Showing papers in "Geological Society, London, Memoirs in 2021"

Chapter 1.2 Antarctic volcanism: volcanology and palaeoenvironmental overview

Abstract: Since Jurassic time (c. 200 Ma), Antarctica has had a greater diversity of volcanism than other southern continents. It includes: (1) voluminous mafic and felsic volcanism associated with the break-up of Gondwana; (2) a long-lived continental margin volcanic arc, including back-arc alkaline volcanism linked to slab rollback; (3) small-volume mafic alkaline volcanism associated with slab-window formation; and (4) one of Earth9s major continental rift zones, the West Antarctic Rift System (WARS), with its numerous large alkaline central volcanoes. Several of Antarctica9s volcanoes are still active. This chapter is a review of the major volcanic episodes and their principal characteristics, in their tectonic, volcanological and palaeoenvironmental contexts. Jurassic Gondwana break-up was associated with large-scale volcanism that caused global environmental changes and associated mass extinctions. The volcanic arc was a major extensional arc characterized by alternating volcanic flare-ups and lulls. The Neogene rift-related alkaline volcanism is dominated by effusive glaciovolcanic eruptions, overwhelmingly as both pāhoehoe- and ‘a‘ā-sourced lava-fed deltas. The rift is conspicuously poor in pyroclastic rocks due to the advection and removal of tephra erupted during glacial intervals. Volcanological investigations of the Neogene volcanism have also significantly increased our knowledge of the critical parameters and development of the Antarctic Ice Sheet.

Chapter 5.2b Erebus Volcanic Province: petrology

Abstract: Igneous rocks of the Erebus Volcanic Province have been investigated for more than a century but many aspects of petrogenesis remain problematic Current interpretations are assessed and summarized using a comprehensive dataset of previously published and new geochemical and geochronological data Igneous rocks, ranging in age from 25 Ma to the present day, are mainly nepheline normative Compositional variation is largely controlled by fractionation of olivine + clinopyroxene + magnetite/ilmenite + titanite ± kaersutite ± feldspar, with relatively undifferentiated melts being generated by

Chapter 7.2 Mount Erebus

Abstract: Erebus volcano, Antarctica, is the southernmost active volcano on the globe. Despite its remoteness and harsh conditions, Erebus volcano provides an unprecedented and unique opportunity to study the petrogenesis and evolution, as well as the passive and explosive degassing, of an alkaline magmatic system with a persistently open and magma-filled conduit. In this chapter, we review nearly five decades of scientific research related to Erebus volcano, including geological, geophysical, geochemical and microbiological observations and interpretations. Mount Erebus is truly one of the world9s most significant natural volcano laboratories where the lofty scientific goal of studying a volcanic system from mantle to microbe is being realized.

Chapter 5.2a Erebus Volcanic Province: volcanology

Abstract: The Erebus Volcanic Province is the largest Neogene volcanic province in Antarctica, extending c. 450 km north–south and 170 km wide east–west. It is dominated by large central volcanoes, principally Mount Erebus, Mount Bird, Mount Terror, Mount Discovery and Mount Morning, which have sunk more than 2 km into underlying sedimentary strata. Small submarine volcanoes are also common, as islands and seamounts in the Ross Sea (Terror Rift), and there are many mafic scoria cones (Southern Local Suite) in the Royal Society Range foothills and Dry Valleys. The age of the volcanism ranges between c. 19 Ma and present but most of the volcanism is

Chapter 3.1a Antarctic Peninsula and South Shetland Islands: volcanology

Abstract: The Antarctic Peninsula contains a record of continental-margin volcanism extending from Jurassic to Recent times. Subduction of the Pacific oceanic lithosphere beneath the continental margin developed after Late Jurassic volcanism in Alexander Island that was related to extension of the continental margin. Mesozoic ocean-floor basalts emplaced within the Alexander Island accretionary complex have compositions derived from Pacific mantle. The Antarctic Peninsula volcanic arc was active from about Early Cretaceous times until the Early Miocene. It was affected by hydrothermal alteration, and by regional and contact metamorphism generally of zeolite to prehnite–pumpellyite facies. Distinct geochemical groups recognized within the volcanic rocks suggest varied magma generation processes related to changes in subduction dynamics. The four groups are: calc-alkaline, high-Mg andesitic, adakitic and high-Zr, the last two being described in this arc for the first time. The dominant calc-alkaline group ranges from primitive mafic magmas to rhyolite, and from low- to high-K in composition, and was generated from a mantle wedge with variable depletion. The high-Mg and adakitic rocks indicate periods of melting of the subducting slab and variable equilibration of the melts with mantle. The high-Zr group is interpreted as peralkaline and may have been related to extension of the arc.

