LINEAMENT FABRIC OF RAJASTHAN AND GURAJAT, INDIA P.C. Bakliwal and SM. Ramasamy, Abstract A study of Landsat imagery covering the states of Rajasthan and Gujarat, on scales of 1:1 million and 1:0.5 million, using black and white paper prints and transparencies, reveals a panorama of lineaments, traversing and criss-crossing different strata of varying lithology and age. These lineaments have variable extent, different azimuthal orientation and fluctuating density distribution. Based on their extent, the lineaments have been classified as major (>300 km), intermediate (300 - 100 km) and minor (<100 km). The major lineaments generally represent the surface signatures of crustal fractures of deep seated nature and seem to have played a significant role in the tectonic evolution of different sedimentary basins of Archaeozoic to Cenozoic. These lineaments have interbasinal extent. The intermediate lineaments are more frequent in number and generally related to the tectonic history of the individual sedimentary basins, representing faults, axial trace of regional folds and group / formational boundaries. These are mostly intra-basinal lineaments. The minor lineaments are maximum in number with varying distribution and are expressions of faults, fractures, dykes and axial traces of large scale folds. The direct relevance of these lineaments with magmatism, mineralisation and tectonism have been identified. INTRODUCTION Linear features on the surface of the earth have long been recognised through geologic, geomorphologic and geophysical data. Their linearity, extent and distribution, could be appreciated only after the availability of satellite and airborne data. Such significant linear and curvilinear features on the earth’s surface were named as ‘lineaments’ by Hobbs (1904). The literature in the later part of the 20th century has helped significantly in understanding the morphology and genesis of the lineaments. Geoscientists by and large accept the view that the lineaments are surface expressions of faults, fractures, continental margins and submarine ridges (Sonder 1947; Wilson, 1948; Kaisar, 1950; Hills, 1963; Billings, 1972; Kelley, 1955; Sharma et al., 1982 and Bakliwal et al., 1983). The satellite MSS data of Rajasthan and Gujarat were studied on all four bands (namely 4,5,6 and 7) on paper prints and transparencies of 1:1 million and 1:0.5 million scales, to infer the linear features, based on tonal and textural contrasts. Such lineaments were further screened for any man made linear features. The man made linear features were filtered out and lineaments related to geological processes were drawn and a lineament map was prepared on 1:106 scale. The analyses of these lineaments show their close relationship with evolution of the different sedimentary basins of varying ages from Proterozoic to Cenozoic, magmatism, Reprinted from Rec. Geol. Surv. India (Jaipur) 113(7) : 54-64 - 1987 mineralisation and groundwater. The paper describes the dispositions, geological and tectonic significance of the important lineaments. REGIONAL GEOLOGY The states of Rajasthan and Gujarat form the western most part of the Bundelkhand craton. This region was an active zone of sedimentation, distinct tectonism and repetitive magmatism. The Banded Gneissic Complex acted as the basement during the Precambrian times for the Proterozoic basins like Aravalli, Delhi (Heron, 1936) and Vindhyan (Coulson, 1928). While the basement rocks comprise a complex assemblage of high grade metamorphites, the Aravalli basin is composed of a thick pile of low-grade metamorphites and complexly folded clastic sediments with minor chemogenic assemblage. The Delhi contains distinctly well defined calcareous, arenaceous and argillaceous assemblages. The characteristic repetitive deformative episodes and magmatism typically signify geosynclinal nature of sedimentation and deformation of these basins, whereas the Vindhyans provide a characteristic example of intracratonic sedimentation with independent style of deformation. The sedimentation, deformation and tectonic evolution of these Proterozoic basins were studied in detail by Heron op. cit., Coulson op. cit., Datta and Ravindra (1980) Gupta et al. (1981) and many others in selected areas. The Vindhyan sedimentation in the end phase was succeeded by the sedimentation of Marwar Supergroup of rocks in the trans-Aravalli region. The western Rajasthan and the northern Gujarat witnessed restricted sedimentation of clastic sediments during the Mesozoic while the Cenozoic sea was widespread in western Rajasthan. Repetitive acidic, basic and ultrabasic magmatism during the Proterozoic, widespread acidic volcanism at the end of Proterozoic and an extrusion of basaltic flows during the end of Mesozoic are significant