Basaltic Volcanic Fields Research Papers (original) (raw)

The geologic history of the Great Escarpment, which includes within it the Drakensberg escarpment, closely follows cycles of tectonic evolution and land surface denudation from the Jurassic to Miocene that affected the entire southern... more

The geologic history of the Great Escarpment, which includes within it the Drakensberg escarpment, closely follows cycles of tectonic evolution and land surface denudation from the Jurassic to Miocene that affected the entire southern African region. Along the Drakensberg escarpment, which includes some of the highest mountain summits in southern Africa, the presence of flat-lying Jurassic basalts has strongly influenced processes and patterns of subsequent weathering, erosion and mass movement, in particular during cooler climate periods of the Quaternary. Distinctive weathering, periglacial and glacial, mass movement and fluvial phenomena have resulted from this interplay between geology, climate and geomorphological processes over the Quaternary and Holocene. The Drakensberg escarpment region also shows a close interconnection between landscape geomorphology, biodiversity and patterns of human cultural occupation during the Holocene. For these reasons, conservation of geomorphological, ecological and cultural sites in the Drakensberg escarpment, and their sustainable management under conditions of climate change, is an important contemporary issue.

An ephemeral (and proximal) outcrop at the quaternary basaltic Puig de la Garrinada cinder volcano was studied in order to decipher eruptive mechanism variations in the course of a single eruption. Once the volcanostratigraphy was... more

An ephemeral (and proximal) outcrop at the quaternary basaltic Puig de la Garrinada cinder volcano was
studied in order to decipher eruptive mechanism variations in the course of a single eruption. Once the
volcanostratigraphy was established (and recorded by photographs), a very detailed sampling of underlying
lava flows, bombs and a large number of fine-sized lapilli and ash beds was carried out. An ad hoc description
card was elaborated for study under stereo microscope in order to identify the different types of materials
that form the volcanic cone. Ten material types were recognised: sedimentary accidental clasts, massive lava
accidental clasts, bombs, xenoliths, xenocrysts and phenocrysts, oxidised scoria, scoria with oxidised film,
fluidal pyroclasts, non-fluidal pyroclasts, and coatings. Subsequent studies under SEM+EDS and basic
chemical characterization of the samples (whole rock XRF for major and trace elements) and EMPA were
conducted. All these studies make possible the reconstruction of the eruptive history of the La Garrinada
volcano, which shows a transition from initial strombolian activity to gradually incorporated phreatomagmatic
activity. This permits the calculation of magma eruption rates, magma column oscillations and aquifer
interactions with magma column. Since our general conclusions agree well with the discrimination of
eruptive episodes obtained from the stereo microscope description card, macroscopic volcanostratigraphy
and chemical results, it is proposed that a similar study protocol (quick volcanostratigraphy logging,
photographic record, detailed sampling, description following this card) might be useful in the
reconstruction of eruptive activity of other cinder cones in the Garrotxa region and elsewhere, and therefore
can provide a good and quick methodological tool, especially when rapid field description and sampling is
required (ephemeral outcrops, risky sampling during active eruptive episodes, etc.). Moreover, the conducted
sampling allows for subsequent studies on the same set of pyroclasts.

The Jorullo monogenetic volcano erupted 250 years ago at the southern border of the Trans-Mexican Volcanic Belt (TMVB), an area that records a long history of magmatic and tectonic activity. The oldest rocks that crop out in the area are... more

The Jorullo monogenetic volcano erupted 250 years ago at the southern border of the Trans-Mexican Volcanic Belt (TMVB), an area that records a long history of magmatic and tectonic activity. The oldest rocks that crop out in the area are early-Oligocene (32.7 ± 0.2 Ma) dioritic to granitic (60–72 wt. % SiO2) plutons intruded by younger to contemporaneous (30.3 ± 0.1 and 33.3 ± 0.7 Ma) aplitic (76–78 wt. % SiO2) dikes and mineralized veins. Volcanic rocks related to these intrusives form a thick sequence exposed in cliffs, from the base of which an altered andesite (58 wt. % SiO2) was collected. The nearby epithermal Cu-mineralization of the Inguarán mining area to the southeast is also related to this Tertiary volcanic episode. The oldest expression of the TMVB in this area is represented by Pliocene (3.2–2.4 Ma) basaltic andesite to andesite (53–63 wt. % SiO2) lavas (with pyroxene ± olivine) forming extensive mesas, eroded mounds, and thick elongate flows, that were unconformably deposited on top of the Oligocene rocks. Their emplacement was followed by erosion approximating a rate of 100 m/Ma over the past 3 Ma. This led to the formation of an inverted topography reflecting the higher resistance to erosion of these lavas that were originally deposited in valleys and today constitute prominent mesas. During the last 1 Ma, at least twenty-six monogenetic scoria cones formed in the study area, erupting about 10.2 km3 of lava and pyroclastics dominantly composed of olivine and pyroxene-bearing andesites (61 vol. % DRE), lesser basaltic andesites (30 vol. % DRE), and a minority of olivine-rich basalts (10 vol. % DRE). These eruptive products include the K-rich basaltic trachyandesites of Cerro La Pilita, a scoria and lava cone located close to Jorullo. The ≤ 27 ka San Hilario and Esmeralda lavas, which are located 13 km southeast of Jorullo, are the southernmost eruptive products of the TMVB and also the youngest volcanoes after Jorullo in this area. Mapping of main faults and scoria cone alignments on regional and local scales reveals that the ascent of dikes feeding Quaternary eruptions in the Jorullo area was controlled by west-northwest and west-southwest basement structures, northeast-oriented subduction-related horizontal compressional stress probably associated with crustal fractures, and a major northwest-trending seismically-active fault zone that passes near Paricutin and Jorullo.

