Submarine Volcanism Research Articles

Earliest BIF and Life Produced via Submarine Volcanism in Carbonated Seawater

Earliest BIF and Life Produced via Submarine Volcanism in Carbonated Seawater

Mercury evidence of intense submarine volcanism and hydrothermal activity during a mid-Tournaisian anoxic event in the Carnic Alps

The mid-Tournaisian Event, or Lower Alum Shale Event (LASE), is linked to severe facies changes including pelagic carbonates and widespread black siliceous shales and radiolarites in many parts of the world. For the first time, high-resolution inorganic geochemistry and framboidal pyrite analyses were applied to decipher depositional condition changes during the mid-Tournaisian event in the Carnic Alps. The predominance of tiny pyrite framboids, high Corg/P, U/Th, and V/Cr ratios, generally higher enrichments of redox-sensitive metals such as Mo, U, V, and depletion in Mn suggest anoxic/euxinic conditions at the sea bottom. Moreover, we found very large anomalous Hg spikes (with maximum values reaching 3650 ppb) for the first time in the mid-Tournaisian deep-water marine succession of the Carnic Alps. Our results suggest intense volcanism during the LASE, which triggered the mid-Tournaisian anoxic event. The most likely candidate for the observed Hg anomalous contents is submarine arc volcanism and hydrothermal activity connected with the collision of the peri-Gondwanan terranes Paleo-Adria and probably Armorican Terrane Assemblage (ATA) and/or Noric terrane during the first phase of the Variscan orogeny.

Climate/ocean dynamics and possible atmospheric mercury depletion events during the Late Sturtian deglaciation

Late Sturtian deglaciation, resulting in development of oxic conditions and deposition of banded iron formations (BIFs), was a pivotal period in evolution of global ocean chemistry. The driving forces behind these Neoproterozoic BIFs and climatic/oceanic changes remain controversial, however. Here we use mercury (Hg) to elucidate the cause(s) of these dramatic changes to earth biogeochemical cycles. In the Guandong section, South China, we observe anomalously low Hg concentrations and Hg to total organic carbon (Hg/TOC) ratios in the Late Sturtian BIFs, suggesting a period of limited continental volcanism during the Late Sturtian deglaciation. We hypothesize that instead of a major LIP event, long-lasting and subdued submarine volcanism slowly increased atmospheric CO2 to trigger the greenhouse climate that caused deglaciation. Negative shifts of Δ199Hg in the studied section suggest that deglaciation was accompanied by atmospheric mercury depletion events (AMDEs). Extremely low TOC levels in the studied section may suggest low oceanic productivity, and this may support a non-biological cause of oceanic oxygenation during the Late Sturtian glaciation, through the release of photochemically produced H2O2 in melting glaciers.

ICESat-2 Applications for Investigating Emerging Volcanoes

Submarine volcanism in shallow waters (<100 m), particularly in remote settings, is difficult to monitor quantitatively and, in the rare formation of islands, it is challenging to understand the rapid-paced erosion. However, these newly erupted volcanic islands become observable to airborne and/or satellite remote sensing instruments. NASA’s ICESat-2 satellite laser altimeter, combined with visible imagery (optical and microwave), provide a novel method of evaluating the elevation characteristics of newly emerged volcanoes and their subaerial eruption products. Niijima Fukutoku-Okanoba (NFO) is a submarine volcano 1300 km south of Tokyo (Ogasawara Archipelago of Japan) that periodically breaches the ocean surface to create new islands that are subsequently eroded. The recent eruption in August 2021 is a rare opportunity to investigate this island evolution using high-resolution satellite datasets with geodetic-quality ICESat-2 altimetry. Lansdat-8 and Planet imagery provide a qualitative analysis of the exposed volcanic deposits, while ICESat-2 products provide elevation profiles necessary to quantify the physical surface structures. This investigation determines an innovative application for ICESat-2 data in evaluating newly emerged islands and how the combination of satellite remote sensing (visible and lidar) to investigate these short-lived volcanic features can improve our understanding of the volcanic island system in ways not previously possible.

