STRUCTURE AND TECTONICS OF THE MANGANESE ORE BELT OF MADHYA PRADESH AND ADJOINING PARTS OF BOMBAY* BY N. A. VEMBAN (Geological Survey of India) CONTENTS PAGE INTRODUCTION ...... .. 125 GEOLOGICAL STRUCTURE : General Statement .. 126 FOLDS AND THRUST SHEETS : 1. Southern Belt of Isoclinal Folding W Q .. 127 2. Northern Belt of Recumbent Folds, etc. 8 • • ° .. 127 3. Central Belt of Gneissic Formations • ° .. 128 4. Regions of Cross-folding and Refolding • ° • ° •. 129 FAULTS AND THRUSTS : I. Strike Faults and Thrusts 131 2. Transverse Faults .. 132 AGE RELATIONS OF FAULTS AND FOLDS 132 FOLIATION AND BANDING .. 132 LINEATIONS ...... 133 CONCLUDING REMARKS .. 133 REFERENCES ...... 134 INTRODUCTION ThE manganese ore belt of Madhya Pradesh and adjoining parts of Bombay lbrms a general ENE trending arcuate belt, 130 miles long and 20 miles wide, extending from Chindwara District in the north-west, through Nagpur and northern Bhandara Districts in the middle to Balaghat District in the * Paper presented to the Symposium on Tectonics, December 1959. The publication of this paper together with the maps has been authorised by the Director, Geological Survey of India. 125 126 N.A. VEMSAN north-east. It is underlain principally by a succession of intensely deformed and metamorphosed prc-Cambrian sediments included by L. L. Fcrmor in the Sausar Series. Amphibolitcs, some para-gncisscs, migmatitcs, ortho- gneisses, granite plutons, pcgmatitcs and vein quartz)all prcsumably prc- Cambrian in age have either bccn mixed up or cmplaccd later in the Sausar Series. Along the southern margin of the belt hypcrsthcne-bcaring char- nockitic rocks occur apparently with intrusive relationship to them. The thin and discontinuous Lamcta formation of late Cretaceous age, and thc succeeding Deccan Trap basalt of late Cretaceous-Eocene age overlie the Sausar Series with profound unconformity, and arc the only other important rock units of this area. The structural trend of these pre-Cambrian rocks conforms to that of the Satpura range in the north, and the detailed mapping of over 2,000 sq. miles in this belt has yielded data on the structural and tectonic history of the Satpura orogeny that deformed the rocks of this area. A synthesis of the geology of various parts of the manganese ore belt indicates that the Satpura orogenic cycle was much more complicated than what has bccn realizcd so far. The 'nappc' structure of Dcolapar, worked out by W. D. West (1936), has bccn confirmed and extended into the adjoining Balaghat District, and additional nappcs have bccn recognized and mapped along the northern part of the belt. At least two definite periods of deformation arc postulated for the present structural disposition of the rocks. 'Cross- folding' of the earlier folds indicating a late stage deformation has bccn distinguished in the Sausar Series. The present paper presents briefly the complicated structural and tectonic history that affected this area during the Satpura cycle. The results presented hcrc are the outcome of three or four seasons ficldwork in the manganese ore belt by the writer and some of his colleagues --S. Narayanaswami, S. C. Chakravarty, K. D. Shukla, M. R. Subramaniam, V. Venkatcsh and G. V. Rao under the general guidance of John A. Straczek. GEOLOGICAL STRUCTURE General statement.--The rocks of the Sausar Series are intensely folded in isoclinal and recumbent folds along E-W axes which generally plunge eastward or westward at low to moderate angles. The folds are generally overturned northward with their axial planes dipping steeply southward at 60°-80 ° along the southern part of the belt, and flattening to moderate southward dips of 30o-50 ° along the central parts where the isoclinal folds are recumbent. In parts of Balaghat District at the north-eastern end of the belt, the recumbent folds are very flat and are overturned to the south Manganese Ore Belt of M.P, and Adjoining Parts of Bombay 127 with low northward dips of 10°-30 ° . Along the northern margin of the map area, the recumbent folds are found to be thrust over older rocks in the_ form of thrust sheets and nappes. The belt is traversed by some major steeply dipping thrust faults trending parallel to the strike, and by minor ,transverse faults, The isoclinal folds of the southern belt and the recumbent folds and thrust sheets of the northern belt have an en echelon disposition as the folds themselves show successive northward shifts when followed to the east and north-east. A similar reverse pattern of northward shifts is also apparent in Chindwara District towards the west. The structure of the belt is further complicated by the refolding or cross-folding of the earlier fold axes of the isoclinal and recumbent folds and thrust sheets. The axes of these cross-folds plunge at low to moderate angles to the west and south- west, Granite plutons and ortho-gneisses are generally found emplaced along the axes of these late cross-folds. FOLDS AND THRUST SHEETS The structure of the belt may be described under the following four divisions: 1. Southern belt of overturned, isoclinal folds. 