Site 1174 penetrated the decollement within the proto-thrust zone (Figure 3-2).

The decollement was observed between 808 and 840 mbsf and was marked by fractures

and brecciation in the lower Shikoku Basin facies (Shipboard Scientific Party, 2001).

The turbidites extended 431 m above the hemipelagic muds of the upper and lower

Shikoku Basin facies (Shipboard Scientific Party, 2001).

 NW SE
X Line900 800 700 600 500 400 300 200


Protothrust
I- zone nefnrmatinn


 "s Site 1174 FrontSite 1173
 E FZ! tl Trench-Wedge Facies
 n Upper Shikoku Basin Facies
 ~ -. Lower Shikoku Basin Facies
 ^ V emen zone .. Volcaniclastic Facies
 _.-- :-- ---_ Ocean Crust .
 1


Figure 3-2. Schematic interpretation of the Muroto Transect showing tectonic domains
 and location of Leg 190 drill sites used in this study (modified from Moore et
 al., 2001).

 Site 1173 was drilled 11 km seaward of the deformation front providing an

undeformed reference site of the incoming sedimentary sequence (Shipboard Scientific

Party, 2001). The turbidite layer at Site 1173 is much thinner (-102 m) than at Site 1174,

because it is farther away from the trench. At Site 1173, the age equivalent of the Site

1174 decollement zone occurs between 390 and 420 mbsf, within the lower Shikoku

Basin facies (Shipboard Scientific Party, 2001).

 At the Nankai accretionary complex, heat flow values ranging from 180 mW/m2 at

Sites 1173 and 1174 to 130 mW/m2 at Site 808 have been estimated (Shipboard Scientific

Party, 2001). These measured high heat flow values are related to the fossil spreading

ridge represented by the Kinan Seamount on the Philippine Sea Plate which ceased

spreading 15 Ma ago (Shipboard Scientific Party, 2001). Previous studies have