Chhotanagpur Granite Gneiss Complex Research Articles

Development of concave-face boudin in Chhotanagpur Granite Gneiss Complex of Jasidih-Deoghar area, eastern India: Insight from finite element modeling

With the help of 2D-finite element modeling the present study analyses the role of syntectonic migmatisation on the development of concave-face boudins within amphibolite dykes in Chhotanagpur Granite Gneiss Complex of Jasidih-Deoghar area, eastern India. Amphibolitic bands embedded in quartzofeldspathic gneiss show concave-face boudins with varied face geometries, resulted due to rheological changes during syntectonic migmatisation. Detailed study reveals that due to couple effect of H2O infiltration and potassium (K+)-metasomatism associated with the invasion of pegmatitic fluid, pyroxene converted to amphibole and later to biotite at the marginal part of the amphibolitic bands and especially, near the separation zone of boudin. In this study, three types of models are prepared to simulate three different patterns of syntectonic rheological changes that can best explain the features observed in the field. Type I is a symmetric rim model representing equal amount of rheological changes in all directions of a rectangular boudin object. Other two are asymmetric rim models (Type II and Type III) with different amount of rheological changes along length and width of the boudin block. The analysis also takes into account the effects of rate of syntectonic rheological changes (D). The study reveals that the pattern and rate of rheological changes have strong influences on the development of concave-face boudin. Type I model produces barrel-shaped fish-mouth boudin with extremely sharp corners, whereas Type III model produces more lensoid shape with relatively tighter fish mouth. For all types of model, U-shaped concave-face boudin develops at lower rate of rheological changes and the face geometry gradually transforms to V-shape with increasing the rate. The progressive change of face curvature (FC), exterior curvature (EC) and aspect ratio (AR) depends on the timing of rheological inversion during progressive deformation.

A review of the ∼1600 Ma sedimentation, volcanism, and tectono-thermal events in the Singhbhum craton, Eastern India

The Palaeoproterozoic–Mesoproterozoic transition (∼1600 Ma) is a significant event in the Earth history as a global thermal perturbation affected the pre-1600 Ma landmasses. Like other cratonic blocks of the world, lithospheric thinning, sedimentation, magmatism, metamorphism and crustal melting/anatexis are associated with this significant geological event in the Singhbhum cratonic province of India. This paper is a review of sedimentological, magmatic and tectono-thermal events in the Singhbhum craton at ∼1600 Ma. The Palaeo-Mesoproterozoic sedimentation and volcanism in the Singhbhum craton took place in a terrestrial intracontinental rift setting. The available geochronological data are indicative of late Palaeoproterozoic to Neoproterozoic tectono-thermal events in the Chhotanagpur Granite Gneissic Complex (CGGC), an east–west trending arcuate belt of granite gneisses, migmatites and metasedimentary rocks. A detailed multidisciplinary geo-scientific investigation of the Dalma volcanic belt and the area to its north (Chandil Formation) and further north in CGGC will enable us to constrain the extant surface processes and crust-mantle interactions, the collision events between the North and South Indian cratonic blocks, and the position of India in the Columbia supercontinent.

Evolution of granulite enclaves and associated gneisses from Purulia, Chhotanagpur Granite Gneiss Complex, India: Evidence for 990–940 Ma tectonothermal event(s) at the eastern India cratonic fringe zone

Migmatitic quartzofeldspathic gneisses at Purulia, Chhotanagpur Granite Gneiss Complex (CGGC) contains layers and enclaves of high Mg–Al granulite and two-pyroxene granulites. Petrographic, geothermobarometric and pseudosection analyses of the high Mg–Al granulite reveal a strongly decompressive (Δ P = 6 kbar) retrograde trajectory after attaining the peak at 870 °C, 11 kbar. The metamorphic evolution ensued through partial melting of biotite-bearing assemblage. Texturally-constrained monazite grains yield population age of ca. 990–940 Ma which might bracket the timing of decompressive metamorphism in the high Mg–Al granulite broadly coinciding with the age of anatexis of the host gneisses. Associated mafic granulites underwent similar metamorphic evolution, but their contrasting bulk chemistries are responsible for mineralogical and textural variability. Formation and stabilization of garnet in one bulk composition of mafic granulite and breakdown of garnet in the other could be reconciled as products two different P– T segments of same metamorphic evolutionary history. Discrete population of older monazite ages (ca. 1800 Ma) in the host gneisses possibly implies variable degrees of inheritance. It is proposed that the ca. 990–940 Ma tectonothermal event caused extensive partial melting in the lower crust of the eastern Indian cratonic fringe zone. Widespread occurrence of ca. 1000–900 Ma metamorphism in the CGGC can be correlated with those in the Rayner–Eastern Ghats Belt in the Indo-Antarctic sector. All these areas experienced high-grade metamorphism as a result of Indo-Antarctic collision during the assembly of Rodinia.

