NW India Research Articles

Origin and Tectonic Implications of I-type Granites, North Delhi Fold Belt, NW, India: Insights from Whole Rock Geochemistry and Mineral Compositions

Abstract A comprehensive whole-rock geochemical and mineral chemistry study was carried out of granites from the Narnaul and surrounding isolated hills of North Delhi Mobile Belt, NW India to constrain their genesis, and tectonic environment. The distinctive features of granites are meta to peraluminous nature and decreasing trend of P2O5 with high SiO2 (>71%) ascribed to its metaigneous origin. In detail the chemical diversity of the studied samples is reflected by their affinity to Calc-alkaline to shoshonite series with high K2O/Na2O (mostly>1), low MgO (< 0.11%) and variation in Mg# (upto 0.5) and maficity with increasing SiO2. The positive Eu anomalies, high LILE, highly enriched LREE (La/Sm = 4.13–19.33) pattern and comparatively elevated concentrations of Cs, La, Ta, Dy, Zr, Pb and Yb suggest different episodes of magmatic differentiation. Our data indicate that melting of older subduction-related igneous rocks and the underwent fractional crystallization in hydrous conditions is the possible mechanism for the generation of I-type granites in collisional tectonic setting.

Neoarchean to Paleoproterozoic crustal evolution of the central Aravalli-Banded Gneissic Complex (NW India): Evidence from zircon U-Pb-Hf isotope systematics and whole-rock composition of Neoarchean sanukitoids, Paleoproterozoic granitoids and metasedimentary rocks

The central Aravalli-Banded Gneissic Complex in NW India is an Archean nucleus that was extensively reworked during the late Paleo- to Neoproterozoic. New results of combined zircon U-Pb-Hf isotopes and whole-rock geochemical data reveal that the basement was affected by felsic magmatism during the Neoarchean and Paleoproterozoic, followed by a passive margin stage. The results provide evidence for coeval emplacement of sanukitoids and TTGs at ca. 2540 Ma, and for granitoid magmatism at ca. 1875 Ma. Similar REE patterns of the synchronous sanukitoids and TTGs, coupled with high SiO2 contents (59.2–70.9 wt%), subchondritic εHf2.55 Ga values (−5.0 to −2.6) and Hf-model ages (3246–3123 Ma) of the Masuda sanukitoids indicate that the sanukitoid magmas were formed mainly by interaction of TTG magmas (generated by the melting of subducted Paleo- to Mesoarchean oceanic crust) with the overlying enriched peridotite. The calc-alkalic and magnesian compositions, enrichment in LREE and LILE along with pronounced depletion in HFSE (Nb, P and Ti) in ca. 1875 Ma granitoid gneisses imply subduction-related magmatism during Paleoproterozoic. The predominance of subchondritic εHf1.87 Ga values, ranging from −4.4 to +1.7, suggests that the parental magmas mainly resulted from the reworking of heterogeneous Meso- to Neoarchean felsic crust. Age-Hf isotope data of detrital zircon grains provide evidence that clastic sedimentary rocks covering the central Aravalli basement were deposited in a passive margin setting at < 1730 Ma, and the detritus was mainly sourced from adjoining Neoarchean and Paleoproterozoic granitoids. Comparison of our new data with other Indian and worldwide cratons indicate that the Aravalli orogen represents a unique terrane, where the Neoarchean TTGs and sanukitoids with subchondritic Hf isotopic signatures were emplaced nearly coeval in a close spatial relationship. The Aravalli Archean basement was subsequently reconfigured by voluminous felsic magmatism during Paleoproterozoic at 1875–1810 Ma. Furthermore, the compiled zircon U-Pb age and Hf-Nd isotope data for the late Paleoproterozoic subduction-related magmatic rocks provide evidence for substantial crustal reworking during assembly of the Columbia supercontinent.