Volcanic tremor associated with the Surtsey eruption of 1963–1967

The formation of the island of Surtsey over 3.5 years, remains one of the best-documented volcanic, island-forming eruptions to date. The basaltic submarine volcanic activity was detected on November 14, 1963, where ocean depth was 130 m prior to the eruption at the southern end of the Vestmannaeyjar archipelago. The eruptions occurred in several phases involving explosive and effusive activity, including the initial submarine phase on November 12–13, 1963. Separate phases of subaerial volcanic activity occurred during November 14, 1963–January 1964, January–April 1964, April 1964–May 1965, May–October 1965, December 1965–August 1966, and August 1966–June 1967. Seismic data quality from this period is inferior compared to that of modern monitoring systems. Four permanent seismic stations were operated in Iceland at the time, whereof only two, located at 115 and 140 km distance, had the sensitivity to record tremor from Surtsey. Nevertheless, the scanned analog seismograms (http://seismis.hi.is/) show that the eruptive activity was accompanied by considerable seismic activity, both earthquakes, and volcanic tremor. Earthquakes were primarily associated with changes in vent location. Both spasmodic and harmonic tremor was identified, both with low (<3 Hz) and higher (3–5 Hz) characteristic frequencies. The results indicate a complicated relationship between tremor and magma flow rate or style of activity. During the explosive eruption, the highest magma flow rates occurred in the first 10–20 days, a period with little observed tremor. The highest tremor is observed in December 1963–March 1964, after the discharge rates had dropped substantially, and on a timescale of hours-to-days, no clear relationship between tremor and eruption style is observed. The same applies to the effusive activity, where no seismic tremor was observed during most of the effusive eruption of Surtungur, despite the fact that magma flow rates were ~3 times higher than during later phases where some tremor was observed. Keywords: Submarine volcanism, eruption precursors, volcanic tremor, precursory tremor, continuous uprush eruptions

The C-O and Zn isotopic compositions of the Laochang Ag-Pb-Zn ore bodies in the Changning-Menglian suture zone, and its geological implications

老厂矿床是昌宁-孟连缝合带内唯一大型矿床，本文报道了老厂矿床Ag-Pb-Zn矿体中Ⅰ号矿体群下部块状矿体和上部网脉状矿体的方解石C-O同位素组成，以及Ⅰ、Ⅱ、Ⅳ三个矿体群内闪锌矿的Zn同位素组成。Ⅰ号矿体群下部块状矿体和上部网脉状矿体方解石δ¹³C_PDB的范围分别为-6.17‰~2.71‰和-2.18‰~3.87‰，δ¹⁸O_PDB的范围分别为-19.57‰~-17.23‰和-22.10‰~-16.21‰；计算获得对应成矿流体的δ¹³C_CO₂为-6.16‰~1.53‰和-2.39‰~6.43‰，δ¹⁸O_H₂O分别为1.62‰~7.62‰和4.36‰~16.92‰，通过与岩浆CO₂（δ¹³C=-2‰~-8‰）和围岩灰岩（δ¹³C=-1.6‰~4.0‰）的δ¹³C值相比较，指示块状矿体成矿流体中的碳主要来自岩浆，网脉状矿体成矿流体中的碳则主要来自围岩，说明老厂矿床深部水岩反应较强。10件闪锌矿的δ⁶⁶Zn和δ⁶⁸Zn值分别为0.17‰~0.25‰和0.33‰~0.49‰，与VMS型矿床以及现代海底热液流体的Zn同位素组成重合，不同标高均一的Zn同位素组成寓示老厂矿床Ag-Pb-Zn矿体中闪锌矿形成过程中几乎未受到温度、分馏和微生物作用的影响，可以直接反映金属源区的Zn同位素组成，揭示老厂矿床Ag-Pb-Zn矿体为VMS成因，成矿金属主要来自于下石炭统海底火山作用。;The Laochang deposit is the only large ore deposit in the Changning-Menglian suture zone. In this study, the C-O isotopic compositions of calcites from the lower massive ore bodies and the upper stockwork ore bodies of No.Ⅰ ore bodies in Laochang Ag-Pb-Zn ore bodies and the Zn isotopic compositions of sphalerites from No.Ⅰ, Ⅱ, Ⅳ ore bodies are investigated. The range of δ¹³C_PDB of calcites from the lower massive ore bodies and the upper stockwork ore bodies of No.Ⅰ ore bodies is -6.17‰~2.71‰ and -2.18‰~3.87‰, respectively, and the range of δ¹⁸O_PDB is -19.57‰~-17.23‰ and -22.10‰~-16.21‰, respectively. The δ¹³C_CO₂ of the corresponding ore-forming fluids are calculated to be -6.16‰~1.53‰ and -2.39‰~6.43‰, respectively, and the δ¹⁸O_H₂O are calculated to be 1.62‰~7.62‰ and 4.36‰~16.92‰, respectively. By comparison with the δ¹³C of magmatic CO₂ (δ¹³C=-2‰~-8‰) and wall-rock limestone (δ¹³C=-1.6‰~4.0‰), it indicates that the carbon in the ore-forming fluids of massive ore bodies mainly comes from magma, while the carbon in the ore-forming fluids of stockwork ore bodies mainly comes from limestone, which further shows that there is strong water-rock reaction in the deep part of Laochang deposit. The δ⁶⁶Zn and δ⁶⁸Zn values of ten sphalerites are 0.17‰~0.25‰ and 0.33‰~0.49‰, respectively, which coincides with the Zn isotopic compositions of VMS deposits and modern submarine hydrothermal fluids. The homogeneous Zn isotopic compositions at different elevations implies that the Zn isotopic compositions of sphalerite from Ag-Pb-Zn orebodies in Laochang deposit are almost unaffected by temperature, fractionation and microbial action. And it can directly reflect the Zn isotopic compositions of the metal source, revealing the genesis type of the Laochang Ag-Pb-Zn ore body as VMS-type, and the metallogenic metal mainly comes from the Lower Carboniferous submarine volcanism.

