Proceedings of the Indian Academy of Sciences Earth and Planetary Sciences, Dec 1, 1997
Microstructures in naturally deformed rocks in the upper crust demonstrate that creep strain in n... more Microstructures in naturally deformed rocks in the upper crust demonstrate that creep strain in nature may be accommodated by a combination of dislocation creep, diffusion/dissolution processes and microcracking. A theoretical approach towards deriving an aggregate flow law is presented, where the strain in the constituent phases is assumed to occur by simultaneous operation of diffusive mass transfer and crystal plastic mechanisms (dislocation creep). Both uniform stress and uniform strain rate situations are considered.
ABSTRACT Abstract: Tectonostratigraphic development of the c. 300 km-long Nellore schist belt (NS... more ABSTRACT Abstract: Tectonostratigraphic development of the c. 300 km-long Nellore schist belt (NSB) of southern India is described in relation to the post-Neoarchaean growth of the Dharwar cratonic nucleus. Lying along the eastern margin of the Dharwar cratonic nucleus, the NSB comprises several geologically and geochemically distinct tracts of deformed Palaeoproterozoic to Mesoproterozoic volcanosedimentary successions: the Vinjamuru Group, the Kandra ophiolite complex (KOC), the Kanigiri ophiolitic melange (KOM) and the Udaigiri Group, arranged in relative order of younging. The high-grade Eastern Ghats belt occurs further to the east of the NSB with a tectonic contact. Thrust-transported oceanic crust remnants occur in the 1.9 Ga KOC, 1.34 Ga KOM, and the Vinjamuru Group, which show multiple deformation, amphibolite facies metamorphism and granitic intrusions. The available geological, geochemical and geochronological data have been examined to tentatively constrain the relative age of the different tectonostratigraphic units of the NSB, tectonic juxtaposition and implications in relation to global events in the Proterozoic. Subduction-related ocean closures outboard and east of the Dharwar Craton, evidenced by the KOC and KOM, possibly had links with the assembly of Columbia and its final dispersal, respectively.
The late Paleoproterozoic to early Mesoproterozoic Nallamalai Group consisting of the arenaceous ... more The late Paleoproterozoic to early Mesoproterozoic Nallamalai Group consisting of the arenaceous Bairenkonda and the argillaceous Cumbum Formations suffered two phases of ductile deformation under greenschist facies (chlorite to biotite grade) metamorphism in the central part of the Nallamalai fold belt (NFB), south India. The N-S trending doubly plunging anticlines and synclines (F 1) largely control the outcrop pattern in the mapped area around Porumamilla. The westerly verging close to open overturned F 1 folds namely the Tekurupeta anticline and the adjoining Porumamilla syncline along with closely spaced disjunctive to slaty cleavage (S 1) and low angle faults suggest an overall E-W fold shortening plus local top-to-west thrust movement. These folds and thrusts are interpreted in terms of a general shear D 1 deformation. F 2 folds associated with a steep crenulation cleavage (S 2) are smaller and overprint earlier folds and cleavage. On the basis of structure and local stratigr...
ABSTRACT Deposition of Cuddapah Basin constrained by 21 detrital zircon samples•Papaghni and lowe... more ABSTRACT Deposition of Cuddapah Basin constrained by 21 detrital zircon samples•Papaghni and lower Chitravati Gps Dharwar Craton formed a rift-passive margin•Nallamalai Gp deposited in foreland basin to Krishna Orogen at ~ 1620 Ma•Kurnool Gp formed intracontinental basin derived from Dharwar Carton•Detrital zircon U-Pb, Hf and muscovite 40Ar/39Ar unravel basin evolution
Microstructures in naturally deformed rocks in the upper crust demonstrate that creep strain in n... more Microstructures in naturally deformed rocks in the upper crust demonstrate that creep strain in nature may be accommodated by a combination of dislocation creep, diffusion/dissolution processes and microcracking. A theoretical approach towards deriving an aggregate flow law is presented, where the strain in the constituent phases is assumed to occur by simultaneous operation of diffusive mass transfer and crystal plastic mechanisms (dislocation creep). Both uniform stress and uniform strain rate situations are considered.
... cleavages in natural examples of phyllites or quartz–mica schists have been put forward (Rast... more ... cleavages in natural examples of phyllites or quartz–mica schists have been put forward (Rast, 1965; Cosgrove, 1976; Marlow and Etheridge ... is the role of chemical reactions in enhancing pressure solution ('incongruent' pressure solution of Beach, 1979; also Knipe, 1981; Rutter ...
... 1979, White 1979, Christie & Ord 1980, Kohlstedt & Weathers 1980, Sch... more ... 1979, White 1979, Christie & Ord 1980, Kohlstedt & Weathers 1980, Schmid 1980, Ord & Christie 1984). ... 1980). Annealing recovery/recrystallization may also substan-tially alter microstructures attained during syntectonic recrystallization (eg Ord & Christie 1984). ...
... finite strain ellipsoid) lying on foliation. The (axis orientations are plotted on a lower he... more ... finite strain ellipsoid) lying on foliation. The (axis orientations are plotted on a lower hemisphere equal area projection and contoured using a computer pro gram (Kutty and Joy, 1997). The raxis fabric can be characterized by ...
... 2011). The available 322 geochronological data suggest the c. 1900 Ma KOC to be much older th... more ... 2011). The available 322 geochronological data suggest the c. 1900 Ma KOC to be much older than the c. 1300 Ma old 323 ophiolitic melanges of Kanigiri (Vijaya Kumar et al. 2010; Dharma Rao et al., 2011). ... metamorphism. Vijay Kumar et al. ...
