Volcanic Chain Research Articles

Ice-marginal volcanic sequence in Iceland found on a nondescript gradual hillslope: An unexpected record of ice thickness late in deglaciation

Volcanism increases when glaciers melt because isostatic rebound during deglaciation decreases the pressure on the mantle, which enhances decompression melting. Anthropogenic climate change is now causing ice sheets and valley glaciers to melt around the world and this deglaciation could stimulate volcanic activity and associated hazards in Iceland, Antarctica, Alaska, and Patagonia. However, current model predictions for volcanic activity associated with anthropogenic deglaciation in Iceland are poorly constrained, in part due to uncertainties in past volcanic output over time compared to ice sheet arrangements. Further work specifically characterizing glaciovolcanic and ice-marginal volcanoes in Iceland is needed to reconstruct volcanic output during time periods with changing ice cover. Here, we describe a previously unrecognized ice-marginal volcanic sequence on a broad, gradual hillslope southeast of Langjökull and the Jarlhettur volcanic chain in Iceland's Western Volcanic Zone. Although previously mapped as interglacial lavas, canyons in this area revealed two southwest-dipping sequences of pillow-bearing tuff-breccias between pāhoehoe lava flows above modern lake Sandvatn. These pillow-bearing tuff-breccias and the quenched meter-scale cavities in coherent lava and cube-jointed facies show lavas came into contact with ice and pockets of trapped meltwater. However, clasts within the tuff-breccias include a mixture of pillow lavas and pāhoehoe fragments, requiring that the subaqueous tuff-breccia facies were derived from subaerial flows. In addition, we observed interfingering of subaerial and transitional subaqueous-subaerial pāhoehoe lava flows with the pillow-bearing tuff-breccias. We propose that during a deglaciation, subaerial lavas sourced upslope from near Skálpanes flowed downslope to the south and came into contact with thin ice north of the modern lake Sandvatn. We constrain the local ice at this time to be ∼30–50 m thick. Importantly, this finding demonstrates that ice-marginal deposits that can provide paleo-environmental constraints may be hidden in terrains without morphologically distinct glaciovolcanic edifices.

Evidence for suboceanic small-scale convection from a “garnet”-bearing lherzolite xenolith from Aitutaki Island, Cook Islands

Garnet peridotite xenoliths have been rarely reported from suboceanic mantle. Petrographic and geochemical characteristics of garnet-bearing oceanic peridotite xenoliths provide precious information on dynamics of the suboceanic lithosphere and asthenosphere interaction. We examined a lherzolite xenolith included in olivine nephelinite lava from Aitutaki Island, a member of the Cook-Austral volcanic chain. The lherzolite xenolith contains reddish fine-grained (< 5 µm in size) mineral aggregates (FMAs) with size range of 0.5–6 mm, consisting of olivine, calcic and sodic plagioclases, aluminous spinel, native iron, and nepheline. Microstructural observations and chemical data corroborate that the FMA is a decomposed pyrope-rich garnet including chromian spinel grains with an irregular highly indented morphology in the center. The FMA is surrounded by pyroxene-poor and olivine-rich aureole. The spatial and morphological relationships of FMA and chromian spinel with pyroxene-depleted margin suggest a reaction of aluminous spinel + pyroxenes → pyrope-rich garnet + olivine, which requires a compression before decomposition of the garnet to FMA. An orthopyroxene grain shows slight but clear chemical zoning characterized by increase in Al, Ca, and Cr from the grain center to the rim. The zoning patterns of Al and Ca in the orthopyroxene grain can be modeled by diffusion-controlled solid-state reactions induced by pressure and temperature changes, keeping surface concentrations in equilibrium with the other coexisting mineral phases. The results indicate that the mantle, from which the lherzolite xenolith was derived, underwent isothermal decompression followed by a weak heating on a time scale of a few tenths of million years before the xenolith extraction. From the deduced compression and decompression histories, we hypothesize that the mantle beneath Aitutaki Island was once dragged down to a garnet-stable deep mantle region and brought up later by small-scale sublithospheric convection.