Pacific and Rapa Nui (Easter Island) volcanologists, geologists, and geochemists have set the stage for archaeological lithic sourcing studies by providing practical data regarding the island's geodynamic activity, geomorphological... more

Pacific and Rapa Nui (Easter Island) volcanologists, geologists, and geochemists have set the stage for archaeological lithic sourcing studies by providing practical data regarding the island's geodynamic activity, geomorphological formation and dating, and the macroscopic, microscopic, and elemental proprieties of Easter Island stone. Drawing upon this information, and the research collaboration between two active archaeological projects on Rapa Nui – the Easter Island Statue Project and the Rapa Nui Geochemical Project – we trace the prehistoric transfer of basalt resources from the Ava o'Kiri and Pu Tokitoki quarry complexes to the moai (statue) quarry at Rano Raraku between AD 1455–1645. Our conclusions better highlight socio-political and economic interaction during Rapa Nui prehistory, while delineating the relationship between adze and pick production and moai manufacture. In this article, we report: 1) a synthesis of a five-meter deep field excavation of moai rr-001-156 in Rano Raraku; 2) a 14C assessment which dates human presence around moai rr-001-156; 3) 31 basalt quarry and source site descriptions; and 4) archaeometric data using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and principal component analyses of 21 archaeological and 117 geological samples.

Monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent. Understanding similarities and differences between these fields may help to characterize key controls on their... more

Monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent. Understanding similarities and differences between these fields may help to characterize key controls on their generation. Such volcanic fields consist of numerous volcanic centers, each of which represents a pathway of magma from its source to the surface. We analyzed the spatial distribution of volcanic centers in 37 monogenetic volcanic fields, and assuming that the distribution of volcanic centers relative to each other is matched by a similar source pattern within the mantle, applied the following methods for each: (1) the Poisson Nearest Neighbor (PNN) analysis, representing the degree to which the distribution of the volcanic centers departs from a predicted Poisson distribution, and (2) a volcanic alignment analysis to ascertain the preferential pathways, if any, used by the magma to reach the surface. This is the first comprehensive global comparison of such analyses. Magma pathways within the brittle upper crust are influenced to various degrees by two end-member situations: (1) formation of new extension fractures perpendicular to the least compressive stress (σ3) and (2) re-activation of pre-existing fractures that are near-parallel to the maximum principal stress (σ1). The results of the PNN analysis show that, independently of the tectonic environment, most volcanic fields display a clustered distribution of their volcanic centers. Alignment analysis shows that either the ambient tectonic environment exerts a strong influence on the preferential orientations of the volcanic alignments, or that it is in competition with other factors (e.g., pre-existing structures, local stress changes due to older intrusions). Overall, these results indicate that the propagation of the magma (and therefore the spatial distribution of the volcanic centers within volcanic fields) is the product of an interplay between deep level influences (i.e., nature of the magma source) and shallow level influences (i.e., stress field, pre-existing crustal structures) of the lithosphere.

Late Miocene to Quaternary intraplate basaltic volcanism in the Al Ghab and Homs regions, northwestern Syria (the Al Ghab volcanic group and the Homs volcanic group), occurred roughly synchronously with the propagation of the Dead Sea... more

Late Miocene to Quaternary intraplate basaltic volcanism in the Al Ghab and Homs regions, northwestern Syria (the Al Ghab volcanic group and the Homs volcanic group), occurred roughly synchronously with the propagation of the Dead Sea Fault System in these regions. Petrographic evidence as well as major and trace element variations suggest that the basalts have undergone varying amounts of crystal fractionation of olivine ± clinopyroxene ± spinel, with feldspar fractionation only in the most evolved samples. The major and trace element chemistry and Nd–Sr–Pb isotopic variations of the basalts reflect both mantle source heterogeneity and relatively minor crustal contamination. Semi-quantitative assimilation–fractional crystallization modelling suggests that some samples may reflect assimilation of no more than 6% of upper continental crust, probably with Late Proterozoic Arabian Shield characteristics. Amongst the least crustally contaminated and relatively primitive samples, basanites are characterized by marked depletion of K, Rb and Zr relative to other neighbouring incompatible elements on primitive mantle normalized trace element diagrams. This, together with their low SiO2 and high TiO2 and Dy/Yb, is consistent with magma genesis involving a large proportion of garnet-bearing hornblendite or similar amphibole-rich metasomatic veins. Associated alkali and tholeiitic basalts with the higher SiO2, lower TiO2, less negative K, Rb and Zr anomalies, and moderately high Dy/Yb are consistent with melt extraction from a largely peridotitic mantle source. It is suggested that the compositional spectrum from basanite via alkali basalt to tholeiitic basalt can be explained by increasing degrees of metasomatic vein–wall-rock interaction, plus asthenospheric melt assimilation. In agreement with this is the identification of three distinct isotopic and chemical characteristics within the spectrum of mafic lavas, each of which can be referred to a unique mantle source (metasomatic vein, lithospheric wall-rock peridotite mantle and asthenospheric peridotite mantle). A decrease in eruption volume and increase in Si-undersaturation of the lavas from south (Homs) to north (Al Ghab) along the northern Dead Sea Fault System from latest Miocene to Quaternary times suggest a diminishing thermal perturbation and increasing importance of the amphibole-rich veins in magma genesis over time. It is proposed that the genesis of the oldest lavas reflects the arrival of asthenospheric melts beneath the Homs region, which with assimilation of lithospheric metasomatic veins and their wall-rocks produced the parental magmas of the Homs volcanic group. Subsequently, upwelling asthenospheric material could have been channelled northwards at the base of the lithosphere, presumably related to the northward propagation of the Dead Sea Fault System in the Pliocene. Cooling of this channelled asthenospheric material, which did not penetrate the lithosphere during this later period of magma genesis, provided the minimal thermal perturbation necessary for melting of amphibole-rich metasomatic veins and wall-rock peridotite within the lithosphere.

