Igneous Activity Research Articles

Mapping the Earth's igneous record: a geospatial database approach

Abstract The record of igneous activity (magmatism and volcanism) can significantly affect natural resource exploration and exploitation, including the search for hydrocarbons, critical minerals, natural hydrogen and geothermal energy sources, as well as using mafic igneous rocks as storage sites for CO 2 . These effects will vary depending on the nature and timing of the activity, the structural framework and the crustal architecture of the affected country-rock. To understand these effects and the interplay with other factors, we must first know the igneous record's distribution, timing, and petrology. In this paper, we describe a new geospatial database of the igneous rock record designed to provide a baseline digital resource that is application-agnostic and can be applied across the broadest range of research and resource exploration activities. We discuss the challenges we have faced and solved at each of the three main stages of geospatial mapping: database design, database population and database visualization. This includes the importance of a comprehensive audit trail so that users can differentiate between well and poorly-constrained interpretations, helping identify areas requiring additional work and data acquisition. The result is a geospatial database that will facilitate a better understanding of the Earth system and natural resource exploration.

Lithological discrimination of the Fawakhir-Atalla belt in the Central Eastern Desert of Egypt based on Landsat-9 remote sensing data, airborne gamma-ray spectrometry, field and petrographic investigations with implications on the evolution of the Arabian Nubian Shield

The Central Eastern Desert (CED) is a key territory for understanding the evolution of the Arabian Nubian Shield (ANS) in Egypt as it contains Cryogenian-Tonian ensimatic supracrustal assemblages, such as ophiolitic and arc volcanic rocks, as well as gold deposits. So, it has been the subject of extensive studies over the last two decades. However, the lithological mapping of the Fawakhir-Atalla belt, located west of the Meatiq gneiss dome (infrastructure) of the CED, is still debated, as the magmatic texture of some rocks was partially obscured owing to the shearing and alteration related to the Najd Fault System, mantle CO2-bearing fluid, and igneous activity in the final stage of the Pan-African Orogeny. In this regard, integrated studies of airborne gamma-ray spectrometry and Landsat-9 satellite imagery processing techniques, as well as field and petrographic investigations, have been used for the lithological mapping of the belt. The results led to the following sequence; ophiolitic rocks > island arc assemblages > older granitoids (syn-tectonic subduction-related) > Hammamat Group (molasse-type origin) > post-Hammamat felsite > younger granite (post-tectonic suture-related). The applied color composite images, selective band ratios, and image transformation techniques show a clear distinction between rock units. Older granitoids are tonalite to quartz diorite, while younger granites are monzo-to syenogranite. They are well-discriminated from each other using band ratios, and younger granites have the highest K, eU, and eTh values coherent with the post-Hammamat felsite. The image enhancement and image transformation techniques show a clear discrepancy between the mélange rocks and Hammamat conglomerates. Mélange rocks are composed of fragments embedded in a foliated matrix, while Hammamat conglomerates are grain-supported with pebbles of volcanic source and have higher K, eU, and eTh values. Volcanic rocks in the belt are not a part of the Dokhan series as they are metamorphosed with a composition range from meta-basalts to meta-rhyolite, and show mainly aphanitic to infrequently porphyritic textures, which are typical of island arc metavolcanics.

Geomorphology and Age Constraints of Seamounts in the Cabo Verde Archipelago, and Their Relationship to Island Ages and Geodynamic Evolution

AbstractThe Cabo Verde Archipelago is related to a mantle plume located close to the rotational pole of the African Plate. It consists of islands and seamounts arranged in a horseshoe‐shaped pattern open to the west, thus forming two volcanic chains, each with a weak east‐west age progression. High‐resolution swath bathymetry of 12 Cabo Verde seamounts is used here to assign each seamount to its pre‐shield, shield or post‐shield evolutionary stage, respectively. The eastern seamounts exhibit degraded and partially eroded morphologies, and are mainly in their post‐shield stage. A new 40Ar‐39Ar date for Senghor Seamount at 14.872 ± 0.027 Ma supports old ages for the eastern seamounts. The western seamounts generally exhibit younger volcanic‐edifice‐construction morphologies, showing fresh effusive and explosive volcanics, including rarely observed deep‐water explosive volcanism in the Charles Darwin Volcanic Field. Furthermore, the two previously unknown seamounts Sodade and Tavares in the westernmost termini of both volcanic chains exhibit pristine volcanic morphologies, in agreement with present‐day volcanism and seismic activity recorded from the western seamounts. The islands and seamounts rest on three submarine platforms to the east, northwest and southwest, respectively. Taken together, the seamount and island data suggest a shift in igneous activity from the eastern to the other platforms at about 8–6 Ma. However, the complex evolution pattern for both volcanic chains includes the simultaneous occurrence of pre‐shield or shield edifices at any time, followed by erosional and rejuvenation stages. The new seamount data still demonstrate ongoing westward submarine‐growth in both volcanic chains.

