CH. 4,5&6 Igneous Rocks: A Comprehensive Study Guide

What is magma?

Magma is molten rock material generated by partial melting of Earth's mantle and crust, containing liquids, crystals, gases, and rock fragments.

What is lava?

Lava is magma that reaches the Earth's surface, which can create various volcanic features and deposits.

What are intrusive (plutonic) rocks?

Igneous rocks formed from magma that cools slowly below the Earth's surface, resulting in large, visible crystals.

What is partial melting?

The process by which only a portion of a solid rock melts, creating magma with a composition depending on the original rock.

What is decompression melting?

Melting that occurs due to a decrease in pressure, significant for magma generation at mid-ocean ridges.

What is the significance of volatile content in magma?

The amount of dissolved gases in magma, which influences its viscosity and eruptive style.

What does the term 'felsic' describe?

Rocks that are rich in silicon and aluminum, typically light-colored, such as granite and rhyolite.

What characterizes mafic rocks?

Mafic rocks are rich in magnesium and iron, usually dark-colored, like basalt and gabbro.

How does cooling rate affect igneous rock texture?

Rapid cooling leads to small crystals or glassy textures, while slow cooling allows for large crystals to form.

What is the difference between phaneritic and aphanitic textures?

Phaneritic textures have visible crystals, whereas aphanitic textures have crystals too small to be seen without magnification.

What is Bowen's Reaction Series?

A model that describes the order of mineral crystallization from magma as it cools.

What are shield volcanoes?

Large, gently sloping volcanoes formed from the accumulation of fluid basaltic lava flows.

What is the IUGS classification system used for?

It is used for classifying igneous rocks based on their modal or normative mineral composition and texture.

What does the term 'pyroclastic texture' refer to?

A texture formed from the accumulation and consolidation of volcanic fragments, such as tuff and breccia.

What are the three Vs controlling eruptive style?

Viscosity, volatiles, and volume.

What is the difference between modal and normative mineralogy?

Modal mineralogy is the actual mineral composition, while normative mineralogy is a calculated composition based on chemical analysis.

What are the eruptive styles associated with low-viscosity and high-viscosity magmas?

Low-viscosity magmas result in effusive eruptions, while high-viscosity magmas lead to explosive eruptions.

What is a caldera?

A large, basin-shaped volcanic depression formed by the collapse of a volcano's summit.

What is the relationship between silica content and magma viscosity?

Higher silica content increases magma viscosity and affects the eruption style.

What is the significance of ophiolites?

Ophiolites represent sections of oceanic crust and upper mantle that have been thrust onto continental crust, providing insights into the formation of oceanic crust.

What type of rock is basalt?

A fine-grained, mafic extrusive rock belonging to the oceanic crust.

How does magma differ from lava?

Magma is molten rock beneath the Earth's surface, while lava is magma that has erupted onto the surface.

What are flood basalts?

Extensive outpourings of basaltic lava that cover large areas, often associated with massive volcanic events.