1991 Fiscal Year Final Research Report Summary
Deformation sequence of minor structures in deformed rocks
| Project/Area Number |
02640594
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
地質学一般
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| Research Institution | Niigata University |
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Principal Investigator |
UEMURA Takesi Niigata Univ. Faculty of Science Prof., 理学部, 教授 (90018250)
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| Project Period (FY) |
1990 – 1991
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| Keywords | deformation sequence / deformed minor structure / deformation facies / Nagatoro metamorphic rocks |
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| Research Abstract |
A temporal sequence of deformation is clarified in the Nagatoro metamorphic rocks, and is divided into the following five stages based on the mutual relations of deformed minor- and micro-structures observable in the field and under the optical microscope : The first stage is characterized by intrafolial fold as minor structure, and the same type of fold, ptygmatic fold and helicitic texture as minor structure. The second stage is expressed by the axial plane cleavage, recumbent fold and boudinage to pinch-and swell structure as minor structure, and crenulation fold, crenulation cleavage and boudinage as micro-struc-ture. The third stage includes the minor structure of upright fold, inclined fold and kink fold, and the micro-structure of open fold, kink to chevron fold and reverse kink band, the last of which is possible to belong to the next stage. The fourth stage is displayed by the mnor structure of reverse kink band alone. The fifth stage is the last one sequenced by the minor-structure of joint-drag type normal kink band, ductile faults and en echelon quartz vein as well as ductile fault as micro-structure.
The deformation history as shown by the above mentioned temporal sequence of deformed structures suggests that the mean ductility has been decreasing with time. As a result, the deformation facies has successively degraded with time. This means that the temporal decrease of both the temperature and the effective confining pressure, and increase of strain rate, or combination of them. Mode of deformation also changes with time from layer parallel simple shear through layer parallel oblique shear to contraction and extension.
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