Apr 21 2014
Introduction
In the field of structural geology, the orientations of real or imaginary lines, surfaces, and planes are represented in three dimensional geometry. Trend and plunge are the two measurements that are used to describe linear features in geology. Plunge is the dip angle that is used to describe linear features.
Trend and plunge are the two numbers that are used to describe the orientation of a linear element in space. Trend is also called the plunge bearing. The plunge of any linear element is the angle measured downward from the horizontal line to the vertical plane. The plunge may also be considered as the deviation from the horizontal in the vertical plane, in which the linear element is contained. Since it is an angle, the value of plunge varies from 0 to 90°. In structural geology, the plunge is always measured in a downward direction to the Earth.
Lines that have a plunge angle between 0 and 30° are called shallowly plunging lines. Those lines that have a plunge angle between 30 and 60° are said to be moderately plunging, while lines plunging between 60 and 90° are said to be steeply plunging. There are a number of conventions that are followed in representing the trend and plunge values. One convention is to write the plunge value followed by an arrow and then the trend value, e.g. 45→065. If the lineation does not have a plunge, then it is represented by a double headed arrow.
References
- Chapter 4: Orientation Description – University of Wisconsin
- Field Geology – University of Sulaimani