Pyroclastic Research Articles

Turonian highly differentiated pyroclastic xenoliths and Cretaceous sedimentary record challenge mantle-plume view of Costa Rican forearc basement successions

The Mesozoic basaltic basement of southern Central America is believed to consist of proxy sections of mantle-plume events leading to the Caribbean igneous province. A significant xenolith assemblage of radiolarite, tuffite, and Turonian (∼93 Ma) highly differentiated pyroclastic rock discovered in basalt of the Costa Rican forearc basement fundamentally challenge this long-held view, revealing bimodal Cretaceous island-arc activity and forearc basin development instead. The pyroclastic materials originally accumulated with monotonous radiolarite deposits in a deep-marine forearc basin slope environment to build part of the Mesozoic sedimentary cover of the evolving arc. Xenolith formation was related to widespread Turonian to Campanian intrusive basaltic activity on the Nicoya Peninsula that affected Albian-Turonian and Berriasian-Barremian radiolarite and pyroclastic deposits as well as Jurassic siliceous strata. Strong correlation with Cretaceous biotite- and hornblende-bearing pyroclastic beds reveals explosive calc-alkaline volcanic arc episodes alongside basaltic activity linked to marine forearc basin development. These materials provide decisive evidence of explosive calc-alkaline volcanic activity of the Cretaceous Costa Rican arc as well as the probable intraoceanic-arc nature of its basaltic forearc basement and a ∼90 Ma aged komatiite suite found at Tortugal. The resulting tectonic scenario shows the Caribbean Plate was separated in southern Central America from any potential Pacific or Galápagos hotspot sources by a subduction zone. This favours in-place origin of the Caribbean Plate and its igneous province between the Americas. The findings also reveal the unsuitability of basaltic forearc basement successions to deduce with certainty mantle-plume events and hotspot evolutions in adjoining oceanic domains.

Obsidian hydration dating helps understand pre-hispanic land use on the volcanic island of Tenerife, Canary Islands, Spain

Critical to the survival of island-based human societies is their resilience and adaptation to volcanic hazards. We here evaluate pre-Hispanic (before 15th century AD) land use patterns on the volcanic island of Tenerife, Canary Islands, Spain using obsidian hydration dating (OHD). The samples studied include archaeological artifacts and natural rock chips from multiple sites of different elevation and micro-climate settings. We systematically collected samples from the southern dry area around Barranco de las Monjas in the Bandas del Sur. These include a total of 28 isolated artifact scatters (here, a scatter is defined as a minimum spatial unit of artifacts distributed spatially limited range on the surveyed surface), one dwelling, and several pyroclastic deposits containing obsidian clasts. We also collected several artifacts adjacent to a large obsidian flow of Tabonal Negro in the Las Cañadas Caldera. Unsystematic surveys in north of Mt. Teide identified large obsidian outcrops located at Tabonal de los Guanches and Charco del Viento. Size differences among surface-derived obsidian artifacts (i.e., Bandas del Sur, Las Cañadas Caldera, Icod Valley) suggest that pre-Hispanic groups utilized obsidian from multiple outcrops over wide areas. Hydration analysis on 136 obsidian flakes collected from both surface and buried contexts showed only minor obsidian hydration rims (5% of total samples) and varied mean rim thicknesses (0.6–3.5μ). The low percentage of hydration rim formation may be caused by environmental factors such as wind erosion, thermal effects from volcanic or natural ground fires, or due to obsidian geochemistry (low SiO2 and water content of phonolitic obsidian). Surface-collected obsidian flakes from the southern dry area do contain hydration rims along internal fissure. The estimated hydration rates from these samples can provide an approximate age when compared to buried obsidian artifacts with associated radiocarbon dates.

Neoarchean environments associated with the emplacement of a large igneous province: Insights from the Carajás Basin, Amazonia Craton

