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A SEM cathodoluminescence study on weathering of quartz grains in faults, central Japan
CATENA
vol. 15, p.l-16
Braunschweig 1988
A SEM CATHODOLUMINESCENCE STUDY ON WEATHERING OF QUARTZ GRAINS IN FAULTS, CENTRAL JAPAN Yuji Kanaori, Gifu-City SUMMARY Cathodoluminescence (CL) of quartz grains or particles was observed using a scanning electron microscope. The quartz grains were collected from fault gouge and fault breccia within the Atotsugawa fault, central Japan, and the quartz particles were obtained by crushing parent rocks of the fault, such as granite and gneiss, in an iron bowl. In comparison with particles from the parent rocks, those from the fault showed the following differences: CL inherited from the parent rock, CL caused by faulting, and CL modified by weathering or alterations of the fault. These differences are attributed to the faulting and subsequent weathering. The CL observations were in general agreement with secondary electron observations; and it is recommended that both methods should be used in parallel. 1
INTRODUCTION
Knowledge of when a fault moved is of great importance in preventing disasters caused by the associated earthquakes. ISSN0341-8162 @1988 by CATENAVERLAG, D-3302 Cremlingen-Destedt,W. Germany 0341-8162/88/5011851/US$ 2.00 + 0.25
When selecting sites for large constructions such as dams or nuclear power stations and determine the seismo-tectonic hazard of the area, it is extremely important to evaluate the activity of the faults distributed in and around the site, as well as to investigate the mechanical properties of the rocks containing the faults. In evaluating the movement age, it is necessary to investigate the properties of intrafault materials such as fault gouge and fault breccia (OGATA 1976, OGATA & HONSHO 1981) . Quartz grains found in fault gouges have been utilized in estimating the age of a fault using the electron spin resonance method (IKEYA et al. 1982), and to learn the relative age of the fault by noting differences in microtextures on the quartz grain surfaces using a scanning electron microscope (SEM) (KANAORI et al. 1980, 1985, KANAORI 1983, 1985). However, the formational processes of the gouges, including the quartz grains, are still not completely understood. Studies of cathodoluminescence (CL) of quartz grains using the SEM were undertaken for sedimentary rocks and deposits by KRINSLEY & HYDE (1971), KRINSLEY & TOVEY (1978), and TOVEY & KRINSLEY (1980). They showed that the CL image was affected
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by forces that the quartz grains experienced during transportation or sedimentation processes. In this study, CL imges as well as secondary electron (SE) images of quartz grains or particles were observed using the SEM. The quartz grains were selected from intrafault materials within the Atotsugawa fault at three outcrop sites (Sites 1, 2 and 3 in fig.l), and the quartz particles were obtained by crushing samples of the parent rocks, such as granite and gneiss, from each of three sites in an iron bowl. The geology of the outcrops and properties of the intrafault materials are reported in detail by KANAORI et al. (1982a, b) and MIYAKOSHI et al. (1982). A search of the literature has not uncovered previous studies of CL images of quartz grains within faults. The CL observations reported in this paper are a new attempt to investigate quartz grains in faults. Furthermore, quartz grains from decomposed granite and from secondary deposits of coarse sands sampled at Site 4 in fig.1 were observed with the same methods used for the intrafault material study. Characteristics of the CL of quartz grains or particles obtained are here described, and the origin of the CL and its development in the samples is considered.
cence and can be understood in terms of the electric bond structure of the solid (SMART & TOVEY 1982). Spectra of the CL emitted from quartz show two emission maxima: (1) in the blue range (430-360 nm), and (2) in the red (610-630 nm), though the spectra depend upon the origin of quartz (ZINKERNAGEL 1978). The CL contrast of quartz is influenced by impurity contents such as Ti and Fe (SPRUNT 1981). When quartz is stressed, the CL alters (SMART & TOVEY 1982, TOVEY & KRINSLEY 1980). For example, HANUSIAK & WHITE (1975) showed that the CL image of damaged c~-quartz was brighter than that of undamaged a-quartz.
3
SAMPLE LOCALITIES AND SAMPLES
The Atotsugawa fault, one of the most widely known active faults, in Japan, extends over 60 km in length (MATSUDA 1966, MIYAKOSHI et al. 1982). The fault probably moved in 1858 at the time of the Hida Earthquake (M = 6.9) (MATSUDA 1966). Remarkable topographic changes caused by faulting can be seen along the entire fault trace (MATSUDA 1966). The sampling sites are described below. Site 1 is a fresh roadcut near the north end of the Atotsugawa fault, in the vicinCATHODOity of the Magawa river, in the southern LUMINESCENCE OF region of Kaminiikawa-Gun, Toyama. At this site, the fault clearly separates QUARTZ Mesozoic granodiorite distributed in the Long-wavelength photons are emitted in northern part of the fault from prethe visible regions of the spectrum when Pleistocene gravel beds distributed in the electrons hit the specimen. This phe- southern part by a single plane (this nomenon is known as cathodolumines- plane is called the "main fault plane" CA'I ENA
An Interdisciplinary Journal of SOIL SCIENCE
HYDROLOGY- G E O M O R P H O L O G Y
CL on Quartz Weathering in Fault, Japan
3
N Toyomo
//)
H°~us(:n\
• Tokoyomo
Yokedoke --360N
Gifu
~
'
\ 136
I
138 °
140 °
I
137*E
138OE
Fig. 1: Location of sampling sites (1 to 4) and lineaments around the Atotsugawa fault (Ato). in this paper). In the boundary between the granodiorite and the gravel beds, is found a zone composed of fine-grained, yellow to yellowish brown gouge materials, 2 to 3 cm in width. The main fault strike is N74°E and the dip. 86°SE. Grains found in gravel beds 10 cm from the plane are fractured and pulverized. The granodiorite up to 13 m from the fault plane is soft and intruded by lamprophyre. Several fracture zones with a width of 10 to 100 cm, and with the same strike as the main fault plane are distributed in the area approximately 100 m from the site.
gouge materials, white to bluish grey in colour, and about 20 cm in width, exists in granite. The fault strike is EW and dips 90 ° . Sound limestone outcrops to the southeast, 3.0 m from the fault. There are no sections showing the transition from the granite into the limestone. The Atotsugawa fault is inferred to pass through this zone of no outcrop, just to the south of Site 2.
