Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

V. Srinivasan ¹

Affiliations
1 Tamil Nadu Geology Branch, Madras, IN

Abstract

No Abstract.

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V. Srinivasan ¹

Affiliations
1 Tamil Nadu Geology Branch, Madras, IN

Abstract

No Abstract.

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V. Srinivasan ¹

Affiliations
1 Department of Geology, Tamil Nadu State Geology Branch, Madras 600032, IN

Abstract

The carbonatite complex (pyroxenite-syenite-carbonatite) of Hogenakal area of Tamil Nadu and adjoining parts of Karnataka were emplaced along NNE - ssw fracture zones within the Precambrian gneissic complex. The carbonatite is Sovite in composition and its characteristics are (1) occurrence as fracture filling dykes, (2) presence of agglomeratic and flow structures and (3) absence of dolomitic carbonatite or beforsite, true fenite and major rare earth mineralization. The carbonatite of Hogenakal belongs to the high temperature and deep level intrusion of sub-volcanic origin. It has certain similarity with that of Strangways Range area of Central Australia and differs in certain respects from other carbonatite occurrences of Tamil Nadu.

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V. Srinivasan ¹, D. K. Saha ², D. C. Naskar ², P. M. Bhattacharya ², J. R. Kayal ²

Affiliations
1 Geological Survey of India, Op TNPK, Chennai, IN
2 Geological Survey of India, Kolkata, IN

Abstract

No Abstract.

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V. Srinivasan ¹

Affiliations
1 Geological Survey of India, Op TNPK, Guindy, Chennai - 600 032, IN

Abstract

Using aerial photographs followed by extensive field checks, a Photo-Geological map for the entire 'Belt of Schuppen' of northeast India has been prepared. The 20 to 30 km wide exposed part of 'Belt of Schuppen' comprises two major thrusts (Haflong-Naga thrust, Disang thrust) and three minor Sub-Thrusts. The Haflong-Naga thrust (frontal thrust of 'Belt of Schuppen') extends NE-SW over a length of 410 km along the break in slope separating the alluvial plain in the west from the ridges of Neogene sedimentary rocks in the east. In the SW at Miyungkhor in the left bank of Jatinga River, it is terminated by Dauki fault. In the NE near Digboi, it is concealed below the alluvium. The Disang thrust (rear thrust of 'Belt of Schuppen') extends NE-SW over a length of 480 km and it defines the eastern margin of Neogene basin. In the SW near Wadrengdisa, it branches out from Haflong-Naga thrust and in the NE at Bulbulia in the right bank of Noa Dihing River, it is terminated by Mishmi thrust, which extends into Myanmar as 'Sagaing fault'. The major thrusts and Sub-Thrusts of belt 'Belt of Schuppen' dtp generally towards SE. Thus the 'Belt of Schuppen' extends between Dauki fault in the SW and Mishmi thrust in the NE over a length of about 500 km. When the SW end of 'Belt of Schuppen' moved upwards and towards east along the Dauki fault, the NE end moved downwards and towards west along the Mishmi thrust, causing it's 'S' shaped bending.

The southern part of 'Belt of Schuppen' extends along the sheared western limb of southerly plunging Kohima synform and it is seismically active. The northern truncated end at Mishmi trust is also seismically active. There is a pronounced seismic gap in the middle part of 'Belt of Schuppen'. The epicenter plots of major earthquakes of Richter magnitude ≥7 in this region reveal that the rupturing at depth which caused these earthquakes are aligned along distinct NE-SW trending parallel zones, perpendicular to the regional compression in NW-SE direction.

Keywords

'Belt of Schuppen', Haflong-Naga Thrust, Disang Thrust, Dauki Fault, Mishmi Thrust, Kohima Synform, Sagaing Fault, Seismic Gap, Northeastern Indla.

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V. Srinivasan ¹, Amit Sahay ², Deepak C. Srivastava ²

Affiliations
1 Geological Survey of India. Op: TNPK, Chennai, IN
2 Earth Sciences, IIT Roorkee, IN

Abstract

No Abstract.

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V. Srinivasan ¹

Affiliations
1 Geological Survey of India, Tripura-Mizoram Division, B.K. Road, Banamalipur, Agartala - 799 001, IN

Abstract

Dauki fault extends roughly E-W along the southern margin of Meghalaya plateau. Using remote sensing techniques followed by critical field checks, the author traced Dauki fault from Dauki towards east upto Leike over a length of 170 km. This fault is a single fault dipping towards south (normal fault). In the footwall block close to the fault trace, the older rocks such as Disang shale (Eocene) and the massive Thick-Bedded sandstories (Barail Group of Eocene- Oligocene) are exposed. In the hanging wall block close to the fault trace, the alternating sandstone shale sequence ('ribbed sequence', a regional marker) belonging to the upper part of Palaeogene is exposed. In the eastern part of hanging wall block, the regional marker abuts against the folded sedimentaries of Surma basin of Neogene along a tectonic contact, which is also co-folded. The N-S trending axial surfaces of folds in Surma basin bend towards NE to ENE while approaching the trace of Dauki fault, indicating dextral strike slip movement along Dauki fault.This inference is further supported by the outcrop pattern of Haflong thrust in the footwall block with the concavity facing west. This thrust belonging to the 'Belt of Schuppen' abruptly terminates against the younger Dauki fault.