The emplacement of Large Igneous Provinces (LIPs) during the Neoarchean is thought to have influenced the Earth's surface by modulating global climate and the supply of nutrients to the oceans. However, the links between Neoarchean LIPs and Earth's surface changes are complex and not fully understood due to a lack of sedimentological constraints documenting the relationships between magmatic activity and concomitant depositional environments. At ca. 2.75 Ga, the Amazonia Craton witnessed the emplacement of the Parauapebas LIP, which is mainly composed of vesicular basalts and associated volcaniclastic rocks. The Carajás Formation conformably overlies the basalts of the Parauapebas LIP. It comprises extensive iron formations (IFs) interbedded with minor carbonate and volcaniclastic horizons, which were deposited in various shallow to deep-water settings. Zircon U–Pb dating of volcaniclastic layers yielded ages between 2732 ± 5 Ma and 2720 ± 6 Ma, which indicates that the volcanic activity continued 30–40 Myrs after the main peak in magmatic activity of the Parauapebas LIP. Above the Carajás Formation, the Igarapé Bahia Group consists mainly of terrigenous sediments that are interleaved at their base with minor IFs. This group does not preserve evidence of contemporaneous volcanic activity and comprises detrital zircon populations with ages between ca. 3.0 and 2.7 Ga. The few IFs horizons at the base of the Igarapé Bahia Group could reflect a long-lasting hydrothermal activity linked with the emplacement of the Parauapebas LIP. This LIP thus exerted a major control on depositional environments both in space and time by favoring the deposition of IFs (e.g., in shallow to deep-water settings) during a period that exceeded 30 Myrs.

Experimental comparison between dynamic and static parameters for volcanic rocks in Sulcis basin (Italy)

This work compares the results of expensive and time-consuming destructive tests and cheap non-destructive ultrasonic analyses for the assessment of rock parameters (i.e. uniaxial compressive strength, Young's modulus, Poisson's ratio, etc.), with the aim to geologically characterize the site and to find correlations between the mechanical and acoustic properties of rocks for applications in the field of the monitoring of CO2 leakage. The assessment considers 60 samples, 10 per each of the six formations of the Sulcis Miocene volcanic sequence. Samples have been initially subjected to non-destructive tests for the measurement of density and compressional and shear wave velocity and then mechanically tested to determine the uniaxial strength. As it happens for other kinds of rock, a linear direct correlation has been found between uniaxial compressive strength and compressional wave velocity, as well as between dynamic and static Young's moduli and for the dynamic and static Poisson's ratios, with a correlation coefficient R2 significantly affected by the nature of the pyroclastic formation. Helpful information on the pyroclastic rocks have been obtained, collecting parameters currently not available in the literature for this kind of geological formations.

Granites

Granites are coarse‐grained igneous intrusive rocks, which, although present in most tectonic settings, are most characteristic of continental crust. While basalts are the most abundant volcanic rocks, granites are the most abundant intrusive rocks. On the scale of the Solar System, while basalts are ubiquitous, granites seem to be restricted to the Earth. The volcanic equivalent of granite is rhyolite, although rhyolites are of much lower abundance than granite, probably because such magmas are more viscous and less likely to reach the surface. In addition, many pyroclastic rocks have a granitic composition and are likely to have their origins in underlying granitic plutons. Granites may originate by differentiation of a basaltic magma, but the abundance of granites and the low abundance of intermediate rocks argues in general against this possibility and granite magmas are generally thought to have formed by melting of pre‐existing rocks. Several distinct types of granite are recognized depending on their origin.

Tunnel Stability Analysis Under Seismic Load Using Finite Element Method: A Case Study of Spillway Tunnel, Sidan Dam, Bali, Indonesia

The location of the Sidan Spillway Tunnel, as shown on the Earthquake Hazard Zone Map of Bali Island, is in a moderate hazard zone. The support system of the spillway tunnel of the Sidan Dam, Indonesia, was empirically designed based on rock mass classification systems. The objective of this research was to verify the performance of the proposed support system by a numerical method considering the uncertainty in using rock mass classification systems for designing a tunnel support system. In addition, being located in an active seismic region, the seismic load was not considered in the empirical tunnel support design. The proposed tunnel support design was numerically modeled in two dimensions using a finite element method and subjected to a seismic load obtained from probabilistic seismic hazard analysis. A numerical analysis without seismic load was also conducted for comparison. Phase2 software was used for the tunnel stability analysis. The input parameters in the numerical analysis were derived from field investigations (surface engineering geological mapping and evaluation of drilling cores) and laboratory tests. The spillway tunnel area consists of pyroclastic rocks, and the Generalized Hoek-Brown Failure Criterion was selected for the strength parameter of rocks. The suggested support designs are systematic rock bolts (20 mm diameter fully grouted), wired mesh, shotcrete, and steel ribs at specific locations. The numerical models determined that applying the proposed tunnel support system recommended based on the empirical method resulted in a roof strength factor of more than 1.5 under static load & 1.1 under seismic load and roof displacements lower than a 10 cm maximum displacement at every stage of construction. The results verify that the tunnel construction will be stable and fulfill the required safety standard, both under and without seismic loads.

