Young Volcanism Research Articles

PERHITUNGAN AWAL IMBUHAN AIRTANAH ALAMI DAERAH ALIRAN SUNGAI CIKAPUNDUNG-GANDOK (KAJIAN PERBANDINGAN)

Groundwater recharge is a crucial factor in determining the permissible groundwater extraction within a watershed. In the Cikapundung watershed, the contribution of groundwater to raw water supply has been continuously declining, prompting a shift from groundwater to surface water usage. This study aims to quantify the groundwater recharge volume and recharge coefficient for each geological formation within the Cikapundung-Gandok watershed, covering an area of 90.4 km², and to compare the results with previous studies. The analysis estimates recharge volumes based on rainfall data from 8 stations around the Cikapundung-Gandok watershed from 2010 to 2019, geological formation data, and alternative recharge coefficients. The difference in recharge volume from previous studies is 393,348 m³/year or 1%. Two formations, Qvu and Qyu, which were not identified in earlier studies, supplement the existing geological dataset. The selected recharge volume for the Cikapundung-Gandok watershed is 33,232,004 m³/year or 1.05 m³/s, with the lowest contribution from the Lava formation (Qyl) at 1,364,504 m³/year or 0.04 m³/s and the highest from the Old Volcanic Product (Qvu) at 14,072,243 m³/year or 0.45 m³/s. The tentative recharge coefficients for each rock formation are as follows: Colluvium (Qc) 30%; Unweathered Old Volcanic Product (Qvu) 20%; Sand Tuff (Qyd) 10%; Lava (Qyl) 25%; Pumiceous Tuff (Qyt) 20%; and Young Volcanic Product (Qyu) 20%. The groundwater recharge data obtained can be used to set groundwater extraction limits and to plan for groundwater management using a conservative approach to ensure long-term sustainability.Keywords: groundwater recharge, recharge coefficient, geological formation, groundwater exploitation, Cikapundung-Gandok Watershed

Morphological evidence of an explosive eruption event in October 2023 at Sofu Seamount in the Izu-Bonin Arc

Sofu Seamount is one of the poorly studied submarine edifices in the Izu-Bonin Arc. There is no known historical record of volcanic activity, thus its eruptive history and volcanic features are completely unknown. However, on October 9, 2023, at least 14 T-phases originating near Sofu Seamount were observed. An 80 km-long raft of floating pumice was observed off Sofu Seamount on October 20. These spatially and temporally coherent observations indicate that an eruption occurred from a deep seafloor vent somewhere near Sofu Seamount. In order to investigate the origin of this submarine eruption, we collected new bathymetric data in 2024 and compared it with older bathymetric data collected in 2022, 2007 and 1987. The bathymetric comparison revealed evidence for explosive eruptions at Sofu Seamount between 2022 and 2024. During this time, a crater, 1.6 km wide and 400 m deep, was formed at the pre-existing central cone on the western part of Sofu Seamount, whose pre-eruption summit depth was 737 m. The maximum negative depth change was 451 m and a volume of 430 × 106 m3 was removed due to the crater formation. A dome-like structure, 1 km wide and 100 m high was constructed northeast of the crater, part of which collapsed as a result of the crater formation. The volcanic products were transported over 6 km downslope and emplaced on the adjacent seafloor where positive depth changes up to 75 m were observed. Landslides also occurred around the crater. The largest slide on the northern flank formed a slide scar that is 3.8 km long and 1 km wide. Here, the maximum negative depth change was 148 m and 140 × 106 m3 of material was removed. The slide materials were deposited downslope where positive depth changes up to 61 m were observed. Considering the occurrence of the earthquake swarm on October 2–8, 2023 and T-phase swarm on October 9, the timing of the eruption can be constrained within October 2023.An analysis of volcanic and tectonic morphology reveals a distinct tectonic influence on volcanism at Sofu Seamount. Sofu Seamount is located in a back-arc rift zone where the N–S trending Torishima and Sofu Rifts have formed. The new bathymetric data showed that the rifts have an asymmetric structure and can be divided into two segments, which are identified here as inner and outer rifts. The inner rifts are bounded by steeper fault scarps that have experienced more subsidence than the outer rifts. The western part of Sofu Seamount, where the eruption occurred, is located within the inner rifts, and is heavily dissected by rifting-related normal faults, while the eastern part is located outward of the inner rifts and is not dissected by faults. The October earthquake swarm was more concentrated in the area of the inner rifts and some large earthquakes showed normal fault focal mechanisms with a tension axis approximately in E–W direction. Our morphological observations combined with recent seismic events show that the inner rifts are the currently active tectonic structures and young volcanism at Sofu Seamount is controlled by the back-arc rifting of the Izu-Bonin Arc.

