Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Announcements Field trip during lab today/tomorrow Field trip this Saturday to Collosal Cave area 7:30 AM at loading dock. We will map some really cool stuff! Please review map symbols and bring stereonets. We may return after sunset. There will be a "What is it" quiz next lecture- review fault rocks and kinematic indicators! Nov. 13 - Draft #1 of fault paper due! Outline for Today 1. More about geometry and kinematics of thrust systems 2. Forced folds the architecture of many fold-thrust belts "thin-skinned" deformation development of duplexes map pattern of a duplex lateral ramps compartmental faulting and tear faults footwall rocks are commonly deformed into synclines Footwall syncline in the Canadian Cordillera Footwall syncline in the Canadian Cordillera also, triangle zones also, triangle zones The observation that faults do not continue around the entire Earth suggests that they must terminate Generally, a gradual decrease in slip toward fault termination Younger and structurally deeper faults lead to rotation of older faults Summary Thrust systems: 1. Accommodate significant crustal shortening 2. Basal detachment/decollement; decoupling within the crust 3. Faults have ramp and flat geometries 4. Thrusts place older/higher grade rocks over younger/lower grade rocks 5. Faults cut up-section 6. Faults generally propagate (get younger) toward the foreland 7. Younger and structurally deeper faults rotate older faults to steeper angles 1. breached anticline What is it? 2. fault tips/ terminati ons 4. klippe 5. window 6. lateral ramp 7. blind thrust 8. branch lines Fold and thrust belts! Mt Kidd Forced folds (D&R 413-423) Free folds: fold profiles are based entirely on physicalmechanical properties of the layers Forced folds: geometry related to movement over fault ramps- "they just go along for the ride, and some of the beds happen to fined themselves in awkward places and are required to stretch or bend" 2-main types of forced folds: fault-bend folds fault-propagation folds Fault-bend folds Fault-propagation folds monoclines as "drape" folds "thick-skinned" basement-involved shortening Colorado Plateau monoclines may be related to thick-skinned deformation Major issues • “mechanical paradox” of thrusting - why such thin sheets (e.g. 100 km long/2-3 km thick) can remain intact during faulting? • What happened to the missing basement? • Why are almost all faults dipping one way when rock mechanics predict equal chance for both? Next lecture: (1) thrust belt mechanics (p. 336-339) (2) Discuss fault project