Chapter 5.1b Northern Victoria Land: petrology

Abstract: Cenozoic magmatic rocks related to the West Antarctic Rift System crop out right across Antarctica, in Victoria Land, Marie Byrd Land and into Ellsworth Land. Northern Victoria Land, located at the northwestern tip of the western rift shoulder, is unique in hosting the longest record of the rift-related igneous activity: plutonic rocks and cogenetic dyke swarms cover the time span from c. 50 to 20 Ma, and volcanic rocks are recorded from 15 Ma to the present. The origin of the entire igneous suite is debated; nevertheless, the combination of geochemical and isotopic data with the regional tectonic history supports a model with no role for a mantle plume. Amagmatic extension during the Cretaceous generated an autometasomatized mantle source that, during Eocene–present activity, produced magma by small degrees of melting induced by the transtensional activity of translithospheric fault systems. The emplacement of Eocene–Oligocene plutons and dyke swarms was focused along these fault systems. Conversely, the location of the mid-Miocene–present volcanoes is governed by lithospheric necking along the Ross Sea coast for the largest volcanic edifices; while inland, smaller central volcanoes and scoria cones are related to the establishment of magma chambers in thicker crust.

Chapter 7.1 Deception Island

Abstract: Deception Island (South Shetland Islands) is one of the most active volcanoes in Antarctica, with more than 15 explosive eruptive events registered over the past two centuries. Recent eruptions (1967, 1969 and 1970) and volcanic unrest episodes in 1992, 1999 and 2014–15 demonstrate that the occurrence of future volcanic activity is a valid and pressing concern for scientists, logistic personnel and tourists that are visiting or are working on or near the island. Over the last few decades, intense research activity has been carried out on Deception Island to decipher the origin and evolution of this very complex volcano. To that end, a solid integration of related scientific disciplines, such as tectonics, petrology, geochemistry, geophysics, geomorphology, remote sensing, glaciology, is required. A proper understanding of the island9s evolution in the past, and its present state, is essential for improving the efficiency in interpreting monitoring data recorded during volcanic unrest periods and, hence, for future eruption forecasting. In this chapter, we briefly present Deception Island9s most relevant tectonic, geomorphological, volcanological and magmatic features, as well as the results obtained from decades of monitoring the island9s seismic activity and ground deformation.

Chapter 5 Tectonic evolution of the Oman Mountains

Abstract: The tectonic evolution of the Oman Mountains as of the Neoproterozoic begins with a major extensional event, the Neoproterozoic Abu Mahara rifting. It was followed by the compressional Nabitah event, still during the Neoproterozoic, in Oman but possibly not in the study area. During the earliest Cambrian, the Jabal Akhdar area was affected by the Cadomian Orogeny, marked by NE--SW shortening. It is unclear, whether the Saih Hatat area was exposed to the Cadomian deformation, too. Still during the lower Cambrian, the Angudan Orogeny followed, characterized by NW--SE shortening. An episode of rifting affected the Saih Hatat area during the mid-Ordovician. During the mid-Carboniferous, both dome areas were deformed by tilting and large-scale open folding in the course of the ‘Hercynian’ event. As a consequence, a major unconformity formed. As another Late Paleozoic event, the Permian break-up of Pangaea and subsequent formation of the Hawasina ocean basin, are recorded in the Southeastern Oman Mountains. As a result, a passive margin formed which existed until the mid-Cretaceous, characterized by deposition of mostly shelfal carbonates. This interval of general tectonic quiescence was interrupted during the early Jurassic by uplift and tilting of the Arabian Platform. The platform collapsed during the late Cretaceous, related to the arrival of the obducted allochthonous nappes including the Semail Ophiolite, transforming the passive margin to an active margin. The Semail Ophiolite formed most likely above a subduction zone within the Neo-Tethys Ocean during the Cenomanian while parts of the Arabian Plate were subducted to the NE. Formation of oceanic lithosphere and SW-thrusting was broadly coeval, resulting in ophiolite obduction onto the Hawasina Basin. The Semail Ophiolite and the Hawasina rocks combined were thrust further onto the Arabian Plate. Their load created a foreland basin and forebulge within the Arabian Platform. Once the continental lithosphere of the Arabian Platform was forced into the subduction zone, a tear between the dense oceanic lithosphere and the buoyant continental lithosphere developed. This led to rapid uplift and exhumation of subducted continental lithosphere of the Saih Hatat area, while obduction was still going on, causing in multiple and intense folding/thrusting within the eastern Saih Hatat Dome. Exhumation of the Saih Hatat Dome was massive. The emplacement of the ophiolite was completed during the Campanian/Maastrichtian. For completeness, we also present alternative models for the developmental history of the Semail Ophiolite. Immediately after emplacement, the Arabian lithosphere underwent intense top-to-the-NE extensional shearing. Most of the Saih Hatat Dome was exhumed during the latest Cretaceous to Early Eocene, associated with major extensional shearing at its flanks. Further convergence during the late Eocene to Miocene resulted in exhumation of the Jabal Akhdar Dome and some gentle exhumation of the Saih Hatat Dome, shaping the present-day Southeastern Oman Mountains. In the coastal area, east and SE of the Saih Hatat Dome, some late Cretaceous to present-day uplift is evident by, e.g., uplifted marine terraces. The entire Oman Mountains are uplifting today, which is evident by the massive wadi incision into various rock units, including wadi deposits which may form overhangs.