Rapa Nui (Easter Island) has been the subject of countless scientific investigations. Much of this work, however, has been dedicated to moai (statues) and ahu (platforms) and how these famous megalithic features venerated the island’s... more

Rapa Nui (Easter Island) has been the subject of countless scientific investigations. Much of this work, however, has been dedicated to moai (statues) and ahu (platforms) and how these famous megalithic features venerated the island’s deceased ancestors and facilitated sociopolitical organization, ideological transmission, economic redistribution, and elite management. Although moai and ahu have been under the research gaze of many international, Chilean, and local academics, archaeological investigation of the island’s many basalt sources and artifacts, including their geological provenance and geochemistry, is practically invisible. Consequently, this lack of comprehensive geochemistry for basalt sources and artifacts has restricted the potential of prehistoric interaction studies on Rapa Nui. To fill this gap in the archaeological literature, the “Rapa Nui Geochemical Project (RNGP)” was established in 2013. Its main goals are: 1) to further recognise the ancient Rapanui as expert geological miners who developed multiple basalt artifact reduction sequences; 2) to identify patterns of prehistoric sociopolitical and economic interaction through the transfer of basaltic material; and 3) to empirically assess cultural interpretations put forward by the socioecological collapse narrative which speculates that Easter Island’s prehistoric inhabitants knowingly participated in unsustainable cultural competition and megalithic development, leading to the island’s reported ecocide and cultural downfall. As such, the RNGP collaborated with more than 20 individuals from 13 institutions from around the globe to conduct field archaeology and geology (four campaigns from 2014–2017), geoarchaeological and material culture documentation (SLR camera and drone photos/videos and artifactual 3D scanning), geochemical analyses including inductively coupled plasma–mass spectrometry (ICP–MS) to detect major and minor elements and isotopic data, and radiometric dating (14C). Final results from this five–year project are discussed for the first time in this presentation.

South African basalt-hosted chalcedonies provided an ideal case study, to (a) achieve information about the origin of mineral-forming fluids, the process of chalcedony formation and weathering alteration and (b) to verify if the... more

South African basalt-hosted chalcedonies provided an ideal case study, to (a) achieve information about the origin of mineral-forming fluids, the process of chalcedony formation and weathering alteration and (b) to verify if the geochemical and micro-textural characterization of chalcedony allowed multiple provenances to be distinguished. For the first time, Drakensberg chalcedonies from the Karoo Jurassic basalts and Windsorton chalcedonies from the alluvial environment of the Vaal River (traversing the Allanridge basaltic-andesitic lavas) were investigated by optical microscopy, laser ablation inductively coupled plasma mass spectroscopy and isotope ratio mass spectrometry (16 O, 18 O). The results showed that the compositional differences observed in Drakensberg and Windsorton chalcedonies could not be explained by changes in host rocks composition. The tholeiitic basaltic-andesitic lavas of the Allanridge Formation (Pniel Group, comparison term for Windsorton samples) and the tholeiitic basaltic-andesitic lavas of the Golden Gate Unit (Drakensberg Group, comparison term for Drakensberg specimens) proved to be very similar, also in terms of alteration degree. Conversely, both geochemical and oxygen isotope compositions clearly supported a relatively low temperature, hydrothermal origin for all the investigated chalcedonies, further indicating that differences mostly occurred during their formation (fluid circulation). Moreover, several characteristics suggested deposition in non-equilibrium conditions, although oxidizing conditions were most likely. Weathering processes were effective in the alluvial environment only, leading to a wider compositional heterogeneity of Windsorton chalcedonies with respect to Drakensberg samples. Lastly, a correlation between color and chromophores (Fe and Mn) amounts was lacking while a correlation between the geochemical composition and the texture was clearly observed in several specimens.

