ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

north it is limited by the Dauki fault and to the east by the
marginal faults of the Barail ranges. Naga-Lushai-Arakan­
Yoma Folded Belts: This is an elongate crescent-shaped
belt extending from the Bay of Bengal to the Mishmi block
in a N-S, NNE-SSW ot NE-SW direction. It is characterised
by parallel ridges and valleys, rugged and intensely dissected
topography and parallel and dendritic drainage.
Likwise, the Bengal - (Brahmaputra) basin is characterised
by flat lying, even and mottled textured terrain with low
relief and anastomosing drainage pattern. The NW-SE
trending lineaments are very prominent running almost parallel
to the stream courses viz. Padma lineament, Jamuna
lineament, Tista lineament etc. Used in conjunction with
discontinuous data in terrains of poor access, this synoptic
medium provides a powerful tool for tectonic analysis.
Boundaries of such tectonic zones, thus identified, are
marked by pronounced lineaments, either straight or curved.
Lineaments of significance include the Dauki fault, Jamuna
lineament, Tista and Padma lineaments, Main boundary
fault of the Himalaya, Siang fracture, Tsangpo suture,
Mishmi and Lohit thrusts, Naga and Disang thrusts, Axial
zone, Volcanic line of Burma, Red river faults, etc. Lineaments
passing from GangaBrahmaputra delta across the
Himalaya to Tibet must be the expression of deep-seated
and fundamental crustal fractures, but are possibly of geologically
recent origin as evidenced from their manifestation
through the recent river deposits of the Bengal basin.
The entire area is representative of a conspicuous polycylic
landscape with diversified soil - landform - drainage types.
The seismo- tectonic activities which are belived to have
become very active, due to plate tectonics (Mayanmar Plate
& East Indian Plate) have exerted much influence in
this evolution.
TIM T. MUNDAY, LISA WORRALL & ANDY A. GREEN
Airborne Electromagnetics - Providing new perspectives
on geomorphic process and landscape development
in regolith dominated terrains
Co-operative Research Centre for Australian Mineral Exploration
Technologies, c/o Csiro, Private Bag, PO Wembley,
Perth, W.A. 6014, Australia
Airborne electromagnetic (Aem) methods have a considerable,
largely untested, potential for mapping regolith materials
in three dimensions and improving our understanding
of those processes involved in their development.
Other, more common, methods used in regolith and geomorphological
mapping have limited skin depths and only
return information on the nature and disposition of regolith
materials at surface (see table 1). This paper examines
the promise of Aem data by reference to examples drawn
from the Lawlers area located in the Archaean .Yilgarn
Craton, Western Australia.
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Technique
Remote Sensing
Radiometries
Radar (Ground (GPR);
Microwaves
Air & Space)
AEM
Magnetics
TABLE 1: AEM Data - Content
Radiation
VisiblelInfrared light
Gamma Rays
1-20 metres
VLF and below
Magnetie field
Skin-depthin typical
regolith materials
< 1 micron
< 1 metre
10-100 metres
not applicable
Air photos, remote sensing imagery and radiometries data
provide useful, though shallow information, whilst magnetics
responds variably to regolith, largely because of the dispersed
character of magnetite relative to fresh rock (Table
1). In more resistive terrains, ground penetrating radar
may provide information on the disposition of regolith materials
at depth. However, the conductivities exhibited by
regolith materials typical of Australia, suggest this technology
would have limited application, with skin-depths
being generally less than 10 m.
Aem surveying methods make use of the response of the
ground to the propagation of electromagnetic fields. A primary
electromagnetic field is generated by a transmitter in
the aircraft. The ground generates secondary electromagnetic
fields in response, which are usually measured in a
receiver towed behind the aircraft. The difference between
the transmitted and received fields reveal the presence of
conductors and provide information on their geometry and
electrical properties. Regolith materials are variably conductive,
depending on their nature and characteristics
(physical and chemical). Their lateral variations can produce
spatially coherent responses in electromagnetic (Em)
data.
We describe a new approach to the processing, display
and interpretation of multichannel, multicomponent Aem
data which draws on statistically-based methods developed
and refined for the analysis of multispectral remote sensing
data. The application of the principal components method
as a technique for addressing data redundancy and for the
display of Aem data for regolith mapping purposes is examined
in this context.
A comparison of existing regolith maps (compiled through
conventional mapping methods, including the use of
air photos and remote sensing data) and Aem data for the
Lawlers area, suggests that the surface distribution of regolith
materials is likely to be a poor indicator of materials
at depth. A significant amount of unmapped, unexplained,
detail is also observed in the latter, notably in areas
of transported cover, comprising alluvium and colluvium.
The application of Aem to regolith mapping and the reconstruction
of landscape history is discussed with reference
to this information. Comment is also made on the
role of Aem in providing information on groundwater
hydrology. Aem data for the Lawlers area indicates the
importance of structural and lithological control on
through-flow.