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Conventionally, volcanic margins have been considered devoid of hydrocarbon, but many discoveries and research in recent past have proved the presence of hydrocarbon prospects within them. However, hydrocarbon exploration within volcanic margin is constrained by seismic imaging. Further, identification of continent to oceanic boundary (COB) is critical to hydrocarbon search as hydrocarbon is found mostly over continental crust. Seaward dipping reflectors, associated with volcano-sedimentary sequences, located along rifted continental margins and represented by highly dipping strong amplitude seismic reflectors, play an important role to study volcanic margins. Keeping in view the problems of hydrocarbon exploration within volcanics, seaward dipping reflectors (SDRs) in Indian context have been studied in detail in this paper. It facilitates mapping of continent-oceanic boundary (COB). It has impact on hydrocarbon prospectivity in volcanic margins as it can provide formidable seal and secondary induced maturity. In India, several discoveries have been made in volcanic margins along west coast, from weathered, fractured basalt and sub-basalt sediments. In the present work, long offset regional seismic data (18 dip lines and 1 cross line), along east coast, have been interpreted. SDRs help in hydrocarbon prospectivity assessment for both discrimination of interbedded sediments and preferential accumulation of hydrocarbon. Mapping of linear features not only helped to demarcate COB but also their presence at 6–10 km depth. For the first time, such comprehensive study on SDRs has been done along Indian peninsular region with indications for hydrocarbon prospectivity at deeper levels along Indian peninsular region. [ABSTRACT FROM AUTHOR]

Rift related magmatism during Permian time in the northern margin of Indian plate is represented by basic dykes in several Himalayan terranes including north western Pakistan. The field relations, mineralogy and whole rock geochemistry of these basic dykes reveal significant textural, mineralogical and chemical variation between two major types (a) dolerite and (b) amphibolite. Intra-plate tectonic settings for both rock types have been interpreted on the basis of low Zr/Nb ratios (< 10), K/Ba ratios (20-40) and Hf-Ta-Th and FeO-MgO-Al2O3 discrimination diagrams. The compositional zoning in plagioclase and clinopyroxene, variation in olivine compositions and major elements oxide trends indicate a vital role of fractional crystallization in the evolution of dolerites, which also show depletion in rare earth elements (REEs) and other incompatible elements compared to the amphibolites. The equilibrium partial melting models from primitive mantle using Dy/Yb, La/Yb, Sm/Yb and La/Sm ratios show that amphibolite formed by smaller degrees (< 5%) of partial melting than the dolerites (< 10%). The trace elements ratios suggest the origination of dolerites from the subcontinental lithospheric mantle with some crustal contamination. This is consistent with a petrogenetic relationship with Panjal trap magmatism, reported from Kashmir and other parts of north western India. The amphibolites, in contrast, show affinity towards Ocean Island basalts (OIB) with a relatively deep asthenospheric mantle source and minimal crustal contribution and are geochemically similar to the High-Ti mafic dykes of southern Qiangtang, Tibet. These similarities combined with Permian tectonic restoration of Gondwana indicate the coeval origin for both dykes from distinct mantle source during continental rifting related to formation of the Neotethys Ocean. [ABSTRACT FROM AUTHOR]

Proterozoic basins in India mostly belong to two periods, viz. Paleo-Mesoproterozoic (~1.9-1.6 Ga) and Meso-Neoproterozoic (1.1-0.7 Ga) periods that show a long hiatus of ~0.5 Ga between the upper and the lower groups. We have considered Mahakoshal - Bijawar, lower Vindhyan and lower Cuddapah (Cuddapah Supergroup) basins in the former group while the latter consists of upper Vindhyan, and upper Cuddapah (Kurnool) basins. They mostly occur along the contemporary Proterozoic collision zones and are sub parallel to them. The Mahakoshal and Bijawar Supergroups occur along the Satpura Mobile Belt (SMB) and Bundelkhand craton, respectively with Bundelkhand craton as basement and are overlain by the Vindhyan Supergroup of rocks along the SMB. They are almost sub-parallel to the mobile bet, SMB. The Cuddapah Supergroup of Paleoproterozoic period and the Kurnool Group of Neoproterozoic period of Cuddapah basin occur along the Eastern Ghat Mobile Belt (EGMB). Based on the exposed contemporary dyke swarms and sills of mafic and ultramafic rocks that are exposed far apart and their extent sub-surface based on geophysical data, it is suggested that a large plume/superplume existed during Paleoproterozoic period (~1.9 Ga) under the Indian continent. It was responsible for the breakup (rifting) of the then cratons and provided margins for deposition of the former older group of rocks with shelf type of sediments and large scale mafic/ultramafic intrusives. The latter younger groups formed during subsequent convergence in Meso-Neoproterozoic period (~1.1-0.7 Ga) as foreland basins on the stable platform of the rifted cratons. That largely explains their undisturbed nature and absence of magmatic rocks. This convergence also caused large scale deformation as folds and faults in the former group of rocks as they collided with adjoining cratons and formed orogenic belts of that time. In the above examples, the Mahakoshal, Bijawar, lower Vindhyan and lower Cuddapah basins of Paleoproterozoic period formed during the rifting phase due to the plume/ superplume while the upper Vindhyan and upper Cuddapah (Kurnool) basins of Neoproterozoic period formed during subsequent convergence as foreland basins. As they formed during different stages of plate tectonics viz. rifting and convergence, they show long hiatus of 0.5-0.6 Ga between the older and the younger groups. The same plume/superplume at 1.9 Ga might also be responsible for the breakup of the contemporary Columbia supercontinent as rocks of similar ages have been reported from other parts of this supercontinent. [ABSTRACT FROM AUTHOR]

