Recent Volcanism Research Articles

Paleoclimatic investigations using isotopic signatures of the Late Pleistocene-Holocene groundwater of the stratified aquifers in Kuwait

The study attempts to determine paleo recharge sources for two major aquifer units of Kuwait, namely, Kuwait Group Aquifer (KGA), and Dammam Formation (DFm) were collected and analyzed for major ions and isotopes. The obtained results of 14C ages indicated that the groundwater samples ranged from 31.9 Ky to 3.9 Ky in DFm and 23.3 Ky to 0.8 Ky in KGA. The variations in δ18O signatures with respect to age reflected that there were two major sources of rainwater such as enriched southern Indian Ocean monsoon and the depleted northwesterly (Mediterranean) vapor source. The samples found to show variations during the three marine isotopic stages (MIS 1–3), Heinrich events, Bolling-Allerod, and Dryas time periods in both aquifers. A shift in the Intertropical convergence zone (ITCZ) was witnessed in the groundwater of both aquifers from 7.8 Ky to 4.9 Ky. The variation in the Holocene climate is mainly due to the influence of tropospheric easterly jet governed by the swing in ITCZ , as a result of Holocene volcanism. The mean δ18O values of DFm samples (-3.81‰) reflect depletion than KGA samples (-2.31‰), and the d-excess values were −0.95‰ and 2.05‰ respectively. Thus it could be inferred that the DFm was predominantly recharged during Late Pleistocene period and it was in a relatively cooler climate than recharge environment of KGA. The study infers that KGA was recharged between 26oN and 26.8oN latitudes, and that of the DFm was noted to be recharged (south west of Kuwait) in two different patches between 25.8oN and 26.2oN and 26.7oN-27.4oN latitudes during Late Pleistocene. The KGA was concluded to be recharged between 25.5oN and 27.5oN latitudes, south of Kuwait, during Holocene.

Refining the Holocene eruptive activity at Tenerife (Canary Islands): The contribution of palaeomagnetism

The timing of the Holocene volcanic activity of Tenerife (Canary Islands) is poorly constrained and the volcanological framework for this area is still incomplete. Most of the eruptions are dated only by a single 14C dating, or the ages are simply stratigraphically determined. We apply palaeomagnetism, increasingly used in the last years to date Holocene volcanism, to improve the knowledge of Tenerife volcanic history. We report on the palaeomagnetic dating, using the SHA.DIF.14K global model, of nine Holocene eruptions that produced scoria cones and major lava flows, and we compare our results with those previously obtained by 14C method. Four of the studied eruptions were previously dated by 14C, four were stratigraphically constrained, and one was never dated so far. Concerning the first group, for Boca Cangrejo and Mña Reventada eruptions, palaeomagnetic and 14C ages agree, while for the others we obtained older or younger ages than radiocarbon data. For the second group, one or more age ranges smaller than stratigraphic intervals were found. Finally, we provided the first dating (790–723 BCE) of the Mña Grande eruption. We confirm that palaeomagnetism can be considered an excellent complement to the radiocarbon method, because it is applicable on volcanics with nearly all compositions and provides higher resolution dating, at least where reliable geomagnetic reference curves are available. The improved framework of the Holocene volcanic activity of Tenerife shows alternating periods characterized by low and high eruptive frequencies, with the last 3 kyr characterized by high eruptive frequency and dominated by basaltic eruptions.

