Thermal Thellier type palaeointensity (PI) experiments are the most popular technique in determining strength of the past geomagnetic field (GMF). However, the method often encounters high failure rate. Mineral magnetic properties can provide useful information to enhance the success rate. We conducted the first ever detailed mineral magnetic and Thellier type PI experiments on lava flows within a 1250 m stratigraphic section of the largest end-Cretaceous ( 65–66 Ma) Deccan flood basalt. The lava flows mostly contain pseudo single domain (PSD) titano-magnetite/magnetite with, low viscosity index (≤ 5), high/moderate Koenigsberger ratio (Qn > 10/ < 10), isothermal remanent magnetisation parameters typical of ferromagnetic minerals, saturation remanence magnetization to saturation magnetization ratio (Mrs/Ms: 0.05–0.31), coercivity of remanence to coercive force ratio (Hcr/Hc: 1.53–3.72) and a single magnetic component pointing to origin or a minor viscous component during alternating field (AF) demagnetizations,. Their thermomagnetic responses are broadly group into 3 categories. The type 1 displays near perfect reversible heating/cooling curves with high Curie temperatures of 570–600 °C; other two types have either widely separated (type2) or quite dissimilar (type 3) heating/cooling curves. 76 samples from 19 flows were subjected to ZI (Zero field-Infield) experiments with pTRM and pTRM tail checks. 24 samples from eight flows display reasonable NRM-TRM linearity and positive pTRM checks and satisfy strict reliability criteria. 42 samples from 11 flows do not satisfy the reliability criteria. Samples of reliable PI results are all characterized by reversible thermomagnetic behaviour with excellent stability during AF/thermal treatment. Samples that failed to meet reliability criteria possess irreversible/widely separated thermomagnetic heating/cooling curves or poor stability to AF/thermal treatment but not significantly different from the successful samples in other magnetic properties. Thus, thermomagnetic behaviour and stability to AF/thermal treatment appear to be the overweighing factors than other mineral magnetic characteristics that govern the success rate of thermal PI experiments. The PI values of upper normal (29N) flows are relatively higher than the lower reverse (29R) flows; this suggests minor time lag in cooling of successive flows. The time averaged PI estimate is an important end-Cretaceous contribution from the Indian subcontinent to the poorly represented database of southern hemisphere.

Palaeo-monsoon and palaeoclimate conditions over Southeast Asia are a matter of debate despite notable studies on the continental and oceanic sedimentary record. The present study investigates the environmental magnetic and geochemical records preserved in the deep marine sediments of the northeastern (NE) Arabian Sea to elucidate the erosion history of the western Himalayas and its link with the prevailing hydroclimatic conditions since the late Miocene. For this, the sediment core retrieved during International Ocean Discovery Program (IODP) Expedition 355 at Site U1457 in the NE Arabian Sea has been explored. The results reveal that the hydroclimatic conditions were predominantly arid during the late Miocene, except for humid intervals from 6.1 Ma to 5.6 Ma. Humid climate conditions in the Indus River Basin returned during the mid-Pliocene and continued to the Pleistocene with an intense chemical weathering regime from 1.9 Ma to 1.2 Ma. The dominant sediment source to the NE Arabian Sea at Site U1457 during the late Miocene and the Pliocene was the Indus River, while during the Pleistocene, mixed sediments brought by the Indus River and the Peninsular Indian rivers were observed. The sediment contribution from a chemically less altered mafic source (the Deccan basalts) increased between 1.2 Ma and 0.2 Ma, possibly linked to a weak Indian Summer Monsoon. The summer monsoon wind strength and associated shift in the Inter-Tropical Convergence Zone (ITCZ) influenced the dominant sediment provenance at Site U1457 of the Laxmi Basin.

