Delhi Terrane Research Articles

“Geochronology and geochemistry of pelitic granulite from the South Delhi Terrane of the Aravalli Delhi Mobile Belt, NW India: implications for petrogenesis and geodynamic model”

AbstractAn attempt has been made to illustrate the evolution of pelitic granulite from south of the Balaram-Abu road, which lies in the South Delhi Terrane (SDT) of the Aravalli-Delhi Mobile Belt (ADMB), using geochemistry and geochronology. The current work offers a plausible explanation for the protolith of pelitic granulite, nature of the sediments and its provenance. The elemental geochemistry of the pelitic granulites reveals that the protolith is an arkosic to shaley type. The rare earth elements pattern shows that there is a negative Eu anomaly and a small excess of LREE over HREE. This means that the source of sediments probably has the same elements as the upper crust. However, the amounts of Sr, Nd and Pb vary a lot, which shows that the sediments supplied from two different types of sources (felsic and mafic) in different proportions from a Proterozoic terrain. The monazite geochronology indicates that the metamorphic overprint occurred between 797 Ma and 906 Ma. Additionally, the ages correlate to the debris that was formed between the 1188 Ma and 1324 Ma from magmatic/sedimentary sources for pelitic granulite. The present research provides a more in-depth understanding of the evolutionary history of the pelitic granulite that comprises the SDT in the ADMB region during the Proterozoic era.

Petrology and Geochemistry of Carbonate Metasediments from Pindwara-Aburoad Belt in the Southern Part of South Delhi Terrane: Implications for Protolith, Provenance and Tectonic Setting

Abstract The carbonate metasediments of Pindwara-AbuRoad Belt (PARB) in the Sirohi district belongs to the Kumbhalgarh Group of the South Delhi Terrane (SDT). The litho-assemblages associated are quartzite, carbonate, mica schist, phyllite, metavolcanics, and granitoids. The present study is made on impure marble and calc-silicates of the study area. The carbonates show mineralogical variations with indiscernible field boundaries. The carbonates composed of calcite, diopside, hornblende, tremolite, actinolite, biotite, muscovite, epidote, quartz, plagioclase with minor proportion of apatite, sphene, garnet, sericite, kyanite, zircon, opaque, and broadly may be termed as calc-silicates. The mineral chemistry, major, trace elements, and REE geochemistry of the carbonates reveal the nature of protolith, provenance, depositional environment, spatial and temporal constraints on metamorphism, and on going tectonic process. The study suggests that the PARB carbonate metasediments were derived from a varied proportion of terrigenous and quartzo-feldspathic felsic provenance and deposited in less saline shallow marine environment in an intracontinental rift setting. These exhibit amphibolite to green-schist facies metamorphism, accompanied by polyphase deformation. The metasediments of the region indicate the Meso-Neoproterozoic transition during the Delhi Orogeny in SDT.

Structural implications of paleofluid pressure and paleostress estimates of the quartz veins from sulfide deposits of the Ambaji-Deri region, Neoproterozoic South Delhi Terrane, Aravalli-Delhi Mobile Belt, North-West India

Structural implications of paleofluid pressure and paleostress estimates of the quartz veins from sulfide deposits of the Ambaji-Deri region, Neoproterozoic South Delhi Terrane, Aravalli-Delhi Mobile Belt, North-West India

Genesis of the late‐stage base metal sulfide mineralisation and its relationship with the regional deformation in Ambaji–Deri, South Delhi Terrane, North‐West India

