Intruded Research Articles

Integrated remote sensing and geochemical studies for enhanced prospectivity mapping of porphyry copper deposits: a case study from the Pariz district, Urmia-Dokhtar metallogenic belt, southern Iran

Mapping hydrothermal alteration zones associated with porphyry copper deposits (PCDs) is crucial for identifying new exploration targets on a regional scale. Hydrothermal alteration indicator layers play a fundamental role in recognizing potential areas for PCDs, highlighting the need for precise delineation of these zones and their integration with geochemical and geological data to reduce uncertainty in mapping porphyry copper prospectivity. This study focuses on the Pariz district within the Urmia-Dokhtar Metallogenic Belt (UDMB) in southern Iran, a region known for its significant porphyry copper mineralization. First, logical operator algorithms (LOA) were applied to ASTER remote sensing data to map and distinguish argillic and phyllic alteration zones associated with PCDs. Subsequently, propylitic alteration zones associated with chlorite-epidote and propylitic alteration associated with calcite were also delineated, as were silica-rich hydrothermal alteration zones. Five evidence layers corresponding to these geologic features were generated and weighted with logistic functions, independent of expert judgment and without consideration of the spatial distribution of known mineral occurrences (KMOs). In addition, two layers of information were developed, including multivariate geochemical signatures and proximity to intrusive rocks. The geochemical analysis identified two significant factors associated with porphyry copper mineralization: Factor-I (Zn, Pb, Cu, Sn, B) and Factor-II (Mo, Cu). These factors contributed to a multivariate geochemical signature in addition to the alteration layers derived from remote sensing. Evaluation using prediction- area (P-A) plots and Normalized density index (ND) confirmed the effectiveness of all seven layers for mineral prospectivity mapping (MPM). Geometric average (GA), data-driven index overlay (IO), and deep autoencoder neural network (DEA) integrated these layers, with IO showing superior performance in identifying high potential zones, as indicated by higher prediction rates compared to other methods. Therefore, IO proves to be the most efficient approach for mapping the regional porphyry copper minerals in the Pariz district of the UDMB.

Deccan Volcanism and Related Seismic Unrest in the Koyna–Warna Region, India

Abstract Koyna–Warna is a region of low-tectonic deformation and normal surface heat flow (∼40 mW/m2) in the Deccan volcanic province, India, where low-to-moderate magnitude earthquakes have continued to occur in the last 60 yr. These earthquakes are uniquely restricted to an 11×16 km2 area and confined to the upper crust between 3 and 9 km depth. Located at the last phase of the interaction of India with the Reunion mantle plume ∼65 Ma ago responsible for extensive volcanism, the cause of sustained seismicity in Koyna region is debated. Using the shear-wave velocity model derived through the joint inversion of the receiver function and surface-wave data from the seismic zone, we propose that earthquakes in the Koyna region occur due to stress concentration arising because of the high-density magma intrusions in the shallow crust at 3–9 km. The high-density mafic-ultramafic body exerts gravitationally induced stress of about ∼12 to 15 MPa. The continuation of earthquakes in the deeper part is inhibited by the possible fluid-filled mush zone imaged as a low-velocity layer at a 9–17 km depth. The magma intrusion as dike can induce a cycle of normal faulting in the overlying rock mass, as observed in the Warna region. We present the first evidence of an extremely high velocity (>4.7 km/s) layer at 40–50 km below Moho, interpreted as the presence of eclogite–peridotite responsible for producing Deccan magma in large volume.

Cryptic degassing and protracted greenhouse climates after flood basalt events

AbstractLarge igneous provinces erupt highly reactive, predominantly basaltic lavas onto Earth’s surface, which should boost the weathering flux leading to long-term CO2 drawdown and cooling following cessation of volcanism. However, throughout Earth’s geological history, the aftermaths of multiple Phanerozoic large igneous provinces are marked by unexpectedly protracted climatic warming and delayed biotic recovery lasting millions of years beyond the most voluminous phases of extrusive volcanism. Here we conduct geodynamic modelling of mantle melting and thermomechanical modelling of magma transport to show that rheologic feedbacks in the crust can throttle eruption rates despite continued melt generation and CO2 supply. Our results demonstrate how the mantle-derived flux of CO2 to the atmosphere during large igneous provinces can decouple from rates of surface volcanism, representing an important flux driving long-term climate. Climate–biogeochemical modelling spanning intervals with temporally calibrated palaeoclimate data further shows how accounting for this non-eruptive cryptic CO2 can help reconcile the life cycle of large igneous provinces with climate disruption and recovery during the Permian–Triassic, Mid-Miocene and other critical moments in Earth’s climate history. These findings underscore the key role that outgassing from intrusive magmas plays in modulating our planet’s surface environment.