The geodynamic events of continental breakup and origin of northwest Indian Ocean led to the development of passive continental margin, off western India. However, causal mechanisms and relative chronology of these geodynamic events are not clearly known because of complex regional-scale ridges-basin physiography, multistage rifting in a short-time span and thick sediment cover. The Laxmi and adjacent Gop basins constitute key tectonic elements and geophysical investigations on them have come up with sharply divergent explanations of continental rifting and ocean spreading. We present geochemical results of the Laxmi Basin (LB) basement, recovered by the International Ocean Discovery Program Expedition-355 and interpreted in light of existing geophysical results. The basement is identified as continental rift basalt, different from the Deccan/Madagascan basalts. We suggest the basement eruption at similar to 75 Ma causing igneous underplating which triggered the extension/rifting in Laxmi and Gop basins. The rifting translated into ocean spreading only in the Gop Basin and not in the Laxmi Basin. The geodynamic events echoed soon with similar relative chronology in western India with Reunion plume impact and the Deccan eruption followed by second extension/rifting that culminated in India-Seychelles breakup.

A giant mass-transport complex was recently discovered in the eastern Arabian Sea, exceeding in volume all but one other known complex on passive margins worldwide. The complex, named the Nataraja Slide, was drilled by International Ocean Discovery Program (IODP) Expedition 355 in two locations where it is ∼300 m (Site U1456) and ∼200 m thick (Site U1457). The top of this mass-transport complex is defined by the presence of both reworked microfossil assemblages and deformation structures, such as folding and faulting. The deposit consists of two main phases of mass wasting, each consisting of smaller pulses, with generally fining-upward cycles, all emplaced just prior to 10.8 Ma based on biostratigraphy. The base of the deposit at each site is composed largely of matrix-supported carbonate breccia that is interpreted as the product of debris-flows. In the first phase, these breccias alternate with well-sorted calcarenites deposited from a high-energy current, coherent limestone blocks that are derived directly from the Indian continental margin, and a few clastic mudstone beds. In the second phase, at the top of the deposit, muddy turbidites dominate and become increasingly more siliciclastic. At Site U1456, where both phases are seen, a 20-m section of hemipelagic mudstone is present, overlain by a ∼40-m-thick section of calcarenite and slumped interbedded mud and siltstone. Bulk sediment geochemistry, heavy-mineral analysis, clay mineralogy, isotope geochemistry, and detrital zircon U-Pb ages constrain the provenance of the clastic, muddy material to being reworked, Indus-derived sediment, with input from western Indian rivers (e.g., Narmada and Tapti rivers), and some material from the Deccan Traps. The carbonate blocks found within the breccias are shallow-water limestones from the outer western Indian continental shelf, which was oversteepened from enhanced clastic sediment delivery during the mid-Miocene. The final emplacement of the material was likely related to seismicity as there are modern intraplate earthquakes close to the source of the slide. Although we hypothesize that this area is at low risk for future mass wasting events, it should be noted that other oversteepened continental margins around the world could be at risk for mass failure as large as the Nataraja Slide.

Knowledge about long-term variation of the geomagnetic dipole field remains in its nascent stage because of the paucity of reliable experimental data over geological periods. Here, we present the first robust experimental data from the largest Cretaceous flood basalt province on Earth, the ~65–66 Ma Deccan basalt within a thick (1250 m) unbiased stratigraphic section down to the basement, recovered from a drill hole of the Koyna Deep Scientific Drilling Project in the Western Ghats, India. Critical analysis of the result along with similar results of the Cretaceous age find that (i) the dipole moment during the end Cretaceous Deccan eruption is the lowest in whole of Cretaceous (ii) dipole moment at the onset/termination of the Cretaceous Normal Superchron is apparently lower relative to that in mid-superchron, however, such differences cannot be deciphered in shorter polarities probably because of insufficient time to develop recognizable variations (iii) inverse relation between dipole moment and reversal rate is lacking and (iv) a cause and effect relation between core-mantle boundary heat flux and low dipole moment that appears to be the principle governing factor in forming the Large Igneous Provinces on the surface of earth.

