How Rocks Deal With Stress Chapter 7: Plate Tectonics

Types of Stress Just like people, the rocks of the crust can get stressed out too! 3 types of stress 1.Compression: squeezes rocks (convergent boundary) 2.Tension: stretches and elongates rocks (divergent boundary) 3.Shear: allows rocks to slip and grind past one another (transform or strike-slip boundary) When rocks can’t take on any more stress, they have reached their elastic limit! At that point they can break or deform.

Let’s Deform! When stress acts on rocks in the crust, they can do one of two things: fold or break. The compression stress is what creates folds in rocks, which is the bending of rock layers. 3 types of folds: 1.Anticline: horizontal stress bends rock layers upward 2.Syncline: horizontal stress bends rock layers downward 3.Monocline: vertical stress bends the rock layers in the center

It Isn't My Fault! As a result of stress in the crust, sometimes instead of folding, the layers of rock break. A fault is a break in the crust along which blocks of rock slide past each other. The blocks on either side of the fault are called the hanging wall and footwall. Easy way to remember which is which: you can HANG off the hanging wall and walk with your FOOT up the footwall.

Who’s At Fault? 3 types of faults 1.Normal: rock layers are pulled apart horizontally by tension, hanging wall down 2.Reverse: rock layers are pressed together due to compression, hanging wall up 3.Strike-slip: shear stress pushes the fault blocks in opposite directions, no hanging wall

Geologic Provinces of VA A geologic (physiographic) province is a landform region, an area delineated according to similar terrain that has been shaped by a common geologic history. Each province is characterized overall by its elevation, relief, lithology, and geologic structure. Appalachian Plateau Valley & Ridge Blue Ridge Piedmont Plateau Coastal Plain

Geologic Provinces, cont’d The Appalachian Plateau has an ancient surface, eroded by stream action over millions of years into what is today a region of high of relief. The Valley and Ridge province has developed thick, folded beds of sedimentary rock deposited during the Paleozoic. The Blue Ridge is composed of complexly folded and faulted igneous (granite) and metamorphic rocks. It is the oldest province! The surface of the Piedmont Plateau rises in elevation from approximately 200 feet above sea level at its eastern margin (the Fall Line) to a general base level of 1000 feet above sea level in the west. The Coastal Plain is the youngest of Virginia's physiographic provinces, its rocks having been deposited after the Atlantic Ocean began to form.