Evidence for a pre-Himalayan metamorphism in the High Himalayan Crystalline of the Miyar Valley (NW India)

Most of the tectonic, metamorphic and geochronological data suggest that the Himalaya is essentially the consequence of a single orogenic cycle associated with the India-Asia collision during the Cenozoic era. Therefore, metamorphic assemblages and tectonic structures across the Himalayan range are systematically considered as post-collisional geological records. However, over the last decades, several observations arguing for geological events predating the continental collision have become increasingly recurrent in the literature. Nevertheless, although some of these arguments are thoroughly documented, they are unduly ignored in the construction of models drawing the tectono-metamorphic evolution of the Himalayan range. Yet, the occurrence of a pre-Himalayan history would have considerable consequences on the classical models for the building of the Himalaya. The recent discovery of inclusions of staurolite crystals in greenschist facies garnets from the Miyar Valley in Upper Lahul region (Himachal Pradesh; NW India) revives the debate on the existence of a pre-Himalayan metamorphism. Indeed, the occurrence of high-temperature staurolites included in greenschist facies garnets suggests that the High Himalayan Crystalline rocks experienced an amphibolite facies metamorphism prior the predominant Himalayan greenschist facies metamorphism observed in this part of the range. In this study, phase petrology, microtectonic investigations combined with preexisting geochronological data infer that the crystallization of the included staurolite predates the growth of Himalayan garnets. These original data bring new arguments to bear on the long lasting debate of the existence of a Pre-Himalayan orogenic cycle. They lead to the conclusion that the growth of staurolite predates the continental collision between India and Asia and reflects a metamorphic event that belongs to a pre-Himalaya orogenic cycle.

Provenance of metasedimentary rocks from the Rewat hill, Degana, NW India

Provenance of metasedimentary rocks from the Rewat hill, Degana, NW India

W-Li Potentials in the Tailing Dumps of Rewat Hill, Degana, Rajasthan, NW India; Constraints from Petrography and Geochemistry

Abstract The largest tungsten deposit at Degana in NW India, hosted in Neoproterozoic (ca. 827±8.2 Ma) peraluminous granite emplaced within Delhi meta-sediments, characterized as vein and greisen types hydrothermal multi-metal deposit. A number of NW-SE trending quartz and pegmatite veins, intruded in granite, host tungsten and lithium of economic significance. Extensive mining for tungsten ore in the past resulted in huge amount of tailing dumps on hill slope of Rewat hill all over. These tailing dumps mainly contain greisenised granite, pegmatite and quartz-mica-wolframite veins which host anomalous W-Li-Sn-Mo-Ta multi-metals. In this study, we provide first-hand information on W-Li and associated rare metals potential of tailing dumps of Rewat hill using petrographic study and geochemical analysis. A total 7 samples from tailing dumps were analysed by ICP-MS indicate significant W values which ranges between 201.47 ppm to 2647.83 ppm with an average of 748.51 ppm, Li (1006.92 ppm to 6701.43 ppm, avg. 2743.64 ppm), Sn (22.77 ppm to 438.87 ppm, avg. 96.49 ppm), Mo (3.43 ppm to 254.21 ppm, avg. 63.0 ppm) and Ta up to 53.09 ppm. Ore beneficiation study on tungsten ore from tailing dumps by NML indicated that at 5% WO3, the grade of the pre-concentrate; a recovery of &amp;gt; 60% could be achieved whereas at 30% WO3 grade the recovery is about 46%. However, IBM results indicated a recovery of 59.8% with 66.30-66.50% WO3 grade of final concentrate from tailing dumps having assay value between 0.14%-0.15% WO3.

Zircon U–Pb, Hf, and O isotopic constraints on the tectonic affinity of the basement of the Himalayan orogenic belt: Insights from metasedimentary rocks, orthogneisses, and leucogranites in Garhwal, NW India

