Objectives of Structural Geology The structural geologist is concerned with three major problems What is the structure? When did it develop? Under what physical conditions did it form?

1. What is the structure? Identification of structure Observation Description Interpretation / Conclusion

1. What is the structure? It is essential to determine the shape and size of the rock bodies. Are they great flat-lying tabular masses covering scores of square miles? Or are the tabular masses that have been thrown into folds with a wavelength of several miles and an amplitude of thousands of feet?

1. What is the structure? To describe the structures three size terms are commonly used, these are: Microscopic – under microscope Mesoscopic – within the vision Macroscopic – beyond the vision

Scale in Structural Geology Microscopic – Need magnification Foliation, Micro folds Mesoscopic – Hand specimens and outcrops Foliation, Folds, Faults Macroscopic – Mountainside to map levels Basins, domes, Metamorphic Core Complexes

1. What is the structure? Small scale structures are easy to recognize and describe

1. What is the structure? Large scale structure are difficult to recognize and establish Geological field mapping / work is indispensable Aerial photographs, Satellite images, Drainage maps, Topographic maps are helpful to ascertain the structures

Satellite image Drainage map

2. When did it develop? One phase of study is to determine the sequence in which the structural features developed. One may find an anticline, a fault and a dyke. What are their relative ages? Anticline may be oldest and the dyke may be the youngest.

How can we determine the relative ages of structural events? Simple way is to look at the relationship to each other. Principle of Cross-Cutting Relations

2. When did it develop? The structural geologist is interested not only in the sequence of events in the area in which he is studying but he also wants to fit them into the geological history of the whole earth. These can be done by paleontological or by radiogenic dating methods.

3. Under what condition did it form? The third objective of the structural geologist is to determine the physical processes that produced the observed structures. What was the temperature and pressure at the time the structural feature formed and what was the stress distribution? Without knowing the stress distribution at the time the structural featured formed, it is difficult to decide whether a given fold was the result of contruction of the earth, subcrustal convection currents or the forceful injection of magma.