The Barzavand and Neysian Copper Deposits, NW Naein, Central Iran zone: Constraints on styles mineralization and geochemical signatures of hydrothermal alterations.

Field observations in the northwest of Naein (Central Iran zone) indicate various types of alteration products have extended into pyroclastic and volcanic units with Oligo- miocene age. It seems the Zefreh (with NW- SE trend) and Kachumesqal (with E-W trend) faults are effective factors in the formation of Neysian and Barzavand copper deposits respectively. Alteration in Barzavand copper deposit (with stratabound form) includes pyritization, propylitization, zeolitization, saussuritization, uralitization and silicification, while in Neysian (with oval form) include phyllic, advanced argillic, argillic and propylitic. Geochemical studies in Barzavand show the positive correlation between (La/Lu)N, (La/Yb)N and (La/Sm)N and CaO (r= 0.70 to 0.96) related to propylitization of host rock basalt and increase in pH of fluids responsible for mineralization that play important role in differentiation of lanthanides in study area. The Barzavand copper deposit has submarine volcanism, diagenesis, burial metamorphism and weathering stages during its evolution. Remarkable geochemical features in Neysian include high (La/Lu)N, Ba and Sr values than La, Ce and Y. It seems that extensive alteration occurred along with hypogene and supergene processes in Neysian. According to alteration properties, mineralogy and the whole-rock geochemistry, the Barzavand and Neysian copper deposits are most similar to Manto- type and porphyry copper deposits respectively.

Ediacaran iron formations from the North Qilian Orogenic Belt, China: Age, geochemistry, Sm–Nd isotopes and link with submarine volcanism

Iron formations (IFs) are relatively rare in the Neoproterozoic, and a few examples are closely related to the Cryogenian (∼717–635 Ma) Snowball Earth glaciations. In this study, we investigated the rare IFs formed during the Ediacaran period (635–541 Ma) which are hosted in volcano-sedimentary successions belonging to the Zhulongguan Group in the North Qilian Orogenic Belt in northwestern China. Detrital zircon U–Pb data from the tuffaceous breccia associated with the Kawa IF in this region show a large variation in ages between 749 Ma and 2706 Ma. However, two ferruginous tuff samples yielded zircon 206Pb/238U ages of 601.9 ± 6.1 Ma and 598.2 ± 5.5 Ma, respectively. These ages indicate that the Kawa volcano-sedimentary successions and associated IF were deposited at ∼ 600 Ma. Banding/lamina are not well developed in the IF and the rock is dominantly composed of hematite and jasper, with minor clay minerals and breccia. The IF shows high TFe2O3 and SiO2 contents (TFe2O3 + SiO2 = 83–90 wt%) with relatively elevated Al2O3, TiO2, HFSEs (e.g., Nb, Hf and Th) and rare earth element (REE) concentrations. The geochemical features are consistent with chemical sediments with significant clastic material input (∼20%). The rocks also show light REE depletion [(La/Yb)PAAS = 0.23–0.34], slightly positive Eu anomalies (Eu/Eu*=1.03–1.12), low Y/Ho ratios of 27.17–29.53, and slightly negative εNd(t) values (−2.03 – −0.70), indicating a submarine hydrothermal source for the iron with dilution by detrital components and seawater. The lack of negative Ce anomalies and redox-sensitive trace element enrichments (e.g., Mo, U, and V), the presence of chamosite, and the relatively high TFe2O3 contents in the ferruginous tuff and slate suggests anoxic and ferruginous conditions. Our results link the post-Cryogenian Kawa IF with submarine volcanism and hydrothermal activity, in response to the breakup of Rodinia.