Site 3 is located in the vicinity of the southwestern end of the Atotsug~ awa fault, in the bed of the Amodani river, in Yoshiki-Gun, Gifu. The fault passes through gneiss, granite, limestone Site 2 is located on the fight bank and porphyrite dikes intruding into these of the Miyakawa fiver, in Yoshiki-Gun, rocks. The fault is composed of five fracGifu. A fault composed of fine-grained, ture zones each having a width of several C A T E N A - - A n I n t e r d i s c i p l i n a r y Journal o f S O I L S C I E N C E - - H Y D R O L O G Y ~ E O M O R P H O L O G y
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Kanaori
metres. The total width of the fault is about 30 m. The strikes of these fracture zones are generally N70°-80°E and the dip 60°--80°NW or SE. Site 4 is located in the vicinity of Shogenji, Sakashita, Gifu. Samples derived from the decomposed granite maintain their original structures, but can be crumbled easily by hand. Sample descriptions are listed in tab.1. 4
preparation. Because such a mottled CL image did not appear on any grains or particles observed in this study, it is inferred that the ultrasonic cleaning did not alter the CL images of the grains or particles. 5 5.1
RESULTS IMAGES OF QUARTZ GRAINS W I T H I N T H E FAULT
METHOD
CL images characteristic of quartz grains found within the fault are shown in Intrafault materials were put into a phot.1 to 4. In these photos, SE images beaker with sufficient water to cause disof the same fields as the CL images are persion of the grains, while samples of shown, in order to compare both images. parent rocks were crushed with an iron The following six types of CL charbar in an iron bowl until reduced to paracteristics are recognized on the quartz ticles. Grains and particles with size befrom within the fault. tween 250 and 850 #m were then selected (F1) Several dark bands or spots are using Tyler sieves. The selected samples recognized in the bright background were then immersed in a solution of 10% (phot.1). HC1 at room temperature to remove car(F2) Dark areas are found in the bright bonate completely, and cleaned in an ultrasonic bath of distilled water for about background (phot.2d). (F3) Dark areas alternate irregularly 10 min. Then, the grains or particles were completely dried after washing, and 10 with bright areas (phot.2b). (F4) Several dark bands are recognized to 15 quartz grains or particles of each sample were randomly selected under an in the faint background (phot.4b). (F5) Numerous dark bands are developtical microscope. The quartz grains or particles were stuck on a sample stub for oped anastomosingly in the faint backthe SEM. They were coated with a 20 to ground (phot.3b and 4d). (F6) CL is not emitted. It was impos40 nm thickness of gold (Au) and were examined at an accelerating voltage of sible to photograph the quartz grains, 25 KeV on a JEOL T-100 SEM, having therefore, only SE images are shown in a photomultiplier with a detecting wave- phot.4ef. length of 400 to 650 nm. Tab.2 indicates grain occurrence numPolished sections of the parent rocks ber of the CL type at each site, The numwere also examined by the same method. ber of samples and grains observed are K R I N S L E Y & TOVEY (1978) indi- variable among sampling sites. Features cated that a mottled CL image, in which of F1 and F3 are found on all samples a small black area irregularly alternated at Site 1, except for one. Feature F5 is with a bright area, appeared on quartz recognized on quartz grains from only grains fractured accidentally during ul- one sample at Site 1, a sample at Site 2 trasonic cleanings at the time of sample and most samples at Site 3; Only this CA'I I:NA
An Interdisciplinary Journal of SOIL SCIENCE
HYDROLOGY GEOMORPHOLOGY
CL on Quartz Weathering in Fault, Japan
Sample locality
Number of samples
5
Geological description
Site 1
12 1 1 4
Fault gouge and fault breccia derived from granodiorite within the Atotsugawa fault Decomposed granodiorite. Matrix of gravel beds. Parent rock, granodiorite.
Site 2
1
Fault gouge derived from granite in an area just north of the Atotsugawa fault.
Site 3
18
Fault gouge and fault breccia derived from gneiss, granite and prophyrite dike within the Atotsugawa fault. Parent rock, gneiss Parent rock, granite
Site 4
2
Decomposed granite. Coarse sands of secondary deposits derived from the decomposed granite.
1
Tab. 1: A list of samples collected. Sample locality
Rock type
Site 1
Intrafault materials Decomposed granodiorite Matrix of gravel beds Parent rock, granodiorite
Number of samples*
F1
F2
CL types F3 F4
12(6o) 1(5) 1(5) 4(6)
24 3 5 16
10 2 0
16 0 0
F5
F6
0 0 0 0
8 0 0
2 0 0 0
Site 2
Intrafault materials
1(13)
0
0
0
0
13
0
Site 3
Intrafault materials Parent rock, gneiss Parent rock, granite
18(83) 3(12) 3(12)
7
0
1
39
22
14
Decomposed granite Secondary deposit
2(4) 1(6)
4 4
Site 4
1
7
4
5
5
3
0 0
0 0
1
1
Tab. 2: CL type occurrence at each site. * The number of quartz grains observed in detail is given in parentheses.
feature is common to all three outcrop sites of the fault. Features F4 and F6 are commonly found on samples at Site 3.
5.2
CL OF QUARTZ PARTICLES OBTAINED BY CRUSHING PARENT ROCKS
Because features F1, F4 and F5 are CL images of quartz particles obtained not related to the SE images, these fea- by crushing parent rocks depend upon tures are probably controlled by the in- the type of parent rock and are specific ternal structures of the grains. to each locality. Among the six CL types Dark areas in features F2 and F3 cor- found in the fault, three CL types F1, respond to undulated areas in the SE F4 and F6 are usually recognized in the images (phot.2). Grains with feature F6 quartz particles from the parent rocks are characterized with considerably un- (tab.2). dulated surfaces, well rounded comers All quartz particles obtained from graand ridges in the SE image. nodiorite at Site 1 display the feature CATENA -- An Interdisciplinary Journal of SOIL SCIENCE--HYDROLOGY~EOMORPHOLOGY
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Kanaori
Photo 1: SE images belonging to Subgroup lh (c) and CL images showing Type F1 (b and d) of quartz grains or particles at Site 1. Scale: 100#m. b and d are the same fields as a and c, respectively, a and b: quartz particles by crushing granodiorite, c and d: quartz grains from intrafault materials. Explanation of SE groups and CL types appears in the text.
of CL type F1 (phot.l). The feature is commonly recognized in the quartz grains obtained, not only from gravel bed matrix at Site 1, but also from decomposed granite and secondary deposits of coarse sands at Site 4. Almost half of quartz particles which were obtained from gneiss and granite at Site 3 display CL type F4 feature. Some quartz particles from gneiss and granite at Site 3 display CL type F6 feature.
CATENA
5.3
CL IMAGES OF POLISHED SECTIONS
Observation of polished quartz grains revealed that almost all dark bands penetrate the grains (phot.5). As shown in phot.6, some dark bands correspond to healed cracks in the parent rock (SPRUNT & BRACE 1974, TAPPONNIER & BRACE 1976, SPRUNT & NUR 1979, TOVEY & KRINSLEY 1980, KANAORI 1986).
An Interdisciplinary Journal of SOIL SCIENCE HYDROLOGY
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CL on Quartz Weathering in Fault, Japan
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Photo 2: SE images belonging to Subgroup Ic (a and c) and CL .images showing Types F3 (b) and F2 (d) of quartz grains from intrafault materials at Site 1. Scale: 100 #m. b and d are the same fields as a and e, respectively.
5.4
COMPARISON OF CL BETWEEN PARENT ROCKS AND FAULT
CL types F1, F4 and F6 are commonly found in both quartz particles obtained from crushing parent rocks and those in the fault. These CL features are essentially inherited from those of the parent rocks. CL type F6 feature found on some quartz grains within the fault forms by modification of the fault, as will be mentioned latter, while the feature found on quartz particles from the parent rocks
is originally inherited from the gneiss. Other features F2, F3 and F5 are characteristics of the CL images ot" quartz grains in the fault.
6
6.1
INTERPRETATION DISCUSSION
AND
CL ORIGIN OF QUARTZ GRAINS WITHIN THE FAULT
As is evident from the comparison of the CL between parent rocks and the fault,
CATENA -- An Interdisciplinary Journal of SOIL SCIENCE--HYDROLOGY~EOMORPHOLOGY
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Kanaori
Photo 3: SE image belonging to Subgroup Ib (a) and CL image showing Type F5 (b ) of quartz grains./horn intrafault materials at Site 1. Scale: 100 #m. b is t h e s a m e field a s a.
the CL of quartz grains in the fault is derived from three origins; CL inherited from the parent rock, CL caused by faulting, and CL modified by weathering or alterations in the fault. 6.1.1
CL inherited from the parent rock
fl - ? transition temperature and eventually revealed that some grains showed a marked change and even a complete reversal in CL contrast. Quartz particles obtained from gneiss at Site 3 do not emit CL, while those from granite at the same site are characterized by the faint CL. Quartz particles obtained from granodiorite at Site 1, and from granite at localities, reported by KANAORI (1984), show the bright CL.