The Western Ghats (WG), with an average elevation of ~1.2 km, is one of the greatest escarpments that spans ~1500 km parallel to the west coast of India. It is a mosaic of disparate geological formations having distinct structural and physical characteristics. In this study, the lithospheric structure in terms of crustal thickness, sub-Moho layer and deformation along and across the WG are investigated using receiver functions (RFs) at 30 broadband seismological stations. Techniques like slant stacking, common conversion point imaging and harmonic decomposition are applied to the RFs. Results reveal a large crustal thickness of ~45 km in the central part of the WG, which decreases to ~39 km in the southern and ~ 37 km in the northern parts, in conformity with the geology. The variation in crustal thickness beneath the WG could be due to the effect of hotspot impingement and subsequent rifting mechanism. Further, the RFs reveal a strong sub-Moho low velocity layer (LVL) along the WG. This observation gains support from a previous inference of a low-density zone in the uppermost mantle beneath the west coast of India. Harmonic decomposition of the RFs reveals that this LVL is anisotropic, while the Moho is dipping/ anisotropic in nature. The trend of the symmetry axis of anisotropy (of the LVL) varies from 58.2∘ to 134.4∘, almost perpendicular to the west coast of India. We postulate that the origin of this LVL can be linked to different rifting episodes along the west coast of India, since LVLs are manifestations of thermal/chemical anomalies. These results support the rifting model proposed for the evolution of WG. • Lateral variation in crustal thickness along the WG with a distinct dipping/anisotropic signature. • Consistent sub-Moho LVL exhibits anisotropy with a plunging axis of symmetry perpendicular to the strike of WG. • Results advocate different rifting episodes along the west coast of India as the key causative factor for the evolution of WG. [ABSTRACT FROM AUTHOR]

Highlights: [•] We obtained the frequency-dependent shear wave quality factor Qs (f). [•] Double Spectral Ratio (DSR) method is used for computation. [•] The zone around Son–Narmada–Tapti (SONATA) obtained low Qs value. [•] Regions little away from SONATA are associated with relatively higher Qs value. [Copyright &y& Elsevier]

The article presents a study on the influence of butte detachment to passive margin escarpments (PME) evolution on continental margins of India and North America. The study examined the morphology of the escarpments and drainage networks on the geological margins. Results reveal that the PMEs are patterned on pre-rift structural and lithological heterogeneities. The study concludes that passive margin topography may self-organize by drainage integration because of butte detachments.

Two recent discoveries have greatly impacted understanding relevant to the origination and emplacement of petroleum and natural gas deposits. One discovery, pertaining to hydrocarbon formation from methane broadens significantly potential regions where abiotic petroleum and natural gas deposits might be found. The other, discovery of the physical impossibility of Earth-mantle convection, restricts the range and domain of geodynamic behaviour, and leads to new insights into the formation of petroleum and natural gas deposits. This article highlights the impact and implications of those discoveries, especially as they relate to petroleum and natural gas exploration in India and throughout the world. From the reasoning developed here, the generality of the considerations involved, the understanding developed with respect to the East African Rift System, and the experience garnered from the larger and older Siberian Traps, the prognosis and potential for the region beneath the Deccan Traps of India to eventually become a major source of petroleum and natural gas seems quite favourable. [ABSTRACT FROM AUTHOR]

