Geology of Rajasthan General The geological history of the northwest Indian craton in Rajasthan region covers a wide span of time from ca. 3.5 Ga to 0.5 Ga. This craton incorporates a wide variety of lithological and tectonic units representing the basement rocks (Banded Gneissic Complex of Heron, 1953), Proterozoic fold belts (Aravalli and Delhi), and Late Proterozoic igneous suites (Malani, Jalore, and Siwana). Basement rocks, comprising the gneissic terrain of the Sandmata Complex (SC), the Mangalwar Complex (MC), and the Hindoli Group (HG) forming the Bhilwara Supergroup (BSG), is essentially Archaean in age. This is evident from ca. 3.5 Ga age of some mafic inclusions within the BGC and from the age of the intrusive granites (2.9 Ga, Untala and Gingla granitoids). Gneisses, comprising the SC and the MC, represent the reclassified Banded Gneissic Complex of Heron (1953). Rock types of the SC are composed largely of granulite facies gneisses of diverse composition, such as metapelites and psammitic gneisses, basic intrusives, and calcareous, clastic and chemogenic metasediments which occur as xenoliths, streaks and patches, and thrust bound large bodies in the gneissic terrain. Although Gupta et al. (1981) have shown in their map of the Aravalli region that the SC forms a distinct litho unit which lies to the west of the MC, the SC occurs as tectonic wedges within the basement gneisses of the MC. Mangalwar Complex The MC of the BSG terrain contains varied lithologic assemblages and tectonic units of a greenstone like sequence, and comprises ultramafic bodies and mafic igneous bodies of volcanic and plutonic precursors, now represented by amphibolites, highly diverse metasediments such as metapelitic and aluminous paragneiss, fuchsite bearing quartzite and low Mg marble and calc silicate gneiss, coarse clastics such as greywacke and tuffaceous sediments represented by graphitic schist. Granodioritic and tonalitic gneisses (Untala, Gingla) represent the consolidation of the early crust at ca. 2.9 Ga and the end Archaean cratonisation is indicated by the Berach Granite (ca 2.6 Ga). Although Archaean cratonisation event is well documented in the BSG rocks of Rajasthan, some authors put controvertible arguments against this end Archaean event and believe that the HG is not a part of the Archaean basement on the equivocal premise that the Berach Granite (2.6 Ga) forms the basement for the HG in SE Rajasthan. Nevertheless, the Archaean Proterozoic boundary can be constrained to a slot of 2.5 to 2.6 Ga in Rajasthan from the available field geochronologic and thematic data base. It may, however, mentioned that the stratigraphic relationships of the different lithologic assembalges of the BSG are not clear as the different rock units are usually demarcated by prominent ductile shear zones (DSZ) running for kilometers. Thus, during the Proterozoic period, the Archaean crust (BSG) was extensively reworked through the development of DSZs and granitic activity. The MC presumed to represent an Archaean primary granite greenstone belt whereas the HG is suggested to represent a secondary granite greenstone belt in NW Indian shield. Hindoli Group The HG occurs in an arcuate belt containing felsic and mafic metavolcanics and metagreywacke forming a turbidite sequence. The end-Archean Berach Granite intrudes the HG. Proterozoic Fold Belts The Proterozoic geologic history of south central Rajasthan is contained in a number of distinct fold belts. The principal fold belts are Lower to Middle Proterozoic Aravalli Fold Belt (AFB) and Middle to Upper Proterozoic South Delhi Fold Belt (SDFB). The basement to these fold belts is the BSG or the BGC. Other time equivalent early Proterozoic cover sequences in this region include Jahazpur Group, Pur Banera Rajpura Dariba-Bhinder Groups, Sawar Group, and others, The Proterozoic history is marked by significant secular, changes in terms of basin development, lithocharacters, and mineralisation types. Some of these cover rock sequences contain Pb Zn whilst others Pb Zn Cu or Cu Ag Au mineralisations. The early Proterozoic Aravalli and the equivalent rock, sequences, including the Jahazpur, Pur Banera Bhinder, and Rajpura Dariba Bethunmi belts, are considered to have developed in ensialic rift basins which except for the main AFB, failed. The isolated basins possibly developed as pull apart basins. These rift basins representing different belts, such as Rajpura Dariba, are strongly tectonised and physical continuity with other belts such as Sawar and Agucha belts is lost in many places. The main AFB evolved as an aulacogen widening southward from a possible triple junction