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A vast portion of the plumbing system of the Siberian Traps Large Igneous Province (STLIP) is emplaced in the Tunguska Basin, where borehole data reveal ubiquitous and abundant sills with great lateral extension. These intrusions intersect Cambrian–Ordovician evaporite, carbonate and siliciclastic series, and locally coal-bearing Permian host rocks, with a high potential for thermogenic gas generation. Here we present new geochemical data from 71 magmatic and 4 sedimentary rock samples from the Tunguska Basin center and periphery, recovered from 15 deep sills intercepted by boreholes. The studied samples are all low-Ti basalt and basaltic andesites, confirming absence of high-Ti and alkaline STLIP magmatism in the Tunguska Basin. The sills derive from picritic parental melts produced by extensive melting of a mantle source with recycled crustal components below a thinned lithosphere (50–60 km), within the spinel stability field. The mantle source was dominantly peridotitic, with enriched pyroxenitic domains formed by recycled lower crust, in agreement with previous models for the main tholeiitic STLIP phase. Limited amounts (up to 5%) of highly radiogenic granitoids or moderately radiogenic metapelites were assimilated in upper crustal magma reservoirs. After emplacement, sills intruded in Cambrian evaporites assimilated marlstones and interacted with the evaporitic host rocks, probably via fluids and brines. This is the first time that such process is described in subvolcanic rocks from all across the volcanic basin. The sills are correlated geochemically with the established chemostratigraphy for the on-craton STLIP lava piles and intrusions (Norilsk region). Sills correlated with the Morongovsky–Mokulaevsky Fm. and the Norilsk-type intrusions are the most voluminous, present all across the central Tunguska Basin, and bear the strongest evidence of interaction with evaporites. Massive discharge of thermogenic volatiles is suggested by explosive pipes and hydrothermal vent structures throughout the Tunguska Basin. We propose that this voluminous pulse of magmatism is a good candidate for the hitherto unidentified early intrusive phase of the STLIP, and may link the deep Tunguska basin sills to the end-Permian environmental crisis.

Systematic exploration has delineated significant gold mineralization in the River Reef Zone and the presence of a siliceous body at Watuputih Hill, which is a Poboya gold prospect in Central Sulawesi, Indonesia. The mineralization is hosted within the Palu Metamorphic Complex. The host rocks consist of granite, biotite gneiss, and biotite schist, which is intercalated by feldspar porphyroblastic biotite schist and amphibolitic schist. The X-ray fluorescence (XRF) analysis of the granite and biotite gneiss suggests that the granitic rocks can be characterized as magnesian arc calc-alkaline rocks, with a weakly peraluminous composition. Alteration minerals were analyzed by a combination of petrographic and X-ray diffraction (XRD). In the River Reef Zone, the hydrothermal alteration zones can be sorted by their proximity to the primary fluid conduit and divided into inner, high-T, and low-T propylitic zones. In Watuputih Hill, the hydrothermal alteration can be divided into advanced argillic and argillic zones. The hydrothermal alteration assemblages indicated that the fluid was at a near-neutral pH in the River Reef Zone, whereas the fluid was acidic within Watuputih Hill. Because the hill is relatively distant from the River Reef Zone, the presence of these zones at Watuputih Hill may be indicative of another mineralization system beneath the hill.

Magmatic sheet intrusions contribute significantly to the upper crustal magma transport network. The emplacement mechanism of the magmatic sheets controls the final geometry of the intrusions and the characteristics of host rock deformation. Previous observations have highlighted the preponderance of brittle structures, associated with shallow-level sheet intrusions. However, recent studies have suggested that non-brittle host rock behaviour also occurs, particularly related to the formation of magma fingers during shallow-level sill intrusion. Here, we examine both brittle and non-brittle intrusion mechanisms and expand upon them with field observations from a series of widespread and variable magmatic systems. Non-brittle emplacement appears primarily associated with viscous flow of the host rock during intrusion and is therefore intimately linked to the contemporaneous host rock rheology as well as magma dynamics. Purely brittle and non-brittle emplacement processes are found to be end members with many intrusions containing evidence of both behaviours. Deriving the host rock characteristics is therefore important for discerning potential diagnostic intrusion indicators and intrusion geometries both within the field and in modelling. Incorporation of variable host material behaviours in numerical and analogue modelling, tuned using direct field observations, may consequently further our understanding of the controls on shallow-level intrusion.

