Student Name: Grade:_____
Physical Geology 101 Laboratory
Structural Geology II - Structure Block Diagram Analyses
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.
Part I. Pre-Lab - Knowing and Understanding Structural Terms and Symbols:
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:
1) Strike of beds is always parallel to the direction of the contacts.
2) Rock layers dip towards the youngest exposed rock layers.
3) Oldest rocks exposed in the center of eroded anticlines and domes.
4) Youngest rocks exposed in the center of eroded synclines and basins.
5) Horizontal folds form parallel sets of belt-like outcrop patterns.
6) Plunging anticlines form โVโ of "U" shaped, belt-like outcrop patterns.
๎ Anticline fold plunges toward closed end of โVโ or โUโ pattern.
7) Plunging synclines form โVโ of โU" shaped, belt-like outcrop patterns.
๎ Syncline fold plunges toward open end of โUโ pattern.
8) Steeper the dip of the layer, the more narrow the width of its outcrop.
9) Hanging wall moves up relative to foot wall in reverse and thrust faults.
10) Hanging wall moves down relative to foot wall in normal faults.
11) Slickenside grooves that are oriented horizontal in fault scarp indicate strike-slip offset.
12) Slickenside grooves that are oriented vertical in fault scarp indicate dip-slip offset.
Part II - In-Lab: Drawing and Interpreting Geologic Structures in Block Diagrams
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.