Waves Generated by Discrete and Sustained Gas Eruptions With Implications for Submarine Volcanic Tsunamis

AbstractSubmarine volcanic eruptions can perturb the water surface and subsequently generate localized tsunamis. Herein waves are produced in analogous laboratory experiments by injections of non‐condensable expanding air into fresh water. By varying source pressures, jet durations and water depths, we obtain two key results. There exists a saturation duration above which the maximum wave height will not increase as the eruption continues. Apart from in extremely shallow or deep water depths, this saturation duration is positively correlated with the source intensity and negatively with the water depth. There also exists a critical water depth where an eruption with a given source intensity can generate the largest waves. When an eruption lasts less than the saturation duration, increasing the eruption duration will increase the critical water depth and the corresponding maximum wave height. The saturation duration and critical water depth are the primary controls on tsunami size and hazard.

Age of Initial Submarine Volcanism in the Paleo-Tsushima Basin and Implications for Submarine Volcanism in the Opening Stage of the Japan Sea in Northern Kyushu

The Tsushima Lapilli Tuff, the thickest tuff in the Taishu Group on Tsushima Island, underwent a thermal event after deposition, and has not previously yielded a reliable age because various ages have been reported. This study clarifies the eruption age and thermal history of the Tsushima Lapilli Tuff based on fission-track (FT) and U–Pb dating of zircon grains using laser ablation inductively coupled plasma mass spectrometry (ICP-LA-MS) and evaluates submarine volcanism during deposition of the Taishu Group in the southwestern Japan Sea, as well as volcanism change on Tsushima Island. This study revealed that thermal events caused rejuvenation in some single-grain FT ages after deposition in the Tsushima Group, and that the eruption age of the Tsushima Lapilli Tuff was 16.2 ± 0.7 Ma; the age of the largest submarine volcanism event in the Taishu Group in Tsushima Island was thus determined. On the basis of our previous studies, this age and tectonism strongly indicate that felsic submarine volcanism occurred between 18 and 16 Ma, accompanied by rapid subsidence, and the volcanism changed from felsic volcanism originating from melting of old continental crust by asthenospheric upwelling to mafic volcanism originating from small-scale lithospheric mantle upwelling from 13.6 Ma onward.

Pulsed volcanism and rapid oceanic deoxygenation during Oceanic Anoxic Event 1a

Abstract Widespread oceanic anoxia, biological crises, and volcanic activity are associated with the onset of Early Aptian (ca. 120 Ma) Oceanic Anoxic Event 1a (OAE1a). Reconstructions of oceanic deoxygenation and its links to broadly contemporaneous volcanism, however, remain poorly resolved. We use geochemical data, including δ53Cr ratios and rare Earth element abundances, to define the timing and tempo of submarine volcanism and global oceanic deoxygenation across this event. Pacific Ocean sediments deposited in the run up to OAE1a record multiple phases of marine volcanism associated with the emplacement of Ontong Java Plateau lavas. Rapid oceanic deoxygenation followed the initial phases of volcanism and a biocalcification crisis. Large swaths of the oceans likely became anoxic from the Tethys to the Pacific Oceans in <30 k.y. Oceanic anoxia persisted for almost one million years after this and was likely sustained through intensified continental and submarine weathering. These results paint a new picture of OAE1a in which volcanism, biological crisis, and oceanic deoxygenation are separated in time and linked through Earth system responses that operate on time scales of tens of thousands of years.