Evidence for Fine-grained Material at Lunar Red Spots: Insights from Thermal Infrared and Radar Data Sets

Lunar red spots are small spectrally red features that have been proposed to be the result of non-mare volcanism. Studies have shown that a number of red spots are silicic, and are spectrally distinct from both highlands and mare compositions. In this work, we use data from LRO Diviner, Mini-RF, and Arecibo to investigate the material properties of 10 red spots. We create albedo maps using Diviner daytime solar reflectance data to use as an input to our improved thermophysical model, and calculate the rock abundance (RA) and H-parameter values that best fit Diviner nighttime thermal infrared radiance measurements. The H-parameter can be considered analogous to the thermal inertia of the regolith, with a high H-parameter corresponding to low thermal inertia. We find that the red spots generally have low RA, and do not have a uniform H-parameter but contain localized regions of high H-parameter. We additionally find that the red spots have a low circular polarization ratio (CPR) in many of the same locations that show a low RA and high H-parameter. Low RA, high H-parameter, and low CPR indicate a relative lack of rocks larger than ∼10 cm, which is consistent with previous findings of a mantling of fine-grained pyroclastic material for at least three red spots. Areas with high H-parameter but that do not show clear signs of pyroclastics in other data sets may be evidence of previously undiscovered pyroclastics, or could be due to the unique physical properties (e.g., porosity, rock strength/breakdown resistance) of the rocks that make up the red spots.

Obsidian clasts as sintered remnants of agglutination processes in volcanic conduits, evidence from the Pepom tephras (Sete Cidades), São Miguel, Azores

The youngest explosive eruptions of the Sete Cidades volcano, São Miguel, Azores, are recorded by a series of relatively small-volume (<0.03 to 0.13 km3 DRE) trachytic pyroclastic deposits termed the Pepom tephra deposits. While dominated by crystal-poor to crystal-moderate (<10%) pumice clasts, these deposits also contain a suite of dense glassy clasts of broadly similar crystallinity. The obsidian clasts from a single deposit vary in texture from entirely dense to those that are moderately vesicular and typically single clasts will contain multiple textural domains. The majority (∼71%) of these dense clasts have compositions both from bulk rock and in-situ glass measurements that are identical to those of the pumice clasts within the same deposit. We interpret these dense clasts to reflect sintering of previously fragmented magma at shallow levels in the conduit prior to being re-entrained and erupted with the vesicular magma, in agreement with recent studies focussing on textural observations. Notably, across the exposed volcanic stratigraphy of São Miguel obsidian domes, flows/coulees are not preserved, arguing against the idea that the dense glass clasts within the Pepom tephras are sourced from existing surficial rocks. In contrast, the neighbouring island of Terceira exhibits domes and coulees with large obsidian bands that cut through the crystalline groundmass. Most silicic rocks of Santa Bárbara and Pico Alto volcanoes on Terceira are peralkaline, comenditic to pantelleritic in composition, and at similar conditions (e.g., temperature and water content) have lower viscosities than the trachytic Pepom obsidian clasts. However, the Santa Bárbara silicic lavas on Terceira (the less peralkaline suite) have more obsidian than the more peralkaline Pico Alto domes and coulees indicating that while peralkalinity, developed during magmatic evolution in the crust, may play a role, sintering occurring at shallow levels within the conduit likely is more important in producing obsidian.

Zeolitized fossil woods from alkaline volcaniclastic rocks: Unravelling an uncommon mineralization process

Mineralization of fossil woods with unusual mineral phases remains an underconstrained process despite its relatively common occurrences. Aside from common mineralization agents such as silica or carbonates, there are also atypical mineralization associations, such as zeolite-group phases, but the zeolitization process has not yet been investigated in detail. We studied zeolitized woods collected from two localities in the Cenozoic alkaline České Středohoří Volcanic Complex (Ohře Rift, Czech Republic), where fossil woods of diverse paleobotanical classification were deposited in volcaniclastic rocks of the same origin (lahar) and stratigraphic formation (Upper Oligocene). The identical geological setting allowed the investigation of potential variables influencing this type of mineralization by combining paleobotanical classification, detailed mineralogy, mineral chemistry, geochemistry, Sr isotope analysis and KAr chronology.The new results demonstrate the significant potential of fossil woods mineralized with zeolite-group minerals to be used to reconstruct the formation and deposition conditions of the lahars in which these woods are contained. The composition of zeolites is strongly dependent on thermal conditions and material exchange between wood and host rocks. Dominant mineral phases are phillipsite and chabazite in variable proportions. The phillipsite/chabazite ratio correlates well with the magnitude of the Eu anomaly, suggesting crystallization of phillipsite at a higher temperature under hot-lahar conditions of deposition. Chabazite lacking an Eu anomaly represents the later, colder mineralization stage. The 87Sr/86Sr ratios ranging 0.7042–0.7047 provide an additional line of evidence of fluid derivation from volcaniclastic deposits of the Upper Oligocene Děčín Fm.