located near Nathdwara Delwara area where rift volcanics are well documented. The fractured arm continued NNE through the SC and was destined to open in Middle Proterozoic time as the south Delhi rift. Aravalli Fold Belt The stratigraphic succession of the Aravalli Fold Belt (AFB) is given by many workers. Most workers have proposed two major stratigraphic sequences within the AFB, a shelf facies with basic lavas and coarse clastics at the base (Delwara and Debari Groups) in the east and a deep sea turbidite facies (Jharol Group) with ultramafic slivers in the west, the latter occurring in a zone approximately marking the contact between the two facies. This zone (Rakhabdev Lineament) has been considered a suture in the AFB. Unconformable relation between the Archaean basement and the overlying grit arkose chert horizon below the Delwara Group signifies a first order erosional unconformity, which in Rajasthan, represents the Archaean Proterozoic boundary. However, at many places, the contact of the Proterozoic sequence and basement is highly tectonised. Delhi Fold Belt The Middle to Upper Proterozoic Delhi Supergroup rocks occur in two belts, namely, (i) the North Delhi Fold Belt (NDFB) in NE Rajasthan, developed in three sub basins in Alwar, Bayana and Khetri areas, and, (ii) the South Delhi Fold Belt (SDFB) along the Aravalli hill range in central Rajasthan. The two belts are separated by a migmatitic gneiss tract around Ajmer in the south, poorly exposed rock assemblage in the middle and by stratigraphically problematic rock sequence extending northward possibly up to Khetri. The Raialo, the Alwar and the Ajabgarh Groups of NE Rajasthan forming the NDFB do not perhaps extend beyond south of the Sambhar Jaipur Dausa wrench fault. The rocks of the SDFB are deposited, in two sub-basins flanking a median basement inlier, west of Bhim. The eastern sub-basin contains pelitic and psammitic rocks of the Rajgarh Group signifying a continental slope facies; and a platformal pelite carbonate sequence of the Bhim Group. The western sub-basin contains basic and felsic volcanics with shallow-water clastics forming the Barotiya and the Sendra Groups. The contacts between the different sequences are defined by prominent ductile shear zones and thrusts. Several conglomerate horizons, such as Shrinagar Ki-shangarh and Bar are developed within the SDFB which signify erosional unconformities. The status of the Bar conglomerate is problematic. An important attribute of the SDFB is the Phulad ophiolite which is best developed in the southern part of the fold belt. The ophiolite zone is interpreted as dismembered fragments of oceanic crust developed within the South Delhi rift basin and is considered to represent a suture zone where high P low T metamorphic imprints are recognizable. From tectonic development and presence of prominent DSZs and basement slivers, the SDFB appears to represent a melange zone. Late Proterozoic The Late Proterozoic event in Rajasthan is marked by the opening of the Sirohi basin within the Pre Delhi terrain to the west of the SDFB in the trans Aravalli region. Two lithologic units, namely, Punagarh and Sindreth Groups are identified by recent workers. These two groups occur in isolated basins, unconformably overlying the Sirohi Group metasediments and the migmatites of the Erinpura Granite affinity. The Sirohi Group itself occurs as isolated inliers within the unclassified sequences of the Erinpura craton. However, the Sirohi Group has been tentatively correlated on litho structural grounds with the Jharol Group of the Aravalli Supergroup. The Punagarh and the Sindreth Groups are represented in the trans-Aravalli range primarily by bimodal acid basic volcanics, volcaniclastics and terrigenous sediments, and are presently placed at the top of the SDFB sequence. In SE Rajasthan, the Great Boundary Fault (GBF), a prominent dislocation zone, marks the boundary between the HG basement rocks and the paratectonic Vindhyan Supergroup rocks of, Proterozoic age. The Vindhyan equivalent sediments also developed in NW Rajasthan in a separate basin and are grouped within the Marwar Supergroup composed of molasse type sediments and evaporites. After the Delhi orogeny, the NW Indian craton across the Aravalli range, witnessed large scale magmatic activity represented by felsic and mafic Malani volcanics, Jalore and Siwana plutons of Late Proterozoic age. Phanerozoic The Paleozoic marine sedimentation in Rajasthan was restricted to three major basins in Jaisalmer, Barmer, Nagaur and Jalore districts. During the Permo Carboniferous period the Bap boulder bed and Bhadura terrigenous sediments were deposited