Enhancement of volcanic eruption in mid-ocean ridge during the last deglaciation: New sedimentary evidence in the middle part of Central Indian Ridge

Sedimentary evidence for enhanced volcanic eruption during the glacial/interglacial transition in the volcanically active mid-ocean ridges is still lacking. Here, we present the sedimentary records of enhanced deglacial volcanic activity in a well-dated sediment core from the middle part of Central Indian Ridge (CIR), which can provide clue for comprehensively understanding of the temporal relation of increase in submarine volcanism relative to glacial/interglacial transition. Notably, the 35-kyr sediment core used in this study contains continuous, discernible pyroclastic deposit layers (0.5–5 cm thick), which are composed mainly of angular and curved fluidal shards with vesicles, possibly suggesting volatile-rich ridge eruptions. High-resolution elemental profiles of the core provide definite records of at least 17 volcanic eruptions during the past 35 kyr. Interestingly, volcanism was sparse during the Last Glacial Maximum (LGM), but increased significantly during the last deglaciation after ~18 kyr BP. The last deglaciation-associated volcanic eruptions in the CIR may be linked to decompression melting during the LGM sea-level lowstand, reaffirming an influence of sea level variability on global ocean ridge magmatism. Combining the previous results, furthermore, simultaneous strengthening of submarine and subaerial volcanic eruptions during the last deglaciation could have accelerated the rise of atmospheric CO2, with the ensuing warming constituting positive feedback upon deglaciation.

Two-phase mineralization of Hongtaiping Cu polymetallic deposit in Yanbian area (NE China): Evidence from sulfide Rb–Sr dating and in-situ trace element analysis

The Hongtaiping Cu polymetallic deposit in Yanbian area (NE China) is located in the tectonic junction between the eastern Central Asian Orogenic Belt and the North China Craton. Two mineralization types are identified at the Hongtaiping deposit, i.e., stratiform mineralization hosted in the pyroclastic rocks of the Middle Permian Miaoling Formation (Fm.) and the quartz-sulfide vein-type mineralization controlled by fractures. To determine temporal and genetic relations between the two mineralization types, sulfide Rb–Sr dating and in-situ LA–ICP–MS trace element analysis were conducted. Seven sulfide samples from stratiform orebodies yielded a Rb–Sr isochron age of 268.3 ± 2.6 Ma, which is similar to the reported zircon U–Pb age of ore-hosting pyroclastic rocks of the Miaoling Fm., suggesting that the stratiform mineralization was syngenetic. The initial 87Sr/86Sr ratios of these sulfide samples show value of 0.7102–0.7103 (average of 0.7103), implying a major crustal origin, with certain mantle-derived input, for the ore-forming materials of the stratiform mineralization. Sulfides from the stratiform and vein-type ores have distinct trace elemental features. High Co/Ni ratio and low Se content in pyrite, and high Sn content and low Zn content in chalcopyrite reflect high temperature and vice versa. In the pyrite from stratiform and vein-type ores, average Se contents are 19.72 ppm and 9.70 ppm, and average Co/Ni ratios are 0.20 and 2.46, respectively. Whilst in the chalcopyrite from stratiform and vein-type ores, average Sn contents are 2.49 ppm and 60.31 ppm and average Zn contents are 346.55 ppm and 236.17 ppm, respectively, indicating that the temperature of the stratiform mineralization is lower than that of the vein-type mineralization. Integrating the geological and geochronological features of the two types of mineralization and wall rocks, as well as trace element compositions of the sulfides, we inferred that the stratiform mineralization at the Hongtaiping deposit can be classified as volcanogenic massive sulfide (VMS)-type, associated with the Middle Permian submarine volcanism caused by the subduction of the Paleo-Asian Ocean. The vein-type mineralization was likely related to the Late Triassic felsic magmatism. In a word, two-phase mineralization implies the VMS-hydrothermal reworking-type for the Hongtaiping deposit.

Offshore Geological Hazards: Charting the Course of Progress and Future Directions

Offshore geological hazards can occur in any marine domain or environment and represent a serious threat to society, the economy, and the environment. Seismicity, slope sedimentary instabilities, submarine volcanism, fluid flow processes, and bottom currents are considered here because they are the most common hazardous processes; tsunamis are also examined because they are a secondary hazard generated mostly by earthquakes, slope instabilities, or volcanic eruptions. The hazards can co-occur and interact, inducing a cascading sequence of events, especially in certain contexts, such as tectonic indentations, volcanic islands, and canyon heads close to the coast. We analyze the key characteristics and main shortcomings of offshore geological hazards to identify their present and future directions for marine geoscience investigations of their identification and characterization. This review establishes that future research will rely on studies including a high level of multidisciplinarity. This approach, which also involves scientific and technological challenges, will require effective integration and interplay between multiscale analysis, mapping, direct deep-sea observations and testing, modelling, and linking offshore observations with onshore observations.