Variability in mineralization of the petrified forests in the UNESCO Global Geopark of Lesvos, Greece

Miocene petrified tree fossils in tuffs from Lesvos Island show a variety of types of mineralization. Trees from the older part of the volcanic succession, including the well-known Petrified Forest near Sigri, are brilliant yellows, reds and browns as a result of Fe–Mn hydrothermal alteration post-dating silicification. Trees from the younger part of the volcanic succession on the southeastern flank of the volcanic chain include some in which the original carbon has not been replaced, others that are completely silicified or completely replaced by calcite, and yet others with cell walls silicified and the lumina filled with a variety of carbonate and sulfide minerals. Widespread Fe–Mn hydrothermal veins are found only in the older part of the volcanic succession and in underlying basement rocks and date from the inversion of the Sigri basin in the mid-Burdigalian and the intrusion of the Mesotopos dykes and laccoliths. The variable petrifaction of fossil wood is thus essentially a consequence of the variability of diagenetic and hydrothermal processes. This study demonstrates the importance of tectonic history in localising volcanic hydrothermal circulation and hence diversity in style of petrifaction.

What controls the magma production rate along the Walvis Ridge, South Atlantic?

The Walvis Ridge is a volcanic chain with the most pronounced topographic anomaly in the South Atlantic. This study analyzes the factors influencing magma production rates along the ridge to provide insights into hotspot-lithosphere interactions. With the sub-lithospheric gravity effect excluded, we determine the crustal thickness in the South Atlantic via gravity inversion. By subtracting the age-averaged crustal thickness, we isolate the excess crustal thickness attributable to ridge magmatism and calculate the magma generation rate along the Walvis Ridge over the past 80 Ma. Our results reveal a relatively lower magma production rate in the Walvis Ridge (peaking at ∼2.5 m3/s) compared to other major hotspot tracks (e.g. Hawaii-Emperor seamount chain, Ninetyeast Ridge, or Deccan-Reunion hotspot). Furthermore, variations in magma production rate show a strong inverse correlation with lithospheric thickness (or crustal age) at the time of loading but no significant correlation with spreading rate. Extensively distributed fracture zones in the lithosphere also promote magma production during the period of ∼70–40 Ma. Together with previously identified spreading-type magmatism in the northeast Walvis Ridge, we infer that external tectonic factors, other than hotspot-related factors, play a crucial role in magma production rate across the entire Walvis Ridge.

Tracing the Origin and Magmatic Evolution of the Rejuvenated Volcanism in Santa Clara Island, Juan Fernández Ridge, SE Pacific

