Paleostress analyses by means of mixed Bingham distributions of healed microcracks in the Ryoke granites, Central Japan

Abstract

This study reports the results of paleostress analysis using the three-dimensional orientation and distribution of healed microcracks (HCs) in quartz within granitic bodies. Although the mechanical constraints of a universal stage together with the Terzaghi factor introduce sampling bias to the orientation and distribution of microstructures, few previous studies have taken this bias into consideration. We devised a series of corrections that allow the investigation of the orientation and distribution of HCs within the Ryoke granites, located along the Median Tectonic Line (MTL) in the Chubu region of Japan. Paleostress values were determined by fitting mixed Bingham distributions to the corrected distribution of each sample, resulting in the clustering of HC orientations in each data set into a few groups, which were then inverted to yield a paleostress state. The state corresponding to the group with the maximum number of HCs was considered to be the most significant stress for each individual sample, and the orientation of σ of this most significant stress in most samples is roughly perpendicular to the trend of the MTL. However, significant variations in the distribution of σ and σ were also identified, suggesting that the orientation of σ probably reflects the regional stress field, whereas the orientations of σ and σ are more dependent on the local stress state within the granitic body.

Kinematic Analyses and Radiometric Dating of the Large‐Scale Paleogene Two‐Phase Faulting Along the Median Tectonic Line, Southwest Japan

“…Therefore, the top-to-the-north normal faulting, the movement direction of which is normal to the trend of the proto-Southwest Japan arc (N75°E in the present orientation), could have been caused by the ridge subduction parallel to the arc. Kanai et al (2014); Kanai and Takagi (2016) estimated the paleostress orientations of the σ 3 axis trending nearly normal to the MTL based on the preferred orientation of healed microcracks in quartz from the Ryoke granite in Central Japan during the Late Cretaceous to Early Paleocene. The inferred orientation of the σ 3 axis indicates that the extensional stress field normal to the MTL is extensive during the Ichinokawa phase, supporting the tectonic interpretation mentioned above.…”

Genetic algorithm for fitting a mixed Bingham distribution to 3D orientations: a tool for the statistical and paleostress analyses of fracture orientations

“…Fracture orientations are important to predict the leakage of geofluid from reservoirs (e.g., Bigi et al ) and to estimate the stability of open pit and tunnel walls (Priest ; Peel et al ). The orientations of dilational fractures such as dikes and mineral veins are clues to paleostresses (Stevens ; Anderson ; McHone ; Delaney et al ; Baer et al ; Jolly & Sanderson ; Yamaji et al ; Sato et al ; Kanai et al ). Since the poles to natural fractures often show multimodal distribution, the clustering of the fracture orientations is essential for the description and paleostress analysis of the fractures.…”

Paleostress directions estimated from healed microcracks in the Cretaceous granitoids:

“…3 HC SC OC Kranz 1983Anders et al 2014Plumb et al, 1984Lespinasse and Pecher, 1986;Vollbrecht et al, 1991;Takeshita and Yagi, 2001;Nadan and Engelder, 2009;HC SC Hay et al, 1988Evans, 1995;Lespinasse, 1999;Laubach, 2003;Fischer et al, 2009 σ 3 σ 3 σ 1 σ 2 Yamaji et al, 2010;Yamaji and Sato, 2011;Yamaji, 2016Yamaji, 2014Yamaji, 2008 HC MTL Nakai, 1976;, 2016 Fig …”