Tim Horner CSUS Geology Department Geologic Structures Physical Geology, Chapter 15.
Geology, geologic structure, and hot springs in southern...
Transcript of Geology, geologic structure, and hot springs in southern...
,� ������������Geology, geologic structure, and hot springs in southern
Kyushu, Japan
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Tetsuo KOBAYASHI+ and Toru YANO
,
+ Earth and environmental Sciences, Faculty of Science, Kagoshima University
+�,+�-/, korimoto, Kagoshima 23*�**0/, Japan, Kagoshima Prefectural Police +*�+, Kamoike-shinmachi, Kagoshima 23*�2/00, Japan
Abstract
The geology, geologic structure, and hot springs in southern Kyushu are discussed in
this paper. The basement rocks of this area are composed mainly of the sedimentary
complexes of the Shimanto Terrane which is divided into two groups : Cretaceous North-
ern Shimanto Terrane and Tertiary Southern Shimanto Terrane. The graben structures
in southern Kyushu have been formed in relation to the opening of the Okinawa Trough
since ca. +* Ma, and followed by contemporaneous volcanism. Volcanism was most active
in between . Ma and , Ma which formed the fundamental graben structure such as Hoku-
satsu Triangular Graben, Hitoyoshi basin, and Kagoshima Graben. Since , Ma, the volcan-
ism within the Kagoshima Graben became most active involving at least three calderas :
Ata, Aira, and Kakuto calderas from south to north. Active volcanoes also exist in this
graben, indicating an active volcano-tectonic depression.
Most hot springs in southern Kyushu are distributed in these grabens, suggesting an
intimate genetic relation between volcanism and hot springs. The heat supply of the hot
springs from the basement rocks is sourced not only from the present magma, but also
from Tertiary granites.
Key words : Shimanto Terrane, Kagoshima Graben, Hokusatsu Triangular Graben,
Okinawa Trough, hot spring
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from Kimura, +32/). Legend + : central graben, , : basin occupied by Pleistocene igneous intrusions,
- : major fault and fault scarp, . : buried major fault and fault scarp, / : eastern boundary of the Ryu-
kyu Ridge, 0 : trench, 1 : active volcanoes, 2 : submarine intrusions or volcanoes since Late Pleisto-
cene time, TG : Tokara Gap, KG : Kerama Gap.
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Fig. , Geologic sketch map of southern Kyushu indicating the distribution of Kagoshima Graben
(modified from Tsuyuki, +303). B : Basement sedimentary complexes of the Shimanto Terrane
and the Chichibu Terrane of Triassic to Tertiary ages, G : Tertiary granitic rocks, V : volcanic
rocks, Kr : Kirishima volcano, S : Sakurajima volcano, Km : Kaimondake volcano,
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Fig. - Distribution of crustal extension of Okinawa Trough and associated
paleomagnetism (after Kamata and Kodama, +33-). Open arrow with PHS
shows the present subduction direction of the Philippine Sea plate.
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Fig. . Contour line map of the basement rocks in southern Kyushu based on drilling data for
hot springs. Figures in parentheses from Kubota (+320) and Agency for Natural Resources
and Energy (+322). H : Hokusatu Triangular Graben, K : Kagoshima Graben.
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Fig. / Distribution of the Kagoshima graben, caldera structure, and Curie point
depths in southern Kyushu (modified from Kubota, ,**0). + : active volcano,
, : graben, - : fault, . : caldera and estimated caldera, / : Cretaceous to Ter-
tiary basement rocks, 0 : Curie point depth (contour interval is + km).
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Fig. 0 Distribution of graben in southern Kyushu (A) and the E-W cross section of the Kagoshima
Graben (B : Hayasaka, +32,). HT : Hokusatsu Triangular Graben, KG : Kagoshima Graben, Kt :
Kakuto caldera, Ar : Aira caldera, At : Ata caldera..
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Fig. 1 Geologic map of southern Kyushu (modified from Yamamoto et al., ,**-).
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Table + Summary of the geology of southern Kyushu.
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Fig. 2 Generalized geologic map of the Shimanto Terrane in southern Kyushu (modified
from Teraoka, ,**.). F is an estimated left-lateral fault.
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Fig. 3 Distribution of Late Quaternary volcanic rocks in southern Kyushu (modified from Nagao,
,**+). Solid lines indicate the depth of subducting slab. V.P. : volcanic province.
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Fig. +* Distribution of natural hot springs in southern Kyushu (modified from Tsuyuki, +33,)
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Fig. ++ Genetic model of hot springs at the foot of Sakurajima volcano (after Tsuyuki, +33,)
Fig. +, Flow model chart of hot springs in the southwestern area of Kirishima volcano (after Tsuyuki,
+33, and Fujita et al., ,***)
����24
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Fig. +- Configuration map of basement rocks underneath Kagoshima city (A : modified from
Hayasaka and Oki, +31+) and the E-W cross section of this area showing the horizon of
hot water in the deposits (B : Tsuyuki, +33,)
����26
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��yPQR �+302� : z{ST����|}~���U�:��V�����| W��^�V��XYJ� .0� +-,/�+-.-.
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