Английская Википедия:Corral de Coquena
Шаблон:Short description Шаблон:Coord Corral de Coquena is a volcanic spatter rampart in the Andes,[1] over the Tropic of Capricorn. The rampart at its highest point is Шаблон:Convert high.[2]Шаблон:Rp
The structure has a width of Шаблон:Convert and is a discontinuous rampart Шаблон:Convert high. This rampart surrounds a sediment-filled crater that is Шаблон:Convert deep beneath the surrounding terrain. The deepest point is Шаблон:Convert high above sea level.[2]Шаблон:Rp The rampart is formed from two main bodies each up to Шаблон:Convert wide with gaps separating them.[2]Шаблон:Rp It is located in the southeastern portion of the moat which surrounds the 4 mya Шаблон:Convert La Pacana caldera.[2]Шаблон:Rp
Coquena formed along an outer ring fault. The caldera wall reaches its highest height in the area of Corral de Coquena.[3]Шаблон:Rp The basement beneath Corral de Coquena is slightly higher than the general Pacana caldera floor.[2]Шаблон:Rp The ring belongs to the post-caldera activity phase of La Pacana. The dating is uncertain; the ring is constructed on top of the Pampa Chamaca ignimbrite (2.4 mya) but one date obtained from the ring is 4.4 ± 0.3 mya,[1] obtained on biotite.[3]Шаблон:Rp The date of the ring is more likely to be incorrect.[1] Other estimates indicate that Pampa Chamaca overlies the Corral de Coquena deposits,[3]Шаблон:Rp an as yet unsettled question. The Atana ignimbrite that clearly pre-dates the Coquena ring has been reassessed as being 3.9-4.2 ± 0.1-0.2 mya old, reducing the estimated age of Corral de Coquena as well.[2]Шаблон:Rp
The rampart is formed by glassy rhyolite,[1] or dacite,[4] typical of the potassium-rich calc-alkaline series of the Central Volcanic Zone.[2]Шаблон:Rp It has a phenocryst content of 20%.[1]
Dacite clasts cover the inward-sloping walls of the rampart. Outwards, lobes and terraces are found possibly formed by agglutinating dacite forming lava flows.[4] The rhyolites too show evidence of flow structures and bedding.[2]Шаблон:Rp
In the Pliocene, destruction of a lava dome resulted in the formation of a pyroclastic deposit around Corral de Coquena. These deposits consists of volcanic ash, pumice and rhyolite,[3]Шаблон:Rp forming layers with angular pumice and ash and an overlying layer of vitric rhyolite, similar to the rampart wall. The deposits are up to Шаблон:Convert thick and cover a surface of Шаблон:Circa Шаблон:Convert.[3]Шаблон:Rp Total volume is less than Шаблон:Convert.[2]Шаблон:Rp A later layer of reworked Atana and Corral de Coquena pyroclastics extends Шаблон:Convert away.[2]Шаблон:Rp
Aside from the lower phenocryst content, this lava is very similar to Morro Negro, another Pacana lava dome.[3]Шаблон:Rp Ilmenite, magnetite and quartz are found in the rhyolite.[2]Шаблон:Rp A water content of 3-4% and temperatures of Шаблон:Convert have been estimated on the basis of composition.[2]Шаблон:Rp The magma that formed Corral de Coquena is probably related to magmas that formed the Atana ignimbrite and were not erupted during that activity phase. Subsequently, part of these leaked out and formed Corral de Coquena.[3]Шаблон:Rp
The appearance of Corral de Coquena is similar to a maar. Despite the arid climate in the area which has persisted since the Miocene, the local water table (Шаблон:Convert beneath the ground on the basis of water levels in nearby lakes) may have been high enough to trigger phreatomagmatic activity. This activity formed the crater. Later, lava itself erupted in the form of lava fountaining. Spatters formed by the fountaining then formed the Corral de Coquena rampart.[2]Шаблон:Rp This is an unusual mode of activity for silicic magmas but also documented at Huaynaputina and the Cerro Chascon-Runtu Jarita complex.[2]Шаблон:Rp
References
- ↑ 1,0 1,1 1,2 1,3 1,4 Ошибка цитирования Неверный тег
<ref>; для сносокLindsaySilva2001не указан текст - ↑ 2,00 2,01 2,02 2,03 2,04 2,05 2,06 2,07 2,08 2,09 2,10 2,11 2,12 2,13 Ошибка цитирования Неверный тег
<ref>; для сносокSelfSilva2008не указан текст - ↑ 3,0 3,1 3,2 3,3 3,4 3,5 3,6 Ошибка цитирования Неверный тег
<ref>; для сносокGardewegRamirez1987не указан текст - ↑ 4,0 4,1 Ошибка цитирования Неверный тег
<ref>; для сносокFrancisSilva1989не указан текст