Weak magnetism of Martian impact basins may reflect cooling in a reversing dynamo

Understanding the longevity of Mars’s dynamo is key to interpreting the planet’s atmospheric loss history and the properties of its deep interior. Satellite data showing magnetic lows above many large impact basins formed 4.1-3.7 billion years ago (Ga) have been interpreted as evidence that Mars’s dynamo terminated before 4.1 Ga—at least 0.4 Gy before intense late Noachian/early Hesperian hydrological activity. However, evidence for a longer-lived, reversing dynamo from young volcanics and the Martian meteorite ALH 84001 supports an alternative interpretation of Mars’s apparently demagnetized basins. To understand how a reversing dynamo would affect basin fields, here we model the cooling and magnetization of 200-2200 km diameter impact basins under a range of Earth-like reversal frequencies. We find that magnetic reversals efficiently reduce field strengths above large basins. In particular, if the magnetic properties of the Martian mantle are similar to most Martian meteorites and late remagnetization of the near surface is widespread, >90% of large ( > 800 km diameter) basins would appear demagnetized at spacecraft altitudes. This ultimately implies that Mars’s apparently demagnetized basins do not require an early dynamo cessation. A long-lived and reversing dynamo, unlike alternative scenarios, satisfies all available constraints on Mars’s magnetic history.

Submarine volcanism in the Sicilian Channel revisited

The origin and role of volcanism in continental rifts remains poorly understood in comparison to other volcano-tectonic settings. The Sicilian Channel (central Mediterranean Sea) is largely floored by continental crust and represents an area affected by pronounced crustal extension and strike-slip tectonism. It hosts a variety of volcanic landforms closely associated with faults, which can be used to better understand the nature and distribution of rift-related volcanism. A paucity of appropriate seafloor data in the Sicilian Channel has led to uncertainties regarding the location, volume, sources and timing of submarine volcanism. To improve on this situation, we use newly acquired geophysical data (multibeam echosounder and magnetic data, sub-bottom profiles) and dredged seafloor samples to: (i) re-assess the evidence for submarine volcanism in the Sicilian Channel and define its spatial pattern, (ii) infer the relative age and style of magmatism, and (iii) relate this to the dominant tectonic structures in the region. Quaternary rift-related volcanism has been focused at Pantelleria and Linosa, at the northwest boundaries of their respective NW-SE trending grabens. Subsidiary and older volcanic sites potentially occur at the Linosa III and Pantelleria SE seamounts, collectively representing the only sites of recent volcanism that can be directly related to the main rift process. These long-lived polygenetic volcanic landforms have been shaped by magmatism that is directly correlated with extensional faulting and buried igneous bodies. Older volcanic landforms, sharing a similar scale and alignment, occur to the north at Nameless Bank and Adventure Bank. These deeply eroded volcanoes have likely been inactive since the Pliocene and are probably related to earlier stages of crustal thinning and underlying feeder structures in the northern region of the Sicilian Channel. Along a similar alignment, Pinne Bank, SE Pinne Bank and Cimotoe in the northern Sicilian Channel lack a surface volcanic signature but are associated with intrusive bodies or deeply buried volcanic rock masses. Terrible Bank, in the same region, also shows evidence of ancient, polygenetic magmatism, but was subject to significant erosion and lacks a prominent alignment. The much younger volcanism at Graham Volcanic Field and along the northern Capo-Granitola-Sciacca Fault Zone differs markedly from that observed in the other study areas. Here, the low-volume and scattered volcanic activity is driven by shallow-water mafic magma eruptions, which gave rise to small individual cones. These sites are associated with large fault structures away from the main rift axis and may have a distinct magmatic origin. Dispersed active fluid venting occurs across both ancient and young volcanic sites in the region and is directly associated with shallow magmatic bodies within tectonically-controlled basins. Our study provides the foundation for an updated tectonic and magmatic framework for the Sicilian Channel, and for future detailed chronological and geochemical assessment of the sources and evolution of magmatic processes in the region.