More than 600,000 people in the three districts in Rarh Bengal, namely Purulia, Bankura and Birbhum live in fluoride endemic area where dental, skeletal and non-skeletal fluorosis is wide spread. Rarh Bengal is in an extended part of Chotanagpur Plateau in Eastern India. Fluoride content in 727 water samples of drinking water and petrography of 34 rock chip samples from these districts have been studied to understand fluoride in the drinking water. About 1753 households (in 410 villages) were surveyed using stratified random and quota sampling techniques to assess the number of people affected by fluorosis. Fluoride risk analysis was performed by applying the standard fluoride hazard index and fluoride vulnerability index. Results showed that granite gneiss and pegmatite are responsible for release of fluoride ions into the soils and groundwater. About 118 villages in 14 blocks of Purulia, 15 villages in 7 blocks in Bankura and 9 villages in 5 blocks in Birbhum are found to be affected by severe fluorosis.

The major-element chemical composition of garnet provides valuable petrogenetic information, particularly in metamorphic rocks. When facing detrital garnet, information about the bulk-rock composition and mineral paragenesis of the initial garnet-bearing host-rock is absent. This prevents the application of chemical thermo-barometric techniques and calls for quantitative empirical approaches. Here we present a garnet host-rock discrimination scheme that is based on a random forest machine-learning algorithm trained on a large dataset of 13,615 chemical analyses of garnet that covers a wide variety of garnet-bearing lithologies. Considering the out-of-bag error, the scheme correctly predicts the original garnet host-rock in (i) > 95% concerning the setting, that is either mantle, metamorphic, igneous, or metasomatic; (ii) > 84% concerning the metamorphic facies, that is either blueschist/greenschist, amphibolite, granulite, or eclogite/ultrahigh-pressure; and (iii) > 93% concerning the host-rock bulk composition, that is either intermediate–felsic/metasedimentary, mafic, ultramafic, alkaline, or calc–silicate. The wide coverage of potential host rocks, the detailed prediction classes, the high discrimination rates, and the successfully tested real-case applications demonstrate that the introduced scheme overcomes many issues related to previous schemes. This highlights the potential of transferring the applied discrimination strategy to the broad range of detrital minerals beyond garnet. For easy and quick usage, a freely accessible web app is provided that guides the user in five steps from garnet composition to prediction results including data visualization.

Mafic dikes are typically emplaced through primary hydraulic fracturing of undeformed crust or may make use of pre-existing crustal inhomogeneities, representing the plumbing systems of a large igneous province. The Eastern Dharwar Craton has dense exposures of several generations of Paleoproterozoic mafic dike swarms ranging from ca. 2.37 Ga to ca. 1.79 Ga. Herein, using anisotropy of magnetic susceptibility fabric data of mafic dikes and associated host granites, the emplacement systematics of the NW- to W-trending ca. 2.21 Ga Anantapur-Kunigal dike swarm, displaying a radiating geometry, have been studied to understand magma flow dynamics. A low-angle relationship between the silicate and opaque fabrics and good correlation with magnetic lineation, identified via petrographic studies and shape preferred orientation analyses of multiple oriented thin sections, suggest a primary flow-related magnetic anisotropy for the studied dike samples. The classic subparallel relationship between the trend of the dike planes and magnetic fabric of the associated host granites suggests that the radiating geometry of the ca. 2.21 Ga dike swarm was supported by a favourable pre-existing structural grain of the country rock. We interpret the magma for the studied dike swarm was fed laterally from a distant plume. It was emplaced as laterally propagating primary dyke fractures as well as injected into the pre-existing subparallel crustal heterogeneities. Corroborating all these inferences, a detailed emplacement model for ca. 2.21 Ga Anantapur-Kunigal dike swarm is also proposed.

In this article, we discuss the potential of airborne hyperspectral data in mapping host rocks of mineral deposits and surface signatures of mineralization using AVIRIS-NG data of a few important geological provinces in India. We present the initial results from the study sites covering parts of northwest India, as well as the Sittampundi Layered Complex (SLC) of Tamil Nadu and the Wajrakarur Kimberlite Field (WKF) of Andhra Pradesh from southern India. Modified spectral summary parameters, originally designed for MRO-CRISM data analysis, have been implemented on AVIRIS-NG mosaic of Jahazpur, Rajasthan for the automatic detection of phyllosilicates, carbonates and Fe–Mg-silicates. Spectral analysis over Ambaji and the surrounding areas indicates the presence of calcite across much of the study area with kaolinite occurring as well in the north and east of the study area. The deepest absorption features at around 2.20 and 2.32 μm and integrated band depth were used to identify and map the spatial distribution of phyllosilicates and carbonates. Suitable thresholds of band depths were applied to map prospective zones for marble exploration. The data over SLC showed potential of AVIRIS-NG hyperspectral data in detecting mafic cumulates and chromitites. We also have demonstrated the potential of AVIRIS-NG data in detecting kimberlite pipe exposures in parts of WKF.