Oceanic intraplate volcanoes sometimes experience late-stage eruptive activity known as rejuvenated volcanism, and contrasting interpretations for its petrogenesis depend on the compositional characteristics. In the Juan Fernández Ridge (JFR), a volcanic chain approximately 800 km in length emplaced on the Nazca Plate, some subaerial occurrences of rejuvenated volcanism have been recognized on the Robinson Crusoe and Santa Clara Islands, both part of the same deeply eroded shield volcano complex. This study aims to understand the origin and magmatic evolution of rejuvenated volcanism on Santa Clara Island, emplaced after ~2.15 Ma of quiescence above the shield sequence, mainly via the analysis of unpublished geochemical and isotopic data. Field reconnaissance identified two nearly coeval rejuvenated sequences on Santa Clara Island: Bahía W (BW) and Morro Spartan (MS), both formed by basanitic and picro-basaltic lava flows with brecciated levels and local intercalations of sedimentary and pyroclastic deposits. In comparison to the chemical signature of the preceding shield-building stage (comprised mainly of basalts and picrites), the two rejuvenated sequences exhibit a notable enrichment in incompatible elements, but the Sr, Nd, and Pb isotopes are very similar to the FOZO mantle endmember, with an apparent additional contribution of HIMU and EM1 components. The geochemistry of lavas revealed the involvement of various processes, including contamination by ultramafic xenoliths, high-pressure fractional crystallization of olivine and clinopyroxene, and potential partial assimilation of oceanic lithospheric components. While the oceanic lithosphere has been considered as a potential source, the isotopic data from Santa Clara lies outside of the mixing curve between depleted mantle (DM, here represented by the North Chile Rise and the East Pacific Rise) and the previous shield stage, suggesting that a lithospheric mantle is not the primary source for the rejuvenated stage volcanism. Therefore, we favor an origin of the rejuvenated volcanism from the mantle plume forming the JFR, supported by similarities in isotopic signatures with the shield stage and high values of 208Pb/204Pb (only comparable to San Félix—San Ambrosio in the vicinity of JFR), implying the presence of a regional source with radiogenic 208Pb/204Pb isotope ratios. In addition, isotopic variations are subparallel to the mixing line between HIMU and EM1 components, whose participation in different proportions might explain the observed trends. In conclusion, we propose that the source of the rejuvenated volcanism on Santa Clara Island is a heterogeneous mantle plume, the same one that fed the shield stage. The rejuvenated volcanism is derived from a secondary melting zone away from the main axis of the plume.

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

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

Pacific seafloor in the 40–52 Myr old portion of the Molokai to Murray corridor

A detailed study of the character of 40–52 Myr old Northeast Pacific seafloor illustrates how volcanism that occurs outside a spreading center axial zone contributes to the morphology of a region. A compilation of new and pre-existing multibeam sonar data forms the basis of our study, which lies within the spreading corridor bounded by Molokai and Murray fracture zones and does not include a major volcanic chain. The broad structure is consistent with constant crustal thickness and lithospheric cooling with age, and our analyses focus on the deviations from this ‘reference’ model. We find three types of volcanic features where typical abyssal hill fabric is generally not observed: 1) volcanic ridges that have a length of 30–120 km and a height of 1–2 km; 2) moderate seamounts that have a diameter of 8–15 km and a height of several 100's m; and 3) fields of very small seamounts, which extend several 10's km and are more common at ∼25% coverage than in other Pacific regions away from major volcanic chains. Gravity analysis suggests that the volcanic ridges and a few of the moderate seamounts are associated with local crustal thickening whereas the fields of very small seamounts do not display a distinct mass anomaly. Quantifying the distribution of past volcanism in this section of the Pacific plate during its evolution after initial accretion helps illustrate the degree of off-axis magmatism. Although we interpret the volcanic ridges as presently inactive, their formation on lithosphere older than at least a few Myr likely had an impact on the local seismic structure.

Monitoring volcanic activity with distributed acoustic sensing using the Tongan seafloor telecommunications cable

AbstractThe devastation caused by the January 2022 eruption of Hunga Tonga-Hunga Ha’apai volcano (HTHH) in the Tongan archipelago reminded us of the importance of monitoring shallow-sea volcanic activity. Seismic observations are essential for such monitoring, but there were no operational seismic stations in Tonga at the time of the eruption. There are only a few islands near Tongan volcanoes, and installation and maintenance of seismic stations on remote islands are expensive. Seismic observations based on distributed acoustic sensing (DAS) using a seafloor cable may provide a more practical and economical solution. To investigate the potential of this approach, we made preliminary DAS observations for 1 week using the seafloor domestic broadband telecommunications cable in Tonga. DAS equipment was installed at the landing station of the seafloor cable at Nuku’alofa on Tongatapu, the main island of Tonga. To provide reference data, we installed several seismometers on Tongatapu. The DAS data we obtained showed high noise levels in areas of shallow coral reef, but noise levels decreased greatly in deeper water areas, indicating that DAS is suitable for seismic observations of the deep seafloor. We detected many local and regional earthquakes during our week of observation and determined 17 earthquake hypocenters by picking P- and S-wave arrival times from the DAS and onshore seismic data. Although most of these were tectonic events related to the subduction of the Pacific plate along the Tonga trench, several events were detected around the volcanic chain of the Tongan archipelago including one event beneath the HTHH crater, implying that activity at HTHH has continued since the 2022 eruption. The much lower cost of installation of DAS equipment compared to that for pop-up type ocean-bottom seismometers and the ability of DAS systems to monitor seismic activity in real-time make it an attractive option for monitoring the activity of HTHH and other volcanoes near seafloor cables in the Tongan archipelago. Graphical Abstract

