Sentinel granodiorite is a type of

granodiorite Granodiorite () is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gra ...

found in

Yosemite National Park Yosemite National Park ( ) is an American national park in California, surrounded on the southeast by Sierra National Forest and on the northwest by Stanislaus National Forest. The park is managed by the National Park Service and covers an ar ...

. It is a poorly understood western "outlier" of the ~93-85- Ma

Tuolumne Intrusive Suite The Tuolumne Intrusive Suite is one of several intrusive suites in Yosemite National Park. These also include # Fine Gold Intrusive Suite # Intrusive Suite of Buena Vista Crest # Intrusive Suite of Jack Main Canyon # Intrusive Suite of Mer ...

of the

Sierra Nevada batholith The Sierra Nevada Batholith is a large batholith which forms the core of the Sierra Nevada mountain range in California, exposed at the surface as granite. The batholith is composed of many individual masses of rock called ''plutons'', which fo ...

. It is only slightly older than the undated Yosemite Creek Granodiorite and the

Kuna Crest Granodiorite Kuna Crest Granodiorite (also called ''Granodiorite of Glen Aulin''), is found, in Yosemite National Park, United States. The granodiorite forms part of the Tuolumne Intrusive Suite (aka Tuolumne Batholith), one of the four major intrusive suites ...

.Structure of the Sentinel Granodiorite, Yosemite National Park, California – Books on Google Play
https://play.google.com/store/books/details/Joseph_M_Petsche_Structure_of_the_Sentinel_Granodi?id=OWfrbPb8hikC
accessdate: March 19, 2017

Its name

Sentinel granodiorite was named after

Sentinel Rock Sentinel Rock is a granitic peak in Yosemite National Park, California, United States. It towers over Yosemite Valley, opposite Yosemite Falls. Sentinel Rock lies northwest of Sentinel Dome. How it was formed Sentinel Rock formed when masse ...

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

.USGS: Geological Survey Professional Paper 160 (The Granitic Rocks of the Yosemite Region)
less uniform in composition than most of the other intrusive bodies. In the western part of the zone crossed by the Yosemite Valley this rock is relatively light-colored and homogeneous; the eastern part is much more streaky and uneven in composition and texture and on the whole is considerably darker than the western part. The eastern portion, again, may be roughly divided into two or three bands that differ mainly in texture.
accessdate: March 19, 2017 The

forms part of the

(Tuolumne Batholith), one of the four major intrusive suites within the

Sierra Nevada The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primarily ...

An overview, its composition

Sentinel granodiorite has a less uniform composition than other Yosemite granites and granodiorites. On the west end of

Yosemite Valley Yosemite Valley ( ; ''Yosemite'', Miwok for "killer") is a U-shaped valley, glacial valley in Yosemite National Park in the western Sierra Nevada (U.S.), Sierra Nevada mountains of Central California. The valley is about long and deep, surroun ...

, it is more homogeneous and light-colored, and on the east, it is more streaky, with an uneven composition. On the east, it is also much darker than on the west. The chemical composition of Sentinel Granodiorite is less uniform than most of the other intrusive bodies. In the western part of the zone crossed by the Yosemite Valley Sentinel Granodiorite is homogeneous and lighter colored, though the eastern part it is more streaky with an uneven in composition; the texture and on the whole is considerably darker than the western part. Sentinel Granodiorite is a light-gray and medium-grained

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more alumino ...

hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks ...

. The

color index In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The lower the color index, the more blue (or hotter) the object is. Conversely, the large ...

is normally about 15, and ranges from 10 to 25. The

is tabular, of

crystals A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosc ...

which are usually 4 - 6

millimeters 330px, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter. The millimetre (American and British English spelling differences#-re, -er, ...

long, and helps to define a weak to moderately strong magmatic foliation and lineation. Hornblende makes up from about 3% to 10% of Sentinel Granodiorite. Biotite makes up about 7% to 15%, and the crystals are one to five millimeters long. It is in an

aggregate Aggregate or aggregates may refer to: Computing and mathematics * collection of objects that are bound together by a root entity, otherwise known as an aggregate root. The aggregate root guarantees the consistency of changes being made within the ...

with the hornblende. Plagioclase makes up about 50% of Sentinel Granodiorite, and in size, ranges from one to ten millimeters.

Interstitial An interstitial space or interstice is a space between structures or objects. In particular, interstitial may refer to: Biology * Interstitial cell tumor * Interstitial cell, any cell that lies between other cells * Interstitial collagenase, ...

potassium feldspar Potassium feldspar refers to a number of minerals in the feldspar group, and containing potassium: *Orthoclase (endmember formula K Al Si3 O8), an important tectosilicate mineral that forms igneous rock *Microcline, chemically the same as orthoclas ...

makes up ten to thirty percent of Sentinel Granodiorite, is two to five millimeters across.

