Evidence of active magmatic rifting in Ma’alalta marginal volcano (Afar, Ethiopia)

2020 ◽  
Author(s):  
Gianmaria Tortelli ◽  
Anna Gioncada ◽  
Carolina Pagli ◽  
Mauro Rosi ◽  
Derek Keir ◽  
...  
Keyword(s):  
Seismic Data ◽  
Lava Flows ◽  
Magmatic Activity ◽  
Magma Storage ◽  
Plumbing System ◽  
Mafic Lava ◽  
Local Seismicity ◽  
Mafic Rocks ◽  
Continental Rifts ◽  
Scoria Cones

<p>Growth of rift segments and development of crustal magmatic systems in continental rifts remain debated issues. We integrate volcanological, geochemical, petrological and seismic data from the Ma’alalta stratovolcano near the western rift margin of Afar to show that active magmatic rifting occurs there. Growth of Ma’alalta started around 0.55 ± 0.05 Ma (Barberi et al. 1972) with the age of the youngest flows unknown. Ma’alalta produced lava flows but also large-volume, caldera-forming ignimbrites, as well as silicic intracaldera domes. The products are mainly trachytic and some are slightly peralkaline. The most recent magmatic activity of Ma’alalta consists of mafic lava fields, scoria cones and peralkaline obsidianaceous silicic domes produced along the ~40 km long magmatic segment and erupted from several vents aligned NNW-SSE rather than from central volcanic activity. Local seismicity (2005-2009 and 2011-2013) also shows a NNW-SSE-trending alignment of earthquakes with good correlation to where the recent magmatic products were erupted. The geochemical features of the mafic rocks (e.g., Ba/La, Rb/Ta and Zr/Ta) as well as the petrogenesis of the recent NNW-SSE-trending silicic domes are similar to the nearby on-rift Dabbahu and Durrie volcanoes. Inferred magma storage depth from mineral geobarometry show that a shallow, silicic chamber existed at ~4-5 km depth below the stratovolcano, while a stacked plumbing system with at least two magma storage levels at ~14 and ~24 km of depth fed the recent basalts. We interpret the wide set of observations from Ma’alalta as evidences that the area is an active rift segment, showing that localised axial extension can be heavily offset towards the rift margin.</p><p> </p><p> </p>

scholarly journals Evidence of active magmatic rifting at the Ma’Alalta volcanic field (Afar, Ethiopia)

2021 ◽  
Vol 83 (6) ◽  
Author(s):  
Gianmaria Tortelli ◽  
Anna Gioncada ◽  
Carolina Pagli ◽  
Mauro Rosi ◽  
Laura De Dosso ◽  
...  
Keyword(s):  
Seismic Data ◽  
Volcanic Field ◽  
Lava Flows ◽  
Magmatic Activity ◽  
Magma Storage ◽  
Plumbing System ◽  
Mafic Lava ◽  
Cinder Cones ◽  
Mafic Rocks ◽  
Seismic Networks

AbstractDuring continental rifting, strain and magmatism are believed to localize to narrow magmatic segments, while the rift margin is progressively abandoned. We integrate volcanological, geochemical, petrological and seismic data from the Ma’Alalta volcanic field (MVF) near the western margin of Afar, to show that the MVF is an active magmatic segment. Magmatism in MVF initiated with lava flows and large-volume, caldera-forming ignimbrites from a central edifice. However, the most recent magmatic activity shifted towards mafic lava fields, cinder cones and obsidian-rich silicic domes erupted from vents aligned NNW-SSE, defining a ~ 35-km-long magmatic segment. Along the same area, a NNW-SSE alignment of earthquakes was recorded by two local seismic networks (2005–2009 and 2011–2013). The geochemistry of the mafic rocks is similar to those of nearby axial volcanoes. Inferred magma storage depth from mineral geobarometry shows that a shallow, silicic chamber existed at ~ 5-km depth below the stratovolcano, while a stacked plumbing system with at least three magma storage levels between 9 and 24 km depth fed the recent basalts. We interpret the wide set of observations from the MVF as evidence that the area is an active magmatic segment, showing that localised axial extension can be heavily offset towards the rift margin.

A 3-D genetic approach to high-resolution geological modelling of the volcanic infill of a paleovalley system. Application to the Volvic catchment (Chaîne des Puys, France)

2012 ◽  
Vol 183 (5) ◽  
pp. 395-407 ◽  
Author(s):  
Simon Rouquet ◽  
Pierre Boivin ◽  
Patrick Lachassagne ◽  
Emmanuel Ledoux
Keyword(s):  
Lava Flow ◽  
Lava Flows ◽  
Genetic Approach ◽  
Hydrogeological Model ◽  
Volcanic System ◽  
Geochemical Composition ◽  
Crystalline Bedrock ◽  
Volcanic Events ◽  
Aa Lava ◽  
Scoria Cones