Volcanic ash from La Palma (Canary Islands, Spain) as Portland cement constituent

The last volcanic eruption on the island of La Palma (Spain) took place in 2021. Significant activity started in September of that year with the vigorous emission of volcanic gases and ash and lasted for three months. It is estimated that the Cumbre Vieja volcano emitted more than ten million cubic meters of ash comprising pyroclastic materials like those found in many parts of the world. Some of these volcanic ash deposits are untapped, despite their potential construction industry applications. Since the chemical composition and mineralogy of the ash depends on the type of magma from it originates, this paper characterizes this material and evaluates its suitability as a major constituent of Portland cement. This volcanic ash is rich in silica (45%) and alumina (15%), meaning it reacts with portlandite. The blended cements with up to 40% replacement content meet the standardized chemical, physical, and mechanical requirements and present good intrinsic durability values (resistivity and capillary absorption), making them viable for the manufacture of low-carbon-footprint eco-cements. This paper seeks to provide society with lasting technical, environmental, and social benefits through recovery of this ash.

Ultra-crystalline pyroclastic deposits and rhyolitic lavas controlled by crystal mushes: insights from the Acoculco Caldera Complex, México

AbstractThe Acoculco Caldera Complex (ACC), located in eastern Mexico, began its activity during the Pleistocene ~ 2.7 Ma. One of the most relevant and largest rhyolitic eruption in the complex, the Piedras Encimadas Ignimbrite (PEI), occurred during the late post-caldera phase at ~ 1.2 Ma. This ignimbrite is unique with respect to the other caldera products and other contemporaneous ignimbrites in the Trans-Mexican Volcanic Belt (TMVB) because of its ultra-high crystallinity and the absence of pumice fragments. The PEI is made almost entirely of crystals where the main constituents are k-feldspars and silica polymorphs that range from ≤ 5 µm to tens of centimeters in size. XRD on bulk rock, geochemical modeling, FTIR, Raman, and EPMA analyses were carried out in all mineral phases to assess the origin and the causes of high crystallinity within the PEI. We interpret the high crystallinity on the basis of magmatic crystallization of a magma body that was remobilized and altered by post-depositional hydrothermal alteration processes. We suggest that ACC rhyolites are geochemically influenced by at least one crystal mush established during the Pleistocene. We suggest that the PEI could be the result of an erupted crystal mush (melt + crystals), or a cumulate, or an ancient and crystallized reservoir generated after the first ACC collapse due to intrusion or underplating of mafic hot magmas. Extensional episodes within the ACC facilitated the ascent of mafic magmas. This interaction increased the liquid fraction of the mush through partial melting/crystal dissolution, generating a drop in density and viscosity in the mush, thus triggering eruption. The PEI provides evidences for an association between the geochemically-diverse ACC rhyolites with the complex interaction between mafic transitional alkaline magmas and a crustal mush system, promoted by continuous changes in the stress field during the Pleistocene.

Dark mantles over domes and rilles on the Moon: Evidence for pyroclastic materials

