Field observation of joint structures in various types of igneous rocks

Shingo Kano, Noriyoshi Tsuchiya

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

In this study, field observations of natural fracture network systems in some intrusive and extrusive rocks were undertaken, to clarify the fracturing mechanism in the rocks. Shallow intrusives, whose depth of emplacement was less than several hundred metres, include the Momo-iwa Dacite dome on Rebun Island (Hokkaido), and Jodogahama Rhyolite in Iwate prefecture. Extrusive complexes studied include the Tojinbo Andesite and Ojima Rhyodacite in Fukui prefecture. Rocks of 'granitic' composition were collected from the Takidani (Japan Alps) and Hijiori (Yamagata prefecture) plutons. The joint structure in Hijiori Granite was evaluated by analysis of core samples extracted from the HDR-3 geothermal production well. Based on detailed field observation, joint structures related to thermal contraction of a rock mass could be classified according to their inferred depth of formation. Joints from a near surface setting, such as shallow intrusive rocks and extrusives, tend to form pentagonal - hexagonal columnar structures (for a variety of rock types), whilst granitic rocks (from a deeper setting) typically exhibit a parallelepiped structure. The apparent differences in joint form are inferred to be dependent on the confining pressure, which acts on joint generation and propagation. In cases of non-confining pressure, such as the near-surface (shallow intrusive/extrusive) setting, joint networks typically form a columnar structure. On the contrary, confining pressure is considerably greater for deeper rock masses, and these form a parallelepiped joint structure.

Original languageEnglish
Title of host publicationWATER DYNAMICS
Subtitle of host publication3rd International Workshop on Water Dynamics
Pages140-147
Number of pages8
DOIs
Publication statusPublished - 2006 May 15
EventWATER DYANMICS: 3rd International Workshop on Water Dynamics - Sendai, Japan
Duration: 2005 Nov 162005 Nov 17

Publication series

NameAIP Conference Proceedings
Volume833
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616

Other

OtherWATER DYANMICS: 3rd International Workshop on Water Dynamics
Country/TerritoryJapan
CitySendai
Period05/11/1605/11/17

Keywords

  • Columnar joint
  • Field observation
  • Intrusive and extrusive rocks
  • Parallelepiped joint
  • Thermal contraction

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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