A Seismic Tomography, Gravity, and Flexure Study of the Crust and Upper Mantle Structure Across the Hawaiian Ridge: 2. Ka'ena

AbstractThe Hawaiian Ridge, a classic intraplate volcanic chain in the Central Pacific Ocean, has long attracted researchers due to its origin, eruption patterns, and impact on lithospheric deformation. Thought to arise from pressure‐release melting within a mantle plume, its mass‐induced deformation of Earth's surface depends on load distribution and lithospheric properties, including elastic thickness (Te). To investigate these features, a marine geophysical campaign was carried out across the Hawaiian Ridge in 2018. Westward of the island of O'ahu, a seismic tomographic image, validated by gravity data, reveals a large mass of volcanic material emplaced on the oceanic crust, flanked by an apron of volcaniclastic material filling the moat created by plate flexure. The ridge adds ∼7 km of material to pre‐existing ∼6‐km‐thick oceanic crust. A high‐velocity and high‐density core resides within the volcanic edifice, draped by alternating lava flows and mass wasting material. Beneath the edifice, upper mantle velocities are slightly higher than that of the surrounding mantle, and there is no evidence of extensive magmatic underplating of the crust. There is ∼3.5 km of downward deflection of the sediment‐crust and crust‐mantle boundaries due to flexure in response to the volcanic load. At Ka'ena Ridge, the volcanic edifice's height and cross‐sectional area are no more than half as large as those determined at Hawai'i Island. Together, these studies confirm that volcanic loads to the west of Hawai'i are largely compensated by flexure. Comparisons to the Emperor Seamount Chain confirm the Hawaiian Ridge's relatively stronger lithospheric rigidity.

Contamination Assessment of Toxic Elements in River Sediments from Baia Mare, Romania—Extreme Pollution from Mining Activities

Sediment samples from the Săsar River and its main tributaries were analyzed for their potentially toxic elements at the site of the Romplumb metallurgical company and near the well-known Pb-Zn-Cu epithermal deposit of Baia Sprie located in the Neogene volcanic chain of the Eastern Carpathians, Romania. The average metal concentrations arranged in order of decreasing abundance are as follows (mg·kg−1): Mn (4098) &gt; Zn (2093) &gt; Pb (918) &gt; Cu (489) &gt; As (160) &gt; Cr (37.51) &gt; Ni (30.25) &gt; Co (28.13) &gt; Cd (9.72) &gt; Hg (1.81). Several pollution indices were successfully used to assess the degree of contamination and ecological risk. The majority of sampling sites indicate high degrees of pollution, with two major hotspots identified. There are further sources, such as the Șuior (Pb-Zn-Au) and Săsar (Au-Ag) epithermal deposits, Cuprom company, and Bozânta tailing ponds, identified as contaminants. The Baia Mare mining district is causing a serious threat to the aquatic systems in the region, and it can be taken as a reference area for the human impact derived from the mining of mineral deposits of Au-Ag-Cu-Pb-Zn. It is imperative to reduce ecological risks and thereby protect the population living within this abandoned mining area.