Characteristics in which several dark bands or spots are recognized in the bright background (CL type F1), is common to quartz grains from intrafault maSPRUNT et al. (1978) found that terials and quartz particles at Site 1 ob- metamophism appeared to homogenize tained by crushing parent rocks. This CL with colour being related to metafeature is thought to be inherited from morphic grade - low temperature causing the CL of quartz in granodiorite. red CL and high temperature, blue. this This feature has been also recognized suggests that the CL contrast depends by KANAORI (1984) on quartz particles upon the degree of metamorphism. which were obtained by crushing granite at two different localities: Hiroshima and Although further studies should be foInabu, Japan. This feature is similar to cussed on the CL of quartz in different CL images seen on thin sections of gran- types of rock at different localities, it is ite observed by the optical microscope of great significance to observe the CL of (SPRUNT & N U R 1979). quartz particles obtained from the rocks, TOVEY & KRINSLEY (1980) exper- in examining the metamorphic grade or imentally heated quartz grains above the the origin of granite or gneiss. t NIENA
A n I n t e r d i s c i p l i n a r y .Iourna] ~31"~,O11 S C I E N ( ! ~
HYDROLO(k';
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CL on Quartz Weathenng in Fault, Japan
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Photo 4: SE images belonging to Subgroup Ic (a and c) and Group III (e and f ) and CL images showing Types F4 (b) and F5 (d) of quartz grains from intrafault materials at Site 3. Scale: 100 I~m. b and d are the same fields as a and c, respectively.
CATENA
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Photo 5: CL images of quartz grains beJore ( a and c) and after ( b and d) polishing. Scale: 100 #m. a and b: a quartz grain from intrafautt materials derived from granodiorite at Site 1. c and d: a grain from intrafault materials derived from gneiss at Site 3.
6.1.2
CL cause by faulting
The CL image which is characterized by anastomosing dark bands in the faint background (CL type F5) is thought to be affected by the internal structure of the grains, because the image is not related to the SE image. This feature is not found on quartz particles obtained by crushing the parent rock, but is common to the fault outcrops at the three sites. This suggests that the feature may be caused by faulting (KANAORI 1986). Quartz grains in the parent rock have
t .\I'ENA
several dark bands in a CL image as mentioned above, though it is still unclear whether or not the parent rock is entirely free of stress. When the parent rock is stressed, it appears that the dark bands increase in number and are distributed anastomosingly in the CL image, to form this feature. 6.1.3
CL modified by weathering or alterations in the fault
Corrosion or precipitation attributed to groundwater forms various kinds of sur-
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CL on Quartz Weathering in Fault, Japan
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Photo 6: SE images (a to c) and a CL image (d) of quartz in a polished section of the parent rock, granodiorite at Site I. Scale of a: 500 #m. b: magnified part of c. Scale: 10/tm. An arrow indicates healed part. c: magnified part of the frame in a. Note network of healed cracks. Scale: 100 #m. d: similar field to c. Scale: 100/an. Some of dark bands correspond to healded cracks.
face textures on intrafault quartz grains (KANAORI et al. 1980, KANAORI 1983). Amorphous silica does not emit CL (GRANT & WHITE 1978, ZINKERNAGEL 1978, TOVEY & KRINSLEY 1980). A quartz grain in which dark areas alternate irregularly with bright areas in the CL images (CL type F3), has a slightly undulating surface in the SE image (photo 2a to 2d). Dark areas (CL type F2), or grains with an absence of CL (CL type F6), have a more undulating surface with well-
rounded comers or edges. This feature is formed by an amorphous film generated from a hydrate of silica, caused by dissolution of quartz in contact with groundwater, and precipitation of amorphous silica from groundwater. These features of the CL and SE images found on quartz grains in the fault are similar to those on quartz grains in sedimentary rocks or deposits, which were illustrated by KRINSLEY & HYDE (1971), KRINSLEY & DOORNKAMP (1973), KRINSLEY &
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Kanaort
TOVEY (1978) and TOVEY & KRINSLEY (1980).
6.2
6.2.1
DEVELOPMENT OF THE CL OF INTRAFAULT QUARTZ GRAINS CL development stage
It is assumed that quartz grains are formed from the breakage of quartz in the parent rock due to fault movement, with corrosion by groundwater occurring on the grain surface after the movement (KANAORI et al. 1980, KANAORI 1983, 1985). K A N A O R I (1984) observed CL images of quartz particles which were obtained by fracturing granite under confining pressures of 6, 10, and 15 MPa and at room temperature, and crushing it with an iron bar. If the grains are subjected to conditions which simulate those undergone by quartz particles which are produced naturally as a result of faulting, most grains are characterized by vague, dull contrast CL which masks the CL inherited from the parent rocks, while other grains display the inherited CL (KANAORI 1984). After this, dissolution of the grain surface caused by groundwater permeating into the fault begins, and the surface zone disrupted by fracturing is removed. This removal clarifies the CL of the parent rock. Further dissolution causes development of a hydrate of SiP2 on the surface, forming an amorphous silica film. In addition, precipitation of amorphous silica from groundwater adheres to the surface. The amorphous silica or overgrowth covers the original CL of the quartz of the parent rock. The more advanced the degree of dissolution or precipitation on the grain surfaces, the thicker the amorphous zone on the surface. This accounts for the absence of CL.
.\1 hNA
Four stages are tentatively classified in the development of the CL of quartz grains within the fault (tab.4).
6.2.2
CL stage development and surface texture change
As compared the CL image with the SE image on the same grain, characteristics of the SE image are described in each CL stage, and are classified on the basis of the standard established by KANAORI et al. (1980) and KANAORI (1983), as shown in tab.3. Fig.2 shows frequency distributions of surface texture groups in each CL type. SE image surface textures of quartz grains having CL features F1, F4 and F5 are categorized into Subgroups Ia to Ic, with a preponderance of Subgroup lb. Quartz grains with features F2 and F3 mainly indicate Subgroup Ic texture, while feature F6 shows Group II or more texture. The comparative results of CL, SE and reflective images are summarized in tab.4.
6.2.3
CL development stage and ESR age
K A N A O R I et al. (1985) examined the correlation between relative ages as determined by the surface texture groups and ages determined by the electron spin resonance (ESR) of quartz grains in the fault at Sites 1 and 3. The results can be interpreted to show that Subgroups Ia and Ib were stable during the period of 0.9 million ages (Ma), and changed through intermediate Subgroup lc in a period ranging from 0.9 to 1.2 Ma, and then to Group II after 1.2 Ma. Therefore, it is clear that surface texture groups can change from Subgroups Ia
All Interdisciplinary Jomnal ol SOIL SCIENCE
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CL on Quartz Weathering in Fault, Japan
13 Corrosion
Rupture
Texture
I
I
Ib
la I
Ic
II
III
IV
I I I I I I
Conehoidal Subeonchoidal O r a n g e peel
I I I I I I l I i I I I I 1 1 I
F i s h scale-like
Moss like Stalactitic Moth-eaten Pot-hole Coral-like
.--
I
Table 3: The shape, and classification of surface textures of quartz grains
(KANAORI 1983). Reflective image
SE image
C L image
Stage Stage 1
Transparent
The surface is fresh and smooth. The edges of the grain a n d ridges on the surface are extremely sharp.
Most grains have dull, vague contrast C L which masks the C L inherited from the parent rock, while other grains show the inherited CL.
Stage 2
Less transparent
Edges or ridges on the smooth surface are slightly blunted at each end.
The inherited C L becomes clear.
Stage 3
Translucent
The surface is partially smooth with small undulations.
D a r k areas alternating irregularly with bright areas mask the inherited CL.
Cloudy
The grain is r o u n d in shape and has an undulated surface.
The inherited C L is increasingly vague a n d ultimately is not emitted.
Stage 4
Tab. 4: Comparison of SE and CL images by the SEM and reflective image by the
optical microscope. and Ib through intermediate Subgroup Ic to Group II with increasing ESR age. The CL development stage agrees well with changes of SE image surface textures. On the basis of this agreement and the relation between ESR ages and the surface texture groups, the CL of intrafault quartz grains in Stage 1 for a short duration just after the faulting, CATENA
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changes through Stage 2, then changes to Stage 3 at around 0.9 Ma ESR age, and develops Stage 4 from about 1.2 Ma ESR age. In evaluation the relative age of the fault by noting differences in microstructures on the grains in the fault (KANAORI et al. 1980, KANAORI 1983), the formation age of quartz grains
HYDROLOGY~EOMORPHOLOGY
Kanaon
14
F3 F2,
FS:
I"~ a n d F(o: C L ~\' w c a t h o r l n q v[~e f a u l t . CL
feature
6IIt
f e a t u r e [odlt1~-d and a ] tetJt l©ns of
caused
by
F6
•
fau]tlnq.