Sphene Titanite, or sphene (from the Greek ''sphenos'' (σφηνώ), meaning wedge), is a calcium titanium nesosilicate mineral, Ca Ti Si O5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals in ...

is abundant, but rarely more than 1% of Sentinel Granodiorite; it is wedge-shapes, and usually about 0.1 to 1 millimeter long, but can reach 2 millimeters in length. Other

accessory minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ...

are

allanite Allanite (also called orthite) is a sorosilicate group of minerals within the broader epidote group that contain a significant amount of rare-earth elements. The mineral occurs mainly in metamorphosed clay-rich sediments and felsic igneous rocks. ...

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of the r ...

, and

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...

."Structure of the Sentinel Granodiorite, Yosemite National Park, Califo" by Joseph M. Petsche
"Structure of the Sentinel Granodiorite, Yosemite National Park, Califo" by Joseph M. Petsche
accessdate: March 20, 2017 A soda-lime

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldsp ...

predominates over potash feldspar, and

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

is abundant.

Hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks ...

and

are present in moderate, nearly equal amounts.USGS: Geological Survey Professional Paper 160 (The Granitic Rocks of the Yosemite Region)
USGS: Geological Survey Professional Paper 160 (The Granitic Rocks of the Yosemite Region)
accessdate: March 18, 2017

Its relationship to Yosemite Creek Granodiorite

From Yosemite Creek Granodiorite, Sentinel Granodiorite varies only in texture: The

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more prope ...

is white on its weathered surfaces, more

euhedral Euhedral crystals (also known as idiomorphic or automorphic crystals) are those that are well-formed, with sharp, easily recognised faces. The opposite is anhedral (also known as ''xenomorphic'' or ''allotriomorphic''): a rock with an anhedral ...

, and the

is smaller, less euhedral. There exists ''transitional Sentinel / Yosemite Creek Granodiorite.

Where is it found

Granodiorite Boulder in Yosemite National Park

is composed entirely of Sentinel Granodiorite, gave it the name.{{cite book, author=George Wuerthner, title=Yosemite: A Visitor's Companion, url=https://books.google.com/books?id=imwYphvLeRgC&dq=%22Sentinel+granodiorite%22+geology&pg=PA322, year=1994, publisher=Stackpole Books, isbn=978-0-8117-2598-9, pages=57– Despite its name,

Sentinel Dome Sentinel Dome is a granite dome in Yosemite National Park, United States. It lies on the south wall of Yosemite Valley, southwest of Glacier Point and northeast of Profile Cliff. Sentinel Dome is known for a Jeffrey Pine that grew from its peak ...

is composed of El Capitan Granodiorite.

Sentinel Fall Sentinel Falls is a long series of cascades descending into Yosemite Valley, in the U.S. state of California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a ...

pours over Sentinel Granodiorite.Geotripper: Under the Volcano: Changing the Emphasis -Part 3
Geotripper: Under the Volcano: Changing the Emphasis -Part 3
accessdate: March 18, 2017

Its age

It is oldest unit in Tuolumne intrusive series. It has been assigned an age in the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

period, perhaps 90 Ma, perhaps as old as 94 Ma, or 96 to 94 Ma.Sentinel publications
Geolex - Sentinel publications
accessdate: March 20, 2017

Where found

The rock forms part of a large irregular intrusive body, but the portion of it here considered is a belt about 2 miles broad that crosses the valley from north to south. The walls of the Yosemite Valley consist mainly of a Sentinel

, a light-gray granitoid rock, from the Three Brothers to nearly as far east as the

Royal Arches The Royal Arches refers to a cliff containing natural occurring granite exfoliation arches, located below North Dome and rising above Yosemite Valley, in Yosemite National Park, California. (). The Royal Arches are located on the north side of t ...

, and from the Fissures on the east, to

Glacier Point Glacier Point is a viewpoint above Yosemite Valley in the U.S. state of California. It is located on the south wall of Yosemite Valley at an elevation of , above Curry Village. The point offers a superb view of several of Yosemite National Park ...

Rock climbing

rock climbing Rock climbing is a sport in which participants climb up, across, or down natural rock formations. The goal is to reach the summit of a formation or the endpoint of a usually pre-defined route without falling. Rock climbing is a physically and ...

, Sentinel Granodiorite is noted for its dihedrals,Search The American Alpine Journal and Accidents
North America, United States, California - Yosemite, In Cold Blood, West Face of Sentinel Rock - AAC Publications - Search The American Alpine Journal and Accidents
accessdate: March 21, 2017 plus for having

dikes Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes, ...

. Dikes of

aplite Aplite () is an intrusive igneous rock in which the mineral composition is the same as granite, but in which the grains are much finer, under 1 mm across. Quartz and feldspar are the dominant minerals. The term ''aplite'' or ''aplitic'' ...

and

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...

commonly intrude on Sentinel Granodiorite. Dikes vary in width from less than one

centimeter 330px, Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its deriveds scales. The Microwave are in-between 1 meter to 1 millimeter. A centimetre (international spelling) or centimeter (American spellin ...

of over one

meter The metre (British spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its prefi ...

, are usually ten to fifteen centimeters wide. They often extend several hundred meters, and have irregularly-shaped or web-like systems that can extend several tens of square meters.

References

External links

A Masters thesis

Geology of California Geology of Yosemite National Park Cretaceous magmatism