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The association between Large Igneous Provinces (LIPs) and mass extinctions and anoxic events is attributed to the radical climatic changes in Earth. Even though the Early Cretaceous Paraná–Etendeka Igneous Province has a comparable erupted volume (>1 Mkm3) to other LIPs (e.g., Deccan, Emeishan and Siberian Traps), it remains controversial why this LIP did not contribute to a mass extinction and whether it is associated with the Weissert Event. This work presents new 40Ar/39Ar dating over a 425-m vertical stratigraphic profile (out of 1,000 m) that spans three formations of the PE-LIP in southern Brazil (low-Ti Vale do Sol, high-Ti Urubici, and high-Ti Palmas). Our data demonstrate that this mafic lava pile was emplaced in c. 2.0 m.y., from c. 135.5 Ma to c. 133.5 Ma, and endorse the hypothesis that the basaltic and andesitic flows of the Vale do Sol Formation (peak of mafic magmatism) contributed to the Weissert Event.

Potential field and Slingram data alongside rock physical properties, drill‐core information and results from geological field mapping were used to investigate the geometry of the geological structures in the Gallivare area in regional scale. The main purpose of this study was to delineate the vertical and lateral extension of the Malmberget felsic volcanic rocks, the Dundret and Vassaravaara units as well as geological structures related to the crustal‐scale Nautanen deformation zone. Furthermore, we aimed at identifying new magnetite‐hematite and sulphide mineralizations and lithologies related to the mineralizations based on the results from regional‐scale potential field modelling which are delineated with rock physical properties and borehole data. The study result indicated that the dome‐shaped Dundret gabbro extends downwards to ∼4 km depth and has its maximum depth at its centre. Hematite and magnetite assemblages occur within the top 2 km of the Dundret complex. Felsic volcanic rocks in the Malmberget area extend vertically down to a maximum depth of ∼3 km and get considerably thinner towards the west. The model for the known magnetite‐rich mineralizations in Malmberget was inferred from earlier drilling activities and was integrated into the profile models, which indicates a reasonable fit to the measured data, in particular on the magnetic anomaly; whereas the small dimensions of the modelled structures make them invisible on the Bouguer anomaly data. Additional magnetite‐rich mineralizations are suggested within the Malmberget felsic rocks. High real component and low imaginary response of the Slingram data suggests conductive zones within the Nautanen deformation zone towards the NE, which given the geology of the area in the high strain zone can indicate disseminated sulphide mineralizations. Drill‐hole data at the eastern parts of W‐E profiles agreed well with the suggested model inferred from potential field data, suggesting presence of mafic intrusions within the ∼top 1 km of the subsurface. The integrated model based on geophysical, petrophysical and geological data improved earlier understanding about the regional geometry of the key structures in the Gallivare area and indicates new magnetite‐rich and sulphide mineralization prospects which can be used as a guide for future exploration activities in the area.

100 TiO2/Al2O3 versus 100 Fe2O3/Al2O3 (a), 100 TiO2/Al2O3 versus 100 TiO2/Fe2O3 (b); La/Sc versus Co/Th (c), and Cr/Th versus Th/Sc (d) diagrams of the basement rocks in the Xiangshan area. Those diagrams show the chemical compositions of protoliths for the Proterozoic sedimentary rocks in the Xiangshan area displaying intermediate‐acid affinity which were composed of 90–70% felsic rocks and 10–30% mafic rocks.