Abstract: Kutch (northwest India) experienced lithospheric thinning due to rifting and tholeiitic and alkalic volcanism related to the Deccan Traps K/T boundary event. Alkalic lavas, containing mantle xenoliths, form plug-like bodies that are aligned along broadly east–west rift faults. The mantle xenoliths are dominantly spinel wehrlite with fewer spinel lherzolite. Wehrlites are inferred to have formed by reaction between transient carbonatite melts and lherzolite forming the lithosphere. The alkalic lavas are primitive (Mg#=64–72) relative to the tholeiites (Mg#=38–54), and are enriched in incompatible trace elements. Isotope and trace element compositions of the tholeiites are similar to what are believed to be the crustally contaminated Deccan tholeiites from elsewhere in India. In terms of Hf, Nd, Sr, and Pb isotope ratios, all except two alkalic basalts plot in a tight cluster that largely overlap the Indian Ridge basalts and only slightly overlap the field of Reunion lavas. This suggests that the alkalic magmas came largely from the asthenosphere mixed with Reunion-like source that welled up beneath the rifted lithosphere. The two alkalic outliers have an affinity toward Group I kimberlites and may have come from an old enriched (metasomatized) asthenosphere. We present a new model for the metasomatism and rifting of the Kutch lithosphere, and magma generation from a CO2-rich lherzolite mantle. In this model the earliest melts are carbonatite, which locally metasomatized the lithosphere. Further partial melting of CO2-rich lherzolite at about 2–2.5 GPa from a mixed source of asthenosphere and Reunion-like plume material produced the alkalic melts. Such melts ascended along deep lithospheric rift faults, while devolatilizing and exploding their way up through the lithosphere. Tholeiites may have been generated from the main plume head further south of Kutch. [Copyright &y& Elsevier]

Antarctica's Lambert graben, Australia's North West Shelf, and the eastern Indian Peninsula all host thick, fault-bounded Permian-Triassic successions. These terranes were adjacent to each other in Gondwana. The Lambert graben intersects the modern coastline, strikes oblique to shelf architecture, and has a geophysical signature that can be traced >1000 km inland. Vitrinite reflectance data from the graben margins record Permian-Triassic infill. Australia's North West Shelf is the relict of an intracontinental Carboniferous-Permian rift that was infilled during the Permian-Triassic then driven to oceanic completion during Jurassic-Cretaceous Gondwana breakup. This rift was compartmentalized over length scales of ∼650 km, corresponding to accommodation zones, margin-normal geophysical lineaments, and long-lived crustal weaknesses. In eastern India, similar compartmentalization is marked by extensive coal-bearing graben systems. Gondwana reconstructions indicate that the Lambert graben corresponds to the orientation and length scale of Carboniferous-Permian rift compartmentalization. The Lambert graben represents an accommodation zone of a wide intracontinental rift that extended from Australia's North West Shelf, between India and Antarctica, to southern Africa. This rift collected Gondwana's thick Permian-Triassic sedimentary blanket and rich alluvial coal deposits. [ABSTRACT FROM AUTHOR]

Abstract: The Aravalli-Delhi orogen of NWIndia hosts extensive bodies of mafic metavolcanics within the Archaean Banded Gneissic Complex (BGC) basement and in the Proterozoic supracrustal belts of Bhilwara, Aravalli, Jharol and Delhi. All metavolcanics within the supracrustal belts are tholeiites, except for the samples from Basantgarh area of Delhi belt which are calc-alcaline. Certain incompatible trace elements ratios (e.g. Nb/Zr, Y/Zr, Ce/Nd, etc.) show clear distinctions between the various belts as well as within the Delhi metavolcanics. The Bhilwara and Aravalli samples show LREE-enriched patterns, whereas the Delhi samples show a wide variation from slightly depleted through flat to highly fractionated patterns. Comparison of multi-element spidergrams with those of various tectonic setting provides support for the plate tectonic model proposed by Sugden et al. (1990) based on geological and structural data. The tholeiitic metavolcanics of the Bhilwara belt erupted along the incipient divergent margin within the Archaean BGC, continent and the basal Aravalli metavolcanics along its rifted western boundary. The Delhi belt metavolcanics support the evaluation of the Delhi island arc through eastward subduction and emplacement of the Basantgarh-Ajari metavolcanics close to the suture on the western fringe of the arc, and those of the Ambaji-Deri region along back arc spreading zones where protracted rifting led to the development of the Ajabgarh basin and eventual emplacement of gabbro-syenite plutons. [Copyright &y& Elsevier]