over the rocks of the Marwar Supergroup. There is no record of any Triassic sedimentation in this region. However, the Jurassic period is marked by large scale marine deposition and proliferation of flora and fauna. The culmination of the Mesozoic witnessed large scale outpouring of basaltic lavas in southeastern Rajasthan. These volcanic rocks form the northern extension of the Deccan Traps. This volcanic activity, however, did not affect the sedimentation in the northwestern Mesozoic basins where deposition of marine and continental sequences continued uninterrupted during the Cenozoic period. Major Terrains of Rajasthan From the distribution and inter relation of important tectonic and stratigraphic units in Rajasthan, four major terrains have been identified. These are (i) the Marwar terrain, (ii) the fold belt terrain which includes the Aravalli and Delhi fold belts, (iii) the basement terrain and (iv) the Vindhyan terrain. Quaternary The rejuvenation of the pre existing faults during the post-Neogene to Recent times facilitated Quaternary sedimentation in marginal fault troughs, grabens and lakes formed by disorganised river courses. A major part of the Quaternary sediments also occurs in the western semi arid zone spreading over 36,000 km2 in Rajasthan. The Quaternary sediments comprising sequence of fluvial, fluvio lacustrine and successive aeolian sediments correspond to different phases of paleoclimatic conditions. At least three arid phases during ca. 200 ka, 18 14 ka and 6 3 ka continuing to Recent are identifiable with intermittent three wet phases during older than 200 ka, 120 ka and 10 6 ka periods. The present day morphology of the Thar desert is the outcome of the aeolian processes operating since the Late Pliestocene. The stratigraphic succession established by GSI in Rajasthan is given in Table below. Regional Tectonics South central Rajasthan contains a mosaic of Proterozoic fold belts within a reworked Archaean basement complex. These fold belts, characterised by resurgent tectonics, are demarcated by, prominent crustal dislocations, marked by ductile shear zones. Moreover, there are prominent shear zones and thrusts within the fold belts which are either vestiges of Proterozoic sutures or ophiolitic melange zones. Aravallii Fold Belt The Aravalli Fold Belt (AFB) has a tectonic contact with the basement gneisses which, in fact, is a tectonised unconformity, marked prominently in the north where the Delwara sequence of the basal Aravallis is tectonically juxtaposed against the BGC along a reworked unconformity. This tectonic zone, the Delwara Dislocation Zone (DDZ), extends south and southeast along the Aravalli basement interface, and truncates a number of litho units. Another important tectonic feature of the AFB is the Rakhbdeo Suture Zone (RSZ) which divides the AFB into two contra sting segments, namely, the platform sequence in the east and deep sea facies (Jharol) in the west. The RSZ, marked by tectonised serpentinite bodies and minor metagabbro and amphiboite is considered the Aravalli suture along which the dismembered Aravalli oceanic/ transitional crust was obducted and the eastern and the western domains were sutured. Delhi Fold Belt The South Delhi Fold Belt (SDFB) has developed on an intracratonic rift basin which was floored by an oceanic /transtional crust. The remnants of this crust are preserved as dismembered ophiolitic melange (Phulad Ophiolite) Apart from the DSZs related to the ophiolitic zone, the SDFB contains an upthrust basement wedge, flanked by two prominent thrust zones. All these tectonic features make the SDFB an imbricate thrust zone which should have deeper crustal significance. The western boundary of the SDFB is defined by a dislocation zone, the Phulad Dislocation Zone (PDZ), against the basement rocks, while the eastern boundary is a prominent thrust zone (Kaliguman Dislocation Zone, KDZ) which separates the Delhi rocks from the Sandrnata Mangalwar Complex rocks in the north and the Aravalli sequence in the south. The imbricate tectonic signatures of the SDFB are also reflected in the tectonics of the adjacent Sandmata/Mangalwar Complex terraine where the granulite facies Sandmata rocks are bound by imbricate DSZs within the amphibolite facies Mangalwar rocks. From tectonic relations it is suggested that the lower crustal rocks of the Sandmata Complex have been emplaced as tectonic wedges at various structural levels, and the gravity high over the Sandmata belt is a probable indication of this feature. The Mangalwar Complex to the east of the Sandmata Complex contains a number of subparallel DSZs which are probably the expression