# Chivinar

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{{Short description|Volcano in northwest Argentina}}
{{coord|24|14|S|67|27|W|type:mountain_region:AR-SA|display=title|notes=<ref name=GioncadaOrlandi2014 />}}
'''Chivinar''' is a {{convert|5125|m}} high Late [Miocene](/source/Miocene) [volcano](/source/volcano) in Northwest Argentina. The volcano is noted for having erupted [rhyolite](/source/rhyolite)s containing [topaz](/source/topaz) in its early stage of evolution, the only known occurrence of such in South America. This topaz did form during the crystallization of the magma in a [fluorine](/source/fluorine)-rich phase thereof at low temperatures and pressures.<ref name=GioncadaOrlandi2014 /> The topazes reach sizes of {{convert|8|cm}}. The topaz bearing rocks cover a surface area of {{convert|8|x|4|km}} that is interrupted by a lava flow.<ref name=KoukharskyPereyra1991 /> Much older [granitoid](/source/granitoid) bodies also lie in the area and are 502–425 million years old.<ref name=RapelaCoira1992 />

The volcano has been constructed in three main phases. First, a set of rhyolite [lava dome](/source/lava_dome)s and plugs was erupted and formed a platform beneath the edifice without evidence of explosive activity or caldera formation. This unit appears on the northern and western flanks of the volcano between {{convert|3500|-|4000|m}} and form about one third of the total volume, with the domes ranging {{convert|0.3|-|1|km}} in width and {{convert|250|m}} in height. They are heavily hydrothermally altered and deformed. A gap during which tectonic and climatic degradation of the earlier domes occurred separates this stage from the next. Subsequently, destruction of domes during eruptions generated a unit consisting of coarse [dacite](/source/dacite) in [pumice](/source/pumice) and [breccia](/source/breccia) form spreading out from the centre. On top of this unit, an andesitic cone formed, dated at 9 [mya](/source/mya_(unit)).<ref name=GioncadaOrlandi2014 /> Some aphyric phenobasalts cover surfaces of the second unit.<ref name=KoukharskyPereyra1991 />

The early phase rhyolites contain [alkali feldspar](/source/alkali_feldspar) (49±2% volume), [plagioclase](/source/plagioclase) containing [sodium](/source/sodium) (14±3% volume) and [quartz](/source/quartz) (36±2% volume). A number of gas rich inclusions and accessory minerals are also present, including topaz, [xenotime](/source/xenotime) and [zircon](/source/zircon). Hydrothermally altered rhyolites contain [rutile](/source/rutile) and secondary silicates in veins. All products are porphyritic, including the late andesites which contain [phenocryst](/source/phenocryst)s of [hornblende](/source/hornblende) and [plagioclase](/source/plagioclase) with smaller amounts of [biotite](/source/biotite), [clinopyroxene](/source/clinopyroxene), [iron oxide](/source/iron_oxide)s and [orthopyroxene](/source/orthopyroxene). Based on crystal analysis, the rhyolites were stored at pressures of {{convert|300|-|400|MPa}} and temperatures of {{convert|720|-|730|C}}.<ref name=GioncadaOrlandi2014 />

The volcano is situated at the point where the main [volcanic arc](/source/volcanic_arc) intersects the ''Calama–Olacapato–El Toro lineament'', a [fault zone](/source/fault_zone) that has formed over fifteen million years a number of volcanic structures including lava domes, stratovolcanoes and monogenetic scoria cones. This fault system has imparted the Chivinar centre an extensional characteristic. The Chivinar centre itself formed over an [Eocene](/source/Eocene)-Miocene basement containing evaporites and sediments.<ref name=GioncadaOrlandi2014 />

== References ==
{{Reflist|refs=
<ref name=GioncadaOrlandi2014>{{cite journal|last1=Gioncada|first1=Anna|last2=Orlandi|first2=Paolo|last3=Vezzoli|first3=Luigina|last4=Omarini|first4=Ricardo H.|last5=Mazzuoli|first5=Roberto|last6=Lopez-Azarevich|first6=Vanina|last7=Sureda|first7=Ricardo|last8=Azarevich|first8=Miguel|last9=Acocella|first9=Valerio|last10=Ruch|first10=Joel|title=Topaz magmatic crystallization in rhyolites of the Central Andes (Chivinar volcanic complex, NW Argentina): Constraints from texture, mineralogy and rock chemistry|journal=[Lithos](/source/Lithos_(journal)) |date=January 2014|volume=184-187|pages=62–73|doi=10.1016/j.lithos.2013.10.023|bibcode=2014Litho.184...62G|hdl=11336/31239|hdl-access=free}}</ref>
<ref name=RapelaCoira1992>{{cite journal|last1=Rapela|first1=C. W.|title=The Lower Paleozoic Magmatism of Southwestern Gondwana and the Evolution of the Famatinian Orogen|last2=Coira|first2=B.|last3=Toselli|first3=A.|last4=Saavedra|first4=J.|journal=[International Geology Review](/source/International_Geology_Review)|date=November 1992|volume=34|issue=11|pages=1081–1142|doi=10.1080/00206819209465657|bibcode=1992IGRv...34.1081R}}</ref>
<ref name=KoukharskyPereyra1991>{{cite journal|last1=Koukharsky|first1=Magdalena|last2=Pereyra|first2=Fernando|last3=Etcheverria|first3=Mariela|last4=Lanes|first4=Silvia|title=La riolita con topacio del Cerro Chivinar, Departmento Los Andes, Provincia De Salta|journal=Revista de la Asociación Geológica Argentina|date=1991|volume=46|issue=3–4|page=350|url=https://books.google.com/books?id=pZjJPpgrXJIC&pg=PA350|accessdate=21 November 2015|language=es|issn=1851-8249}}</ref>}}

Category:Miocene volcanoes
Category:Volcanoes of Salta Province

{{Volcanology-stub}}

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Adapted from the Wikipedia article [Chivinar](https://en.wikipedia.org/wiki/Chivinar) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Chivinar?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.