Module 6- The Earth's Crust and Natural Resources-Learning Objectives

Describe how oceanic crust has differentiated from the mantle and where this occurs

• mid-ocean ridges through seafloor spreading

• decompression melting occurs at mantle material upwells, reducing pressure and triggering partial melting

• produces mafic magma, crystalizes into basalt

• homogenous, thin, young

Describe how continental crust has differentiated from mantle and where it occurs

• forms at subduction zones

• flux melting (partial melt producing mafic magma)

• mafic magma ponds at base of less dense crus and undergroes fractional crystallization make more SiO2 magma rocks

• heat from ponded magma partially melts overlying continental crust forming felsic magma

Determine if element will be higher in the crust or mantle and what data you’ll need to determine this

• Kd(partition coefficient)

• compatible if Kd>1, means solid at the mantle

• will it sub into olivine SiO4-

explain general trend in oxygen sharing

• silicates with more shared oxygens crystallize at cooler temps;

• later forming have increasing oxygen sharing, forms sheets and frameworks;

• early forming have tetrahedra or single chains

Fe and Mg concentration

early crystallizing minerals → high in Fe and Mg (mafic)

later crystallizing minerals → low in Fe and Mg, high in Si (felsic)

incompatible element abundances

remain in melt and crystallize heat

Goldich’s weathering series

Minerals that crystallize at high temps weather quickly at surface, igneous materials least stable

4 most Common types of chemical weathering

• Dissolution: dissolve mineral into its ions with water

• acid dissolution: acid water dissolves minerals

• oxidation: reduction electron transfer

• hydrolysis: water splitting, important for silicate minerals, irreversible, form new mineral from reaction of silicate minerals with water and acid

differential weathering

one rock weathers faster than other on the same rock,

felsic silicates weather slower, intermediate silicates weather faster

how hydrocarbons are formed

• source rock wwith abundant carbon buried deep where high T converts orgo matter to petroleum

• diagenesis: change orgo matter to waxy kerogen w/ hight T and P

• Catagenesis: thermal cracking of kerogen to produce crude oil

• metamorphism: complete reakdown of crude oil methan using high T and P

good hydrocarbon quality

high H to C ratio, low sulfur+heavy metal/other impurities, high porosity and permeability

Magmatic ore deposits

• chromitite: formed by fractional crystallization of ultramafic or mafic magma

• pegmatites: late crystallizations of felsic magmas

• sulfide deposits: sulfur rich, sink to bottom

hydrothermal ore deposits

hot, saline brines dissolve and transport metals, lower T and P, Au, Ag, sulfides