Coronae–Sources of Young Volcanism on Venus: Topographic Features and Estimates of Productivity

Coronae–Sources of Young Volcanism on Venus: Topographic Features and Estimates of Productivity

Lunar Evolution in Light of the Chang'e-5 Returned Samples

The Chinese spacecraft Chang'e-5 (CE-5) landed on the northern Ocean Procellarum and returned 1,731 grams of regolith. The CE-5 regolith is composed mostly of fragments of basalt, impact glass, agglutinates, and mineral fragments. The basalts could be classified as of a low-Ti and highly fractionated type based on their TiO2 content of ∼5.3 wt% and Mg# of ∼28. Independent of petrographic texture, the CE-5 basalts have a uniform eruption age of 2,030 ± 4 Ma, demonstrating that the Moon remained volcanically active until at least ∼2.0 Ga. Although the CE-5 landing site lies within the so-called Procellarum KREEP [potassium (K), rare earth elements (REE), and phosphorus (P)] Terrane, neither the CE-5 basalts nor the mantle source regions of those basalts were enriched in KREEP components, such as incompatible elements, water, sulfur, or chlorine. Therefore, it would be a new and stimulating task in the future to look for the triggering mechanism of the young volcanism on the Moon. ▪The CE-5 spacecraft returned 1,731 grams of lunar regolith in December 2020. It was the first new lunar sample since the last collection in August 1976.▪CE-5 regolith is basaltic in chemical composition, with only ∼1% highland materials of anorthosite, Mg suite, alkali suite, and KREEP.▪The CE-5 basalt is low Ti and highly differentiated. It was extruded at ∼2.0 Ga, being the youngest lunar basalt identified so far from the Moon.▪The triggering mechanism of the ∼2.0 Ga lunar volcanism is not clearly understood because its mantle source was dry and contained low abundances of KREEP elements.

Полевые тефростратиграфические работы на о. Итуруп (Южные Курильские острова) в 2024 г.

The report presents the results of the fieldwork (July 2024) aimed at studying the traces of prehistoric ashfalls in the city of Kurilsk and nearby settlements: the villages of Kitovy, Rybaki, and Reydovo (Iturup, South Kuril Islands). The work was traditionally based on tephrostratigraphic studies, during which the sections of the soil-pyroclastic cover were studied. In total, more than 10 sections were studied. The materials obtained during the fieldwork, after carrying out radiocarbon dating and material composition studies, will be used in further regional studies on young volcanism of the South Kuril Islands, as well as in studies on assessing volcanic hazard and volcanic zoning.

Old impacts ignite young volcanism

Old impacts ignite young volcanism

Low Ni and Co olivine in Chang’E-5 basalts reveals the origin of the young volcanism on the Moon

Mare basalts returned by the Chang’E-5 (CE5) mission extend the duration of lunar volcanism almost one billion years longer than previously dated. Recent studies demonstrated that the young volcanism was related neither to radiogenic heating nor to hydrous melting. These findings beg the question of how the young lunar volcanism happened. Here we perform high-precision minor element analyses of olivine in the CE5 basalts, focusing on Ni and Co. Our results reveal that the CE5 basalt olivines have overall lower Ni and Co than those in the Apollo low-Ti basalts. The distinctive olivine chemistry with recently reported bulk-rock chemistry carries evidence for more late-stage clinopyroxene-ilmenite cumulates of the lunar magma ocean (LMO) in the CE5 mantle source. The involvement of these Fe-rich cumulates could lower the mantle melting temperature and produce low MgO magma, inhibiting Ni and Co partitioning into the magma during lunar mantle melting and forming low Ni and Co olivines for the CE5 basalts. Moreover, the CE5 olivines show a continuous decrease of Ni and Co with crystallization proceeding. Fractional crystallization modeling indicates that Co decreasing with crystallization resulted from CaO and TiO2 enrichment (with MgO and SiO2 depletion) in the CE5 primary magma. This further supports the significant contribution of late-stage LMO cumulates to the CE5 volcanic formation. We suggest that adding easily melted LMO components resulting in mantle melting point depression is a key pathway for driving prolonged lunar volcanism. This study highlights the usefulness of olivine for investigating magmatic processes on the Moon.