Structural assessment and geochemistry of thermal waters at the Cerro Machin Volcano (Colombia): An approach to understanding the geothermal system

Through a detailed structural assessment of faults, carried out by remote sensing and a slip-dilation tendency analysis along with water geochemistry of thermal waters, it was possible to characterize the geothermal system of Cerro Machin Volcano (CMV) located in the western flank of the Cordillera Central of Colombia. The study shows that the geothermal system presents a favorable structural setting for the transport of fluids (e.g. fault intersection), where the structural component is marked by faults striking NW-SE, NE-SW, and N-S, controlling its deformational model, permeability and therefore, the fluid flow path. In addition, hydro-geochemistry allows identifying two sets of water (i) Na-HCO3 and (ii) Ca-HCO3 types. Na-HCO3 springs are representatives of a more direct upflow in the system, where fluid uses critically stressed areas to ascend. In contrast, Ca-HCO3 springs are more strongly affected by subsurface process such as mixing and water-rock interaction. The geothermal system is characterized of a convection-dominated geothermal play associated with recent volcanism, which is recharged by meteoric waters that flow through fractures and faults and is strongly influenced by a CO2-rich fluid coming from deeper levels. The reservoir occupies a fracture zone within the Cajamarca complex with an estimated temperature of around 220 °C, according to solute and multicomponent geothermometry.

Holocene volcanism at the Quetrupillán Volcanic Complex (39°30’ S, 71°43’ W), southern Chile

This paper provides the first detailed description of Holocene volcanism at the Quetrupillán Volcanic Complex. This volcanic complex consists of a truncated and eroded stratocone plus sixteen well-preserved satellite vents on its lower flanks. Intense scouring of the stratocone’s flanks (presumably by ice) has removed much evidence of its Holocene eruptions, and thus the Holocene construction of the stratocone (i.e. number and volume of eruptions) cannot be determined. The sixteen satellite vents are the products of an uncertain number of eruptions, with trachyte comprising ~97% of the lava erupted. Geochemical analysis of tephra layers from three logged sections in nearby valleys provides evidence of three explosive eruptions from Quetrupillán. In these sections, no evidence of pyroclastic density current deposits was identified, which may suggest that explosive volcanic hazards from Quetrupillán are less than indicated on current hazard maps.

Analysis of the relation between bottom hole temperature data and Curie temperature depth to calculate geothermal gradient and heat flow in Coahuila, Mexico

Estimations of the Curie temperature depth using aeromagnetic data are commonly employed to study the thermal structure of the crust. In this research, we estimated the Curie temperature-depth with the “de-fractal” method and calculated the geothermal gradient and the heat flow of 24 blocks uniformly distributed in the Mexican state of Coahuila. The reliability of the “de-fractal” method was evaluated by comparing the geothermal gradient results with the Bottom Hole Temperature data available from petroleum boreholes. The maps show that the regional faulting is associated with recent volcanism characterized by shallow Curie temperature-depth (~17 km); furthermore, changes of the fractal parameter have a relationship to the tectonic history of this region and the geology of each analyzed block. The results of our statistical analyses showed that the geothermal gradient estimated with the “de-fractal” method is more closely related to the Bottom Hole Temperature data than the estimations obtained with the “centroid” method. Additionally, the similarity between Bottom hole temperature and Curie temperature-depth calculated geothermal gradient indicated that conduction is the predominant heat transfer mechanism.

Large-scale structure of the Doldrums multi-fault transform system (7-8ºN Equatorial Atlantic): preliminary results from the 45th expedition of the R/V A.N. Strakhov

The Equatorial portion of the Mid Atlantic Ridge is displaced by a series of large offset oceanic transforms, also called “megatransforms”. These transformdomains are characterized by a wide zone of deformation that may include different conjugated fault systems and intra-transform spreading centers (ITRs).Among these megatransforms, the Doldrums system (7-8oN) is arguably the less studied, although it may be considered the most magmatically active. Newgeophysical data and rock samples were recently collected during the 45th expedition of the R/V Akademik Nikolaj Strakhov. Preliminary cruise results allowto reconstruct the large-scale structure and the tectonic evolution of this poorly-known feature of the Equatorial Atlantic. Swath bathymetry data, coupled withextensive dredging, were collected along the entire megatransform domain, covering an area of approximately 29,000 km2. The new data clearly indicate thatthe Doldrums is an extremely complex transform system that includes 4 active ITRs bounded by 5 fracture zones. Although the axial depth decreases toward thecentral part of the system, recent volcanism is significantly more abundant in the central ITRs when compared to that of the peripheral ITRs. Our preliminaryinterpretation is that a region of intense mantle melting is located in the central part of the Doldrums system as consequence of either a general transtensive regimeor the occurrence of a more fertile mantle domain. Large regions of basement exposure characterize the transform valleys and the ridge-transform intersections.We speculate that different mechanisms may be responsible for the exposure of basement rocks. These include the uplift of slivers of oceanic lithosphereby tectonic tilting (median and transverse ridges formation), the denudation of deformed gabbro and peridotite by detachment faulting at inner corner highs, andthe exposure of deep-seated rocks at the footwall of high-angle normal faults at the intersection of mid-ocean ridges with transform valleys

