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| Titel |
Changes in pH and ion composition in liquid media caused by mineral grinding: its dependency to mineral species |
| VerfasserIn |
T. Saito, H. Tanaka |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030694
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| Zusammenfassung |
| In natural fault zone, rocks and minerals were fractured by seismic slip, resulting in increase
in surface area of minerals. Increasing in surface area cause minerals to be chemically
activated. Therefore, fluid-rock interaction is enhanced in fluid-rich area such as subduction
zone and shallow intra-plate fault zone. Fluid-rock interaction would change the physical and
chemical properties of the fault zone materials. Therefore, fluid-rock reaction is important for
understanding feedback relationship during earthquake cycle. However, the fundamental
chemical processes of fluid-rock interaction caused by fracturing are still poorly understood.
In natural fault zones, fault gouges are found as one of the pulverized rock. Fault
gouges is also considered as a product of chemical reactions between rocks and
surrounding groundwater. However, these chemical reactions are not completely
understood.
In this study, we concentrated on changes in fluid media by rock fracturing with water,
especially changes in pH and dissolved chemical composition.
The questions concerning changes in fluid media are addressed in this study: (1) what
type chemical process is dominant? (2) To what extent is fluid-rock interaction depend on
mineral species. To answer these questions, we conducted grinding experiment, which
analogous to pulverization in natural fault.
We performed grinding experiment using ball mill to investigate fluid-mineral interaction
accompanied by mineral fracturing. Starting materials are silicate minerals (quartz,
plagioclase, alkali feldspar, biotite, muscovite, and mixture of quartz and other minerals) as
solid media, and pure water as fluid media. In regard to the mixture samples of quartz and
other minerals, several mixing ration was used. We measure pH and chemical composition in
water after grinding experiment.
Results of experiment showed that pH changes in fluid media and chemical composition.
Result of quartz experiment showed pH decrease. Result of plagioclase, alkali feldspar,
biotite, muscovite other minerals, which contain metal ion showed increase in pH. These
results about pH were corresponding to previous work (Saruwatari et al., 2003, 2004). Results
of plagioclase, alkali feldspar, biotite, muscovite showed increase in ion concentration.
Results of mixture of quartz and minerals that contain metal ion showed the value between
result of quartz and that of other minerals.
These experimental results demonstrate that the mixing ratio of quartz and other minerals
affect pH and ion composition in fluid media after grinding. The pH value may strongly
affects chemical processes such as precipitation and dissolution of minerals in fault zone after
seismic slip occurred. According to the experimental results discussed above, mineral
composition of rocks in fault zone may be crucial for chemical process after seismic slip
(especially, immediately after seismic slip).
However, the timescale in these chemical processes is still unknown. We will discuss in
presentation that application of these experimental results to natural brittle fault zone. |
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