Скачать или смотреть Metamorphic structures and textures; isograds and facies

Here's a breakdown of metamorphic structures and textures, isograds, and facies:

Metamorphic Structures and Textures:

Structures: These are large-scale features formed during metamorphism, reflecting the forces and conditions involved.

Foliations: Layered structures like slate cleavage and schistosity, caused by the alignment of minerals under pressure.
Lineations: Elongated features like mineral streaks or boudinage, indicating the direction of stress.
Folds: Bends in rocks due to compressional forces.
Faults: Fractures where rocks have moved past each other.
Textures: These are the microscopic characteristics of metamorphic rocks, revealing details about the mineral composition and grain size.

Crystalline textures: Grain size and shape, ranging from fine-grained in slates to coarse-grained in gneisses.
Mineral orientations: Alignment of minerals due to pressure, contributing to foliation development.
Isograds:

Definition: Lines on a map that mark the first appearance of a specific index mineral in metamorphic rocks.
Significance: Indicate the boundary between zones of different metamorphic grades (intensity of metamorphism).
Examples: The Barrovian sequence, where the appearance of minerals like chlorite, biotite, garnet, etc., signifies increasing metamorphic grade.
Facies:

Definition: A set of metamorphic rocks with similar mineral assemblages formed under specific pressure-temperature (P-T) conditions.
Common Facies:
Greenschist Facies: Low-grade metamorphism with minerals like chlorite, muscovite, and quartz.
Amphibolite Facies: Higher-grade metamorphism with minerals like hornblende, plagioclase, and garnet.
Granulite Facies: Very high-grade metamorphism with minerals like pyroxene, garnet, and kyanite/sillimanite.
Relationship with Isograds: Isograds often mark the boundaries between different metamorphic facies.
Understanding these features helps geologists:

Reconstruct the metamorphic history of a region.
Determine the P-T conditions experienced by the rocks.
Interpret the tectonic processes involved in mountain building and other geological events.