Zircon U–Pb geochronology and Hf–O isotope geochemistry of metasedimentary rocks, orthogneisses, and leucogranites in Garhwal, NW India, provide new insights into the tectonic affinity of the basement of the Himalayan orogenic belt. Detrital zircon U–Pb ages from metasedimentary rocks in both the Lesser Himalayan Sequence (LHS) and the overlying Main Central Thrust (MCT) zone yielded dominant Paleoproterozoic ages with the youngest age peak of 1840 Ma. Along with that, the variable ɛHf (t) values (−14.56 to 8.44) indicate that these metasedimentary rocks could have been derived from the juvenile Paleoproterozoic orthogneiss basement in the Himalayas and/or the ancient Indian craton in the south. In contrast, the metasedimentary rocks in the Ediacaran Harsil Formation are dominated by the ca. 1200–800 Ma zircons with the youngest age peak of ca. 630 Ma and variable ɛHf (t) values (−16.57 to 13.32), which belong to the underlying High Himalayan Crystalline Sequence (HHCS), rather than the overlying Tethyan Himalayan Sequence. Orthogneisses in the MCT zone record ca. 1.87–1.85 Ga felsic magmatism associated with the Nuna supercontinent. The Bhagirathi leucogranites intruding the Harsil Formation were formed at ca. 496–490 Ma. These Paleoproterozoic orthogneisses and early Paleozoic leucogranites show only positive ɛHf (t) values (0 to +15) correlatable with a juvenile mantle input. However, the zircon Hf model ages older than the U–Pb ages and the oxygen isotope values (δ18O: 7.74–8.91 ‰), significantly higher than zircons crystallized from mantle-derived magma, indicate large degrees of melting and contamination of crust materials in both the granitoids. In combination with the pre-existing geochronological data, the current study indicates that the Garhwal HHCS is characterized by bimodal Neoproterozoic zircons at ca. 1100–900 Ma and ca. 860–800 Ma with wide εHf (t) values which are similar to those in the outer LHS and the Cathaysia Block (including the Jiangnan Orogen) of the South China Craton. These observations suggest that a close relationship existed between North India and South China during the Neoproterozoic since Tonian. The provenance of the Neoproterozoic HHCS is possibly a mixed source from both southern Gondwana terranes (e.g., east Antarctica) and northern South China.

Interpretation of deformation microstructures in syntectonic granite: insights from Phulad granite, Rajasthan, NW India

Interpretation of deformation microstructures in syntectonic granite: insights from Phulad granite, Rajasthan, NW India

An Integrated Approach to Quantify Changes in NW Indian Himalayan Ice and Snow in Large Spatial Extent

An Integrated Approach to Quantify Changes in NW Indian Himalayan Ice and Snow in Large Spatial Extent

Concealed architecture, volcanism and tectonics of Deccan LIP related alkaline complexes of Rajasthan, NW India: Constrained from high resolution aero-geophysical data

In the north-western Indian shield two important alkaline complexes (Sarnu-Dandali and Mer-Mundwara) are linked to end-Cretaceous Deccan large igneous province (LIP) bear significance for REE mineralization, CO2 outgassing and mass extinctions near the K-Pg boundary. Although both of them bear numerous similarities, but, the geomorphology and magmatic emplacement are quite conflicting. Here, the subsurface crustal architecture of these two alkaline complexes is reported for the first time on the basis of high resolution airborne geophysical anomaly data (magnetic and spectrometric). Aeromagnetic anomalies distinguish prominent NW-SE and E-W trending linear deep seated crustal structures in the Sarnu-Dandali alkaline complex. The E-W trending structure mimics the older tectonic tendencies of the regional crustal-scale Narmada-Tapti tectonic zone. The NW-SE trending linear are linked to subsurface rift-oblique networks of fault systems of the petroliferous Barmer basin. The ensemble of numerous fracture patterns at various depths may attest to the rejuvenation of fracture systems and recurrent magmatism, leading to the polychronous nature of Sarnu-Dandali alkaline complex. On the contrary, the Mer-Mundwara alkaline complex exhibits broad magnetic circular features representing the deeper sections of a magmatic plumbing system. The geometry also resembles the subsurface magma chambers for Deccan basalt volcanism, occurring as rootless cones. Paleo stress pattern is derived from the fractures and when compared with the results obtained from geophysical data, these analyses demonstrate a high degree of compliance, reinforcing the validity and accuracy of both methods. Further, the inversion modeling, profile depth analysis and computed Euler depth solutions led us to infer that the subsurface magma sources of the Sarnu-Dandali are deeper than those of the Mer-Mundwara alkaline complex.