NW-SE trending mafic dykes in the Bundelkhand Craton of the Indian shield manifest Palaeoproterozoic igneous activity. These dykes are Fe-rich tholeiitic basalts with compositions varying from near primary melts to more evolved magmas (Mg#: 0.64-0.35) and show enrichment of large-ion lithophile and light rare earth elements relative to primordial mantle values. Despite very subtle variations of elemental abundances and similar structural trend, at least two groups are identified, mainly based on incompatible element ratios and rare earth element patterns. Group 1 samples are characterized by relatively low Ti/Y (av. 222 +/- 22) and Ti/Nb (av. 609 +/- 108), high Zr/TiO2 (av. 117 +/- 15), more light to heavy rare earth element fractionation (La/Vb)(CN): 2.7-5.1) and mild negative Eu anomaly (Eu* = 0.77 +/- 0.10). Group 2 samples possess high Ti/Y (av. 334 +/- 46) and Ti/Nb (av. 1349 +/- 198), low Zr/TiO2 (av. 70 +/- 7) and minor light to heavy rare earth element fractionation ((La/Vb)(CN): 1.5-2.7) without any Eu anomaly (Eu* = 0.97 +/- 0.04). Both groups show relative depletions in Nb, Sr and P while the Group 1 also shows Ti depletion. A third group is apparent but is less certain. Group 2 dykes constitute the 1.98 Ga Jhansi swarm, whilst the Group 1 and unclassified samples are likely to be of older age (similar to 2.18-2.20 Ga and similar to 2.37 Ga) based on available U-Pb ages and palaeomagnetic considerations. Despite the compositions indicate different batches of magma, the dykes have near similar petrogenetic evolutionary pattern as if the entire population constitutes a single clan. Samples of both groups (a) do not indicate significant crustal contamination (b) derived from two different batches of magmas formed by similar to 10-12% fractional melting of mantle near the spinel-garnet transition zone and (c) evolved through initial fractionation of olivine and thereafter clinopyroxene and plagioclase became important fractionation phases. The more primitive compositions of both groups indicate mantle potential temperatures of similar to 1550-1600 degrees C suggesting thermal anomaly. The dyke magmas inherited variably enriched compositions as a result of interaction of upwelling mantle melts with metasomatised subcontinental lithospheric mantle. Low H2O-CO2-rich silicate melts/fluids are likely the dominant metasomatic agents to develop the Indian subcontinental lithosphere in the Archaean (c. 3.0 Ga).

In this paper we have synthesized the published and unpublished geochemical data on the Palaeoproterozoic mafic magmatism in the Indian Shield. Palaeoproterozoic mafic magmatism is widespread in the Indian Shield; it mostly emplaced as dyke intrusions within the cratons and south Indian granulite region and as intrusives/traps in the intra-cratonic basins and the Eastern Ghat Mobile Belt. Integration of the U-Pb ages with palaeomagnetic results identified at least four discrete Palaeoproterozoic igneous events at 2.36-2.37 Ga, 2.1-2.2 Ga, 2.0-2.1 Ga 1.89-1.99 Ga and probably two other events at about 2.4 Ga and 1.8 Ga. The Palaeoproterozoic magmatism across the Indian cratons seems geochemically monotonous and exclusively mafic and sub-alkalic tholeiitic basalt/basaltic andesite in composition with typical enrichment of large ion lithophile and light rare earth elements. Fractional crystallization is the dominant mechanism controlling the geochemical spectrum of the Indian Palaeoproterozoic magmas with little indications ofcrustal assimilation. Asthenosphere mantle is the major supplier of material for the Palaeoproterozoic igneous activity. Sub-Continental Lithosphere Mantle (SCLM) seems to be the major contributor for the enriched characteristics of the Palaeoproterozoic mafic magmas erupted in the Indian Shield. Thermal energy for the initiation of melting is likely contributed by mantle plumes although a passive rifling is not ruled out. Geochemistry of the Palaeoproterozoic mafic magmas in some way appears to have similarities to that of the end-Cretaceous Deccan basaltic magmas and do reflect plume-lithosphere interaction. The SCLM beneath the Indian Shield was possibly enriched by addition offluids/ melts of deep mantle origin. We suggest that the major segments of the Indian SCLM were generated at around 3 Ga coinciding with a major crustal building activity in the Indian shield.