Petrological observations and major elements analyses in olivine crystals in small xenoliths (>1.5 cm in diameter) from the Jeziorna locality, SW Poland, are presented. The olivines show very large variations in the composition of Mg, Fe, Ca and Ni, which suggests the influence of many possible factors, such as (1) regional variability of the samples; (2) changes in temperature during movement and storage of Cenozoic magmas; (3) weathering; and (4) the interaction of basaltic magma with xenoliths in the mantle or during magma ascent. The latter processes are the final changes recorded in the olivine composition. This study contributes to our understanding of which of the changes in chemical composition can be attributed to these final changes, whether they occur only at the xenolith–host rock contact, or whether they also change the olivine composition inside the xenolith.

A wide number of genetic models have been proposed for volcanically transported ruby and sapphire deposits around the world. In this contribution we compare the trace element chemistry, mineral and melt inclusions, and oxygen isotope ratios in blue to reddish-violet sapphires from Yogo Gulch, Montana, U.S.A., with rubies from the Chantaburi-Trat region of Thailand and the Pailin region of Cambodia. The similarities between Thai/Cambodian rubies and Yogo sapphires suggest a common origin for gem corundum from both deposits. Specifically, we advance a model whereby sapphires and rubies formed through a peritectic melting reaction when the lamprophyre or basalts that transported the gem corundum to the surface partially melted Al-rich lower crustal rocks. Furthermore, we suggest the protolith of the rubies and sapphires was an anorthosite or, in the case of Thai/Cambodian rubies, an anorthosite subjected to higher pressures and converted into a garnet-clinopyroxenite. In this model the rubies and sapphires are rightfully considered to be xenocrysts in their host basalts or lamprophyre; however, in this scenario they are not \"accidental\" xenocrysts but their formation is intimately and directly linked to the magmas that transported them to the surface. The similarities in these gem corundum deposits suggests that the partial melting, non-accidental xenocryst model may be more wide-reaching and globally important than previously realized. Importantly, in both cases the gem corundum has an ostensibly \"metamorphic\" trace element signature, whereas the presence of silicate melt (or magma) inclusions shows they ought to be considered to be \"magmatic\" rubies and sapphires. This discrepancy suggests that existing trace element discriminant diagrams intended to separate \"metamorphic\" from \"magmatic\" gem corundum ought to be used with caution.

The Oligocene to the Miocene was a critical period for the growth of the Tibetan Plateau. This growth is commonly considered to have been controlled by deep geodynamic processes. The ultrapotassic and adakite-like igneous rocks that developed during this period offer constraints on these deep-seated processes in southern Tibet. Whole-rock geochemistry, U-Pb zircon geochronology, and in situ zircon Hf isotopes have been determined for the mafic enclaves and host adakite-like granitoids in the Oligocene Chongmuda-Mingze intrusive complex of southern Tibet. The host rocks, including granodiorite and monzogranite, are mainly high-K and calc-alkaline in composition. Their whole-rock geochemistry (low MgO, Ni, and Cr contents; negative εNd(t) values [-2.5 to -3.4]; and low 87Sr/86Sr(i) values [0.7061-0.7066]) and in situ zircon εHf(t) values (0.6-6.1) indicate that they were derived by partial melting of a juvenile lower crust, implying that the southern Tibetan crust was already thickened to up to 50 km before ∼30 Ma. Mafic enclaves show typical igneous textures, acicular apatites, backveining structures, quenched margins, and crystallization ages identical to those of the host granites, indicating that they are of magmatic origin. The mafic enclaves have high-K to shoshonitic metaluminous compositions and are strongly enriched in large-ion lithophile elements and light rare earth elements, are depleted in high-field-strength elements, have negative εNd(t) values (-2.6 to -4.9), have relatively high 87Sr/86Sr(i) values (0.7060-0.7072), and have low zircon εHf(t) values (2.3-5.5), indicating that they were derived from a relatively enriched lithospheric mantle source. Our new data, together with previously published work, lead us to suggest that deep geodynamic processes below the southern Tibetan region during the Oligocene to the Miocene were characterized by convective removal of the lower lithosphere. Upwelling of the asthenosphere induced by the delamination of the southern Tibetan lithospheric root could have supplied heat to induce anatexis of the residual lithosphere of southern Tibet, generating the adakite-like rocks and related mafic enclaves there.