The aim of this atlas is to provide examples of
the relationship between three-dimensional structure and potential-field
response. We have used the Noddy modelling system, which was developed
as a result of an AGCRC/AMIRA/ARC project. This allowed us to create a
variety of structural models which allow interpretive skills to be developed,
through the specific comparison of structures and their responses. These
models also provide a starting point for the interpretation of actual survey
results. All of the history files used to create these models are provided
in digital form, so that in combination with the Noddy software,
variations to the models can be easily examined. In addition this addition
of the atlas contains wavelet
transforms of the data so that the interpretive skills needed for this
new visualisation technique can be learned.
In order to reduce printing problems, a PDF version of this Atlas is also available, and a PDF version with embedded links also exists.
This Table of Contents lists each page in
text form, the Image Index (much
slower to load) contains one example image from each page,
and the Help page describes the meaning of
each element in a page, and how to configure your browser to load the various
file types. The atlas contains a complete set of images models calculated for both Southern and Northern Hemispheres,
and each set can be accessed separately from the home page of the Atlas.
SECTION 1 BASIC
INTERPRETATION PRINCIPLES In
this section a number of basic intepretation principles are reviewed. The
model geometries are kept very simple so that the effects of depth, latitude,
and possible causes of potential-field anomaly asymmetries can be separated
from the more complex issues of three-dimensional structures. Many of these
principles can in fact be demonstrated in two-dimensions using profiles,
and the reader is encouraged to draw profiles across the data sets in order
to see these effects.
SECTION 2 SIMPLE
STRUCTURAL TYPES In
this section the potential-field response of simple structures is displayed.
In some cases some earlier feature, such as a dyke, has been added to clarify
the point being made. This chapter concentrates on contrasting different
deformation geometries and demonstrating the effects of structurally controlled
or field inclination controlled anomaly asymmetries.
SECTION 3 COMPLEX
STRUCTURES This section provides a number of examples of the
interaction of two or more episodes of deformation, some derived from specific
locations, others simply to demonstrate scenarios which may or may not
be resolved by using the magnetic or gravity data sets.
SECTION 4 TOPOGRAPHIC
EFFECTS This section provides
two simple examples of the effects of topography on potential-field data.
The two normal survey modes of draped and barometric flying are compared.
SECTION 5 REMANENCE
AND ANISOTROPY This section demonstrates the effects of a uniform
or variable remanent magnetisation component, and a uniform or variably
oriented magnetic anisotropy. A comparison of alteration haloes and remanent
magnetisation haloes around igneous bodies is also made.
SECTION 6 ALTERATION
ZONES In this section two
examples are given which compare the effects results of having alteration
haloes associated with igneous intrusion, for regions with pre-existing
APPENDIX A: GEOLOGICAL
MODELLING In this appendix the geometries resulting form each
type of structural event are displayed for a chequerboard model.
APPENDIX B: Wavelet Transforms This appendix includes two papers
describing the basis for the wavelet transforms models are given. In addition, a number of VRML models of 3D structures are provided which can be viewed interactively..
All models created using Noddy
© 1998-2002 AGCRC &