Discovery of cyanobacteria fossils in the Bayan Obo Fe-Nb REE deposit and its geological significance

<p indent=0mm>The Bayan Obo deposit in China is known for its huge Fe-Nb-REE resource. The genesis of the ore-hosted H8 dolomite is of great significance to the understanding of the Fe-Nb-REE mineralization. Generally, there are two opposite views established: (1) Intense differentiated mantle-derived carbonates as intrusions or submarine volcanics, and (2) sedimentary origin which was metasomatized by extreme REE-enriched mantle fluids sourced from carbonatitic magmas. However, neither of them could well interpret the fuzzy information given by geochemistry and Fe-Nb-REE mineralization, hence a definite sign should be found. This paper reports the newly discovered cyanobacteria fossils in the massive Fe-Nb-REE ores from the western ore deposit and provides detailed petrographic studies of the cyanobacteria and the spatial relationship with the Fe-Nb-REE mineralization and minerals, aiming to give a reasonable interpretation for the genesis of H8 dolomite. The samples are massive Fe-Nb-REE ores, composed mainly of microorganism dolomite fragments, massive Fe-Nb-REE layers, and coarse-grain dolomite veins. The cyanobacteria is distributed in the “dirty” fine-grained dolomites, consisting of a row of ellipsoidal cells, with a maximum diameter of <sc>~131 μm</sc> and a length of <sc>614 μm.</sc> The outline of the fossil is long columnar, without bifurcation, with a cylindrical front end and pointed back end. The morphology of the fossil is similar to the cyanobacterial filaments. The cell structure is clear under the BSE images, with Ca-Si mineralization for the cell wall and Fe-Mg carbonatization for the cavity. Two groups of cyanobacteria could be distinguished based on their different colors under a polarizing microscope. One group shows yellow translucent probably related with the calcite mineralization and the other group is black opacity related with the Fe-Mg carbonatization. Accessory minerals in the cyanobacteria dolomites include calcite, magnetite, hematite, pyrite, REE minerals, barite, and other carbonate and sulfate minerals. Detailed works reveal that the cyanobacteria dolomites and massive Fe-Nb-REE layers are mutually contained and then filled by coarse-grain dolomite veins along the cracks, based on that (1) their host dolomites show very clear BSE boundary with different components, Mg-Ca vs. Fe-Mn, (2) fragments of the Fe-Nb-REE layers could be found in the cyanobacteria dolomites, while cyanobacterial bioclasts are developed in the Fe-Nb-REE layers, and (3) cyanobacteria fossils are included in coarse-grained dolomites by recrystallization of fine-grained dolomites. Therefore, the cyanobacteria dolomites and massive Fe-Nb-REE layers should be syngenetic sedimented in a locally turbulent shallow sea setting. However, we would like to point out that the massive Fe-Nb-REE layers are not the original composition of sedimentary, but the products of modification by igneous carbonatites and the original composition are most likely to be Fe-Mn carbonates. In this paper, we tend to consider that the Bayan Obo H8 dolomite may be composed dominantly of iron-bearing carbonate formation, and is a classic case of microbial dolomite. Furthermore, photosynthesis is needed during the growth of cyanobacteria, therefore, a depth of < <sc>50 m</sc> is the best speculation for the sedimentary of H8 dolomite. The photosynthesis of cyanobacteria was important for the alteration of the paleoenvironment. Extra oxygen produced by the microbial activity could promote the precipitation of Fe-REE minerals within the dolomite. The magmatic emplacement of Nb-REE rich carbonatites and hydrothermal fluid may have facilitated Fe deposition and contributed some iron. Therefore, the life activities of cyanobacteria may indirectly control the Fe-REE migration and mineralization process in Bayan Obo, thus forming the protore of Fe-REE mineralization.

