16) Foliated and Non-foliated rocks

what gives indication of the pressure and temperature the rock was subjected to?

mineral assemblage

definition of metamorphic facies

characterized by particular mineral associations, indicative of pres and temp conditions of the rock in the formation process

mineral characteristics that describe the formation of a meta rock

what are the 4 dotted lines on this diagram

geothermal gradients, first is wet partial melting of granite

A: high, contact metamorphism, low P, high T, large change in temp without getting too deep
B: normal, regional/burial meta, high P, high T, compressional tectonics, pushed deep into the earth and heated up
C: low, subduction, high P, low T, not much change in temp, big change in pres, ocean crust is cold and dense, sinking down and cold

explain geothermal gradient

going on the line, you;ll have a certain assemblage of mineral, then as the pres and temp change, the minerals change to be a more stable version at those pres and temp conditions (all in solid state)

fill in the blank

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characteristics of foliated rocks

platy or elongate and oriented parallel or sub-parallel to each other to make a planar fabric
compressive stress in one direction

metamorphic grade order for shale pelite protolith

slate, phyllite, schist, gneiss, migmatite

slate

protolith: shale
elongated and platy minerals aligned and compressed
breaks smoothy along foliation planes
very fine grained

phyllite

micas start growing
perpendicular to stress, shiny surface from micas
fine grained

schist

micas growing parallel
coarser than phyllite, will break along cleavage planes
often folded (higher pressure)

gniess

minerals segregated into light and dark bands
can be tightly folded
coarser than schist, won’t break along foliation planes
recrystallized, more angular than expected

unfoliated textures

granoblastic: grains approx equidimensional, platy and elongate minerals subordinate
hornfelsic: grains irregular and intercluded, elongate at random orientation
cataclasic: clastic textures from breaking or grinding, angular/rounded fragments set in a finer grained, sometimes streaked or layered groundmass

quartzite

non-foliated
recrystallized sandstone
almost pure quartz
no pore space or matrix

marble

non-foliated
recrystallized calcite
any fossils will be recrystallized as well
if impure there can be banding