<
I
F1 a n d F4: C L f e a t u r e i n h e r i t e d f r o m the p a r e n t r o c k .
•
~I I ,
F2 I
"I
.1
I,I
~:...
E .:.:L;~, '7[
•
50%
n=17
.
1/
F5 .:.:.:.:.: !:!:)~!: .:.:,:,,..:
:-$:~ .i....i.i. -.-.-.-.-.
~.:'.'~!'.-."."~:!:~:.~!:~
F4
-
. .......
rl z
~.
50%
n=~l /
Fig. 2: Histograms showing surface texture groups in each CL type. n: number of quartz grains observed. Surface texture groups are shown in tab.3.
/
/
Surface Texture Groups
should be known more concisely by observing CL images as well as SE images of the grain.
7
CONCLUSIONS
Characteristics have been described of CL images of quartz grains within the Atotsugawa fault of central Japan and those of quartz particles obtained by
t!Al
ENA
An
crushing parent rocks such as granite and gneiss. The CL images of the grains were found to be derived from three origins: CL inherited from the parent rocks, CL caused by faulting, and CL modified by weathering or alterations of the faults, as was evident from comparison with the CL of the quartz particles obtained from the parent roek. The CL observations were in general agreement with
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of SOIL
SCIENCE
HYDROLOGY
GEOMORPHOLOG~'
CL on Quartz Weathering in Fault, Japan
secondary electron observations; and it is recommended that both methods should be used in parallel. Although further studies should concentrate on observing CL of quartz grains from other large faults, both CL and SE images of quartz grains in the fault are an important clue to investigating mechanical and chemical histories that the fault has experienced since inception. ACKNOWLEDGEMENT
The author is thankful to Prof. S. Mizutani, Nagoya University, and Messrs S. Ogata and K. Kitano of the Siting Technology Dept., Central Research Institute of Electric Power Industry (CRIEPI), for their useful advice. Moreover, he would like to thank Messrs. Y. Satake, T. Kakuta, K. Miyakoshi, S. Inohara, K. Tanaka and M. Chigira of the CRIEPI for discussion. REFERENCES GRANT, P.R. & WHITE, S.H. (1978): Cathodoluminescence and microstructure of quartz overgrowth on quartz. Scanning Electron Microscopy, SEM Inc. AMF O'Hare, IL60666, Chicago, 189-194. HANUSIAK, W.M, & WHITE, W.E. (1975): SEM cathodoluminescence for characterisation of damaged and undamaged alpha quartz in respirable dusts. Scanning Electron Microscopy, Proceedings of 8th Annual SEM Symposium, IITRI, Chicago, 125-131. IKEYA, M , MIKI, T. & TANAKA, K. (1982): Dating a fault by electron spin resonance on intrafault materials. Science 215, 1392-1393. KANAORI, Y. (1983): Fracturing mode analysis and relative age dating of faults by surface textures of quartz grains from fault gouges. Engineering Geology 19, 261-281. KANAORI, Y. (1984): Activity evaluation of faults by cathodoluminescence (part II) characteristics of quartz particles obtained by fracturing of granite under confining pressures. Central
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Research Institute of Electric Power Industry, Report No. 381011, 18 p. KANAORI, Y. (1985): Surface textures of intrafault quartz grains as an indicator of fault movement. CATENA 12, 271-279. KANAORI, Y. (1986): A SEM cathodoluminescence study of quartz in mildly deformed granite from the region of the Atotsugawa fault, central Japan. Tectonophysics 131, 133-146. KANAORI, Y., MIYAKOSHI, K., KAKUTA, T. & SATAKE, Y. (1980): Dating fault activity by surface textures of quartz from fault gouges. Engineering Geology 16, 243-262. KANAORI, Y., INOHARA, Y., MIYAKOSHI, K. & SATAKE, Y. (1982a): Characteristics of intrafault materials within the Atotsugawa fault of central Japan (part I). Journal of the Japan Society of Engineering Geology 23, 137-155. KANAORI, Y., MIYAKOSHI, K., 1NOHARA, Y. & SATAKE, Y. (1952b): Characteristics of intrafault materials within the Atotsugawa fault of central Japan (part II). Journal of the Japan Society of Engineering Geology 23, 201-213. KANAORI, Y., TANAKA, K. & MIYAKOSHI, K. 0985): Further studies on use of quartz grains from fault gouges to establish the age of faulting. Engineering Geology 21, 175-194. KRINSLEY, D.H. & DOORNKAMP, J.C. (1973): Atlas of quartz sand surface textures. Cambridge University Press, Cambridge, 91 p. KRINSLEY, D.H. & HYDE, P. (1971): Cathodoluminescence studies of sediments. Scanning Electron Microscopy, Proceedings of 4th Annual SEM Symposium IITRI, Chicago, 409-416. KRINSLEY, D.H. & TOVEY, N.K. (1978): Cathodoluminescence in quartz sand grains. Scanning Electron Microscopy, SEM Inc. AMF O'Hare, IL60666, Chicago, 887-894. [MATSUDA 1966] MATSUDA, T.: Strike-slip faulting along the Atotsugawa fault Japan. Bulletin of Earthquake Research Institute 44, 11791212. MIYAKOSHI, K., INOHARA, Y. & SATAKE, Y. (1982): Characteristics and activity of the Atotsugawa fault - - description and analysis of fault outcrops. Central Research Institute of Electric Power Industry, Report No. 381036, 169 p. OGATA, S. (1976): Activity evaluation of faults in the basement terrain - - characteristics of its fracture thickness and filled materials. Journal of the Japan Society of Engineering Geology 17, 30-33.
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OGATA, S. & HONSHO, S. (1981): Fault activity evaluation in the case of electric power plants. Journal of the Japan Society of Engineering Geology 22, 67 87. SMART, P. & TOVEY, N.K. (1982): Electron Microscopy of soils and sediments: techniques. Claredon Press, Oxford, 264 p. SPRUNT, E.S. (1981): Causes of quartz cathodoluminescence colours. Scanning Electron Microscopy, SEM Inc., AMF O'Hare, Chicago, I L60666, 525-535. SPRUNT, E.S., DENGLER, L.A. & SLOAN, D. (1978): Effects of metamorphism on quartz cathodoluminescence. Geology 6, 305 308. SPRUNT, E.S. & NUR, A. (1979): Microcracking and healing in granite: new evidence from cathodoluminescence. Science 205, 495-497. SPRUNT, E.S. & BRACE, W.F. (1974): Direct observation of microcavities in crystalline rocks. International Journal of Rock Mechanics, Mining Science & Geomechanical Abstract 1 !. 139 150. TAPPONNIER, P. & BRACE, W.F. (1976): Development of stress-induced microcracks in Westerly granite. International Journal of Rock Mechanics, Mining Science & Geomechanical Abstract 13, 103 112. TOVEY, N.K. & KRINSLEY, D.H. (1980): A cathodoluminescent study of quartz sand grains. Journal of microscopy 120, 279-289. ZINKERNAGEL, U. (1978): Cathodoluminescence of quartz and its application to sandstone petrology. Contribution to Sedimentology, E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, 69 p.
