igneous rocks

(average crustal geothermal gradient)

= 20 °C/km

-- 5 main mafic minerals

1. olivine 2. pyroxene 3. hornblende 4. biotite mica 5. Ca-rich plagioclase feldspar

3 main types of magma(BAR)

1. Basaltic magma 2. Andesitic magma 3. Rhyolitic magma

3 main types of rocks

1. igneous rocks = formed from solidification of magma 2. sedimentary rocks = formed from sedimentation of materials transported in solution(precipitated) or suspension 3. metamorphic rocks = formed by alteration of preexisting sedimentary or igneous rocks in response to increased pressure + temp

-- 4 main felsic minerals

1. quartz 2. potassium feldspar 3. Na-rich plagioclase feldspar 4. muscovite mica

IGNEOUS ROCK CLASSIFICATION

= based on: -- where it cooled (under or above ground) -- where it's magma submerges(plate boundary + parent rock) -- composition of felsic + mafic minerals

plutons

= bodies of intrusive igneous rock

altering temp

= by increasing heat or lowering rock melting temp through pressure + water pressure alone → increases heat → raises temp of DRY rocks/minerals pressure + water → water lowers melting temps + pressure lowers melting temps -- water creates fluid pressure → causes rock to melt with dissolved H₂O

solidification of magma

= cooling + crystallization -- magma can crystalize into hundreds of different types of igneous rocks 1. minerals that crystalize FIRST(@ higher temp) become separate from the melt → "fall out" 2. fractional crystallization = melt evolves(changes) as more crystals form and fall out(squeezed out, sink)

(andesite line)

= corresponds to subduction zones 250 km from trench

(crystal nucleation)

= crystallization of magma → as magma cools atoms bond together to form crystals crystal size correlates to cooling rate: -- small crystals = fast cooling -- large crystals = slow cooling

volcanic pipe

= cylindrical conduit that once fed a volcanic vent volcanic neck = solidified volcanic pipe

IGNEOUS ROCK COMPOSITION

= depends on mineral composition in magma magma is a mixture of varying levels of mafic and felsic minerals minerals show where magma originated from --> ocean or continental crust

Bowen's one magma modle

= he argued that a single magma could crystallize into both basalt and rhyolite

(ophiolite suite)

= large magma chamber(bubble) at divergent plate boundaries causes fragments of earth's lithosphere(crust + underlying mantel) to be uplifted + exposed → such fragments are called ophiolites 6 places where ophiolite suites are: 1. Newfoundland 2. Cyprus 3. India-Himalayas 4. Oman 5. New Zealand 6. philippines

ophiolite

= layered igneous rock that reflects the 4 compositional layers of the sea floor(oceanic lithosphere): 1. sea floor→ thin top layer of sediment 2. upper oceanic crust→ layer of extrusive(basalt) igneous rock 3. lower oceanic crust→ thick layer of intrusive(gabbro) igneous rock 4. mantel(below Moho)→ layer of peridotite able to reflect the layers of the seafloor that are so deep, not even drilling could reach them

Extrusive igneous rocks

= magma cools above ground into small crystals(smooth) 1. rhyolite -- composition: felsic -- plate boundary: convergent continent-contient (in contiental crust) -- magma: rhyolitic -- color: pinkish orange 2. andesite: -- composition: intermediate -- plate boundary: subduction zone ocean-contient (in ocean + contient crust) -- magma: andesitic -- color: light to medium gray 3. basalt -- composition: mafic -- plate boundary: divergent spreading ridge/hotspot (in ocean crust) -- magma: basaltic -- color: black to dark green

intrusive igneous rocks

= magma cools under ground into large crystals(course grained) 1. granite -- composition: felsic -- plate boundary: convergent continent-contient (in contiental crust) -- magma: rhyolitic -- color: orange, black, clear 2. diorite -- composition: intermediate(mixed) -- plate boundary: subduction zone ocean-contient (in ocean + contient crust) -- magma: andesitic -- color: black + white 3. gabbro -- composition: mafic -- plate boundary: divergent spreading ridge/hotspot (in ocean crust) -- magma: basaltic -- color: black 4. peridotite -- composition: ultramafic -- plate boundary: comes from mantel magma -- color: green

how is magma made?`

= mantel + crust are solid → SO magma requires mechanisms to cause melting either through: -- increasing heat OR -- lowering rock melting temp