Heavy minerals of the aeolian sediments in the East Slovak Basin (Western Carpathians) – Implications for their origin, transport process and sedimentary history

Aeolian sediments usually indicate glacial or periglacial arid-climate conditions, and knowledge of their sedimentary character and mineral composition can reveal the locality’s palaeo-environment and palaeo-geographic history. Reconstruction is provided by heavy-mineral surface micro-textural and geochemical analysis, and this detected the source area, source rocks and transport conditions for the Würmian wind-blown sands which form several dune types in the East Slovak Basin. The heavy-mineral morphology, surface micro-textures and low mineral maturity of the aeolian sediments preserve traces of past sub-aquatic environments and local aeolian transport. The heavy-mineral geochemistry suggests initial detrital derivation from local sources. This was formed by re-worked and re-mobilised Magura Nappe flysch sandstones in the Western Carpathians, with likely contribution of the Pieniny Klippen Belt flysch sediments indicated in sporadic pyrope-rich garnet. The associated detrital pyroxene and amphibole geochemistry denotes primary andesite source rocks which dominate lithology in the surrounding Neogene volcanic mountain chains. These are the Slanské vrchy, Vihorlatské vrchy and Zemplínske vrchy Mountains. The further occurrence of detrital hydrogrossular indicates derivation from contact-metamorphic zones associated with the volcanic rocks. Although different garnet types in the distinct dune profile zones may have resulted from heavy mineral re-sorting during active dune movement, they suggest sources changed by local wind directions. Orientation of basic linear features of the dunes derived from the digital terrain model indicates (paleo)wind generally from the north.

Boreal to temperate forests transition within Kunashir Island (the Kuril Archipelago): Insights from the novel vegetation map

The vegetation of the Kuril Islands remains insufficiently explored due to their remote location and harsh environment. Understanding the factors that influence vegetation distribution in this extensive volcanic chain of islands, spanning over a thousand kilometers, is important for global biogeography. Our paper presents the first vegetation map of Kunashir Island from the Kuril archipelago, compiled using Sentinel-2 medium-resolution multispectral satellite imagery, incorporating original field research data and the Random Forest machine-learning algorithm. The temperate broad-leaved forests are mainly composed of Acer mono subsp. mayrii and Quercus mongolica, predominantly limited to the southwestern coast, and true-boreal dark-coniferous Abies sachalinensis–Picea jezoensis forests located in the northeast part of Kunashir. The vegetation distribution pattern is associated with the warming effect of the Soja current on the east coast of Kunashir Island and the cooling effect of the Kuril current on the west coast. Kunashir's vegetation displays features of an ecotone between temperate and boreal zones. Still, the boundary between these zones should be drawn within the island, rather than between Kunashir and Hokkaido or Kunashir and Iturup, as suggested in some previous biogeographic generalizations.

Metasomatic enrichment of the sub-arc mantle: Evidence from the petrography and geochemistry of the xenolith-bearing andesites from Dinem Island, Batanes, Philippines

The Babuyan Segment of the Luzon Arc in the Philippines is divided into an older west volcanic chain (WVC) and a younger east volcanic chain (EVC) based on the geochemical and geochronological characteristics of their volcanic rocks. Mantle and crustal xenoliths have been previously reported in the volcanic rocks of young Batan (EVC) and Sabtang (WVC). In this work, we present new petrographic and geochemical data on volcanic rocks from Dinem Island (EVC), which also host mantle and crustal xenoliths. These volcanic rock data are compared to the data of other volcanic centers in the region to better understand magmatic-metasomatic processes that occur beneath island arcs.The Dinem volcanic rocks are generally porphyritic andesites, with plagioclase and hornblende phenocrysts, minor clinopyroxene and Fe-Ti oxides. Correlation between major oxides (i.e., K2O, Na2O, TiO2, CaO and Al2O3) and trace elements (i.e., Ni and Cr) with FeO*/MgO suggests that the Dinem volcanic rocks are related by magmatic differentiation. These rocks also record enrichment in large ion lithophile elements (e.g. Rb, Ba, Th) and depletion in high field strength elements (e.g. Nb, Ta, Ti), which are typical of arc volcanic rocks. The volcanic rocks from Dinem also have elevated (La/Sm)N and Th/Yb and low Ba/Th values relative to WVC volcanic rocks. These trace element ratios and enriched LREE signature suggest that the Dinem and younger Batan volcanic rocks of the EVC were derived from a mantle wedge that is highly metasomatized by slab-derived fluids/melts relative to the source region of the WVC volcanic rocks.

