Abstract The Munsiari thrust (MT) sheet is a dominant thrust sheet in the Himalaya and forms the ... more Abstract The Munsiari thrust (MT) sheet is a dominant thrust sheet in the Himalaya and forms the frontal ridge in the Gorubathan recess of the Darjiling Himalaya. The geometry of the MT sheet in the recess was poorly constrained thereby inhibiting the understanding of how the geometry and kinematics of the sheet varied from the Nepal to the Bhutan Himalaya. We present new structural data and infer the deformation mechanisms and the geometry of the MT sheet in the Gorubathan recess in the Darjiling Himalaya to fill this knowledge gap. The MT sheet was dominated by large-scale, overturned antiforms and synforms. The entire MT sheet was later folded to a north-easterly plunging synformal fold with NE-SW axial trend due to the effect of a Himalayan cross fault in the region named the Gish Transverse fault. A new brittle, out-of-sequence and neotectonically active, Phaparkheti thrust, was recognized in the MT sheet. Deformation microstructures indicate that the temperature of deformation in the MT fault zone and the sheet was ~500 °C to 700 °C and ~400 °C, respectively. Our approach of first mapping major and minor structures and then integrating these studies with deformation microstructure and tectonic geomorphology data resulted in an improved understanding of the structural characteristics of the MT sheet in the Darjiling Himalaya. Our study also suggests that there is considerable variation in the geometry and kinematics of frontal thrust sheets along the Himalayan arc that must be studied systematically in the context of Himalayan salients and recesses.
The long-conceived idea of the glacial origin of Blaini diamictite of Lesser Himalayan Neoprotero... more The long-conceived idea of the glacial origin of Blaini diamictite of Lesser Himalayan Neoproterozoic succession reached its maxima when the diamictites and capping pink limestone were attributed to the Neoproterozoic Snowball Earth event and its aftermath, respectively. Occurrences of diamictite-limestone association in two different levels have also been correlated with the Sturtian and Marinoan glaciations. Critical review, however, reveals that the interpretations of the glacial origin of diamictites are not well founded. The diamictite-limestone association, which occurs at the lower part of a thick, light brown shale unit and laterally grades into light brown shale, primarily indicates episodic surge events in an otherwise tranquil condition favorable for hemipelagic sedimentation. The lithology, bed geometry, internal organization, and disposition of the diamictite bodies suggest deposition of debris flow fan lobes along fault scarps in a rift setting. Emplacement of subaqueo...
The Proterozoic Cuddapah Basin of south India is one of the most important Purana basins of Penin... more The Proterozoic Cuddapah Basin of south India is one of the most important Purana basins of Peninsular India. It hosts the Cuddapah Supergroup and the Kurnool Group of rocks. The structure of the Cuddapah Basin reveals that it forms the frontal part of a larger fold–thrust belt, named the Cuddapah fold–thrust belt (CFTB). The CFTB formed in response to the amalgamation of the Prince Charles Mountains–Rayner Complex of Antarctica with the Krishna province of India during the formation of the Rodinia Supercontinent. The CFTB, bounded by the Nellore–Khammam schist belt and Eastern Ghats terrane in the east and Peninsular Gneissic complex of the Dharwar Craton to the west, includes two frontal thrusts and foreland of an orogen. The frontal Nallamalai thrust structurally separates the basin into two blocks – the eastern Nallamalai fold belt and the western foreland. A model of evolution of the CFTB has been proposed. The CFTB, forming the front-most segment of a larger orogen associated ...