A collection of dark mantles covering volcanic domes and surrounding rilles were examined. Remotely sensed information on FeO and TiO2 content, clinopyroxene (CPX) and olivine (where olivine is an assumed proxy for glass) abundance, band center positions near 1 and 2 μm, and a parameter related to OH and/or H2O content were assessed for these mantling deposits. Based on our examination of these dark mantles associated with domes and rilles we found that all of the examined dark mantles had higher FeO abundances than the surroundings. The Birt E pit of Rima Birt and the mantle over the Manilius-1 dome are higher in glass and lower in CPX than their surroundings and with deeper band depth near 3 μm: all these indicators suggest higher pyroclastic glass abundance. The mantle at Rima Calippus is also nominally glass-rich although its band depth near 3 μm is comparable to nearby mare basalts and thus is not taken to be unusually hydrated. The dark mantles associated with the Yangel-1 and Cauchy-5 domes are higher in CPX, lower in glass, and higher in TiO2 content with low band depth near 3 μm indicating they are glass-poor and nominally rich in ilmenite. The Hyginus crater of Rima Hyginus is distinct from the other studied mantles in that it has higher TiO2 content, lower CPX abundance, higher glass or olivine, and weak 3 μm band depth. Also, the band minimum near 1 μm deos not occur at a longer wavelength than surrounding mare suggesting that in this instance the higher olivine (as a proxy for glass) might actually be due to olivine rather than glass. Thus, in the study of dark mantles associated with domes and rilles each represents deposits and eruptions that need to be characterized on a case-by-case basis rather than as a collective group.

Geology, fluid inclusions, and isotope signatures reveal hydrothermal evolution and genesis of the Aqishan Pb-Zn deposit in Eastern Tianshan and implications for exploration of skarn mineralization

The Aqishan deposit (1.97 Mt at 1.05 % Pb + Zn) is located in the Aqishan-Yamansu arc, on the southwest section of the Eastern Tianshan, Northwest China. Pb-Zn mineralization is mainly hosted by garnet skarn and the volcaniclastic rocks of the Yamansu Formation. To decipher the evolution of ore fluids and source(s) of ore-forming components, and constrain the ore genesis, a combination of geological work, fluid inclusions, and C-O-S-Pb isotope systematics is presented. Detailed field and microscopic observations reveal that the skarn alteration and ore formation at Aqishan could be divided into four hydrothermal stages, consisting of prograde skarn (I), retrograde skarn (II), quartz–sulfides (III), and carbonate stage (IV). Sphalerite and galena are the dominant ore minerals generally occurring as disseminations and veins with locally laminated ores in stage III. Fluid inclusion data show that the fluids responsible for prograde skarn are high-temperature (342–518 °C) and high-salinity (7.3–44.2 wt% NaCl equiv.), and recorded fluid phase separation from an intermediate-salinity supercritical fluid, which was exsolved from crystallizing granitic magma. Microthermobarometry results limit the retrograde alteration within the temperature range of 313 to 388 °C and trapping pressures of 98 to 241 bars (1.0–2.5 km), with pressure dropping from lithostatic to hydrostatic regimes associated with a phase separation event. The boiling fluid inclusions in ore stage quartz show that the Pb-Zn mineralization formed at 205–357 °C, with a decrease in temperature facilitating the precipitation of ore-forming metals from hydrothermal system. Carbon and oxygen isotope compositions of calcite indicate a predominantly magmatic source for ore fluids at Aqishan with later meteoric water involved. Bulk and in situ sulfur values of sulfides range from −6.4 to −0.7 ‰, consistent with a dominantly magmatic origin. Sulfides together with the granite porphyry and tuff, show relatively homogeneous Pb isotope compositions, indicating that abundant ore-forming metals were sourced from a magmatic reservoir with contribution from country rocks. Fluid inclusion study and available calcite C-O isotopes suggest that significant decrease in temperature and fluid-rock interactions remarkably contributed to the metal deposition at Aqishan. The skarn alteration with typical alteration assemblages of garnet–diopside is proposed as an effective mineral exploration target of skarn(–like) ores in Eastern Tianshan.

PETROLOGICAL and GEOCHEMICAL CHARACTERISATION of the KGWEBE VOLCANIC FORMATION in the ghanzi-chobe BELT PORTION of the KALAHARI COPPER BELT, western Botswana.