Proceedings of the Indian Academy of Sciences Earth and Planetary Sciences, Dec 1, 1997
Microstructures in naturally deformed rocks in the upper crust demonstrate that creep strain in n... more Microstructures in naturally deformed rocks in the upper crust demonstrate that creep strain in nature may be accommodated by a combination of dislocation creep, diffusion/dissolution processes and microcracking. A theoretical approach towards deriving an aggregate flow law is presented, where the strain in the constituent phases is assumed to occur by simultaneous operation of diffusive mass transfer and crystal plastic mechanisms (dislocation creep). Both uniform stress and uniform strain rate situations are considered.
ABSTRACT Abstract: Tectonostratigraphic development of the c. 300 km-long Nellore schist belt (NS... more ABSTRACT Abstract: Tectonostratigraphic development of the c. 300 km-long Nellore schist belt (NSB) of southern India is described in relation to the post-Neoarchaean growth of the Dharwar cratonic nucleus. Lying along the eastern margin of the Dharwar cratonic nucleus, the NSB comprises several geologically and geochemically distinct tracts of deformed Palaeoproterozoic to Mesoproterozoic volcanosedimentary successions: the Vinjamuru Group, the Kandra ophiolite complex (KOC), the Kanigiri ophiolitic melange (KOM) and the Udaigiri Group, arranged in relative order of younging. The high-grade Eastern Ghats belt occurs further to the east of the NSB with a tectonic contact. Thrust-transported oceanic crust remnants occur in the 1.9 Ga KOC, 1.34 Ga KOM, and the Vinjamuru Group, which show multiple deformation, amphibolite facies metamorphism and granitic intrusions. The available geological, geochemical and geochronological data have been examined to tentatively constrain the relative age of the different tectonostratigraphic units of the NSB, tectonic juxtaposition and implications in relation to global events in the Proterozoic. Subduction-related ocean closures outboard and east of the Dharwar Craton, evidenced by the KOC and KOM, possibly had links with the assembly of Columbia and its final dispersal, respectively.
The late Paleoproterozoic to early Mesoproterozoic Nallamalai Group consisting of the arenaceous ... more The late Paleoproterozoic to early Mesoproterozoic Nallamalai Group consisting of the arenaceous Bairenkonda and the argillaceous Cumbum Formations suffered two phases of ductile deformation under greenschist facies (chlorite to biotite grade) metamorphism in the central part of the Nallamalai fold belt (NFB), south India. The N-S trending doubly plunging anticlines and synclines (F 1) largely control the outcrop pattern in the mapped area around Porumamilla. The westerly verging close to open overturned F 1 folds namely the Tekurupeta anticline and the adjoining Porumamilla syncline along with closely spaced disjunctive to slaty cleavage (S 1) and low angle faults suggest an overall E-W fold shortening plus local top-to-west thrust movement. These folds and thrusts are interpreted in terms of a general shear D 1 deformation. F 2 folds associated with a steep crenulation cleavage (S 2) are smaller and overprint earlier folds and cleavage. On the basis of structure and local stratigr...
ABSTRACT Deposition of Cuddapah Basin constrained by 21 detrital zircon samples•Papaghni and lowe... more ABSTRACT Deposition of Cuddapah Basin constrained by 21 detrital zircon samples•Papaghni and lower Chitravati Gps Dharwar Craton formed a rift-passive margin•Nallamalai Gp deposited in foreland basin to Krishna Orogen at ~ 1620 Ma•Kurnool Gp formed intracontinental basin derived from Dharwar Carton•Detrital zircon U-Pb, Hf and muscovite 40Ar/39Ar unravel basin evolution
Microstructures in naturally deformed rocks in the upper crust demonstrate that creep strain in n... more Microstructures in naturally deformed rocks in the upper crust demonstrate that creep strain in nature may be accommodated by a combination of dislocation creep, diffusion/dissolution processes and microcracking. A theoretical approach towards deriving an aggregate flow law is presented, where the strain in the constituent phases is assumed to occur by simultaneous operation of diffusive mass transfer and crystal plastic mechanisms (dislocation creep). Both uniform stress and uniform strain rate situations are considered.
... cleavages in natural examples of phyllites or quartz–mica schists have been put forward (Rast... more ... cleavages in natural examples of phyllites or quartz–mica schists have been put forward (Rast, 1965; Cosgrove, 1976; Marlow and Etheridge ... is the role of chemical reactions in enhancing pressure solution ('incongruent' pressure solution of Beach, 1979; also Knipe, 1981; Rutter ...
... 1979, White 1979, Christie & Ord 1980, Kohlstedt & Weathers 1980, Sch... more ... 1979, White 1979, Christie & Ord 1980, Kohlstedt & Weathers 1980, Schmid 1980, Ord & Christie 1984). ... 1980). Annealing recovery/recrystallization may also substan-tially alter microstructures attained during syntectonic recrystallization (eg Ord & Christie 1984). ...
... finite strain ellipsoid) lying on foliation. The (axis orientations are plotted on a lower he... more ... finite strain ellipsoid) lying on foliation. The (axis orientations are plotted on a lower hemisphere equal area projection and contoured using a computer pro gram (Kutty and Joy, 1997). The raxis fabric can be characterized by ...
... 2011). The available 322 geochronological data suggest the c. 1900 Ma KOC to be much older th... more ... 2011). The available 322 geochronological data suggest the c. 1900 Ma KOC to be much older than the c. 1300 Ma old 323 ophiolitic melanges of Kanigiri (Vijaya Kumar et al. 2010; Dharma Rao et al., 2011). ... metamorphism. Vijay Kumar et al. ...
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