Phylogeography of the Volcano Rabbit (Romerolagus diazi): the Evolutionary History of a Mountain Specialist Molded by the Climatic-Volcanism Interaction in the Central Mexican Highlands

Processes such as climate fluctuations together with recent volcanism have driven the diversification and local persistence of biodiversity within the Mexican highlands. We reconstruct the phylogeographic pattern and historical demography of the volcano rabbit, Romerolagus diazi, an endemic lagomorph in central Mexico, to elucidate the effect of the climate-volcanism interaction on its evolutionary history. We sequenced two mtDNA regions for 152 individuals from 45 sample sites located at the volcanic fields Sierra Chichinautzin and Sierra Nevada. We surveyed the genetic diversity, and reconstructed and dated an intraspecific phylogeny. The effective population size trough time was estimated, and an Ecological Niche Model was projected onto the past. Results showed a well-supported phylogeny with five monophyletic lineages with a north to south geographic pattern at Sierra Nevada, and east to west at Sierra Chichinautzin. Dating estimates indicated that those lineages might have started their diversification ca. 1.4 Ma, which agrees with the geological dating reported for the volcanic fields rising. We detected changes in demographic history and potential distribution, with a global population expansion during the Last Glacial Maximum and a retraction during the Last Interglacial period. The molecular evidence showed that the volcano rabbit had a dynamic evolutionary history molded by geological and climatic events during the Pleistocene. The volcanic events that shaped Sierra Chichinautzin and Sierra Nevada generated regions that allowed the colonization, isolation and posterior in-situ diversification of their populations. Additionally, the climatic fluctuations of the latest glacial-interglacial cycles promoted altitudinal populations shifts, with a sky-island dynamic that allowed their persistence.

Upper mantle deformation signatures of craton–orogen interaction in the Carpathian–Pannonian region from SKS anisotropy analysis

SUMMARYSince the Mesozoic, central and eastern European tectonics have been dominated by the closure of the Tethyan Ocean as the African and European plates collided. In the Miocene, the edge of the East European Craton and Moesian Platform were reworked in collision during the Carpathian orogeny and lithospheric extension formed the Pannonian Basin. To investigate the mantle deformation signatures associated with this complex collisional-extensional system, we carry out SKS splitting analysis at 123 broad-band seismic stations in the region. We compare our measurements with estimates of lithospheric thickness and recent seismic tomography models to test for correlation with mantle heterogeneities. Reviewing splitting delay times in light of xenolith measurements of anisotropy yields estimates of anisotropic layer thickness. Fast polarization directions are mostly NW–SE oriented across the seismically slow West Carpathians and Pannonian Basin and are independent of geological boundaries, absolute plate motion direction or an expected palaeo-slab roll-back path. Instead, they are systematically orthogonal to maximum stress directions, implying that the indenting Adria Plate, the leading deformational force in Central Europe, reset the upper-mantle mineral fabric in the past 5 Ma beneath the Pannonian Basin, overprinting the anisotropic signature of earlier tectonic events. Towards the east, fast polarization directions are perpendicular to steep gradients of lithospheric thickness and align along the edges of fast seismic anomalies beneath the Precambrian-aged Moesian Platform in the South Carpathians and the East European Craton, supporting the idea that craton roots exert a strong influence on the surrounding mantle flow. Within the Moesian Platform, SKS measurements become more variable with Fresnel zone arguments indicating a shallow fossil lithospheric source of anisotropy likely caused by older tectonic deformation frozen in the Precambrian. In the Southeast Carpathian corner, in the Vrancea Seismic Zone, a lithospheric fragment that sinks into the mantle is sandwiched between two slow anomalies, but smaller SKS delay times reveal weaker anisotropy occurs mainly to the NW side, consistent with asymmetric upwelling adjacent to a slab, slower mantle velocities and recent volcanism.