ABSTRACT Neoproterozoic orogenesis in East Antarctica and India led to the amalgamation of northe... more ABSTRACT Neoproterozoic orogenesis in East Antarctica and India led to the amalgamation of northern Prince Charles Mountains-Rayner complex of Antarctica with the Krishna Province of India along the present eastern coast of India with the development of ~990–900 Ma old fold-thrust belt. The frontal part of the fold-thrust belt [henceforth called the Cuddapah fold-thrust belt (CFTB)], recognized in the intercratonic, Palaeoproterozoic–Neoproterozoic Cuddapah Basin, includes two frontal thrust sheets carried by the eastern Velikonda and the western Nallamalai thrusts, along with a part of the undeformed foreland, constituting frontal part of a larger fold-thrust belt now fragmented and separated in different continents of Gondwanaland. Therefore, the intercratonic deformation now preserved in the Palaeoproterozoic–Neoproterozoic Cuddapah Basin is related to the collision of the Indian shield to the Antarctic block during the amalgamation of the Rodinia Supercontinent. CFTB is dominated by quasi-plastic deformational structures, representing exhumed deeper level fault-propagation folding related to the Velikonda thrust, while the Nallamalai thrust represents the forelandward thrust of the CFTB dominated by elastico-frictional deformation structures.
... 6ac). It dips steeply with a mean orientation of 317°/83°NE (Fig. ... Axial surfaces are occ... more ... 6ac). It dips steeply with a mean orientation of 317°/83°NE (Fig. ... Axial surfaces are occasionally curved; they dip steeply and are usually parallel to the general attitude of bedding in BFQ. The mean orientation of F 1 axial planes is 320°/85°NE (Fig. ...
ABSTRACT Fault zones with a complex history may show reactivation in successive faulting events. ... more ABSTRACT Fault zones with a complex history may show reactivation in successive faulting events. Successive generations of grain-scale microcracks in reactivated fault zone produce multiphase cataclastic rocks with characteristic microcracks. The optical and cathodoluminescence microscopic study can be fruitfully utilized to analyze the complex deformation history of brittle fault zone rocks developed in response to successive brittle deformation. Within the reactivated Cretaceous Sainthia-Brahmani Fault, cutting the Precambrian Chhotonagpur gneiss and Jurassic sandstone along the western margin of Bengal Basin, three generations of cataclasis can be recognized. The first generation (Ct1) cataclastic rock is infrequently preserved as clasts within the second phase (Ct2) cataclastic rocks. The last phase cataclasis (Ct3) affected both Ct1 and Ct2 cataclastic rocks in a discrete manner producing inhomogeneous network of thin sintered micro-zones of gouge. The cataclastic rocks are formed by progressive cataclasis of granitoid rocks with several pulses of fluid-induced brittle deformation during a history of frictional flow. The repeated cataclasis attest to a prolonged history of repeated failure and reactivation of fault movement in elastico-frictional regime operated in pulses with repeated embrittlement and mechanical failuret. This observation led to the idea of repeated reactivation of the fault, related to the extensional tectonics during early Cretaceous period linked to India's passage over the Kerguelen and Crozet Hot-Spots presently located in the Indian Ocean. Fracturing and comminution are dominant deformation mechanisms in the formation of cataclastic rocks, and subordinate but evident dissolution and recrystallization of quartz, and mild plastic deformation of quartz, feldspar and biotite are also seen. Dissolution and recrystallization processes during cataclasis, and absence of pseudotachylyte in the fault rocks provides an example of aseismic shear displacement within the brittle shear zone.
Abstract Shear zones are areas of intense deformation in localized zones which can be used as nat... more Abstract Shear zones are areas of intense deformation in localized zones which can be used as natural laboratories for studying deformation characteristics. Metre-to micro-scale structures that develop in response to a progressive simple shear in a shear zone are characterized by a protracted history of deformation and are immensely useful in delineating the history of progressive deformation. To decipher these localized zones of deformation and to establish the continuous non-coaxial character of deformation, detail ...
Structural investigations in the Precambrian Singhbhum Shear Zone of eastern India document an in... more Structural investigations in the Precambrian Singhbhum Shear Zone of eastern India document an intimate relationship between micro-to meso-scale structures and the deformation history. Shear zone rocks are characterized by composite foliation, a well-developed stretching lineation, folds, shear planes, and quartz veins. These structures reflect thrusting of the Proterozoic north Singhbhum hanging wall block over the Archaean south Singhbhum footwall block. Microstructural analysis of multiple foliation and mylonitic ...
Abstract: The early Archaean oval-shaped, high-grade Gurgunta schist belt in the northern part of... more Abstract: The early Archaean oval-shaped, high-grade Gurgunta schist belt in the northern part of the eastern Dharwar craton of south India constitutes a part of the intensely deformed migmatized basement of the low-grade volcano-sedimentary sequence of the Dharwar ...