An evolutionary system of mineralogy, Part VIII: The evolution of metamorphic minerals

Abstract Part VIII of the evolutionary system of mineralogy focuses on 1220 metamorphic mineral species, which correspond to 755 root mineral kinds associated with varied metamorphic rock types, most of which likely formed prior to the Phanerozoic Eon. A catalog of the mineral modes of 2785 metamorphic rocks from around the world reveals that 94 mineral kinds often occur as major phases. Of these common metamorphic minerals, 66 are silicates, 14 are oxides or hydroxides, 8 are carbonates or phosphates, 4 are sulfides, and 2 are polymorphs of carbon. Collectively, these 94 minerals incorporate 23 different essential chemical elements. Patterns of coexistence among these 94 minerals, as revealed by network analysis and Louvain community detection, point to six major communities of metamorphic phases, three of which correspond to different pressure-temperature (P-T) regimes of metamorphosed siliceous igneous and sedimentary rocks, while three represent thermally altered carbonate and calc-silicate lithologies. Metamorphic rocks display characteristics of an evolving chemical system, with significant increases in mineral diversity and chemical complexity through billions of years of Earth history. Earth's first metamorphic minerals 27 formed in thermally altered xenoliths and contact zones (hornfels and sanidinite facies) associated with early Hadean igneous activity (> 4.5 Ga). The appearance of new Hadean lithologies, including clay-rich sediments, arkosic sandstones, and carbonates, provided additional protoliths for thermal metamorphism prior to 4.0 Ga. Orogenesis and erosion exposed extensive regional metamorphic terrains, with lithologies corresponding to the Barrovian sequence of index mineral metamorphic zones appearing by the Mesoarchean Era (> 2.8 Ga). More recently, rapid subduction and rebound of crustal wedges, coupled with a shallowing geothermal gradient, has produced distinctive suites of blueschist, eclogite, and ultrahigh pressure metamorphic suites (< 1.0 Ga). The evolution of metamorphic minerals thus exemplifies changes in physical and chemical processes in Earth's crust and upper mantle.

Early Jurassic large igneous province carbon emissions constrained by sedimentary mercury

Large igneous province eruptions and their carbon emissions often coincide with, and are hypothesized to have driven, severe environmental perturbations in the geological past. However, the vast scale of large igneous provinces and uncertainties in magmatic volatile contents and radioisotopic dates limit our ability to resolve gas emissions in detail over time. Here we employ high-resolution (~5–200 kyr) sedimentary mercury data from the Llanbedr (Mochras Farm) borehole, Wales, to derive quantitative large igneous province degassing estimates over a 20-million-year-long Early Jurassic interval (195–175 million years ago). Intervals of relatively elevated sedimentary mercury coincide with episodes of carbon-cycle change, including the Toarcian Oceanic Anoxic Event (183–182 million years ago). We use excess mercury loading to estimate large igneous province-associated carbon emissions, revealing that multi-millennial episodes of activity plausibly drove recognized pCO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p_{{\\mathrm{CO}}_2}$$\\end{document} and temperature increases. However, previous carbon-cycle model-based carbon emission scenarios require faster and larger carbon inputs than our proposed emissions. Resolving this discrepancy may require climate–carbon-cycle feedbacks or co-emitted gases to substantially exacerbate the carbon-cycle response, processes potentially underestimated in current models. Our long and near-continuous record of Early Jurassic large igneous province activity demonstrates mercury’s potential as a tool to resolve past carbon fluxes.