of subsurface imbricate thrust zones between the lower and the upper crustal rocks. Great Boundary Fault (GBF) The GBF is an important dislocation zone in southeastern Rajasthan. The geological and structural setting indicates that the GBF, a reverse fault, is also an imbricate fault zone which sliced the Vindhyan and pre Vindhyan rocks. The trace of the GBF is curvilinear, and it appears to be a rotational fault with the hinge located nearly 20 km south of Chittaurgarh. These features indicate that the GBF is related to indentation tectonics caused by impingement of the Bundelkhand massif with the Vindhyan cover rocks on the Precambrian terrain of Rajasthan, as a result of regional crustal deformation of the Indian plate after the collision and jamming of the Indian and the Asian plates. In this context, the GBF has a regional crustal significance in the tectonic development of the NW Indian plate segment in Late Tertiary and Quaternary times, and it is likely that this fault Zone is still active. Rajasthan Shelf The Mesozoic and Cenozoic sediments of Western Rajasthan are contained in structurally controlled basins of the Rajasthan shelf which formed a part of the Indus Shelf. This shelf region is divided into several segments by sub surface basement ridges. The Delhi Lahore ridge separates the Indus Shelf from the Punjab Shelf and marks the northern boundary of the Indus Shelf. The Jaisalmer Mari High differentiates the Jaisalmer Basin. The Devikot Pokharan Nachna High is a prominet NW SE trending gravity high. This basement ridge and the Fatehgarh Fault to the south of this ridge delimit the Jaisalmer Basin, in the southeast and the Barmer Basin in the northwest. The structural style of the Jaisalmer Basin is controlled by major fault from the western edge of the outcropping belt up to Dangiwala-Lang areas in the northwest and to the south of Lunar Miajlar area. These faults exhibit flower structure and are the result of wrench fault tectonics. Another basement ridg passes through Radhanpur Barmer. Structurally, the Cambay, Graben is connected with the Rajasthan Shelf through the Sanchor and Barmer Grabens. Marwar Craton In Marwar Craton several lineaments have been identified. The major lineaments are the Luni Sukri Lineament (LSL) and the Jaisalmer Barwani Lineament (JBL). The LSL trends NE SW and is aligned along Luni and Sukri rivers forming a significant linear/curvilinear feature in the desert tract of Rajasthan. It extends for 750 km from Great Rann of Kachchh in the southwest to Sambhar Lake in the northeast with a ENE WSW to NE SW trend. The northeastern extension of the LSL between Bakhasar and Sambhar Lake is controlling the Luni and Sukri rivers in the desert country. This lineament might, represent the northwestern limit of the Delhi basin. The absence of Cambrian or Eocambrian sediments belonging to the Marwar Supergroup beyond southeast of this lineament would have limited the Late Proterozoic to Early Palaeozoic basin in the, Southeast during the evolution of the Marwar basin. The alignment of earthquake epicentres of varying intensities from 1819 to 1976 A.D. in Kachchh area and adjoining areas indicate neotectonism along this lineament. The JBL is 1000 km long lineament extending from Barwani in the southeast to Jaisalmer in the northwest in a NNW SSE to NW SE direction, the major segment of which passes through the desert tract. It delimits the southwestern boundary of the Aravalli basin near Godhra and abruptly cuts the Delhi rocks in their southwestern extension in Vadnagar and Palanpur areas. North of Barmer, it delimits the western boundary of the Tertiary basin and crops out as a well defined fault within the Mesozoics of Jaisalmer area. A few circular features, located along this lineament in Jaisalmer area, are interpreted as sub surface domes and basins associated with tectonism of this lineament, and these may be promising zones for hydrocarbon accumulation. Table: Stratigraphy of Rajasthan Era/Period Supergroup Group Formation Lithounit Recent Sub Recent Quaternary Shumar Alluvium and blown sand, clay, sandstone, limestone, loose sand Calcretised conglomerate, sand with fluvial and aeolian deposits Tertiary Eocene Bandah/ Kapurdi/ Jogira/ Khuiala/ Mandai/ Marh Gypseous clay, fossiliferous limestone, fuller’s earth, sandstone, gypseous clay, limestone Paleocene Sanu/Akli/Palana Sandstone, shale, limestone, bentonitic clay ---------------------------------------------------- Unconformity ----------------------------------------------------------------- Cretaceous Deccan Traps Abur/Fatehgarh (=Garu) Pariwar Sandstone, limestone, clay, shales, variegated sandstone