1991 Fiscal Year Final Research Report Summary
Fluid Inclusions in Granite and Their Thermal Microcracking
| Project/Area Number |
02452224
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
資源開発工学
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| Research Institution | Tohoku University |
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Principal Investigator |
SUZUKI Shunichi Tohoku Univ., Fac. Eng. Professor, 工学部, 教授 (80005214)
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| Co-Investigator(Kenkyū-buntansha) |
OKUMURA Kiyohiko Tohoku Univ. Fac. Eng. Technical Off., 工学部, 技官 (40177184)
KOJIMA Takashi Tohoku Univ. Fac. Eng. Research Assoc., 工学部, 助手 (20192057)
MATSUKI Koji Tohoku Univ. Fac. Eng. Assoc. Prof., 工学部, 助教授 (10108475)
SUZIKI Shunichi Tohoku Univ., Fac. Eng. Professor (80005214)
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| Project Period (FY) |
1990 – 1991
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| Keywords | Fluid Inclusion / Decrepitation / Acoustic Emission / Microcracking / Granite |
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| Research Abstract |
The Inada granite was selected as the test material. Modal analysis yields 36 % quartz, 28% alkali-feldspar, 32% plagiclase, 4 % biotite, less than 1 % accessory minerals. Quartz and feldspar in the Inada granite contain 10^5 fluid inclusions per cubic millimeter. Fluid inclusions average 2 micrometers in diameter, and consist of two phases (liquid and vapor) at room temperature.
Homogenization and decrepitation of fluid inclusions were observed under the microscope with heating stage, using doubly polished thin sections. Fluid inclusions in quartz homogenize at temperatures ranging from 85ﾟto 260ﾟC with peak at about 175ﾟC, and in feldspar from 150ﾟto 230ﾟC with peak at 180ﾟC.
The orientations of microcracks caused by decrepitation of fluid inclusions were mostly parallel and perpendicular to the c-axis of quartz, and parallel to the cleavages of feldspar. The microcracks are generally less than 100 micrometers.
Acoustic emission measurements were performed on free particle samples and disk core samples. Free particle samples separated from the Inada granite are doubly ground thin grains 1 mm thick. Disk core samples are 29 mm in diameter, and three different thickness, respectively, 1, 5 and 10 mm. These samples were heated at 2ﾟC/min, and acoustic emission signals were detected by using AE trunsducer.
Acoustic emission of free particle samples are caused by decrepitation of fluid inclusions. Acoustic emission profiles for free particles of quartz show the wide range of decrepitation temperature with peak at 38OﾟC, and for feldspar at 360ﾟC. It is obvious that decrepitation of fluid inclusions contributes greatly to the acoustic emission profiles of the Inada granite below temperature of the alpha-beta transition of quartz.
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