Preceded by 14 days of intense seismic activity, a new eruption started on the south flank of Mt. Etna, Sicily (Italy) early in the morning of 11 March 1669 opening up a series of NS eruptive fissures. The eruption is one of the most... more

Preceded by 14 days of intense seismic activity, a new eruption started on the south flank of Mt. Etna, Sicily (Italy) early in the morning of 11 March 1669 opening up a series of NS eruptive fissures. The eruption is one of the most destructive flank eruptions of Etna in historical times; it lasted until 11 July, and was characterized by simultaneous explosive and effusive activity during the first three months, while only lava flow output in the last month. The activity built up the large composite cone of the " Monti Rossi " at the lower end of the eruptive fissures, and caused severe damage to the nearby inhabited areas. The prolonged effusive activity generated lava flows for > 15 km, which destroyed several villages and the western part of the town of Catania before reaching the coastline and entering the sea. In this paper, we examine the tephro-stratigraphy of the products of the explosive activity. An in-depth analysis of historical accounts was used to define the chronology of the main eruptive phases (precursors, explosive activity and initial effusive phenomena). The geology of the cone and of the fallout deposits were defined through a field survey over a distance of 5 km from the Monti Rossi. Textural (grain-size, morphological, componentry), density and petrological analyses of tephra samples provided a sedimentological, physical and geochemical characterization of erupted products. Integrating ground and historical data enabled defining the evolution of the cone, identifying and correlating four main cone-forming units. By tracing the dispersal map of the main distal tephra beds (the finer ash being dispersed mainly to the NE as far as Calabria and to the south of Sicily and the 10-cm isopach of the total deposit covering an area up to 53 km 2), we estimated a total tephra fallout volume, including the Monti Rossi cone, of about 6.6 × 10 7 m 3 (about 3.2 × 10 7 m 3 DRE). The 1669 event can be considered an archetype of the most hazardous expected eruption on the densely populated flanks of Etna. Reconstructing the eruptive chronology and styles of the 1669 eruption therefore, represents the basic data to assess volcanic hazard from eventual similar flank events in the future.

The geological position and geochemistry of the basaltic sill and tuffs occurring within the Berriasian–?Albian pelagic limestones of the Czorsztyn Succession are described. The volcanic rock succession of the Velykyi (= Veliky)... more

The geological position and geochemistry of the basaltic sill and tuffs occurring within the Berriasian–?Albian pelagic limestones of the Czorsztyn Succession are described. The volcanic rock succession of the Velykyi (= Veliky) Kamenets’/Vilkhivchyk (= Vulkhovchik, Vulhovchik, Olkhivchyk) sites is related to intra-plate submarine volcanism, which took place at the southeastern termination of the Pieniny Klippen Belt. This volcanism was probably associated with the Early Cretaceous opening of the Magura/Fore-Magura basinal system, bounded by the Silesian/Marmarosh and Czorsztyn palaeoridges to the north and south respectively. The alkaline volcanic rocks from the Velykyi Kamenets’/Vilkhivchyk sites are geochemically similary to the basaltic block from Biała Woda (Małe Pieniny Mts., Poland), which is an olistolith a few metres across within the Jarmuta conglomerates (Maastrichtian/Paleocene). This basaltic block was eroded from the frontal part of the Czorsztyn Nappe and was deposited in the uppermost part of the Grajcarek Succession at the southeastern margin of the Magura Basin.

source. The results indicate that the spatial-compositional variation of the ENA basaltic rocks is likely related to differing amounts of melting of mantle sources that reflect the uniqueness of their regional accreted terranes (Carolinia... more

source. The results indicate that the spatial-compositional variation of the ENA basaltic rocks is likely related to differing amounts of melting of mantle sources that reflect the uniqueness of their regional accreted terranes (Carolinia and West Avalonia) and their post-accretion, pre-rift structural histories.

The basaltic Al-Du’aythah volcanic cones lie in the northern part of the extensive lava field of Harrat Rahat, and only 13 km from the centre of Al-Madinah City, in the Kingdom of Saudi Arabia. Historical records indicate they may have... more

The basaltic Al-Du’aythah volcanic cones lie in the
northern part of the extensive lava field of Harrat Rahat, and
only 13 km from the centre of Al-Madinah City, in the Kingdom
of Saudi Arabia. Historical records indicate they may
have erupted in AD 641. The four cones are formed by deposits
that record a transition from phreatomagmatic to magmatic
explosions followed by minor lava effusion. Three
cones display elongated tuff rings at the base, and two produced
late-stage lava flows. The cones themselves are symmetrical
and constructed mostly by the accumulation of ballistically
ejected pyroclasts. Spherical bombs and lapilli (cannonball
bombs/lapilli), occasionally with country-rock fragments
inside (both cored and loaded bombs/lapilli) are common
within the tuff ring deposits. LiDAR data show a total
volume of 1,664×10−6 km3 for the four cones (418×10−6 km3
DRE). Whole-rock chemical analyses indicate alkali-basalt
compositions (SiO2 44.7–45.9 wt%), with little compositional
variation and no relationship between chemistry and eruptive
styles. Small differences in composition may reflect variations
in fractional crystallisation of clinopyroxene and olivine. A
magnetotelluric 2D cross-section shows that the cones are
located adjacent to a buried sediment-filled alluvial channel
along a NNW-SSE fault dipping to the east. The Al-
Du’aythah eruption was related to the ascent of magma
through this structure, with the first phase of the eruption
triggered by the interaction of the magma with water from
the northern Harrat Rahat aquifer that exists in the Al-
Madinah basin. This initial water source was rapidly
exhausted, while the eruption progressed roughly from north
to south and from west to east, the latter motion probably
along the fault-controlled feeding dyke. Our work draws attention
to the existence of recent explosive phreatomagmatic
eruptions in the Al-Madinah basin, which, despite the hyperarid
climate of the area, must be considered a potential future
eruption hazard.

