Petrology

Where are do pyroclastic rocks form?

• diatreme (intrusive)

Diatreme

• carrot shaped

• Si-poor magma

• sharp contact with country rock

• has pyroclastic breccia

• associated with tuff rings and maars

• result of short explosive event

Diapir

type of intrusion with low and high density fluid that creates a wide top and thin bottom, spreads out at neutral bouancy depth

Ways room is made for magma

• doming

• partial melting and assimilation

  • requires a lot of heat

• stoping

  • requires country rock to be more dense

  • requires crust to be brittle

• ductile deformation

  • deep

• faulting or folding

• extensional setting

  • can’t take much magma fast

contact zone processes

• mixing with country rock

• contact metamorphism

• alternation and melt of country rock

• chill zones

• shearing and foliations

Maar

explosive volcanic landform with central crater lower than tuff ring. caused by magma and groundwater reaction to steam, 0.2-3km diameter

hydromagmatic eruption

eruption resulting from magma interacting with groundwater creating highly explosive eruption

Meteoric water

another name for surface or groundwater

tuff ring

associated with diatremes, result of hydromagmatic eruption, normally basaltic, higher magma to water ratio than maar, ring of pyroclsatic scoria and ash, 0.2-3km diameter

Tuff cone

steeper version of tuff ring as a result of less explosive but longer hydromagmatic eruption, bedding dips both into and out of crater, 0.1-1.5km

country rock

rock outside of a pluton

pluton

intrusive igneous form, tabular or non-tabular

discordant

pluton that cross-cuts layers

concordant

pluton that intrudes parallel to layers

Tabular intrusive body

result of magma filling a fracture, sill or dike

sill

concordant tabular body that intrudes between sedimentary beds, fed by dike

dike

discordant tabular body that cross-cuts bedding or other structures,

swarm

related set of numerous dikes or sills, parallel or radial

radiating dike swarm

intrusive igneous body that forms in a radial pattern around rising magmatic bodies

ring dike

intrusive igneous rock that occurs when the density of the overlying rock is less than the density of the magma

olivine, clinopyroxene, orthopyroxene, and plagioclase

minerals found in mafic volcanic rock

plagioclase, k-feldspar, pyroxenes, amphibole

minerals found in intermediate volcanic rocks

kspar, plagioclase, quartz, biotite, muscovite

minerals found in felsic volcanic rocks

olivine, pyroxenes, plagioclase, opaque minerals

minerals found in mafic plutonic rocks

olivine, pyroxenes, plagioclase, opaque minerals

minerals found in ultramafic plutonic rocks

plagioclase, pyroxenes, amphibole, quartz, feldspars, opaque minerals

minerals found in intermediate and felsic plutonic rocks

Granite

felsic plutonic rock with highest silica content and coarse grains, includes kspar, quartz, Na-rich plagioclase, muscovite, biotite, and amphibole.

granodiorite

intermediate plutonic rock with 60-70% silica content and coarse grains, includes kspar, quartz, Na-rich plagioclase, biotite, amphibole, maybe some muscovite

diorite

mafic or intermediate plutonic rock with coarse grains and silica content ~55%, includes quartz, plagioclase, biotite, and amphibole

gabbro

mafic plutonic rock with 50% silica content and coarse grains, includes ca-rich (black) plagioclase, pyroxenes, and some olivine

peridotite

ultramafic plutonic rock with 40% silica content, coarse grains, includes pyroxene, Ca-rich (black) plagioclase, and olivine

rhyolite

felsic or intermediate volcanic rock with fine grains, high silica content, and includes kspar, quartz, Na-rich plagioclase, muscovite, biotite, and amphibole

andesite

intermediate to mafic volcanic rock that has middling silica content, fine grains, and includes quartz, plagioclase, biotite, amphibole, and maybe some pyroxene

basalt

mafic to ultramafic volcanic rock with low silica content and fine grains, composed of ca-rich plagioclase, pyroxene, and olivine

differentiated

when terrestrial planets are made of distinct types of layers, like mantle, core, or asthenosphere

characteristics of volcanic rocks

porous, vesicular, glass, microlites

zonation

tree-ring pattern in a crystal that formed as a result of slow cooling and fractional crystallization, generally a change in composition or temperature

Minimum pressure of the melt, and temperature

What information can we get from water and CO2 inclusions in phenocrysts in igneous rocks