Volcanic evolution of an ultraslow-spreading ridge

Nearly 30% of ocean crust forms at mid-ocean ridges where the spreading rate is less than 20 mm per year. According to the seafloor spreading paradigm, oceanic crust forms along a narrow axial zone and is transported away from the rift valley. However, because quantitative age data of volcanic eruptions are lacking, constructing geological models for the evolution of ultraslow-spreading crust remains a challenge. In this contribution, we use sediment thicknesses acquired from ~4000 km of sub-bottom profiler data combined with 14C ages from sediment cores to determine the age of the ocean floor of the oblique ultraslow-spreading Mohns Ridge to reveal a systematic pattern of young volcanism outside axial volcanic ridges. Here, we present an age map of the upper lava flows within the rift valley of a mid-ocean ridge and find that nearly half of the rift valley floor has been rejuvenated by volcanic activity during the last 25 Kyr.

Distribution of Soil Nutrients and Ancient Agriculture on Young Volcanic Soils of Ta‘ū, American Samoa

Soils and agriculture are inextricably linked, in the past as well as today. The Pacific islands, which often represent organized gradients of the essential soil-forming factors of substrate age and rainfall, represent excellent study systems to understand interactions between people and soils. The relationship between soil characteristics and indigenous agricultural practices are well documented for some locations, but there is a paucity of data for much of the region. Given the extent of ecological adaptation that has been documented, specifically for Hawai‘i, new Pacific datasets are expected to provide important insights into indigenous agricultural practices. To contribute to this discussion, we analyzed patterns in soil chemistry and vegetation in the Manu‘a islands of American Samoa. Soils were sampled along transects that crossed through precontact settlement zones in the upland of Fiti‘uta on Ta‘ū island, a location characterized by young (<100 ky) volcanic substrates and very high (>3800 mm y−1) annual rainfall. Soils were analyzed for several soil fertility properties that have been proposed as predictors of intensive rainfed tuber production in Hawai‘i and Rapa Nui. Surveys of remnant economic plants were conducted to assess patterns of past land use. Soils demonstrated moderate values of soil fertility as measured by pH, base saturation, exchangeable calcium, and total and exchangeable phosphorus, despite the high rainfall. Previously identified soil fertility indicators had some application to the distribution of traditional agriculture, but they also differed in important ways. In particular, low exchangeable calcium in the soils may have limited the agricultural form, especially the cultivation of tubers. Significant shifts in both soil parameters and remnant economic crops were documented, and alignment suggests cropping system adaptation to soil biochemistry. Archaeological samples combined with surveys of relict vegetation suggest that agroforestry and arboriculture were key components of past agricultural practices.

The Fukutoku Volcanic Complex: Implications for the northward extension of Mariana rifting and its tectonic controls on arc volcanism

