The axial trace is the line representing the intersection of a fold's axial plane with a surface.
Understanding the Axial Trace in Geology
In the study of geological folds, the axial trace is a crucial element for understanding the structure and orientation of folded rock layers. According to structural geology principles, it is the trace of axial plane which contains hinge lines on all surfaces in a folded multilayer complex.
Think of the axial plane as an imaginary, often planar, surface that cuts through the fold, ideally dividing it symmetrically and containing the hinge line (the line of maximum curvature) of each individual folded layer within the rock sequence. The axial trace is simply the line created where this axial plane intersects another surface. This surface could be:
- The ground surface: As seen on a geological map.
- A cross-section: A vertical slice through the folded structure, as shown in a geological diagram.
Axial Trace vs. Axial Plane
It's important to distinguish between the axial plane and the axial trace:
- Axial Plane: A three-dimensional plane that extends through the fold and contains the hinge lines of all folded layers.
- Axial Trace: A two-dimensional line, representing where the 3D axial plane intersects a specific 2D surface (like the ground or a cross-section).
Visualizing the Axial Trace
As referenced, in a fold profile (a cross-sectional view), the axial trace can be visualized as the line formed by joining hinge points—the points of maximum curvature—on each folded layer within that specific profile. When mapping geological structures, geologists plot the axial traces on maps. These lines help define the geometry and orientation of the fold across the landscape. The trend and plunge of the axial trace indicate the orientation of the fold structure itself.
Key Characteristics
Here are the key characteristics of an axial trace:
- It is a line.
- It is the intersection of the axial plane with another surface.
- It helps define the orientation of a geological fold.
- It can be mapped on geological maps or shown on cross-sections.
- Its path on a map reflects the geometry of the fold at the surface.
Understanding the axial trace is fundamental for interpreting geological maps and constructing accurate models of subsurface structures.