The Western Ghats is one of the largest escarpments on earth, containing Reunion plume derived Deccan Traps, it is an excellent example to probe epeirogenic uplift, extension and subsidence in volcanic continental margins. The most continuous unbiased stratigraphic section of basalt down to the basement within a 1250 m drill hole of the Continental Scientific Deep Drilling Project is a valuable resource to investigate the above aspects. The flows across the entire drill core are geologically subaerial in character with basement exposed ~300 m below the mean sea level; they clearly display more evolved compositions from primary melts of mantle in terms of petrology, and only a single geomagnetic polarity transition in palaeomagnetic data. These results, combined with existing geological and geophysical data, constitute a multi-method approach that demonstrates (a) igneous underplating caused uplift prior to frequently suggested flexural isostasy (b) plume impact and eruption are near-simultaneous and extension/rifting essentially followed soon after volcanism and (c) lithosphere beneath the continental margin, while returning to normal temperatures following the Seychelles-India breakup, experienced thermal collapse and subsidence causing slumping of basalt basement below sea level.

Anorthosite occurrences in the south Indian shield are well known. Recent studies obtained Neoproterozoic age for many of them, yet their petrological and mineralogical data are very limited. This paper presents first comprehensive report of the physical attributes of petrography and rockmagnetism of two prominent anorthosite occurrences, one from the Oddanchatram and the other from theKadavur in the southern granulite terrain of India. Petrography highlights the occurrence of exsolution lamellae of magnetite in plagioclase with clouding appearance in the Oddanchatram anorthosite (ODAN). The Kadavur anorthosite (KDAN) contains magnetite in the form of discrete grains. The distinctions are sharply reflected in the rockmagnetic attributes also. The Oddanchatram occurrence is characterized by high Koenigsberger ratios (Q value mostly >10), median destructive field (MDF > 50 mT) and coercivity of remanence (H-cr; 45-86 mT), dominance of remanence magnetism over induced magnetism, harder natural remanence over saturation isothermal remanence, Curie temperatures of 570-580 degrees C and high ratio of saturation remanence magnetization to saturation magnetization (M-rs/M-s: 0.08-0.35) with low ratio of Hcr to coercive force (H-cr/H-c: 1.78-2.27) as determined from hysteresis loops indicating single (SD)/pseudo-single-domain (PSD) magnetite as the chief magnetic carrier. In contrast, the Kadavur occurrence is characterized by lower Q value (mostly <1), MDF (<10 mT) and H-cr (23-65 mT), dominance of induced magnetism over remanence, harder saturation isothermal remanence over natural remanence, Curie temperatures of 580-600 degrees C and low M-rs/M-s (0.02-0.04) with high H-cr/H-c (2.61-3.76) indicating presence of a dominant multidomain magnetite along with small quantities of canted antiferromagnetic mineral (haemo-ilmenites). These differences in physical attributes are explained in terms of crustal depths of their emplacement. The ODAN possessing SD/PSD exsolved magnetite lamellae in plagioclase formed at deeper levels (>= 6 Kbars; similar to 20 km). The KDAN was emplaced at relatively shallower depths corresponding to pressures of the order of 4-5 Kbars. These differences in depth of emplacement may not be related to differential exhumation, but may indicate differential erosion or an easterly regional tilt.

