View source for Earth:Cerro Chascon-Runtu Jarita complex

{{coord|21|53|02|S|67|54|18|W|type:mountain_region:BO-P|display=intitle|notes=<ref name=Tierney2011 />}}
'''Cerro Chascon-Runtu Jarita''' is a complex of [[Earth:Lava dome|lava dome]]s located inside, but probably unrelated to, the Pastos Grandes caldera. It is part of the more recent phase of activity of the Altiplano-Puna volcanic complex.

Accompanied with little explosive activity on the main dome Cerro Chascon, it contains ten lava domes arranged in a chain. Located in the floor  of the Pastos Grandes caldera, these domes were erupted after injection of [[Earth:Mafic|mafic]] magmas in the deep less than 100,000 years ago. The largest dome has a volume of {{convert|5|km3}}.
== Geology ==
The complex is a chain of seven [[Earth:Lava dome|lava dome]]s named Runtu Jarita whose largest member is named Cerro Chascon. This chain is comparable with the [[Earth:Mono–Inyo Craters|Mono-Inyo craters]] in the United States. Together with other lava domes like [[Earth:Cerro Chao|Cerro Chao]] this complex is part of the young surface expression of the APVC and may indicate the future location of a caldera.<ref name=SilvaSelf1994 /> 
=== Origins ===
The lava domes are contained within the moat and floor of the [[Earth:Pastos Grandes|Pastos Grandes]] caldera, but it may not be part of that caldera complex proper.<ref name=WattsSilva1999 /><ref name=SilvaSelf1994 /> The lava dome complex is part of the Altiplano-Puna volcanic complex, an igneous province located in the Central Andes. During the Late Miocene-[[Earth:Pleistocene|Pleistocene]], large [[Earth:Ignimbrite|ignimbrite]] eruptions took place covering an area of {{convert|70000|km2}} triggered by the formation of melts deep in the crust and their subsequent rise to the upper crust.<ref name=WattsSilva1999 /> 

Geochemical analysis led de Silva (1994) to suggest that they may be the latest eruptive cycle of the APVC, either as part of a reactivation or waning of that system. Pastos Grandes is the source of two major ignimbrites, the 8.1 [[Physics:Mya (unit)|mya]] Sifon and the 5.3 mya Chuhuilla ignimbrite, as well as the 3.1 mya Cerro Juvina ignimbrite shield on the northern caldera flank.<ref name=WattsSilva1999 /> The eruption of this complex may have been formed by a [[Earth:Dike (geology)|dyke]].<ref name=SilvaSelf1994 />

=== Structure ===
The volcanic complex extends from {{coord|21|53|S|67|54|W}} to {{coord|22|02|S|67|49|W}} with base altitudes {{convert|4600|-|4900|m}}. The complex is split into a northern group encompassing Cerro Chascon and three other domes (named Cerro Guichi, Morro Chascoso and Pabelloncita Loma), and a southern group of six domes. Their orientation in northwestward direction is consistent with the regional trends but may also be influenced by the Pastos Grandes caldera structure. The arid climate of the area has impeded erosion in the area, leaving the volcanic complex relatively unaltered.<ref name=WattsSilva1999 />

Cerro Chascon is formed from a cicle of lava flow lobes<ref name=SilvaSelf1994 /> with a central plug with a diameter of {{convert|200|m}}.<ref name=WattsSilva1999 /> Explosive activity occurred before the dome formation and generated a {{convert|1|m}} thick [[Earth:Pumice|pumice]] deposit composed from rhyolitic [[Chemistry:Obsidian|obsidian]] beneath the dome.<ref name=SilvaSelf1994 /> The lava dome has a volume of {{convert|5|km3}}<ref name=Tierney2011 /> with a maximum altitude of {{convert|5190|m}}. Its surface is covered by mounds ({{convert|20|m}} high) of presumably [[Earth:Diapir|diapiric]] origin, with sand trails eroded from the mounds separating them.<ref name=WattsSilva1999 />

Morro Chascoso and Pabelloncita Loma are cone shaped domes with blocky slopes with [[Earth:Scree|talus]] and central depressions. The much smaller Cerro Guichi ({{convert|6|m}} high and {{convert|25|m}} long) may be an exposed intrusion, considering that it lacks any indication of surface flow. The two southernmost domes of the southern group have similar shapes to Chascoso and Pabelloncita. However the second southernmost dome is accompanied with an andesitic lava flow. The rest of the domes contain a silicic core with surrounding andesitic flows. The domes become less andesitic towards the north.<ref name=WattsSilva1999 />

=== Petrology ===
The lavas of this complex are of [[Chemistry:Potassium|potassium]]-rich calc-alkaline origin, and are highly viscous with large difference between two magma types.<ref name=WattsSilva1999 /> The lava domes are formed from [[Earth:Andesite|andesite]] in the south and [[Earth:Dacite|dacite]] in the north. The dacites are crystal rich and some lavas show evidence of magma mixing.<ref name=SilvaSelf1994 /> [[Earth:Phenocryst|Phenocryst]] contents ranges from 35% by volume in dacite and 48% by volume of rhyolite.<ref name=Takeuchi2011 /> In the northern group these are primarily composed from [[Chemistry:Feldspar|feldspar]] with minor components of [[Chemistry:Amphibole|amphibole]], [[Chemistry:Biotite|biotite]] and [[Chemistry:Quartz|quartz]]. The southern group rocks have similar petrologies, but are of rhyolitic composition and contain [[Earth:Mafic|mafic]] components. They contain a rhyolitic core surrounded with andesitic lavas that contains primarily [[Chemistry:Plagioclase|plagioclase]] phenocrysts.<ref name=WattsSilva1999 /> Temperatures of {{convert|926|-|1000|C}} for dacitic lava and {{convert|625|-|727|C}} for [[Earth:Rhyolite|rhyolite]] lava have been estimated.<ref name=Takeuchi2011 />