In the western part of hanging wall block of Dauki fault, the same marker horizon abuts against the non-folded, undeformed, near horizontal sedimentaries of Sylhet trough of Neogene. It is proposed that the Sylhet sediments were deposited in a pull-apart basin in the releasing bend of Dauki fault during the dextral strike slip movement. Thus the net slip for Dauki fault involves a vertical component and a dextral strike slip component (oblique-slip fault). sonapur 'landslide zone is located very dose to this fault and the recurring landslide indicates that this fault is still active. The densely populated areas, such as Dacca and Silchar, are located on the loose alluvial sediments not far away from the active Dauki fault.

Keywords

Dauki Fault, Haflong Thrust, Surma Basin, Sylhet Trough, Meghalaya Plateau.

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V. Srinivasan ¹

Affiliations
1 Geological Survey of India, Tripura-Mizoram Division, B.K. Road, Banamalipur, Agartala - 799 001, IN

Abstract

The Siwalik belt in Arunachal Pradesh, which extends from Bhutan border in the west to Pasighat in the east over a distance of about 350 km, was studied in detail using recent aerial photos and IRS-1C LISS 3 digital data products for understanding its stratigraphy and structure. Critical field checks were subsequently carried out.

The Siwalik belt, which is roughly 20 km wide, is exposed between Brahmaputra alluvium in the south and pre-Tertiary rocks in the north. Main Boundary Fault (MBF) defines the northern limit of Siwalik sedimentaries.

Two major en echelon E-W to ENE-WSW trending, northerly dipping faults (Fault-1, 2) have divided the Siwalik belt into three tectonic blocks (Tectonic Block-1, 2 and 3). Fault-1 branches out from MBF in the west and extends through Siwalik belt to Subansiri River in the middle part of the study area. Here Fault-2 in the north, branches out from MBF and extends through Siwalik belt to Nari in the eastern part.

The poorly cemented pebble/cobble beds and soft, immature sandstones/sand rocks of Tectonic Block-1 (south of Fault-1) are considered to represent the youngest part of Siwalik Group and they were folded to NE plunging (5° to 10°) open, mega anticline. The well-bedded sandstones of Tectonic BJock-2 (north of Fault-1 or south of Fault-2) and thickly bedded sandstones with huge pebble bed horizons of Tectonic Block-3 (north of Fault-2) reveal gentle to moderate (10° to 30°) homoclinal dip towards north to NW.

Two contradicting models are proposed to explain the tectonic setup of Siwalik belt. In the first model, MBF, which is dipping at -60° due north at the surface level, is considered to become gentle at depth and towards north. Fault-1 and Fault-2 are considered as diverging splay thrusts from the main thrust, MBF. In the second model, it is proposed that MBF, Fault-1 and Fault-2 extend downwards as near-vertical faults, even though they reveal moderate northerly dip at the surface level. This second model, which involves reactivation of basement weaker zones and differential vertical movement in a non-compressive environment, explains in a convincing way the overall tectonic setup of Siwalik belt in Arunachal Pradesh.

Keywords

Remote Sensing, Stratigraphy, Structure, Siwaliks, Arunachal Himalaya.

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V. Raiverman ¹, V. Srinivasan ²

Affiliations
1 708, Maitri Apartments, 255, NSC Bose Road, Kolkata - 700 047, IN
2 Geological Survey of India, Tripura-Mizorarn Division, B.K. Road, Banamalipuram, Agartala-790 001, IN

Abstract

No Abstract.

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V. Srinivasan ¹

Affiliations
1 Geological Survey of India, Tripura-Mizoram Division, B.K. Road, Banamalipur, Agartala - 790 001, IN

Abstract

Based on digital image processing of Landsat TM digital data covering Shillong plateau, it is proposed that the landmass in the east and west of Shillong plateau could have moved upwards with respect to the middle part. This differential uplift within the plateau could be due to vertical movement along NNE-SS W trending deep-seated faults and granite batholith emplacement.

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V. Srinivasan ¹

Affiliations
1 Geological Survey of India (NER), Kumud Villa Complex, Shillong- 793 003, IN

Abstract

Major normal faults in Raigad and Thane Districts in the West Coast area of Maharashtra trend roughly N-S, with their eastern blocks upthrown and western blocks downthrown. The amounts of throw increase systematically from south to north for two normal faults (Mangaon Fault, Mahim Fault). With respect to the Mahim Fault, which is located in the over-steepened limb of Panvel Monoclinal Flexure, the blocks were drag folded on regional scale during their respective vertical movement along the fault surface. The gently southerly plunging (1 in 90) anticlinal drag flexure in eastern upthrown block was deeply dissected and eroded (especially in up the plunge direction), thus exposing the oldest lava flows. On the contrary, the youngest members of Deccan Trap (like volcanic agglomerates, acidic and intermediate extrusives, intertrappean rocks, spilites etc) could be preserved from erosion in the synclinal drag flexure of western downthrown block of Mahim Fault.

There are few more normal faults (like Matheran Fault, Ulhas River Fault) trending roughly N-S between Mahim Fault and Western Ghat scarp. The eastern block of each of these faults is distinctly upthrown with respect to the western block, thereby developing a series of step-faults between the coastline and the Western Ghat scarp. Mumbai (Bombay), with a population of more than 12 million, is located on the western downthrown block of the western most normal fault in this step-faulting configuration.

Keywords

Raigad, Thane, West Coast, Maharashtra, Post-Deccan Trap Normal Faults, Step Faults.

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R. K. Bajpai ¹, V. Srinivasan ²

Affiliations
1 Repository Projects Section, Back End Technology and Development Division, Bhabha Atomic Research Centre, Mumbai - 400 084, IN
2 Geological Survey of India, Shillong, IN

Abstract

No Abstract.

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