The Seismic Structure of the Antarctic Upper Mantle

Abstract: The deployment of seismic stations and the development of ambient noise tomography as well as new analysis methods provide an opportunity for higher-resolution imaging of Antarctica. Here we review recent seismic structure models and describe their implications for the dynamics and history of the Antarctic upper mantle. Results show that most of East Antarctica is underlain by continental lithosphere to depths of approximately 200 km. The thickest lithosphere is found in a band 500–1000 km inboard from the Transantarctic Mountains, representing the continuation of cratonic lithosphere with Australian affinity beneath the ice. Dronning Maud Land and the Lambert Graben show much thinner lithosphere, consistent with Phanerozoic lithospheric disruption. The Transantarctic Mountains mark a sharp boundary between cratonic lithosphere and the warmer upper mantle of West Antarctica. In the southern Transantarctic Mountains, cratonic lithosphere has been replaced by warm asthenosphere, giving rise to Cenozoic volcanism and an elevated mountainous region. The Marie Byrd Land volcanic dome is underlain by slow seismic velocities extending through the transition zone, consistent with a mantle plume. Slow-velocity anomalies beneath the coast from the Amundsen Sea Embayment to the Antarctic Peninsula are likely to result from upwelling of warm asthenosphere during subduction of the Antarctic–Phoenix spreading centre.

Chapter 5.1a Northern Victoria Land: volcanology

Abstract: Neogene volcanism is widespread in northern Victoria Land, and is part of the McMurdo Volcanic Group. It is characterized by multiple coalesced shield volcanoes but includes a few relatively small stratovolcanoes. Two volcanic provinces are defined (Hallett and Melbourne), with nine constituent volcanic fields. Multitudes of tiny monogenetic volcanic centres (mainly scoria cones) are also scattered across the region and are called the Northern Local Suite. The volcanism extends in age between middle Miocene (c. 15 Ma) and present but most is

Chapter 2 Tectonostratigraphy of the eastern part of the Oman Mountains

Abstract: This chapter provides comprehensive descriptions of 52 numbered formations/rock units of the Southeastern Oman Mountains, based on available literature. The oldest eight siliciclastic and carbonate formations are positioned below the ‘Hercynian’ Unconformity. The overlying formation (9–16) mostly represent carbonates which accumulated in a passive margin platform setting during or after the opening of the Neo-Tethys Ocean. The passive margin slope and platform collapsed during the late Cretaceous because of the obduction of the Semail Ophiolite along with the deep marine Hawasina sedimentary rocks. The collapsing passive margin interval was recorded within the syn-obductional Aruma Group (17; Muti Formation). Above this formation are the allochthonous units (18–42) of the tectonically lower Hawasina deep-sea basin and the structurally overlying Semail Ophiolite. The former contains Permian to Upper Cretaceous formations, while the latter is Cenomanian in age. Above the allochthonous rocks, the Neo-autochthonous formations were deposited, starting with the post-obductional uppermost Cretaceous Aruma Group (43; Al-Khod Formation) until the Quaternary deposits (52). All these formations/rock units are depicted on an accompanying map and stratigraphic chart.