Rb-Sr geochronology and petrogenesis of granitoids from the Chhotanagpur granite gneiss complex of Raikera-Kunkuri region, Central India

The Precambrian Chhotanagpur granite gneiss complex (CGGC) terrain covers more than 80,000 sq km area, and is dominated by granitoid gneisses and migmatites. Recent geochronological data indicate that the CGGC terrain has witnessed five tectonomagmatic thermal events at: (i) 2.5–2.4 Ga, (ii) 2.2–2.0 Ga, (iii) 1.6–1.4 Ga, (iv) 1.2–1.0 Ga, and (v) 0.9–0.8 Ga. Of these, the third and the fourth events are widespread. The whole-rock Rb-Sr isotopic analysis of twenty granite samples from the CGGC of Raikera-Kunkuri region, Jashpur district, Chhattisgarh, Central India, yields two distinct isochrons. The eleven samples of grey granites define an isochron age of 1005±51 Ma with moderate initial 87Sr/86Sr ratio of 0.7047±0.0065, which corresponds to the fourth tectonomagmatic event. On the other hand, the nine samples of pink granites indicate younger isochron age of 815±47 Ma with a higher initial 87Sr/86Sr ratio of 0.7539±0.0066 that matches with the fifth phase of the thermal event. The data suggest emplacement of large bodies of grey granite at ∼1005 Ma that evolved possibly from precursors of tonalitic-granodioritic composition. Furthermore, the younger age (∼815 Ma) suggests the age of metasomatism, involving isotopic resetting, that resulted in genesis of pink granite bodies of limited areal extent. By analogy, the age of metasomatism (∼815 Ma) may also be taken to represent the age of Y-mineralisation in the Raikera-Kunkuri region of the CGGC terrain.

Amphibole—a key indicator mineral for petrogenesis of the Purulia carbonatite, West Bengal, India

The Purulia carbonatite of West Bengal, India is a dyke occurring within the 100 km long South Purulia Shear Zone (SPSZ), which marks the boundary between the Singhbhum Group of Rocks and the Chhotanagpur Granite Gneissic Complex (CGGC). It is composed essentially of calcite with apatite, amphibole, phlogopite, biotite, magnetite and ilmenite as common accessories. Based on optical properties and mineral chemistry two varieties of the amphibole are recognized: magnesiokatophorite and richterite. The latter is characterized by a relatively high content of Si and Na, while the former is enriched in Al and Ca. Such a composition of the amphibole is characteristic for the intermediate to the late stage carbonatite development. These two co-existing amphiboles reflect a sudden variation in total pressure within the magma chamber during the intrusion of the carbonatite dyke. It is inferred that the magnesiokatophorite started crystallizing first along with calcite and apatite. Subsequently, the ascent of carbonatitic magma to a more shallow depth (hypabyssal) resulted in the formation of the richterite. The difference in amphibole composition reflects a variation in the total pressure within the magma chamber that took place during the formation of the Purulia carbonatite. However, an alternative explanation, such as wallrock contamination, or liquid immiscibility, followed by carbonate magma segregation or magma mixing, may also be possible. There is, however, no evidence corroborating such an interpretation.