3D Seismic analysis of complex faulting patterns and fluid escape features and their relation to late Cenozoic magmatism in the Bass Basin, offshore southeast Australia

Abstract Igneous intrusions in sedimentary petroleum basins are often perceived as having a negative impact on the elements of the petroleum system, though the impact of intrusion-related deformation features on petroleum systems and broader geoenergy applications is not well understood. In this study, we use 3D seismic reflection data to document a variety of deformation styles that are spatially and temporally associated late Cenozoic magmatic activity in the Bass Basin, offshore southeastern Australia; three types of normal fault systems (conjugate faults, concentric faults, radial faults) and fluid escape pipes. These deformation features occur in the overburden up to ∼600 m above underlying igneous intrusions, within the Eocene to Miocene Demons Bluff and Torquay formations. The conjugate faults bound grabens and are interpreted to have formed in response to underlying dyke intrusions. The radial faults are interpreted to have formed in response to overburden uplift, though the link between these and associated igneous activity is less clear. We identify 101 fluid escape features that show variation in both the morphology of their surficial depressions and of the seismic reflection characteristics of their infilling deposits. These features are interpreted to be hydrothermal or volcanic vents with underlying pipe-like feeders, depending on their spatial association with adjacent or underlying igneous intrusions. The concentric fault systems are associated with surficial depressions, and quantitative analysis of reflection sags within these depressions suggest that they are a result of subsurface subsidence in response to formation of maar-craters. The intrusion-related deformation features documented in this study may have multiple effects on working petroleum systems, such as providing secondary fluid flow pathways that can either reduce seal integrity, or enabling migration of fluids into shallower reservoirs.

Large igneous province activity drives oceanic anoxic event 2 environmental change across eastern Asia

During mid-Cretaceous Oceanic Anoxic Event 2, significant increase of atmospheric carbon dioxide concentrations from the eruption of the large igneous provinces is hypothesized to have induced a humid climate and an elevation in nutrient runoff from continents to the oceans, resulting in oxygen depletion in the ocean. However, hitherto there is limited insight into the driving factors of Oceanic Anoxic Event 2 from the Pacific and Asian continental margins, even though the former and the latter were the largest ocean and landmass at that time. Here, a multiproxy analysis for the Oceanic Anoxic Event 2 interval of the Yezo Group –deposited on northwestern Pacific along the active Asian continental margin– is interpretated to identify seven volcanic pulses, five of which may have elevated humidity, weathering intensity, and vegetational change in the eastern margin of Asia. Moreover, oxygen depletion occurred simultaneously in the northwest Pacific. Given that these environmental changes in the eastern margin of Asia were penecontemporaneous with the global carbon burial intervals during Oceanic Anoxic Event 2, the elevated nutrient supply from the Asian continental margin to the Pacific Ocean may have, in part, contributed to the worldwide depletion of oxygen of the ocean during Oceanic Anoxic Event 2.

Petrogenesis of the late Cenozoic potassium-rich volcanism in the NW Tibetan Plateau: Constraints on the mantle evolution through post-orogenic events

The late Cenozoic Heishi Beihu volcanic rocks represent potassium-rich magmatic events at the northwesternmost margin of the Tibetan Plateau following the Indian–Asian continental collision. The petrogenesis of this juvenile igneous activity plays a crucial role in revealing the geochemical features of the deep mantle and contributes to our understanding of orogenic geodynamic evolution. This study, identified three eruption episodes at Heishi Beihu volcano (7.1–6.2, 4.3–1.4, and 1.3–1.0 Ma) using SHRIMP zircon U-Pb dating. Geochemically, the three episodes are characterized by shoshonitic affinities (K2O = 2.96–4.36 wt%) and crust-like trace-element signatures (negative Ta, Nb, and Ti anomalies), with enrichment in light rare earth (LREE) and large-ion lithophile elements (LILE), depletions in high-field-strength elements (HFSE), and small negative Eu anomalies (0.74–0.86). Their enriched whole-rock Sr ([87Sr/86Sr]i = 0.7072–0.7090), Nd (εNd(t) = −6.91 to −6.24), and zircon Hf (εHf(t) –5.64 to −9.13) isotopic compositions, and high zircon δ18O values (+7.4‰ to +10.6‰), are indicative of an enriched and heterogeneous mantle source (EMII-type) that contained recycled continental crust. The Heishi Beihu volcanic rocks were derived by low-degree (2%) partial melting of a mantle source with dominant pyroxenite and minor peridotite under conditions of the garnet-eclogite-facies. Results obtained from clinopyroxene–liquid geothermobarometry are indicative of diverse magma reservoirs, ranging from deep crustal levels (41–56 km) during Episode I to shallower depths for Episodes II (26–35 km) and III (17–29 km). In combination with the geological development of the area, we infer that magmatism at Heishi Beihu was genetically related to asthenospheric upwelling and induced by underthrusting of the Indian lithosphere beneath Western Kunlun.