Address of author: Yuji Kanaorl Department of Geological Sciences, Faculty of General Education, Gifu University, 1-1 Yanagido, Gifu City Gifu 501-11, Japan
('AIENA
An Interdisciplinary Journal of SOIL SCIENCE
HYDROLO(}Y
GEOMORPHOLOGY
vol. 15, p.l-16
Braunschweig 1988
A SEM CATHODOLUMINESCENCE STUDY ON WEATHERING OF QUARTZ GRAINS IN FAULTS, CENTRAL JAPAN Yuji Kanaori, Gifu-City SUMMARY Cathodoluminescence (CL) of quartz grains or particles was observed using a scanning electron microscope. The quartz grains were collected from fault gouge and fault breccia within the Atotsugawa fault, central Japan, and the quartz particles were obtained by crushing parent rocks of the fault, such as granite and gneiss, in an iron bowl. In comparison with particles from the parent rocks, those from the fault showed the following differences: CL inherited from the parent rock, CL caused by faulting, and CL modified by weathering or alterations of the fault. These differences are attributed to the faulting and subsequent weathering. The CL observations were in general agreement with secondary electron observations; and it is recommended that both methods should be used in parallel. 1
INTRODUCTION
Knowledge of when a fault moved is of great importance in preventing disasters caused by the associated earthquakes. ISSN0341-8162 @1988 by CATENAVERLAG, D-3302 Cremlingen-Destedt,W. Germany 0341-8162/88/5011851/US$ 2.00 + 0.25
When selecting sites for large constructions such as dams or nuclear power stations and determine the seismo-tectonic hazard of the area, it is extremely important to evaluate the activity of the faults distributed in and around the site, as well as to investigate the mechanical properties of the rocks containing the faults. In evaluating the movement age, it is necessary to investigate the properties of intrafault materials such as fault gouge and fault breccia (OGATA 1976, OGATA & HONSHO 1981) . Quartz grains found in fault gouges have been utilized in estimating the age of a fault using the electron spin resonance method (IKEYA et al. 1982), and to learn the relative age of the fault by noting differences in microtextures on the quartz grain surfaces using a scanning electron microscope (SEM) (KANAORI et al. 1980, 1985, KANAORI 1983, 1985). However, the formational processes of the gouges, including the quartz grains, are still not completely understood. Studies of cathodoluminescence (CL) of quartz grains using the SEM were undertaken for sedimentary rocks and deposits by KRINSLEY & HYDE (1971), KRINSLEY & TOVEY (1978), and TOVEY & KRINSLEY (1980). They showed that the CL image was affected
C A T E N A - - A n Interdisciplinary Journal o f S O I L S C I E N C E - - H Y D R O L O O Y - - G E O M O R P H O L O G Y
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by forces that the quartz grains experienced during transportation or sedimentation processes. In this study, CL imges as well as secondary electron (SE) images of quartz grains or particles were observed using the SEM. The quartz grains were selected from intrafault materials within the Atotsugawa fault at three outcrop sites (Sites 1, 2 and 3 in fig.l), and the quartz particles were obtained by crushing samples of the parent rocks, such as granite and gneiss, from each of three sites in an iron bowl. The geology of the outcrops and properties of the intrafault materials are reported in detail by KANAORI et al. (1982a, b) and MIYAKOSHI et al. (1982). A search of the literature has not uncovered previous studies of CL images of quartz grains within faults. The CL observations reported in this paper are a new attempt to investigate quartz grains in faults. Furthermore, quartz grains from decomposed granite and from secondary deposits of coarse sands sampled at Site 4 in fig.1 were observed with the same methods used for the intrafault material study. Characteristics of the CL of quartz grains or particles obtained are here described, and the origin of the CL and its development in the samples is considered.
cence and can be understood in terms of the electric bond structure of the solid (SMART & TOVEY 1982). Spectra of the CL emitted from quartz show two emission maxima: (1) in the blue range (430-360 nm), and (2) in the red (610-630 nm), though the spectra depend upon the origin of quartz (ZINKERNAGEL 1978). The CL contrast of quartz is influenced by impurity contents such as Ti and Fe (SPRUNT 1981). When quartz is stressed, the CL alters (SMART & TOVEY 1982, TOVEY & KRINSLEY 1980). For example, HANUSIAK & WHITE (1975) showed that the CL image of damaged c~-quartz was brighter than that of undamaged a-quartz.
3
SAMPLE LOCALITIES AND SAMPLES
The Atotsugawa fault, one of the most widely known active faults, in Japan, extends over 60 km in length (MATSUDA 1966, MIYAKOSHI et al. 1982). The fault probably moved in 1858 at the time of the Hida Earthquake (M = 6.9) (MATSUDA 1966). Remarkable topographic changes caused by faulting can be seen along the entire fault trace (MATSUDA 1966). The sampling sites are described below. Site 1 is a fresh roadcut near the north end of the Atotsugawa fault, in the vicinCATHODOity of the Magawa river, in the southern LUMINESCENCE OF region of Kaminiikawa-Gun, Toyama. At this site, the fault clearly separates QUARTZ Mesozoic granodiorite distributed in the Long-wavelength photons are emitted in northern part of the fault from prethe visible regions of the spectrum when Pleistocene gravel beds distributed in the electrons hit the specimen. This phe- southern part by a single plane (this nomenon is known as cathodolumines- plane is called the "main fault plane" CA'I ENA
An Interdisciplinary Journal of SOIL SCIENCE
HYDROLOGY- G E O M O R P H O L O G Y
CL on Quartz Weathering in Fault, Japan
3
N Toyomo
//)
H°~us(:n\
• Tokoyomo
Yokedoke --360N
Gifu
~
'
\ 136
I
138 °
140 °
I
137*E
138OE
Fig. 1: Location of sampling sites (1 to 4) and lineaments around the Atotsugawa fault (Ato). in this paper). In the boundary between the granodiorite and the gravel beds, is found a zone composed of fine-grained, yellow to yellowish brown gouge materials, 2 to 3 cm in width. The main fault strike is N74°E and the dip. 86°SE. Grains found in gravel beds 10 cm from the plane are fractured and pulverized. The granodiorite up to 13 m from the fault plane is soft and intruded by lamprophyre. Several fracture zones with a width of 10 to 100 cm, and with the same strike as the main fault plane are distributed in the area approximately 100 m from the site.
gouge materials, white to bluish grey in colour, and about 20 cm in width, exists in granite. The fault strike is EW and dips 90 ° . Sound limestone outcrops to the southeast, 3.0 m from the fault. There are no sections showing the transition from the granite into the limestone. The Atotsugawa fault is inferred to pass through this zone of no outcrop, just to the south of Site 2.