Mesozoic Badesar Sandstone, grit, sandy limestone Jurassic Baisakhi Gypsum-bearing clay, shale, limestone Jaisalmer Fossiliferous limestone, sandstone Lathi Conglomerate, arkosic sandstone with lignite and gymnosperm fossil wood. ---------------------------------------------------- Unconformity ----------------------------------------------------------------- Palaeozoic Permo-Carboniferous Badhura Bap Fossiliferous ferruginous sandstone Boulder bed ---------------------------------------------------- Unconformity ----------------------------------------------------------------- Cambrian (?) Marwar Nagaur Tunklian Nagaur Sandstone Sandstone Hanseran/ Evaporite/ Bilara Pondlo Gotan Dhanapa Dolomite Limestone Dolomite Jodhpur Girbhakar Sandstone Sonia Sandstone Pokharan Boulder bed Upper Bhander Dholpur Balwan Maihar Sirbu Bundi Hill Samria Lakheri Ganurgarh Shale Limestone Sandstone Shale Sandstone Shale Limestone Shale Rewa Taragarh Fort Jhiri Indergarh Panna Sandstone Shale Sandstone Shale Kaimur Kaimur/Chittaurgarh Conglomerate, sandstone Vindhyan Lower Suket Shale Khorip Nimbahera Limestone Nimbahera Bari Jiran Shale Sandstone Lasrawan Binota Kalmia Shale Sandstone Sand Palri Sawa Bhagwanpura Shale Sandstone Limestone Satola Khardeola Khairmalia Sandstone Andesite, pyroclastic and tuff Proterozoic Malani Igneous Suite, Siwana, Jalore and Malani Granites Erinpura, Sewariya, Balda Granites Albitites and Lamprophyres Newaniya Carbonatite, Kishangarh Syenite Sendra Granite Delhi (South) Sirohi/Ras/ Punagarh Mica schist, marble, basic volcanics Bhim Dungarkhera Todgarh Pelitic and semi-pelitic schist Calc-gneiss and marble Rajgarh Pelitic schist with quartzite Sendra Metavolcanics, impure marble, pelitic schist Barotiya Barotiya Nanana Barr Metavolcanics, impure marble Marble Mica schist, conglomerate Gogunda Quartzite Ajitgarh, Dadikar, Bairat, Harsora, Saladipura, Udaipur and Seoli Granite Arauli-Mandhan Bharkol Quartzite, staurolite schist, phyllite Quartzite with carbon phyllite Ajabgarh Thana Gazi Carbon phyllite and schist Delhi (North) Kankwari Rajgarh Schist and quartzite Sita Conglomerate and quartzite ---------------------------------------------------- Unconformity ----------------------------------------------------------------- Weir-Sariska Kushalgarh Ferruginous quartzite Limestone and phyllite Damdama Conglomerate, quartzite Alwar Bayana Badalgarh Jogipura Quartzite, schist Feldspathic quartzite and shale Quartzite Raialo (?=Delwara Group) Tehla/Jahaj-Govindpura Nithar/Serrate Dogeta Metavolcanics with quartzite, schist Conglomerate, quartzite Siliceous dolomite marble, phyllite ---------------------------------------------------- Unconformity ----------------------------------------------------------------- Darwal/Anjana Granite Jharol Rakhabdev Jharol Iswal Serpentinite, talc-tremolite schist Phyllite with thin quartzite bands Conglomerate, quartzite ---------------------------------------------------- Unconformity ----------------------------------------------------------------- Leucogranite Intrusion Aravalli Debari Zawar/Jahazpura, Sawar Rampura-Agucha, Pur-Banera Rajpura-Dariba Udaipur Umra Jhamarkotra Debari/Jaisamand Pb-Zn bearing dolomite Greywacke, phyllite Carbon phyllite Phosphorite-bearing dolomite Conglomerate, quartzite, arkose ---------------------------------------------------- Unconformity ----------------------------------------------------------------- Pink granite intrusion Delwara Negaria Basic volcanics, quartzite, dolomite ---------------------------------------------------- Unconformity ----------------------------------------------------------------- Berach / Jahazpura Granite (2.5 Ga) Hindoli Phyllite and greywacke with metavolcanics Untala/Gingala and Annasagar Granites (?) (2.8 Ga) Archaean Ran Igneous Complex Norite dykes, augen gneiss and tonalite/ granodiorite gneiss Mangalwar Complex Tanwan Sawadri Amphibolites, greywacke, quartzite, marble Amphibolite, carbon phyllite Bhilwara/ Banded Gneissic Complex Sandmata Complex Two-pyroxene granulite, leptinite, charnockite-enderbite, pelitic granulite Useful References Gupta, B. C. (1934). The Geology of Central Mewar, Mem. Geol. Surv. Ind., v. 65(2) Heron, A. M. (1953). The Geology of Central Rajputana, Mem. Geol. Surv. Ind., v. 79, pp. 1-389 Gupta, S. N., Arora, Y. K., Mathur, R. K., Iqballuddin, Parsad, B., Sahai, T. N. and Sharma, S. B. The Precambrian Geology of the Aravalli Region, Southern Rajasthan and NE Gujarat. Mem. Geol. Surv. Ind., v. 123, pp. 1-262. Its Lithstatigraphic Maps were published in 1981.
Posted on: Wed, 19 Mar 2014 12:54:19 +0000
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