High-pressure (HP) granulites provide telling records of mineral reactions at upper mantle to lower crustal levels and key information on the fate of material in subduction systems. The latter especially applies when they abut eclogite and mantle dunite because such rock associations are crucial for understanding the incompletely known processes at the interface of converging plates. A continental arc, active c. 520-395 Ma ago, formed an enigmatic example of such a rock association in the Songshugou area, Qinling Orogen. To unravel the juxtaposition of the distinct rocks, this study combines petrography, phase equilibria modelling, conventional thermobarometry, and zircon U-Th-Pb-Ti-REE analysis. Two mafic HP granulites, which contain the mineral assemblages garnet-clinopyroxene-plagioclase-rutile-mesoperthite-quartz and garnet-clinopyroxene-plagioclase-rutile, experienced peak metamorphic conditions of ≤1.4 GPa, 860°C and ~1.3 GPa, ≥910°C, respectively. During decompression and cooling, at 489 ± 4 Ma, amphibole lamellae unmixed from a clinopyroxene solid solution and orthopyroxene in part replaced garnet. A felsic HP granulite shows equilibration of garnet, perthite, antiperthite, kyanite, quartz, and rutile at 810-860°C, ~1.2 GPa, sillimanite growth during decompression, and upper amphibolite facies cooling at 510 ± 4 Ma. Though the thermobarometric data are just within the methodological errors, the U/Pb zircon ages imply the HP granulites did not evolve coherently. The HP granulites either represent foundered lower arc crust or originated from subduction erosion because their geochemistry is indistinguishable from that of the hanging-wall plate. Published and new pressure-temperature-time-deformation paths converge at ~710°C, ~0.9 GPa, and ≲470 Ma, implying exhumation tectonics juxtaposed the HP granulites with a melange of eclogite and mantle dunite at lower crustal levels. This study highlights that lower arc crust can comprise material of diverse evolution.

Fifteen Lower Permian siliciclastic rocks from central Tibet were analysed for the major and trace elements, and ten samples among them were chosen for determination of Nd isotopic compositions. They are characterized by low concentrations of SiO2 and low ratios of SiO2/Al2O3, moderate abundances of Fe2O3 + MgO (mudstones, 7.28-9.72 wt.%; sandstones, 4.62-10.02 wt.%) and TiO2 (mudstones, 0.55-0.95 wt.%; sandstones, 0.53-0.99 wt.%), significant enrichments of light rare-earth elements (LREEs) relative to the heavy REEs (HREEs; average (La/Yb)(N) = 9.8 [mudstones] and 9.48 [sandstones]), flat HREE distribution, obvious negative Eu anomalies (average Eu/Eu* = 0.68), higher Th/Sc and La/Sc ratios, and negative initial epsilon(Nd) values (on average -7.2 and -8.5 for sandstones and mudstones, respectively). The mixing modal analysis based on some elemental pairs and Nd isotopic composition, respectively, Nd depleted mantle model age (T-DM) and initial epsilon(Nd) values, uniformly indicates that about 30-40% mafic materials could have been added into these sedimentary rocks. These siliciclastic rocks could have formed in a setting of rifting between the Lhasa and Qiangtang blocks, when a 280 Ma mantle plume upwelling event was occurring in northern Gondwana.

A systematic dataset of petrography, mineralogy, geochronology, and geochemistry is reported for the enclave-bearing calc-alkaline I-type granitoids from the Chinese Altai, Central Asian Orogenic B...

Field and geochemical observations of the granitoids of the Homrit Waggat area in the central Eastern Desert of Egypt reveal two magmatic phases. The early phase of weakly deformed subduction‐related calc‐alkaline rocks includes tonalite and granodiorite. We name the later phase the Homrit Waggat Pluton (HWP); it includes undeformed syenogranite, alkali feldspar granite, and minor albitized granite. The tonalite and granodiorite have distinct negative Nb–Ta anomalies and lower alkalis, REE, Nb, Zr, and Hf than the HWP. The early magmatic pulse is a subduction‐related suite, likely generated by underplating of mantle‐derived magmas that triggered partial melting of mafic lower crust; mixing of these melts led to intermediate magma that further fractionated to tonalite and granodiorite. The HWP granites of the late magmatic pulse are transitional from a subduction‐related to an anorogenic within‐plate environment, plausibly generated by post‐collisional lithosphere delamination. Although the parent magma of the HWP was I‐type, extensive fractional crystallization produced residual liquids with A₂‐type character. Albitized granites are found only along the outer margin of the HWP, and contacts with the alkali feldspar granite are gradational, suggesting fluid interactions at a late stage of crystallization. The original textures of the albitized granites are preserved, but their bulk composition was modified by the production of Na‐rich minerals and the removal of K, REE, and some trace elements by fluids.

