Unformatted text preview: e‐dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present‐day rock geometries to uncover information about the history of deformation (strain) in the rocks, and ultimately, to understand the stress field that resulted in the observed strain and geometries. This understanding of the dynamics of the stress field can be linked to important events in the regional geologic past; a common goal is to understand the structural evolution of a particular area with respect to regionally widespread patterns of rock deformation (e.g., mountain building, rifting) due to plate tectonics. The study of geologic structures has been of prime importance in economic geology, both petroleum geology and mining geology. Folded and faulted rock strata commonly form traps for the accumulation and concentration of fluids such as petroleum and natural gas. Folds: The term fold is when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of plastic deformation. Folds in rocks vary in size from microscopic crinkles to mountain‐sized folds. Folds form under varied conditions of stress, hydrostatic pressure & pore pressure Fold terminology: • • • • • • • Hinge(Axis): is the point of minimum radius of curvature for a fold Axial Plane: is the surface defined by connecting all the hinge lines Crest(Apex): is the highest point of the fold surface Crest Surface: is a plane connected all crests Trough: the lowest point in a cross section Trough surface: is the plane connecting all troughs Plunge: is the attitude of the axial line of fold Types of Folds: • • • • • • • • • • • • • • • • Anticline: folded upward, and the two limbs dip away from the hinge of fold Syncline: folded downward, & two limbs dip inward toward the hinge of fold. Symmetrical Fold: If the two limbs dip away from axis with the same angle Asymmetrical fold: If the limbs dip away from axis at different angles Isoclinal Fold: the limbs have the same angle & equal direction Overturned Fold: Axial plane is inclined & Both limps in the same directio...
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- Spring '10
- Geology, Volcano, Tephra, Volcanic Ash, Geology & Geophysics, Mahmoud Ahmed Sroor