Back-arc rifting in the Okinawa Trough |
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| Authors: | Masaaki Kimura |
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| Institution: | Department of Marine Sciences, College of Science, University of the Ryukyus, Senbaru 1, Nishihara, Okinawa 903-01, Japan |
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| Abstract: | Geological and geophysical data reveal that the Okinawa Trough shows incipient continental rifting, and crustal separation started from about 2 Ma. The early extensional movements in the trough are probably of Miocene age. In addition to the Miocene phase, two main periods of extension are recognized: a Pleistocene phase between 1.9 and 0.5 Ma and the present day phase. During the stage short central rifts (Central Grabens) were formed. The opening however, may have occurred only in the southern part of the trough basin having an average half spreading rate of 2 cm yr?1 since Early Pleistocene time, producing its present width of several tens of kilometres. These activities were well represented by igneous intrusions, sedimentary facies and sedimentary structures in and around the Okinawa Trough. The width of the zone affected by back-arc extension (defined as Greater Okinawa Trough) is larger than the present Okinawa Trough, whose width is 200–250 km. The present form of the Greater Okinawa Trough started to form at the same time as that of the Okinawa Trough. |
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| Keywords: | Okinawa Trough Back-arc rifting |
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