LATE MESOZOIC RARE-METAL GRANITES, PEGMATITES, AND GREISENS OF MONGOLIA: AGE, MINERALOGY, GEOCHEMISTRY, ORE POTENTIAL, AND PETROGENESIS

Comparative analysis of the earlier obtained and new geological data, age, mineral, petrological, and geochemical compositions of plutons of calc-alkalic granitoids and rare-metal Li–F granites shows their evolution in a wide time interval during the formation of Mesozoic areas of granitoid magmatism. Mineralogical and geochemical analysis of the evolution of plutons of palingenetic calc-alkalic granitoids (Baga Hentiyn (MZ1) and Ikh Narotiin = Hiid (MZ2)) and intrusions of rare-metal Li–F granites of Central and Eastern Mongolia revealed their petrological and geochemical differences. The closure of the Mongol–Okhotsk Basin with the formation of large plutons of calc-alkaliс granitoids, obviously related to collisional processes, did not cause significant enrichment of the late granite phases with lithophile and ore elements. Within the peripheral zones of еру MZ1 and MZ2 magmatic areas, mineralization is often associated with Mongolian multiphase plutons and small intrusions of rare-metal Li–F granites. The rare-metal granites are characterized by a decrease in indicative K/Rb, Nb/Ta, and Zr/Hf values and a regular increase in F, Li, Rb, Cs, Sn, W, Be, Ta, and Nb contents during the evolution of Li–F magmas. Igneous and, particularly, metasomatic rocks in most intrusions of ore-bearing rare-metal Li–F granites are characterized by significant variations in Sn and W contents. At the magmatic stage, the pegmatoid varieties of amazonite–albite granites and pegmatites of the zonal Baga Gazriin (MZ1) and Barun Tsogto (MZ2) plutons are significantly enriched in both Sn and W. Maximum Sn and W enrichment has been established in greisenized granites and zoned greisen bodies (zwitters), which is due to the percolation of ore-bearing solutions into the upper horizons and the mineralization of ore elements in the late phases of intrusions and in metasomatites. The wide variations in the age (321–126 Ma) and trace element and isotope compositions of Mongolian rare-metal Li–F granites within various zones of large magmatic areas suggest the influence of mantle plume sources on the composition of rare-metal granitic magmas and on their ore potential in intermediate chambers in the continental crust.

An Early Permian transpressional continental arc and arc-arc collision recorded in the Baidunzi Complex, southern Central Asian orogenic belt, NW China

Our multidisciplinary study of the southern Beishan orogen in NW China, situated between the Tienshan and Solonker suture zones, sheds light on the closure of the Paleo-Asian Ocean and termination of orogeneses in the Central Asian Orogenic Belt. We identify the Baidunzi Complex, an exotic Permian transpressional continental arc terrane, characterized by sheared and isoclinally folded metasedimentary and syn-kinematic plutonic rocks transformed into upper greenschist to amphibolite tectonites. The complex comprises basement rocks of thick-bedded orthoquartzite and orthogneiss, the Carboniferous to Permian meta-sedimentary strata including volcaniclastic sedimentary rocks, marble, and marl interlayered psammite, and the Baidunzi Intrusive Suite featuring 294–289 Ma hornblende diorite, tonalite, granodiorite, and granite. The Late intrusive rocks, including leuco-granite to trondhjemite sills and a stitching gabbro unit, suggest an amalgamation age of 281–280 Ma between the Baidunzi and Ganquan arcs. The spatial and temporal linkage between the Baidunzi continental arc and the Liuyuan backarc-Ganquan arc suggests they were either built on a coeval doubly vergent subduction system or from the same north-vergent subduction system and structurally juxtaposed by sinistral convergence. Geochronological and Hf isotope evidence, along with continental rock affinity, indicates a close association between the Baidunzi Complex and the northern margin of the Tarim Craton during the Gondwana breakup and Pangea assembly.

