FOLIATION If you were to take a piece of paper and compress
it, you would find that the flat dimensions would orient
themselves perpendicular to the direction that you compressed
it from. Likewise, when a metamorphic rock is compressed or
stressed, the platy minerals, such as chlorite and micas, orient
themselves so that their long dimensions are perpendicular to
the maximum compressive stress. The planar fabric that
results from this process is known as a foliation.
Slaty cleavage is a specific type of foliation, in which the
parallel arrangement of microscopic platy minerals causes the
rock to break in parallel plate-like planes. Schistosity forms
at higher metamorphic grades and is a foliation defined by a
wavy or distorted plane containing large visible oriented minerals
such as quartz, mica, and feldspar.
MINERAL ASSEMBLAGES As rocks are progressively heated
and put under more pressure during metamorphism, different
mineral assemblages are stable. Even though the rock may
retain a stable overall composition, the minerals will become
progressively recrystallized and the mineral assemblages (or
parageneses) will change under different P-T conditions.
Tidak ada komentar:
Posting Komentar
Catatan: Hanya anggota dari blog ini yang dapat mengirim komentar.