In 2017, the Metal Earth multi‐disciplinary exploration project acquired a total of 921 km of regional deep seismic reflection profiles and 184 km of high‐resolution seismic reflection profiles in the Abitibi and Wabigoon greenstone belts of the Superior province of Canada. The Abitibi belt hosts several world‐class mineral deposits, whereas the Wabigoon has sparse economic mineral deposits. Two high‐resolution surveys in the Swayze area, a poorly endowed part of the western Abitibi greenstone belt, served as pioneer surveys with which to better understand subsurface geology and design a strategy to process other surveys in the near future. Swayze seismic data were acquired with crooked survey geometries along roads. Designing an effective seismic processing flow to address these geometries and complex geology required straight common midpoint lines along which both two‐dimensional prestack dip‐moveout correction and poststack migration processing were applied. The resulting seismic sections revealed steeply dipping and subhorizontal reflections; some correlate with folded surface rocks. An interpreted fault/deformation zone imaged in Swayze north would be a target for metal endowment if it extends the Porcupine–Destor structure. Because of the crooked line geometry of the surveys, two‐dimensional /three‐dimensional prestack time migration and swath three‐dimensional processing were tested. The prestack time migration algorithm confirmed reflections at the interpreted base of the Abitibi greenstone belt. The swath three‐dimensional images provided additional spatial details about the geometries of some reflections, but also had less resolution and did not detect many reflectors observed in two dimensions. Geological contacts between felsic, mafic and ultramafic greenstone rock layers are thought the main cause of reflectivity in the Swayze area.

Sample decomposition using inverse aqua regia at elevated temperatures and pressures (e.g., Carius tube or high‐pressure asher) is the most common method used to extract highly siderophile elements (HSEs: Ru, Rh, Pd, Re, Os, Ir, Pt and Au) from geological samples. Recently, it has been recognised that additional HF desilicification is necessary to better recover HSEs, potentially contained within silicate or oxide minerals in mafic samples, which cannot be dissolved solely by inverse aqua regia. However, the abundance of interfering elements tends to increase in the eluent when conventional ion‐exchange purification procedures are applied to desilicified samples. In this study, we developed an improved purification method to determine HSEs in desilicified samples. This method enables the reduction of the ratios of isobaric and polyatomic interferences, relative to the measured intensities of HSE isotope masses, to less than a few hundred parts per million. Furthermore, the total procedural blanks are either comparable to or lower than conventional methods. Thus, this method allows accurate and precise HSE measurements in mafic and ultramafic geological samples, without the need for interference corrections. Moreover, the problem of increased interfering elements, such as Zr for Pd and Cr for Ru, is circumvented for the desilicified samples.

