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Part1 Knowing and Understanding Structural Terms and Symbols Part 2 Drawing and Interpreting Geologic Structures in Block Diagrams.
Typology: Exercises
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Student Name: Grade:_____
Introduction & Purpose: Structural geology is the study of how geologic rock units are initially arranged and later deformed. Changing spatial relations between geologic units and the stress and strain that occur during deformation events are key aspects in understanding geologic structures. The purpose of this lab is to both learn and apply the concepts of structural geology to reading and interpreting geologic structures, including tilted beds, folds, and faults. The terms and concepts of geologic structures, the application of structural geology to mountain building events, and the techniques used to interpret geologic structures will be presented and discussed. The three types of graphic representations of geologic structures: 1) geologic maps, 2) geologic cross sections, and 3) block diagrams will also be highlighted and discussed.
A. Review of Rules for Interpreting Geologic Structures There is a set of rules of structural geology used for interpreting geologic structures found in Figure 10.11 in your lab manual. Carefully study and make use of these rules for completing Part II. The most important rules are listed below:
Strike of beds is always parallel to the direction of the contacts.
Rock layers dip towards the youngest exposed rock layers.
Oldest rocks exposed in the center of eroded anticlines and domes.
Youngest rocks exposed in the center of eroded synclines and basins.
Horizontal folds form parallel sets of belt-like outcrop patterns.
Plunging anticlines form โVโ of "U" shaped, belt-like outcrop patterns. Anticline fold plunges toward closed end of โVโ or โUโ pattern.
Plunging synclines form โVโ of โU" shaped, belt-like outcrop patterns. Syncline fold plunges toward open end of โUโ pattern.
Steeper the dip of the layer, the more narrow the width of its outcrop.
Hanging wall moves up relative to foot wall in reverse and thrust faults.
Hanging wall moves down relative to foot wall in normal faults.
Slickenside grooves that are oriented horizontal in fault scarp indicate strike-slip offset.
Slickenside grooves that are oriented vertical in fault scarp indicate dip-slip offset.
Introduction: Three-dimensional geologic block diagrams are scaled-down, abstract, simple representations, or models of Earth's crustal rock structures, which include 1) formations, 2) unconformities, 3) faults, 4) folds, and 5) topography. Block diagrams are a 3-dimensional composite of both, a geologic map (horizontal map-view) and geologic cross-sections (vertical side-views). The key to successfully completing the block diagrams lies in visualizing the 2-D representations as 3-D structure.
a) Planar Object #X - Strike = _______ Dip = _____
b) Planar Object #Z - Strike = _______ Dip = _____
Estimate the strike and dip of the fault: _____________ Estimate the dip of beds. _____