Petrographic, Geochemical and Isotopic (Sr–Nd–Pb–Os) Study of Plio-Quaternary Volcanics and the Tertiary Basement in the Jorullo-Tacámbaro Area, Michoacán-Guanajuato Volcanic Field, Mexico

AbstractThe origin of the large diversity of rock types erupted along the subduction-related Trans-Mexican Volcanic Belt (TMVB) remains highly debated. In particular, several hypotheses have been proposed to explain the contemporary eruption of calc-alkaline and alkaline magmas along the belt. The Michoacán-Guanajuato Volcanic Field (MGVF) is an atypical, vast region of monogenetic activity located in the western-central part of the TMVB. Here we present new petrographic, geochemical, and isotopic (Sr–Nd–Pb–Os) data on recent volcanics in the Jorullo-Tacámbaro area that is the closest to the oceanic trench. TMVB-related volcanics in this area are Plio-Quaternary (<5 Ma) and mainly form a calc-alkaline series from basalts to dacites, with rare (<5 vol. %) alkaline rocks that range from trachybasalts to trachydacites, and transitional samples. Crystal textures are consistent with rapid crystallization at shallow depth and processes of mixing of similar magma batches (magma recharge). All of the samples exhibit an arc-type trace element pattern. Alkaline and transitional magmas have higher Na2O and K2O, lower Al2O3, and higher concentrations in incompatible elements (e.g. Sr, K, Ba, Th, Ce, P) compared to calc-alkaline rocks. Calc-alkaline rocks are similar isotopically to transitional and alkaline samples, except for a few low 87Sr/86Sr samples. Sr, Nd and Pb isotopes do not correlate with MgO or 187Os/188Os, indicating that they were not significantly influenced by crustal contamination. Isotopic and trace-element systematics suggest that the Tacámbaro magmas are produced by melting of a mantle wedge fluxed by fluids derived from a mixture of subducted sediments and altered oceanic crust. Alkaline and transitional magmas can be derived from a lower degree of partial melting of a similar source to that of the calc-alkaline rocks, whereas the few low 87Sr/86Sr calc-alkaline rocks require a lower proportion of fluid derived from oceanic sediments and crust. Volcanism at the trenchward edge of the MGVF was thus driven purely by subduction during the last 5 Ma, hence discarding slab rollback in this sector of the TMVB.

El Escondido tuff cone (38 ka): a hidden history of monogenetic eruptions in the northernmost volcanic chain in the Colombian Andes

El Escondido is a dacitic monogenetic volcano situated in the Samana monogenetic volcanic field, within the Central Cordillera of Colombia. The tuff cone was emplaced in a deeply incised and rainy mountainous zone, ca. 38 ky ago by an explosive eruption that affected not only the metamorphic and igneous basement but also the remnants of the ~ 154 ka Pela Huevos volcano. The El Escondido volcaniclastic deposits are composed of juvenile pumice and lithic fragments including dense volcanic rocks from the Pela Huevos volcano, as well as metamorphic and igneous rocks from the basement. The pumice shows tubes and spongy textures. The volcanic lithics are dominantly angular and fresh, and exhibit different mineralogy and whole-rock geochemistry in comparison to the pumice. Plagioclase and amphibole are ubiquitous; however, biotite and quartz crystals occur only in the pumice fragments (~ 70 wt% SiO2 volatile-free), whereas olivine and pyroxene crystals are only found in the volcanic lithics (~ 65 wt% SiO2 volatile-free). The El Escondido tuff cone is strongly eroded and Pela Huevos is a dome-like remnant in the SE sector. Because of this, along with the highly vegetated tropical zone where the volcanoes are emplaced as well as difficult political issues in the region, the edifices were not recognized until recently; this is why the younger cone was named “El Escondido” (which means “The Hidden”). These eruptions evidence that recent volcanism has occurred in a zone of the Central Cordillera that has been considered as non-volcanogenic in recent studies.