A combination of petrography and geochemistry was utilised to investigate the magma sources, magma evolution and petrogenesis of the Kgwebe Volcanic Formation (KVF) rock units. Based on their texture, the KVF rock units comprise amygdaloidal rocks, porphyritic mafic flows, pyroclastic rocks, porphyritic subvolcanic bodies, quartz-feldspar porphyries and clastic sedimentary rocks, that are intercalated with amygdaloidal rocks. The amygdaloidal rocks are commonly crosscut by calcite veins and characterised by amygdales (filled vesicles) set in the hyalopilitic groundmass. The porphyritic mafic flows are composed of plagioclase laths set in an aphanitic groundmass. The pyroclastic rocks are generally characterised by up to 75% of both mineral and lithic fragments originating from explosive volcanic activities. Porphyritic subvolcanic bodies are characterised by high content of subrounded epidote (after plagioclase) set in a microcrystalline groundmass. The quartz-feldspar porphyries are characterised by quartz and feldspar phenocrysts in variable proportions set in a fine-grained groundmass of variable colour. Rock units of the KVF represent two geochemically contrasting series that are not co-genetic and are derived from different geotectonic settings. The amygdaloidal rocks, porphyritic mafic flows, pyroclastic rocks and porphyritic subvolcanic bodies are sub-alkaline and basaltic in composition, whereas the quartz-feldspar porphyries span from the rhyolite/dacite (mostly) to the andesite/andesite basalt (accessorily) field compositions. Likewise, while quartz-feldspar porphyries are consistently high-K calc-alkaline bodies, their spatially associated amygdaloidal rocks, porphyritic mafic flows, pyroclastic rocks and porphyritic subvolcanic bodies counterparts are calc-alkaline. Similarly, quartz-feldspar porphyries are within plate bodies, whereas the more mafic KVF units are arc-related. Furthermore, the ferroan quartz-feldspar porphyries generated from the crust and the magnesian amygdaloidal rocks, porphyritic mafic flows, pyroclastic rocks and porphyritic subvolcanic bodies are mantle-derived, with however, significant crustal contamination fingerprints. Textural evidence (resorbed, embayed and rounded phenocrysts) and the inferred high-water content (as supported by the abundance of plagioclase phenocrysts) also suggest a rapid magma ascent and magma mingling occurred during the KVF eruption, which was both effusive and explosive. Concomitant volcanism and sedimentary processes likely occurred as supported by the intercalation of clastic sedimentary rocks within volcanics of the KVF.

Revisiting the occurrence and distribution of Indian Ocean Tephra: Quaternary marine Toba ash inventory

The Toba Caldera on Sumatra, Indonesia is the host of the Young Toba eruption (∼74 ka), globally one of the largest and most recognized eruptions during the Quaternary and regionally concentrated in the eastern Indian Ocean. Three older deposits (Middle, and Old Toba Tuff as well as Haranggaol Dacite Tuff) are also attributed to Toba caldera, with their eruption products distributed over the Indian Ocean.We present the Quaternary marine tephra record from an array of 14 sites and 28 holes from deep ocean drilling programs, complementing earlier work on distal to ultra-distal Indian Ocean sediment cores and terrestrial distribution data of Toba deposits. A unique set of major and trace element glass-shard compositions on 115 primary ash layers together with glass shard morphologies, core pictures and statistical analysis support geochemical fingerprinting between marine tephra layers and known deposits from Toba and five so far unidentified medium to large eruptions assigned to northern Sumatra. Additionally, zircon crystallization ages have been determined for the Haranggaol Dacite Tuff resulting in a new maximum eruption age of 1.42 ± 0.034 Ma.Tephra volumes and magma masses for the (co-ignimbrite) fallout are estimated based on the compiled marine tephra distribution that are complemented by published proximal ignimbrite volumes. For YTT the resulting tephra and DRE volumes of 5600 km3 and 3600 km3, respectively, are in between the previous estimates. For MTT (253 km3 DRE), ODT (1550 km3 DRE), HDT (129 km3 DRE), and the five additionally identified eruptions from Northern-Sumatran volcanoes, new magma volumes have been determined. Overall, the Indian Ocean tephra record reveals in one large eruption every 200 kyr in the Quaternary that is derived from northern Sumatra. Plain language summaryThe Toba Caldera on Sumatra, Indonesia, is a famous spot for volcanism since it is the host of one of the largest and most recognized eruptions on the world, the ∼74 ka Young Toba supereruption. It produced widespread volcanic particles (volcanic ash) that were distributed around the globe by winds, but most deposits are concentrated in the eastern Indian Ocean. Next to the Young Toba Tuff (YTT), three older deposits from probably similar large eruptions are known from this caldera that are also found as ash layers in the Indian Ocean.We investigated this marine tephra record, including 28 locations from the three phases of the deep ocean drilling program (DSDP, ODP, IODP), and created a unique set of glass-shard trace element (LA-ICP-MS) compositions that complements our major element (EMP) data on 115 primary ash layers. Comparing these compositions between the different marine locations and to known terrestrial deposits of the Toba eruptions is done by geochemical fingerprinting where the characteristic chemical “fingerprint” of marine ash layers is correlated between oceanic and to on-land deposits to find out from which eruption it originated. Glass shard morphologies, core pictures and statistical analysis complement this approach to support the correlations to four known tephras from Toba (Young, Middle, and Old Toba Tuff, as well as Haranggaol Dacite Tuff) and five so far unidentified eruptions from Northern Sumatra.The distribution of all tephras in the Indian Ocean allows to estimate erupted volumes by mapping out the occurrence and thicknesses of the tephras on the seafloor using drill cores. The resulting magma volumes amount to, for example, between 3600 km3 and 129 km3 magma for Young, Middle, and Old Toba Tuff as well as the Haranggaol Dacitic Tuff. Together with the five additionally identified (northern)Sumatra eruptions, these results indicate that one large eruption has happened every 200 kyr in northern Sumatra over the last 2.4 Ma.