Proterozoic stratiform VMS‐type Ambaji–Deri Zn–Pb–Cu deposits in the Aravalli‐Delhi mobile belt of North‐West India are hosted within meta‐sedimentary sequences of the South Delhi Terrane. Several fracture‐filled discordant late‐stage base metal mineralised quartz veins have intruded along with the fractures and foliation at very high Pf (σ2 < Pf < σ1) with typical hydrothermal alteration zones. Temperatures estimated from hydrothermal chlorite vary from 226 to 293°C (mean. 260°C). 40Ar‐39Ar dating of hydrothermal muscovite yielded a plateau age of 625.5 ± 3.3 Ma. Detailed fluid inclusion (FI) analysis reveals three types of primary and four types of secondary FI. Primary H2O‐NaCl‐CO2 ± N2 type 1a FI has medium to high salinity (11.21–21.96 wt% NaCl equivalent) and high density (0.90–1.04 g/cm3), while the secondary type 1b FI with same compositions are characterized by medium salinity (~12.6 wt% NaCl equivalent) and lower density (0.89–0.90 g/cm3). Phase separation/fluid immiscibility is the primary mechanism of mineralisation in the Ambaji–Deri that caused the original fluid to evolve separately as gaseous (CO2) type 2a, b and aqueous type 3a, b (H2O‐NaCl) with similar salinity and density for the aqueous inclusions and low density for the gaseous inclusions (lowering up to 0.58 g/cm3). The ore‐forming fluid with magmatic signatures possibly originated from the cooling G3 granites, remobilized the pre‐existing metals, and precipitated at ~265°C and ~1 kbar at the epizonal depths in the dilated fractures. Later these fluids are mixed with meteoric water and evolved into low saline aqueous fluids that produced supergene alterations.

Tectonic Fabric, Geochemistry, and Zircon-Monazite Geochronology as Proxies to Date an Orogeny: Example of South Delhi Orogeny, NW India, and Implications for East Gondwana Tectonics

We have dated the South Delhi orogeny, Aravalli-Delhi Mobile Belt (ADMB), NW India, using the tectonic fabric, geochemistry, and zircon-monazite geochronology as the proxies. The South Delhi Terrane (SDT), a passive margin domain in the ADMB, consists of multiply deformed (D1–D4) greenschist facies rocks and several granite plutons. The D1deformation is characterized by pervasive isoclinal recumbent F1fold and axial planar tectonometamorphic fabric, S1, developed in all rock types. The S1minerals belong to peak greenschist facies metamorphism, M1, suggesting syntectonic nature of M1with D1. The age of the D1-M1is constrained by the syncollisional peralkaline S type Sewariya granite which is characterized by magmatic/submagmatic fabric (Sm) coplanar with the S1. The margin of the pluton is turned into quartzofeldspathic gneiss carrying the evidence of high temperature deformation. The age of Sewariya granite is estimated at ca. 878 Ma by zircon geochronology. The D1-M1is further constrained by monazite geochronology of the mica schist at ca. 865–846 Ma. The other granite plutons and metarhyolite are pre-D1and emplaced at ca. 992–946 Ma. The D2deformation produced NE-SW trending open upright F2folds coaxial with the F1, and northwesterly vergent F2–axial planar thrusts. Monazite geochronology constrains the D2at ca. 811–680 Ma. The D3is characterized by small to large scale NW-SE folds, and the D4by faults and fractures marking the brittle deformation in the rocks. The D4is constrained by monazite geochronology at ca. 588–564 Ma. There are upper amphibolitic tectonic slivers along the D2-Phulad thrust, belonging to the pre-Delhi rocks, which show ca. 1,638 Ma metamorphism age. From the above study, it is suggested that the South Delhi orogeny belongs to ca. 878–680 Ma marking the final amalgamation of Marwar Craton with the rest of India. This overlaps the early phase of the Pan-African orogeny (900–630 Ma). The brittle deformation, D4, coincides with Kuunga orogeny (650–500 Ma). Our study implies that India, like other continents in the East Gondwana, underwent amalgamation of internal blocks until the late part of the Neoproterozoic.

