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Remote sensing for resources development and environmental management
Damen, M. C. J.

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Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Regional geologic mapping of digitally enhanced Landsat imagery
in the southcentral Alborz mountains of northern Iran
Sima Bagheri
New Jersey Institute of Technology, Newark, USA
Ralph W.Kiefer
University of Wisconsin-Madison, USA
ABSTRACT: This study evaluates the utility of using Landsat MSS data in regional geologic mapping of linea
ments. Both conventional image interpretation techniques and digital enhancement techniques were utilized.
The presence and orientation of lineaments can have great structural significance and a correlation may exist
between them and zones of weakness characterized by seismic activity and mineral concentrations. The
lineaments detected on computer-enhanced imagery of the study area exhibited definite trends providing a
regional view of the geological "grain" of the area. When lineament alignments located by Landsat image
analysis were plotted, a correlation was found between lineaments detected on the enhanced scene and
earthquake epicenters, as well as the mapped location of phosphate deposits of the study area.
Landsat images are widely used in regional geologic
studies. They are especially useful for displaying
extended structural elements such as intrusive
bodies, domes, folded mountain belts, and fault and
fracture zones. This study is concerned with the
utilization of Landsat data for the detection of
geologic lineaments in the southcentral Alborz
Mountains of northern Iran. The term "lineament", as
used here, is defined by Siegal and Gillespie (1980),
as follows:
Lineament: a two-dimensional geomorphological term
referring to a mappable, simple or composite
linear feature of a surface, whose parts are
aligned in a rectilinear or slightly curvilinear
relationship and which differs distinctly from the
patterns of adjacent features and presumably
reflects a subsurface phenomenon.
The study area is located in the southcentral part of
the Alborz Mountains of northern Iran (Figure 1).
The region is one of high to moderate relief which
consists of marine sedimentary rocks of Paleozoic and
Mesozoic ages and volcanic rocks of Tertiary age.
The primary objective of this research was to
delineate geological structures by means of digital
image processing techniques, since the presence and
orientation of these features may have great
structural significance and correlation may exist
between them and seismic activities, as well as
mineral concentrations.
The data used here include both film products and
digital data of four Landsat MSS bands imaged in
November 1976. The scene is characterized by a
relatively low sun elevation angle (31°) and a light
continuous snow cover in the mountainous areas,
characteristics that are advantageous for mapping and
interpreting the structural features. A lineament
map and a rock type classification map were produced
from the computer enhanced MSS data. These maps were
compared with an earthquake epicenter map and the
mapped location of ore deposits (mainly phosphate
minerals) in order to investigate relationships
between them.
Recent discoveries indicate that the traditional
concept of Iran as a pair of orogenic belts (the
Alborz and Zagros Mountains) with a median mass
between them has been invalid. Nor can central Iran
be regarded as an eugeosyncline. The only distinct
ion between the Alborz Mountain and central Iran is
one of relief and the two areas are structurally and
stratigraphically very similar (Stocklin, 1968). The
Bouguer gravity anomaly map conforms with the reg
ional structural pattern revealing no separation of
the Alborz as an independent zone from Central Iran.
The Alborz Mountains are continuation of the Alpine
type mountains, which are a complex, asymmetric belt
of folded and faulted rocks. The Alpine orogeny of
the Iranian ranges is characterized by the absence of
nappes present in the European Alps which extend over
a width of 1200 km (Stocklin, 1968). The compressive
stress of Alpine orogeny results in thrusts and high-
angle reverse faults in the central Alborz and a wide
range of fold systems throughout the mountain chain.
These structural features are surface manifestations
of underlying faults, joints, folds, lithologic
contacts or other geologic discontinuities and are
expressed as lineaments of different dimensions on
Landsat imagery. An understanding of these features
and their significance in the regional geologic
framework is essential in analyzing both earthquake
prone areas and mineral potential locations of the
Alborz Mountains.
Physiographically the range is divided into three
segments—Western, Central and Eastern Alborz—with
the central part subdivided into seven lithostruct-
ural units (Gansser & Huber, 1962). The study area
is 3500 sq-km in size and is located between Karaj
River to the west and Damavand volcano to the east
and includes the following units of the southern
Central Zone: (1) the Tertiary Central Zone, (2) the
Southern Paleozoic-Mesozoic Zone and (3) the Southern
Tertiary Zone.
Two methods of analysis were utilized, visual image
interpretation and computer-assisted interpretation.