2 - Plate tectonics

basic shit

do “tectonics” necessarily imply PLATE tectonics

no, theres other types that are not geo related

it just means how a system is structured, move and interact under stress or change

how many plates are there?

debated: 7-12 major, 50 minor

depends on how they’re defined

what theory did we have before plate tectonics?

geosynclinal theory

what is geosynclinal theory? and what was wrong about it - what piece were they missing?

Things go up, then they go down — example: basin at mountain range = syncline, uplifts/subsides

They were missing lateral motions (side to side)

what composes oceanic plates

oceanic crust, lithosphere

what composes continental plates

continental crust, lithosphere

the lithosphere is… plastic/rigid

rigid

the asthenosphere is…. platic/rigid

plastic

average crustal density of oceanic lithosphere

2.9 g/cm3

what rocks compose the oceanic lithosphere (from top to bottom)

Ocean sediments: shales, limestones, turbidites, chert, fossils

Basalts: pillow basalts, basalts cut by dikes

Gabbro: metamorphosed

—--MOHO——-

Partial hydrated serpentinized mantle: peridotites, metamorphosed

average crustal density of continental lithosphere

2.6-2.9 g/cm3

which is more uniform?: continental or oceanic lithosphere?

oceanic

what rocks compose the continental lithosphere (from top to bottom)

upper crust: sediments, magmatic bodies = felsic, no metam

middle crust: meta-sediments, granitic plutons = felsic-andesitic, partly metam

lower crust: meta-sediments, large plutons = felsic-mafic, hella metam

—MOHO—-

Sub-continental lithospheric mantle: eclogite, peridotite = ultramafic

what do we call the arrangement of rocks in the oceanic lithosphere?

the ophiolite suite

which is thicker? continental or oceanic lithosphere?

continental

which has a more diverse/larger crustal column? continental or oceanic lithosphere?

continental

in general, are rocks in the continental lithosphere mafic or felsic or intermediate?

intermediate to felsic, because they are less dense than oceanic crust (except for the deepest parts)

what does the continental lithospheric mantle consist of?

deep peridotites, typically spinel-grade, locally even garnet-bearing under the very thick crust

what is isostasy

lithosphere is floating on asthenosphere

• EQUILIBRIUM between crust — rising if material is removed, sinking if material is deposited

do tectonic forces cause equilibrium or disrupt it

disrupt it

determing factors of isostasy

density and height (to compensation depth)

example of a modern orogenic belt

rockies, western canada in Berta

example of ancient orogenic belt

appalachians

Rockies vs appalachians: which is higher?

Rockies

Rockies vs appalachians: which is thicker?

rockies

Lower elevation = ______ (thicker/thinner) crust below

thinner, less crust below you

how many plate boundaries are there?

3

is it common for a plate vector to be exactly parallel/perpendicular?

no, its unlikely in real life, there are transiting boundaries

what is a transtensional boundary

combo of divergent and transform

what is a transpressional boundary

combo of convergent and transform