The structure of the mantle transition zone and its implications for mantle upwelling beneath the central Tibetan plateau from triplicated P-waveforms modeling

The Tibetan plateau is considered as an ideal place for studying the continental collisions, tectonic movements and regional geodynamics. Although multiple episodes of igneous activities in Tibetan plateau have been suggested derived from mantle upwelling, their origins and corresponding geodynamic models remain vigorously debate. This study presents a high-resolution upper mantle velocity model of P-wave and its lateral variation beneath the central Tibetan plateau based on triplicated waveform modeling. The results show that, compared with IASP91 model, the 660-km discontinuity is deepened approximately 17–28 km from the Qiangtang terrane to the Beishan block. The lower mantle transition zone (MTZ) is characterized by high P-wave velocity anomalies (HVA) in range of 0.3%–0.9%. We infer that they are mainly related to the hydrous materials with low temperature in the lower MTZ. Besides, the depression of the 410-km discontinuity is about 6–15 km. A remarkable low velocity layer (LVL) is detected atop the 410-km discontinuity, exhibiting the thickness of 31–40 km and low P-wave velocity anomaly of −2.5% to −1.6%. This is against completely temperature-dominated origin of the LVL, and suggests that the material composition has also contributes. Additionally, we propose a new geodynamic model to demonstrate the asthenospheric upwelling beneath the Qiangtang and Songpan-Ganzi terranes, which suggests that the passively ascending water-enriched materials from the lower MTZ and their dehydration are responsible for the observed LVL atop the 410-km discontinuity, as well as the origin of the Cenozoic magmatic intrusion and volcanic eruption of the northern Tibet volcano in Pleistocene.

A volcanic inventory of the Moon

The volcanic and magmatic activity of the Moon is intimately tied to its internal thermal and geodynamic evolution through time. While the extrusive nearside maria dominate the volcanic record, little is known regarding their underlying structure and the details of their emplacement. Intrusive activity is even more enigmatic, with most intrusions expressing little to no surface signature. Although prior studies have provided insights into the local igneous activity, no global compilation has been conducted. Here, we present a volumetric inventory of extrusive and intrusive activity. Gravity and topography data are inverted using a two-layer loading model to constrain mare and cryptomare thickness. The mean thickness of mare units is found to be 2.8 km, though with substantial lateral variations, with average values of 7.9 km within large mare basins compared to 1.6 km outside of these basins. This substantial variation in mare thickness associated with minimal change in the surface topography may be explained by some combination of long-distance transport of low viscosity mare and/or a buoyancy control limiting mare eruptions to a constant level surface. Our preferred volumes of mare and cryptomare are 18.2×106 km3 and 2.2×106 km3, respectively. Crustal intrusions associated with linear gravity anomalies, floor-fractured craters, ring dikes, graben, and beneath volcanic constructs, are investigated and yield a total volume of 9.1×106 km3. Our inventory reveals that intrusive activity dominates in the farside (intrusive:extrusive ratio of 5:2), whereas extrusive volcanism is more pronounced in the nearside (1:5). The combined volume of intrusives and extrusives is found to be 3 times greater in the nearside than in the farside. Both are related to the lunar asymmetry in which the thinner crust and warmer subsurface beneath the Procellarum KREEP terrane enables enhanced melting and magma ascent. These observations may have implications for the interpretation of the thermal and geodynamic history of other celestial bodies, where intrusive volcanism remains poorly constrained.

Origin of Redbeds in the Neoproterozoic Socheong Formation and Their Relation to the Dashigou Large Igneous Province

During the latest Mesoproterozoic–Early Neoproterozoic era, extensional regimes generated a number of sedimentary basins in various regions in the Sino-Korean Craton. Mantle-plume emplacements are widely recognized in the sedimentary strata as mafic dikes and sills of the Dashigou Large Igneous Province (LIP). The occurrence of Fe-rich redbeds is first reported in the Neoproterozoic Socheong Formation of the Sangwon Supergroup in the Pyeongnam Basin. Their geochemical and mineralogical characteristics indicate basin-wide Fe enrichment due to hydrothermal fluid input. The episodic yet repetitive hydrothermal injection into the basin generated short-lived anoxia, recorded as greenish-gray coloration in the ferruginous beds. This hydrothermal fluid was likely sourced from the mafic igneous activities involved in the Dashigou LIP. The redbeds can be utilized as key beds for intra- or inter-basinal stratigraphic correlation and to study the negative carbon isotope excursions that occurred in the genetically related basins in the region (e.g., the Sangwon, Xu-Huai, and Dalian basins).