U–Pb geochronology and metamorphic history of gneissic rocks from Sarwar‐Junia Fault Zone, Rajasthan, NW India: Implications for the tectonothermal evolution of the Aravalli‐Delhi Mobile Belt

The gneisses of the Sarwar‐Junia Fault Zone (SJFZ), in the Mangalwar Gneissic Complex, a part of the Banded Gneissic Complex (BGC‐II) of northwest India recorded two phases of metamorphism. The pelitic gneiss from SJFZ mainly consists of biotite, sillimanite, garnet, quartz, K‐feldspar and plagioclase. On the other hand, the granitic gneiss from SJFZ mainly consists of quartz, plagioclase, K‐feldspar and biotite. From zircon and monazite geochronology, the protolith of pelitic gneiss was deposited on basement granitic gneiss and the metamorphism occurred at ca. 950 Ma affecting both the granitic gneiss and the pelitic gneiss. Estimation of the P‐T conditions of metamorphism and pseudosection modelling of the pelitic gneiss revealed that the peak stage metamorphic condition of M2 culminated at ~850°C and ~7 kbar pressure followed by a near‐isobaric cooling. Large garnet porphyroblasts in contact with retrograde biotite shows Fe‐Mg resetting close to the core region, which implies a slow cooling. Therefore, the possible exhumation during the subduction‐collision tectonics was very slow, if not completely ceased, at ca. 950 Ma. The shared tectonothermal history of the Sandmata Metamorphic Complex and Mangalwar Metamorphic Complex in the BGC‐II is now evident from the present study of the SJFZ, and confirms the presence of Grenvillian‐aged tectonothermal events in the eastern part of BGC‐II. The abovementioned near‐isobarically cooled and hydrated crust of the SJFZ records subsequent event(s) of shallow crustal brittle faulting as evident by the presence of pseudotachylyte veins and cataclastic fabric observed in the studied gneisses. Brittle faulting possibly occurred between ca. 905 Ma and ca. 750 Ma, as interpreted from the present geochronological data.

Paleostress analysis and rift kinematics of the petroliferous Barmer rift basin, western Rajasthan, India

The NW-trending Barmer rift in western Rajasthan is one of the major petroliferous Indian basins. The basin rifted twice: (i) NW – SE extension in Early Cretaceous, and (ii) NE – SW extension during Late Maastrichtian to Early Paleogene. We performed structural fieldwork mainly along the rift margins to decipher the rift kinematics through geologic time. We collected ∼500 fault-slip data from limited outcrops along the basin's western and eastern margins. Paleostress analysis was performed for the first time in this basin using Win_Tensor, T-Tecto and FaultKin software. The outcome of this analyses shows that a strike-slip stress regime was prevalent in the western rift margin whereas the eastern margin experienced extension to transtension. Four paleostress regimes, DΔ, Dα, DΦ, and Dβ, were identified by inverting the fault-slip data. The two separate extensional regimes, during the Early Cretaceous and in the Late Maastrichtian to Early Paleogene, are confirmed. These are Dα (NW – SE extension) and Dβ (NE – SW extension). The analysis also presents two strike-slip regimes with varying maximum horizontal stress (SHMax) orientation, viz. DΔ and DΦ. Exact age correlation for these strike-slip regimes remains indeterminate. However, we deduced DΔ and DΦ were associated with the first extensional phase (Dα) during Early Cretaceous linked to India – Madagascar oblique separation. The Barmer rift extended obliquely guided by pre-existing structures. Remote sensing image analysis indicates that part of the western margin is neotectonically active as inferred from the drainage morphometry. The stress inversion analysis of earthquake focal mechanism data depicts a strike-slip transpressive regime prevailing at present in the NW India along with ∼ N-trending SHMax. This is mainly responsible for the neotectonic activities in the basin. We documented several fault gouge zones along moderately-dipping faults in the Cretaceous outcrops at the eastern margin. The lower the fault dips, the thicker the gouge zones associated with the faults. Such thick fault gouge of around 100 cm or more may act as a structural fault bound trap for Cretaceous reservoirs at depth. (Words: 324).

