Normal faults in an accretionary complex formed at trench‐trench‐ridge triple junction, as an indicator of angle between the trench and subducted ridge

Abstract

Normal faults parallel to the trend of an active ridge are formed in the accretionary prism at trench-trench-ridge triple junction, due to continuous spreading of the subducted ridge. Normal faults are observed in the Nabae and Mugi sub-belts, accretionary zones formed by ridge subduction in the Shimanto Belt. Igneous and sedimentary dykes intrude through the previous normal faults. Using these fault and dyke data, intermediate principal axis of stress relating to the normal faulting is determined, and is fitted to the trend of the subducted ridge.Normal faults formed by ridge subduction are useful for plate reconstruction.

The cessation of igneous activity and uplift when an actively spreading ridge is subducted beneath an island arc

“…From the plots in Fig. 2, estimating these small gaps is difficult due to errors associated with radiometric formation ages, but the plots of the Green Tuff volcanic and volcaniclastic rocks are sporadic along Cl-C2, except for plots of high magnesian andesite and adakite (Okamura et al. 1993;Uematsu et al 1995) and also near-trench igneous rocks.…”

“…In the absence of direct radiometric ages, including 'in situ basalts', time values (t) are based on radiolarian ages of sedimentary rocks. The 'in situ basalts', so-named and identified by Kiminami et al (1994)' were erupted in or upon terrigenous and hemipelagic sediments of accretionary complexes, and generated at a mid-ocean ridge in the vicinity of the triple junction (Miyashita & Katsushima 1986;Osozawa et al 1990;Kiminami et al 1992Kiminami et al , 1994Osozawa 1993). Distances (L) are measured from the Amami Oshima Island to the outcrop of the 'in situ basalt' along-strikes of accretionary complexes (Fig.…”

Introduction: An overview of ridge-trench interactions in modern and ancient settings

“…Sakaguchi (1996) noted high geothermal gradients in the accretionary prism coincide with this magmatic activity, which is consistent with the ridge subduction model. Osozawa (1993) also identifi ed a series of normal faults associated with this event.…”

“Block-in-matrix” fabrics that lack shearing but possess composite cleavage planes: A sedimentary mélange origin for the Yuwan accretionary complex in the Ryukyu island arc, Japan

“…While some mélanges are occasionally associated with basalt intrusive activity, and the pre-served chill margins may be observed (Osozawa et al, 1990;Osozawa, 1993;Kiminami et al, 1994;Osozawa and Yoshida, 1997), there is little or no indication that the original igneous structures have been perturbed by the expected intense shearing. In some cases, mélanges clearly represent lithologic components interlayered with coherent hemipelagic and terrigenous units (e.g., Taira et al, 1992;Osozawa, 1993;Osozawa et al, 2004).…”

“…In some cases, mélanges clearly represent lithologic components interlayered with coherent hemipelagic and terrigenous units (e.g., Taira et al, 1992;Osozawa, 1993;Osozawa et al, 2004). This scenario might appear to require stratigraphic shear stress to be concentrated, particularly in the horizontal plane, to allow the formation of a mélange layer, although this process remains conjectural.…”