MAGMA

= melted rock

(melting minerals)

= minerals in rocks melt at different temps

rocks

= mixture of minerals

partical melting

= most magma forms through this incomplete melting of rock this is what causes there to be chemical differentiation → different types magma need about a 10% partial melting for melt to separate from residual solid + move up

igneous rocks confirm plate tectonics

= ocean spreading centers are a product of basaltic magma rising ophiolites found at spreading centers help confirm that basaltic magma comes from the asthenosphere

partial melting theory

= prevalent mechanism for magma generation B→A→R: mantel peridotite → basalt → andesite → rhyolite 1. peridotite rock(mantle) partially melts to form basaltic magma -- basalt magma solidifies into basalt rock 2. basalt rock (oceanic crust) partially melts to form andesitic magma -- andesite magma solidifies into andesite rock 3. andesite rock(continental crust) partially melts to rhyolite magma -- rhyolite magma solidifies into rhyolite rock

Bowen

= recognized that diff minerals crystalize + form at diff temps

Bowens series

= series of rocks ordered based on melting + crystallization(form) temp -- divided into 2 groups based on discontinuous and continuous crystallization Felsic: last to form(crystalize) = first to melt→ larger crystals → melting temp = low → crystallization temp = very low → quartz = last to crystallize = most stable(usually slower cooling) Mafic: first to form(crystalize) = last to melt →smaller crystals → melting temp = very high → crystallization temp = high

problem with Bowen's one magma model

= single magma could not crystalize into both basalt and rhyolite, bc these minerals originate from 2 different materials: rhyolitic magma → comes from continental crust basaltic magma → comes from oceanic crust RATHER magma did this through different "stages"/events of partial melting → partial melting theory

3 main places where magma melts + submerges

= through the melting of: basalt rock→ Baltic(mafic) magma: -- submerges @: divergent plate boundaries (via hotspots + mid ocean ridges) -- magma originates from: melted peridotite (mantel) andesite rock → andesitic(intermediate) magma: -- submerges @: convergent plate boundaries(via subduction zone: ocean-continent) -- magma originates from" melted oceanic crust(basalt rock) rhyolite rock → rhyolitic(feltzic) magma: -- submerges @: convergent plate boundaries(via collision zone: contient-contient) -- magma originates from: melted contiental crust(andesite rock)

(wet partical melting)

= water lowers of the melting point of oceanic crust and mantle rock → causing it to partially melt into andesitic magma

igneous rock textures

Aphanitic = small crystals, < 1mm → EXTRUSIVE Phaneritic = visible crystals, 1-10 mm → INTRUSIVE Pegmatitic = very course crystals, > 1 cm → INTRUSIVE Glassy = very fine, like glass → EXTRUSIVE Porphyritic = 2 distinct sizes(2 diff cooling stages), phenocrysts = large Vesicular = open holes from gas bubbles → EXTRUSIVE Pyroclasts = grains → EXTRUSIVE -- ash: < 2 mm -- lapilli: 2-64 mm -- bombs: > 64 mm

(3 types of volcanos based on the 3 types of magma)