Site 3 is located in the vicinity of the southwestern end of the Atotsug~ awa fault, in the bed of the Amodani river, in Yoshiki-Gun, Gifu. The fault passes through gneiss, granite, limestone Site 2 is located on the fight bank and porphyrite dikes intruding into these of the Miyakawa fiver, in Yoshiki-Gun, rocks. The fault is composed of five fracGifu. A fault composed of fine-grained, ture zones each having a width of several C A T E N A - - A n I n t e r d i s c i p l i n a r y Journal o f S O I L S C I E N C E - - H Y D R O L O G Y ~ E O M O R P H O L O G y
142 ~
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metres. The total width of the fault is about 30 m. The strikes of these fracture zones are generally N70°-80°E and the dip 60°--80°NW or SE. Site 4 is located in the vicinity of Shogenji, Sakashita, Gifu. Samples derived from the decomposed granite maintain their original structures, but can be crumbled easily by hand. Sample descriptions are listed in tab.1. 4
preparation. Because such a mottled CL image did not appear on any grains or particles observed in this study, it is inferred that the ultrasonic cleaning did not alter the CL images of the grains or particles. 5 5.1
RESULTS IMAGES OF QUARTZ GRAINS W I T H I N T H E FAULT
METHOD
CL images characteristic of quartz grains found within the fault are shown in Intrafault materials were put into a phot.1 to 4. In these photos, SE images beaker with sufficient water to cause disof the same fields as the CL images are persion of the grains, while samples of shown, in order to compare both images. parent rocks were crushed with an iron The following six types of CL charbar in an iron bowl until reduced to paracteristics are recognized on the quartz ticles. Grains and particles with size befrom within the fault. tween 250 and 850 #m were then selected (F1) Several dark bands or spots are using Tyler sieves. The selected samples recognized in the bright background were then immersed in a solution of 10% (phot.1). HC1 at room temperature to remove car(F2) Dark areas are found in the bright bonate completely, and cleaned in an ultrasonic bath of distilled water for about background (phot.2d). (F3) Dark areas alternate irregularly 10 min. Then, the grains or particles were completely dried after washing, and 10 with bright areas (phot.2b). (F4) Several dark bands are recognized to 15 quartz grains or particles of each sample were randomly selected under an in the faint background (phot.4b). (F5) Numerous dark bands are developtical microscope. The quartz grains or particles were stuck on a sample stub for oped anastomosingly in the faint backthe SEM. They were coated with a 20 to ground (phot.3b and 4d). (F6) CL is not emitted. It was impos40 nm thickness of gold (Au) and were examined at an accelerating voltage of sible to photograph the quartz grains, 25 KeV on a JEOL T-100 SEM, having therefore, only SE images are shown in a photomultiplier with a detecting wave- phot.4ef. length of 400 to 650 nm. Tab.2 indicates grain occurrence numPolished sections of the parent rocks ber of the CL type at each site, The numwere also examined by the same method. ber of samples and grains observed are K R I N S L E Y & TOVEY (1978) indi- variable among sampling sites. Features cated that a mottled CL image, in which of F1 and F3 are found on all samples a small black area irregularly alternated at Site 1, except for one. Feature F5 is with a bright area, appeared on quartz recognized on quartz grains from only grains fractured accidentally during ul- one sample at Site 1, a sample at Site 2 trasonic cleanings at the time of sample and most samples at Site 3; Only this CA'I I:NA
An Interdisciplinary Journal of SOIL SCIENCE
HYDROLOGY GEOMORPHOLOGY
CL on Quartz Weathering in Fault, Japan
Sample locality
Number of samples
5
Geological description
Site 1
12 1 1 4
Fault gouge and fault breccia derived from granodiorite within the Atotsugawa fault Decomposed granodiorite. Matrix of gravel beds. Parent rock, granodiorite.
Site 2
1
Fault gouge derived from granite in an area just north of the Atotsugawa fault.
Site 3
18
Fault gouge and fault breccia derived from gneiss, granite and prophyrite dike within the Atotsugawa fault. Parent rock, gneiss Parent rock, granite
Site 4
2
Decomposed granite. Coarse sands of secondary deposits derived from the decomposed granite.
1
Tab. 1: A list of samples collected. Sample locality
Rock type
Site 1
Intrafault materials Decomposed granodiorite Matrix of gravel beds Parent rock, granodiorite
Number of samples*
F1
F2
CL types F3 F4
12(6o) 1(5) 1(5) 4(6)
24 3 5 16
10 2 0
16 0 0
F5
F6
0 0 0 0
8 0 0
2 0 0 0
Site 2
Intrafault materials
1(13)
0
0
0
0
13
0
Site 3
Intrafault materials Parent rock, gneiss Parent rock, granite
18(83) 3(12) 3(12)
7
0
1
39
22
14
Decomposed granite Secondary deposit
2(4) 1(6)
4 4
Site 4
1
7
4
5
5
3
0 0
0 0
1
1
Tab. 2: CL type occurrence at each site. * The number of quartz grains observed in detail is given in parentheses.
feature is common to all three outcrop sites of the fault. Features F4 and F6 are commonly found on samples at Site 3.
5.2
CL OF QUARTZ PARTICLES OBTAINED BY CRUSHING PARENT ROCKS
Because features F1, F4 and F5 are CL images of quartz particles obtained not related to the SE images, these fea- by crushing parent rocks depend upon tures are probably controlled by the in- the type of parent rock and are specific ternal structures of the grains. to each locality. Among the six CL types Dark areas in features F2 and F3 cor- found in the fault, three CL types F1, respond to undulated areas in the SE F4 and F6 are usually recognized in the images (phot.2). Grains with feature F6 quartz particles from the parent rocks are characterized with considerably un- (tab.2). dulated surfaces, well rounded comers All quartz particles obtained from graand ridges in the SE image. nodiorite at Site 1 display the feature CATENA -- An Interdisciplinary Journal of SOIL SCIENCE--HYDROLOGY~EOMORPHOLOGY
6
Kanaori
Photo 1: SE images belonging to Subgroup lh (c) and CL images showing Type F1 (b and d) of quartz grains or particles at Site 1. Scale: 100#m. b and d are the same fields as a and c, respectively, a and b: quartz particles by crushing granodiorite, c and d: quartz grains from intrafault materials. Explanation of SE groups and CL types appears in the text.
of CL type F1 (phot.l). The feature is commonly recognized in the quartz grains obtained, not only from gravel bed matrix at Site 1, but also from decomposed granite and secondary deposits of coarse sands at Site 4. Almost half of quartz particles which were obtained from gneiss and granite at Site 3 display CL type F4 feature. Some quartz particles from gneiss and granite at Site 3 display CL type F6 feature.
CATENA
5.3
CL IMAGES OF POLISHED SECTIONS
Observation of polished quartz grains revealed that almost all dark bands penetrate the grains (phot.5). As shown in phot.6, some dark bands correspond to healed cracks in the parent rock (SPRUNT & BRACE 1974, TAPPONNIER & BRACE 1976, SPRUNT & NUR 1979, TOVEY & KRINSLEY 1980, KANAORI 1986).
An Interdisciplinary Journal of SOIL SCIENCE HYDROLOGY
GEOMORPHOLOGY
CL on Quartz Weathering in Fault, Japan
7
Photo 2: SE images belonging to Subgroup Ic (a and c) and CL .images showing Types F3 (b) and F2 (d) of quartz grains from intrafault materials at Site 1. Scale: 100 #m. b and d are the same fields as a and e, respectively.
5.4
COMPARISON OF CL BETWEEN PARENT ROCKS AND FAULT
CL types F1, F4 and F6 are commonly found in both quartz particles obtained from crushing parent rocks and those in the fault. These CL features are essentially inherited from those of the parent rocks. CL type F6 feature found on some quartz grains within the fault forms by modification of the fault, as will be mentioned latter, while the feature found on quartz particles from the parent rocks
is originally inherited from the gneiss. Other features F2, F3 and F5 are characteristics of the CL images ot" quartz grains in the fault.
6
6.1
INTERPRETATION DISCUSSION
AND
CL ORIGIN OF QUARTZ GRAINS WITHIN THE FAULT
As is evident from the comparison of the CL between parent rocks and the fault,
CATENA -- An Interdisciplinary Journal of SOIL SCIENCE--HYDROLOGY~EOMORPHOLOGY
8
Kanaori
Photo 3: SE image belonging to Subgroup Ib (a) and CL image showing Type F5 (b ) of quartz grains./horn intrafault materials at Site 1. Scale: 100 #m. b is t h e s a m e field a s a.
the CL of quartz grains in the fault is derived from three origins; CL inherited from the parent rock, CL caused by faulting, and CL modified by weathering or alterations in the fault. 6.1.1
CL inherited from the parent rock
fl - ? transition temperature and eventually revealed that some grains showed a marked change and even a complete reversal in CL contrast. Quartz particles obtained from gneiss at Site 3 do not emit CL, while those from granite at the same site are characterized by the faint CL. Quartz particles obtained from granodiorite at Site 1, and from granite at localities, reported by KANAORI (1984), show the bright CL.