From May – September 2014 and from January – February 2015, I conducted archaeological and geological fieldwork on Rapa Nui for my doctorate at the University of Queensland (UQ). These six months were the most challenging and rewarding of... more

From May – September 2014 and from January – February 2015, I conducted archaeological and geological fieldwork on Rapa Nui for my doctorate at the University of Queensland (UQ). These six months were the most challenging and rewarding of my career, as I had to navigate the social politics on the island to be granted authorization to conduct scientific research and to remove geological and archaeological samples off the island
for technological and geochemical analyses. In this report, I: 1) review the process to attain research permits on Rapa Nui; 2) highlight six months of living and doing scientific investigation on Rapa Nui; and 3) describe the components of my Ph.D.

The wadi-fill basalt of Harrat El Fahda was derived from the youngest volcanic activity in northeast Jordan and forms one of the most recent harrats of the Arabia plate. It is characterized by the presence of abundant well-preserved... more

The wadi-fill basalt of Harrat El Fahda was derived from the youngest volcanic activity in northeast Jordan and forms one of the most recent harrats of the Arabia plate. It is characterized by the presence of abundant well-preserved pressure ridges and pahoehoe lava structures. It was developed due to intermittent eruption from an isolated volcanic center in a form of 3–5 successive basaltic pahoehoe flows. The associated pressure ridges are elliptical in shape, up to 50 m high and 200 m long. The orientation with regard to flow direction is sub-parallel along the margins and perpendicular along the center of the flow. These ridges were formed by inflation and heaving pressure from below. Petrographical data show that the basalt is hollocrystalline, fine-grained and golmeroporphyritic. Modally, three petro-types are recognized, olivine-plagioclase basalt (20%), olivine-pyroxene basalt (25%) and olivine basalt (55%). Geochemically, the three petro-types can be classified as alkaline to sub-alkaline and termed as alkali olivine basalt. They have similar compositional ranges of major and trace elements. The magmas may have been derived from low degrees (i.e. 5–9%) of partial melting, of an enriched garnet peridotite mantle source with limited fractionation and crustal contamination.

Magma transport through dikes is a major component of the development of monogenetic volcanic fields. These volcanic fields are characterized by numerous volcanic centers, each typically resulting from a single eruption. Therefore, magma... more

Magma transport through dikes is a major component of the development of monogenetic volcanic fields. These volcanic fields are characterized by numerous volcanic centers, each typically resulting from a single eruption. Therefore, magma must be transported from source to surface at different places, which raises the question of the relative importance of (1) the self-propagation of magma through pristine rock and (2) the control exerted by pre-existing fractures. To address this issue, we have carried out a series of analogue experiments to constrain the interaction of a propagating dike through a medium with pre-existing fractures. The experiments involved the injection of air into an elastic gelatin solid, which was previously cut into its upper part to simulate pre-existing fractures. The volume of the dikes, their distance from the fractures, and the ambient stress field were systematically varied to assess their influence on potential dike-fracture interactions. The results show that distance and angle between dikes and fractures influence these interactions and the dike trajectory. Dike geometry and dynamics are also affected by both the presence of the fractures and the dike volume; dikes propagating in between fractures tend to decelerate. In nature, interactions are expected for dikes and fractures separated by less than about 200 m, and dikes with a volume less than about 10−2 km3 would experience a velocity decrease. These results highlight the influence of pre-existing fractures on the mechanics and dynamics of dikes. These heterogeneities must be considered when studying the transport of magmas within the crust.

Petrologic monitoring of Kīlauea Volcano from January 1983 to October 2013 has yielded an extensive record of glass, phenocryst, melt inclusion, and bulk‐lava chemistry from well‐quenched lava. When correlated with 30+ years of... more

Petrologic monitoring of Kīlauea Volcano from January 1983 to October 2013 has yielded an extensive record of glass, phenocryst, melt inclusion, and bulk‐lava chemistry from well‐quenched lava. When correlated with 30+ years of geophysical and geologic monitoring, petrologic details testify to physical maturation of summit‐ to‐rift magma plumbing associated with sporadic intrusion and prolonged magmatic overpressurization. Changes through time in bulk‐lava major‐ and trace‐element compositions, along with glass thermometry, record shifts in the dynamic balance of fractionation, mixing, and assimilation processes inherent to magma storage and transport during near‐continuous recharge and eruption. Phenocryst composition, morphology, and texture, along with the sulfur content of melt inclusions, constrain coupled changes in eruption behavior and geochemistry to processes occurring in the shallow magmatic system. For the first 17 years of eruption, magma was steadily tapped from a summit reservoir at 1–4 km depth and circulating between 1180 and 1200°C. Furthermore, magma cooled another 30°C while flowing through the 18 km long rift conduit, before erupting olivine‐spinel‐phyric lava at temperatures of 1150–1170°C in a pattern linked with edifice deformation, vent formation, eruptive vigor, and presumably the flux of magma into and out of the summit reservoir. During 2000–2001, a fundamental change in steady state eruption petrology to that of relatively low‐temperature, low‐MgO, olivine(‐spinel)‐clinopyroxene‐plagioclase‐phryic lava points to a physical transformation of the shallow volcano plumbing uprift of the vent. Preeruptive comagmatic mixing between hotter and cooler magma is documented by resorption, overgrowth, and compositional zonation in a mixed population of phenocrysts grown at higher and lower temperatures. Large variations of sulfur (50 to >1000 ppm) in melt inclusions within individual phenocrysts and among phenocrysts in most samples provide an unequivocal glimpse of rapid crystal growth amid sulfur degassing at <30 MPa in a turbulent preeruptive environment. We speculate that, during the last decade, one or more shallow open‐system reservoirs developed along the conduit between the summit and Pu'u 'Ō'ō and now serve to buffer the magmatic throughput associated with ongoing recharge and eruption. Lava with identical trace‐element signatures erupted simultaneously at the summit and at Pu'u 'Ō'ō from 2008 to 2013 confirms magmatic continuity between the vents. Complementary changes in compositions of matrix glasses, phenocrysts, and melt inclusions of summit tephra are mirrored by similar changes in contempo-raneous rift lava at eruption temperatures 20–35°C lower than those at the summit. Petrologic parameters measured at opposite ends of the shallow magmatic plumbing system are both correlated with summit deformation, demonstrating that effects of summit magma chamber pressurization are translated throughout interconnected magma pathways in the shallow edifice.