Chapter 3.2a Bransfield Strait and James Ross Island: volcanology

Abstract: Following more than 25 years of exploration and research since the last regional appraisal, the number of known subaerially exposed volcanoes in the northern Antarctic Peninsula region has more than trebled, from less than 15 to more than 50, and that total must be increased at least three-fold if seamounts in Bransfield Strait are included. Several volcanoes remain unvisited and there are relatively few detailed studies. The region includes Deception Island, the most prolific active volcano in Antarctica, and Mount Haddington, the largest volcano in Antarctica. The tectonic environment of the volcanism is more variable than elsewhere in Antarctica. Most of the volcanism is related to subduction. It includes very young ensialic marginal basin volcanism (Bransfield Strait), back-arc alkaline volcanism (James Ross Island Volcanic Group) and slab-window-related volcanism (seamount offshore of Anvers Island), as well as volcanism of uncertain origin (Anvers and Brabant islands; small volcanic centres on Livingston and Greenwich islands). Only ‘normal’ arc volcanism is not clearly represented, possibly because active subduction virtually ceased at c. 4 Ma. The eruptive environment for the volcanism varied between subglacial, marine and subaerial but a subglacial setting is prominent, particularly in the James Ross Island Volcanic Group.

Appendices to: The Geology and Tectonics of the Jabal Akhdar and Saih Hatat Domes, Oman Mountains

Abstract: See foldout. A more detailed topographic map can be found in the online publication. Figure A.3 provides a correlation/comparison of Permian ages between the ‘International Stratigraphic Chart’ and the ‘Tethyan Time Scale’. Prof. Christopher Bailey (College of William & Mary, USA) creates and provides a number of helpful and interesting blogs about the fascinating geology of Oman: 1. https://wmblogs.wm.edu/cmbail/inside-ghubrah-bowl-oman-dropstones-double-duckbills-pencil-structures-oh/ 2. https://wmblogs.wm.edu/cmbail/omans-geological-triple-point/ 3. https://wmblogs.wm.edu/cmbail/the-road-to-the-moho/ 4. https://wmblogs.wm.edu/cmbail/wadi-bani-ghafir-at-sidaq-gorge-water-versus-rock-in-oman/ 5. https://wmblogs.wm.edu/cmbail/omans-mega-sheath-folds/ 6. https://wmblogs.wm.edu/cmbail/dispatches-from-oman-juxtaposition/ 7. https://wmblogs.wm.edu/cmbail/dispatches-from-oman-fodder-for-the-tectonic-cannon/ 8. https://wmblogs.wm.edu/cmbail/dispatches-from-oman-wadi-jizzi-standing-at-the-bottom-of-the-tethys-ocean/ 9. https://wmblogs.wm.edu/cmbail/dispatches-from-oman-ophiolite-to-aflaj/ 10. https://wmblogs.wm.edu/cmbail/finding-sharqiya-sands-oman/ Inconsistencies are found between the BRGM 1:100 000 and 1:250 000 maps within the Hawasina formations. In all cases we have followed the 1:100 000 maps rather the 1:250 000 map. 1. The geological map of Nazwa (1:250 000; Bechennec …

Chapter 4.1b Antarctic Peninsula: petrology

Abstract: Scattered occurrences of Miocene–Recent volcanic rocks of the alkaline intraplate association represent one of the last expressions of magmatism along the Antarctic Peninsula. The volcanic rocks were erupted after the cessation of subduction which stopped following a series of northward-younging ridge crest–trench collisions. Volcanism has been linked to the development of a growing slab window beneath the extinct convergent margin. Geochemically, lavas range from olivine tholeiite through to basanite and tephrite. Previous studies have emphasized the slab-window tectonic setting as key to allowing melting of peridotite in the asthenospheric void caused by the passage of the slab beneath the locus of volcanism. This hypothesis is revisited in the light of more recent petrological research, and an origin from melting of subducted slab-hosted pyroxenite is considered here to be a more viable alternative for their petrogenesis. Because of the simple geometry of ridge subduction, and the well-established chronology of ridge crest–trench collisions, the Antarctic Peninsula remains a key region for understanding the transition from active to passive margin resulting from cessation of subduction. However, there are still some key issues relating to their tectonomagmatic association, and, principally, the poor geochronological control on the volcanic rocks requires urgent attention.

Chapter 7.4 Active volcanoes in Marie Byrd Land

Abstract: Two volcanoes in Marie Byrd Land, Mount Berlin and Mount Takahe, can be considered active, and a third, Mount Waesche, may be as well; although the chronology of activity is less well constrained. The records of explosive activity of these three volcanoes is well represented through deposits on the volcano flanks and tephra layers found in blue ice areas, as well as by the presence of cryptotephra layers found in West and East Antarctic ice cores. Records of effusive volcanism are found on the volcano flanks but some deposits may be obscured by pervasive glacerization of the edifices. Based on a compilation of tephra depths–ages in ice cores, the activity patterns of Mount Takahe and Mount Berlin are dramatically different. Mount Takahe has erupted infrequently over the past 100 kyr. Mount Berlin, by contrast, has erupted episodically during this time interval, with the number of eruptions being dramatically higher in the time interval between c. 32 and 18 ka. Integration of the Mount Berlin tephra record from ice cores and blue ice areas over a 500 kyr time span reveals a pattern of geochemical evolution related to small batches of partial melt being progressively removed from a single source underlying Mount Berlin.

