VIDEO 3

Summary

This video explores the Bowen's reaction series, which explains how different types of rocks form from a single magma. The process begins with the heaviest minerals like olivine sinking to the bottom of the magma chamber, while lighter minerals like plagioclase rise to the top. The video delves into the formation of diverse rock types, such as basalt, andesite, and granite, and explains how partial melting of the mantle leads to the creation of continents. The lecture also covers real-world examples like the Palisade sill, Hawaii, and Yellowstone, illustrating how magma composition influences volcanic activity and land formation.

Takeaways

• 😀 The Bowen's Reaction Series explains how magma differentiates into different types of rocks based on their mineral composition and crystallization order.
• 😀 Olivine, the first mineral to crystallize in the Bowen's Reaction Series, is dense and settles at the bottom of the magma chamber, creating a mafic rock.
• 😀 As crystallization progresses, pyroxenes and plagioclase feldspars form, leading to the creation of intermediate to felsic rocks towards the top of the magma chamber.
• 😀 The Palisades Sill in New York demonstrates the Bowen's Reaction Series, where basalt forms at the bottom, followed by layers of olivine, pyroxenes, and feldspar.
• 😀 The mantle's composition, primarily peridotite, is key to understanding how basaltic and other rock types form at mid-ocean ridges and subduction zones.
• 😀 The partial melting of basaltic ocean plates results in andesitic or granitic magma, which contributes to the formation of continents over time.
• 😀 Continents first formed from andesitic volcanic islands, which eventually merged and grew into larger landmasses.
• 😀 At mid-ocean ridges, basaltic lava forms from ultramafic peridotite, creating new oceanic crust that is mafic in composition.
• 😀 Hawaii is an example of a hotspot where ultramafic peridotite melts to create highly mafic lava, leading to the formation of green sand beaches.
• 😀 Yellowstone is a result of a hotspot beneath the North American plate, where initially basaltic lava flows later evolved into felsic magma, forming a supervolcano.

Q & A

What is the Bowen's reaction series, and how does it relate to the formation of different rocks in a magma chamber?

The Bowen's reaction series is a sequence of mineral crystallization in cooling magma. It explains how different minerals form at various temperatures, starting with olivine (most iron and magnesium-rich) at the highest temperature and progressing to feldspars and silica-rich minerals. This leads to the formation of different types of rocks, such as mafic rocks at the bottom and more felsic rocks at the top of a magma chamber.

What is the significance of the Palisade Sill in New York, and how does it illustrate Bowen's reaction series?

The Palisade Sill is a geological formation along the Hudson River where basaltic magma injected between sandstone layers. The formation of different minerals, such as olivine, plagioclase, and pyroxenes, follows Bowen's reaction series, illustrating how the magma crystallized into mafic rock (basalt) at the bottom and more felsic minerals at the top.

Why is the formation of different rocks in a magma chamber not uniform throughout?

The formation of different rocks in a magma chamber is not uniform because minerals crystallize at different temperatures as described by Bowen's reaction series. Heavier minerals like olivine (rich in iron and magnesium) crystallize first and sink to the bottom, while lighter minerals, which crystallize at lower temperatures, remain higher in the chamber.

How does partial melting of mantle material contribute to the formation of different types of magma?

Partial melting occurs when only part of the mantle material melts, creating magma that is more mafic (basaltic) rather than ultramafic (peridotitic). The minerals with higher melting points, like olivine and pyroxenes, remain in the mantle, while those with lower melting points contribute to the formation of andesitic or granitic magma at the surface.

How does the Bowen's reaction series help explain the differences between oceanic and continental volcanic rocks?

The Bowen's reaction series explains that oceanic volcanic rocks, like basalt, are derived from the partial melting of ultramafic mantle material (peridotite), whereas continental volcanic rocks, like andesite and granite, are the result of partial melting of mafic oceanic crust or already formed volcanic rocks, which have a lower melting point.

Why does the Earth's mantle remain ultramafic, even though it contributes to the formation of more felsic rocks?

The mantle remains ultramafic because not all of it melts. Only the more easily melted parts of the mantle contribute to magma formation, resulting in more felsic volcanic rocks. The higher melting point minerals, such as olivine and pyroxenes, remain in the mantle while only the lower melting point minerals are brought to the surface.

What role does the Bowen's reaction series play in the formation of continents?

The Bowen's reaction series explains that the first continental crust likely formed from volcanic islands made of andesitic magma. As partial melting of oceanic plates occurs, the resulting magma produces more felsic rocks, which accumulate and eventually form continents over time.

Why is Hawaii a hotspot for mafic material, and what does this imply about its geological formation?

Hawaii is a hotspot because it is located over a mantle plume where ultramafic material from the mantle melts to create basaltic magma. The result is the formation of volcanic islands composed of very mafic material, such as olivine, which contributes to the characteristic green sand beaches.

How does the formation of basalt at mid-ocean ridges relate to the composition of the Earth's mantle?

Basalt forms at mid-ocean ridges because the mantle material beneath these ridges is ultramafic (peridotite). As this material partially melts due to pressure and temperature changes, it forms basalt, a mafic rock. This basalt eventually makes up the oceanic crust.

What is the connection between the Yellowstone Caldera and mantle hotspot activity?

The Yellowstone Caldera is a result of a mantle hotspot beneath North America. Originally, this hotspot melted the basaltic mantle to form large lava flows, but over time, as the North American plate moved, the hotspot began melting the overlying felsic crust, creating a volcanic system that could eventually result in the formation of a supervolcano.