Biotite‐rich selvedges developed between mafic schollen and semipelitic diatexite in migmatites at Lac Kenogami in the Grenville Province of Quebec. Mineral equilibria modelling indicates that partial melting occurred in the mid‐crust (4.8–5.8 kbar) in the range 820–850°C. The field relations, petrography, mineral chemistry and whole‐rock composition of selvedges along with their adjacent mafic schollen and host migmatites are documented for the first time. The selvedges measured in the field are relatively uniform in width (~1 cm wide) irrespective of the shape or size of their mafic scholle. In thin section, the petrographic boundary between mafic scholle and selvedge is defined by the appearance of biotite and the boundary between selvedge and diatexite by the change in microstructure for biotite, garnet, plagioclase and quartz. Three subtypes of selvedges are identified according to mineral assemblage and microstructure. Subtype I have orthopyroxene but of different microstructure and Mg# to orthopyroxene in the mafic scholle; subtype II contain garnet with many mineral inclusions, especially of ilmenite, in contrast to garnet in the diatexite host which has few inclusions; subtype III lack orthopyroxene or garnet, but has abundant apatite. Profiles showing the change in plagioclase composition from the mafic schollen across the selvedge and into the diatexite show that each subtype of selvedge has a characteristic pattern. Four types of biotite are identified in the selvedges and host diatexite based on their microstructural characteristics. (a) Residual biotite forms small rounded red‐brown grains, mostly as inclusions in peritectic cordierite and garnet in diatexite; (b) selvedge biotite forms tabular subhedral grains with high respect ratio; (c) diatexite biotite forms tabular subhedral grains common in the matrix of the diatexite; and (d) retrograde biotite that partially replaces peritectic cordierite and garnet in the diatexite. The four groups of biotite are also discriminated by their major element (EMPA) and trace elements (LA‐Q‐ICP‐MS) compositions. Residual biotite is high in TiO2 and low in Sc and S, whereas retrograde biotite has high Al2O3, but low Sc and Cr. Selvedge and diatexite biotite are generally very similar, but selvedge biotite has higher Sc and S contents. Whole‐rock compositional profiles across the selvedges constructed from micro‐XRF and LA‐Q‐ICP‐MS analyses show: (a) Al2O3, FeO, MgO and CaO all decrease from mafic scholle across the selvedge and into the diatexite; (b) Na2O is lowest in the mafic scholle, rises through the selvedge and reaches its maximum about 20–30 mm into the diatexite host; (c) K2O is lowest in the mafic scholle and reaches its highest value in the first half of the selvedge, then declines before reaching a higher, but intermediate value, about 20 mm into the diatexite. Of the trace elements, Cs and Rb show distributions very similar to K2O.

Rocks of ophiolitic affinity occurring in east Arunachal Pradesh, India consist of a number of dismembered units of mantle peridotites, mafic intrusives, amphibolites, volcano-sedimentaries and met...

Xenoliths of plutonic rocks sporadically torn off by erupting magmas are known to carry valuable information about volcano plumbing systems and the lithosphere in which they emplace. One of the main steps to interpret such information is to quantify the pressure and temperature conditions at which the xenolith mineral assemblages last equilibrated. This chapter discusses some aspects of geothermobarometry of mafic and ultramafic rocks using the xenolith populations of Hualalai and Mauna Kea volcanoes, Hawaii, as case studies. Multiple- reaction geobarometry, recently revisited for olivine + clinopyroxene + plagioclase  spinel assemblages, provides the most precise pressure estimates (uncertainties as low as 1.0 kbar). An example is shown that integrates these estimates with calculated seismic velocities of the xenoliths and the available data from seismic tomography. The results allow to better constrain some km-scale horizontal and vertical heterogeneities in the magmatic system beneath Hawaii. Ultramafic xenoliths at Hualalai are the residuals of magma crystallization at 16–21 km depth, below the pre-Hawaiian oceanic crust. Few available gabbronorites and diorites record instead lower pressures and likely represent conduits or small magma reservoir crystallized at 0–8 km depth. At Mauna Kea, on the other hand, a significant portion of the xenolith record is composed by olivine-gabbros, which crystallized almost over the entire crustal thickness (3– 18 km). Ultramafic xenoliths are less abundant and might represent the bottom of the same magma reservoirs that crystallized in the deeper portion of the magmatic systems (11–18 km). Some unresolved issues remain in geothermometry of mafic and ultramafic rocks representing portions of magma reservoirs that cooled and recrystallized under subsolidus conditions. This suggests that further experimental and theoretical work is needed to better constrain the thermodynamics and kinetics of peridotitic and basaltic systems at low (< 1000 ̊C) temperatures.