Chapter 1.4 Antarctic volcanism: active volcanism overview

Abstract: In the last two centuries, demographic expansion and extensive urbanization of volcanic areas have increased the exposure of our society to volcanic hazards. Antarctica is no exception. During the last decades, the permanent settlement and seasonal presence of scientists, technicians, tourists and logistical personnel close to active volcanoes in the south polar region have increased notably. This has led to an escalation in the number of people and the amount of infrastructure exposed to potential eruptions. This requires advancement of our knowledge of the volcanic and magmatic history of Antarctic active volcanoes, significant improvement of the monitoring networks, and development of long-term hazard assessments and vulnerability analyses to carry out the required mitigation actions, and to elaborate on the most appropriate response plans to reduce loss of life and infrastructure during a future volcanic crisis. This chapter provides a brief summary of the active volcanic systems in Antarctica, highlighting their main volcanological features, which monitoring systems are deployed (if any), and recent (i.e. Holocene and/or historical) eruptive activity or unrest episodes. To conclude, some notes about the volcanic hazard assessments carried out so far on south polar volcanoes are also included, along with recommendations for specific actions and ongoing research on active Antarctic volcanism.

Chapter 5.4b Marie Byrd Land and Ellsworth Land: petrology

Abstract: In Marie Byrd Land and Ellsworth Land 19 large polygenetic volcanoes and numerous smaller centres are exposed above the West Antarctic Ice Sheet along the northern flank of the West Antarctic Rift System. The Cenozoic (36.7 Ma to active) volcanism of the Marie Byrd Land Volcanic Group (MBLVG) encompasses the full spectrum of alkaline series compositions ranging from basalt to intermediate (e.g. mugearite, benmoreite) to phonolite, peralkaline trachyte, rhyolite and rare pantellerite. Differentiation from basalt is described by progressive fractional crystallization; however, to produce silica-oversaturated compositions two mechanisms are proposed: (1) polybaric fractionation with early-stage removal of amphibole at high pressures; and (2) assimilation–fractional crystallization to explain elevated 87Sr/86Sri ratios. Most basalts are silica-undersaturated and enriched in incompatible trace elements (e.g. La/YbN >10), indicating small degrees of partial melting of a garnet-bearing mantle. Mildly silica-undersaturated and rare silica-saturated basalts, including tholeiites, are less enriched (La/YbN 20) materials. Geophysical studies indicate a deep thermal anomaly beneath central Marie Byrd Land, suggesting a plume influence on volcanism and tectonism.

Chapter 3.2b Bransfield Strait and James Ross Island: petrology

Abstract: Young volcanic centres of the Bransfield Strait and James Ross Island occur along back-arc extensional structures parallel to the South Shetland island arc Back-arc extension was caused by slab rollback at the South Shetland Trench during the past 4 myr The variability of lava compositions along the Bransfield Strait results from varying degrees of mantle depletion and input of a slab component The mantle underneath the Bransfield Strait is heterogeneous on a scale of approximately tens of kilometres with portions in the mantle wedge not affected by slab fluids Lavas from James Ross Island east of the Antarctic Peninsula differ in composition from those of the Bransfield Strait in that they are alkaline without evidence for a component from a subducted slab Alkaline lavas from the volcanic centres east of the Antarctic Peninsula imply variably low degrees of partial melting in the presence of residual garnet, suggesting variable thinning of the lithosphere by extension Magmas in the Bransfield Strait form by relatively high degrees of melting in the shallow mantle, whereas the magmas some 150 km further east form by low degrees of melting deeper in the mantle, reflecting the diversity of mantle geodynamic processes related to subduction along the South Shetland Trench

