Geol Lec 10 PDF - Rock Deformation

GEOL 11 LEARNING MATERIALS (A.Y. 2024-2025) NOVEMBER 12, 2024 Week 10 Presented by John Paul M. Mondala (1st Semester, A.Y. 2024-2025) Rock Deformation Learning Objectives At the end of the lecture, the student should be able to: Know the difference between Stress and Strain Be familia...

GEOL 11 LEARNING MATERIALS (A.Y. 2024-2025) NOVEMBER 12, 2024 Week 10 Presented by John Paul M. Mondala (1st Semester, A.Y. 2024-2025) Rock Deformation Learning Objectives At the end of the lecture, the student should be able to: Know the difference between Stress and Strain Be familiar with the types of stresses that and how they affect the type of deformation of a rock mass Be able to distinguish brittle deformation from ductile deformation Be able to identify various landforms formed from rock deformation, and Be able to tell the type of deformation (brittle or ductile) and type of stress associated with a certain landform Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Rock Deformation The movement of tectonic plates creates stresses which cause rocks to deform Change in volume and/or shape Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Stress The force acting on a body of rock per unit area Uniform/confining – stress is equal in all directions Differential – stress is not equal in all directions Compressional Tensional Shear Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Stages of Deformation When a rock is subjected to increasing stress it passes through 3 successive stages of deformation: Elastic Deformation; pass the elastic limit, an object will undergo: Ductile Deformation, and finally Fracturing or Brittle Deformation Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Stress vs. Strain Stress (σ) refers to the force applied to a material per unit area Strain (ε) Deformation or change in the shape of the material that results from the applied force Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Stages of Deformation A. Elastic Deformation reversible, non-permanent the rock will return to its original shape when the stress is removed occurs at very low stresses B. Ductile/Plastic Deformation irreversible, permanent change in volume or shape the rock will bend or fold C. Fracture/Brittle Deformation permanent strain where the rock breaks or fracture Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Stages of Deformation Notice the differences between a brittle and a ductile material in terms of their regions of elastic and ductile deformation Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Ductile Deformation Irreversible changes that involve deformation of rocks into a series of wrinkles or folds (small or large-scale) Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Anatomy of a Fold Axial plane the imaginary surface that divides a fold as symmetrically as possible Fold axis the line made by the length-wise intersection of the axial plane with beds in the fold Limbs correspond to the two sides of a fold Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Anatomy of a Fold Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Types of Fold Based on Symmetry Symmetric folds Axial plane is vertical Limbs on either side of the axial plane are “mirror image” of each other Asymmetric folds Axial plane is tilted Limbs are not symmetrical about the axial plane Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Types of Fold Based on Symmetry Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Types of Fold Based on Symmetry Horizontal Fold Fold axis is horizontal Plunging Fold Fold axis is not horizontal The elevation of the crest of the fold is not the same all throughout It “plunges” into the ground Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Types of Fold Based on Symmetry Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Landforms Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Landforms Anticline Oldest at the center Upfolding A-shaped Syncline Youngest at the center Downfolding U-shaped Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Landforms Antiform No known age Upfolding A-shaped Synform No known age Downfolding U-shaped Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Landforms Dome Central uplift Youngest at the sides; oldest at the center Basin Central sinking Oldest at the sides; youngest at the center Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Landforms Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Fault A fracture showing displacement of rock masses on either side of the trace Dip-slip vertical displacement Strike-slip Lateral displacement Oblique Combination Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Brittle Deformation Fault Anatomy Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Brittle Deformation Fault Anatomy Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Brittle Deformation Dip-Slip Faults (Vertical Displacement) Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Brittle Deformation Oppositely dipping normal faults Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Brittle Deformation Strike-slip Faults Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Brittle Deformation Strike-slip Faults Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Brittle Deformation Oblique Faults Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. |  Identify the fault Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Brittle Deformation Fault Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Rock Deformation Brittle Deformation Fault Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. |  (a) Plasticine model of escape tectonics involving a rigid indenter and several laterally moving blocks. (b) Sketch of the deformation in (a). Note the pull-apart basins along both faults (F1 and F2). (From P. Tapponnier, G. Peltzer, A. Y. Le Dain, R. Armijo, and P. Cobbold, 1982, Geology, v. 10, p. 611–616.) Geol 11 | Lecture 10: Rock Deformation Mondala, J.P.M. | Tarbuck, E. J., & Lutgens, F. K. (2012). Earth Science. Prentice Hall/Pearson. Wicander, R., & Monroe, J. S. (2016). Historical Geology. Cengage Learning. Gill, R. (2010). Igneous Rocks and Processes: A Practical Guide. Wiley. Geol 11 | Lecture 8: Metamorphism, Metamorphic Rocks & Resources Mondala, J.P.M. |