Petrogenesis of three East Fork Member rhyolites of the Jemez volcanic field, Valles caldera, New Mexico, USA

The most recent volcanism in the Valles caldera is represented, in stratigraphic order, by the El Cajete Pyroclastic Beds (ECPB), Battleship Rock Ignimbrite (BRI), the VC-1 rhyolite (not studied herein), and Banco Bonito Flow (BBF), which are collectively known as the East Fork Member (EFM) of the Valles Rhyolite. The EFM was erupted approximately 74 to 68 ka after an approximate 460 ka lull in ring-fracture volcanism.Crystal assemblages consist of plagioclase, biotite, clinopyroxene, orthopyroxene, amphibole, sanidine, quartz, and oxides, in order of abundance. Electron probe microanalysis and detailed petrography indicates that two distinct crystal populations are present in the ECPB, BRI, and BBF. Large (≥1 mm), typically resorbed or subhedral crystals represent one population, and small (≤0.5 mm), generally euhedral crystals represent the other. The large resorbed plagioclase crystals typically have oligoclase to andesine rim overgrowths. 40Ar/39Ar geochronology performed on euhedral biotite and groundmass glass from the BBF returned isochron ages of 478 ± 3 ka and 575 ± 2 ka and total gas ages of 125 ± 1 ka and 129 ± 1 ka, respectively. High molar Mg numbers of large euhedral biotite and 40Ar/39Ar ages older than the accepted age range indicate these crystals are xenocrystic. Radiogenic isotopes are consistent with mixing between the mantle and lower crustal reservoirs. General trends are evident between whole-rock major and trace elements with increasing SiO2 and Nb, respectively. In general, incompatible trace elements increase and compatible trace elements decrease with increasing Nb. For the major elements, MgO, P2O5, Al2O3, FeO* show decreasing trends while K2O and Na2O show increasing trends with increasing SiO2. Incompatible trace element ratios (Ta/Yb, Y/Yb, Th/Yb, Th/Nb) indicate the presence of a single magma batch.The heterogeneity in crystal morphology and chemistry can be explained by a model in which partial melting of mid- to deep continental crust occurred due to an intrusion of an intermediate composition magma. Magma mixing and an exchange of crystals took place between the partial melt and the intruding magma. The hybrid magma rose to the upper crust, where it underwent fractional crystallization prior to eruption. The geochemical and isotopic data from this study are best explained by a modified version of the rapid production and eruption model put forth by Huppert and Sparks (1988).