Fukutoku-Oka-no-Ba (FOB) volcano is one of the most active submarine volcanoes in the Izu-Bonin-Mariana Arc. Historically, explosive eruptions associated with new island formation have occurred, and pumice rafts and discolored water have been frequently observed. Multiple geochemical studies focusing on the pumice erupted from FOB have been conducted to date, however, volcanic and tectonic features around FOB are poorly understood due to the scarcity of bathymetric and geological data. We compiled previously collected multibeam bathymetry data and major element compositions of dredged volcanic rocks to reveal the nature of magmatic and tectonic activity around FOB. Bathymetry data collected by 6 ship-based surveys between 1999 and 2006 define relatively young volcanic structures consisting of undeformed circular craters, steep-sided edifices and flank edifices on Kita-Fukutoku Bank, Kita-Fukutoku Caldera and Minami-Ioto which surround FOB. All the edifices with signs of relatively young volcanism exist on a common basal platform, together forming a large volcanic complex that is 50 km long and 25 km wide. We have named this feature the Fukutoku Volcanic Complex. Previously unreported N-S trending grabens and faults on the complex were identified from inspection of the bathymetry data. Some faults are continuous of the fault scarps bounding the northern Mariana Trough to the south, suggesting they are surface manifestations of the northward extension of Mariana Trough rifting. Vertical offsets of the grabens and faults decrease northward and the northernmost tip of Mariana rifting can now be observed to extend to 24°28′N on Kita-Fukutoku Bank. The basal platform and some young edifices on the Fukutoku Volcanic Complex are elongated or aligned in the N-S direction suggesting that arc volcanism here is tectonically influenced by Mariana rifting. Compiled major element compositions demonstrate two compositional types of magma with trachytic and basaltic rocks erupted around FOB. Although previous geochemical studies implied the association of basaltic magma with the FOB trachytic eruptions, the distribution of basaltic volcanism on the seafloor had not been well-defined. The presence of basaltic rocks around FOB, whose alkali compositions are similar to those of the northern Mariana Trough, and rift-related tectonic morphology suggest that the intrusion of basaltic magmas may be associated with the northward extension of Mariana rifting. Our detailed regional study provides new insights into the interplay of arc volcanism and extensional tectonics in the earliest stage of the Izu-Bonin-Mariana rift system.

Deep-sea organogenic-carbonate buildups in the northern zone of the Mid-Atlantic Ridge

Research subject. Carbonate formations raised from depths up 1986 to 2973 m in the off-axis zone of the rift valley of the North Atlantic Ocean in areas of active young volcanism. The ocean floor here is composed of basaltoids and serpentinized gabbro-peridotites fragmentarily overlain by carbonate pelagic sediments.Aim. To confirm the organogenic nature of these carbonate formations and to reveal new features of deep-water carbonate structures of this type.Materials and methods. The research objects comprised 100 samples of branched and cone-shaped/crater-like carbonate formations, the primary studies of which were carried out directly on the research vessel. Analytical methods included optical microscopy, electron microscopy, X-ray fluorescence spectroscopy, X-ray diffractometry, infrared spectroscopy, inductively coupled plasma mass spectrometry, and isotope mass spectrometry.Results. Among the most important features of the studied formations were found to be a concentric-zonal structure, which forms around the axial channel, and a thin dark brown crust of carbonate-ferromanganese composition. The abundance of planktonic fauna fossils and the distribution of mineralized biofilms with bacteriomorphic structures and glycocalyx were found in the body of crusts of the studied formations. More than 50 trace elements were found, including 11 essential (vital), 18 physiogenicallly-active and 22 antibiotic elements. The ratios of group contents of essential and antibiotic elements vary from 0.67 in the upper part of the structures to 0.001 in their lower part and up to 0.0006 in the volcanogenic substrate of the carbonate buildups. The ratio of the concentrations of essential zinc to physiogenically-active copper behaves similarly. In calcite, the isotopic composition of carbon, δ13СPDB = = –0.16 ± 1.03‰, corresponds to marine sedimentary carbonates; conversely, while oxygen exhibits anomalously isotopically heavy values, δ18OSMOW = 34.44 ± 3.21‰. In ferromanganese carbonates, the corresponding values are –3…1 and 32– 35‰.Conclusions. The studied carbonate formations are solid solutions based on calcite in their body and based on siderite-rhodochrosite binary series in the composition of brown crusts. Specific features of the chemism and minal compatibility of carbonate solid solutions reflect the conditions of microbially-stimulated mineral formation. The conducted isotopic studies discovered the phenomenon of a combination of carbon and oxygen, fundamentally different in genetic nature, in the studied formations. For the explanation of this fact, a scheme for isotopic exchange of oxygen between marine bicarbonate and sulfate with the active participation of sulfate-reducing bacteria was proposed.

