Regional Geology and Structure of the Sakoli Belt, India
from Space Data Application
S. G. Krishna, S. M. Dutta
Geological Survey of India, Nagpur 440 006
Abstract
The Sakoli belt, covering 7000 sq km (20° 30' - 21°30' N/79°15' - 80°15'E) in Maharashtra, defines a distinct triangular shaped structural outline within Central Indian Precambrian shield and was evolved through mutual interplay of the multiphase compressional/extensional tectonism. Complex structural - metamorphic history of the terrain can only be understood with collation and synthesis of all types of regional geological parameters. The objective of present study was to add remote sensing knowledge inputs in defining structural evolution of the domain.
Synoptic overview of the regional geological/structural assimilation inherent in the satellite data products depict interrelationship of different structural phenomena in shaping the rock fabric over the sakoli belt. Visual interpretation of IRS-FCC of bands 2,3, & 4 on 1:250,000 scale supplemented by geocoded FCC on 1:50,000 scale from critical locales helped in deriving the following important conclusions; (I) Sakoli belt comprises steeply dipping assemblages of meta sediments/meta sediments, meta volcanics, (ii) ENE-SW and N-S are the two major lineament trends strongly influencing the regional structural fabric and geology, (iii) ENE-WSW is younger than N-S lineament, transacting the later in number of occasions (iv) strong interplay along these two lineaments in different magnitudes/dimensions, often shapes the deformed rock fabric similar the deformed rock fabric similar to fold geometry, (v) ENE-SW lineaments greatly obliterated earlier fold geometry by dragging and displacement, (vi) Northern tip of the sakoli triangle has been affected most, by the two major transaction lineaments resulting in deformation sand translation of rock bodies considerably along ENE trend.
The study thus revels that faulting rather than folding has played dominant role in shaping the belt and evolving it structural/metamorphic history. Genetic interrelation of ENE-WSW and N-S linear structural trends, role of faults/lineaments in shaping the deformed rock fabrics similar to fold geometry and dragging of major folds towards NEN are among the main observations from the critical synthesis of visually interpreted remotely sensed data inputs.
Introduction
The sakoli belt, a part of Central Indian shield, still remains a main domain of geological studies or its complex basin geometry, structural, metamorphic and metallogenetic characters. This had called for intensive and exhaustive regional geological studies for the tectonic evolution of the region. The prime objectives of the study were, therefore to dicipher : (I) regional geological/structural set up through recognition of macroscopic scale structural elements and their correlation (ii) effects of linear fabrics on the mappable rock units (iii) influence of extensional/compressional tectonic grains in shaping basing geometry. Present study with space-borne data products was intended to supplement and update the existing data base as well as to upbuild the knowledge of tectonic history.
Sakoli belt covers about 7000 sq km area (20030' - 21030'N/79015'- 80015'E) in the eastern part of Maharashtra, India. The study was carried out mainly on IRS-LISS-I FCC of bands 2,3,4 on 1:250,000 scale aided by geocoded FCC on 1:50,000 scale of critical locales and analysis / synthesis of derived knowledge inputs with the back ground of available geological informaion about the domain. Tome, texture, drainage patterns, cover types, percepted relief, hues, features orientation and association form the essential input image parameters (Subins 1978) for the interpretation of broad lithological /structural fabrics, delineation of regional geological elements as well as their mutual/spatial interrelation within the study domain.
Regional Geology
The sakoli group of rocks define a broad triangular shaped outcrop pattern on IRS data products. The edges of the triangle, delineating the contact between the major rock groups and the older basement, are of structural original obliterated considerably by later deformation episodes. Analysis/synthesis of visually interpreted image parameters aided by real world feedbacks by critical areas reveal that the board lithological assemblages of this belt comprise group of metasedimentaries (Quartzite, Banded Iron Formation (BIF), Phylites, mica schists) and metabasics (metabasalts and amphibolites). The sakoli group is bordered by Nandgaon acid volcanics/quatrtzites and Amgaon gneisses to the east and Tirodi gneisses to the northwest and north. These major staraightgrahic contacts are defined by regional shears/faults, depicted n the imagery as prominent linear morpho-tectonic signatures. The tectonic contacts were further corroborated from the ground truth by the presence of brecciated quarts veins and mylonites. The southern contact of the belt with the basement gneiss is not well defined probably due to the mutual effects in varying degree and magnitude of basement structural fabrics and later phases of deformation magmatism the contacts with Sullavai meta sediments to the south/southwest and Dongargarh granites to the south-east could be easily demarcated on the imagery because of their distinct physiograhic expressions.
Morphologic Expression :
The area exhibits significant denudational topography with subdued, structure-controlled ridges and plains at various elevations showing higher degrees of areal plantation that linear stream erosion. The basement gneiss dotted with residual hillocks of granites, quantzites and ultramafics covers major part of the study domain as low planted topography with n imprint of structure-controlled dendritic to subrectangular drainage network. The gneissic country west of Wainganga river forms a distinct textural unit on the imagery due to the presence of number of valley fills and intense agricultural activity. Quartzires, Bonded Iron Formation (BIF), meta-basic and some of intercalated quants-phyllites of sakoli metasedimentaly possess characteristic relief, prominent linearity and tonal variations. Around Chandori, Lakhni and Palandur, meta sediments comprising schist/phyllite form planated topography in the central part of the belt.
