metamorphism

Metamorphism: protolith + heat and pressure => changes in the mineral composition / orientation in solid states until energy-minimizing state “comfortable with each other and their surrounding.”

Given 25 deg C per KM, we know only 250-850 deg c is required for it: so, only need about 10km required for metamorphism.

protolith

starting point of the rock, from shale, etc.

why heat?

Heat causes atoms to vibrate rapidly: stretching, bending, breaking chemical bonds. Atoms detach from neighbors, form new bonds with more stable different atoms.

solid-state diffusion

When a smallish amount of heat is added at high temp + pressure, the solid morphs into a new mineral configuration while staying solid.

stresses

A key differentiating property is where stress is applied.

differential stress

one key way that metaphoric rocks are analyzed is that

sheer stress

sheering

Metamorphic Rocks

Main progression; differer from different cases!

• clay / shale: burying it deeper and deeper (low-grade) slate => (higher-grade) different
• quartz: no mater how deep you bury, it s still sio2

effects of metamorphism

• recrystallization: we take something that has small shale, and it crystalizes into stronger rock
• phase change
• neocrystallization: you get new minerals (felsic and mayfic minerals tend to seperate and begin banding)

foliation

quasiplanar orientation (“bandns”): parallel planar fabric. “sheets of rocks”.

“slate”—earliest grad of metamorphic rocks

metamorphism in different settings

high temperature, low pressure

Hornfeld’s Metamorphism. This basically happen next to magmatism (i.e. you are baking the rocks because of a magmetic plume)

regional metamorphism

because of subduction, shoving a rock down really deep underground

low temperature, high pressure

this is when you are shoved down quickly by a deep ocean plate, the ocean plate insulates you but you are going reeeeallyl deep.

This tends to form high-grade cool blue metamorphic rock.

Rock Cycle

There’s a pathway that takes any rock and take it into any other rocks.

• ignerous rock can be deposited into sedementary rock
• sedementary rock can be shoved down into a collisional mountain bent, and h the metamomphic orock
• metamorphic rock can then be melted back into ignerous rocks