Geochemistry of Hindoli Group Metasediments, SE Aravalli Craton, NW India: Implications on Provenance Characteristics and Tectonic Setting

Abstract The NE-SW trending Jahazpur Belt in NW India has been considered correlative with the Aravalli Fold Belt, based on lithological similarities and greenschist facies metamorphic assemblages. The 2.54 Ga ‘Jahazpur Granite’ constitutes the basement for the overlying Hindoli and Jahazpur Group sediments in this belt. These meta sedimentary sequences presently occur as a greenschist facies ensemble of phyllite, marble, greywacke, and meta-conglomerate. In this study, the trace and Rare Earth Elements geochemistry of the Paleoproterozoic Hindoli Group metapelites and metagreywackes was evaluated for source characterization and tectonic setting. The transition metals and Th, La abundances, and Th/Sc, Zr/Sc and La/Sc ratios (1.19 and 1.5, 21.31 and 17.35 and 4.02 and 2.97, for metapelites and metagreywackes, respectively) of Hindoli Group suggest a felsic source for them and some degree of sediment maturity. Both Hindoli metapelites and metagreywackes are enriched in LREE and display significant negative Eu anomalies, further substantiating a predominant felsic component in the source region. The provenance modeling calculations indicate that the detritus was mainly sourced from Mangalwar Complex, along with some inputs from Jahazpur Granite, Bundelkhand TTG and Hindoli volcanics. Geochemical characteristics also discriminate a continental collision associated with an Active Continental Margin tectonic setting for the deposition of Hindoli sediments.

Omphacite breakdown, symplectite formation and carbonate metasomatism in a retrograded continental eclogite: Implications for the exhumation of the Tso Morari Crystalline Complex (Trans-Himalaya, NW India)

The India-Eurasia collision zone in eastern Ladakh, India, is marked by the Tso Morari Crystalline Complex (TMCC), which underwent continental subduction, eclogite grade metamorphism, and rapid exhumation during the Himalayan orogeny. The TMCC is characterized by eclogitic enclaves, metamorphic evolution of which has been extensively studied in the past. Detailed petrography, mineral chemistry, Raman spectroscopy, and P-T-X pseudosection modelling of two such eclogite samples from the core and western margin of TMCC were carried out to address the differences and discrepancies from previous studies. Our study suggests peak metamorphism at ∼2.75 ± 0.1 GPa and ∼550 ± 50 °C, followed by a decompression stage at ∼1.50 ± 0.1 GPa and ∼580 ± 50 °C and subsequent high-temperature overprint at ∼0.85 ± 0.1 GPa and ∼680 ± 50 °C. Fine-grained grain boundary omphacite + garnet + amphibole symplectite colonies indicate exhumation along with fluid infiltration. The transition of omphacite into a more calcic variety and its subsequent replacement with amphibole are also observed. Presence of diopside + plagioclase symplectite indicates post-peak decompression and fluid infiltration. Carbonates in the matrix as veins and within fractures indicate late-stage fluid infiltration and metasomatism. Our study shows that lawsonite and/or Na-amphibole have not played any significant role in the metamorphic evolution of TMCC. In contrast to most of the previous studies carried out in TMCC, we opine that omphacite breakdown and metasomatism through externally derived carbonaceous fluids played a vital role in the exhumation and retrogression. We further opine that our mineral chemistry data and metamorphic modelling resemble a continental eclogite and mark differences from oceanic eclogites.

Unsupervised machine learning-based prospectivity analysis of NW and NE India for carbonatite-alkaline complex-related REE deposits

Rare Earth Elements (REE) form critical raw materials in environment-friendly, high-technology devices and components, and therefore have been classified as “critical minerals and metals” by most countries. About 62% of the global resources of REE occur associated with carbonatite-alkaline complexes; however, the entire production of REE in India currently comes from secondary deposits, even though India contains a variety of REE-enriched primary source rocks, particularly carbonatites and alkaline complexes. There is, therefore, a significant potential in the county for new REE deposit discoveries associated with carbonatite-alkaline complexes. This research attempts to identify exploration targets for REE associated with carbonatite-alkaline complexes in northern India utilising a Self-Organising Maps (SOM)-driven workflow. This unsupervised machine-learning-based workflow eliminates the hand-crafting of input predictor features. The algorithm creates clusters of features directly from primary gridded geophysical and topographical datasets. The obtained clusters are then analysed based on available geological knowledge and empirical spatial associations with known occurrences in the study areas to identify prospective clusters and generate prospectivity maps. Nine new targets are identified across the Shillong plateau in northeastern and Western Rajasthan in northwestern India. These new targets, in addition to the known carbonatite-alkaline complexes, are recommended for further data collection and follow-up exploration. It is noteworthy that these targets conform to the targets identified by Aranha et al. (2022a, 2022b) using mineral systems-guided fuzzy inference systems.