Recent developments in the availability of very high-resolution satellite imagery through platforms like GoogleEarth (Google, Santa Clara County, CA, USA) and Bing Maps (Microsoft, Redmond, WA, USA) have greatly opened up the... more

Recent developments in the availability of very high-resolution satellite imagery through platforms like GoogleEarth (Google, Santa Clara County, CA, USA) and Bing Maps (Microsoft, Redmond, WA, USA) have greatly opened up the possibilities of their use by researchers. This paper focusses on the exclusive use of free remote sensing data by the Western Harra Survey (WHS), an archaeological project investigating the arid "Black Desert" of northeastern Jordan, a largely impenetrable landscape densely strewn with basalt blocks. The systematic analysis of such data by conducting a holistic satellite survey prior to the commencement of fieldwork allowed for the precise planning of ground surveys, with advanced knowledge of which sites were vehicle-accessible and how to efficiently visit a stratified sample of different site types. By subsequently correlating the obtained ground data with this analysis, it was possible to create a typological seriation of the site forms known as "wheels", determine that at least two-thirds of sites are within 500 m of valleys or mudflats (highlighting these features' roles as access routes and resource clusters) and identify numerous anthropogenic paths cleared through the basalt for site access and long-distance travel. These results offer new insights into this underrepresented region and allow for supra-regional comparisons with better investigated areas by a method that is rapid and cost-effective.

Monogenetic volcanic fields (MVFs) comprise numerous volcanic centers, distributed across large areas. Understanding the relative importance of various tectonic and magmatic controls on field evolution is pivotal to hazard analyses, and... more

Monogenetic volcanic fields (MVFs) comprise numerous volcanic centers, distributed across large areas. Understanding the relative importance of various tectonic and magmatic controls on field evolution is pivotal to hazard analyses, and is of particular importance in New Zealand, where the highest population density resides on the active Auckland Volcanic Field (AVF). This thesis provides insights into this problem through studies at different scales (from multiple volcanic fields, to a single volcanic field, to propagation of a single dike) and different dimensions (from 2D surficial spatial analysis to 4D spatio-temporal analysis of the chemical composition of erupted products). Tectonic control or the influence of pre-existing faults is often invoked to explain alignments and statistical distributions of volcanic centers in MVFs; however, a global comparison has been lacking. I present a new global analysis of the spatial distribution of volcanic centers within 37 MVFs, and show: 1) a common clustered distribution of volcanic centers, 2) independency of clustering on tectonic environment, 3) dependency of volcanic field shape on tectonic environment, and 4) influence of tectonic environment on the number of preferred orientations of volcanic alignments. Controls on volcanic alignments are explored using analogue models to evaluate the impact of pre-existing faults on dike propagation. These reveal that lateral distance between fault(s) and dikes, and angle of approach, have the greatest control on the tendency of a dike to modify its trajectory to intercept pre-existing faults, thus modifying the distribution of volcanic centers. Pre-existing faults also affect dike geometry and velocity, as did dike volume. The AVF is an outlier in the global comparison, having an apparently random distribution. Taking advantage of newly available geochemical data and geochronological models, I present a new methodology that combines time, location and chemistry of each eruption, to evaluate the evolution of this MVF. The method looks for the spatio-temporal evolution of volcanic centers using the nearest neighbour analysis and statistical correlations between chemical composition of erupted products and time, distance and volume between successive eruptions. In spite of data limitations, the nearest neighbour analysis reveals that the magma source shows a constant spatial behaviour through time and the statistical correlations show that the spatial distribution of volcanic centers, i.e. the release of magma, is controlled by the behaviour of the source. As well as offering insight to the deep workings of the AVF, this method offers considerable potential to understand the behaviour of monogenetic basaltic volcanism elsewhere.

We provide detailed observations on the shape of dikes from well-exposed field locations in the Isle of Rum, Scotland, and Helam Mine, South Africa. The basaltic Rum dikes crop out on a smaller scale than the Helam kimberlite dikes and... more

We provide detailed observations on the shape of dikes from well-exposed field locations in the Isle of Rum, Scotland, and Helam Mine, South Africa. The basaltic Rum dikes crop out on a smaller scale than the Helam kimberlite dikes and have a smaller length to thickness ratio (~100:1 Isle of Rum, ~1000:1 Helam Mine). We compare the dike thickness field measurements with the geometry predicted by elastic theory, finding best-fit models to estimate magma overpressure and regional stress gradients at the time of dike emplacement. Most of the dike shapes fit poorly with elastic theory, being too thick at the dike ends and too narrow in the middle. Even for dikes where the model fit is acceptable, the calculated overpressures and stress gradients are very large and much larger than independent estimates based on rock strength, particularly for the small-scale basaltic dikes on Rum, where calculated overpressures average 687 MPa, and calculated stress gradients average 622 MPa m–1. The Swartruggens dikes have calculated overpressures of between 4 and 40 MPa and calculated stress gradients in the range of 15–87 kPa m–1. Dike shape can be explained by a combination of host-rock inelastic deformation prior to and coeval with magma emplacement, and by magma chilling at the dike’s tapering edges, which prevented its closure as magma pressure declined during emplacement; this sequence provides the most complete explanation for the mismatches between the data and the model. The permanent wedging of the dike edges due to chilling has implications for crustal magma transport and strain response in the crust due to dike emplacement.

Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the... more

Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and
eruption. We use multiparameter geophysical and geochemical data to show that the 110-square kilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014–2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, nearexponential decline of both collapse rate and the intensity of the 180-day- long eruption.

RESUMO As águas das nascentes do Noroeste da ilha Terceira, localizadas nas freguesias dos Altares, Raminho e Serreta, foram analisadas de forma a se proceder á sua caracterização físico-química. Essa caracterização, permitiu identificar... more

RESUMO As águas das nascentes do Noroeste da ilha Terceira, localizadas nas freguesias dos Altares, Raminho e Serreta, foram analisadas de forma a se proceder á sua caracterização físico-química. Essa caracterização, permitiu identificar traçadores químicos que distinguem as nascentes por grupos: as dos Altares, as do Raminho e as da Serreta. As nascentes dos Altares, possuem elevados rácios molares bicarbonato/sílica quando comparados com as nascentes do Raminho e da Serreta. Tais rácios, crêem-se associados a mecanismos de lixiviação de feldspatos. As águas dos Altares apresentam os valores médios mais baixos de nitratos, cloretos, sulfatos, potássio e magnésio bem como os valores médios mais baixos de pH. No que se refere ao anidrido carbónico livre, é nessas águas que se observam os valores médios mais elevados. As águas das nascentes do Raminho, possuem rácios molares Cl-/SiO2 praticamente constantes, revelando-se essa razão um bom traçador das águas dessas nascentes, distinguindo-as relativamente às dos outros agrupamentos estudados. As águas do Raminho apresentam os valores médios mais elevados de cloretos, fluoretos, cálcio e magnésio e os valores médios mais baixos de bicarbonatos. É neste grupo de nascentes que a relação entre os vários parâmetros químicos mais se aproxima da relação verificada para a água do mar. As águas da Serreta, são aquelas que apresentam maiores valores médios de pH, temperatura, bicarbonatos, nitratos, sulfatos, sílica, potássio e sódio, bem como, os menores valores médios de anidrido carbónico livre e fluoretos. Esperava-se que, sendo as nascentes da Serreta aquelas que se encontram mais próximas do mar, fossem aquelas em que predominassem as semelhanças com a composição química média das águas do mar. Tal não se verificou, sendo o rácio molar Cl-/Na + o mais baixo dos três grupos de nascentes.

The El-Lajjoun basalt (hereafter, LB) is a Wadi-fill flow that covers an area of about 10 km2 in Central Jordan. The tectonic evaluation carried out through lineament and fracture analyses indicates that the regional development is... more

The El-Lajjoun basalt (hereafter, LB) is a Wadi-fill flow that covers an area of about 10 km2 in Central Jordan. The tectonic evaluation carried out through lineament and fracture analyses indicates that the regional development is tectonically related to the opening of the Red Sea, and the development of the Dead Sea transform fault and other distinct regional tectonic features. The age of the LB (middle Pleistocene) can be correlated with the second stage of the opening of the Red Sea over the last 5 Ma. Petrographic data shows that rocks are plagioclase, olivine, pyroxene, and magnetite-phyric basalts. They correspond to alkali olivine basalts and basanites. The LB rocks are very similar in composition, and have comparable ranges of major and trace element concentrations. They are of undersatured silica type and belong to sodic to mildly alkaline magma series. The distinctive geochemical characteristics of LB indicated that LB was derived from a slightly fractionated magma as reflected by its high MgO (7-8 wt%) concentration, the Mg-number (0.60-0.63), the low silica content (<43-46 wt%), and the relatively high Ni and Cr concentrations (193-271 ppm and 243-374 ppm, respectively). This basalt is resulted from a low degree of partial melting (10%) of a homogeneous garnet peridotite mantle source in the asthenosphere at a depth > 100 km.

The origin of bimodal (mafic–felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to... more

The origin of bimodal (mafic–felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose ‘progressively inhibited crustal assimilation’ (PICA) as a major cause of bimodality in continental volcanism.

In the Spratly Islands (Truong Sa Islands) and adjacent areas, volcanic activities are quite strong after the sea-floor spreading in the Cenozoic Era. However, it is difficult to define their ranges and spatial locations. Based on the... more

In the Spratly Islands (Truong Sa Islands) and adjacent areas, volcanic activities are quite strong after the sea-floor spreading in the Cenozoic Era. However, it is difficult to define their ranges and spatial locations. Based on the different characteristic between eruptive volcanic basalt and sedimentary rocks near the surface, it can be said that, the blocks which are higher density and magnetization than those surroundings could be identified as eruptive volcanic basalt. This paper presents the methods of reduction to the magnetic equator in low latitudes to bring out a better correlation between magnetic anomalies and their causing-sources; High-frequency filtering is to separate gravity and magnetic anomalies as well as information about the volcanic basalts in the upper part of the Earth's crust; 3D total gradient is to define the spatial location of high density and magnetic bodies. The potential structures of eruptive volcanic basalt are predictively determined by multi-dimensional correlation analysis between high-frequency gravity and magnetic anomalies with weighted total gradient 3D. The results from the above-mentioned methods have shown that the distribution of the eruptive volcanic basalt mainly concentrates along the Spratly Island's seafloor-spreading axis, transitional crust, Manila trench and some large fault zones. These results are improved by available seismic data in the study area. Keyword: Spratly Islands, Reduction to the equator, 3D total gradient, Eruptive volcanic basalt.