A sequence of quartzite, banded phyllite and slate in the southern part of the Nallamalai fold be... more A sequence of quartzite, banded phyllite and slate in the southern part of the Nallamalai fold belt shows a series of macroscopic gently plunging folds (DI) with NW-SE striking axial plane and a pervasively developed axial planar slaty cleavage. A weak later deformation has produced sporadic gentle folds (D2) with axial planes at high angle to the D1 fold axial planes. The rocks along the eastern contact of the belt are mylonitized and the intensity of deformation gradually dies away towards west. A zone of tectonic dislocation is envisaged between the basement granite gneiss towards the east and the supracrustal Nallamalai rocks.
The emplacement of thrust sheets in a fold and thrust belt is an integral part in the evolution o... more The emplacement of thrust sheets in a fold and thrust belt is an integral part in the evolution of orogenic belts. The signatures of deformation present in a thrust sheet is often very useful to elucidate the history of deformation and also to understand the mechanisms of deformation that operates in stages during the emplacement of thrust sheets. The Himalayan orogenic belt has experienced multiple stages of thrusting and duplex formation. Ramgarh thrust sheet (RTS), one of the major thrust sheets bounded by the Main Central Thrust to ...
Banded ferruginous quartzite (BFQ) in the Sandur Schist Belt belongs to the Archaean Dharwar Supe... more Banded ferruginous quartzite (BFQ) in the Sandur Schist Belt belongs to the Archaean Dharwar Supergroup of Karnataka and contains primary depositional and diagenetic features. These include banding of different types, ripple marks. syneresis cracks, scour-and-fill structures, globular and nodular structures and penecontemporaneous faults. The significance of these structures in terms of the environment of deposition of BFQ has been considered. The BFQ was deposited as chemical precipitates and passed through a hydroplastic stage of lithification. Shallow water environment of dcposition in a more or less quiet condition with intermittent local disturbances has been envisaged.
Abstract The Munsiari thrust (MT) sheet is a dominant thrust sheet in the Himalaya and forms the ... more Abstract The Munsiari thrust (MT) sheet is a dominant thrust sheet in the Himalaya and forms the frontal ridge in the Gorubathan recess of the Darjiling Himalaya. The geometry of the MT sheet in the recess was poorly constrained thereby inhibiting the understanding of how the geometry and kinematics of the sheet varied from the Nepal to the Bhutan Himalaya. We present new structural data and infer the deformation mechanisms and the geometry of the MT sheet in the Gorubathan recess in the Darjiling Himalaya to fill this knowledge gap. The MT sheet was dominated by large-scale, overturned antiforms and synforms. The entire MT sheet was later folded to a north-easterly plunging synformal fold with NE-SW axial trend due to the effect of a Himalayan cross fault in the region named the Gish Transverse fault. A new brittle, out-of-sequence and neotectonically active, Phaparkheti thrust, was recognized in the MT sheet. Deformation microstructures indicate that the temperature of deformation in the MT fault zone and the sheet was ~500 °C to 700 °C and ~400 °C, respectively. Our approach of first mapping major and minor structures and then integrating these studies with deformation microstructure and tectonic geomorphology data resulted in an improved understanding of the structural characteristics of the MT sheet in the Darjiling Himalaya. Our study also suggests that there is considerable variation in the geometry and kinematics of frontal thrust sheets along the Himalayan arc that must be studied systematically in the context of Himalayan salients and recesses.
The long-conceived idea of the glacial origin of Blaini diamictite of Lesser Himalayan Neoprotero... more The long-conceived idea of the glacial origin of Blaini diamictite of Lesser Himalayan Neoproterozoic succession reached its maxima when the diamictites and capping pink limestone were attributed to the Neoproterozoic Snowball Earth event and its aftermath, respectively. Occurrences of diamictite-limestone association in two different levels have also been correlated with the Sturtian and Marinoan glaciations. Critical review, however, reveals that the interpretations of the glacial origin of diamictites are not well founded. The diamictite-limestone association, which occurs at the lower part of a thick, light brown shale unit and laterally grades into light brown shale, primarily indicates episodic surge events in an otherwise tranquil condition favorable for hemipelagic sedimentation. The lithology, bed geometry, internal organization, and disposition of the diamictite bodies suggest deposition of debris flow fan lobes along fault scarps in a rift setting. Emplacement of subaqueo...