Dynamics and Detection of Pulsed Tremor at Whakaari (White Island), Aotearoa New Zealand

AbstractVolcanic tremor is a crucial indicator for assessing the state and hazard potential of volcanic systems. At Whakaari (White Island volcano, Aotearoa New Zealand), a pulsed tremor signal emerged after a hydrothermal explosion in August 2012. The tremor accompanied the extrusion of a lava dome, before gradually disappearing prior to the onset of renewed hydrothermal activity in January 2013. We interpret this seismic signal to represent discrete gas transfers from a magmatic intrusion toward a permeable cap—possibly a hydrothermal seal—in the upper layers of Whakaari's hydrothermal system. Such tremor may thus be associated with heightened potential for hazardous explosive activity but is difficult to detect using conventional seismic monitoring parameters. To highlight the emergence of subtle periodic signals, we experiment with Lomb‐Scargle periodograms (LS). LS detect the tremor 5 days before it becomes visible in seismograms, thus facilitating the recognition of such elusive seismic patterns.

Evaluation of Granite Fertility Utilizing Porphyry Indicator Minerals (Zircon, Apatite, and Titanite) and Geochemical Data: A Case Study from an Emerging Metallogenic Province in the Taimyr Peninsula, Siberian High Arctic

The Taimyr Peninsula in the Russian High Arctic comprises a late Paleozoic-early Mesozoic collisional belt where several porphyry-type mineralization occurrences were identified during the last decade, making this area a potential exploration target for Cu-Mo deposits. In order to further evaluate the metallogenic potential of the poorly outcropped northeastern part of Taimyr, samples from seven granitoid intrusions were investigated in this study aimed to evaluate the granite fertility based on petrography, geochemistry, and composition of porphyry indicator minerals (zircon, apatite, and titanite). The studied intrusions represent small to moderate-sized bodies (40–800 km2) composed of biotite (±amphibole) quartz monzonites, granodiorites, granites, and biotite leucogranites that formed in the course of late Paleozoic-early Mesozoic tectono-magmatic events at the Siberian margins. The late Carboniferous Tessemsky massif represents suprasubduction granitoid series, while the Pekinskiy, Shirokinskiy, Dorozhinskiy, Kristifensenskiy, and Yuzhno-Lodochnikovskiy massifs are correlated with the early Triassic Siberian Traps LIP. The rocks of intrusions comprise a relatively uniform geochemically, predominantly magnesian, slightly peraluminous, calc-alkaline high-K amphibole-bearing I-type granitoid series with adakitic affinity, where Triassic plume-related granitoids inherit geochemical signatures of Carboniferous supra-subduction granitoids, and all rock types are marked by enrichment in LILE and negative Ta, Nb, and Ti anomalies. It is suggested that the adakitic geochemical characteristics of the Taimyr granites are a result of derivation from a relatively homogeneous mafic lower crustal source that formed at the stage of Carboniferous continental subduction and continued to produce granitic melts in the course of the early Mesozoic magmatic evolution. Whole rock geochemistry and composition of porphyry mineral indicators (zircon, apatite, and titanite) indicate that the Taimyr granites crystallized from oxidized water-saturated magmas at moderate temperatures, with the majority of samples showing characteristics typical for porphyry-fertile granites worldwide (fO2 = ΔFMQ +1 to +3 with zircon Eu/Eu* > 0.4 and apatite SO3 > 0.2 wt.%). Data from Dorozhinskiy, Kristifensenskiy, Pekinskiy, and Tessemskiy intrusions fully match geochemical criteria for porphyry-fertile granitoids, and these massifs are considered the most prospective for Cu-Mo mineralization. Granites from Shirokinskiy and Yuzhno-Lodochnikovskiy intrusions only partially match compositional constraints for fertile melts and can be considered as second-tier exploration targets. Finally, available data for the Simsovsky massif preclude its classification as a porphyry-fertile body. These conclusions are in line with previously developed exploration criteria for the northeastern Taimyr, showing that geochemical indicators of granite-fertility can be used on a regional scale in parallel with other exploration methods.