Mafic Alkaline Magmatism and Rare Earth Element Mineralization in the Mojave Desert, California: The Bobcat Hills Connection to Mountain Pass

AbstractOccurrences of alkaline and carbonatite rocks with high concentrations of rare earth elements (REE) are a defining feature of Precambrian geology in the Mojave Desert of southeastern California. The most economically important occurrence is the carbonatite stock at Mountain Pass, which constitutes the largest REE deposit in the United States. A central scientific goal is to understand the genesis of the carbonatite ore body in the context of widespread REE‐rich igneous activity. A swarm of mafic alkaline (shonkinite) dikes has been mapped and sampled at Bobcat Hills, 65 km southeast of the Mountain Pass mine. Whole‐rock geochemistry and zircon geochronology demonstrate a clear affinity to the ca. 1.4 Ga Mountain Pass intrusive system. Bobcat Hills dikes have comparably high REE concentrations (La ∼1,000× chondritic) and an error‐weighted mean 207Pb/206Pb zircon crystallization age of 1,426 ± 2 Ma (2σ). Unlike the alkaline intrusions at Mountain Pass, which have abundant inherited zircon from Paleoproterozoic basement rocks and crustally influenced oxygen isotope compositions (δ18Ozircon = 6.5–7.5‰), the Bobcat Hills dikes lack any evidence of crustal assimilation and have oxygen isotope values that overlap a mantle range (Bobcat Hills average δ18Ozircon = 5.6 ± 0.3‰). The dikes were a high‐temperature, early center of mafic alkaline magmatism in the Mojave Desert that serve as a snapshot of melt generation from a spatially extensive, metasomatized mantle source. We propose that modification of the crust over many tens of Myr at Mountain Pass created an environment that favored crustal assimilation and enabled ascent of late‐stage, REE‐rich carbonatite magmas.

Geochronological and petrological investigations of Miocene felsic igneous rocks in the Amakusa Islands, southwest Japan: Possible extension of the Setouchi Volcanic Belt

AbstractThe opening of the Japan Sea led to the separation of southwest Japan from the Eurasian continent. Subsequent to this event, a diverse range of igneous activities occurred in southwest Japan. On the back‐arc side of the region, igneous activity commenced at approximately 22 Ma and persisted for an extended period. In the trench‐proximal region of southwest Japan, magmatism initiated around 15.6 Ma, immediately following the cessation of the Japan Sea opening, in correlation with the subduction of the Philippine Sea plate beneath southwest Japan. The Amakusa Islands in western Kyushu host felsic to intermediate igneous rocks with Miocene radiometric ages. There has been a debate regarding the attribution of the igneous rocks in Amakusa Island among the Miocene igneous rocks in southwest Japan. To address this issue, we conducted zircon U–Pb dating and analyzed the major‐ and trace‐element compositions of felsic igneous rocks in the Amakusa Islands to elucidate their characteristics. The obtained U–Pb ages range from 14.5 to 14.8 Ma, suggesting contemporaneity between magmatism in the Amakusa Islands and the Setouchi Volcanic Rocks in the trench‐proximal region of southwest Japan. The major and trace element compositions of the felsic igneous rocks exhibit similarities to the dacites of the Setouchi Volcanic Rocks. These findings support previous suggestions that the magmatism in the Amakusa Islands can be correlated with the Setouchi Volcanic Rocks, based on the discovery of a high‐Mg andesite dike and paleo‐stress analysis utilizing the direction of dikes and sills. Therefore, the Setouchi Volcanic Belt is proposed to extend further west than the previously identified Ohno volcanic rocks in eastern Kyushu. The subduction of the Shikoku Basin of the Philippine Sea plate toward western Kyushu supports the hypothesis that the Kyushu‐Palau Ridge was positioned west of Kyushu at ~15 Ma.