Garnet is a commonly occurring accessory mineral in many anorthosite plutons, and it is variably interpreted as a metamorphic, magmatic, or xenocrystic mineral. The Neoproterozoic Oddanchatram anorthosite in the South Indian granulite terrain is one such example. Igneous textures are remarkably well preserved, with large grains (up to 5 cm) of garnet in the margins of the pluton. Typical prograde metamorphic textures, such as garnet formation by isobaric reaction between mafic silicate and plagioclase or by dehydration breakdown of amphibole, are lacking, and Fe-Ti oxides mostly occur as exsolutions in the associated plagioclase or scarce disseminated oxide grains. The garnets are almandine rich in composition, with higher CaO (>5 wt%) than the low-CaO (<2 wt%) almandine of garnets in the adjoining metamorphic assemblages. They cannot be described as xenocrysts because of their large size, compared to their smaller size in the country rocks, apart from the chemical distinctions. A reaction of hydrous fluid influx with plagioclase and mafic phases in the anorthosite, as described for similar large-garnet formation in the Adirondacks by McLelland and Selleck, appears to be a more reasonable explanation. The fluid source may be external, released from hydrous minerals of the hornblende-biotite-bearing gneiss country rock during the prograde metamorphism that the terrain experienced, or internal, from the late magmatic enriched hydrous liquids, as evident from primary amphibole. Formation of garnet and exsolution of Fe-Ti oxides appear to have developed when the anorthosite was still at a depth corresponding to upper-amphibolite-facies metamorphic conditions and experienced isothermal decompression and exhumation subsequently, as evidenced by the plagioclase-orthopyroxene symplectite development from garnet.sOnline enhancements: supplemental table.

The paper presents new palaeomagnetic results and reassesses complete set of published palaeomagnetic results on the lamproite intrusions in the Gondwana formations of the Eastern India. Altogether eleven sites register reliable characteristic magnetisations corresponding to the c. 110 Ma emplacement age of the lamproites. A mean ChRM is estimated with D=331.3°; I=−62.4° (α95=6.2°, k=55; N=11). The palaeomagnetic pole of λ=14.9°: Φ=287.6° (A95=8.4°) is established for the lamproites and it averaged the secular variation and confirms to the Geocentric Axial Dipole (GAD). The pole compares remarkably well with the grand mean pole reported for the Rajmahal traps that are attributed to represent location of the Kerguelen mantle plume head. The palaeolatitudes transferred to Rajmahal coordinates (25.05°: 87.84°) are situated ∼6° north of the present location of the Kerguelen hotspot location. The interpretations are consistent with earlier suggestions of southward migration of the plume based on palaeomagnetic results of Site 1138 of the ODP Leg 183 and with the predictions of numerical models of global mantle circulation.

•Pottery samples come from 300–500 BC rare archaeological site in southern India.•Rock magnetic properties confirmed SD/PSD type of ferrimagnetic mineral.•New Archeointensity and Virtual Axial Dipole Model results are present.•New results are compared with recently updated GEOMAGIA.V3 database.

A reassessment of the recent palaeomagnetic data on Proterozoic mafic dykes in the Bundelkhand and Bastar cratons permits a robust estimate of 1.466 Ga (Calymmian) pole (λ = 49.4°N; Φ; = 132.9°E; A 95 = 6.6°; N = 11) for the Indian shield. The pole corresponds to a mean direction of D = 40.5°; I = 56.4° (α 95 = 5.5°; K = 70). The Indian pole at c. 1.65 Ga (Statherian) is suggested to have been situated at λ = 59.6°N and Φ = 47.9°E (A 95 = 8.1°; N = 6); it is estimated from a mean direction of D = 336.4°; I = 66.0°N (α 95 = 5.3°; K = 159). The 1.466-Ga-old dykes are confined to the Eastern Ghats orogenic front in the easternmost part of the Bastar craton. Geochemically, the shoshonitic/high-K calc-alkaline affinity of these dykes is uniquely distinct from the tholeiitic composition found in Mesoor Palaeoproterozoic dykes in other parts of the Indian shield. Testing the existing pre-Rodinia Mesoproterozoic tectonic reconstructions negates the Columbia reconstructions in which the Indian shield is shown in juxtaposition with North China/Laurentia. On the other hand, palaeomagnetic and geological data suggest that the linkages between the Indian shield and Western Australia proposed earlier for the Palaeoproterozoic appear to persist during the Mesoproterozoic as well. The linkages may be further extended into Baltica.