Abstract The Volvic natural mineral water is catched in a complex volcanic aquifer located in the northern part of the “Chaîne des Puys” volcanic system (Auvergne, France). In the watershed, water transits through scoria cones and basaltic to trachybasaltic lava flows. These aa lava flows, emitted by strombolian cones between 75,000 and 10,000 years ago, are emplaced in deep paleovalleys incised within the variscan crystalline bedrock. The volcanic infill is highly heterogeneous. In order to build a hydrogeological model of the watershed, a simple but robust methodology was developed to reconstruct the bedrock morphology and the volcanic infill in this paleovalley context. This methodology, based on the combination of genetic and geometric approaches, appears to be rather efficient to define both the substratum and the lava flows geometry. A 3D geological model is then proposed. It synthesizes the data from 99 boreholes logs, 2D geoelectric profiles, morphologic clues, datings and petrographic data. A genetic approach, integrating aa lava flow morphology and emplacement behaviour, was used to reconstruct the chronology of the volcanic events and lava flow emplacement from the upper part of the Dômes plateau to the Limagne plain. The precision of the volcanic reconstruction is discussed: the main limitation of the methodology are related to the homogeneity of the petrographic and geochemical composition of the lava flows succession (except for the trachyandesitic Nugere lava), the spatially variable borehole density, the lack of a real petrographical and geological description on most of the available geological logs. Nevertheless, the developed methodology combining spatial and genetic approaches appears to be well adapted to constrain complex lava flow infill geometries in paleovalley context.

Chemical evolution and periodic eruption of mafic lava flows in the west moat of Long Valley Caldera, California

1994 ◽  
Vol 99 (B10) ◽  
pp. 19829-19842 ◽  
Author(s):  
T. A. Vogel ◽  
T. B. Woodburne ◽  
J. C. Eichelberger ◽  
P. W. Layer
Keyword(s):  
Chemical Evolution ◽  
Lava Flows ◽  
The West ◽  
Mafic Lava ◽  
Long Valley Caldera ◽  
Long Valley

Tracking reservoir dynamics across a complete caldera cycle at Rabaul, Papua New Guinea

2021 ◽  
Author(s):  
Gareth N. Fabbro ◽  
Chris O. McKee ◽  
Mikhail E. Sindang ◽  
Jeffrey A. Oalmann ◽  
Caroline Bouvet De La Maisonneuve
Keyword(s):  
Papua New Guinea ◽  
Explosive Eruption ◽  
New Guinea ◽  
Storage Conditions ◽  
Plumbing System ◽  
Mafic Lava ◽  
Mafic Magmas ◽  
Silicic Magmas ◽  
Highly Evolved ◽  
Minor Activity

<p>Caldera-forming eruptions are some of the most devastating events on Earth; however, the volcanoes that produce these eruptions frequently have much more minor activity. Knowing if a restless caldera is currently primed for a large eruption, therefore, has important implications for hazard assessment and risk management. Many calderas, including Rabaul in Papua New Guinea, show cycles of activity with multiple caldera-forming eruptions interspersed with more minor activity. We present data that spans an entire cycle, from one caldera-forming eruption to the next and estimate the storage conditions for each eruption. The last complete caldera cycle of Rabaul started at ~10.5 ka, with the eruption of the dacitic Vunabugbug Ignimbrite. Following the Vunabugbug, little volcanic activity was preserved until ~4.4 ka, suggesting either a period quiescence or destruction and burial during the subsequent caldera-forming eruptions of the region. From 4.4 ka, there is an increase in the volume and SiO<sub>2</sub> contents of volcanic deposits that are preserved, which culminated in the eruption of the dacitic Memorial Ignimbrite at ~4.1 ka. The Memorial Ignimbrite was smaller than the Vunabugbug Ignimbrite and Rabaul Pyroclastics and may not have formed a caldera; however, it does appear to have altered the plumbing system and allowed deeper, hotter basalts to reach the surface. Following the eruption of these basalts, the system gradually evolves towards more silicic magmas, until the eruption of the dacitic Rabaul Pyroclastics at ~1.4 ka. After the Rabaul Pyroclastics hotter, more mafic magmas can again reach the surface, both as more mafic lava flows and as hybrid andesites that contain crystal cargos transported from deeper in the system.</p><p>Two-pyroxene, clinopyroxene–liquid and plagioclase–liquid thermobarometers suggest that the dacites, including those erupted during the caldera-forming eruptions, were stored at pressures of ~1 kbar (~4 km depth) and at temperatures of ~930 °C. There is a tight relationship between the temperature and the SiO<sub>2</sub> content of the magmas, with the basalts erupted after the large ignimbrites recording temperatures of up to 1100 °C. Some of the more mafic magmas also record deeper storage, at pressures of 3–4 kbar (11–15 km). Plagioclase–liquid pairs suggest melt H<sub>2</sub>O contents of ~2.8 wt.% for the dacites, although some of the more mafic magmas have slightly higher melt H<sub>2</sub>O contents (3.2–4.0 wt.%)—this may be because the basalts were saturated and stored at greater pressures. Magnetite–liquid pairs record relatively constant oxygen fugacities of ~1.2 log units above the FMQ buffer.</p><p>At Rabaul it would take on the order of a few millennia to differentiate or accumulate enough dacitic magma to produce a large explosive eruption. The eruption of highly evolved, crystal-poor, cold, hydrous magmas geochemically similar to those erupted prior to the Memorial Ignimbrite and Rabaul Pyroclastics may provide a warning of an impending large explosive eruption.</p>

scholarly journals Extrusion dynamics of deepwater volcanoes revealed by 3-D seismic data