The Seismo‐Acoustics of Submarine Volcanic Eruptions

AbstractMany of the world’s volcanoes are hidden beneath the ocean’s surface where eruptions are difficult to observe. However, seismo‐acoustic signals produced by these eruptions provide a useful means of identifying active submarine volcanism. A literature survey revealed reports of 119 seismo‐acoustically recorded submarine eruptions since 1939. Submarine eruptions have been recorded in all major tectonic settings, with a range of geochemistries, and at a variety of water depths, but the reports are dominated by eruptions in the Pacific and at only a few locations. Many of the reports offer little detail, with over half of the observations made from distances &gt;500 km, and only about half were confirmed as eruptions by non‐seismo‐acoustic evidence. The reported seismo‐acoustic signals cover a wide variety of processes, including earthquakes, explosions, various types of tremor, signals related to lava extrusion, and landslides. Recorded signals can sometimes be difficult to classify or confidently associate with an eruption, although there has been progress in this regard. Real‐time monitoring of submarine eruptions has been on‐going for several decades on regional and global scales with growing interest and effort in local networks. Real‐time networks are complemented by short‐term instrument deployments that often give more detailed insights into the dynamics and processes of submarine eruptions. Thorough seismo‐acoustic monitoring and study has increased our understanding of submarine eruptions, especially of deep‐sea volcanoes and spreading centers. Despite this, there are still many outstanding questions that need to be addressed for submarine volcanoes to be as well understood and monitored as their terrestrial counterparts.

Determining the style and provenance of magmatic activity during the Early Aptian Oceanic Anoxic Event (OAE 1a)

Large igneous province (LIP) volcanism has been proposed as a key trigger of several major climate and environmental perturbations during the Phanerozoic Aeon. Large-scale carbon emissions associated with one or both of magmatic degassing from the Greater Ontong-Java Plateau (G-OJP) and intrusion of organic-rich sediments by High Arctic LIP (HALIP) sills have been widely suggested as the trigger of the Early Aptian Oceanic Anoxic Event (OAE 1a: ~120 Ma). However, the respective roles of the two LIPs and associated carbon sources in causing this crisis remain debated. Here, six records of OAE 1a from the Pacific, Tethyan, Arctic, and South Atlantic realms are investigated, combining mercury (Hg) concentrations and osmium- (Os-) isotope ratios as proxies of LIP activity. Together with previously published datasets, the results indicate globally consistent Os-isotope evidence for LIP activity during OAE 1a, but geographically variable stratigraphic Hg trends. Clear mercury enrichments that match Os-isotope evidence of LIP activity, and suggest a Hg-cycle perturbation during the onset of OAE 1a, are documented at one Pacific site extremely proximal to the G-OJP, but not in Arctic, Tethyan or Atlantic records. This pattern highlights significant G-OJP volcanism during the onset of OAE 1a, and re-emphasises the limited potential for submarine LIP eruptions to cause Hg-cycle perturbations except in areas very proximal to source. The absence of clear Hg peaks in basal OAE 1a strata from the Arctic (or anywhere outside of the Pacific) does not support intense HALIP activity at that time, suggesting that the G-OJP was the more volcanically active LIP when OAE 1a commenced. Thus, G-OJP emissions of mantle carbon were more likely to have played a major role in initiating OAE 1a than thermogenic volatiles associated with the HALIP. A transient pulse of HALIP-related subaerial eruptions and/or thermogenic volatile emissions during the early–middle part of OAE 1a, potentially evidenced by more widespread Hg enrichments in strata from that time (including in the Arctic), might have prolonged the event. However, a non-volcanic cause of these later Hg influxes cannot be excluded. These findings challenge previous suggestions that magmatic CO 2 emissions from LIPs were incapable of causing major carbon-cycle perturbations alone, and highlight the need for further investigations to establish whether the high volume/emplacement rate of the G-OJP (potentially an order of magnitude greater than other LIPs) made it a unique case that stands in contrast to other provinces where the role of thermogenic volatiles was likely more crucial. • Hg/TOC and Os-isotope records of OAE 1a combined to determine style of LIP activity • Hg and Os evidence of volcanism only correlates near to Greater Ontong-Java Plateau • Supports submarine volcanism as the trigger of OAE 1a, rather than HALIP activity

Mercury record of intense hydrothermal activity during the early Cambrian, South China