Favourable IOCG and polymetallic environs in Marwar - Khetri, NW Indian Shield imprints from aerogeophysical data analysis

The analysis of aeromagnetic data reveals two significant broad oval-shaped aeromagnetic anomalies oriented in the NE-SW direction, west of Laxmangarh and east of Fatehpur. These significant anomalies identified beneath sand-alluvium-covered areas of Rajasthan's Marwar region are of a low dominance nature. These magnetic signatures are associated with gravity gradients in the regional Bouguer gravity map. Magnetic anomalies and subsurface modeling revealed that the remanence source had a high magnetic susceptibility. The ground gravity profiles across the Laxmangarh anomaly show a high gravity variation of 5 mGal/km. The integration of geochemical distribution patterns, spectrometric elemental concentrations, different ratios, and composite image maps has brought out alteration/shear zones that are favourable for mineralization. The results of selective 2D-profiles, plate modeling, and 3D-inversion modeling of these anomalies reveal that the depth of the causative source varies from 300 to 1000 m. The higher-order magnetic susceptibilities, geochemical dispersion pattern, and spectrometric ratio maps and composite images distinguished hydrothermal alteration zones characterised by potassium enrichment. The results indicate the possibility of concealed source rocks with high magnetic mineral content (magnetite, maghemite, titanomaghemite, pyrrhotite, and franklinite?) and a relatively high density. The geophysical signatures observed around Fatehpur and Laxmangarh, with high magnetic contrast, low dominance, and remanence coupled with high gravity values, as well as hydrothermal alteration zones, appear to have striking similarities with the geophysical and geochemical scenarios of some of Australia's Iron Oxide Copper-Gold (IOCG) prospects in the Gawler, Arunta, Tennant, and Mount Isa regions. Therefore, these anomalous areas may be explored for the possibilities of an IOCG or polymetallic type of mineral.

Geochemical constraints on the provenance and tectonic setting of metasedimentary rocks from the South Delhi Supergroup, NW India: implications for tectonic evolution of western margin of the Aravalli orogen

ABSTRACT The provenance and tectonic setting of the Stenian (<1200 to 1015 Ma) metasedimentary sequences of the South Delhi Supergroup, NW India, are least understood and thus debatable. The results of this study show that the protoliths of the metasedimentary rocks received detritus dominantly from felsic sources, particularly from Mesoproterozoic granitoids exposed in northern and eastern India. The weathering indices suggest low to moderate weathering in the source areas and that the sediment compositions reflect mixing of provenance components having different compositions. Overall, the REE patterns of the South Delhi rocks are similar with variable negative Eu anomalies and absolute ∑REE contents. The low REE abundances in the quartzites are the consequence of quartz dilution during hydraulic sorting. The tectonic multidimensional discrimination diagrams suggest a passive margin setting for the South Delhi metasedimentary rocks, which is in consonance with the detrital zircon age spectra and regional geology of the western margin of Aravalli orogen, NW India.

Early Neoproterozoic tectonics in the Marwar Crustal Block, NW India, the relevance of the Phulad Shear Zone, and implications for Rodinia reconstruction