Characteristics in which several dark bands or spots are recognized in the bright background (CL type F1), is common to quartz grains from intrafault maSPRUNT et al. (1978) found that terials and quartz particles at Site 1 ob- metamophism appeared to homogenize tained by crushing parent rocks. This CL with colour being related to metafeature is thought to be inherited from morphic grade - low temperature causing the CL of quartz in granodiorite. red CL and high temperature, blue. this This feature has been also recognized suggests that the CL contrast depends by KANAORI (1984) on quartz particles upon the degree of metamorphism. which were obtained by crushing granite at two different localities: Hiroshima and Although further studies should be foInabu, Japan. This feature is similar to cussed on the CL of quartz in different CL images seen on thin sections of gran- types of rock at different localities, it is ite observed by the optical microscope of great significance to observe the CL of (SPRUNT & N U R 1979). quartz particles obtained from the rocks, TOVEY & KRINSLEY (1980) exper- in examining the metamorphic grade or imentally heated quartz grains above the the origin of granite or gneiss. t NIENA
A n I n t e r d i s c i p l i n a r y .Iourna] ~31"~,O11 S C I E N ( ! ~
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I~EI)MORPHOLOGY
CL on Quartz Weathenng in Fault, Japan
9
Photo 4: SE images belonging to Subgroup Ic (a and c) and Group III (e and f ) and CL images showing Types F4 (b) and F5 (d) of quartz grains from intrafault materials at Site 3. Scale: 100 I~m. b and d are the same fields as a and c, respectively.
CATENA
An Interdisciplinary Journal of SOIL S C I E N C E - - H Y D R O L O G y ~ E O M O R P H O L O G Y
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Kanaori
Photo 5: CL images of quartz grains beJore ( a and c) and after ( b and d) polishing. Scale: 100 #m. a and b: a quartz grain from intrafautt materials derived from granodiorite at Site 1. c and d: a grain from intrafault materials derived from gneiss at Site 3.
6.1.2
CL cause by faulting
The CL image which is characterized by anastomosing dark bands in the faint background (CL type F5) is thought to be affected by the internal structure of the grains, because the image is not related to the SE image. This feature is not found on quartz particles obtained by crushing the parent rock, but is common to the fault outcrops at the three sites. This suggests that the feature may be caused by faulting (KANAORI 1986). Quartz grains in the parent rock have
t .\I'ENA
several dark bands in a CL image as mentioned above, though it is still unclear whether or not the parent rock is entirely free of stress. When the parent rock is stressed, it appears that the dark bands increase in number and are distributed anastomosingly in the CL image, to form this feature. 6.1.3
CL modified by weathering or alterations in the fault
Corrosion or precipitation attributed to groundwater forms various kinds of sur-
A n Interdisciplinary Journal ol S O I L S C I E N C E
HYDROLOGY
GEOMORPHOLOGY
CL on Quartz Weathering in Fault, Japan
11
Photo 6: SE images (a to c) and a CL image (d) of quartz in a polished section of the parent rock, granodiorite at Site I. Scale of a: 500 #m. b: magnified part of c. Scale: 10/tm. An arrow indicates healed part. c: magnified part of the frame in a. Note network of healed cracks. Scale: 100 #m. d: similar field to c. Scale: 100/an. Some of dark bands correspond to healded cracks.
face textures on intrafault quartz grains (KANAORI et al. 1980, KANAORI 1983). Amorphous silica does not emit CL (GRANT & WHITE 1978, ZINKERNAGEL 1978, TOVEY & KRINSLEY 1980). A quartz grain in which dark areas alternate irregularly with bright areas in the CL images (CL type F3), has a slightly undulating surface in the SE image (photo 2a to 2d). Dark areas (CL type F2), or grains with an absence of CL (CL type F6), have a more undulating surface with well-
rounded comers or edges. This feature is formed by an amorphous film generated from a hydrate of silica, caused by dissolution of quartz in contact with groundwater, and precipitation of amorphous silica from groundwater. These features of the CL and SE images found on quartz grains in the fault are similar to those on quartz grains in sedimentary rocks or deposits, which were illustrated by KRINSLEY & HYDE (1971), KRINSLEY & DOORNKAMP (1973), KRINSLEY &
C A T E N A - - A n Interdisciplinary J o u r n a l o f S O I L S C I E N C E - - H Y D R O L O G Y ~ E O M O R P H O L O G Y
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Kanaort
TOVEY (1978) and TOVEY & KRINSLEY (1980).
6.2
6.2.1
DEVELOPMENT OF THE CL OF INTRAFAULT QUARTZ GRAINS CL development stage
It is assumed that quartz grains are formed from the breakage of quartz in the parent rock due to fault movement, with corrosion by groundwater occurring on the grain surface after the movement (KANAORI et al. 1980, KANAORI 1983, 1985). K A N A O R I (1984) observed CL images of quartz particles which were obtained by fracturing granite under confining pressures of 6, 10, and 15 MPa and at room temperature, and crushing it with an iron bar. If the grains are subjected to conditions which simulate those undergone by quartz particles which are produced naturally as a result of faulting, most grains are characterized by vague, dull contrast CL which masks the CL inherited from the parent rocks, while other grains display the inherited CL (KANAORI 1984). After this, dissolution of the grain surface caused by groundwater permeating into the fault begins, and the surface zone disrupted by fracturing is removed. This removal clarifies the CL of the parent rock. Further dissolution causes development of a hydrate of SiP2 on the surface, forming an amorphous silica film. In addition, precipitation of amorphous silica from groundwater adheres to the surface. The amorphous silica or overgrowth covers the original CL of the quartz of the parent rock. The more advanced the degree of dissolution or precipitation on the grain surfaces, the thicker the amorphous zone on the surface. This accounts for the absence of CL.
.\1 hNA
Four stages are tentatively classified in the development of the CL of quartz grains within the fault (tab.4).
6.2.2
CL stage development and surface texture change
As compared the CL image with the SE image on the same grain, characteristics of the SE image are described in each CL stage, and are classified on the basis of the standard established by KANAORI et al. (1980) and KANAORI (1983), as shown in tab.3. Fig.2 shows frequency distributions of surface texture groups in each CL type. SE image surface textures of quartz grains having CL features F1, F4 and F5 are categorized into Subgroups Ia to Ic, with a preponderance of Subgroup lb. Quartz grains with features F2 and F3 mainly indicate Subgroup Ic texture, while feature F6 shows Group II or more texture. The comparative results of CL, SE and reflective images are summarized in tab.4.
6.2.3
CL development stage and ESR age
K A N A O R I et al. (1985) examined the correlation between relative ages as determined by the surface texture groups and ages determined by the electron spin resonance (ESR) of quartz grains in the fault at Sites 1 and 3. The results can be interpreted to show that Subgroups Ia and Ib were stable during the period of 0.9 million ages (Ma), and changed through intermediate Subgroup lc in a period ranging from 0.9 to 1.2 Ma, and then to Group II after 1.2 Ma. Therefore, it is clear that surface texture groups can change from Subgroups Ia
All Interdisciplinary Jomnal ol SOIL SCIENCE
HYDROLOGY GEOMORPHOLOGY
CL on Quartz Weathering in Fault, Japan
13 Corrosion
Rupture
Texture
I
I
Ib
la I
Ic
II
III
IV
I I I I I I
Conehoidal Subeonchoidal O r a n g e peel
I I I I I I l I i I I I I 1 1 I
F i s h scale-like
Moss like Stalactitic Moth-eaten Pot-hole Coral-like
.--
I
Table 3: The shape, and classification of surface textures of quartz grains
(KANAORI 1983). Reflective image
SE image
C L image
Stage Stage 1
Transparent
The surface is fresh and smooth. The edges of the grain a n d ridges on the surface are extremely sharp.
Most grains have dull, vague contrast C L which masks the C L inherited from the parent rock, while other grains show the inherited CL.
Stage 2
Less transparent
Edges or ridges on the smooth surface are slightly blunted at each end.
The inherited C L becomes clear.
Stage 3
Translucent
The surface is partially smooth with small undulations.
D a r k areas alternating irregularly with bright areas mask the inherited CL.
Cloudy
The grain is r o u n d in shape and has an undulated surface.
The inherited C L is increasingly vague a n d ultimately is not emitted.