Chapter 2.1b Ferrar Large Igneous Province: petrology

Abstract: The Lower Jurassic Ferrar Large Igneous Province consists predominantly of intrusive rocks, which crop out over a distance of 3500 km. In comparison, extrusive rocks are more restricted geographically. Geochemically, the province is divided into the Mount Fazio Chemical Type, forming more than 99% of the exposed province, and the Scarab Peak Chemical Type, which in the Ross Sea sector is restricted to the uppermost lava. The former exhibits a range of compositions (SiO2 = 52–59%; MgO = 9.2–2.6%; Zr = 60–175 ppm; Sri = 0.7081–0.7138; eNd = −6.0 to −3.8), whereas the latter has a restricted composition (SiO2 = c. 58%; MgO = c. 2.3%; Zr = c. 230 ppm; Sri = 0.7090–0.7097; eNd = −4.4 to −4.1). Both chemical types are characterized by enriched initial isotope compositions of neodymium and strontium, low abundances of high field strength elements, and crust-like trace element patterns. The most basic rocks, olivine-bearing dolerites, indicate that these geochemical characteristics were inherited from a mantle source modified by subduction processes, possibly the incorporation of sediment. In one model, magmas were derived from a linear source having multiple sites of generation each of which evolved to yield, in sum, the province-wide coherent geochemistry. The preferred interpretation is that the remarkably coherent geochemistry and short duration of emplacement demonstrate derivation from a single source inferred to have been located in the proto-Weddell Sea region. The spatial variation in geochemical characteristics of the lavas suggests distinct magma batches erupted at the surface, whereas no clear geographical pattern is evident for intrusive rocks.

Chapter 5.4a Marie Byrd Land and Ellsworth Land: volcanology

Abstract: Nineteen large (2348–4285 m above sea level) central polygenetic alkaline shield-like composite volcanoes and numerous smaller volcanoes in Marie Byrd Land (MBL) and western Ellsworth Land rise above the West Antarctic Ice Sheet (WAIS) and comprise the MBL Volcanic Group (MBLVG). Earliest MBLVG volcanism dates to the latest Eocene (36.6 Ma). Polygenetic volcanism began by the middle Miocene (13.4 Ma) and has continued into the Holocene without major interruptions, producing the central volcanoes with 24 large (2–10 km-diameter) summit calderas and abundant evidence for explosive eruptions in caldera-rim deposits. Rock lithofacies are dominated by basanite and trachyte/phonolite lava and breccia, deposited in both subaerial and ice-contact environments. The chronology of MBLVG volcanism is well constrained by 330 age analyses, including 52 new 40Ar/39Ar ages. A volcanic lithofacies record of glaciation provides evidence of local ice-cap glaciation at 29–27 Ma and of widespread WAIS glaciation by 9 Ma. Late Quaternary glaciovolcanic records document WAIS expansions that correlate to eustatic sea-level lowstands (MIS 16, 4 and 2): the WAIS was +500 m at 609 ka at coastal Mount Murphy, and +400 m at 64.7 ka, +400 m at 21.2 ka and +575 m at 17.5 ka at inland Mount Takahe.

Chapter 7.3 Mount Melbourne and Mount Rittmann

Abstract: Mount Melbourne and Mount Rittmann are quiescent, although potentially explosive, alkaline volcanoes located 100 km apart in Northern Victoria Land quite close to three stations (Mario Zucchelli Station, Gondwana and Jang Bogo). The earliest investigations on Mount Melbourne started at the end of the 1960s; Mount Rittmann was discovered during the 1988–89 Italian campaign and knowledge of it is more limited due to the extensive ice cover. The first geophysical observations at Mount Melbourne were set up in 1988 by the Italian National Antarctic Research Programme (PNRA), which has recently funded new volcanological, geochemical and geophysical investigations on both volcanoes. Mount Melbourne and Mount Rittmann are active, and are characterized by fumaroles that are fed by volcanic fluid; their seismicity shows typical volcano signals, such as long-period events and tremor. Slow deformative phases have been recognized in the Mount Melbourne summit area. Future implementation of monitoring systems would help to improve our knowledge and enable near-real-time data to be acquired in order to track the evolution of these volcanoes. This would prove extremely useful in volcanic risk mitigation, considering that both Mount Melbourne and Mount Rittmann are potentially capable of producing major explosive activity with a possible risk to large and distant communities.

Chapter 6.2 Englacial tephras of East Antarctica

Abstract: Driven by successful achievements in recovering high-resolution ice records of climate and atmospheric composition through the Late Quaternary, new ice–tephra sequences from various sites of the East Antarctic Ice Sheet (EAIS) have been studied in the last two decades spanning an age range of a few centuries to 800 kyr. The tephrostratigraphic framework for the inner EAIS, based on ash occurrence in three multi-kilometre-deep ice cores, shows that the South Sandwich Islands represent a major source for tephra, highlighting the major role in the ash dispersal played by clockwise circum-Antarctic atmospheric circulation penetrating the Antarctic continent. Tephra records from the eastern periphery of the EAIS, however, are obviously influenced by explosive activity sourced in nearby Antarctic rift provinces. These tephra inventories have provided a fundamental complement to the near-vent volcanic record, in terms of both frequency/chronology of explosive volcanism and of magma chemical evolution through time. Despite recent progress, current data are still sparse. There is a need for further tephra studies to collect data from unexplored EAIS sectors, along with extending the tephra inventory back in time. Ongoing international palaeoclimatic initiatives of ice-core drilling could represent a significant motivation for the tephra community and for Quaternary Antarctic volcanologists.