Petrology indicates that the andesitic lavas of the southern domes are derived from the more silicic magmas by addition of more mafic andeistes. Conversely, the northern dome magmas formed by fractional crystallization with the most evolved components being erupted explosively.<ref name=WattsSilva1999 /> 
=== Geologic history ===
The lava domes were erupted between 89,000-94,000 years ago.<ref name=SalisburyJicha2010 /> In Runtu Jarita, Argon-argon dating on [[Chemistry:Sanidine|sanidine]] has yielded ages of 88,000±4,000 to 97,000±2,000 [[Earth:Before Present|BP]].<ref name=WattsSilva1999 /> The eruption may have been caused by the injection of [[Earth:Mafic|mafic]] magmas in the magmatic system.<ref name=Tierney2011 /> Presumably, the magmas were in the process of forming a pluton when the injection of new magmas led to eruption. The eruptions of Chascon initially were phreatomagmatic and influenced by local lakewaters. In the southern domes, some time occurred between the formation of the andesitic magmas by mixing and the eruption. Both andesitic and rhyolitic magmas were simultaneously extruded.<ref name=WattsSilva1999 />
== See also ==
* Altiplano-Puna volcanic complex
* [[Earth:Cerro Chanka|Cerro Chanka]]
* [[Earth:Cerro Chao|Cerro Chao]]
* [[Earth:Chillahuita|Chillahuita]]
* [[Earth:Corral de Coquena|Corral de Coquena]]
* [[Earth:Pastos Grandes|Pastos Grandes]]
* [[Earth:Tocorpuri|Tocorpuri]]

== References ==
{{Reflist|refs=
<ref name=SilvaSelf1994>{{cite journal|last1=de Silva|first1=S. L.|last2=Self|first2=S.|last3=Francis|first3=P. W.|last4=Drake|first4=R. E.|last5=Carlos|first5=Ramirez R.|title=Effusive silicic volcanism in the Central Andes: The Chao dacite and other young lavas of the Altiplano-Puna Volcanic Complex|journal=Journal of Geophysical Research|date=1994|volume=99|issue=B9|pages=17805|doi=10.1029/94JB00652}}</ref>
<ref name=SalisburyJicha2010>{{cite journal|last1=Salisbury|first1=M. J.|last2=Jicha|first2=B. R.|last3=de Silva|first3=S. L.|last4=Singer|first4=B. S.|last5=Jimenez|first5=N. C.|last6=Ort|first6=M. H.|title=40Ar/39Ar chronostratigraphy of Altiplano-Puna volcanic complex ignimbrites reveals the development of a major magmatic province|journal=Geological Society of America Bulletin|date=21 December 2010|volume=123|issue=5–6|pages=821–840|doi=10.1130/B30280.1}}</ref>
<ref name=Tierney2011>{{cite web|last1=Tierney|first1=Casey|title=Timescales of large silicic magma systems: implications from accessory minerals in Pleistocene lavas of the Altiplano-Puna Volcanic Complex, central Andes|url=http://ir.library.oregonstate.edu/xmlui/handle/1957/21754|website=ScholarsArchive@OSU|publisher=[[Organization:Oregon State University|Oregon State University]]|accessdate=26 November 2015}}</ref>
<ref name=Takeuchi2011>{{cite journal|last1=Takeuchi|first1=Shingo|title=Preeruptive magma viscosity: An important measure of magma eruptibility|journal=Journal of Geophysical Research|date=5 October 2011|volume=116|issue=B10|doi=10.1029/2011JB008243|doi-access=free}}</ref>
<ref name=WattsSilva1999>{{cite journal|last1=Watts|first1=Robert B.|last2=de Silva|first2=Shanaka L.|last3=Jimenez de Rios|first3=Guillermina|last4=Croudace|first4=Ian|title=Effusive eruption of viscous silicic magma triggered and driven by recharge: a case study of the Cerro Chascon-Runtu Jarita Dome Complex in Southwest Bolivia|journal=Bulletin of Volcanology|date=10 September 1999|volume=61|issue=4|pages=241–264|doi=10.1007/s004450050274}}</ref>}}

== Further reading ==
* {{cite book|last1=Watts|first1=Robert W.|title=Evolution of the Cerro Chascon-Runtu Jarita Complex in Southwest Bolivia: Implications for Silicic Dome Formation|date=1995|publisher=[[Organization:Indiana State University|Indiana State University]]}}
* {{cite web|title=Chascon|url=http://volcano.oregonstate.edu/oldroot/CVZ/chascon/index.html|website=volcano.oregonstate.edu|publisher=[[Organization:Oregon State University|Oregon State University]]|accessdate=29 November 2015|ref=none}}
* {{cite GVP|vn=355829|name=Cerro Chascon}}

{{DEFAULTSORT:Chascon-Runtu Jarita}}

{{Sourceattribution|Cerro Chascon-Runtu Jarita complex|1}}