Geochemical and mineralogical responses to thermal alteration by an igneous intrusion in the Dashucun Coal Mine of the Fengfeng coalfield, Hebei, North China

Igneous intrusions into coal affect the safety, productivity, and economic viability of many coal mines. Also, the alterations in coal caused by igneous intrusions encompass a deterioration in coal quality, a decrease in permeability, an enhancement of coal rank, and geochemical and mineralogical compositions. Although there have been some studies related to the effects of igneous intrusions on the inorganic constituents in the coal, the mechanism of newly formed chemical and mineralogical associations caused by igneous intrusions has not been fully understood.This paper investigates the mineralogical and geochemical responses of coal to thermal alteration by igneous intrusion into an Early Permian coal seam in Hebei Province, North China. The Fengfeng coalfield is structurally complex, experiencing variable rates of burial and uplift, with abundant intrusions during the upper Jurassic and maximum burial in the Cretaceous resulting in an increase in rank to the north. In the search for critical minerals and elements, intrusions and hydrothermal alteration are often cited as the source for elevated concentrations.Towards the intrusion, the coal rank indicators increase from semi-anthracite to anthracite over a 500-cm distance, as does the mineral matter. The clay minerals present in coals include NH4-illite, kaolinite, paragonite, and chlorite (chamosite and cookeite), which were all resulted from igneous intrusions. The epigenetic minerals mainly include quartz, ankerite, calcite, pyrite, and apatite, which were derived from fluids permeating into the coal seam and chemically interacting with the original minerals or precipitating directly to form new minerals.Geochemical indicators in this coal indicate hydrothermal solutions derived from igneous intrusion. The enrichment of Li and Hg is linked to the igneous activity, potentially influencing the utilization of the coal adjacent to the intrusions. However, the concentrations of the remaining elements in the coal closest to the intrusion show no significant changes, thereby supporting the notion of a “non-universal effect” of igneous intrusions on the elemental composition and concentrations.

Turbulent paleoenvironment linked to astronomical forcing during the Permian–Triassic transition

The Milankovitch cycles are essential for establishing high-resolution chronological frameworks, which can provide a reliable timescale for biological and environmental events. However, astronomical solutions for the Paleozoic are still imperfect. Moreover, global paleoenvironmental turbulence during the Permian-Triassic (PT) transition caused interference with most proxies reflecting astronomical cycles. This study discovered that the Sb/Cd series can reflect astronomical cycle signals through a time-series analysis of geochemical elemental data from cores around the Lopingian–Lower Triassic in the Lower Yangtze region. Combined with zircon SHRIMP dating of volcanic ashes, a reliable absolute astronomical timescale with a duration of 2.5 Myr was established from 100-kyr eccentricity-tuned results. Based on the coupling analysis of palaeoenvironmental proxies, this study evaluated the effect of astronomical forcing and volcanism on the paleoenvironment. The sea level change was influenced by obliquity during the Lopingian–Early Triassic. During the Wuchiapingian–Changhsingian (WC) and PT transitions, regional volcanic activities at South China and the Siberian Traps Large Igneous Province (STLIP) intervened the normal trend of a low-temperature arid climate dominated by the obliquity forcing, respectively. Thus, South China exhibited a hot humid climate during the WC and PT transitions. Conversely, the low-temperature climate in South China was significantly modulated by obliquity forcing during the middle Changhsingian. Besides the influences of intense igneous activities and related environmental effects, disruption the long-term stable low-temperature environment by the abnormal high-temperature around the PT transition was a tremendous challenge to the biological ecological adaptation, and thereby may have contributed to the end-Permian mass extinction.

Petrogenesis of the Morobe Granodiorite and their shoshonitic mafic microgranular enclaves in Maramuni arc, Papua New Guinea