Long‐Lived and Continual Volcanic Eruptions, Tectonic Activity, Pit Chains Formation, and Boulder Avalanches in Northern Tharsis Region: Implications for Late Amazonian Geodynamics and Seismo‐Tectonic Processes on Mars

AbstractTharsis is the largest volcanic province on Mars. It consists of a few large shield volcanoes, one of which is Alba Mons (AM), located in northern Tharsis, with the Ceraunius Fossae (CF) graben system to the south of it. Previous workers argued in favor of episodic building of Tharsis volcanoes. In contrast, we show that volcanism in the AM and CF regions occurred continually, at least in the last few hundred million years, based on ages of >1,000 stratigraphically young lava flows. Central volcanism in AM terminated around 200 Ma, while subsequent young volcanism, fed by both small shields and fissures, migrated to the south in CF. Several generations of grabens hosting thousands of simple to complex pit chains were formed by magmatic intrusion through feeder dikes, and these activities also migrated to the south during the Late Amazonian epoch. Thousands of boulder avalanches mark the slopes of grabens, pit chains, and impact craters, with ages ranging from a few tens to thousands of years. The local geological settings of the boulder falls suggest that both tectonic and volcanic marsquakes triggered the boulder avalanches. The broad zone of boulder falls in northern Tharsis defines the potential epicentral zone of (MW 4.1) 18 September 2021 marsquake. We infer that long‐lived and active magma chambers and subcrustal magma underplating driven by a mantle plume are present beneath the AM volcano and that these probably migrated south toward CF in the Late Amazonian epoch.

Neogene and Quaternary reef terraces of Mangaia, Rarotonga and Aitutaki (southern Cook Islands, South Pacific) revisited: gauges of sea-level change and island uplift?

New sedimentological data of facies and diagenesis as well as chronological data including strontium (87Sr/86Sr)-isotope ratios and uranium (U)-series dating, radiocarbon (14C) accelerator mass spectrometry (AMS) dating and biostratigraphy from elevated reef terraces (makatea) in the southern Cook Islands of Mangaia, Rarotonga and Aitutaki contribute to controversial discussions regarding age and sea-level relationships of these occurrences during the Neogene and Quaternary. The oldest limestones of the uplifted makatea island of Mangaia include reef-related facies which are mid-Miocene in age, based on new Sr-isotope and biostratigraphical data. In between these older deposits and the lowest coastal reef terrace of marine isotope stage (MIS) 5e, various older Pleistocene reef-related facies were identified. Based on Sr-isotope ratios, these were deposited during earlier Pleistocene highstands (as old as 2.28 Ma). Rare reef terraces on Rarotonga belong to the Plio-Pleistocene and the late Miocene, according to 87Sr/86Sr ratios. The late Miocene age is enigmatic as it exceeds the age of subaerially exposed volcanic rocks of Rarotonga island. The fossil reef could have formed on an older submarine volcanic high that was later displaced by younger volcanism to its present position, or the Sr-age could be too old due to diagenetic resetting. The Plio-Pleistocene Rarotonga reef terraces are overlain irregularly by Holocene reef deposits that are interpreted as storm rubble. Reef terraces on Aitutaki represent evidence of a higher-than-present (up to 1 m) sea-level during the late Holocene, based on 14C AMS age data. They are very similar to elevated late Holocene reefs of adjacent French Polynesia with regard to composition, elevation and age.

Fusible mantle cumulates trigger young mare volcanism on the cooling Moon.

The Chang’E-5 (CE5) mission has demonstrated that lunar volcanism was still active until two billion years ago, much younger than the previous isotopically dated lunar basalts. How the small Moon retained enough heat to drive such late volcanism is unknown, particularly as the CE5 mantle source was anhydrous and depleted in heat-producing elements. We conduct fractional crystallization and mantle melting simulations that show that mantle melting point depression by the presence of fusible, easily melted components could trigger young volcanism. Enriched in calcium oxide and titanium dioxide compared to older Apollo magmas, the young CE5 magma was, thus, sourced from the overturn of the late-stage fusible cumulates of the lunar magma ocean. Mantle melting point depression is the first mechanism to account for young volcanism on the Moon that is consistent with the newly returned CE5 basalts.

