View source for Earth:Kuna Crest Granodiorite

{{Short description|Kuna Crest Granodiorite, Granodiorite of Glen Aulin is a granodiorite found Yosemite National Park}}

{{Infobox rockunit
|name         = Kuna Crest Granodiorite
|age          = 91 [[Physics:Mya (unit)|Ma]]
|period       = turonian
|image        =
|imagesize    = 300px
|type         = [[Earth:Geological formation|Geological formation]]
|prilithology =[[Earth:Granodiorite|Granodiorite]]
|region       = Yosemite National Park
|country      = United States
|map          = Map of Cathedral Peak Granodiorite.svg
|map_caption  = A geologic map of Yosemite National Park
|namedfor     = Kuna Crest
}}

'''Kuna Crest Granodiorite''' (also called ''Granodiorite of Glen Aulin''),<ref name="sjsu.edu">{{cite thesis |last= Petsche|first=Joseph M. |date=2008 |title=Structure of the Sentinel Granodiorite, Yosemite National Park, California |type= MS|publisher=San Jose State University |url=http://scholarworks.sjsu.edu/etd_theses/3655/ |access-date=21 March 2017}}</ref> is found, in Yosemite National Park, United States. The [[Earth:Granodiorite|granodiorite]] forms part of the Tuolumne Intrusive Suite (aka '''Tuolumne Batholith'''), one of the four major [[Earth:Intrusive suite|intrusive suite]]s within the Sierra Nevada. Of the Tuolumne Intrusive Suite, it is the oldest and darkest rock.<ref name="yosemite.ca.us">The Geologic Story of Yosemite National Park (1987), "Rocks, the building materials," by N. King Huber: [http://www.yosemite.ca.us/library/geologic_story_of_yosemite/rocks.html the oldest and darkest rock in the Tuolumne Intrusive Suite], accessdate: 7 March 2017</ref>

Kuna Crest granodiorite forms most of the outer part of the Tuolumne Intrusive Suite, on the edges.<ref name="oup.com">{{cite journal |last1=Solgadi |first1=F. |last2=Sawyer |first2=E. W. |title=Formation of Igneous Layering in Granodiorite by Gravity Flow: a Field, Microstructure and Geochemical Study of the Tuolumne Intrusive Suite at Sawmill Canyon, California |journal=Journal of Petrology |date=2008 |volume=49 |issue=11 |pages=2009–2042 |doi=10.1093/petrology/egn056|bibcode=2008JPet...49.2009S |doi-access=free }}</ref>

==Name==
The word ''Kuna'' probably derives from a Shoshonean word, with a meaning "fire," appearing in the [[Social:Mono language (California)|Mono dialect]] of the area, with meaning of ''firewood''.<ref name="Place Names of the High Sierra">{{cite web |url=https://www.yosemite.ca.us/library/place_names_of_the_high_sierra/k.html | title=Place Names of the High Sierra | publisher=yosemite.ca.us | date=1926 | access-date=6 February 2019 | author=Farquhar, Francis P.}}</ref><ref name="California place names of Indian origin">{{cite web |url=https://archive.org/stream/californiaplacen00kroerich/californiaplacen00kroerich_djvu.txt | title=California place names of Indian origin | date=2007 | access-date=6 February 2019 | author=Kroeber, A.L.}}</ref> The rocks on Kuna Peak can be a red color<ref name="guroute.com">Attractions in Kuna Peak: [https://www.guroute.com/Tours/Index/368584#box=DetailsBox:id=poi_368584 Attractions in Kuna Peak], accessdate: 10 March 2017</ref> and Kuna Peak is the highest point on Kuna Crest. Kuna Crest granodiorite was first identified on Kuna Crest, from which Kuna Peak rises.<ref name="Wuerthner1994">{{cite book|author=George Wuerthner|title=Yosemite: A Visitor's Companion|url=https://books.google.com/books?id=wLNIty6rCKsC&pg=PA57|year=1994|publisher=Stackpole Books|isbn=978-0-8117-2598-9|pages=57–}}</ref><ref name="summitpost.org">Kuna Peak : Climbing, Hiking & Mountaineering : SummitPost: [http://www.summitpost.org/kuna-peak/150596 Kuna Peak : Climbing, Hiking & Mountaineering : SummitPost], accessdate: 11 March 2017</ref>

==Geology==
Kuna Crest Granodiorite makes up most of the outer part of the Tuolumne Intrusive Suite. Of the Tuolumne Intrusive Suite, it is the most melanocratic of the granodiorites containing many [[Earth:Mafic|mafic]] microgranular enclaves. It is fine- to medium-grained (0.1–4&nbsp;mm). The mafic minerals are generally oriented and define a [[Earth:Foliation (geology)|foliation]].

[[Chemistry:Plagioclase|Plagioclase]] is its most abundant mineral and is generally in euhedral crystals with rare inclusions. Thus [[Chemistry:Plagioclase|plagioclase]] is viewed the first [http://serc.carleton.edu/research_education/equilibria/phaserule.html phase] to crystallize from the [[Biology:Magma|magma]].

The cores of some crystals are irregularly shaped, and have more [[Chemistry:Sodium|sodium]] than outer parts. There is evidence that magma producing Kuna Crest Granodiorite mixed with other magmas.

[[Chemistry:Magnetite|Magnetite]] crystals and those of [[Chemistry:Titanite|titanite]] in the Kuna Crest granodiorite are usually euhedral, and occur in aggregates. So, they are interpreted to be early phases ([[Earth:Primocryst|primocryst]]s), who crystallized together. The magnetite crystals are smaller (~0.1–0.5&nbsp;mm) than those of titanite (~0.5–3&nbsp;mm). The titanite crystals commonly display compositional zoning. The [[Chemistry:Biotite|biotite]] crystals are 1–3&nbsp;mm across, being more or less euhedral; but they contain small inclusions of titanite and magnetite, indicating that biotite [[Physics:Crystallization|crystallization]] began after them.