Preface

GeoProNHIII National scientific conference with foreign participants “Geodynamical Processes and Natural Hazards”This issue presents the proceedings of the GeoProNH – III National scientific conference with foreign participants “Geodynamical Processes and Natural Hazards”. The conference was held May 27-31, 2019 in Yuzhno-Sakhalinsk, Russia, and considered the following topic areas:- the seismicity of the Russian Far East and Eastern Siberia;- the tectonics and geodynamics of the northwestern Pacific;- manifestations of tsunamis and other marine hazards;- recent volcanism and methods of its monitoring;- geological and geomorphological aspects of the coastal assimilation strategy;- environmental problems and geoecological hazards.The Sakhalin and Kuril Islands are parts of the Pacific Ring of Fire, so this region undergoes almost all possible geohazards: earthquakes, tsunamis, volcano eruptions, etc. More than 120 scientists, experts and postgraduates from Belarus, Egypt, France, Japan, Kyrgyzstan, and Russia took part in the GeoProNH Conference and discussed the current state of the art and advances in geosciences related to the analysis of natural hazards and/or their preventions. The conference also considered fundamental and applied problems of geology, geophysics, geodynamics, geoecology, oceanology, seismology, volcanology, etc. related to the dangerous natural phenomena mentioned. The Conference Program included four days of plenary and topical sessions, poster presentations, and two days of field geological excursions. The ultimate goal of the conference was to highlight and share the best ways to reduce negative impacts of the above hazards using modern monitoring systems. The published proceedings, hopefully, will serve the same purpose. The issue is addressed to researchers, experts, and students who deal with geohazard assessments and relevant topics of geosciences.

An Improved Global Analysis of Population Distribution in Proximity to Active Volcanoes, 1975–2015

Better and more detailed analyses of global human exposure to hazards and associated disaster risk require improved geoinformation on population distribution and densities. In particular, issues of temporal and spatial resolution are important for determining the capacity for assessing changes in these distributions. We combine the best-available global population grids with latest data on volcanoes, to assess and characterize the worldwide distribution of population from 1975–2015 in relation to recent volcanism. Both Holocene volcanoes and those where there is evidence of significant eruptions are considered. A comparative analysis is conducted for the volcanic hot spots of Southeast Asia and Central America. Results indicate that more than 8% of the world’s 2015 population lived within 100 km of a volcano with at least one significant eruption, and more than 1 billion people (14.3%) lived within 100 km of a Holocene volcano, with human concentrations in this zone increasing since 1975 above the global population growth rate. While overall spatial patterns of population density have been relatively stable in time, their variation with distance is not monotonic, with a higher concentration of people between 10 and 20 km from volcanoes. We find that in last 40 years in Southeast Asia the highest population growth rates have occurred in close proximity to volcanoes (within 10 km), whereas in Central America these are observed farther away (beyond 50 km), especially after 1990 and for Holocene volcanoes.

Short‐ and Long‐Term Variations in the Reykjanes Geothermal Reservoir From Seismic Noise Interferometry

AbstractThe Reykjanes Geothermal System (RGS) is a high‐temperature geothermal system located on the Reykjanes peninsula, a transtensional plate‐boundary zone located on the southwestern tip of Iceland. The area is characterized by high seismicity, recent volcanism, and high‐temperature geothermal fields. We use seismic noise records from April 2014 to August 2015 to study stress changes and potential deformation of the subsurface caused by injection and production operations at RGS through seismic interferometry. We retrieve continuous time series of waveform similarity values and seismic velocity changes during this period. The S‐transform of the similarity values allows us to clearly identify three variations in the mechanical properties of the Reykjanes peninsula related to rapid changes of RGS production. In addition, we observe a slow seismic velocity decrease of 0.36%/year in the reservoir due to the water deficit and seasonal variations associated with the energy production demand.

Lithospheric foundering and underthrusting imaged beneath Tibet

Long-standing debates exist over the timing and mechanism of uplift of the Tibetan Plateau and, more specifically, over the connection between lithospheric evolution and surface expressions of plateau uplift and volcanism. Here we show a T-shaped high wave speed structure in our new tomographic model beneath South-Central Tibet, interpreted as an upper-mantle remnant from earlier lithospheric foundering. Its spatial correlation with ultrapotassic and adakitic magmatism supports the hypothesis of convective removal of thickened Tibetan lithosphere causing major uplift of Southern Tibet during the Oligocene. Lithospheric foundering induces an asthenospheric drag force, which drives continued underthrusting of the Indian continental lithosphere and shortening and thickening of the Northern Tibetan lithosphere. Surface uplift of Northern Tibet is subject to more recent asthenospheric upwelling and thermal erosion of thickened lithosphere, which is spatially consistent with recent potassic volcanism and an imaged narrow low wave speed zone in the uppermost mantle.

