paleostress directions estimated from healed microcracks in the Cretaceous granitoids:

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  • Kanai Takuto
    Department of Earth Science and Environmental and Resources Engineering, Graduate School of Science and Engineering, Waseda University
  • Takagi Hideo
    Department of Earth Sciences, Faculty of Education and Integrated Arts and Sciences, Waseda University

Bibliographic Information

Other Title
  • 中部地方白亜紀花崗岩類中に発達するヒールドマイクロクラックを用いた古応力解析：
  • 中部地方白亜紀花崗岩類中に発達するヒールドマイクロクラックを用いた古応力解析 : 特に中央構造線と直交方向に沿った変化について
  • チュウブ チホウ ハクアキ ハナオカガンルイ チュウ ニ ハッタツ スル ヒールドマイクロクラック オ モチイタ コ オウリョク カイセキ : トクニ チュウオウ コウゾウセン ト チョッコウ ホウコウ ニ ソッタ ヘンカ ニ ツイテ
  • their variation along a transect normal to the Median Tectonic Line, central Japan
  • 特に中央構造線と直交方向に沿った変化について

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<p>Paleostress analyses using the three-dimensional orientation distribution of healed microcracks (HCs) in quartz from Cretaceous granitoids have been performed along a ca. 60 km transect normal to the Median Tectonic Line (MTL), central Japan. The paleostress was determined by fitting mixed Bingham distributions to the HC distribution for each sample. As a result, the orientations of the HCs in each data set were grouped into 2–5 clusters, and the group with the maximum density of HCs was regarded as the dominant stress for the data set. The nonparametric correlation coefficients of angular differences of stress for each axis (σ1, σ2, and σ3) were projected onto best-fit great circles on a stereoplot, yielding distances from the MTL of 0.06, 0.09, and 0.43, respectively. The σ3 axis is orthogonal to the MTL strike in the vicinity of the MTL, but rotates counterclockwise in areas away from the MTL and is roughly parallel to the MTL strike at ca. 60 km from the MTL. The dominant σ3 axis (NW–SE), which is normal to the MTL in the vicinity of the MTL (southeastern area), is considered to be related to extensional faulting on the MTL at 63–58 Ma (Ichinokawa Phase), whereas the dominant σ3 axis (NE–SW) parallel to the MTL at a distance from the MTL suggests the influence of the plate convergence direction (NW) at about 75–67 Ma, rather than the influence of MTL-normal extension. The orientations of σ1 and σ2 show no correlation with distance from the MTL, indicating that their orientations depend on the local stress state within the granitic body.</p>

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