The Proterozoic Cuddapah Basin of south India is one of the most important Purana basins of Penin... more The Proterozoic Cuddapah Basin of south India is one of the most important Purana basins of Peninsular India. It hosts the Cuddapah Supergroup and the Kurnool Group of rocks. The structure of the Cuddapah Basin reveals that it forms the frontal part of a larger fold–thrust belt, named the Cuddapah fold–thrust belt (CFTB). The CFTB formed in response to the amalgamation of the Prince Charles Mountains–Rayner Complex of Antarctica with the Krishna province of India during the formation of the Rodinia Supercontinent. The CFTB, bounded by the Nellore–Khammam schist belt and Eastern Ghats terrane in the east and Peninsular Gneissic complex of the Dharwar Craton to the west, includes two frontal thrusts and foreland of an orogen. The frontal Nallamalai thrust structurally separates the basin into two blocks – the eastern Nallamalai fold belt and the western foreland. A model of evolution of the CFTB has been proposed. The CFTB, forming the front-most segment of a larger orogen associated ...
ABSTRACT Neoproterozoic orogenesis in East Antarctica and India led to the amalgamation of northe... more ABSTRACT Neoproterozoic orogenesis in East Antarctica and India led to the amalgamation of northern Prince Charles Mountains-Rayner complex of Antarctica with the Krishna Province of India along the present eastern coast of India with the development of ~990–900 Ma old fold-thrust belt. The frontal part of the fold-thrust belt [henceforth called the Cuddapah fold-thrust belt (CFTB)], recognized in the intercratonic, Palaeoproterozoic–Neoproterozoic Cuddapah Basin, includes two frontal thrust sheets carried by the eastern Velikonda and the western Nallamalai thrusts, along with a part of the undeformed foreland, constituting frontal part of a larger fold-thrust belt now fragmented and separated in different continents of Gondwanaland. Therefore, the intercratonic deformation now preserved in the Palaeoproterozoic–Neoproterozoic Cuddapah Basin is related to the collision of the Indian shield to the Antarctic block during the amalgamation of the Rodinia Supercontinent. CFTB is dominated by quasi-plastic deformational structures, representing exhumed deeper level fault-propagation folding related to the Velikonda thrust, while the Nallamalai thrust represents the forelandward thrust of the CFTB dominated by elastico-frictional deformation structures.
... 6ac). It dips steeply with a mean orientation of 317°/83°NE (Fig. ... Axial surfaces are occ... more ... 6ac). It dips steeply with a mean orientation of 317°/83°NE (Fig. ... Axial surfaces are occasionally curved; they dip steeply and are usually parallel to the general attitude of bedding in BFQ. The mean orientation of F 1 axial planes is 320°/85°NE (Fig. ...
ABSTRACT Fault zones with a complex history may show reactivation in successive faulting events. ... more ABSTRACT Fault zones with a complex history may show reactivation in successive faulting events. Successive generations of grain-scale microcracks in reactivated fault zone produce multiphase cataclastic rocks with characteristic microcracks. The optical and cathodoluminescence microscopic study can be fruitfully utilized to analyze the complex deformation history of brittle fault zone rocks developed in response to successive brittle deformation. Within the reactivated Cretaceous Sainthia-Brahmani Fault, cutting the Precambrian Chhotonagpur gneiss and Jurassic sandstone along the western margin of Bengal Basin, three generations of cataclasis can be recognized. The first generation (Ct1) cataclastic rock is infrequently preserved as clasts within the second phase (Ct2) cataclastic rocks. The last phase cataclasis (Ct3) affected both Ct1 and Ct2 cataclastic rocks in a discrete manner producing inhomogeneous network of thin sintered micro-zones of gouge. The cataclastic rocks are formed by progressive cataclasis of granitoid rocks with several pulses of fluid-induced brittle deformation during a history of frictional flow. The repeated cataclasis attest to a prolonged history of repeated failure and reactivation of fault movement in elastico-frictional regime operated in pulses with repeated embrittlement and mechanical failuret. This observation led to the idea of repeated reactivation of the fault, related to the extensional tectonics during early Cretaceous period linked to India's passage over the Kerguelen and Crozet Hot-Spots presently located in the Indian Ocean. Fracturing and comminution are dominant deformation mechanisms in the formation of cataclastic rocks, and subordinate but evident dissolution and recrystallization of quartz, and mild plastic deformation of quartz, feldspar and biotite are also seen. Dissolution and recrystallization processes during cataclasis, and absence of pseudotachylyte in the fault rocks provides an example of aseismic shear displacement within the brittle shear zone.
