Pica gap

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Pica gap is a segment in the Central Volcanic Zone of Chile where volcanic activity is absent. [1] It is named after the Altos de Pica region. [2]

This segment is 100 kilometres (62 mi) long and extends between the volcanoes Isluga in the north and Irruputuncu in the south. [1] Volcanoes in the gap are old, Miocene to Pliocene in age and are heavily eroded. Examples include Cerro Napa  [ sv ], Cerro Cariquima and Cerro Tatjachura. [3]

At the latitude of the Pica gap, an underwater rise known as the Iquique rise is subducted in the Peru-Chile Trench. It is unclear if the subduction of this rise is the cause for the lack of recent volcanism in the Pica gap. [3] The lack of volcanism in the Pica gap appears to be due to unfavourable mantle flow patterns, which prevent the ascent of magma. [4]

Geologically, the Pica gap lies between two crustal domains which are defined by their divergent lead isotope ratios, [5] the northerly Arequipa-Antofalla block of Proterozoic age and the southern Chilenia terrane of Paleozoic age. [6] Other phenomena which coincide with the Pica gap are the absence of tectonic horsts west of the Andes, [2] an area where a zone of high electrical conductivity in the deep crust beneath the forearc does not extend to the actual volcanic arc (and thus may reflect the absence of molten magma), [7] the lack of a low seismic velocity zone in the crust, [8] a symmetry plane of the Andes, the Salar de Uyuni basin behind the arc and the location of the actual bend in the Andes that is usually placed at the Arica Bend. These phenomena may be unrelated to the Pica gap, however. [3]

The Cerro Porquesa lava dome and ignimbrite are the only volcanic centres with late Pleistocene activity in the area. [3] Some evidence of recent volcanic activity exists at the Pliocene volcano Sillajuhay, where geothermal activity and deformation of the ground were observed. [1]

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References

  1. 1 2 3 Pritchard, M. E.; Henderson, S. T.; Jay, J. A.; Soler, V.; Krzesni, D. A.; Button, N. E.; Welch, M. D.; Semple, A. G.; Glass, B. (2014-06-01). "Reconnaissance earthquake studies at nine volcanic areas of the central Andes with coincident satellite thermal and InSAR observations". Journal of Volcanology and Geothermal Research. 280: 96. doi:10.1016/j.jvolgeores.2014.05.004.
  2. 1 2 Reutter, Klaus-Joachim; Scheuber, Ekkehard; Wigger, Peter (2012-12-06). Tectonics of the Southern Central Andes: Structure and Evolution of an Active Continental Margin. Springer Science & Business Media. p. 84. ISBN   9783642773532.
  3. 1 2 3 4 Wörner, Gerhard; Hammerschmidt, Konrad; Henjes-Kunst, Friedhelm; Lezaun, Judith; Wilke, Hans (2000-12-01). "Geochronology (40Ar/39Ar, K-Ar and He-exposure ages) of Cenozoic magmatic rocks from Northern Chile (18-22°S): implications for magmatism and tectonic evolution of the central Andes". Revista Geológica de Chile . 27 (2): 205–240.
  4. ↑ Araya Vargas, J.; Sanhueza, J.; Yáñez, G. (November 2021). "The Role of Temperature in the Along-Margin Distribution of Volcanism and Seismicity in Subduction Zones: Insights From 3-D Thermomechanical Modeling of the Central Andean Margin". Tectonics. 40 (11). doi:10.1029/2021TC006879.
  5. ↑ Wörner, Gerhard; Moorbath, Stephen; Harmon, Russell S. (1992-12-01). "Andean Cenozoic volcanic centers reflect basement isotopic domains". Geology. 20 (12): 1105–1106. doi:10.1130/0091-7613(1992)020<1103:ACVCRB>2.3.CO;2. ISSN   0091-7613.
  6. ↑ de Silva, Shanaka L.; Davidson, Jon P.; Croudace, Ian W.; Escobar, Angel (1993). "Volcanological and petrological evolution of Volcan Tata Sabaya, SW Bolivia". Journal of Volcanology and Geothermal Research. 55 (3–4): 309. doi:10.1016/0377-0273(93)90043-q.
  7. ↑ Echternacht, Friedrich; Tauber, Sebastian; Eisel, Markus; Brasse, Heinrich; Schwarz, Gerhard; Haak, Volker (1997). "Electromagnetic study of the active continental margin in northern Chile". Physics of the Earth and Planetary Interiors. 102 (1–2): 85. doi:10.1016/s0031-9201(96)03261-x.
  8. ↑ Kühn, Christine; Brasse, Heinrich; Schwarz, Gerhard (1 June 2018). "Three-Dimensional Electrical Resistivity Image of the Volcanic Arc in Northern Chile—An Appraisal of Early Magnetotelluric Data". Pure and Applied Geophysics. 175 (6): 2153–2165. doi:10.1007/s00024-017-1764-y. ISSN   1420-9136. S2CID   133920227.
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