Metamorphic P–T evolution of Hercynite-quartz-bearing granulites from the Diwani Hill, North East Gujarat (NW India)

Diwani Hill granulites occurring on the southern tip of the South Delhi Terrane (SDT) of Aravalli Mobile Belt (AMB), comprises rocks of granulite facies and represent the deeper level of the crust. The SDT represents an admixture of charnockites, granites, calc-granulites and hercynite-quartz-bearing pelitic granulites. The symplectite and corona textures recorded in the hercynite-quartz-bearing granulites from a part of SDT provides a wide spectrum of P-T sensors in support of the petrological evolution. P-T evolution of these hercynite-quartz-bearing granulites has been constrained through the use of THERMOCALC program, conventional thermobarometry, and pseudosection modelling in the NCKFMASHTO model system using Perple_X software. The unification of these three calculations, demonstrates that the hercynite-quartz-bearing granulites experienced peak pressure and temperature at 6.7 kbar and 750 °C, respectively. The textural imprints, multistage reaction textures, P-T pseudosections as well as the application of multi-equilibrium calculation give evidence for decompressive history related to their exhumation. SHRIMP U-Pb chronological results yield ages between 780 and 680 Ma as a time of metamorphic overprint, and the ages between 1591 and 1216 Ma corresponding with detritus derived from magmatic source for hercynite-quartz-bearing granulites. Zircon ages reflect that continental crust in the SDT resulted from the Mesoproterozoic protolith of an igneous origin whereas sedimentary succession was deposited between 1216 and 780 Ma. The present study envisages that the South Delhi basin would have been a remnant of the proto-Mozambique Ocean in NW India which was closed due to subduction. This subduction metamorphosed the sediments of the basin to granulite facies and the rocks were subsequently, uplifted because of the thrust sheet tectonics during the Neoproterozoic times.

Modification of pre-existing folds in a shear zone: A case study from Kumbhalgarh–Ranakpur area, South Delhi Fold Belt, Rajasthan, India

Pre-existing structures (e.g., folds, foliations, lineations) are usually rotated and modified within a shear zone, depending on their attitude with respect to the kinematic framework (i.e., orientation of instantaneous stretching axes (ISA), kinematical vorticity number of the flow (Wk)) of the shear zone. In addition, new folds may also form within a shear zone, and it is not always easy to distinguish between the pre- and syn-shearing structures in the field, especially if they form on the same rock type. The present contribution describes the reorientation and shape modification (tightening) of pre-existing and syn-shearing folds in metamorphosed calcareous rocks of the Kumbhalgarh Group (part of Delhi Supergroup) due to shearing along the Ranakpur Shear Zone (RSZ), in Kumbhalgarh–Sayra–Ranakpur area of South Delhi Fold Belt (SDFB), also called South Delhi Terrane (SDT). From field-based study and measurements, it is shown that the shallow-plunging, upright second generation (DF2) folds of SDFB/SDT have been rotated to subvertical, tight folds within the RSZ. Fold shape analysis using layer thickness and limb dip of folds (i.e., Ramsay’s classification) and by Fourier transform shape analyses of fold profile sections corroborates and roughly quantifies the tightening and shape modification of pre-existing folds within the RSZ. In contrast, syn-shearing folds have formed on the foliations in calc-silicate rocks which show strongly non-cylindrical geometry with apical deflection in an oblique direction. From the available shear sense indicators like rotated porphyroclast tails and vergence of asymmetric folds, the shear sense of the RSZ is interpreted as oblique reverse (east-side-up) with subordinate sinistral (east-towards-north) shear component, which is similar to the shear sense interpreted by some earlier workers.

Extension driven brittle exhumation of the lower-middle crustal rocks, a paleostress reconstruction of the Neoproterozoic Ambaji Granulite, NW India