Crustal structure of Bengal Basin and Shillong Plateau: Extension of Eastern Ghat and Satpura Mobile Belts to Himalayan fronts and seismotectonics

Gravity data from the East India and the Bangladesh are processed and compiled together to provide a composite complete Bouguer anomaly map of this region. Modelling of gravity profiles across the East Indian Shield (Chhotanagpur Granite Gneiss Complex, CGGC), the Shillong Plateau and the Bengal basin in Bangladesh, constrained from seismic studies suggest crustal thickness of 37–38 km and thrusted high density rocks in the middle crust under the East Indian Shield reducing to 30–32 km with thick sediments of 12–14 km under Bangladesh. Reduced crustal thickness under Bangladesh is attributed to oceanic type of crust, which is connected to Indian continent along Hinge zone characterized by linear gravity highs connecting east coast of India to the Shillong Plateau. Thrusted high density rocks under the CGGC and the Shillong Plateau are in comparison to those under the Eastern Ghat and the Satpura Mobile belts (EGMB, SMB) respectively suggest the north ward and east ward extensions of these orogenies. Margins of the thrusted block under Shillong Plateau when projected on surface coincide approximately with the south dipping Dauki and the Brahmaputra faults which coincides with central bulge due to lithospheric flexure indicating their surface expositions.

Pattern and genesis of lineaments in and across son-Narmada lineament zone in a part of central India around Renukoot, district Sonbhadra, U.P.

Lineament studies are not only important for the interpretation of hidden architectures of the rocks but also can be applied to decipher the analysis of structural deformation patterns and tectonism of a region besides numerous other applications in the field of earth sciences. In central part of India, SonNarmada-Tapti (SONATA) is aprominent ENEWSW trending lineament zone which is bound by two major faults namely Son-Narmada South Fault (SNSF) and Son-Narmada-North Fault (SNNF), reaching upto Moho (Jain et a l . , 1995). The lineament zone extends about 1300 km from southern margin of Kathiawar peninsula in the west to the margins of the Vindhyan basin in the east. Throughout the geological history the zone has witnessed resurgent tectonism (Acharyya and Roy, 2000). According to Jain et al. (1995) and Acharyya and Roy (2000), there seems to have been no major post Vindhyan reactivation of SNNF, on the other hand, SNSF has witnessed protracted reactivation from Precambrian to Phanerozoic. In Precambrian rocks of the Son valley area lineaments have been observed in the Chhotanagpur Granite Gneiss Complex (CGGC), the Mahakoshal Group and the Vindhyan Supergroup (Semri and Kaimur Groups). The presence of lineaments in the Kaimur Group (Upper Vindhayan) attracted the attention of authors because the flat lying horizontally bedded sandstones of the Kaimur Group in the Son valley region are generally considered tectonically undeformed. Therefore, an attempt in the present work has been made to study the lineaments present in the southern part of Sonbhadra district Uttar Pradesh and adjoining regions of neighbouring states, where the Precambrian rocks of the Chhotanagpur Granite Gneiss Complex (CGGC), the Mahakoshal Group and the Semri and Kaimur Groups of Vindhyan Supergroup are exposed. The lineaments occurring across the SONATA zone of this region have been studied in context of their genesis. The study area (Fig. 1) is bound between latitudes 23 ~ 46' N to 24 ~ 42' N and longitudes 82 ~ 35' E to 83031' E forming parts of the Survey oflndia toposheet nos. 63L/14, L/15, L/16; 63 P/2, P/3, P/4, P/6, P/7, P/8; 641/13 and 64M/1 covering 7713 km 2 of area around Renukoot in the Sonbhadra district

The Nature of Mesoproterozoic Central Indian Tectonic Zone with Exhumed and Reworked Older Granulites

