igneous rocks & processes (mod #6)

🍂

magma

Molten rock beneath the Earth’s surface;

Temperature: ~600-1200ºC

consists of varying amounts of liquids, solid, and dissolved gas

True

TRUE OR FALSE:

Some components of magma include:

• Liquid: Ions of Si, O, Al, K, Ca, Na, Fe, Mg

• Solid: minerals, rock fragments

• Dissolved gas: H₂O, CO₂, SO₂

Mohorovicic discontinuity

UNDER MAGMA:

this serves as the boundary zone where rising mantle melts interact with, accumulate beneath, or intrude into the Earth's crust

anatexis

MAGMA GENERATION:

partial melting of source rock in the upper mantle / lower crust

• where low-melting-point minerals melt first while high-melting-point (refractory) minerals remain solid

partial melting

MAGMA GENERATION:

refers to differential melting of minerals between low and high melting temperature minerals

liquid melt fraction & residual rock

2 PRODUCTS OF DIFFERENTIAL/PARTIAL MELTING:

1. ________ - enriched in low temperature constituents

2. ________ - enriched in high temperature refractory elements

increase in temperature, decrease in pressure, addition of volatiles

3 processes involve in partial melting (PVT)

original heat, radioactive decay, nearby conduction, mantle upwelling

MAGMA GENERATION DRIVERS (INC TEMP):

possible heat sources:

1. ____ ___ at the time of Earth formation

2. ________ decay

3. ______ from a nearby body of magma

4. Mantle ______

True

TRUE OR FALSE:

Magma generation may occur along plate boundaries or within a plate (intraplate).

hot spot

UNDER MAGMA GENERATION (INC TEMP):

increase in temps happen in these abnormally hot regions where the mantle rises up through lithosphere (e.g. Hawaii, Iceland, Yellowstone)

decompression partial melting

MAGMA GENERATION DRIVERS (DEC PRESSURE):

this process include:

• reducing the pressure lowers the melting temperature

• Melting by (adiabatic) pressure reduction

divergent plate boundaries (rift valley, mid-ocean ridges, hydrothermal vents)

MAGMA GENERATION DRIVERS (DEC PRESSURE):

decrease in pressure occurs along these areas

flux melting

MAGMA GENERATION DRIVERS (ADD VOLATILES):

refers to lowering melting temperature under pressure from addition of volatiles like H2O and CO2;

Volatiles sourced from hydrous minerals from subducted slab that are released to overlying mantle wedge

convergent plate boundaries

MAGMA GENERATION DRIVERS (ADD VOLATILES):

flux melting occurs along these areas

• more specifically, ____ ____, — where crust & sediment dehydration of slab happens

ultramafic (peridotitic)

MAGMA TYPES:

SiO₂ content: < 45%

Temp range: > 1200

Rel. Density: High

Rel. Viscosity: Low

Gas Content: Low

mafic (basaltic/gabbroic)

MAGMA TYPES:

SiO₂ content: 45-52%

Temp range: 1000-1200

Rel. Density: 2nd highest

Rel. Viscosity: 2nd lowest

Gas Content: 2nd lowest

intermediate (andesitic/dioritic)

MAGMA TYPES:

SiO₂ content: 52-63%

Temp range: 800-1000

Rel. Density: 2nd lowest

Rel. Viscosity: 2nd highest

Gas Content: 2nd highest

felsic/acidic (rhyolitic/granitic)

MAGMA TYPES:

SiO₂ content: > 63%

Temp range: 650-800

Rel. Density: lowest

Rel. Viscosity: highest

Gas Content: highest

magmatic differentiation

Any process that causes magma composition to change;

includes assimilation, magma mixing

assimilation

MAGMATIC DIFFERENTIATION PROCESSES:

country rock incorporated, melt and then assimilate into the magma

magma mixing

MAGMATIC DIFFERENTIATION PROCESSES:

mixing and comingling of two magmas forming a composition in- between the two magma that mixed (homogenization)