An early Miocene (Aquitanian) mangrove fossil forest buried by a volcanic lahar at Barro Colorado Island, Panama

We describe remains on an Early Miocene mangrove forest, based on a fossil wood assemblage, discovered on Barro Colorado Island, Panama. Sedimentological and stratigraphic analysis suggests that the fossil trees grew in marginal marine to coastal fluvial settings and were buried under a volcanic lahar flow in a single event. Radiometric analyses of a tuff associated with the fossils gives a date of ∼22.79 Ma indicating an assignment to the Aquitanian stage of Early Miocene. At this time, central Panama was part of a long and narrow peninsula with intense volcanic activity that connected it with North America and was separated from South America by the Central American Seaway. A total of 121 fossil wood specimens were located. Wood anatomy indicates that most of the identifiable specimens belonged to the same morphotype, which has anatomical traits similar to Sonneratia (Lythraceae), a mangrove tree that is native to Southeast Asia. We named this morphotype as a new fossil species: Sonneratioxylon barrocoloradoensis Pérez-Lara., sp. nov. Biomechanical estimates indicate that S. barrocoloradoensis had a mean tree height of 25 m with some specimens reaching 40 m, in contrast to modern Sonneratia and other extant mangrove forests, which generally have lower mean heights. The dominance of S. barrocoloradoensis, its similarity to Sonneratia, and the depositional setting suggest that the fossil wood assemblage on Barro Colorado Island comprised a mangrove forest growing along the coast of the volcanic chain of central Panama.

The Petrology and Geochemistry of REE-Enriched, Alkaline Volcanic Rocks of Ambitle Island, Feni Island Group, Papua New Guinea

Ambitle in the Feni Island Group is located within the NW trending Tabar–Lihir–Tanga–Feni (TLTF) volcanic island chain, Melanesian Arc, northeastern Papua New Guinea. The TLTF chain is renowned for its alkaline magmatism, geothermal activity, copper–gold mineralization, and world-class gold mining. Although its geochemical patterns indicate island arc signatures (i.e., high LILE and depleted HFSE), TLTF volcanism is not directly related to the older Melanesian Arc subduction system. However, it may have been influenced by source mantle metasomatism linked to the older subduction. The purpose of this study is to (1) present and interpret the petrographic, mineralogical, and geochemical data from Feni within the context of the tectonic evolution of the TLTF and (2) propose a geodynamic, petrogenetic model for the Feni volcanic rocks. The key methodologies used in this study are field mapping and sampling, petrographic analysis using the optical microscope, whole-rock geochemical analysis via XRF and ICP MS, and mineralogical analysis using an electron microprobe. The main rock types sampled in this study include feldspathoid-bearing basalt, trachybasalt, phonotephrite, trachyandesite, and trachydacite. Minerals identified include forsteritic olivine, diopside, augite, labradorite, andesine, anorthitic plagioclase, nepheline, and leucite in the primitive mafic suites, whereas the more evolved intermediate and felsic hypabyssal suites contain amphibole, albite, orthoclase, biotite, and either rare quartz or feldspathoids. Amphibole composition is primarily magnesiohastingsite with minor pargasite formed under polybaric conditions. Accessory minerals include apatite, titanite, and Ti-magnetite. We propose that limestone assimilation followed by fractional crystallization are plausible dominant processes in the geochemical evolution of the Ambitle volcanics. Clinopyroxene fractionation is dominant in the mafic volcanics whereas hornblende fractionation is a major petrologic process within the intermediate suites proven by the enrichment of LREE and depletions in MREE and HREE. Feni magmas are also highly enriched in REEs relative to neighboring arcs. This study is globally significant as alkaline magmas are important sources of Cu, Au, and REE as critical elements for green energy and modern technology.