Abstract Palaeomagnetic studies in the Malani Igneous Suite (ca. 770–750 Ma) of the Marwar Crustal Block, NW India, provide essential constraints on palaeogeographic reconstructions of the Rodinia Supercontinent. The Malani Igneous Suite is intrusive into megacrystic granite and granitegneissic enclaves of the Marwar Crustal Block. A crustalscale NE–SW ductile transpressional shear zone with a southeasterly dip known as the Phulad Shear Zone (820–810 Ma) separates this Marwar Crustal Block from the rocks farther east. The preshearing tectonic evolution of the Marwar Crustal Block is poorly understood. Three phases of ductile deformations (D1, D2, and D3, with associated fabrics S1, S2, and S3) were identified in the Marwar Crustal Block. The D1 deformation is restricted to enclave gneisses. The megacrystic granite was emplaced syntectonically during D2 deformation. The S2 magmatic foliation (NNW–SSE) in the megacrystic granite is oblique to the Phulad Shear Zone. The D3 deformation in the megacrystic granite is synchronous with the Phulad Shear Zone mylonites. Another porphyritic granite (Phulad granite, ca. 820 Ma) emplaced syntectonically during D3 deformation along and across the Phulad Shear Zone. U-Pb zircon dates in the Marwar Crustal Block document ca. 890 Ma and ca. 860 Ma magmatic dates. U-Pb-Th monazite dates in the Marwar Crustal Block show a strong peak at ca. 820 Ma. By integrating critical field relations, deformational patterns, and geochronology, we argue that the Marwar Crustal Block shows distinct geological evolution prior to its accretion with the remaining parts of India. We propose that the accretion of the Marwar Crustal Block must be younger than ca. 860 Ma and culminated during ca. 820–810 Ma to form the Greater India landmass along the Phulad Shear Zone.

The absence of remotely triggered seismicity in Gujarat, NW India during the Nepal earthquake, 2015

Gujarat in the Northwestern Deccan Volcanic Province of India is among the most seismically earthquake-prone. The region may be susceptible to remote dynamic triggering, especially the Kachchh region, which recently hosted the Mw7.7 Bhuj earthquake in 2001. Its aftershocks continue because it is critically stressed and contains nucleation points more frequently close to failure. From waveforms and catalog data, we examine whether remote dynamic triggering occurs following 25 April 2015, Mw7.8 Nepal mainshock in the Gujarat region, Northwestern India. The 2015 Nepal event perturbed the Gujarat region with a peak dynamic stress of ∼53 kPa, much higher than the global lower limit of 1 kPa. Due to the large magnitude and high peak dynamic stress, ideally, the 2015 mainshock should have resulted in the triggered seismicity in the study region. To study the remote dynamic triggering in detail, we also have examined the other recent regional large earthquakes with comparable peak dynamic stresses (&amp;gt;50 kPa), namely, 16 April 2013, Mw7.7 Iran, 24 September 2013, Mw7.7 Pakistan, and 26 October 2015, Mw7.7 Afghanistan. Our result shows that despite their significant peak dynamic stress, there is no significant change in the local seismicity. The analysis suggests that the surface wave amplitude is not the only factor that governs the remote dynamic triggering. Our results also indicate that the faults were not critically stressed during the mainshock candidates in the study region.

“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.

Zircon U-Pb, whole-rock Rb-Sr and K-Ar ages of metamorphosed and metasomatized paleosol at the base of the Paleoproterozoic Aravalli Supergroup, NW India: A two-billion-year record of tectono-thermal events

The Precambrian paleosols are good proxies for deciphering paleoredox conditions. They are also good indicators of thermal events that affect the metamorphic terrane. The Rb-Sr isochron ages of the Precambrian paleosols are good indicators of the timing of alkali metasomatism. This work presents zircon U-Pb, whole-rock Rb-Sr isochron, and K-Ar ages of a metamorphosed and metasomatized paleosol occurring at the base of the Paleoproterozoic Aravalli Supergroup, Northwestern India, to constrain the time of major thermal events. The Aravalli paleosols (sericite schists) have witnessed a complex history of metamorphism and metasomatism. The LA-ICP-MS U-Pb ages of zircons from the two paleosol samples are 2586 ± 45 Ma and 2793 ± 21 Ma, similar to the zircon ages for the parent Ahar River Granite. Five paleosol samples define an Rb-Sr isochron age of 1394 ± 22 Ma with (87Sr/86Sr)i of 0.7493 ± 0.0034 (2σ) and an MSWD of 3.9, pointing to the timing of the latest alkali metasomatism affecting the paleosols. The whole-rock K-Ar ages of sericite-rich paleosol samples range from 940 ± 30 to 873 ± 25 Ma, corresponding with the emplacement of Erinpura Granite. Thus, the Aravalli paleosol recorded more than two billion years of thermal events in its multi-geochronometers. The correlation between Rb-Sr isotope compositions and REE contents in paleosol samples suggests the REE mobility during K-metasomatism.