• Different magma with different physical properties like density, buoyancy, viscosity

magma mingling

incomplete blending of two distinct magmas that meet but retain their individual identities;

occurs when contrasting temperatures, high viscosity differences, or rapid cooling prevent the melts from fully diffusing into one another

fractional crystallization

process of crystallizing & removal of crystals from magma;

separates the components of a mixture based on differences in their crystallization temperature or solubility

• minerals crystallize at diff temps

Bowen’s reaction series

UNDER FRACTIONAL CRYSTALLIZATION:

describes the temperature at which minerals crystallize when cooled, or melt when heated;

False; should be inverse

TRUE OR FALSE:

In Bowen’s reaction series, temperature and mineral composition have a direct relationship:

• as magma cools from high to low temperatures, the crystallizing minerals shift from being Fe-, Mg-, Ca-rich to being Silica, Na, K-rich.

size, shape, mineral grain arrangement

igneous rock textures describes the appearance of rock based on ___, ____, and ____ ____ arrangement;

it also reveals the history and setting of formation of the rock

• Rate of Cooling

• Amount of Volatiles

• Amount of Silica

3 things that can influence igneous rock textures (CVS)

1. abyssal/plutonic

2. hypabyssal/subvolcanic

TYPES OF INTRUSIVE IGNEOUS ROCKS (DEPTH):

1. ____/____ - formed deep beneath the surface

2. ____/____ - formed at shallow depths

1. aphanitic

2. phaneritic

IGNEOUS ROCK TEXTURES (CRYSTAL SIZE):

1. fine-grained; rapid cooling & volcanic (ex. rhyolite, basalt, andesite)

2. large, coarse-grained (visible to the naked eye); slow cooling & plutonic (ex. granite, gabbro, diorite)

porphyritic

IGNEOUS ROCK TEXTURES (CRYSTAL SIZE):

with two distinct crystal sizes—large crystals floating in a fine-grained or glassy background matrix, meaning it also has a 2-stage cooling process

• has phenocryst & groundmass

phenocryst, groundmass

PORPHYRITIC COMPONENTS:

• ______ - large, visible crystals.

• ______ - fine-grained surrounding material

pegmatitic

IGNEOUS ROCK TEXTURES (CRYSTAL SIZE):

igneous rock texture where all or most crystals are very large (> 3cm) & is very coarse-grained;

undergoes extremely slow cooling deep underground

True

TRUE OR FALSE:

A pegmatitic texture is formed from magma rich in volatiles.

• The high volatile content allows ions to move very quickly to build massive crystals rather than starting new tiny ones

euhedral

IGNEOUS ROCK TEXTURES (CRYSTAL SHAPE):

a.k.a. idiomorphic;

refer to crystals who are completely bounded by well-developed, sharp, and recognizable crystal faces;

they form when a mineral has plenty of space

subhedral

IGNEOUS ROCK TEXTURES (CRYSTAL SHAPE):

hypidiomorphic;

crystals that are only partially bounded by good crystal faces, while other sides are irregular or crowded out by neighboring minerals

anhedral

IGNEOUS ROCK TEXTURES (CRYSTAL SHAPE):

xenomorphic/allotriomorphic;

these lack any recognizable crystal faces or geometric shapes;

happens when a mineral crystallizes last, filling in leftover spaces remain between previously formed crystals

holocrystalline, harzburgite

IGNEOUS ROCK TEXTURES (CRYSTALLINITY):

100% crystals;

very slow cooling rate;

intrusive

• ex. ______

holohyaline, obsidian

IGNEOUS ROCK TEXTURES (CRYSTALLINITY):

100% glass;

very rapid cooling (quenching);

extrusive

• ex. ______

hypocrystalline, porphyritic andesite

IGNEOUS ROCK TEXTURES (CRYSTALLINITY):

crystals and glass

moderate cooling;

shallow intrusive (near surface/dikes)

