Magma Differentiation .mov

Summary

This lecture explains the Bowen's Reaction Series, describing how magma differentiates to form various rocks such as basalt, andesite, and granite. Starting with ultramafic peridotite in the mantle, the process of partial melting leads to the creation of oceanic crust and the formation of continents over time. Real-world examples like the Palisades Sill, Hawaii’s green sand beaches, and Yellowstone’s supervolcano illustrate these geological processes. The lecture emphasizes the importance of Bowen's Reaction Series in understanding magma differentiation, volcanic activity, and the ongoing evolution of Earth’s crust.

Takeaways

• 😀 The Bowen's Reaction Series explains how different minerals crystallize at different temperatures in a magma chamber, leading to the formation of diverse rock types from the same magma.
• 😀 Olivine, being rich in iron and magnesium, crystallizes first in the Bowen's reaction series and falls to the bottom of the magma chamber.
• 😀 As magma cools, minerals like pyroxene and plagioclase feldspar crystallize next, creating a layered structure in the magma chamber with basalt at the bottom and more felsic rocks at the top.
• 😀 The Palisade Sill in New York is an example of how basaltic magma was injected between layers of sandstone, showing the complex mineral layering due to Bowen's Reaction Series.
• 😀 Bowen's Reaction Series helps to explain puzzling geological phenomena, such as the formation of basalt at mid-ocean ridges from mantle-derived ultramafic magma.
• 😀 Continental formation relies on partial melting of oceanic crust at subduction zones, where only felsic components of the basaltic ocean plate melt to form more silica-rich magma like andesite or granite.
• 😀 Continents are built through the slow accumulation of felsic volcanic material from partially melted basaltic ocean plates, with the first landmasses being andesitic islands.
• 😀 The mantle's ultramafic composition remains because certain minerals like olivine and pyroxene have high melting points and don't melt when the magma undergoes partial melting.
• 😀 At mid-ocean ridges, ultramafic rocks like peridotite melt to form basaltic lava, while more felsic material is left behind in the mantle, which is why oceanic crust is primarily basalt.
• 😀 Hotspot volcanism, such as the one beneath Hawaii, is a source of more mafic lava, including basalt and olivine, leading to features like green sand beaches that are rich in olivine.
• 😀 The Yellowstone Caldera is the result of a hotspot that once melted the Earth's mantle, producing basaltic lava flows and later transitioned to melt the felsic crust, forming a massive volcanic system.

Q & A

What is Bowen's reaction series and how does it relate to magma differentiation?

Bowen's reaction series explains the order in which minerals crystallize from magma. It suggests that minerals with higher iron and magnesium content, like olivine, crystallize first and sink to the bottom, while minerals with higher silica content, like feldspar, crystallize last, forming a differentiation of rock types in a magma chamber.

How does Bowen's reaction series help explain the formation of different types of rocks in a magma chamber?

Bowen's reaction series helps explain that as magma cools, minerals crystallize in a specific order based on their melting points. The first minerals to form, like olivine, are iron and magnesium-rich, while the last to form, like feldspar, are more silica-rich, leading to the formation of different rock types within the same magma chamber.

What is the significance of the Palisades Sill in understanding Bowen's reaction series?

The Palisades Sill in New York is a practical example of Bowen's reaction series in action. It shows how basaltic magma injected between layers of sandstone crystallized minerals like olivine, calcium-rich plagioclase, and sodium-rich plagioclase at different levels within the magma chamber, resulting in a layered rock formation.

How does Bowen's reaction series address the apparent discrepancy between mantle composition and surface rock types?

Bowen's reaction series clarifies that the mantle, which is ultramafic, produces basaltic magma that is more mafic (iron and magnesium-rich). However, through partial melting, only the more felsic minerals (silica-rich) melt and rise to the surface, forming rocks like andesite and granite, which appear to contradict the composition of the mantle.

Why does the mantle not melt entirely when forming magma, according to Bowen's reaction series?

The mantle does not melt entirely because the minerals with higher melting points, such as olivine and pyroxene, remain solid, while the minerals with lower melting points melt first. This results in only partial melting of the mantle, creating more felsic magma while the mafic components stay behind.

How does the partial melting of oceanic plates contribute to the formation of continents?

Partial melting of basaltic oceanic plates produces andesitic or granitic magma, which is more felsic and lighter than the original basalt. Over time, this magma accumulates to form the first landmasses, such as andesitic volcanic islands, eventually leading to the formation of continents.

Where would you find mafic lava, and what is its characteristic composition?

Mafic lava is typically found at mid-ocean ridges and hotspots. It has a higher content of iron and magnesium, making it more dense and darker in color, and it forms rocks like basalt. Hawaii is a prime example, where mafic lava from the mantle creates features like green sand beaches made of olivine.

What is the significance of the mantle being ultramafic in the context of volcanic activity?

The mantle's ultramafic composition, rich in minerals like olivine and pyroxene, plays a key role in volcanic activity. When partial melting occurs, only the more felsic components of the mantle melt and rise to form volcanic rocks like basalt, andesite, or granite, contributing to the composition of Earth's crust.

How does the Yellowstone Caldera relate to Bowen's reaction series and the formation of volcanic rocks?

The Yellowstone Caldera is located above a hotspot where the mantle melts and produces felsic magma. This felsic magma eventually forms explosive volcanic activity. Bowen's reaction series explains this by showing that the more mafic mantle partially melts, producing the felsic magma that causes the large volcanic eruptions in Yellowstone.

What role does Bowen's reaction series play in understanding the origins of Earth’s continents?

Bowen's reaction series helps explain the formation of Earth's continents by showing how partial melting of the oceanic crust creates felsic magma that accumulates to form landmasses. As magma from the mantle melts and rises, it produces volcanic islands, which eventually grow into continents through further geological processes.