Chapter 1.3 Antarctic volcanism: petrology and tectonomagmatic overview

Abstract: Petrological investigations over the past 30 years have significantly advanced our knowledge of the origin and evolution of magmas emplaced within and erupted on top of the Antarctic Plate. Over the last 200 myr Antarctica has experienced: (1) several episodes of rifting, leading to the fragmentation of Gondwana and the formation by c. 83 Ma of the current Antarctica Plate; (2) long-lived subduction that shut down progressively eastwards along the Gondwana margin in the Late Cretaceous and is still active at the northernmost tip of the Antarctic Peninsula; and (3) broad extension across West Antarctica that produced one of the Earth9s major continental rift systems. The dynamic tectonic history of Antarctica since the Triassic has led to a diversity of volcano types and igneous rock compositions with correspondingly diverse origins. Many intriguing questions remain about the petrology of mantle sources and the mechanisms for melting during each tectonomagmatic phase. For intraplate magmatism, the upwelling of deep mantle plumes is often evoked. Alternatively, subduction-related metasomatized mantle sources and melting by more passive means (e.g. edge-driven flow, translithospheric faulting, slab windows) are proposed. A brief review of these often competing models is provided in this chapter along with recommendations for ongoing petrological research in Antarctica.

Chapter 2.1a Ferrar Large Igneous Province: volcanology

Abstract: Preserved rocks in the Jurassic Ferrar Large Igneous Province consist mainly of intrusions, and extrusive rocks, the topic of this chapter, comprise the remaining small component. They crop out in a limited number of areas in the Transantarctic Mountains and southeastern Australia. They consist of thick sequences of lavas and sporadic occurrences of volcaniclastic rocks. The latter occur mainly beneath the lavas and represent the initial eruptive activity, but also are present within the lava sequence. The majority are basaltic phreatomagmatic deposits and in at least two locations form immense phreatocauldrons filled with structureless tuff breccias and lapilli tuffs with thicknesses of as much as 400 m. Stratified sequences of tuff breccias, lapilli tuffs and tuffs are up to 200 m thick. Thin tuff beds are sparsely distributed in the lava sequences. Lava successions are mainly 400–500 m thick, and comprise individual lavas ranging from 1 to 230 m thick, although most are in the range of 10–100 m. Well-defined colonnade and entablature are seldom displayed. Lava sequences were confined topographically and locally ponded. Water played a prominent role in eruptive activity, as exhibited by phreatomagmatism, hyaloclastites, pillow lava and quenching of lavas. Vents for lavas have yet to be identified.

Aeolian Processes and landforms

Abstract: A number of major factors have driven the volume and nature of aeolian geomorphology in the second half of the twentieth century: the growth of process studies, the availability of remote sensing, the development of new dating techniques (e.g. optical dating), the utilisation of new technologies (e.g. data loggers and global positioning systems),computer modelling of dune forms and wind action and sediment movement, the recognition of the importance of aeolian forms and processes in extra-terrestrial settings (especially Mars), the role of aeolian dust in atmospheric processes, the search for analogues for ancient hydrocarbon-bearing strata, the appreciation of the importance of climatic changes in desert areas, a concern with what may happen to arid environments in a warmer world, and an increasing realisation that aeolian phenomena could be hazardous. This chapter does not deal with coastal dunes, but concentrates on those of the major lower latitude drylands. It discusses the main controls on dune forms, the nature of sand seas, ancient and modern, and the nature of dune sediments. It also shows that during the 1970s there was a burgeoning interest in dust storms. In addition, with the availability of remote sensing imagery it was possible to see for the first time that wind-furrowed yardangs were striking features with a wide global distribution. The origin of closed depressions (pans) generated a large literature and hypotheses for their formation were put forward which included wind erosion, solution, excavation by animals, karstic and pseudo-karstic solution, and tectonic subsidence. Remote sensing showed just how important they were in drylands. Other phenomena that attracted attention and some controversy were stone pavements and peri-desert loess. Finally, it is suggested that the nature of aeolian processes and forms will be modified in a warmer world.