Geochemical and H–O–Sr–B isotope signatures of Yangyi geothermal fields: implications for the evolution of thermal fluids in fracture-controlled type geothermal system, Tibet, China

High-temperature hydrothermal systems are mainly distributed in the north–south graben systems of southern Tibet as an important part of the Mediterranean–Tethys Himalayan geothermal belt in mainland China. As the largest unit capacity and second stable operating geothermal power station in China, Yangyi is the fracture-controlled type geothermal field in the center of Yadong–Gulu Graben. In this paper, hydrogeological and hydrochemical characteristics, isotope composition (δD and δ18O, 87Sr/86Sr and δ11B) of borehole water, hot springs, and surface river samples were analyzed. From the conservative elements (such as Cl− and Li+) and δD and δ18O values, the geothermal water of the Yangyi high-temperature geothermal field is estimated to be of meteoric origin with the contributions of chemical components of the magmatic fluid, which is provided by partially molten granite as a shallow magmatic heat source. According to logging data, the geothermal gradient and terrestrial heat flow value of the Yangyi high-temperature geothermal field are 6.48 ℃/100 m and 158.37 mW m−2, respectively. Combining the hydrothermal tracer experiment, 87Sr/86Sr and δ11B ratios obtained with gradually decreasing reservoir temperatures from the Bujiemu stream geothermal zone to Qialagai stream geothermal zone, we suggested the deep geothermal waters were mixed with local cold groundwater and then flow northeastward, forming the shallow reservoir within the crushed zone and intersect spot of faults in the Himalayan granitoid. Furthermore, in the process of ascent, the geothermal water is enriched in K+, Na+, and HCO3− during the interaction with underlying Himalayan granitoid and pyroclastic rocks that occur as wall rocks. The detailed description and extensive discussion are of great significance for the further exploitation and utilization of north–south trending geothermal belts in Tibet.

Rieden tephra layers in the Dottinger Maar lake sediments: Implications for the dating of the Holsteinian interglacial and Elsterian glacial

This study reconstructs the tephrochronology of the infilled Dottinger Maar lake (Eifel, Germany) by analysing the mineralogical composition of tephra layers in lake sediments from the Middle Pleistocene. Three sediment cores document deposits from the Rieden Volcanic Complex. Four distinct tephra layers were identified as the Rieden-leucite-phonolite tuff 1, 3, and 4, and the Weibern-leucite-phonolite tuff 1, which were previously dated by 40Ar/39Ar and indicate a volcanic active phase between 390 and 440 ka before present. In addition, the cores reveal an interglacial section with a typical Holsteinian vegetation succession superimposing Elsterian dust deposits. Annual layer counts, tephrochronology, and high-resolution Corg(chlorins) data were used to align the Dottinger Maar sediments to the EPICA ice core stratigraphy and to link it to Marine Isotope Stages 11 and 12. A comparison of clastic (aeolian) sediments in the Dottinger Maar lake record with the Antarctic EPICA dust stack displays thicker annual layer deposits during higher dust accumulation rates. Based on these lines of evidence, the Dottinger lake sediments date back to 385–457 ka before present.

