Shatsky Rise
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The Shatsky Rise is the world's third largest oceanic plateau (behind the Ontong Java Plateau and the Kerguelen Plateau ) and is located in the northwestern Pacific, east of Japan . The plateau is an igneous province (English: large igneous province, LIP ) from an entire Cretaceous series in the Pacific, which also includes the LIP Hess Rise , Magellan Rise and Ontong Java-Manihiki-Hikurangi. The namesake is the Soviet geologist Nikolai Schatski , who specialized in the tectonics of old overburden .
The elevation consists of three large volcanic massifs, called Tamu , Ori and Schirschow , otherwise there are few traces of magmatic nature on the surrounding seabed. The Tamu massif can be described as the largest volcano ever discovered on earth.
Expansion and volume
The Shatsky Rise covers an area of approximately 480,000 km² (this is comparable to the area of Germany, Austria and Switzerland combined) and has an estimated volume of 4,300,000 km³. Below the formation, however, the Mohorovičić discontinuity (Moho, the boundary between the earth's crust and mantle ) disappears at a depth of 20 kilometers , which is normally located at a depth of about 17 km. Furthermore, the earth's crust thickness below the Shatsky Rise is almost twice as high as normal; so that according to another opinion, assuming that the entire rock from the rise and affected crust was formed during the same volcanic processes, the formation occupies an area of 533,000 km² and a volume of 6,900,000 km³.
Ups and downs
After its formation, the Shatsky Rise rose by around 2,500 to 3,500 meters and then sank again by 2,600 to 3,400 meters - both movements were more extensive than the corresponding uplifts and depressions of the Ontong Java Plateau. The smallest subsidence can be found in the center of the Tamu massif (about 2600 meters), on its northern flank and on the Ori massif, this value rises to about 3300 meters to reach a maximum on the flank of the Ori massif. The cause of these (different) subsidence is possibly basaltic magma in the subsurface, which is caught at the Mohorovičić discontinuity or already in the crust and more or less "dented" the crust itself due to the differences in density with the surrounding rock. The settlement of the Shirschow massif further to the north is much lower at around 2900 meters and thus presumably points to a temporally separated and later volcanic phase.
Controversies on Genesis
Scientific studies on the size, shape and frequency of eruptions of the Shatsky Rise allow the conclusion that the elevation was formed above a mantle diapir , other studies, which deal with paleomagnetism and the reconstruction of plate tectonic processes, provide the result that the rise was formed on a triple plate boundary and was tectonic was moved over 2000 kilometers in the early Cretaceous period (the period between 100 and 140 million years ago). A study from 2016 draws the conclusion that the Tamu massif was formed on a mid-ocean ridge , which interacted with a plume and that the Ori massif was slightly displaced, presumably by a plume extension. The formation was thus formed at a triple junction, but the thickness of the plateau in connection with the depth and intensity of the melting processes differs from ordinary mid-ocean ridge basalt (MORB, the type of basalt that forms during eruptions in the rift valley), so that a "Recycled" slab is a more likely source. The reduction in magmatic volume over time is more in line with the involvement of a diapir.
Tectonic history
The formation was formed during the late Jurassic and the early Cretaceous period on the triple plate boundary of the Pacific plate with the Farallon plate and the Izanagi plate , so that it can with some justification be called the oldest preserved oceanic plateau. Since the formation was before the so-called Cretaceaous silent period (a long period of time without polarity reversal of the earth's magnetic field), this can be precisely dated. The magnet lines, understood as isochrones , on and along the Shatsky Rises can be dated to an age between 147 million years before today on the south-western ridge and 124 million percent on the northern tip.
Individual evidence
- ^ J. Geldmacher, P. van den Bogaard, K. Heydolph, K. Hoernle: The age of Earth's largest volcano: Tamu Massif on Shatsky Rise (northwest Pacific Ocean) . (PDF) In: International Journal of Earth Sciences . 103, No. 8, 2014, pp. 2351-2357. doi : 10.1007 / s00531-014-1078-6 .
- ^ S. Ingle, JJ Mahoney, H. Sato, MF Coffin, JI Kimura, N. Hirano, M. Nakanishi: Depleted mantle wedge and sediment fingerprint in unusual basalts from the Manihiki Plateau, central Pacific Ocean . (PDF) In: Geology . 35, No. 7, 2007, pp. 595-598. doi : 10.1130 / G23741A.1 .
- ^ A b William W. Sager: What built Shatsky Rise, a mantle plume or ridge tectonics? . (PDF) In: Geological Society of America Special Papers . 388, 2005, pp. 721-733. doi : 10.1130 / 0-8137-2388-4.721 .
- ^ WW Sager, J. Zhang, J. Korenaga, T. Sano, AA Koppers, M. Widdowson, JJ Mahoney: An immense shield volcano within the Shatsky Rise oceanic plateau, northwest Pacific Ocean . (PDF) In: Nature Geoscience . 6, No. 11, 2013, pp. 976-981. doi : 10.1038 / ngeo1934 .
- ^ A b William W. Sager: What built Shatsky Rise, a mantle plume or ridge tectonics? . (PDF) In: Geological Society of America Special Papers . 388, 2005, pp. 721-733. doi : 10.1130 / 0-8137-2388-4.721 .
- ^ J. Zhang, WW Sager, J. Korenaga: The seismic Moho structure of Shatsky Rise oceanic plateau, northwest Pacific Ocean . (PDF) In: Earth and Planetary Science Letters . 441, 2016, pp. 143–154. doi : 10.1016 / j.epsl.2016.02.042 .
- ↑ K. Shimizu, N. Shimizu, T. Sano, N. Matsubara, W. Sager: Paleo-elevation and subsidence of Shatsky Rise inferred from CO 2 and H 2 O in fresh volcanic glass . (PDF) In: Earth and Planetary Science Letters . 383, 2013, pp. 37-44. doi : 10.1016 / j.epsl.2013.09.023 .
- ^ S. Li, Y. Suo, S. Yu, T. Wu, I. Somerville, W. Sager, X. Li, X. Hui, Y. Zhang, Y. Zang, Q. Zheng: Orientation of joints and arrangement of solid inclusions in fibrous veins in the Shatsky Rise, NW Pacific: implications for crack-seal mechanisms and stress fields . (PDF) In: Geological Journal . 51, No. S1, 2016, pp. 562-578. doi : 10.1002 / gj.2777 .
- ↑ K. Heydolph, DT Murphy, J. Geldmacher, IV Romanova, A. Greene, K. Hoernle, D. Weis, J. Mahoney: Plume versus plate origin for the Shatsky Rise oceanic plateau (NW Pacific): Insights from Nd, Pb and Hf isotopes . (PDF) In: Lithos . 200, No. 49-63, 2014. doi : 10.1016 / j.lithos.2014.03.031 .