The early Cambrian was an important interval in Earth history, marked by significant evolution of both life and the marine environments it inhabited. While enhanced hydrothermal activity has been proposed as a trigger for ecosystem perturbations in the early Cambrian, it remains unclear how intense and how long such perturbations may have been. To address this, we examined mercury (Hg) concentrations and mercury isotopes, as well as major and trace elements, of organic-rich black shales of the lower Cambrian Niutitang Formation, in the Tongren area of Guizhou Province, South China. Our data show that Hg in these sediments is hosted dominantly by organic matter. Elevated raw and normalized Hg contents provide direct evidence of intense hydrothermal activity during the early Cambrian in South China. We suggest that high metal flux (e.g., Mo, U, and Ba) into the seawater occurred through this intense submarine volcanism, altering seawater compositions. Intense hydrothermal activity was likely a significant trigger of environmental and biological evolution during the early Cambrian in South China.

Discovery of Precambrian deep-water turbidites and submarine volcanism in the Brasília Belt, Central Brazil: The Quilombo Formation

A deep-water volcano-sedimentary sequence exposed along the Brasília Orogenic Belt was discovered and is herein presented and ascribed to a new stratigraphic unit. This sequence was previously unknown to contain volcanic rocks and to represent a turbidite record. It has been earlier loosely assigned to the Vazante Group based only on map continuity and interpreted as part of the Neoproterozoic passive margin of the western São Francisco Craton, but comprehensive studies have not been conducted for this specific sequence. Based on recent detailed fieldwork integrated with petrology, stratigraphy, geochronology and geochemistry, we describe a previously ignored succession of volcanic rocks interleaved in deep-water turbidites in the Brasilia Belt, and named as the Quilombo Formation. This formation comprises two sub-units, the Ribeirão da Porteira Member (lithoarenite, greywacke, siltstone, shale, and minor conglomerate) and the Ribeirão do Franco Member (fine-grained greywacke, siltstone, shale, and minor intermediate volcanic layers interpreted as subaqueous lavas). The lavas are strongly altered by SiO2 enrichment and depletion of Ca, K and Na. Based on immobile and rare earth elements analysis results, the volcanic rocks are classified as andesite to basaltic-andesite with a calk-alkaline to shoshonitic signature. U–Pb zircon dating of crystals extracted from lava samples yielded an age of 1394.46 ± 19.4 Ma, considered as the maximum depositional age of the sequence. Nonetheless, given the scarcity of zircon grains in the volcanic sample and the possible presence of xenocrysts, the exact age of the volcanic rocks still demands confirmation. The Quilombo Formation is for sure stratigraphically positioned between the Traíras Group (maximum depositional age of ca. 1543 ± 31 Ma) and the Bambuí Group (Ediacaran age). However, it is not yet possible to establish a confident correlation with either the Vazante, Paranoá, Canastra or (Upper) Traíras groups. Nonetheless, the volcanic rocks found represent the first tangible chance to obtain an absolute age for one of these groups, up to now only dated via detrital zircon ages.

Submarine basaltic eruptions across the Guadalupian-Lopingian transition in the Emeishan large igneous province: Implication for end-Guadalupian extinction of marine biota

Massive CO2 and SO2 degassed from large igneous provinces (LIPs) are thought to cause ocean acidification and calcification crisis with a significant loss of calcified marine biota. The ocean acidification caused by the Emeishan LIP event has been proposed as one of the important factors that triggered the end-Guadalupian (Middle Permian) crisis, although the driving mechanism remains unclear. Here we represent a detailed field investigation combined with LA-ICP-MS, SIMS and CA-ID-TIMS zircon geochronology of tuffs from four volcanic sections in the eastern part of the Emeishan LIP. Our new data combined with previous results from this LIP confirm that: (i) the submarine volcanism occurred between ~260.7 Ma and ~ 257.9 Ma, with most basaltic eruptions at ~260.1 Ma to 259.5 Ma; and (ii) explosive tuff eruptions occurred during ~257.9 Ma to ~256.9 Ma in the subaerial environment. We propose a model involving SO2 release from the submarine basaltic eruptions in the Emeishan LIP as the trigger of the end-Guadalupian ocean acidification, due to the high solubility of SO2 in seawater that could produce strongly acidic conditions. The late explosive silicic volcanism in the subaerial setting during Early to Middle Wuchiapingian (Late Permian) might have been a potential strong driver of the global Wuchiapingian cooling event.