The source of intraplate basalts has long been a controversial topic, particularly in continental settings where ambiguity increases because both crustal contamination and crystal fractionation may mask important source characteristics.... more

The source of intraplate basalts has long been a controversial topic, particularly in continental settings where ambiguity increases because both crustal contamination and crystal fractionation may mask important source characteristics. We present geochemical data to constrain the source and the chemical evolution of the continental intraplate magmas from the Aleppo Plateau and vicinity, NW Syria. New 40Ar/39Ar ages, coupled with published 40Ar/39Ar and K–Ar ages, reveal two discrete Miocene volcanic phases, ~ 19–18 Ma (Phase 1) and ~ 13.5–12 Ma (Phase 2), in the studied area. New chemical and isotopic compositions [87Sr/86Sr = 0.7036–0.7051, εNd = + 4.5 to + 1.1 and (187Os/188Os)t = 0.151–0.453] of the lavas reflect the unequivocal influence of crustal assimilation and fractional crystallisation (AFC). Despite the effects of the AFC processes, there still appear to be some differences between the most-primitive, least contaminated magmas of the two volcanic phases, interpreted as a result of source heterogeneity. Whereas the Phase 1 lavas, with relatively high Si, low Ti and trace-element contents, are consistent with partial melting of a largely peridotitic mantle source, the origin of the Phase 2 lavas is more complicated. The latter are characterised by a source component depleted in Si and enriched in Ti, Fe, Ca, P, alkalis, light and middle rare earth elements (REEs) relative to heavy REEs and with sub-chondritic Th–(U)/Nb, Pb/Ce and Zr/Sm. They approach compositions of experimental melts of amphibole-rich metasomatic veins. The compositional variations among the most primitive Phase 2 lavas are difficult to reconcile with varying degrees of partial melting of either the metasomatic veins or peridotite, but could be explained if partial melts of both lithologies were variably mixed, a scenario that could be sensibly envisioned as ascending (peridotitic) plume/asthenosphere derived melts assimilating highly fusible metasomatic veins during their traverse through the lithosphere. This process can be loosely quantified by trace-element forward partial melting modelling that suggests mixing of up to 80% metasomatic melts derived from ~ 40% melting of amphibole-rich metasomatic veins (which themselves were inevitably compositionally and mineralogically heterogeneous) with 20% plume/asthenospheric melts derived from ~ 7% melting of a garnet peridotite. Within the compressional framework of northern Arabia, invocation of diapiric material reasonably accounts for the generation of the intraplate basalts in Syria. Derivation of the Phase 2 hybrid melts was probably triggered by lateral flow of this diapiric material beneath the lithosphere subsequent to its arrival, with the migrating flow-front controlling the locus of volcanism. The increase in degree of Si-undersaturation with time for the Phase 1 and Phase 2 lavas is best explained by decreasing temperatures of this flow-front that resulted in less melt contribution from the diapiric mantle while the amphibole-rich veins within the lithosphere continued to be easily fusible, although we cannot totally exclude the possibility that the Phase 2 volcanism tapped a vein-richer domain which formed subsequent to the Phase 1 volcanism

The 2002–03 Mt Etna flank eruption began on 26 October 2002 and finished on 28 January 2003, after three months of continuous explosive activity and discontinuous lava flow output. The eruption involved the opening of eruptive fissures on... more

The 2002–03 Mt Etna flank eruption began on 26 October 2002 and finished on 28 January 2003, after three months of continuous explosive activity and discontinuous lava flow output. The eruption involved the opening of eruptive fissures on the NE and S flanks of the volcano, with lava flow output and fire fountaining until 5 November. After this date, the eruption continued exclusively on the S flank, with continuous explosive activity and lava flows active between 13 November and 28 January 2003. Multi-disciplinary data collected during the eruption (petrology, analyses of ash components, gas geochemistry, field surveys, thermal mapping and structural surveys) allowed us to analyse the dynamics of the eruption. The eruption was triggered either by (i) accumulation and eventual ascent of magma from depth or (ii) depressurisation of the edifice due to spreading of the eastern flank of the volcano. The extraordinary explosivity makes the 2002–03 eruption a unique event in the last 300 years, comparable only with La Montagnola 1763 and the 2001 Lower Vents eruptions. A notable feature of the eruption was also the simultaneous effusion of lavas with different composition and emplacement features. Magma erupted from the NE fissure represented the partially degassed magma fraction normally residing within the central conduits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is typical of most Etnean eccentric eruptions. We believe that there is a high probability that Mount Etna has entered a new eruptive phase, with magma being supplied to a deep reservoir independent from the central conduit, that could periodically produce sufficient overpressure to propagate a dyke to the surface and generate further flank eruptions.