4D imaging of the volcano feeding system beneath the urban area of the Campi Flegrei caldera

This paper describes an approach to analyze ground deformation data collected by InSAR (Interferometric Synthetic Aperture Radar) imaging the volcano feeding system (VFS) beneath a caldera. The approach is applied to the Campi Flegrei caldera in southern Italy, a densely populated area at high risk for volcanic eruption. The method is a 4D tomographic inversion that considers a combination of 3D pressure sources and dislocations (strike-slip, dip-slip and tensile) acting simultaneously. This is in contrast to traditional methods that assume a priori geometries and type for the volcanic source. Another novelty is that we carry out a time-series analysis of multifrequency InSAR displacement data. The analysis of these multiplatform and multifrequency InSAR data from 2011 to 2022 reveals an inflating source at a depth of 3–4 km that is interpreted as a pressurized magmatic intrusion. The source broadens and migrates laterally over time, with a possible new magmatic pulse arriving in 2018–2020. The model also identifies a shallow region (at 400 m depth) that may be feeding fumaroles in the area. The analysis also reveals a zone of weakness (dip-slip) that could influence the path of rising magma. This method provides a more detailed dynamic 4 - dimensional image of the VFS than previously possible and could be used to improve hazard assessments in active volcanic areas.

Identification of Paleovolcanic Centers in the Bima District, East Sumbawa Island (Indonesia) as Guidance for Future Exploration of Cu-Au Deposits

The formation of Cu-Au mineralization, such as porphyry and epithermal deposits, is strongly associated with volcanic processes in specific tectonic settings, such as subduction zones. The identification of the presence of ancient volcanoes is one of the important steps to finding mineral deposits. This study aims to identify the presence of ancient volcanoes in the Bima District, eastern part of Sumbawa Island, as a step toward determining the potential indication of Cu-Au mineralization. The methods used in this research consist of a literature study, image analysis and remote sensing, field survey and data collection, and petrographic analysis. Image analysis using DEMNAS (Digital Elevation Model), including texture and pattern analysis using the concept of volcanic anatomy, aims to identify the remaining forms of ancient volcanoes. Field surveys and data collection include volcano geomorphology, lithology and sampling, and also geological structures. Petrographic analysis is conducted to qualitatively characterize the texture, structure, and mineralogy of volcanic rocks. The identification results show that there are at least ten volcanoes (crown) identified through image analysis, namely Doro Mbangga, Doro Baku, Doro Donggo Masa, Doro Rompo, Doro Sape, Doro Kowo, Doro Jia, Doro Sambori, Doro Mangge, and Doro Lambu. Each of these volcanoes has one or more eruption center (hummock). The eruption center identified in the central, proximal, to distal facies of the volcano, even superimposing one volcano product with another, and spread around 80-90% in the study area. The volcanic facies in the study area are characterized by the central part being composed of lithologies such as intrusive rocks, lava, and diatreme breccia, while the proximal and distal facies are composed of breccia, volcanic breccia, and tuff. Hydrothermal alteration zones are identified in the central and proximal facies of the volcano. These alterations were associated with the presence of eruption centers, where the abundance of eruption centers means that hydrothermal alterations are particularly well developed and pervasively formed. Identified argillic and advanced argillic alteration associated with stockworks forming a lithocap environment. In addition, the presence of intrusive rocks such as diorite and dacite with chloritic and sericitic alteration in the central facies of Doro Baku can be associated with the presence of deposits such as porphyry and epithermal, so the identification of ancient volcanic eruption centers in the Bima district has implications for the potential discovery of Cu-Au mineralization, such as porphyry and epithermal deposits.

AGE AND GEODYNAMIC SETTINGS FOR FORMATION OF CARBONATITE COMPLEXES AND ASSOCIATED RARE METAL DEPOSITS OF THE SOUTH URAL

The Ilmen-Vishnevogorsky and Buldym carbonatite complexes occurring in the Southern Urals represent linear deformed carbonatite complexes. Their origin, as well as the age and geodynamic conditions remain the subject of debate. The isochron methods (Rb-Sr, Sm-Nd, TIMS) and local U-Pb-dating of zircons (SHRIMP II and LA-ICP MS) of these carbonatite complexes were employed to determine the age and duration of the stages of alkali-carbonatite magmatism and associated rare-metal ore formation. The Silurian-Devonian U-Pb zircon ages of the early phases of Ilmen-Vishnevogorsky miaskites and carbonatites were determined as 420.7±11 Ma (S2) and 417±2.8 Ma (D1), respectively. In the later phases of miaskites and carbonatites, early zircons are resorbed, they have broken isotope systems, and later zircon generations form a cluster of 386±7.6 Ma (D2). The Lower Permian U-Pb age of zircon 280±8 Ma (P1) was determined in the miaskite-pegmatite and late carbonatite. The isochron dating of late ore-bearing varieties of carbonatites provided the ages from the Lower Permian to the Early Triassic (P1–T1): 254±18 Ma, Sm-Nd and 247±4 Ma, Rb-Sr, IVC; 280±53 Ma, Sm-Nd, Buldym complex. Thus, the generation and intrusion of alkaline magmas in the Urals occurred ~420 Ma (S2–D1), synchronously with the formation of island-arc complexes. They are related to rifting on the emerging continental margins. The tectonic activity and formation of alkaline rocks and carbonatites proceeded in the Middle Devonian (~380 Ma, D2); it correlates with the accretion-collision stage of the Urals development. At the stage of "hard" collision (~280 Ma, P1), the Ilmen-Vishnevogorsky and Buldym complexes were plastically deformed, underwent melting and emplaced conformably with collision-slip tectonic structures. Recrystallization of rocks and minerals, plastic and brittle deformations, processes of pegmatitic, carbonatitic and rare-metal ore formation are associated with palingenic-metasomatic transformation of rifting alkaline complexes of Silurian-Devonian age at the collision and post-collision (~250 Ma, P3–T1) stages of the Urals emplacement.