2. Northern belt of recumbent folds and thrust blocks or nappes. 3. Central belt of gneissic formations of the nature of crystalline axis with narrow and linear outcrops of infolded schists. 4. Regions of refolding or cross-folding and associated granite plutons. (1) Southern belt of isoclinalfolding.--This belt, characterized by steeply dipping, overturned, isoclinal folds extends along the southern portion of the manganese ore belt from Kelod-Salai-Parseoni in north-western Nagpur District, through Mansar-Goguldoho in northern and north-eastern Nagpur District_ and Dongari Buzurg-Chikhla-Bhajiadand-Waraseoni region innor- thern Bhandara and Balaghat Districts to Bharweli-Ukwa region in easteln Balaghat District. The axes of these folds trend WNW-ESE to east- west in Nagpur District, and gradually veer to ENE and NE in Bhandara and Balaghat Districts. They plunge at low angles of 20°-30 ° eastward, though westerly plunges are also noticeable at intervals due to the cross- folding. (2) Northern belt of recumbent folds, thrust blocks and nappes.--This belt extends from Sapghota-Ambajhiri in north-western Nagpur through Deolapar region (W. D. West, 1936) in northern Nagpur District to the Sonawani and the Dhansua R.F. in northern and north-eastern Balaghat B2 128 N.A. V~ District. The belt is characterized by at least four thrust blocks or nappes which have not yet been connected together along their strike. These are (1) Sapghota thrust block, (2) Ambajhiri thrust block, (3) Deolapar nappe and (4) Sonawani thrust block. They consist of younger rocks of the Sausars (Chorbaoli to Bichua stages) which have been thrust over the Tirodi biotite-gneiss, and form steep to moderate dipping overturned, iso- elinal folds and fiat-dipping recumbent folds whose axes are conformable to the regional fold axes. In the Sapghota-Ambajhiri and Deolapar thrusts, the thrust plates reveal steep to moderate southerly dips along their southern margins and low to flat dips along their northern margins. The Sonawani thrust block shows low to moderate dips to the north, but the northern limit of the thrust has not yet been mapped. The folds within the thrust blocks or nappes are generally doubly plunging synclinal structure which are themselves folded, recumbent folds; the succession of rocks in the case of Ambajhiri and Deolapar nappes is reversed, but is normal in the case of Sonawani and adjacent thrust blocks. 3. Central belt of gneissic formations with narrow infolded schgsts.-- This belt consisting of extensive stretches of Tirodi biotite-gneiss arid charac- terized by numerous narrow, linear, infolded runs of schists occupies the region between the two structural divisions described above and appears to represent the central crystalline axis of the tectonic framework. An extensive area of this belt is exposed in Balaghat District between the Bawan- thari River in the south-west, Tangla and Karwahi RF on the west and Kurai and Sonawani RF in the north and extends through the alluvial plains of Katangi, Waraseoni and Balaghat up to the Dhansua RF and other hilI tracks in north-eastern Balaghat District. The individual out- crops are mostly less than 200 ft. in width and some are four to five miles in length, and occur within the biotite gnesis with a general ENE-WSW to NE-SW regional trend. They are considered to be remnants of steep to flat dipping infolded, recumbent, refolded folds, consisting chiefly of Mansar muscovite schist and'the associated manganese ore horizon and Sitasongi quartz-muscovite-schist. The Tirodi-Sukli-Garra area is under- lain by the largest number of these infolded runs of Mansar schists and manganese ore bodies in an apparently inverted sequence. There are three other detached areas that form part of this belt: (1) An east-west area in the Warpani R.F. in north-western Nagpur District, (2) An east-west area extending westward from Mangarli to west of Paunia in Northern Nagpur District, and (3) A small area extending westward from Aoleghat in north-eastern Nagpur District. The area to the east of Mangarli is characterized by numerous infolded Mansar schist outcrops. Manganese Ore Belt of M.P. and Adjoining Parts of Bombay i29 4. Regions of Cross-folding and refolding.--Evidences are found through- out the manganese ore belt for a late stage deformation which has affected the earlier folds to varying degrees. These later folds which may be des- eribed as cross-folds are classified into the following groups: (1) These cross-folds have their axes at about 45 ° to the axes of earlier folds, and plunge at moderate angles in the opposite direction. They are found in force in the central part of the belt from Ramtek in Nagpur District to Pusada in northern Bhandara and Tirodi area in Balaghat District.