Tectonic complexities in the bonin arc system |
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| Authors: | DE Karig GF Moore |
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| Institution: | Department of Geological Sciences, Cornell University, Ithaca, N.Y.U.S.A. |
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| Abstract: | The Bonin arc system is anomalous in that it does not appear to fit the tectonic pattern observed in most arc systems. Re-examination of this arc system, with a new bathymetric chart and against a background of recent studies in other arcs, leads to reasonable explanations for its anomalous characteristics. The frontal-arc volcanics on the Bonin Islands, which now form part of the trench slope break, can best be explained by the northward rifting of the Bonin Islands block from a position along the frontal arc under the influence of oblique subduction. The very large positive gravity anomaly over the islands results from the greater than normal density and volume of the volcanics compared to most trench slope breaks. The dominant northeast—southwest ridge and trough topography, into which the Iwo Jima Ridge (frontal arc) is broken may have resulted from compressions of the arc along its trend. This compression would be attributed to the southward movement of Japan as the Yamato Basin of the Sea of Japan opened in the Late Oligocene and Early Miocene. Recent extension is occurring in the Bonin arc system, as earlier suggested, but in an east—west direction. Features associated with extension can best be identified at the south end of the arc, but may persist for its entire length. This extension is either more rapid, or began first at the south end. |
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