Plate Tectonics: Rock Response to Stress

Rocks react to stress by deforming elastically, with granite and quartzite tending to fracture in a brittle manner, while shale, limestone, and marble tend to deform plastically
Temperature affects rock response, with higher temperatures favoring plastic deformation
Pressure also influences rock behavior, with high non-directed pressure favoring plastic behavior
Time is another factor, with slow application of stress favoring plastic deformation

Any feature produced by rock deformation, including folds and faults
For deformation to occur, rock material must be able to deform under pressure and heat, with higher temperatures making rocks more elastic
Deformation requires slow application of stress, without exceeding the internal strength of the rock

A bend in a rock, indicating plastic deformation with little or no fracturing
Characteristics of folds include:
- Results from compression
- Shortens horizontal distances in rocks
- Occurs as part of a group of many similar folds
Types of folds:
- Anticline: a fold arching upward, commonly caused by compressive stress
- Syncline: a fold arching downward, often forming basins
- Monocline: an open, step-like structure with layers inclined in the same direction

A fracture where one side of the rock has moved relative to the other side
Types of faults:
- Normal fault: formed due to tensional stress, often resulting in stretching of the Earth's crust
- Reverse fault: formed due to compressive forces, often resulting in fracturing of rocks
- Thrust fault: a special type of reverse fault that is nearly horizontal
- Strike-slip fault: a fracture where rocks on opposite sides of the fault move past each other horizontally

Fractures in rocks where the rocks on either side of the fracture have not moved
Formed by tectonic forces, becoming less abundant with depth

Different types of plate boundaries produce different tectonic stresses and resulting folds and faults
Types of convergent boundaries:
- Oceanic-oceanic: one crust sinks underneath, triggering melting and volcanic activity
- Oceanic-continental: denser oceanic crust sinks beneath the continental crust, forming volcanic arcs and trenches
- Continental-continental: folding occurs, forming mountain ranges
Divergent boundaries: plates drift apart, producing normal faults and grabens, with little folding
Transform fault boundaries: plates slide past each other, with no creation or destruction of land

Proposed by Alfred Wegener, suggesting horizontal movement of continents
Evidences include:
- Fit of continental shorelines
- Similar rock types and fossils across continents
- Fossil evidence of similar plants and animals across continents
- Climatic evidence, including glacial striations

Proposed by Harry Hess, suggesting that the oceanic crust is moving, with magma rising to form new ocean floor at mid-ocean ridges

Confirmation of seafloor spreading hypothesis, showing that continents are not moving above a fixed mantle
The asthenosphere behaves like a fluid, allowing the lithosphere to float and move above it
Convection currents in the asthenosphere drive plate movement

Continental crust: less dense, made of older material, and comprises silica and aluminum-based granite
Oceanic crust: denser, formed at the bottom of the oceans, and comprises silica and magnesia-based basalt content

The theory that the Earth's crust is divided into several plates that glide over the mantle
Major tectonic plates include African, Antarctic, Arabian, Australian, Caribbean, Cocos, Eurasian, Indian, Juan de Fuca, Nazca, North American, Pacific, Philippine, Scotia, and South America
Plate boundaries are regions where tectonic plates are moving relative to each other