The exhumation of the deep crustal rocks through brittle crust by extensional tectonics is recognized in orogens of all ages. Paleostress analysis are generally used to understand the brittle exhumation process. In this study, we reconstructed the paleostress of faults of the Neoproterozoic Ambaji Granulite, South Delhi Terrane of the Aravalli-Delhi Mobile Belt, NW India by analyzing the fault slip data in Win Tensor program. Several NE-SW and WNW-ESE faults have been mapped in the area and found to be normal faults with a few strike-slip faults. The strike-slip faults are pre-kinematic to normal faults. Tensor solutions for 237 fault slip data points estimate WNW-ESE extension for strike slip faults and NW-SE direction extension for normal faults. From these results, we interpret that the NE-SW striking, orogen-parallel normal faults were produced from a NW-SE directed extensional stress and are primarily responsible for brittle exhumation of the granulite through crustal extension and thinning at 764–650 Ma. This is comparable to earlier studies on brittle exhumation along the Southern Tibet detachment in the Higher Himalayas. On a more regional scale, our results are in agreement with the extensional tectonics that affected the entire Aravalli-Delhi Mobile Belt and adjoining continents of the Neoproterozoic-Cambrian Gondwanaland Supercontinent.

Petrology, geochemistry and geochronology of Neoarchean A-type granite from Alwar Basin, North Delhi Terrane, NW India

A 2.53 Ga old Jhiri granite has been dated using zircon U–Pb systematics from the lowermost succession of North Delhi Terrane (NDT). The granite is an intrusive into the rocks of meta-volcano sedimentary sequence of basal Raialo Group of the Delhi Supergroup. Geochemically, the pluton is peraluminous, magnesian, alkali-calcic to alkali in character with strong negative anomaly for Ba, Ta, P and Ti and positive anomaly for K, Pb and Th. The plots on tectonic discrimination diagrams show the Jhiri granite to be of A-type with an affinity to the volcanic arc related granitoids. The comparison of Jhiri pluton with other Neoarchean granitoids of the Aravalli Delhi Mobile Belt (ADMB) and Bundelkhand craton shows the granite to be more evolved and have strong depletions for HREEs with (La/Yb)N >20. A hybrid source, having component of fractional crystallization-derived mafic melt mixing with melt generated by partial melting of early formed felsic crust in a back-arc extension or post-orogenic extension setting is proposed as the possible scenario for the generation and emplacement of Jhiri pluton.

Paleostress and Fluid Pressure Analysis of Vein Opening Using 3D Mohr Circle from the Quartz Vein Orientation Data of the South Delhi Terrane, Ambaji Area, NW India

In many instances the sulphide mineralization is associated with quartz vein-related hydrothermal alteration zone. The syntectonic quartz veins display preferred orientation as their intrusion is controlled by normal stress (σn) acting across the foliation/fracture planes and the fluid pressure (Pf) of the quartz veins. The Pf and paleostress (ϕ = tectonic stress ratio) are measurable by using stereoplot and 3D Mohr plot. We have determined the above parameters from the quartz veins in the Cu–Pb–Zn mineralization belt of South Delhi terrane, NW India. The mineralization occurs in the mica schist and metabasalt. The rock types show three phases of folding (F1–F3), greenschist facies metamorphism and multiple phases of granite intrusion. Attitude of 170 quartz veins have been measured, the NE–SW direction is the most prominent. Though some of the quartz veins show a cross-cutting relationship, we have treated them broadly synchronous. Stereoplot shows a girdle distribution pattern with an elliptical void area at the centre and σ1σ2 plane strikes N52° E. Further, σ1 = 120°/75°, σ2 = 052°/07°, and σ3 = 323°/07° indicate that maximum extension was NW–SE. The θ2 = 12°, θ3 = 40°. R ' = 0.95, ϕ = 0.90 indicate high value for R ' leading to dilation of wide range of fractures and the high ϕ value suggesting uniaxial extension. 3D Mohr plot indicates that Pf fluctuated between σ2 < Pf < σ1. Since sulphide mineralization is related to quartz vein intrusion, we interpret similar stress field for mineralization.

