Structural Analysis and Synthesis

A Laboratory Course in Structural Geology

Stephen M. Rowland, Ernest M. Duebendorfer, Alexander Gates

• Publisher: Wiley-Blackwell
• Year: 2021
• ISBN:
  9781119535485
• Edition: 4
• Topic: Scienze fisiche
• Subtopic: Geologia e scienze della terra

STRUCTURAL ANALYSIS & SYNTHESIS

STRUCTURAL ANALYSIS & SYNTHESIS A LABORATORY COURSE IN STRUCTURAL GEOLOGY

Structural Analysis and Synthesis is the best-selling laboratory manual of its kind. Specifically designed to support the laboratory work of undergraduates in structural geology courses, the book helps students analyze the various aspects of geological structures, and to combine their analyses into an overarching synthesis.

This book is intended for use in the laboratory portion of a first course in structural geology. As is explicit in the book's title, it is concerned with both the analysis and synthesis of structural features. In this fourth edition, the has been broadened to include a range of new content and features, including:

• Video content that demonstrates how to perform some of the more challenging structural geology techniques
• An acknowledgment of the increasing importance of environmental applications of structural geology – vital to students who may go on to pursue careers in the environmental sphere
• An increased emphasis on quantitative techniques, complete with descriptions of computer program applications
• Contingent with this quantitative emphasis, the book also outlines the limitations of such techniques, helping students to appropriately apply the techniques and evaluate their trustworthiness

Structural Analysis and Synthesis is a renowned and widely recognized aid to students in grasping and mastering the techniques required in structural geology, and will find a home wherever the principles and practices of structural geology are taught.

1
Attitudes of Lines and Planes

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Objectives

• Measure planes and lines in the field using standard techniques.
• Become familiar with the azimuth and quadrant methods for defining the orientations of planes, lines, and lines within planes.
• Draw and read back orientations on maps.

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This chapter investigates the orientations of lines and planes in space. The structural elements that we measure in the field are lines and planes, and analyzing them on paper or on a computer screen helps us visualize and understand geologic structures in three dimensions. In this chapter, we examine nomenclature, measurement, and representation of these structural elements. Solving apparent‐dip problems is commonly also included in a chapter on lines and planes, but these problems are much more easily solved using a stereonet and will be included in Chapter 3.

All orientations contain two components: an inclination and a declination. The declination is a horizontal angle of rotation from a reference point, most commonly true north. Declinations include the strike of a planar feature (Figure 1.1) and the trend of a linear feature (Figure 1.2). Inclination is the angle that a plane or line is sloped relative to the horizontal plane of the earth’s surface. For planes, this quantity is the dip (Figure 1.1), and for lines, it is the plunge (Figure 1.2).

The orientation of planar features is measured with a strike and dip. By convention, they are labeled strike, dip, and dip‐direction, though there are variations. The dip direction is the quadrant toward which the dip is inclined. Dips must be perpendicular to their corresponding strike and are indicated by the dip direction. A northeast (NE) strike, for example, can only have a southeast (SE) or northwest (NW) dip direction. The orientation of linear features is measured with trend and plunge and is reported as plunge/trend. Lines do not require a dip direction, so the written orientation is readily distinguished from that of a plane.

There are two ways of expressing the strikes of planes and the trends of lines (Figure 1.3). The azimuth method is based on a 360° clockwise circle and the quadrant method is based on the four 90° compass quadrants – north, south, east, and west. The quadrant system is the most commonly used in the United States, but in other countries the azimuth system is the convention. Strikes are traditionally measured from the north‐half of the transit or compass, but it is understood that the line extends in both directions. Unless horizontal, trends must be measured from the direction that they plunge, so they can be in any direction.

Figure 1.1 Strike and dip of a plane.

Figure 1.2 Trend and plunge of an apparent dip.

Figure 1.3 Azimuth and quadrant methods of expressing compass directions.

A plane that strikes due northwest–southeast and dips 50° southwest could be described as 315°, 50°SW (azimuth) or N45°W, 50°SW (quadrant). Similarly, a line that trends due west and plunges 30° may be described as 30°/270° in azimuth (sometimes written as 30° → 270° or 30°, 270°) or 30°/N90°W in quadrant. For azimuth notation, always use three digits (e.g. 008°, 065°, 255°), so that a bearing cannot be confused with a dip (one or two digits). In this book, the strike is given before the dip, and the plunge is given before the trend. We recommend that you use the azimuth convention in your work. It is much easier to make err...