The First Results of Tephrochronological Study of Late Pleistocene–Holocene Volcanic Eruptions in the Zhom–Bolok River Valley (Eastern Sayan)

The first results of tephrochronological studies of Late Pleistocene–Holocene volcanic eruptions in the Zhom-Bolok River valley (Eastern Sayan) are reported. Based on the analysis of bottom sediments of the glacial lake Kaskadnoe-1, a detailed chronological scale of volcanic activity in this region has been worked out. It is established that the eruptions began at least 14 300 years ago and continued, gradually weakening, to 6280 years ago. In this period, ten groups of peaks of sediment enrichment in microtephra are registered for Kaskadnoe-1 Lake. The average interval between the stages of eruptions in this period was ~500–600 years. Between 14 300 and 13 400 years ago, the most large-scale volcanic events took place, eruptions were practically not interrupted, and the explosive activity was the most intense. The volcanic activity in the region in the period between 6280 and 2000 years ago is characterized by a relative rest. Later, eruptions resumed reaching peak values 1150 years ago and completing 800 years ago.

Ina, Moon: Geologic setting, scientific rationale, and site characterization for a small planetary lander concept

The Ina Irregular Mare Patch (IMP) in the central lunar nearside (18.7°N, 5.3°E) is a small, two-by-three-kilometer exposure of uncommon volcanic deposits. The unusually well-preserved deposits occurring at Ina suggest that they were recently emplaced and that the Moon experienced small-scale, ongoing volcanic eruptions during the last 100 million years. The existence of young volcanism on the Moon, if confirmed, would indeed challenge our current notions of how the Moon is structured and how it evolved, an interpretation still vigorously debated. Because of the possibility for unique volcanic materials, Ina is a high-priority destination for future study, and determination of relatively recent volcanism at Ina and the other IMPs requires ground-truth. We assessed the geologic setting, scientific rationale, and several potential landing sites at Ina. We also developed a SmallSat-class lander design and mission architecture, along with a corresponding science payload, to address the top science objectives at Ina. We named the mission concept IMPEL (Irregular Mare Patch Exploration Lander). The primary objective of the IMPEL mission is to determine the presence and abundance of any sub-meter-scale fractures or pits in Ina's deposits that would inform their origins and age. Secondary objectives include characterizing Ina's composition and physical properties. The spacecraft configuration (named the Dual ESPA Module Planetary Lander, DEMPL) that we developed in this study employs two ESPA (Evolved Expendable Launch Vehicle, EELV, Secondary Payload Adapter) modules integrated with flexible tethers and bands. One of the modules is used to decelerate the spacecraft from direct lunar insertion and the other functions both as additional propulsion and as a detached lander containing most of the spacecraft subsystems and the science payload. Our novel spacecraft configuration provides a new mechanism for surface exploration in deep space using small-scale planetary landers. The lander is an adaptable platform that can deliver up to 9 kg of science payload to the lunar surface. This approach is very capable for deep space exploration at the small spacecraft scale, and it has the potential to provide access to the lunar surface using a low-cost, low-mass, affordable, simplified configuration. The Ina IMP is one of many possible destinations.

Geochemistry of hot-springs at the SuSu Knolls hydrothermal field, Eastern Manus Basin: Advanced argillic alteration and vent fluid acidity

