Structural and Stratigraphic Evolution of the Sumisu Rift, Izu-Bonin Arc

Abstract

The Sumisu Rift, which is ~ 120 km long and 30-50 km wide, is bounded to the north and south by structural and volcanic highs west of the Sumisu and Torishima calderas and longitudinally by curvilinear border fault zones with both convex and concave dips. The zigzag pattern of normal faults (average strikes N23°W and N5°W) indicates fault formation in orthorhombic symmetry in response to N76° ± 10°E extension, orthogonal to the volcanic arc. Three oblique transfer zones divide the rift along strike into four segments with different fault trends and uplift/subsidence patterns. Differential strain across the transfer zones is accommodated by interdigitating, rift-parallel faults and some cross-rift volcanism, rather than by strike-or oblique-slip faults. From estimates of extension (2-5 km), the age of the rift (~2 Ma), and the accelerating subsidence, we infer that the Sumisu Rift is in the early syn-rift stage of backarc basin formation. Following an early sag phase, a half graben formed with a synthetically faulted, structural rollover facing large-offset border fault zones. In the three northern rift segments, the largest faults are on the arc side and dip 60°-75°W, whereas in the southern segment they are on the west side and dip 25°-50°E. The present, "full graben" stage is dominated by hanging-wall antithetic faulting, basin widening by footwall collapse, and a concentration of subsidence in an inner rift. The hanging wall collapses but not necessarily as a result of border fault propagation from adjacent rift segments. Whereas the border faults may penetrate the Theologically weak lithosphere (T e ~ 3 km), many of the hanging-wall and footwall collapse structures are detached only a few kilometers below the seafloor. Where drilled, the arc margin has been uplifted 1.1 ±0.5 km concurrently with ~l.l km of rift basin subsidence. Backarc volcanism, usually erupted along faults, occurs in the rift and along the proto-remnant arc during both stages. A linear zone of weakness caused by the greater temperatures and crustal thickness along the arc volcanic line controls the initial locus of rifting. Rifts are better developed between the arc edifices; intrusions may be accommodating extensional strain adjacent to the arc volcanoes. No obvious correlations are observed between the rift structures and preexisting cross-arc trends. Episodic eruptions of the arc volcanoes are the dominant sediment source; sediment is primarily fed into the northern and southern ends of the rift basin. Sediments are distributed throughout the region by eruptive events and redeposited in the rift basin by unconfined mass flows. Extremely high sedimentation rates, up to 6 m/1000 yr in the inner rift, have kept pace with syn-rift faulting, create a smooth basin floor, and result in sediment thicknesses that mimic the differential basin subsidence.

Sumisu volcano, Izu-Bonin arc, Japan: site of a silicic caldera-forming eruption from a small open-ocean island

“…These workers eliminated Sumisu caldera from consideration because a ridge of small knolls separating the northern and southern basins of the Sumisu rift was thought capable of blocking pumiceous gravity currents originating in the north. Klaus et al (1992), however, presented bathymetry showing that the blocking ridge identified by Nishimura et al (1992) actually contains a narrow channel through which pyroclastic gravity currents from Sumisu could have traveled to Sites 790/791. Major-and trace-element data from Sumisu caldera, Minami Sumisu caldera and Torishima obtained by us and others since the early 1990s permit a reevaluation of pumice provenance (Table 3).…”

“…(e.g. Taylor et al 1990; Klaus et al 1992). Iwabuchi (1999) carried out the first manned submersible investigations in the Sumisu area, and the present study builds on his pioneering work.…”

Models for origin and emplacement of Jurassic ophiolites of Northern California

“…Thus, this model is not useful in explaining Jurassic ophiolites of California because subduction was active along the continental margin for tens of millions of years prior to their formation (Schweickert, 1976(Schweickert, , 1981Dickinson, 1981aDickinson, , 1981bSaleeby and Busby-Spera, 1992;Dilek and Moores, 1995;Ingersoll, 1997). The preponderance of lithospheric rifting in western Pacific arc-trench systems has been within or behind active arcs (e.g., Karig, 1972;Carey and Sigurdsson, 1984;Klaus et al, 1992;Marsaglia, 1995). Saleeby (1981Saleeby ( , 1992 suggested that oblique forearc rifting created the Jurassic ophiolites of California.…”

Rifting of a Mississippian continental arc system: Little Salmon formation, Yukon–Tanana terrane, northern Canadian Cordillera

“…4, 5) forming sediment plains (Fig. This block diagram is a modified version of the Klaus et al (1992) block diagram of the Sumisu rift, southwest Pacific, highlighting the clear resemblance between modern and ancient island arc systems. The thick sequence of siliciclastic deposits of the southern upper succession with their quartz-rich content are likely derived from a felsic source of volcanic origin (Little Kalzas arc) and (or) recycled continental-crust-derived sediments (Snowcap complex?…”

“…11; Klaus et al 1992;Taylor 1992), in which extension within the arc front has led to the development of rift basins of various sizes both in forearc and back-arc settings. 11; Klaus et al 1992;Taylor 1992), in which extension within the arc front has led to the development of rift basins of various sizes both in forearc and back-arc settings.…”