magmatic events of the region. LINEAMENTS The lineaments of Rajasthan and Gujarat show a spectacular network traversing the rock types of varied ages (Fig.1). These lineaments vary from 2 km to more than even 1000 km in length with linear and curvilinear expressions. The study of these lineaments in relation to geology, structure, magmatism, mineralisation and deep geophysical responses etc. led to the classification of these lineaments into various groups and classes. Based on the length of individual lineaments, such lineaments in other parts of the world have been classified by Heman (1961) as mesofractures (> 2 miles) and microfractures (<2 miles) and by Blanchet (1957) as microfractures (less than 2 miles) and macrofractures (2 to 50 miles). The lineaments of Rajasthan and Gujarat have been broadly classified as major (more than 300 km in length), intermediate (300 – 100 km) and minor (less than 100 km) – Ray et al. 1980, Sharma et al. 1982, Bakliwal and Ramasamy, 1983a, 1983b. Bakliwal et al. (1983) have classified these lineaments on the basis of their geological significance into inter basinal and intra basinal lineaments, the former traversing a number of basins of varying ages and the latter confined to a single sedimentary basin. The authors in the present communication have 55 further analysed these lineaments and brought out their detailed morphology and their geological significance. The well exhibited lay-out of major lineaments of the area under study broadly fall under three azimuthal distributions with NNW-SSE, ENE-WSW and NW-SE orientations. The intermediate lineaments fall almost under the above three lineament systems showing sub parallelism to the nearby major lineaments. The minor lineaments, however, are randomly oriented in the area with rare preferred orientations. The major lineaments are very broadly and unequidistantly spaced, whereas the intermediate lineaments exhibit with moderate density with more frequency in Aravalli, Delhi and Vindhyan basins. However, the density of major, intermediate and minor lineaments is poor in the western desert tract of Rajasthan. MAJOR LINEAMENTS The present area is traversed by a number of major lineaments running for more than 300 km to even upto 1000 km across Archaean to Cenozoic rocks and hence the majority of them are interbasinal lineaments. These major lineaments are predominantly aligned in NNE-SSW, NW-SE and ENE – WSW directions, systematically disposed / placed and regionally control the geology of the area. The detailed study shows that these lineaments played significant role in the tectonic evolution of the different sedimentary basins from Proterozoic to recent times (Bakliwal et al. 1983). A brief description of the major lineaments is given as follows. NNW – SSE and NNE – SSW Trending Lineaments : Udaipur – Sardarpur lineament (No.I) The Udaipur – Sardarpur lineament trends in a NW – SE direction between Udaipur (24º34’ : 73º42’) in the northwest and Sardarpur (22º38’ : 75º00’) in the southeast for a distance of about 300 km. In its southern part it is expressed as a linear escarpment in Deccan Trap and controls the Mahi river course in its central part. It forms the contact between the Debari and Udaipur Group of rocks (Aravallis) and in the northern part it is a well defined boundary fault between the Aravalli basin and the pre-Aravalli basement rocks (Bhilwara Super Group). The occurrence of tight isoclinal folds with NW – SE trend in the Debari Group (Aravallis) of rocks in the east and tight upright synclines and anticlines with the same trend in the Udaipur Group (Aravallis) of rocks in the west of this lineament, most probably, indicate that this lineament has acted as a barrier during deformation. It would have also been the source of synsedimentational basic volcanic rocks during the inception of the Aravalli basin. The occurrence of Gingla Granite (2960 m.y.) along this lineament may probably indicate their inter-relationship. This lineament forms the eastern boundary / fault of the Aravalli basin. The occurrence of base metal mineralisation in Phalet (24º 31’: 73º55’) and Kotri (24º 45’ : 73º 47) area at the contact of pre-Aravalli basement and the Aravallis along this lineament zone indicates that this lineament warrants detailed studies throughout its strike length for incidence of base metal mineralisation. 56 Rakhabdev Lineament (No.II) Rakhabdev lineament, named after the Jain pilgrim centre, is a curvilinear lineament whose curvature conforms to the western margin of the Bundelkhand massif and it extends from Nathdwara (24º55’ : 73º50’) in the north to Barwani (22º00’ :74º 56’) in the south for a distance of about 350 km. This lineament which was known for a distance of about 140 km. between Nathdwara in the north and