Dynamics, EPMA Th‐U‐Total Pb Monazite Geochronology and Tectonic Implications of Deformational Fabric in the Lower‐Middle Crustal Rocks: A Case Study of Ambaji Granulite, NW India

AbstractStrain fabric and monazite microstructure were studied and dated by Electron Probe Microanalyser (EPMA) in situ Th‐U‐total Pb monazite geochronology in the Ambaji granulite, South Delhi terrane, NW India. The Ambaji granulite comprises pelitic, calcareous, and mafic granulites with several phases of granite intrusions, G0‐3. The granulites were deformed by three phases of folding, F1–3, during South De lhi orogeny and marked by a subhorizontal pervasive fabric, S1, axial planar to isoclinal‐recumbent F1 folds that developed during granulite facies metamorphism. S1 is overprinted by discrete sets of subvertical shear zones associated with a mylonitic fabric, S2, that were developed axial planar to NE‐SW striking upright F2 folds and facilitated exhumation of granulite facies rocks to the upper crust. The shear zones show early history of high‐temperature thrust sense shear and late stage low‐temperature sinistral shear. The NW‐SE striking F3 folds also affected the granulite facies rocks resulting in interference patterns and variations in regional structural trends. Brittle strike slip, and normal fault (Sf fabric) that developed post F3, led the final exhumation of the granulite facies rocks to the surface. The S1 monazites are Y‐depleted and recrystallized through dislocation creep, and the S2‐Sf monazites are Y‐enriched and recrystallized through dissolution‐precipitation creep. Different monazite population yielded distinct ages of circa 875‐857, 834‐778, and 764‐650 Ma for S1, S2, and Sf strain, respectively, indicating that the South Delhi orogeny spanned 875‐650 Ma overlapping with the early phase of the Pan‐African orogeny or representing a transition between Grenvillian and Pan‐African orogeny.

Palaeostress and magma pressure measurement of granite veins in the Neoproterozoic Ambaji granulite, South Delhi terrane, Aravalli–Delhi mobile belt, NW India: Implication towards the extension-driven exhumation of the middle–lower crustal rocks

Neoproterozoic Ambaji granulite, in the South Delhi terrane (SDT) of the Aravalli–Delhi mobile belt (ADMB), is multiply deformed at different stages of its exhumation from the middle–lower crust. It was intruded by four phases of granites, \(\hbox {G}_{0-3}\), of which the \(\hbox {G}_{{3}}\) was syntectonic with brittle shearing. The orientation of the \(\hbox {G}_{{3}}\) granite veins was used, in this paper, to measure the palaeostress and magma pressure during its intrusion. The \(\hbox {G}_{{3}}\) granite has a porphyritic texture with quartz, microcline and biotite minerals and contains magmatic foliation; biotites are aligned oblique to such foliation, suggesting the syntectonic intrusion of the granite with normal faulting. Stereoplot of the poles of the granite veins shows concentration in the NW and SW quadrants and lack data over an elliptical area at the centre, indicating a girdle pattern. This implies that the magma pressure \(P_{\mathrm{m}}>\) \(\sigma _{2}\), compression \(\sigma _{1}\) was vertical and extension \(\sigma _{3 }\) was NW–SE horizontal. Values of \(\theta _{2} = 16{^{\circ }}\) and \(\theta _{3} = 40{^{\circ }}\) were obtained from the stereoplot, used to calculate stress ratio \(\Phi = 0.81\), driving pressure \(R^\prime = 0.92\) and the construction of the 3D Mohr plot for \(P_{\mathrm{m}}\) and principal stresses. Result suggests that the \(\hbox {G}_{{3}}\) granite intruded under extensional tectonics that probably contributed to the exhumation of the Ambaji granulite.

