Question

Mount Whitney, the highest summit \((4421\) meters or 14,505 feet \(])\) in the contiguous United States, is located in the Sierra Nevada batholith. Based on its location, is Mount Whitney likely composed of granitic, andesitic, or basaltic rocks?

Short answer

Mount Whitney is likely composed of granitic rocks.

Step-by-step solution

Understand the Sierra Nevada Batholith

The Sierra Nevada batholith is a large geologic feature formed primarily by the intrusion of magma into the crust which then solidified below the surface. It is primarily composed of granitic rock. This characteristic composition is crucial for identifying the type of rock Mount Whitney is likely composed of.

Characteristics of Granitic Rock

Granitic rock is an intrusive igneous rock, characterized by a coarse-grained texture and primarily composed of quartz, feldspar, and mica. Its formation is associated with continental crust processes and is typical of mountain ranges formed by plate tectonics, like the Sierra Nevada.

Comparison with Andesitic and Basaltic Rocks

Andesitic rocks are intermediate in composition, typically found at volcanic arcs, and have moderate silica content. Basaltic rocks are extrusive igneous rocks, mainly composed of pyroxene and olivine, with low silica content, often found at mid-ocean ridges and volcanic islands. These characteristics do not match the continental setting of the Sierra Nevada batholith.

Conclusion Based on Location and Composition

Given that Mount Whitney is part of the Sierra Nevada batholith, which is largely granitic, it is most likely composed of granitic rocks rather than andesitic or basaltic rocks. The continental intrusive setting favors the presence of granitic rocks.

Key concepts

Sierra Nevada batholith

The Sierra Nevada batholith is an impressive geological structure made up of large bodies of intrusive igneous rock. Situated in California, it stretches over 650 kilometers, forming the backbone of the Sierra Nevada mountain range. This batholith was primarily shaped by magma that intruded into the Earth's crust during the Mesozoic Era before solidifying. This process made it predominantly granitic in composition.

Granitic rocks are crucial because they form when magma cools slowly beneath the Earth’s surface, leading to the formation of large crystals, evident in their coarse-grained texture. The Sierra Nevada batholith stands as a testament to significant geological processes, known as plutonism, which contributed to the configuration of continental features we see today.

• The formation of the batholith involved tectonic movements that allowed magma to invade the crustal layers.
• This region exhibits a vast array of granitic compositions, which vary based on specific geological conditions at the time of magma intrusion.

The Sierra Nevada batholith is often studied for its rich geological history and the insights it provides into Earth's continental crust development.

intrusive igneous rock

Intrusive igneous rocks are formed from magma that cools and solidifies beneath the Earth’s surface. This process occurs slowly, allowing time for the growth of large, visible crystals, such as in granite. These rocks are also referred to as "plutonic rocks," originating from the mythic god Pluto, ruler of the underground.

In contrast to extrusive rocks, which cool rapidly and often have a fine-grained texture, intrusive rocks allow minerals like quartz, feldspar, and mica to crystallize fully. This results in the characteristic coarse-grained texture.

Key characteristics of intrusive igneous rocks include:

• Slow cooling process leading to large crystal formation
• Located deep within the Earth’s crust
• Generally forms larger masses known as plutons

Granitic rocks from the Sierra Nevada batholith are excellent examples, displaying the typical traits of intrusive igneous processes within continental crust.

continental crust processes

Continental crust processes encompass the various geological activities that occur within the Earth's continents, shaping their structure and composition. One of the significant contributors to these processes is magma intrusions that form intrusive igneous rocks.

These processes include tectonic activities such as plate collisions and mountain-building events, which provide the pressure and heat necessary to create magma. Over time, this leads to the formation of significant geological features like batholiths, mountain ranges, and more.

The development of the Sierra Nevada batholith involved several continental crust processes:

• Subduction of oceanic plates beneath continental plates, generating magma
• Magma intrusion into crustal layers forming large plutonic bodies
• Uplift and erosion exposing the granitic formations

Such processes not only sculpt the physical features of continents but also significantly influence their geological composition, making them a rich area of study for understanding Earth's dynamic nature.