Breakthrough technologies for mineral exploration

Breakthrough technologies for mineral exploration are discussed from two perspectives. The first perspective is intended to discuss the important factors required for exploration technologies, derived deductively from a review of the role and expectations of exploration in the mining industry and the current situation of the mining industry. The second perspective is intended to discuss the common characteristics of breakthrough technologies for mineral exploration derived inductively from a review of specific examples of technological breakthroughs that actually brought about innovation to exploration: e.g. induced polarization (IP); airborne electromagnetics (EM); airborne gravity gradiometry (AGG); spectroscopic methods; global navigation satellite system (GNSS); unmanned survey platform; and neural networks/deep learning. The specific issues to be solved as breakthroughs in exploration technology in the near future are summarized as follows: Significant improvement in economic efficiency, namely: labor-saving, automated or unmanned operation, e.g. unmanned aerial vehicle (UAV)-based exploration and automatic spectroscopic scanning of drill cores; higher accessing capability, e.g. improvement of various airborne exploration techniques including airborne EM, AGG, and especially airborne IP; higher work efficiency and productivity, e.g. automatic data processing by neural networks/deep learning; and lower cost to implement, e.g. less expensive platforms such as UAVs.To obtain information that is really needed for exploration, specifically: IP effect of sulfide minerals associated with mineralization, i.e. practical spectral IP (SIP); geophysical characterization of the deep underground, e.g. enhancement of superconducting quantum interference device (SQUID)-based time-domain electromagnetic (TDEM); and removal of effects of the surface layer, e.g. very conductive deeply-weathered overburden and younger volcanics rich in magnetic minerals.To obtain information that could not be obtained by the conventional methods, specifically: distribution of endmember minerals related to mineralization, i.e. hyperspectral mapping with high spatial resolution.

Distinguishing Volcanic Contributions to the Overlapping Samoan and Cook-Austral Hotspot Tracks

Abstract To deconvolve contributions from the four overlapping hotspots that form the “hotspot highway” on the Pacific plate—Samoa, Rarotonga, Arago-Rurutu, and Macdonald—we geochemically characterize and/or date (by the 40Ar/39Ar method) a suite of lavas sampled from the eastern region of the Samoan hotspot and the region “downstream” of the Samoan hotspot track. We find that Papatua seamount, located ~60 km south of the axis of the Samoan hotspot track, has lavas with both a HIMU (high μ = 238U/204Pb) composition (206Pb/204Pb = 20.0), previously linked to one of the Cook-Austral hotspots, and an enriched mantle I (EM1) composition, which we interpret to be rejuvenated and Samoan in origin. We show that these EM1 rejuvenated lavas at Papatua are geochemically similar to rejuvenated volcanism on Samoan volcanoes and suggest that flexural uplift, caused by tectonic forces associated with the nearby Tonga trench, triggered a new episode of melting of Samoan mantle material that had previously flattened and spread laterally along the base of the Pacific plate under Papatua, resulting in volcanism that capped the previous HIMU edifice. We argue that this process generated Samoan rejuvenated volcanism on the older Cook-Austral volcano of Papatua. We also study Waterwitch seamount, located ~820 km WNW of the Samoan hotspot, and provide an age (10.49 ± 0.09 Ma) that places it on the Samoan hotspot trend, showing that it is genetically Samoan and not related to the Cook-Austral hotspots as previously suggested. Consequently, with the possible exception of the HIMU stage of Papatua seamount, there are currently no known Arago-Rurutu plume-derived lava flows sampled along the swath of Pacific seafloor that stretches between Rose seamount (~25 Ma) and East Niulakita seamount (~45 Ma), located 1400 km to the west. The “missing” ~20-million-year segment of the Arago-Rurutu hotspot track may have been subducted into the northern Tonga trench, or perhaps was covered by subsequent volcanism from the overlapping Samoan hotspot, and has thus eluded sampling. Finally, we explore tectonic reactivation as a cause for anomalously young volcanism present within the western end of the Samoan hotspot track.