The geological evolution of the Silala River basin, Central Andes

AbstractImproved understanding of the geology and stratigraphic architecture of the Silala River basin and its evolution, reviewed here, has been important in providing scientific evidence to an international dispute between Chile and Bolivia on the nature and origin of the waters of the Silala River. The dispute was submitted in 2016 to International Court of Justice (ICJ), which issued its judgment in 2022. The Silala River has evolved within an active volcanic chain, in the western region of the Andean plateau. Various volcanic structures, at different stages of their evolution, have determined the basin's development. The first evidence of alluvial drainage associated with the Silala fluvial system appeared in the Lower Pleistocene (ca. 2.6–1.6 Ma), a record of alluvial deposits with paleoflow directions toward the Southwest and South‐Southwest. These deposits had an important role in forming a highly permeable horizon, confined between two pyroclastic deposits (the Cabana and Silala Ignimbrites) which comprise the main regional aquifer in the basin, although there are other minor locally important aquifers. The second stage in the evolution of the river system occurred in the late Upper Pleistocene‐Lower Holocene (ca. 11–8.5 ka BP), when an erosive period carved the current trans‐boundary ravine in the Silala Ignimbrite. Morphological evidence clearly shows that the ravine was carved by fluvial action. The only documented tectonic activity during the development of the Silala River basin is the Cabana reverse fault and associated normal faults, representing an East–West shortening, which occurred between 2.6 and 1.6 Ma.This article is categorized under: Science of Water &gt; Water and Environmental Change Science of Water &gt; Hydrological Processes Water and Life &gt; Nature of Freshwater Ecosystems Human Water &gt; Water Governance

Isotopic and geochemical characteristics of mid- to-late-Miocene continental and oceanic arc volcanic and intrusive rocks, central North Island and offshore, New Zealand

Abstract Mid- to late-Miocene continental arc volcanism on the North Island of New Zealand is found in the Coromandel Peninsula, the Kiwitahi volcanic chain and the Taranaki Basin (Kora Volcano) offshore the western margin of the North Island. Coeval oceanic arc volcanism is also found along the offshore Colville Ridge/Kermadec Ridge north of New Zealand. This Pb–Sr–Nd–Hf isotopic study aims to evaluate mantle sources and potential crustal contaminants along these sections of the Miocene arc system. The Colville/Kermadec Ridge and Kora lavas have the lowest Sr (0.7029–0.7045) and highest Nd (0.51305–0.51292) ratios; the Coromandel and Kiwitahi lavas overlap (Sr = 0.704–0.706; Nd = 0.51268–0.51296). The Colville/Kermadec Ridge, Kora, and Coromandel/Kiwitahi rocks form three distinct arrays on Pb–Pb plots, all above the Northern Hemisphere Reference Line, but none trend towards local Mesozoic basement greywackes. Isotopic and trace element ratio variations suggest that subducted sediments are a component in Coromandel/Kiwitahi mafic lava sources. The younger, southern Kiwitahi lavas have a more depleted mantle source than that for the older, northern Kiwitahi chain. Evolved lavas commonly have interacted with Waipapa basement rocks. Kora rocks have compositions similar to those of back-arc lavas and have been emplaced as sills in a rift environment above a distinct subduction-modified mantle.

