igenous rocks 1 (textures, compo classification)

bowens rxn series.

What causes rocks to melt

temp inc (800-1400c), P decrease(causes melting point to plummet), addition of water to dry rock (acts as catalyst)

explain decompression melting

when a decreased P causes the melting point of a rock to decrease, even at constant T

aphanitic

mins to small to see with eyes, magma cooled quickly, commonly seen in extrusive rocks

glassy

texture that has no crystals formed, dark coloured, silica rich.

vesicular

common to basaltic lava flows and shallow dykes, gas escaped to form

amygdaloidal

texture formed when gas bubbles escape and form holes that are eventually filled with groundwater

phaneriitic 

mins can be seen w the eyes, magma cooled slowly underground, intrusive rocks

porphyritic (have phenocrysts)

bimodal crystal sizes, two magmatic historys, can be intrusive or extrusive

felsic

high silica content (~70%), light coloured with qaurtz, K-feld, Na-plag, minor biotite and hornblende ex. granite

intermediate

medium silica content (~60%), grey coloured/black and white, plagi feldspar, pyroxene, hornblende, no qaurtz ex. diorite

mafic 

low silica content(~50%), rich in Mg and Fe, dark coloured, olivine, pyroxene, amphibole, Ca-plagioclase feldspar.  ex. gabbro 

ultramafic

very low silica content (~45%), dark coloured green and brown olivine and pyroxene. low plagioclase, no qaurtz. ex. periodotite.

bownes reaction series

the order in which certain minerals melt and cool that shows researchers how rocks form in order of coolness and heating.

pillow basalt

a type of material formed in deep water, where the pressure is high. 

LIPs (large igneous province)

areas where large volumes of lava or ash erupted over a small period of geological time.

features of felsic volcanos

high is Si content, cooler lavas, lo win Mg and Fe, highly viscous

composite volcanoes

volcanoes (normally felsic) that are built by layers of lava and tephra (volcanic ejecta)