GEOL 4110 Advanced Earth Science for Teachers STRUCTURAL GEOLOGY Structural Geology The study of how earth materials respond to largescale differential stresses in the Earth’s crust TECTONIC DEFORMATION Small Scale Response - Foliation Characteristic of Convergent Zones Accompanied by Metamorphism TECTONIC DEFORMATION Large-scale Response – Folding & Faulting Elastic – Ductile –Brittle Behavior Tensile Strength Point up to which strain is entirely recoverable (Brittle behavior) (Ductile behavior) (Deformation) Effects of Temperature, Pressure and Strain Rate Ductile Behavior is favored over brittle behavior with: Increased Temperature Increased Pressure Decreased Strain Rate Increasing Temperature Decreasing Tensile Strength Orientation of Strata Strike and Dip Strike Line – the line traced by the intersection of the plane of interest with a horizontal plane Dip Line – tick mark drawn at 90° from strike line drawn on the side of the strike line where the plane forms an acute angle with the horizontal plane = Fall Line Dip Angle – degree angle between the horizontal and the plane of interest Drawing a Strike and Dip Symbol 40o Reporting the Strike and Dip North Hemisphere Method N45E/40oSE Right-hand Azimuth Method 45/40o Strike and Dip Symbology US Geological Survey Recommendations for Symbology USGS Open-file Report 99-430 http://pubs.usgs.gov/of/1999 /of99-430/ Legend from the Duluth quad (Green & Miller, 2008) Simple Structures of Strata Flat-lying Monocline Homocline From Spencer (2000) Flat-lying Strata of Fillmore County Dendritic Map Pattern Another Example of Flat-lying Strata The Grand Canyon Topographic Contour Lines connects points of equal elevation Rules: • Lines never cross •Lines never end •Lines “V” upstream •Lines encircle hills and depressions Reading Topography Map Patterns of Tilted Strata in Valleys Vertical strata contacts straight across topography Flat-lying strata contacts || to topography and V upstream Strata tilted downslope steeper than slope contacts V downstream Strata tilted upslope - contacts V upstream Strata tilted downslope shallower than slope - contacts V upstream From Spencer (2000) Map Patterns of Tilted Strata Steeply Tilted PatternNarrower and less affected by topography ModeratelyTilted Pattern From Bulter and Bell (1988) Fold Terminology Upright Fold Recumbent Fold Inclined Fold Overturned Fold Assymetrical Symmetrical Orientations of Folds Based on Hinge Line (Fold Axis) and Axial Plane Types of Folds Horizontal Normal Horizontal Inclined Plunging Normal Plunging Inclined Vertical From Spencer (2000) Recumbent Reclined Fold Symbology Longer arrow on shallower limb Horizontal Fold Patterns Symmetrical Asymmetrical Plunging Fold Patterns Domes and Basins Elongate Basin or Doubly Plunging Syncline Refolded Folds Multiple Deformational Events F1 F2 Types of Faults And Applied Stesses Horizontal Compression Listric faults Normal Mid-Crustal Horizontal Compression Horizontal Extension Horizontal Shear Thrust to Reversed Horizontal Compression + Shear Horizontal Extension + Shear Terminology of Faults FTP FB FP – Fault Plane FPT – Trace of Fault Plane FB – Footwall Block HB – Hanging Wall Block HB Slickensides – Lineations on the fault plane that record the direction of slip FTP Displacement Parameters ad – Apparent Displacement s – Slip (or dip) separation (measured on FP) d – Stratigraphic displacement u – Throw (vertical displacement) FP ad FB HB HB FB Fault Symbology Determining Type of Fault from Offset of Lithostratigraphic Units Hard to tell just from one offset example Normal Left Lateral Strike-slip Oblique (Left Lateral + Reversed) Normal Normal Oblique (Left Lateral + Normal) Regional Fault Features Divergent Tectonics Convergent Tectonics Thrust Faulting Thickening and Stacking Older Rocks on Younger Rocks Mapping With Google Earth