Subaqueous volcanic eruptive facies, facies model and its reservoir significance in a continental lacustrine basin: A case from the Cretaceous in Chaganhua area of southern Songliao Basin, NE China

The conventional lithofacies and facies model of subaerial and marine pyroclastic rocks cannot reflect the characteristics of subaqueous volcanic edifice in lacustrine basins. In order to solve this problem, the lithofacies of subaqueous eruptive pyroclastic rocks is discussed and the facies model is established by taking the tuff cone of Cretaceous Huoshiling Formation in the Chaganhua area of the Changling fault depression, Songliao Basin as the research object. The results indicate that the subaqueous eruptive pyroclastic rocks in the Songliao Basin can be divided into two facies and four subfacies. The two facies are the subaqueous explosive facies and the volcanic sedimentary facies that is formed during the eruption interval. The subaqueous explosive facies can be further divided into three subfacies: gas-supported hot pyroclastic flow subfacies, water-laid density current subfacies and subaqueous fallout subfacies. The volcanic sedimentary facies consists of pyroclastic sedimentary rocks containing terrigenous clast subfacies. A typical facies model of the tuff cone that is formed by subaqueous eruptions in the Songliao Basin was established. The tuff cone is generally composed of multiple subaqueous eruption depositional units and can be divided into two facies associations: near-source facies association and far-source facies association. The complete vertical succession of one depositional unit of the near-source facies association is composed of pyroclastic sedimentary rocks containing terrigenous clast subfacies, gas-supported hot pyroclastic flow subfacies, water-laid density current subfacies and subaqueous fallout subfacies from bottom to top. The depositional unit of the far-source facies association is dominated by the subaqueous fallout subfacies and contains several thin interlayered deposits of the water-laid density current subfacies. The gas-supported hot pyroclastic flow subfacies and the pyroclastic sedimentary rocks containing terrigenous clast subfacies are favorable subaqueous eruptive facies for reservoirs in continental lacustrine basins.

New Insights into Aristarchus Crater with LRO LAMP Far-ultraviolet Observations

Aristarchus crater is a Copernican-age impact crater well known for its high-albedo ejecta blanket and nearby flow features rich in pyroclastic materials. The Lyman Alpha Mapping Project (LAMP) is a far-ultraviolet (FUV) spectrograph (57–197 nm) on board the Lunar Reconnaissance Orbiter (LRO). LAMP data identified Aristarchus crater as having a high Off-band (155–184 nm) to On-band (130–155 nm) albedo (Off/On) ratio, providing new insight into the mineral composition of the area. Previous LAMP observations of bright crater rays and lunar swirls show that regions of high Off/On-band ratios may indicate highly feldspathic compositions. In this study we use LAMP data to understand FUV compositional signatures at Aristarchus. We investigate four well-characterized regions of interest around Aristarchus crater, and we compare Off/On-band ratios at Aristarchus crater to laboratory-derived ratios of several endmembers such as anorthite and olivine. We further analyze LAMP FUV spectra alongside near-infrared spectra from the Moon Mineral Mapper (M3) on board Chandrayaan-1 to characterize the mineralogy in several regions of interest. We find that LAMP Off/On-band ratios are able to distinguish between plagioclase feldspars and minerals such as quartz and mafic-dominated compositions. The LAMP Off/On-band ratios at Aristarchus are higher than previously reported ratios for plagioclase-rich regions, suggesting that the composition is unique to Aristarchus. Spectra from LAMP and M3 both show that the central peak and high-albedo ejecta around Aristarchus contain shocked, possibly alkalic, plagioclase feldspar.

Magnetic Susceptibility of Pumice at Mount Singgalang, West Sumatera

Volcanic activity produces eruptions that release pyroclastic material at the time of the explosion. Mount Singgalang is a volcano that has experienced an eruption after 1600. Several types of volcanic rocks around the Mount Singgalang area are Basalt, Andesite, Tuff Breccia, Lava Breccia, and Pumice Tuff. Pumice is formed when saturated liquid magma gas bursts like a carbonated beverage and soon cools, causing the froth that results to solidify into a glass full of gas bubbles. Some minerals contained in pumice are obsidian, cristobalite, feldspar, and tridymite. Pumice contains magnetic minerals, namely ilmenite (FeTiO3), and magnetite (Fe3O4). The purpose of this study is to quantify the magnetic susceptibility and quantity of pumice on Mount Singgalang in West Sumatera. When utilizing the Bartington Magnetic Susceptibility Meter to analyze a sample, magnetic susceptibility parameters are utilized to pinpoint the features of a magnetic rock mineral. The value of the magnetic susceptibility of pumice on Mount Singgalang, in West Sumatera has a value that varies between 2763.3 x 10-8m3/kg - 2192.1 x 10-8m3/kg. The results showed that the tested samples had antiferromagnetic magnetic mineral properties with frequency-dependent susceptibility values (χfd), indicating that all of the measured samples contained almost no superparamagnetic (SP) grains and were generally dominated by multi-domain (MD) grains.