Comparative Study of Gajah and Ijo Volcano Mineralization in Kulon Progo Dome based on Textural and Mineralogical Characteristics

Gajah Volcano and Ijo Volcano are two tertiary volcanoes located in the Kulon Progo Dome area, Yogyakarta. Gajah Volcano is located in the middle of the Kulon Progo Dome which is the oldest in the complex and belongs to Early Oligocene volcanism period (± 29 mya). On the other hand, Ijo Volcano is a product of younger volcanism period, occurred in the Late Oligocene (± 25 mya). The tectonic deformation occurred during the Late Oligocene-Early Miocene led to the formation of geological structures like faults and joints, which also serve as pathway for acid-intermediate intrusion rocks. The intrusions are associated with hydrothermal alteration and ore mineralization in both volcanoes. There has been no research comparing the characteristics of hydrothermal deposits that formed on Gajah Volcano and Ijo Volcano. This will be the main objective of this research. The research was carried out at two mineralization prospect locations representing each volcano, namely the Kaligono area (Gajah Volcano) and the Hargorojo area (Ijo Volcano). The results were obtained from geological and alteration mapping as well as representative rocks/veins sampling...Petrology,..petrography, mineragra- phy, and XRD analyzes conducted on altered rock and vein samples from the two prospects indicated some differences. Kaligono prospect area (Gajah Volcano) consists various of alteration types ie. phylic (quartz-sericite-illite-pyrite),..propylitic..(chlorite-calcite-pyrite±epi- dote±actinolite), and argillic (illite-smectite-kaolinite±quartz). The mineralized veins found on Gajah Volcano show vein swarm, brecciated, stockwork, and massive vein structure with massive vein textures. The veins in Kaligono show NE-SW and NW-SE trends and hosted by Andesite, Dacite, and Andesite Lava. Gangue minerals that are found in the vein samples are quartz, illite, iron oxide, pyrite, and carbonate minerals. The ore minerals consist of magnetite, chalcopyrite, and sphalerite. Meanwhile in Hargorojo prospect area (Ijo Volcano), the types of alteration found including phylic (quartz-sericite-pyrite),..propylitic..(pyrite-calcite±ch- lorite), and argillic (illite-smectite-kaolinite-quartz). The mineralized veins found on Ijo Volcano have a massive vein structure, brecciation, and stockwork with comb, drussy, and massive vein textures. The veins have NNE-SSW and E-W trend and hosted by Andesite and Dacite. The gangue minerals are carbonate minerals, oxide minerals, pyrite, barite, quartz and chalcedony. The ore minerals include chalcopyrite, silver, galena, and sphalerite. Based on the vein characteristics of Kaligono prospect, such as a complex stockwork structure, hydrothermal breccia, and massive vein texture, which contain high temperature hydrothermal minerals, ie. epidote, actinolite, and magnetite, maybe indicate this deposit is controlled by deep..structure..related..to..the..porphyry miner alization. Whereas in the Hargorojo prospect shows the typical textures of shallow epithermal system (open space filling), such as comb and drussy, which contain lower temperature hydrothermal minerals, such as chalcedony, silver, and galena. Based on textural and mineralogical characteristics, Kaligono prospect suggests that the alteration and mineralization takes place deeper or closer to the magmatic source. On the other hand, Hargorojo prospect suggests the alteration and mineralization process relatively far from the source.

Variations in magmatism and the state of tectonic compensation of the Mariana subduction system

AbstractWe investigate the variations in the state of isostatic compensation of the Mariana subduction system. We first calculate and analyse the gravity‐derived crustal thickness and non‐isostatic topography of this region. The Mariana back‐arc spreading centre and West Mariana Ridge are both close to Airy isostatic compensation. In contrast, the Mariana Trench axis is associated with a clearly defined zone of negative non‐isostatic topography and free‐air gravity anomaly (FAA), which have been shown to be caused by the flexural bending of the subducting Pacific Plate. The new analyses reveal that the southern Mariana Arc at 12.5°–16.7°N is associated with positive non‐isostatic topography and a local zone of positive FAA, which we interpret to be the result of accretion of young volcanism on a relatively strong lithospheric plate and/or supported by the tectonic stresses induced by the interaction of the subducting Pacific Plate with the upper Mariana micro‐plate.