Stage 4
Tab. 4: Comparison of SE and CL images by the SEM and reflective image by the
optical microscope. and Ib through intermediate Subgroup Ic to Group II with increasing ESR age. The CL development stage agrees well with changes of SE image surface textures. On the basis of this agreement and the relation between ESR ages and the surface texture groups, the CL of intrafault quartz grains in Stage 1 for a short duration just after the faulting, CATENA
An Interdisciplinary Journal of SOIL SCIENCE
changes through Stage 2, then changes to Stage 3 at around 0.9 Ma ESR age, and develops Stage 4 from about 1.2 Ma ESR age. In evaluation the relative age of the fault by noting differences in microstructures on the grains in the fault (KANAORI et al. 1980, KANAORI 1983), the formation age of quartz grains
HYDROLOGY~EOMORPHOLOGY
Kanaon
14
F3 F2,
FS:
I"~ a n d F(o: C L ~\' w c a t h o r l n q v[~e f a u l t . CL
feature
6IIt
f e a t u r e [odlt1~-d and a ] tetJt l©ns of
caused
by
F6
•
fau]tlnq.
<
I
F1 a n d F4: C L f e a t u r e i n h e r i t e d f r o m the p a r e n t r o c k .
•
~I I ,
F2 I
"I
.1
I,I
~:...
E .:.:L;~, '7[
•
50%
n=17
.
1/
F5 .:.:.:.:.: !:!:)~!: .:.:,:,,..:
:-$:~ .i....i.i. -.-.-.-.-.
~.:'.'~!'.-."."~:!:~:.~!:~
F4
-
. .......
rl z
~.
50%
n=~l /
Fig. 2: Histograms showing surface texture groups in each CL type. n: number of quartz grains observed. Surface texture groups are shown in tab.3.
/
/
Surface Texture Groups
should be known more concisely by observing CL images as well as SE images of the grain.
7
CONCLUSIONS
Characteristics have been described of CL images of quartz grains within the Atotsugawa fault of central Japan and those of quartz particles obtained by
t!Al
ENA
An
crushing parent rocks such as granite and gneiss. The CL images of the grains were found to be derived from three origins: CL inherited from the parent rocks, CL caused by faulting, and CL modified by weathering or alterations of the faults, as was evident from comparison with the CL of the quartz particles obtained from the parent roek. The CL observations were in general agreement with
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CL on Quartz Weathering in Fault, Japan
secondary electron observations; and it is recommended that both methods should be used in parallel. Although further studies should concentrate on observing CL of quartz grains from other large faults, both CL and SE images of quartz grains in the fault are an important clue to investigating mechanical and chemical histories that the fault has experienced since inception. ACKNOWLEDGEMENT
The author is thankful to Prof. S. Mizutani, Nagoya University, and Messrs S. Ogata and K. Kitano of the Siting Technology Dept., Central Research Institute of Electric Power Industry (CRIEPI), for their useful advice. Moreover, he would like to thank Messrs. Y. Satake, T. Kakuta, K. Miyakoshi, S. Inohara, K. Tanaka and M. Chigira of the CRIEPI for discussion. REFERENCES GRANT, P.R. & WHITE, S.H. (1978): Cathodoluminescence and microstructure of quartz overgrowth on quartz. Scanning Electron Microscopy, SEM Inc. AMF O'Hare, IL60666, Chicago, 189-194. HANUSIAK, W.M, & WHITE, W.E. (1975): SEM cathodoluminescence for characterisation of damaged and undamaged alpha quartz in respirable dusts. Scanning Electron Microscopy, Proceedings of 8th Annual SEM Symposium, IITRI, Chicago, 125-131. IKEYA, M , MIKI, T. & TANAKA, K. (1982): Dating a fault by electron spin resonance on intrafault materials. Science 215, 1392-1393. KANAORI, Y. (1983): Fracturing mode analysis and relative age dating of faults by surface textures of quartz grains from fault gouges. Engineering Geology 19, 261-281. KANAORI, Y. (1984): Activity evaluation of faults by cathodoluminescence (part II) characteristics of quartz particles obtained by fracturing of granite under confining pressures. Central
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Research Institute of Electric Power Industry, Report No. 381011, 18 p. KANAORI, Y. (1985): Surface textures of intrafault quartz grains as an indicator of fault movement. CATENA 12, 271-279. KANAORI, Y. (1986): A SEM cathodoluminescence study of quartz in mildly deformed granite from the region of the Atotsugawa fault, central Japan. Tectonophysics 131, 133-146. KANAORI, Y., MIYAKOSHI, K., KAKUTA, T. & SATAKE, Y. (1980): Dating fault activity by surface textures of quartz from fault gouges. Engineering Geology 16, 243-262. KANAORI, Y., INOHARA, Y., MIYAKOSHI, K. & SATAKE, Y. (1982a): Characteristics of intrafault materials within the Atotsugawa fault of central Japan (part I). Journal of the Japan Society of Engineering Geology 23, 137-155. KANAORI, Y., MIYAKOSHI, K., 1NOHARA, Y. & SATAKE, Y. (1952b): Characteristics of intrafault materials within the Atotsugawa fault of central Japan (part II). Journal of the Japan Society of Engineering Geology 23, 201-213. KANAORI, Y., TANAKA, K. & MIYAKOSHI, K. 0985): Further studies on use of quartz grains from fault gouges to establish the age of faulting. Engineering Geology 21, 175-194. KRINSLEY, D.H. & DOORNKAMP, J.C. (1973): Atlas of quartz sand surface textures. Cambridge University Press, Cambridge, 91 p. KRINSLEY, D.H. & HYDE, P. (1971): Cathodoluminescence studies of sediments. Scanning Electron Microscopy, Proceedings of 4th Annual SEM Symposium IITRI, Chicago, 409-416. KRINSLEY, D.H. & TOVEY, N.K. (1978): Cathodoluminescence in quartz sand grains. Scanning Electron Microscopy, SEM Inc. AMF O'Hare, IL60666, Chicago, 887-894. [MATSUDA 1966] MATSUDA, T.: Strike-slip faulting along the Atotsugawa fault Japan. Bulletin of Earthquake Research Institute 44, 11791212. MIYAKOSHI, K., INOHARA, Y. & SATAKE, Y. (1982): Characteristics and activity of the Atotsugawa fault - - description and analysis of fault outcrops. Central Research Institute of Electric Power Industry, Report No. 381036, 169 p. OGATA, S. (1976): Activity evaluation of faults in the basement terrain - - characteristics of its fracture thickness and filled materials. Journal of the Japan Society of Engineering Geology 17, 30-33.
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Kanaori
OGATA, S. & HONSHO, S. (1981): Fault activity evaluation in the case of electric power plants. Journal of the Japan Society of Engineering Geology 22, 67 87. SMART, P. & TOVEY, N.K. (1982): Electron Microscopy of soils and sediments: techniques. Claredon Press, Oxford, 264 p. SPRUNT, E.S. (1981): Causes of quartz cathodoluminescence colours. Scanning Electron Microscopy, SEM Inc., AMF O'Hare, Chicago, I L60666, 525-535. SPRUNT, E.S., DENGLER, L.A. & SLOAN, D. (1978): Effects of metamorphism on quartz cathodoluminescence. Geology 6, 305 308. SPRUNT, E.S. & NUR, A. (1979): Microcracking and healing in granite: new evidence from cathodoluminescence. Science 205, 495-497. SPRUNT, E.S. & BRACE, W.F. (1974): Direct observation of microcavities in crystalline rocks. International Journal of Rock Mechanics, Mining Science & Geomechanical Abstract 1 !. 139 150. TAPPONNIER, P. & BRACE, W.F. (1976): Development of stress-induced microcracks in Westerly granite. International Journal of Rock Mechanics, Mining Science & Geomechanical Abstract 13, 103 112. TOVEY, N.K. & KRINSLEY, D.H. (1980): A cathodoluminescent study of quartz sand grains. Journal of microscopy 120, 279-289. ZINKERNAGEL, U. (1978): Cathodoluminescence of quartz and its application to sandstone petrology. Contribution to Sedimentology, E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, 69 p.
Address of author: Yuji Kanaorl Department of Geological Sciences, Faculty of General Education, Gifu University, 1-1 Yanagido, Gifu City Gifu 501-11, Japan
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