Ryukyu Arc: Difference between revisions

Revision as of 09:24, 18 November 2022

Revision as of 06:41, 19 November 2022

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{{Short description|Volcanic island arc between Kyushu and Taiwan}}

[[File:The Ryukyu Arc Map.png|thumb|upright=1.35|Map of the Ryukyu Arc. Red triangles represent volcanoes based on Aster Volcano Archive (NASA-METI) data. Contours in 1000m interval. Figure made with GeoMapApp (www.geomapapp.org) / CC BY / CC BY (Ryan et al., 2009).]]

The '''Ryukyu Arc''' is an [[island arc]] which extends from the south of [[Kyushu]] along the [[Ryukyu Islands]] to the northeast of [[Taiwan]], spanning about {{convert|1200|km|mi}}.<ref name=":1">Kiszaki, K. (1978). Tectonics of the Ryukyu Island Arc. ''Journal of Physics of the Earth, 26''(Supplement), S301–S307. https://doi.org/10.4294/jpe1952.26.Supplement_S301</ref><ref name=":2">Shinjo, R., & Kato, Y. (2000). Geochemical constraints on the origin of bimodal magmatism at the Okinawa Trough, an incipient back-arc basin. ''Lithos, 54''(3-4), 117-137. https://doi.org/10.1016/S0024-4937(00)00034-7</ref><ref name=":3">Park, J. O., Tokuyama, H., Shinohara, M., Suyehiro, K., & Taira, A. (1998). Seismic record of tectonic evolution and backarc rifting in the southern Ryukyu island arc system. ''Tectonophysics, 294''(1-2), 21-42. https://doi.org/10.1016/S0040-1951(98)00150-4</ref> It is located along a section of the [[Convergent boundary|convergent plate boundary]] where the [[Philippine Sea Plate]] is subducting northwestward beneath the [[Eurasian Plate]] along the [[Ryukyu Trench]]<ref name=":2" /><ref name=":3" /><ref name=":4">Shinjo, R., Chung, S.-L., Kato, Y., and Kimura, M. (1999), Geochemical and Sr-Nd isotopic characteristics of volcanic rocks from the Okinawa Trough and Ryukyu Arc: Implications for the evolution of a young, intracontinental back arc basin, ''J. Geophys. Res., 104''( B5), 10591– 10608, doi:10.1029/1999JB900040.</ref>. The arc has an overall northeast-southwest trend and is located northwest of the [[Pacific Ocean]] and southeast of the [[East China Sea]]<ref name=":6">Nakae, S. (2013). The radiolarian evidence for the accretion of the Fu-saki Formation with the inferred oceanic plate stratigraphy: A case of weakly-metamorphosed accretionary complex in Ishigaki Jima, southern Ryukyu Arc, Japan. ''Journal of Asian Earth Sciences, 73'', 21-30.</ref>. It strikes parallel to the Ryukyu Trench, an active volcanic belt, and the [[Okinawa Trough]]<ref name=":5">Kizaki, K. (1986). Geology and tectonics of the Ryukyu Islands. ''Tectonophysics, 125''(1-3), 193-207.</ref>. The Ryukyu Arc, based on its geomorphology, can be segmented from north to south into Northern Ryukyu, Central Ryukyu, and Southern Ryukyu; the Tokara Strait separates Northern Ryukyu and Central Ryukyu at about 130˚E while the [[Miyako Strait|Kerama Gap]] separates Central Ryukyu and Southern Ryukyu at about 127 ˚E<ref name=":1" /><ref name=":4" /><ref name=":5" />. The geological units of the arc include [[Igneous rock|igneous]], [[Sedimentary rock|sedimentary]], and [[Metamorphic rock|metamorphic rocks]], ranging from the [[Paleozoic]] to [[Cenozoic]] in age.