Strain Estimation of Folds, Orbiculites and Quartz Phenocrysts in the Ambaji Basin of the South Delhi Terrane, Aravalli-Delhi Mobile Belt, NW India and its Tectonic Implication

Abstract Ambaji basin in the south Delhi terrane of Aravalli-Delhi Mobile Belt consists of greenschist facies rocks which are intruded by 850-750 Ma Ambaji granites and several phases of quartz and pegmatite veins. The basin is tectonically juxtaposed against the Balaram-Kui-Surpagla-Kengora Granulite Complex. In this paper the deformation structures of the Ambaji basin has been studied and strain has been measured using different markers like folds, orbiculites and quartz phenocrysts and its tectonic implication has been discussed. Strain due to folding has been expressed in terms of shortening that has been estimated using wavelength / arc length ratio. Since the folds belong to Class 1C geometry, the arc length of the parent Class 1B fold has been calculated after removing the homogeneous strain component from Class 1C fold. The above technique was verified by drawing a Class 1B fold and modifying to Class 1C by homogeneous strain in Macromedia FreeHand MX software. Further, this was cross checked by measuring strain in two strain ellipses that represent respectively shortening in Class 1B and Class 1C folds. The shortening was estimated to be ca. 65% and 55% during F1 and F2 folding respectively. In order to know the finite strain in the folded rocks the deformed orbiculites in the metabasalt and quartz phenocrysts in the metarhyolite and granites have been analysed by Normalized Fry techniques. An apparent flattening strain with about 10 to 23 % volume loss has been estimated; correlation between inclinations of the longer axis of strain ellipse with strain suggests layer parallel shear to be the primary cause of folding. It has been suggested that buckling associated with moderate shortening and low volume loss are responsible for the deformation in the low grade rocks of Ambaji basin during evolution of South Delhi Terrane.

Tectonic setting of the Balaram-Kui-Surpagla-Kengora granulites of the South Delhi Terrane of the Aravalli Mobile Belt, NW India and its implication on correlation with the East African Orogen in the Gondwana assembly

Granulites are developed in various tectonic settings and during different geological periods, and have been used for continental correlation within supercontinent models. In this context the Balaram-Kui-Surpagla-Kengora granulites of the South Delhi Terrane of the Aravalli Mobile Belt of northwestern India are significant. The granulites occur as shear zone bounded lensoidal bodies within low-grade rocks of the South Delhi Terrane and comprise pelitic and calcareous granulites, a gabbro-norite-basic granulite suite and multiple phases of granites of the Ambaji suite. The granulites have undergone three major phases of folding and shearing. The F 1 and F 2 folds are coaxial along NE-SW axis, and F 3 folds are developed across the former along NW-SE axis. Thus, various types of interference patterns are produced. The granulite facies metamorphism is marked by a spinel–cordierite–garnet–sillimanite–quartz assemblage with melt phase and is synkinematic to the F 1 phase of folding. The peak thermobarometric condition is set at ≥850 °C and 5.5–6.8 kb. The granulites have been exhumed through thrusting along multiple ductile shear zones during syn- to post-F 2 folding. Late-stage shearing has produced cataclasites and pseudotachylites. Sensitive High Resolution Ion MicroProbe (SHRIMP) U–Pb dating of zircon from pelitic granulites and synkinematically emplaced granites indicate that: (1) the sedimentary succession of the South Delhi Terrane was deposited between 1240 and 860 Ma with detritus derived from magmatic sources with ages between 1620 and 1240 Ma; (2) folding and granulite metamorphism have taken place between ca. 860 and 800 Ma, and exhumation at around ca. 800–760 Ma; and (3) the last phase of granitic activity occurred at ca. 759 Ma. This shows, for the first time, that the granulites of the South Delhi Terrane are much younger than those of the Sandmata Granulite Complex of the northern part of the Aravalli Mobile Belt, the Saussar granulites of the Central India Mobile Belt and the Eastern Ghats Mobile Belt. Instead, they show similarities to the Neoproterozoic granulites of the Circum Indian Orogens that include the East African Orogen (East Africa and Madagascar), the Southern Granulite Terrane of India and much of Sri Lanka. We suggest that the South Delhi Basin probably marks a trace of the proto-Mozambique Ocean in NW India within Gondwana, that closed when the Marwar Craton, arc fragments (Bemarivo Belt in Madagascar and the Seychelles) and components of the Arabian-Nubian Shield collided with the Aravalli-Bundelkhand Protocontinent at ca. 850–750 Ma.