Chapter 5.3b Mount Early and Sheridan Bluff: petrology

Abstract: This study discusses the petrological and geochemical features of two monogenetic Miocene volcanoes, Mount Early and Sheridan Bluff, which are the above-ice expressions of Earth9s southernmost volcanic field located at c. 87° S on the East Antarctic Craton. Their geochemistry is compared to basalts from the West Antarctic Rift System to test affiliation and resolve mantle sources and cause of melting beneath East Antarctica. Basaltic lavas and dykes are olivine-phyric and comprise alkaline (hawaiite and mugearite) and subalkaline (tholeiite) types. Trace element abundances and ratios (e.g. La/Yb, Nb/Y, Zr/Y) of alkaline compositions resemble basalts from the West Antarctic rift and ocean islands (OIB), while tholeiites are relatively depleted and approach the concentrations levels of enriched mid-ocean ridge basalt (E-MORB). The magmas evolved by fractional crystallization with contamination by crust; however, neither process can adequately explain the contemporaneous eruption of hawaiite and tholeiite at Sheridan Bluff. Our preferred scenario is that primary magmas of each type were produced by different degrees of partial melting from a compositionally similar mantle source. The nearly simultaneous generation of lower degrees of melting to produce alkaline types and higher degrees of melting forming tholeiite was most likely to have been facilitated by the detachment and dehydration of metasomatized mantle lithosphere.

Chapter 6.1 Marine record of Antarctic volcanism from drill cores

Abstract: We review here data and information on Antarctic volcanism resulting from recent tephrostratigraphic investigations on marine cores. Records include deep drill cores recovered during oceanographic expeditions: DSDP, ODP and IODP drill cores recovered during ice-based and land-based international cooperative drilling programmes DVDP 15, MSSTS-1, CIROS-1 and CIROS-2, DVDP 15, CRP-1, CRP-2/2A and CRP-3, ANDRILL-MIS and ANDRILL-SMS, and shallow gravity and piston cores recovered in the Antarctic and sub-Antarctic oceans. We report on the identification of visible volcaniclastic horizons and, in particular, of primary tephra within the marine sequences. Where available, the results of analyses carried out on these products are presented. The volcanic material identified differs in its nature, composition and emplacement mechanisms. It was derived from different sources on the Antarctic continent and was emplaced over a wide time span. Marine sediments contain a more complete record of the explosive activity from Antarctic volcanoes and are complementary to those obtained by land-based studies. This record provides important information for volcanological reconstructions including approximate intensities and magnitudes of eruptions, and their duration, age and recurrence, as well as their eruptive dynamics. In addition, characterized tephra layers represent an invaluable chronological tool essential in establishing correlations between different archives and in synchronizing climate records.

Mantle convection and possible mantle plumes beneath Antarctica – insights from geodynamic models and implications for topography

Abstract: This chapter describes large-scale mantle flow structures beneath Antarctica as derived from global seismic tomography models of the present-day state. In combination with plate reconstructions, the time-dependent pattern of palaeosubduction can be simulated and is shown from the rarely seen Antarctic perspective. Furthermore, a dynamic topography model demonstrates which kind and scales of surface manifestations can be expected as a direct and observable result of mantle convection. The last section of this chapter features an overview of the classical concept of deep-mantle plumes from a geodynamic point of view and how recent insights, mostly from seismic tomography, have changed the understanding of plume structures and dynamics over past decades. The long-standing and controversial hypothesis of a mantle plume beneath West Antarctica is summarized and addressed with geodynamic models, which estimate the excess heat flow of a potential plume at the bedrock surface. However, the predicted heat flow is small, while differences in surface heat-flux estimates are large; therefore, the results are not conclusive with regard to the existence of a West Antarctic mantle plume. Finally, it is shown that global mantle flow would cause the tilting of whole-mantle plume conduits beneath West Antarctica such that their base is predicted to be displaced about 20° northward relative to the surface position, closer to the southern margin of the Pacific Large Low-Shear Velocity Province.

Stappen High-Bjørnøya tectono-sedimentary element, Barents Sea

Abstract: The Stappen High-Bjornoya tectono-sedimentary element (TSE) is located in the western Barents Shelf and is one of the prominent tectonic elements in the area. The Stappen High comprises a shallow platform, and Bjornoya forms its highest point with exposed outcrops. Modern seismic reflection data of improved quality in the southern part of the TSE and vintage seismic data in the northern portion are utilised. Together with updated geological information at Bjornoya, the study provides insights into the Palaeozoic to early Cenozoic evolution of the Stappen High-Bjornoya TSE. In this context, we discuss structural inheritance, the rift development, and we account for confirmed and potential hydrocarbon systems and plays.