Deep plutonic bodies over low-frequency earthquakes revealed from receiver-side Green's functions

Seismological heterogeneity in subduction zones provides insights into slow earthquakes and potential megathrust earthquakes. Studies at the Kii Peninsula in the Nankai subduction zone suggest that there are high-density and high-velocity plutonic bodies in the accretionary prism over the subducting slab, potentially influencing megathrust earthquakes. The lateral variation of heterogeneity and the spatial extent of plutonic bodies remain to be investigated well. Our passive-source imaging of receiver-side Green's functions, from widely distributed campaign seismic observations, reveals a sharp negative S-wave velocity contrast on the top surface of the subducting Philippine Sea plate common to all along-dip profiles and a positive phase tilted upward in the forearc crust. The low permeability of the forearc crust prevents the infiltration of slab-dehydrated fluid further into the upper crust. In the western area, we also found positive phases tilted upward in the forearc crust. The negative phase extends towards the deeper extent of slow-earthquake sources. Meanwhile, the positive phase likely represents the top surface of plutonic rocks of the Kumano and Ohmine plutons that span all the way down to the plate interface. Together with observations of gravity anomaly, intraslab seismicity, and seismic tomography, our interpretation supports the presence of plutonic bodies which extend deep beneath the forearc crust as well as laterally over the subducting PHS slab, rather than a serpentinized mantle wedge. The upper plate is generally low in permeability, but areas with localized high permeability may exist on the updip side of tremor sources. This condition, wherein fluid can infiltrate upwards locally, may maintain the relatively less active slow earthquakes in the western area. The lateral variation of the upper-plate lithology likely influences fluid processes and slow earthquake activities.

Northward drift of the Burma Terrane with India during the Cenozoic and implications for the India–Asia collision

The past location of the Burma Terrane during the convergence of the Indian and Asian tectonic plates is key to unravelling the regional geodynamic, palaeoenvironmental and palaeobiogeographical history of the eastern edge of the Himalayan orogen. Palaeomagnetic data provide the ability to constrain the location of the Burma Terrane, but it has been very difficult to find rocks with palaeomagnetic records of primary characteristic remanent magnetizations. We present here new palaeomagnetic results spanning the Paleocene to late middle Eocene within the Burma Terrane, complementing palaeolatitudes previously established from Late Cretaceous intrusive rocks and late middle Eocene sedimentary rocks. Our palaeomagnetic data indicate that the Burma Terrane remained at equatorial latitudes during the Paleocene and early Eocene, at a considerable distance from the South Asian margin. In addition, palaeomagnetic results from mid- to late Eocene sedimentary rocks yield a predominantly north–south orientation of the Burma Terrane over the past 45 Myr, showing that it was not part of the NW–SE-oriented Sundaland margin before its collision with India. Our results support collision models involving a Trans-Tethyan subduction system during the Late Cretaceous and early Paleocene. We propose that this system incorporated the Burmese volcanic arc and continental fragments of Argoland before drifting north with India towards Asia. The new palaeogeographical model considers a reduced amount of oblique subduction of the Indian plate below Burma during the Cenozoic. A possible source of sediments filling the thick Myanmar basins from the Gangdese belt during the Eocene supports the hypothesis of an India–Asia collision around ∼50 Ma. The new palaeogeography supporting the formation of the Myanmar Cretaceous amber on an isolated Trans-Tethyan Arc is also a key element in discussions of the palaeobiogeographical evolution of the numerous faunas it contains.

