Earth:Cerros Bravos-Barros Negros
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Cerros Bravos-Barros Negros is a volcanic complex in the Maricunga Belt in Chile . This 200-kilometre-long (120 mi) volcanic belt formed during the Oligocene-Miocene west of the Puna; the present-day Central Volcanic Zone lies northeast of the Maricunga Belt.[1]
The complex is formed by the coalesced Cerros Bravos and Barros Negros volcanoes,[1] and has a width of 25 kilometres (16 mi).[2] Cerros Bravos may have collapsed towards the northeast in its history,[3] ignimbrites may have formed during this collapse.[4] The bulk of the surface area of the complex is formed by lavas; ignimbrites or tuffs and lava domes are subordinate.[5] The Cerros Bravos Ignimbrite covers a surface of 10.57 square kilometres (4.08 sq mi) and other ignimbrites of 20.44 square kilometres (7.89 sq mi).[6] The Esperanza lava dome complex is associated with the volcanoes, it was constructed on the northeast flank of Cerros Bravos.[2] The volcanoes are limited towards the northeast by the Quebrada Salitral and to the southwest by the Quebrada La Cienaga fault.[7] The first of these faults directed the formation of the Esperanza domes.[3]
Rock compositions range from rhyodacite over dacite to andesite. Minerals identified include biotite, hornblende and pyroxene. Epithermal gold and silver is found at Esperanza.[2] In 1993, gold reserves of 120 m.t. and silver reserves of 7,200 m.t. were estimated.[8] These were mostly formed by acid sulfate alteration.[9]
Volcanism at Cerros Bravos-Barros Negros commenced 26-22 million years ago,[1] and were the only stratovolcanoes of the Maricunga Belt from that time. Small ignimbrites formed the first stage of activity, followed lava flows and eventually lava domes. The Esperanza dome complex was emplaced later between 23.2 ± 1.4 to 19.3 ± 0.7 million years ago, accompanied by Plinian eruptions.[2]
References
- ↑ 1.0 1.1 1.2 Kay et al. 1994, p. 1082.
- ↑ 2.0 2.1 2.2 2.3 Kay et al. 1994, p. 1084.
- ↑ 3.0 3.1 Mpodozis et al. 1995, p. 281.
- ↑ Guzmán et al. 2014, p. 184.
- ↑ Kay et al. 1994, p. 1083.
- ↑ Guzmán et al. 2014, p. 174.
- ↑ Mpodozis et al. 1995, p. 280.
- ↑ Palacios, Carlos M.; Townley, Brian C.; Lahsen, Alfredo A.; Egaña, Antonio M. (1993). "Geological development and mineralization in the Atacama segment of the South American Andes, northern Chile (26°15′–27°25′S)". Geologische Rundschau 82 (4): 660. doi:10.1007/BF00191492. ISSN 0016-7835.
- ↑ Mpodozis et al. 1995, p. 282.
Sources
- Guzmán, Silvina; Grosse, Pablo; Montero-López, Carolina; Hongn, Fernando; Pilger, Rex; Petrinovic, Ivan; Seggiaro, Raúl; Aramayo, Alejandro (2014-12-01). "Spatial–temporal distribution of explosive volcanism in the 25–28°S segment of the Andean Central Volcanic Zone". Tectonophysics 636: 170–189. doi:10.1016/j.tecto.2014.08.013.
- Kay, Suzanne Mahlburg; Mpodozis, Constantino; Tittler, Andrew; Cornejo, Paula (1994-12-01). "Tertiary Magmatic Evolution of the Maricunga Mineral Belt in Chile". International Geology Review 36 (12): 1079–1112. doi:10.1080/00206819409465506. ISSN 0020-6814.
- Mpodozis, Constantino; Cornejo, Paula; Kay, Suzanne M.; Tittler, Andrew (1995-12-01). "La Franja de Maricunga: sintesis de la evolucion del Frente Volcanico Oligoceno-Mioceno de la zona sur de los Andes Centrales" (in es). Andean Geology 22 (2): 273–313. ISSN 0718-7106. http://www.andeangeology.cl/index.php/revista1/article/view/V22n2-a10.
External links
- Epithermal silver-gold minerallzation at the Esperanza area, Maricunga Belt, High Andes of northern Chile
- Estrato volcanes y domos coalescendentes del Oligoceno superior-Mioceno inferior en la franja de Maricunga: los sistemas cerros Bravos-Esperanza y la Coipa
- Aspectos mineralógicos y termométricos del prospecto Esperanza-Cerros Bravos, Maricunga, III región, Chile
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