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The geological and structural features of Southern Ryukyu are quite different from those of Northern and Central Ryukyu; Southern Ryukyu, and Northern and Central Ryukyu may have had a different geological history before the middle [[Miocene]]<ref name=":1" />. [[Accretionary wedge|Accretionary complexes]] in Northern and Central Ryukyu are considered as the extension of the Outer Zone of Southwest Japan<ref name=":5" /><ref name=":25">Taira, A., Ohara, Y., Wallis, S. R., Ishiwatari, A., & Iryu, Y. (2016). Geological evolution of Japan: an overview. ''The geology of Japan'', 1-24.</ref><ref name=":26">Takami, M., Takemura, R., Nishimura, Y., & Kojima, T. (1999). Reconstruction of oceanic plate stratigraphies and unit division of Jurassic-Early Cretaceous accretionary complexes in the Okinawa Islands, central Ryukyu Island Arc. ''The Journal of the Geological Society of Japan, 105''(12), 866-880. https://doi.org/10.5575/geosoc.105.866</ref>, whereas metamorphic rocks in Southern Ryukyu are associated with the Inner Zone of Southwest Japan<ref name=":24" />. The arc might be united into the present configuration in the [[Pliocene]]-[[Pleistocene]] due to different rates of southeastward migration as tectonics proceeded<ref name=":1" />.

[[File:Location of the Ryukyu Islands.JPG|thumb|upright=1.5|Location of the Ryukyu Islands. From user: Uchinanchu]]

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The Okinawa Trough is the [[back-arc basin]] of the Ryukyu Arc and is formed by lithospheric extension of the continental Eurasian Plate<ref name=":2" />. En echelon, extensional [[Graben|grabens]] with a width of about 10 km and a length of about 50-100 km can be found in the middle to southern parts of Okinawa Trough<ref name=":2" /><ref name=":4" />. Of the whole Okinawa Trough, the southern part is the most evolved and active, in that, its maximum depth, which is greater than other parts, is about 2200 m<ref name=":3" />. The Okinawa Trough accommodates [[Terrigenous sediment|terrigenous sediments]] from the [[continental shelf]] of Asia and the Ryukyu Arc at a high rate<ref name=":3" />.

[[File:Volcanic Arc System SVG en.svg|thumb|upright=2|Schematic of island arc system. From user: MagentaGreen]]

=== Seismicity ===

The Ryukyu Arc is a site of active seismicity characterised by shallow earthquakes, given the ongoing convergence between the Philippine Sea Plate and Eurasian Plate <ref name=":9" />. Seismic data of earthquakes have been used to detect seismic structures below the Ryukyu Arc <ref name="a">Roecker, S. W., Yeh, Y. H., & Tsai, Y. B. (1987). Three‐dimensional P and S wave velocity structures beneath Taiwan: Deep structure beneath an arc‐continent collision. ''Journal of Geophysical Research: Solid Earth, 92''(B10), 10547-10570.</ref>. [[Low-velocity zone|Low seismic velocity zones]], which are possibly associated with the upwelling of magma, have been discovered beneath active volcanoes and the Okinawa Trough<ref name="a"></ref>.

[[File:M≥6.0 (1960-2022) Earthquakes in the Ryukyu Arc.png|thumb|546x480px|M≥6.0 (1960-2022) Earthquakes in the Ryukyu Arc. Earthquake data from USGS-ANSS Catalog. Contours in 1000m interval. Figure made with GeoMapApp (www.geomapapp.org) / CC BY / CC BY (Ryan et al., 2009).]]

=== Volcanoes ===

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== Tectonics ==

[[File:Evolution of the Ryukyu Arc.png|thumb|513x480px|right|Evolution of the Ryukyu Arc. Adapted from Ujiié (1994)<ref name=":21" />]]

Along the Ryukyu Trench, the Philippine Sea Plate is subducting northwestward under the Eurasian Plate at an estimated velocity of 5-7 cm/year<ref name=":7" />. The subduction angles become increasingly oblique to the arc toward south<ref name=":7">Seno, T., Stein, S., & Gripp, A. E. (1993). A model for the motion of the Philippine Sea plate consistent with NUVEL‐1 and geological data. ''Journal of Geophysical Research: Solid Earth, 98''(B10), 17941-17948.</ref>.

Global Positioning System data show that southern Kyushu and the Ryukyu Arc migrate southeastward (toward the Ryukyu Trench) relative to Eurasia, as compared to the westward-northwestward migration of other arcs of Japan <ref name=":8">Sagiya, T., Miyazaki, S. I., & Tada, T. (2000). Continuous GPS array and present-day crustal deformation of Japan. ''Pure and applied Geophysics, 157''(11), 2303-2322.</ref>.