• ex. ______

1. vesicular

2. amygdaloidal

3. pyroclastic/framgental

OTHER IGNEOUS TEXTURES:
1. pitted with vesicles

2. vesicles filled with secondary minerals (amygdules)

3. composed of consolidated fragments

False; should be amygdules

TRUE OR FALSE:

Phenocrysts are the secondary mineral infilling of a gas pore (void) and forms after the rock has already formed and cooled (post-emplacement).

felsic, < 25%

IGNEOUS ROCK CLASSIFICATION (COLOR INDEX):

light colored, < ___% dark minerals

intermediate, 25-45%

IGNEOUS ROCK CLASSIFICATION (COLOR INDEX):

___ to ___% dark minerals

mafic, 45-85%

IGNEOUS ROCK CLASSIFICATION (COLOR INDEX):

dark colored, ____ to ___% dark minerals

ultramafic, > 85%

IGNEOUS ROCK CLASSIFICATION (COLOR INDEX):

dark to greenish colored, > ___% dark minerals

check mod 5 for igneous rock classfication based on mineral assemblage !

check mod 5 for igneous rock classfication based on mineral assemblage !

1. pumice

2. scoria

IGNEOUS ROCK CLASSIFICATION (COLOR INDEX FOR VESICULAR):

1. forms from felsic/rhyolitic magma

2. forms from mafic/basaltic magma

1. > 66%

2. 52-66%

3. 45-52%

4. 45%

IGNEOUS ROCK CLASSIFICATION (WEIGHT % SILICA):

1. felsic/acidic/silicic: > ___% SiO₂ (silica rich)

2. intermediate: ____ to ____% SiO₂

3. basic / mafic: ___ to ____% SiO₂

4. ultrabasic / ultramafic: < ___% SiO₂; enriched with Fe & Mg

Batholith

INTRUSIVE IGNEOUS STRUCTURES:

plutons with surface exposures more than 100 km²

• plutons: large body of intrusive igneous rock that forms when molten magma cools and solidifies deep underground within the Earth's crust

stock

INTRUSIVE IGNEOUS STRUCTURES:

plutons with surface exposures less than 100 km²

Concordant

2 INTRUSION CLASSIFICATIONS:

intrusion contacts oriented parallel to pre-existing layering

• sill, laccolith, lopolith

Discordant

2 INTRUSION CLASSIFICATIONS:

intrusion boundaries oriented at a sharp angle to country rock layering;

• neck, diatreme, dike

sill

CONCORDANT INTRUSIVE STRUCTURES:

tabular, concordant pluton that looks like tabletops

Laccolith

CONCORDANT INTRUSIVE STRUCTURES:

blister-like concordant pluton with flat floor and domed roof

Lopolith

CONCORDANT INTRUSIVE STRUCTURES:

dish to funnel-shaped concordant plutons that have relatively flat roofs

Neck

DISCORDANT INTRUSIVE STRUCTURES:

cylindrical plutonic dikes that were ancient conduit pipes

Diatreme

DISCORDANT INTRUSIVE STRUCTURES:

carrot-shaped, cylindrical pipe that developed from explosive intrusions from deep within the mantle;

discordant

Dike

DISCORDANT INTRUSIVE STRUCTURES:

tabular intrusion that cross-cut the country rock;

discordant

geothermal energy

this refers to energy stored in the form of heat beneath the earth's surface;

Steam produced from heated underground water is used to power turbines to produce electricity;

Renewable and sustainable

third, ~14%

GEOTHERMAL ENERGY:

Philippines is the ___ largest geothermal producer & geothermal energy is around ___% of the country’s energy mix.

Tongonan, Makiling-Banahaw, Tiwi

OPERATING POWER PLANTS & GEOTHERM CAPACITIES (2026):

1. T_____- 722.7 MW

2. M____-B____- 458.5 MW

3. T____- 234 MW

4. Palinpinon- 192.5 MW

5. Bacon-Manito- 130 MW

6. Mindanao (Mt. Apo) - 108.5 MW

7. Nasulo- 49.4 MW

8. Maibarara- 20 MW