The Geological and Tectonic Evolution of Feni, Papua New Guinea

Feni is located at the southeastern end of the NW-trending Tabar–Lihir–Tanga–Feni (TLTF) volcanic island chain, in northeastern Papua New Guinea. This island chain is renowned for hosting alkaline volcanics, geothermal activity, copper–gold mineralization, and mining. There is no agreed consensus on the tectonic and petrogenetic evolution of Feni. Thus, the purpose of our paper is to present the geology of Feni within the context of the regional tectonic evolution of the TLTF chain and offer a succinct and generic geodynamic model that sets the stage for our next paper. The methodologies used in this study include a critical review of published and unpublished literature in conjunction with our geological observations on Feni. The Pliocene-to-Holocene TLTF chain is a younger arc situated within the greater Eocene-to-Oligocene Melanesian Arc bounded by New Ireland to the west, the Kilinailau Trench and Ontong Java Plateau in the east, and the New Britain Trench to the south. The geological units mapped on Feni include a large volume of basaltic lava flow and trachyandesite stocks intruding a limestone and siltstone basement. Younger units include the trachyte domes, pyroclastic flow, and ash fall deposits. The major structures on Feni are normal or extensional faults such as the Niffin Graben. Feni magmatism is attributed to the petrogenetic processes of polybaric or decompression melting and crystal fractionation of magmas previously influenced by sediment assimilation, mantle wedge metasomatism, slab tears, slab melts, and subduction. Deep lithospheric normal faults provide the fluid pathways for the Feni alkaline magmas.

Time-lapse imaging of seismic scattering property and velocity in the northeastern Japan

Investigating spatio-temporal changes in crustal structure is a key to understanding the dynamic processes in the earth's crust associated with large earthquakes and volcanic activities. The dense seismic network in the northeast part of Japan (Tohoku region) allows us to apply seismic interferometry to continuous records of ambient noise data for studying crustal changes related to the 2008 Mw 6.9 Iwate-Miyagi Nairiku earthquake and the 2011 Mw 9.0 Tohoku-oki earthquake. We track changes in both seismic scattering properties and velocities over five years and spatially localize them based on the coda wave decorrelation and travel time sensitivity kernels calculated from the solution of the radiative transfer equation. The 2008 Iwate-Miyagi Nairiku earthquake caused significant changes in both seismic scattering properties and seismic velocities in the vicinity of the epicenter subjected to dynamic or/and static stress perturbations. Changes in scattering properties associated with the 2011 Tohoku-Oki earthquake around some active volcanoes in the Tohoku region are likely related to geofluid migrations triggered by strong vibrations during the large earthquake. The decrease in seismic velocity exists mainly along the eastern coastal region and extends to the central Quaternary volcanic chains under the combined dynamic and static stress changes by the earthquake. The waveform correlation is possibly sensitive to the fluid content and might be a useful indicator of fluid migration in the crust. This is the first comprehensive demonstration and comparison of the spatio-temporal changes of seismic scattering properties and velocities at long-term and regional scales under the influence of two large earthquakes.

Reviewing the geodynamic impact of aseismic ridges subduction on the tectonic-magmatic evolution of the Southern Puna plateau

The Southern Puna (∼24° S to 27° S) is an outstanding segment of the Central Andes where the subduction of aseismic ridges, multi-scale lithospheric foundering, and the transition from normal Andean subduction to the Chilean-Pampean flat slab occur. The exponential increase in the volcanological and geophysical knowledge of the Southern Puna provides a unique opportunity to reappraise its geodynamic evolution. This paper presents an updated review of the spatial-temporal distribution of the volcanism along with a reassessment of the main geophysical and morphostructural features of this region. Contrasting our observations with new kinematic reconstructions of the Taltal and Copiapó ridges, we infer that their subduction under the Southern Puna plateau has played a fundamental role in its Neogene-Quaternary geodynamic evolution (e.g shallow subduction, lithospheric delamination). Specifically, we propose a new alternative hypothesis where the Transversal Volcanic Chains (TVCs), characterizing the Southern Puna, are related to slab tearing. Slab tearing is a valid explanation for the occurrence of local anomalous peaks of melt productivity in a relatively cold retreating mantle wedge during slab shallowing. In our model, slab tearing under the Southern Puna was influenced by the flexural deformation related to slab dip changes as a result of the anomalous slab buoyancy during the subduction of Copiapó and Taltal ridges.