The ESE-WNW trending Central Indian Tectonic Zone (CITZ) divides the Indian subcontinent into southern and northern crustal provinces. Its narrow northern belt consists of closed early Proterozoic Mahakoshal rift zone, which is presently confined between two Moho reaching faults that characterize the Son-Narmada (SONA) lineament. The Mesoproterozoic Sausar Mobile Belt (SMB), the Chhotanagpur Granite Gneiss Complex (CGGC) and the Gneissic Complex of Northeast India represent the wider southern belt. The Mahakoshal rift belt has a thick pile of mafic-ultramafic rocks and possibly oceanic components. The basin closed due to a south-directed subduction creating a magmatic arc that was sutured to its southern boundary during 1.8-1.7 Ga. A south dipping ductile shear zone, known as the Son-Narmada South Fault affects both its supracrustals and intrusive granitoids. The Son-Narmada South Fault generally delimits the northern boundary of the Gondwana Basins, whereas the Son-Narmada North Fault, delineates the northern boundary of the Mahakoshal Mobile Belt and the southern boundary of the Meso-Neoproterozoic Vindhyan Basin. The SMB, representing the southern belt of the CITZ in the central sector, comprises strongly folded and metamorphosed non-volcanic and Mn-rich Sausar sediments, intermixed with reworked basement gneisses, migmatites and granulites representing the pre-Sausar assemblage. The Sausar Orogeny closed during terminal Mesoproterozoic (ca. 1.0 Ga). On the other hand, metamorphism in the basement gneiss, migmatites, and northern and southern granulite belts pre-dates the Sausar Orogeny. The earliest structure of the SMB truncates and rotates the N-S oriented structures of the southward-located Sakoli and the Dongargarh belts of Neoarchaean-Palaeoproterozoic age. The northern granulite belt of the SMB and the CGGC, and the high-grade supracrustals from the Sonapahar area in NE India, all indicate very high P-T conditions during 1.7-1.5 Ga peak metamorphism, which was followed by decompressional cooling. The setting resembles continental collision, which was followed by tectonic exhumation and denudation. On the other hand, the southern granulite belt from the SMB documents a late Archaean (2.6 Ga) event and a later 1.4 Ga event. The Dalma Volcanic Belt located close to the southern tectonized boundary of the CGGC belt, and possibly the assemblage of copious mafic enclaves within the ca. 550 Ma granite plutons from NE India, represent back arc-like setting during 1.6-1.5 Ga. The setting is caused due to the southward subduction of the north Indian block beneath the southern block leading to continental collision. The metasedimentary belt, located further to the south of the Dalma Volcanic Belt and flanking the Archaean Singbhum Craton to the north, on the other hand, is Palaeoproterozoic in age, but has been metamorphosed during ca. 1.6 Ga because of the northern collision-related orogeny. Reworking and incorporation of basement gneisses and granulites from the mid-crust level to the younger Sausar cover sediments denote renewed spell of thrust tectonics that remobilized the collision zone rocks of the earlier orogeny. The tectonic transport was from the north to the south with north-dipping thrusts. Thus there was a reversal in the direction of convergence from the preceding orogeny. The Sausar Orogeny closed during ca. 1.0 Ga. It caused anatectic event producing granitoid plutons, migmatites and charnockites in the CGGC belt, and migmatites in the Gneissic Complex in NE India.

Geometrical classification of multilayered folds

A new classification scheme based on the degree of fluctuation in the geometry of different layers of a multilayered fold is suggested. The classification scheme uses the degree of fluctuation in geometry in terms of the standard deviation ( σ n ) of the thickness parameters t α ′ (orthogonal thickness parameter) and T α ′ (axial plane parallel thickness parameter) for n number of layers, and dip angle α. The degree of fluctuation in the geometry of a multilayered fold can be represented by σ n ( t α ′) or σ n ( T α ′) versus α plots on a Cartesian plane. In the proposed classification scheme, multilayered folds have been divided into two broad categories, namely `isodeviatoric' and `anisodeviatoric'. Isodeviatoric folds have a constant fluctuation in the geometry of different layers recorded in terms of σ n ( t α ′) or σ n ( T α ′) for α>10°. A special type of isodeviatoric fold is recognised as `analogous fold' in which each layer exhibits identical geometry [ σ n ( t α ′) or σ n ( T α ′)=0]. Plots of isodeviatoric folds lie parallel to the abscissa ( α) and those of analogous folds lie along the abscissa in the σ n ( t α ′) or σ n ( T α ′) (ordinate) versus α (abscissa) diagram. Analogous folds have been divided into ten varieties (1A1, 1A2, 1A3, 1B, 1C, 2, 3A, 3B, 3C and composite-analogous types). The anisodeviatoric folds do not exhibit constant fluctuation (deviation) in the geometry of different constitutive layers. Such folds have been subdivided into `peri-analogous', `sub-analogous', `sub-non-analogous', `non-analogous' and `strongly non-analogous' types. This classification scheme is applied to folds developed in low-grade metasedimentary rocks of the Mahakoshal Group and low- to medium-grade rocks of the Chhotanagpur Granite Gneiss Complex in central India.