Abstract SuSu Knolls is an area of ongoing magmatic activity and recent volcanism located in the back-arc spreading environment of the Manus Basin in the Bismarck Sea, Papua New Guinea. In 2006, hydrothermal fluids were collected from three areas of submarine hot-spring venting and analyzed for the chemical and isotopic composition of major and trace species. Fluids were characterized by temperatures that varied from 226–325 °C, and formed grey to black smoke as they mixed with bottom seawater. The compositions of seawater derived vent fluids are regulated by the relative contributions of fluid-rock and fluid-sediment interaction, phase separation, and the addition of volatiles from magmatic degassing. In addition to phase separation, leaching of Cl from felsic rocks that compose the lithosphere in back-arc environments may produce Cl concentrations in excess of seawater values. The measured pH25°C of SuSu Knolls smoker fluids varied from 1.5–3.7, a range that includes values substantially more acidic than typically observed in fluids at mid-ocean ridge spreading centers. Late stage addition of magmatic volatiles in the shallow seafloor is directly responsible for the most acidic fluids (pH25°C values below 2). In contrast, the acidity of vent fluids characterized by pH25°C values between 2 and 3 is not the direct result of the direct addition of magmatically-derived acidic species. Instead, the pH of these fluids likely reflects reaction with rocks that were previously altered by highly acidic magmatic fluids to an advanced argillic alteration assemblage containing quartz-illite-pyrophyllite-anhydrite ± alunite in hydrothermal upflow zones. Fluids that do not react with advanced argillic alteration assemblages during upflow have measured pH25°C values between 3 and 4.

Heterogeneous upper mantle structure beneath the Ross Sea Embayment and Marie Byrd Land, West Antarctica, revealed by P-wave tomography

We present an upper mantle P-wave velocity model for the Ross Sea Embayment (RSE) region of West Antarctica, constructed by inverting relative P-wave travel-times from 1881 teleseismic earthquakes recorded by two temporary broadband seismograph deployments on the Ross Ice Shelf, as well as by regional ice- and rock-sited seismic stations surrounding the RSE. Faster upper mantle P-wave velocities (∼+1%) characterize the eastern part of the RSE, indicating that the lithosphere in this part of the RSE may not have been reheated by mid-to-late Cenozoic rifting that affected other parts of the Late Cretaceous West Antarctic Rift System. Slower upper mantle velocities (∼−1%) characterize the western part of the RSE over a ∼500 km-wide region, extending from the central RSE to the Transantarctic Mountains (TAM). Within this region, the model shows two areas of even slower velocities (∼−1.5%) centered beneath Mt. Erebus and Mt. Melbourne along the TAM front. We attribute the broader region of slow velocities mainly to reheating of the lithospheric mantle by Paleogene rifting, while the slower velocities beneath the areas of recent volcanism may reflect a Neogene-present phase of rifting and/or plume activity associated with the formation of the Terror Rift. Beneath the Ford Ranges and King Edward VII Peninsula in western Marie Byrd Land, the P-wave model shows lateral variability in upper mantle velocities of ±0.5% over distances of a few hundred km. The heterogeneity in upper mantle velocities imaged beneath the RSE and western Marie Byrd Land, assuming no significant variation in mantle composition, indicates variations in upper mantle temperatures of at least 100°C. These temperature variations could lead to differences in surface heat flow of ∼±10 mW/m2 and mantle viscosity of 102 Pas regionally across the study area, possibly influencing the stability of the West Antarctic Ice Sheet by affecting basal ice conditions and glacial isostatic adjustment.

Settlement and Subsistence in the Remote Western Pacific: Archaeological and Radiocarbon Data from Alamagan, Northern Mariana Islands

ABSTRACTSmall, remote islands were marginal environments for prehistoric human populations. We report archaeological and radiocarbon data from Alamagan, a small and isolated island in the northern part of the Mariana Islands archipelago. Challenging environmental conditions, including rugged terrain, active or recent volcanism, and uncertain freshwater availability posed significant challenges for permanent settlement throughout the Northern Islands. The Alamagan archaeological investigations documented 14 megalithic domestic structures, or latte sets, as well as isolated and non-portable Latte Period artifacts, and one historical site. Test excavations were undertaken at two of the latte features. These investigations add to a growing body of data suggesting colonization of the Northern Islands during the middle part of the Latte Period (probably during the late a.d. 1200s or early 1300s). We consider the implications of these data for the study of human adaptations to marginal insular environments in the Pacific.