Abstract The Miocene tectonics of Papua New Guinea, where subduction, arc-continent collision, and changes in subduction direction are considered to have occurred, is very complex and various tectonic models have been proposed. The Maramuni arc, active in the Miocene, is composed of a chain of granitoid bodies. As the chain-like distribution indicates the generation of igneous activities in a wide range of the same tectonic settings, the study of the Maramuni arc magmatism is important for elucidating the geologic events of the time. We provide data on the petrological and geochemical characteristics of the Morobe Granodiorite that form part of the Maramuni arc. The Morobe Granodiorite consists of metaluminous I-type granitoids, belonging to the medium-K to high-K series. The whole-rock major element variations in the granitoids can be explained by the fractionation of hornblende and plagioclase. They are generally within the composition range of experimental partial melts of amphibolites, and the whole-rock trace element compositions have characteristics of slab failure magma rather than arc. This suggests that the granitoids were generated by partial melting of the torn slab after slab failure. The mafic microgranular enclaves (MMEs) in the granitoids are classified as shoshonite, and their trace element compositions suggest that they were formed by partial melting of phlogopite-bearing mantle. The occurrences of native gold and barite within the MME show that MMEs transport Au from the mantle metasomatized by slab-derived sediment melt and/or fluid to the crustal magma chamber.

Assessment of potentially hazardous elements in soils of the Boyacá industrial corridor (Colombia) using GIS, multivariate statistical analysis, and geochemical indexes

In the industrial corridor of Boyacá, Colombia, population growth is accompanied by anthropogenic activities such as industrial operations, vehicle exhaust fumes, mining, smelting, atmospheric deposition, and excessive use of chemical products to promote crop growth. These activities are known to have a significant impact on urban and rural soils, contributing significantly to elevated concentrations of potentially hazardous elements in the environment. This industrial corridor is an area of economic and social development that needs to provide reference information that will allow us to know the state of soil quality to preserve and manage the public and geoenvironmental health of this region. Anthropogenic activities have contributed to the accumulation of potentially hazardous elements in the environment, affecting various levels of life and creating risks with economic and social implications. However, igneous activity or detrital deposition also enriches soils and creates geochemical anomalies in specific locations. In these cases, the identification of potentially hazardous elements involves the determination of likely sources of contamination and their relationship to the geological setting. In this study, the concentrations of As, Cd, Pb, Mn, Fe, Zn, Hg, Cu and Ni were determined in eighty-one soil samples from the Boyacá industrial corridor (Colombia). The sequential trend of the concentrations of potentially hazardous elements was as follows: Fe > Mn > Zn > Ni > Cu> Pb > As > Cd > Hg. Furthermore, the application of spatial analysis criteria in GIS software with multivariate statistical tools and geochemical indices allowed the identification of anthropogenic and geogenic sources. Most of the potentially hazardous elements were found in soils exposed to industrial and agricultural activities, except for iron. This element showed low variability in all samples, regardless of the geological formations. Due to the lack of reference values for potentially hazardous elements in Colombia, the concentrations were compared with the environmental standards of the Environmental Protection Agency (EPA) and the Ecuadorian Ministry of Environment, Water and Ecological Transition (MAE). The results demonstrate the complexity of the soil and represent the first exploratory study of potentially hazardous elements in this industrial corridor. These results are the starting point for the establishment of geochemical background lines in Colombia and for inspection policies for areas where productive activities converge.

Timing of Izanagi-Pacific ridge subduction beneath Eurasia: Constraints from metamorphic soles in Hokkaido, Japan

The subduction of the Pacific Plate beneath Eurasia controls not only Cenozoic intraplate volcanism, but also deep-focus earthquakes along the continental margin of eastern Asia. However, the timing of subduction of the Paleo-Pacific (Izanagi)−Pacific ridge and the initial subduction of the Pacific Plate beneath Eurasia remain subjects of debate. Metamorphic soles provide key evidence for ridge subduction, and together with coeval igneous activity, they are widely used to constrain the timing of ridge subduction. Here, we present the results of a study of amphibolites from the Hidaka metamorphic belt, Hokkaido, northern Japan, which are interpreted to be metamorphic soles. Our integrated study involved secondary ion mass spectrometry (SIMS) U-Pb zircon dating, mineral chemistry, whole-rock geochemistry, and Sr-Nd-Pb-Hf isotopic analyses. SIMS U-Pb zircon dating indicates that the amphibolite-facies sole metamorphism occurred in the late Eocene. Phase equilibria modeling suggests that the peak P−T conditions of metamorphism were 8.0−9.5 kbar/700−730 °C. The amphibolites belong to the tholeiitic series, and they are relatively enriched in heavy rare earth elements relative to light rare earth elements, with depletions in Nb, Ta, P, and Ti. They have (87Sr/86Sr)i = 0.704207−0.704998, εNd(t) = +11.65 to +11.96, εHf(t) = +14.28 to +16.32, (206Pb/204Pb)i = 18.240−18.255, and (207Pb/204Pb)i = 15.522−15.525. The geochemistry of these amphibolites reveals that their protoliths had normal mid-oceanic-ridge basalt affinities, and their Pb isotopic signatures indicate Indian-type mantle rather than Pacific-type mantle. Considering the geochemistry of coeval igneous rocks, we conclude that the late Eocene metamorphism in the Hidaka metamorphic belt records the intraoceanic subduction that followed heat transfer from the incipient mantle wedge toward the top of the subducting plate, and it provides a key constraint on the timing of subduction of the Izanagi-Pacific ridge.

