Page 281 - Global Tectonics

266 CHAPTER 9

(a)
Honshu
EURASIAN
PLATE Median
Tectonic Smb
Line Jp
CSb
Izu collision zone
Kyushu CzSb
CM 1178 Nankai Trough
1175 1176 S-Mb
CA
808 1174 Ava
583 1173
298 582 17-12 Ma igneous activity
1177 Muroto Prior ODP/DSDP sites
N Transect PHILLIPPINE
297 Ashizuri SEA PLATE ODP Leg 190 sites
Transect
0 100 km

(b)
PTZ Nankai Trough
Mio-Pliocene package Pio-Pleistocene package Recent package Trench

0 Site Zone of out-of sequence thrusting 0
1178 Trench slope break
1 Cover sequence Site Site Hemipelagic 1
Trench slope 1175 1176
2 Frontal out-of sequence thrust unit 2
basin
Site
Trench
3 Imbricate series Imbricate series Site Site turbidites 1173 3
808 1174
4 Frontal thrust 4 Depth (km)
5 5
Fault traces
6 6
0 10 km
7 Décollement Deformation 7
VE 2.5 front
8 Décollement Underplated sediments Proto-décollement 8
Seismogenic zone? zone
Figure 9.20 (a) Geologic map of the Nankai accretionary prism showing the Leg 190/196 Ocean Drilling Program
(ODP, black circles) and previous ODP/Deep Sea Drilling Program (DSDP, open circles) drill sites (modified from Moore

et al., 2001, by permission of the American Geophysical Union. Copyright © 2001 American Geophysical Union). CA,
Cape Ashizuri; CM, Cape Muroto; Smb, Sanbagawa metamorphic belt; Jp, Jurassic accretionary prism; CSb, Cretaceous
Shimanto belt; CzSb, Cenozoic Shimanto belt; S-Mb, Shimanto and Mineoka belts; Ava, Accreted volcanic arc; PTZ,
protothrust zone. (b) Generalized cross-section of the Muroto transect showing main structural provinces (modifi ed
from Moore et al., 2005, by permission of the American Geophysical Union. Copyright © 2005 American Geophysical
Union).
although some older thrusts may remain active during to the base of the prism by thrust faulting above the
their rotation and some new thrusts may form and cut décollement. Unlike the off-scraped sediments at the
across older imbricate thrusts. These latter, cross cutting toe, this underplated material may become deeply
faults are termed out-of-sequence thrusts (Fig. 9.20b) buried and undergo high pressure metamorphism
because they do not conform to the common arcward (Section 9.9). Tectonic underplating, together with
progression of faulting. In addition to frontal accretion, internal shortening, thickens the wedge and causes the
some incoming material is carried downward past the slope of its upper surface to increase (Konstantinovs-
deformation front where it is transferred, or underplated, kaia & Malavieille, 2005).