Solid Earth ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 1269-1282 ◽  
Author(s):  
Qiliang Sun ◽  
Christopher A.-L. Jackson ◽  
Craig Magee ◽  
Samuel J. Mitchell ◽  
Xinong Xie
Keyword(s):  
Seismic Data ◽  
Seismic Reflection ◽  
Minor Component ◽  
Lava Flows ◽  
Lava Tubes ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Seafloor Sediments ◽  
Seabed Sediments ◽  
Emplacement Depth

Abstract. Submarine volcanism accounts for ca. 75 % of the Earth's volcanic activity. Yet difficulties with imaging their exteriors and interiors mean that the extrusion dynamics and erupted volumes of deepwater volcanoes remain poorly understood. Here, we use high-resolution 3-D seismic reflection data to examine the external and internal geometry and extrusion dynamics of two late Miocene–Quaternary deepwater (> 2 km emplacement depth) volcanoes buried beneath 55–330 m of sedimentary strata in the South China Sea. The volcanoes have crater-like bases, which truncate underlying strata and suggest extrusion was initially explosive, and erupted lava flows that feed lobate lava fans. The lava flows are > 9 km long and contain lava tubes that have rugged basal contacts defined by ∼90±23 m high erosional ramps. We suggest the lava flows eroded down into and were emplaced within wet, unconsolidated, near-seafloor sediments. Extrusion dynamics were likely controlled by low magma viscosities as a result of increased dissolved H2O due to high hydrostatic pressure and soft, near-seabed sediments, which are collectively characteristic of deepwater environments. We calculate that long-runout lava flows account for 50 %–97 % of the total erupted volume, with a surprisingly minor component (∼3 %–50 %) being preserved in the main volcanic edifice. Accurate estimates of erupted volumes therefore require knowledge of volcano and lava basal surface morphology. We conclude that 3-D seismic reflection data are a powerful tool for constraining the geometry, volumes, and extrusion dynamics of ancient or active deepwater volcanoes and lava flows.

A major Aphebian–Helikian unconformity within the Central Mineral Belt of Labrador: definition of new groups and metallogenic implications

1978 ◽  
Vol 15 (12) ◽  
pp. 1954-1966 ◽  
Author(s):  
W. R. Smyth ◽  
B. E. Marten ◽  
A. B. Ryan
Keyword(s):  
Volcanic Rocks ◽  
Lava Flows ◽  
Grenville Province ◽  
Mafic Lava ◽  
Polyphase Deformation ◽  
Mineral Belt ◽  
Group A ◽  
Grenvillian Orogeny ◽  
Definition Of ◽  
Granitic Batholith

The Central Mineral Belt of Labrador consists of a belt of supracrustal rocks that occupies the northern foreland region of the Grenville Province of the Canadian Shield. Recent mapping in this belt has shown that the Proterozoic Croteau Group consists of two distinct sequences separated by an observed angular unconformity. It is therefore proposed that the name Croteau Group be abandoned and that the lower, Aphebian, marine sequence of sandstone, dolostone, slate, argillite, and mafic volcanic rocks be named the Moran Lake Group and that the upper, Helikian, continental sequence of conglomerate, tuffaceous sandstone, and a calc-alkalic volcanic assemblage be named the Bruce River Group.The Moran Lake Group underwent polyphase deformation, which has been assigned to the Hudsonian Orogeny, prior to deposition of the Bruce River Group around 1474 Ma. The Bruce River Group was intruded by a large granitic batholith, the Otter Lake Granite, for which a preliminary Rb–Sr isochron age of 1445 Ma has been obtained; this age correlates with the Elsonian magmatic event, an event well documented in northern Labrador. The Seal Lake Group, a Neohelikian (1278 Ma) sequence of quartzites, conglomerates, and intercalated mafic lava flows, was unconformably deposited upon the Bruce River Group and the Otter Lake Granite. During the Grenvillian Orogeny, the Bruce River and Seal Lake Groups were deformed together into a major easterly trending syncline. Deformation and metamorphism decrease across these groups to the north.The Bruce River Group forms part of the Labrador uranium area and hosts 14 known uranium occurrences. Occurrences are concentrated in the basal sandstones and conglomerates of the group, above the Aphebian–Helikian unconformity, and in ignimbrites and acid tuffs near the top of the group. No uranium occurrences are known from the Moran Lake Group except in fault-related fractures below the unconformity.

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