Clockwise rotation of SW Japan and timing of Izanagi–Pacific ridge subduction revealed by arc migration

Igneous rocks associated with the Cretaceous to Paleogene volcanic arc in SW Japan show ages that young from west to east in a direction parallel to the Median Tectonic Line suggesting corresponding translation of a heat source traditionally interpreted in terms of oblique subduction of a spreading ridge. However, recent oceanic plate reconstructions suggest ridge subduction may be younger than the main arc activity. Age compilations of 1227 points of felsic to intermediate Cretaceous and Cenozoic igneous rocks from the Japan arc show arc magmatism that can be separated into an early active period 130–60 Ma (stage 1), a subsequent period of quiescence 60–46 Ma (stage 2), which is followed by a resumption of igneous activity from 46 Ma onward (stage 3). In southwest Japan, the orientations of the magmatic arcs of stages 1 and 3 show and angular discordance of about 20°. The lack of active arc magmatism and the occurrence patterns of adakitic and high-Mg andesitic magmas indicate that ridge subduction occurred during stage 2. The arc age distribution pattern of stage 1 is explained by the slab shallowing related to a younging of the subducting slab as the ridge approaches. Furthermore, the obliquity of the arcs formed at stages 1 and 3 is explained by a 20° clockwise rotation of the inner zone of southwest Japan during the ridge-subduction phase. Oceanic plate reconstructions show counterclockwise rotation in the subduction direction after the ridge subduction phase, and coupling of the subducting oceanic plate with the upper plate would support microplate rotation in the inner zone. The new proposed tectonic reconstructions provide a framework to related Paleogene subduction of an active spreading ridge along the east Asia margin not only to the distribution of granitic bodies but also to rift-related basin formation on the eastern margin of the Eurasian continent and to rotation of crustal blocks indicated by paleomagnetic data of Cretaceous terranes.

Detrital Zircon Geochronology and Provenance of Metasedimentary Rocks from the Susong Complex Zone in the Dabie Orogen

AbstractThe Susong complex zone is a relatively low‐grade metamorphic unit located in the southern part of the Dabie orogen and preserves a variety of metasedimentary rocks, mostly with epidote–amphibolite facies. However, their depositional age, provenance and tectonic setting of sedimentary protolith remain controversial due to the lack of fossils, precise dating and integrated geochemical investigation. This study has conducted whole‐rock elemental, and zircon U‐Pb SHRIMP dating and Lu‐Hf isotope analyses on three types of representative metasedimentary rocks including garnet‐bearing mica‐quartz schist, graphite‐muscovite‐quartz schist and dolomitic marble from the Susong complex zone. The U‐Pb SHRIMP dating data indicate that the sedimentary protolith of these rocks have the maximum depositional ages of less than 840–750 Ma and have various sedimentary provenances. In combination with zircon Lu‐Hf isotope compositions, the provenance of the metasedimentary rocks in the region is for the first time documented to be mainly derived from four groups of magmatic rocks formed at ∼2.5 Ga, ∼2.0 Ga, ∼1.4 Ga and ∼0.8 Ga in response to four episodes of igneous activity in the northeastern margin of the Yangtze Block. The conventional geothermobarometry combined with rare metamorphic zircon ages indicate that the studied rocks underwent the Late Triassic continental subduction‐related metamorphism with peak epidote–amphibolite facies conditions at P = 0.34–0.91 GPa and T = 427–532°C. In addition, results of the elemental contents (i.e., La, Ce, Th and ΣREE) and ratios (i.e., Eu/Eu* and LaN/YbN) suggest that the protoliths of the metasedimentary rocks were mainly shales, wackes and limestones, most probably related to the Rodinia supercontinent rifting along the northern margin of the Yangtze Block during the Neoproterozoic.