Basaltic volcanoes = occurs at spreading ridges within oceanic(Hawaii hotspot) or continental(Columbia River plate, Yellowstone) crusts Andesitic volcanoes = occurs at subduction zones that are usually ocean-continent (St. Helens, Krakatoa) → most active volcanoes Rhyolite volcanoes = occurs at convergent plate boundaries between/beneath continental plates (Long Valley, CA, parts of Yellowstone) → most explosive volcanoes

mafic minerals

COLOR: dark (green, dark green, dark gray-white) ELEMENTS IT IS RICH IN: -- silica -- magnesium -- iron MELTING TEMP: high(1200°C) ROCKS IT FORMS: extrusive -- basalt -- gabbro FOUND IN: ocean crust/rocks(basalt rock + magma) + asthenosphere(peridotite)

felsic minerals

COLOR: light (tan, gray, pink-orange, white) ELEMENTS IT IS RICH IN: -- silica -- sodium -- calcium MELTING TEMP: low(700°C) ROCKS IT FORMS: -- granite -- rhyolite FOUND IN: continental rocks(rhyolitic magma/rock)

3. rhyolitic magma

COMPOSITION: partially melted andesite rock ORIGIN: contient-contient convergent plate boundaries cause a lot of pressure and form volcanoes/mountains that extrude: → these LARGE volcanoes/mountains contain large amounts of water vapor + water bearing minerals because all of this pressure causes the mantel to upwell with basaltic magma→ which provides heat for wet partial melting of the continental crust(which is andesite rock) → creating this lava HOW IT COMES TO THE SURFACE: plums of this magma rarely rise to the surface completely because they are the most viscous lava → causing it to rise slowly, thus giving it solidify as pressure decreases → but if plum does rise to the surface it creates the most explosive volcanoes

2. andesitic magma

COMPOSITION: partially melted basalt rock(mantel wedge/contiental crust) ORIGIN: Ocean-contient subduction zone (convergent plate boundaries) → these subduction zones have water mixed with sediment + basalt crust, which promotes wet partial melting above the downing oceanic plate (@ 100 km deep) → causing melted basaltic rock rise and heat up, melt, and mix with mantel→ forming this lava HOW IT COMES TO THE SURFACE: plum of this magma can rise and be released by volcanic activity → forms continental crust

1. basaltic magma

COMPOSITION: partially melted peridotite(mantel) ORIGIN: comes from mantel(peridotite) → deep asthenosphere → NO water in it = dry melting process HOW IT COMES TO THE SURFACE: plum of partially melted peridotite rises from mantel to lithosphere causing divergent plate boundaries: hotspots + mid ocean ridges → forms oceanic crust

IGNEOUS ROCKS

FORMED: -- cooling + solidification of magma(melted rock) COMPOSITION: -- random interlocking of mineral grains/crystals (similar to jigsaw puzzler) TEXTURE: -- reflects its formation: crystal nucleation 2 TYPES: 1. intrusive 2. extrusive

extrusive

FORMED: -- fast/very fast cooling of viscous magma -- cooling occurs on/above earth's surface COMPOSITION: -- small crystals (fast) -- glass (very fast) TEXTURE: -- small(fine) crystalline rock = aphanite EX: basalt, andesite, rhyolite

intrusive

FORMED: -- slow cooling of liquid magma -- cooling occurs beneath Earth's surface COMPOSITION: -- large crystals TEXTURE: -- corse crystalline rock = Phanerite EX: granite, diorite, gabbro

minor pluton structures

dike = tabular sheet-like body of igneous rocks that cuts across layering or fabric of rock it intrudes sill = irregularly shaped tabular + sheet-like igneous rock that run parallel to layering or fabric laccolith = similar to sill but layers above intrusion are bent upward into a dome shape

frequency of rock type

earth's crust: igneous rocks dominate earth's surface: sediments + sedimentary rocks

extrusive: pyroclasts, tephra, and tuffs

pyroclasts = fragments of rock that are ejected during a volcanic eruption -- they travel through air and then accumulate on the ground tephra = accumulation of pyroclasts(broken fragments + newly solidified magma) -- is igneous rock when it goes up, BUT sedimentary when it comes down -- greek word for ash

major igneous pluton structures

stocks = irregular shaped intrusives(no larger than 10km) that are usually associated with larger batholith batholiths + stocks = intrusive igneous body, of irregular shape, that cuts across layering or other fabric of host rock -- largest kind of pluton