Leucogranite intrusions in Eastern Kazakhstan: age, composition and mechanisms of formation

There are several large intrusions composed of 70–75% leucogranites within Eastern Kazakhstan. Information on the age of the intrusions is provided, the features of the composition of the rocks are considered, and conclusions about the petrogenetic mechanisms of forming of leucogranite magmas are drawn. Two stages of leucogranite intrusive magmatism have been established – in the Early Permian and in the Early Triassic. Their formation occurred in an intraplate geodynamic setting. Leucogranite magmas were formed as a result of partial melting of crustal substrates under the thermal influence of mafic magmas. Geochemical differences in leucogranites were due to different compositions of crustal substrates and different degrees of their melting.

Caldera resurgence and the case-history of Campi Flegrei

Large calderas formed by explosive eruption are often characterized by a structural uplift of the caldera floor that has been named resurgent dome or block. The analysis of recent unrest at several calderas suggests that the resurgent dome is likely formed by the intrusion of magma at shallow depth below the light caldera infill. Campi Flegrei is an active volcano considered the highest risk volcano in Italy and Europe and has been in a state of unrest in the last 70 years. The analysis of the past volcanological history point to an unrest localized in a central resurgent block. Different or paired interpretations on the current unrest suggest either an intrusion of magma at shallow depth (3-5 km) or a deformation governed by the poro-elastic response of a shallow hydrothermal system to changes in fluid pressure and temperature. The invariance of the shape of the deformation, as well as the diffuse degassing of the Solfatara area, hint that the unrest is related with the uplift of the resurgent block driven by magma intrusion at shallow depth.

National-Scale Geospatial Modelling of Pyrrhotite in Bedrock Across Canada: A Pilot Study

The most abundant iron sulphide minerals in igneous, metamorphic, and some sedimentary rocks are FeS2 (pyrite/marcasite) and Fe1-xS (pyrrhotite). The oxidation of pyrite and pyrrhotite in bedrock aggregates and mine tailings is undesirable to infrastructure and the environment because such chemical reactions are linked with concrete deterioration and acid mine drainage, respectively. The oxidation rate of pyrrhotite is up to one hundred times greater than that of pyrite; thus, pyrrhotite oxidation is of particular concern to society. Pyrrhotite-bearing concrete aggregates may lead to rapid expansion cracking and failure of critical concrete infrastructure including bridges, buildings, and houses, posing a significant safety concern. Additionally, premature disintegration of concrete requires replacement of concrete, leading to excessive aggregate resource extraction and associated increases in CO2 emissions. Considering the widespread concrete infrastructure across Canada, the distribution of pyrrhotite in bedrock used for aggregate is of fundamental importance to the short- and long-term safety of Canadians at the national, regional, and local scales. This pilot study details the initial steps taken to generate national-scale geospatial models of pyrrhotite occurrences in bedrock across Canada and illustrates the associated map products. In total, 12,577 known pyrrhotite occurrences were identified from publicly available provincial and territorial mineral occurrence datasets. The overall modelling strategy involved normalizing the number of pyrrhotite occurrences with respect to the total surface area of major bedrock types and characterizing three different classes of pyrrhotite occurrence density (< 1, 1–4, and 4–10 occurrences/1000 km2). The maps illustrate that pyrrhotite occurrence density is highest in volcanic rocks and undifferentiated sedimentary and volcanic rocks, moderate in intrusive and unknown rocks, and lowest in sedimentary and metamorphic rocks. Sedimentary rocks with no pyrrhotite occurrences span large surface areas across central-western Canada thus resulting in an overall low pyrrhotite occurrence density (< 1 occurrence/1000 km2) for this rock type, despite the fact that numerous pyrrhotite occurrences are identified in sedimentary rocks and may be abundant locally or regionally. Volcanic, undifferentiated sedimentary and volcanic, intrusive, and unknown rocks occur throughout the Canadian Shield of central and northern Canada, the Cordillera of western Canada, and the Appalachians of eastern Canada, but bedrock type and associated occurrence density are highly variable within these geological domains. Comparison of pyrrhotite occurrence density maps for Canada with pyrrhotite permissive geology maps for the United States of America illustrates that rocks with a high pyrrhotite occurrence density in Canada (volcanic rocks and undifferentiated sedimentary and volcanic rocks), are contiguous overall with areas of pyrrhotite potential in the United States. Inconsistencies across the international border reflect the differing methodologies and assumptions consisting of a statistically based approach for Canada and a qualitative approach for the United States. In the Cordillera and Appalachians, such discontinuities across the international border may reflect the underestimation of pyrrhotite occurrences in sedimentary rocks of Canada because of the impact of high surface area on the pyrrhotite occurrence density calculations. The maps presented herein are a first step in illustrating the distribution of pyrrhotite-bearing bedrock across Canada and greater North America. These national-scale map products are useful first-order references for selecting regions for follow-up studies on bedrock pyrrhotite occurrences. Regional and local geospatial analysis combined with field work for ground truthing will be important aspects of future research, especially in the vicinity of population centres where bedrock is utilized for concrete aggregate. Detailed regional and local studies of pyrrhotite occurrences in bedrock will help guide the extraction of safe concrete aggregate and contribute to the long-term sustainability of bedrock resources, safe infrastructure, and a habitable climate.

