The Rock Cycle and Igneous Processes

Vocabulary flashcards covering the systems, mechanisms, and classifications of the rock cycle and igneous processes based on the Week 29 lecture.

Magma

Molten rock located beneath the Earth's surface, consisting of liquid molten minerals, crystals, and dissolved gases such as $H_2O$, $CO_2$, and $SO_2$.

Lava

Molten rock that has reached the Earth's surface.

Convection

The transfer of heat through the physical movement of a fluid driven by density differences, where warmer fluid rises and cooler fluid sinks.

Hotspot volcanism

A magma-making mechanism driven by hot plumes deep in the mantle or radioactive decay, which can occur in oceanic settings like Hawaii or continental settings like Yellowstone.

Decompression melting

A process where magma forms because rock rises and pressure drops while the temperature remains the same, occurring at mid-ocean ridges and continental rifts.

Hydrous melting

Also known as flux melting, this occurs in subduction zones where the addition of water lowers the melting point of pure rock from approximately $1200\text{°C}$ to between $800\text{°C}$ and $1000\text{°C}$.

Solidus

The specific temperature and pressure conditions below which a rock or mineral mixture remains completely solid.

Intrusive rocks

Igneous rocks formed from magma that cools slowly underground, resulting in fewer but larger, coarse-grained crystals (1-5\text{\ne mm}).

Extrusive rocks

Igneous rocks formed from lava that cools rapidly above ground, resulting in many tiny, fine-grained crystals (

Mafic Magma

Basaltic magma high in $Mg$ and $Fe$ with low silica (45-52\text{\ne %}), characterized by dark color, low viscosity, and gentle eruptions.

Felsic Magma

Granitic magma high in silica (>66\text{\ne %}) and light-colored, characterized by high viscosity (sticky) and highly explosive eruptions.

Viscosity

A measure of a fluid's resistance to flow; low viscosity magma flows easily and allows gases to escape, while high viscosity magma traps gases and builds pressure.

Andesitic magma

An intermediate magma type between basalt and granite, typically found in subduction zones and associated with explosive eruptions.

Dolerite

A medium-grained (1-3\text{\ne mm}), mafic, dark gray/black rock that cools at intermediate depths of 2-3\text{\ne km}; referred to as diorite in the U.S.

Hexagonal jointing

An efficient contraction pattern formed as basaltic lava cools quickly and fractures to relieve stress evenly in all directions.

Giant's Causeway

A UK igneous province in Northern Ireland formed 60\text{\ne Ma} by stacked basaltic lava flows during the opening of the North Atlantic Ocean.

The Cheviots

A 380\text{\ne Ma} andesitic volcanic complex in Northumberland that suggests ancient subduction zone volcanism.

Whin Sill

A quartz-dolerite intrusion formed approximately 295\text{\ne Ma} when rifting began and magma spread horizontally between sedimentary layers at 2-3\text{\ne km} depth.