Abstract Shear zones are areas of intense deformation in localized zones which can be used as nat... more Abstract Shear zones are areas of intense deformation in localized zones which can be used as natural laboratories for studying deformation characteristics. Metre-to micro-scale structures that develop in response to a progressive simple shear in a shear zone are characterized by a protracted history of deformation and are immensely useful in delineating the history of progressive deformation. To decipher these localized zones of deformation and to establish the continuous non-coaxial character of deformation, detail ...
Structural investigations in the Precambrian Singhbhum Shear Zone of eastern India document an in... more Structural investigations in the Precambrian Singhbhum Shear Zone of eastern India document an intimate relationship between micro-to meso-scale structures and the deformation history. Shear zone rocks are characterized by composite foliation, a well-developed stretching lineation, folds, shear planes, and quartz veins. These structures reflect thrusting of the Proterozoic north Singhbhum hanging wall block over the Archaean south Singhbhum footwall block. Microstructural analysis of multiple foliation and mylonitic ...
Abstract: The early Archaean oval-shaped, high-grade Gurgunta schist belt in the northern part of... more Abstract: The early Archaean oval-shaped, high-grade Gurgunta schist belt in the northern part of the eastern Dharwar craton of south India constitutes a part of the intensely deformed migmatized basement of the low-grade volcano-sedimentary sequence of the Dharwar ...
A sequence of quartzite, banded phyllite and slate in the southern part of the Nallamalai fold be... more A sequence of quartzite, banded phyllite and slate in the southern part of the Nallamalai fold belt shows a series of macroscopic gently plunging folds (DI) with NW-SE striking axial plane and a pervasively developed axial planar slaty cleavage. A weak later deformation has produced sporadic gentle folds (D2) with axial planes at high angle to the D1 fold axial planes. The rocks along the eastern contact of the belt are mylonitized and the intensity of deformation gradually dies away towards west. A zone of tectonic dislocation is envisaged between the basement granite gneiss towards the east and the supracrustal Nallamalai rocks.
The emplacement of thrust sheets in a fold and thrust belt is an integral part in the evolution o... more The emplacement of thrust sheets in a fold and thrust belt is an integral part in the evolution of orogenic belts. The signatures of deformation present in a thrust sheet is often very useful to elucidate the history of deformation and also to understand the mechanisms of deformation that operates in stages during the emplacement of thrust sheets. The Himalayan orogenic belt has experienced multiple stages of thrusting and duplex formation. Ramgarh thrust sheet (RTS), one of the major thrust sheets bounded by the Main Central Thrust to ...
Banded ferruginous quartzite (BFQ) in the Sandur Schist Belt belongs to the Archaean Dharwar Supe... more Banded ferruginous quartzite (BFQ) in the Sandur Schist Belt belongs to the Archaean Dharwar Supergroup of Karnataka and contains primary depositional and diagenetic features. These include banding of different types, ripple marks. syneresis cracks, scour-and-fill structures, globular and nodular structures and penecontemporaneous faults. The significance of these structures in terms of the environment of deposition of BFQ has been considered. The BFQ was deposited as chemical precipitates and passed through a hydroplastic stage of lithification. Shallow water environment of dcposition in a more or less quiet condition with intermittent local disturbances has been envisaged.
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