What does K concentration of a melt indicate and why

rate of cooling and distance from surface, K prefers the melt over the crystal, as K concentration increases, crystallization increases

lithostatic pressure

density x gravity x depth

25C per km, result of heat from tectonics and radioactive decay

how does temperature increase with depth and why

geothermal gradient

how temperature changes with depth in the earth

How do we know the outer core is liquid

s waves do not propagate through liquid

lithosphere

name for crust and upper mantle

oceanic crust characteristics

made of pillow basalt, sheeted dikes, massive gabbro, and ultramafic gabbro, 10km thick, mostly made of basalt

continental crust characteristics

20-90km thick, highly variable composition, mostly granodiorite

Moho

boundary between crust and mantle, seismic discontinuity where s-waves increase from 3.5km/2 to 4.5km/s, 5-10km under ocean floor, composition changes from basalt to peridotite

olivine, wadsleyite, ringwoodite

mineral composition of the upper mantle

Which part of the mantle has a higher velocity

the lower mantle

porphyritic, xenolith, pahoehoe, glomeroporphyritic, euhedral, anhedral, skeletal, trachytic

Textures of mafic volcanic rocks

porphyritic, microlites, phenocrysts, sieve, skeletal, mineral zoning

textures of intermediate volcanic rocks

embayed quartz, vitric, aphyritic, pumiceous, perlitic, spherulitic

textures of felsic volcanic rocks

adcumulate, orthocumulate, poikilitic

textures of mafic plutonic rocks

exsolution lamellae, xenoliths

textures of ultramafic plutonic rocks

equigranular, pegmatitic, perthitic, aplitic, mafic enclaves, rapakivi

textures of intermediate and felsic plutonic rocks

bomb, fiamme, vesicles, lithic

textures of pyroclastic rocks

ophitic, porphyritic, holocrystalline

textures of hypabyssal rocks

holocrystalline

made entirely of crystals

hypocrystalline

made of crystals and glass

vitric

made entirely of glass

aphanitic

minerals cannot be seen by the naked eye

phaneritic

minerals can be seen by the naked eye

cryptocrystalline

minerals are too small to see under a microscope

fine-grained

minerals are smaller than 1mm

medium-grained

minerals are between 1-5mm

coarse grained

minerals are greater than 5mm

very coarse grained

minerals are greater than 5cm

pegmatitic

very coarse grained (granitic) rock

aplitic

sugar-like texture, equigranular grains that are fine to medium in size

equigranular

minerals are about the same size

porphyritic

grains have a bimodal size distribution

phenocryst

large crystal in a fine matrix

megacryst

large crystal in a matrix that is either a phenocryst or a xenocryst

xenocryst

nonnative crystal

groundmass

the matrix that contains phenocrysts etc. can be fine-grained or glassy

glomeroporphyritic

rock where phenocrysts occur in clusters

aphyric

rock without phenocrysts

euhedral

crystal with distinct facies

subhedral

crystal bound by some faces

anhedral

crystal with no distinct faces

corroded

subhedral or anhedral crystal due to partial resorption into melt, embayed

types of crystal habits

equant, prismatic, columnar, acicular, fibrous, tabular, platy, micaceous, lath

Poikilitic

contains several smaller crystals of a different mineral

oikocryst

crystal that contains poikilitic crystals

graphic

an intergrowth where quartz forms an angular wedge in microcline

granophyric

an intergrowth where quartz and feldspar grow together in a feathery irregular pattern

exsolution lamellae

bands of a phase that exsolved from another in one mineral

perthitic

irregular exsolution in veins, patches, or lenses of plagioclase from alkali/k feldspar

antiperthitic

exsolution of kspar from na-rich plagioclase

symplectite

one mineral replaced by an intergrowth of two or more minerals

myrmekite

secondary texture of wormy blebs of quartz in plagioclase

spherulitic

radial intergrowth of small fibrous minerals, commonly quartz and kspar

ophitic

large pyroxene grains in small plagioclase laths

lath habit

long and thin habit

intergranular

small grains of pyroxene, oxides, and olivine in a random network of large plagioclase laths

cumulate

interstitial growth of minerals between earlier minerals, earlier minerals are all in contact, comes from magma reservoir

orthocumulate

minerals filling interstitial spaces between earlier minerals

adcumulate

cumulate texture where early minerals grow to fill pore space

mesocumulate

in between adcumulate and orthocumulate

pele’s hair

glassy hair-like strands specific to pyroclastic rocks