Protracted mantle heat conduction after lithospheric foundering beneath the Malagasy orogen

Ultrahigh-temperature metamorphism (UHTM) is important for the evolution and long-term stability of continental crust. The Anosyen domain in southeastern Madagascar is a well-preserved UHTM terrane that formed during the amalgamation of Gondwana. The heat source(s) required to reach peak conditions is(are) a matter of debate. One potential cause of extreme crustal heating is the intrusion of mantle-derived melts into the crust. Foundering of the mantle lithosphere can also lead to increased heat flow. To assess the role of these heating mechanisms, we measured zircon δ18O, εHf(t) compositions, and U-Pb dates for plutonic rocks in the midcrustal UHTM domain. Our results indicate that pluton emplacement predated UHTM by as much as 40 m.y. and that all zircons have crustal O and Hf isotopic compositions. We propose that mantle lithosphere foundering caused melting in the lower crust, producing the magmas responsible for plutonism during the early stages of orogenesis. Prolonged conductive heating of the crust—combined with above-average radiogenic heating—may explain why UHTM occurred ∼40 m.y. after foundering. This suggests that foundering of the mantle lithosphere can swiftly lead to partial melting in the lower crust, as well as protracted heating of the middle crust that culminates tens of millions of years later.

GEOCHEMISTRY OF GROUNDWATERS AND SURFACE WATERS, AND GROUND ICE OF THE OKA PLATEAU, EASTERN SAYAN (RUSSIA)

The study area is located in the Eastern Sayan hydrogeological folded area. The objects of the study were groundwaters, surface waters and ground ice in the Sentsa River basin on the Oka Plateau. Cold and thermal groundwaters are associated with Proterozoic and Paleozoic metamorphic and igneous rocks. Their discharge as springs occurs in the river valleys along fault zones. Ground ice was studied in mineral frost mounds (lithalsas) composed of clays, clayey silts and silts of lacustrine-alluvial and fluvioglacial genesis. It has been established that thermal and cold groundwaters have HCO3 Ca-Na compositions, river and lake waters, as a rule, have HCO3 Ca-Na compositions, and ground ice melts – HCO3, SO4-HCO3 and NH4-HCO3 Ca. Thermal waters are largely enriched in Li, Be, B, Si, Mn, Ga, Ge, Se, As, Br, Rb, Sr, Cs, Ba and all REE relative to river and rain waters, and have the highest values of trace elements enrichment factor (EFREE). The latter shows that atmospheric precipitation participates in the formation of the composition of groundwaters (cold and thermal) and surface waters. The specificity of the geochemistry of ground ice is determined by the composition of precipitation, the injection of ice-forming groundwater from taliks, the interaction in the water-rock system, and the presence of organic matter in unconsolidated sediments. The participation of river water and groundwater in the formation of the frost mound ice core is also evidenced by similar values of stable isotopes (δ18O, δD) in surface water, groundwater and ground ice. The 3He/4He ratio points to a possible influx of mantle helium into thermal waters, and δ13С points to the magmatic and thermometamorphic mechanisms of carbon dioxide accumulation in thermal waters. The 87Sr/86Sr ratio in travertines indicates a significant contribution of intrusive rocks to the formation of fluid composition.