The distinguishing feature of the Kuna Crest granodiorite is the presence of anhedral crystals of [[Chemistry:Hornblende|hornblende]] abounding in inclusions of the other minerals. So hornblende might have been the last mafic primocryst mineral to have finished growing.

Between the other crystals, the last minerals to crystallize were K-feldspar and [[Chemistry:Quartz|quartz]]. So the quartz is denoted ''interstitial quartz''. These have all axes of the same length (1–3&nbsp;mm), and are anhedral, and show no evidence of significant post-crystallization strain.

[[Chemistry:Apatite|Apatite]] and [[Chemistry:Zircon|zircon]] are common accessory minerals, and occur as relatively euhedral crystals. Because none of the mafic minerals are  fractured or bent and the interstitial quartz keeps all axes the same length, the strong orientation shown by the euhedral minerals and the [[Chemistry:Hornblende|hornblende]] is viewed to be a [[Earth:Magmatic foliation|magmatic foliation]]. The absence of well-balanced, 120° facial [[Angle|angle]]s between the minerals indicates that no major readjustment of the grain boundaries took place after the magma had [[Physics:Crystallization|crystallized]].<ref name="oup.com"/>

Estimates from petrographic observation of average mineral proportion of non-layered rocks of Kuna Crest granodiorite follows:

{| class="wikitable"
|-
!  Mineral
!     Its percentage
|-
| [[Chemistry:Plagioclase|Plagioclase]]
|     40%
|-
| [[Chemistry:Quartz|Quartz]]
|     20%
|-
| [[Chemistry:Biotite|Biotite]]
|     15%
|-
| K-feldspar
|       9%
|-
| [[Chemistry:Hornblende|Hornblende]]
|     15%
|-
| [[Chemistry:Titanite|Titanite]]
|       0.5%
|-
| [[Chemistry:Magnetite|Magnetite]]
|       0.5%
|}

Of the Tuolumne Intrusive Suite, in Kuna Crest granodiorite, the proportion of the mafic minerals is greatest, at 21%. The abundance of light rare earth elements (the cerium group of elements) is similar in [[Earth:Half Dome Granodiorite|Half Dome Granodiorite]] and [[Earth:Cathedral Peak Granodiorite|Cathedral Peak Granodiorite]], but is lowest in Kuna Crest granodiorite.<ref name="oup.com"/>

==Where it is found==

Kuna Crest granodiorite is tied to Kuna Peak, also in Yosemite, and Kuna Crest, being first identified on Kuna Crest, from which Kuna Peak rises.<ref name="summitpost.org"/><ref name="Wuerthner1994"/>

It is exposed at Glacier Point, and is found, on the east end of Yosemite Valley. 
<ref>{{Cite book
 | last = Glazner
 | first = Allen F.
 |author2=Greg M. Stock
 | year = 2010
 | title = Geology Underfoot in Yosemite
 | publisher = Mountain Press Publishing Company
 | location = Missoula, Montana
 | page = 49
 | isbn = 978-0-375-72626-2
}}</ref><ref name="yosemite.ca.us" /> It is also found on the west side of the pluton and near Tioga Pass on the east side of the Sierra Nevada batholith.<ref name="http://memim.com/cathedral-peak-granodiorite.html">Cathedral Peak Granodiorite: [http://memim.com/cathedral-peak-granodiorite.html Cathedral Peak Granodiorite], accessdate: 12 March 2017</ref> It is found, on Kuna Crest.<ref name="Wuerthner1994"/>

It is also found near May Lake, though [[Earth:Till|till]] covers it.<ref>{{Cite book
 | last = Glazner
 | first = Allen F.
 | author2=Greg M. Stock
 | year = 2010
 | title = Geology Underfoot in Yosemite
 | publisher = Mountain Press Publishing Company
 | location = Missoula, Montana
 | page = 189
 | isbn = 978-0-375-72626-2
}}</ref>

==Its age==
It is about 91 million years old, the oldest granodiorite of the Tuolumne Meadows area.<ref name="yosemite.ca.us" />

==See also==
* [[Earth:Cathedral Peak Granodiorite|Cathedral Peak Granodiorite]]
* [[Earth:El Capitan Granite|El Capitan Granite]]
* Geology of the Yosemite area
* [[Earth:Half Dome Granodiorite|Half Dome Granodiorite]]
* Johnson Granite Porphyry
* [[Earth:Kuna Crest|Kuna Crest]]
* [[Earth:Sentinel granodiorite|Sentinel granodiorite]]
* Tuolumne Intrusive Suite

==References==
{{reflist}}
{{refbegin}}
* {{cite journal|title=Magma addition and flux calculations of incrementally constructed magma chambers in continental margin arcs: Combined field, geochronologic, and thermal modeling studies|first1=SR|last1=Paterson|first2=D|last2=Okaya|first3=V|last3=Memeti|first4=R|last4=Economos|first5=RB|last5=Miller|journal=Geosphere|year=2011|volume=7|issue=6|pages=1439–1468|doi=10.1130/GES00696.1|bibcode=2011Geosp...7.1439P|doi-access=free}}
* {{cite book
|last= Glazner and Stock
|date= 2010
|title= Geology Underfoot in Yosemite National Park
|location= Yosemite National Park
|publisher= Mountain Press Publishing Company
|isbn= 978-0-87842-568-6
}}
{{refend}}

[[Category:Cretaceous magmatism]]

{{Sourceattribution|Kuna Crest Granodiorite}}