Volcanomagnetic signals related to the 2021 Tajogaite volcanic eruption in the Cumbre Vieja rift (La Palma, Canary Islands)

After almost 50 years of quiescence, the Cumbre Vieja rift in La Palma underwent a reactivation process that culminated in the eruption of the Tajogaite volcano from September 19 to December 13, 2021. In July 2021, a magnetic station (CFU) was deployed in the western flank of the Cumbre Vieja rift, 2 km away from the site where the eruptive vents would open two months later. In September 2021, a second magnetic station (SAN) was installed near the southern end of the rift. In this paper we study two months of geomagnetic data at CFU before the eruption and three months of geomagnetic data at SAN during the eruption. The analysis of these time series revealed a magnetic signal at the CFU station with an amplitude of 10 nT and a duration of 10 days by mid-August, one month before the eruption onset. We studied possible correlations with other physical parameters (ground deformation, long-period and very-long-period seismic activity) and concluded that this signal could be related to changes in the magnetization of rocks beneath the volcanic edifice caused by magma intrusion and volcanic/hydrothermal fluids circulation preceding the eruption. At the SAN magnetic station, the time series suggests that a slight decrease in the geomagnetic field could reflect the end of the eruptive process.

Petrogenesis of episodic volcanic-intrusive rocks in SE China: Crystal-melt segregation and magma mixing

Crystal-melt segregation and magma mixing are key magmatic processes that generate compositional variabilities in igneous rocks. Distinguishing these processes can provide insight into the evolution of volcanic calderas and the driving force of plate subduction. Intensive episodic magmatism occurred in Southeast China during the Cretaceous, producing a series of volcanic-intrusive rocks during different magmatic stages in chain-like calderas. We conducted comprehensive petrological, geochemical, isotopic, and zircon trace element analyses on two representative calderas (Xiaoxiong and Shiniushan).The results show that the magmatism produced multistage volcanic and coexisting intrusive rocks regarding their crystallization ages (102–88 Ma) and NdHf isotopic compositions (zircon ɛHf(t) = −11.7 to −1.8, whole-rock εNd(t) = −8.3 to −2.4). The volcanic and intrusive rocks are related by fractional crystallization.In general, the erupted silicic rhyolitic rocks are characterized by distinctly negative Eu anomalies (δEu = 0.10–0.71) and depletions of Ba, Sr, P, and Ti, while the coexisting intrusive rocks show distinct or complementary geochemical signatures, such as neglectable Eu anomalies (δEu = 0.92–1.09) and positive Ba anomalies. Furthermore, the whole-rock samples from the calderas have variable δ41K values (from −0.14 ‰ to −0.59 ‰) that show strong correlations with indices of fractional crystallization such as Eu anomaly, Sr content, and K2O/Na2O ratios, indicating a key role of plagioclase during crystal-melt segregation. This is also supported by petrographic evidence for crystal accumulation such as the synneusis of plagioclase phenocrysts. Mafic microgranular enclaves in the volcanic-intrusive rocks indicate that magma recharge events occurred in the magma reservoir. Synthesizing these lines of evidence, we argue the multiple magmatism in plate subduction zone can be sustained by recharge events in the magma reservoir along with crystal-melt segregation processes. Particularly, the volcanic rocks tend to have isotopically lighter K than intrusive rocks, and strongly support that the volcanic rocks represent the extracted melt that is complementary to the cumulative intrusive rocks.

Influence of Magmatic Intrusion on Abnormal Hydrocarbon Generation and Expulsion of Source Rock: A Case Study of the Dongying Sag, Bohai Bay Basin

AbstractHow gabbro affects the generation and expulsion of hydrocarbons in muddy surrounding rocks is clarified by analyzing thin section, major and trace elements, total organic carbon (TOC), pyrolysis, extracts and vitrinite reflectance data from source rocks in the Chunxi area the Dongying Sag, Bohai Bay Basin, eastern China. The results show that a magma intrusion brings copious heat to the source rocks, which promotes abnormal maturation of organic matter (OM) and rapid hydrocarbon generation. The CH4 and H2 produced by gabbro alteration play a role in hydrocarbon generation of source rocks. The hydrothermal process during magma intrusion provides many different minerals to the source rock, resulting in carbonate‐rich surrounding mudstone. The carbonate and clay minerals produced by volcanic mineral alteration jointly catalyze the hydrocarbon generation of the source rock. The high‐temperature baking of the intrusion results in hydrothermal pressurization and hydrocarbon generation pressurization, causing many fractures in the surrounding rock. The generated oil and gas are discharged through the fractures under diffusion and pressure. Mantle‐derived CO2 is also conducive to the expulsion of hydrocarbons because of its strong enrichment capacity for hydrocarbons.