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The Drake Passage is an oceanic gateway of about 850 km width located between South America and the Antarctic Peninsula that connects the southeastern Pacific Ocean with the southwestern Atlantic Ocean. It is an important gateway for mantle flow, oceanographic water masses, and migrations of biota. This sector developed within the framework of the geodynamic evolution of the Scotia Arc, including continental fragmentation processes and oceanic crust creation, since the oblique divergence of the South American plate to the north and the Antarctic plate to the south started in the Eocene. As a consequence of its complex tectonic evolution and subsequent submarine processes, as sedimentary infill and erosion mainly controlled by bottom currents and active tectonics, this region shows a varied physiography. We present a detailed map of the bathymetry and geological setting of the Drake Passage that is mainly founded on a new compilation of precise multibeam bathymetric data obtained on 120 cruises between 1992 and 2015, resulting in a new Digital Bathymetric Model with 200 × 200 m cell spacing. The map covers an area of 1,465,000 km2 between parallels 52°S and 63°S and meridians 70°W and 50°W at scale 1:1,600,000 allowing the identification of the main seafloor features. In addition, the map includes useful geological information related to magnetism, seismicity and tectonics. This work constitutes an international cooperative effort and is part of the International Bathymetric Chart of the Southern Ocean project, under the Scientific Committee on Antarctic Research umbrella. © 2018, © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Map.

The Drake Passage is an oceanic gateway of about 850km width located between South America and the Antarctic Peninsula that connects the southeastern Pacific Ocean with the southwestern Atlantic Ocean. It is an important gateway for mantle flow, oceanographic water masses, and migrations of biota. This sector developed within the framework of the geodynamic evolution of the Scotia Arc, including continental fragmentation processes and oceanic crust creation, since the oblique divergence of the South American plate to the north and the Antarctic plate to the south started in the Eocene. As a consequence of its complex tectonic evolution and subsequent submarine processes, as sedimentary infill and erosion mainly controlled by bottom currents and active tectonics, this region shows a varied physiography. We present a detailed map of the bathymetry and geological setting of the Drake Passage that is mainly founded on a new compilation of precise multibeam bathymetric data obtained on 120 cruises between 1992 and 2015, resulting in a new Digital Bathymetric Model with 200x200 m cell spacing. The map covers an area of 1,465,000km2 between parallels 52°S and 63°S and meridians 70°W and 50°W at scale 1:1,600,000 allowing the identification of the main seafloor features. In addition, the map includes useful geological information related to magnetism, seismicity and tectonics. This work constitutes an international cooperative effort and is part of the International Bathymetric Chart of the Southern Ocean project, under the Scientific Committee on Antarctic Research umbrella.

The continental margin of Gondwana preserves a record of long-lived magmatism from the Andean Cordillera to Australia. The crustal blocks of West Antarctica form part of this margin, with Palaeozoic–Mesozoic magmatism particularly well preserved in the Antarctic Peninsula and Marie Byrd Land. Magmatic events on the intervening Thurston Island crustal block are poorly defined, which has hindered accurate correlations along the margin. Six samples are dated here using U-Pb geochronology and cover the geological history on Thurston Island. The basement gneisses from Morgan Inlet have a protolith age of 349±2 Ma and correlate closely with the Devonian–Carboniferous magmatism of Marie Byrd Land and New Zealand. Triassic (240–220 Ma) magmatism is identified at two sites on Thurston Island, with Hf isotopes indicating magma extraction from Mesoproterozoic-age lower crust. Several sites on Thurston Island preserve rhyolitic tuffs that have been dated at 182 Ma and are likely to correlate with the successions in the Antarctic Peninsula, particularly given the pre-break-up position of the Thurston Island crustal block. Silicic volcanism was widespread in Patagonia and the Antarctic Peninsula at ~ 183 Ma forming the extensive Chon Aike Province. The most extensive episode of magmatism along the active margin took place during the mid-Cretaceous. This Cordillera ‘flare-up’ event of the Gondwana margin is also developed on Thurston Island with granitoid magmatism dated in the interval 110–100 Ma.

Trough-mouth fans (TMFs) are large depocentres of glacially influenced sediments formed at the mouths of some glacially carved cross-shelf troughs (Vorren et al. 1989). They develop in front of ice streams grounded at, or near to, the shelf edge, which transported large volumes of glacigenic sediment to the outer shelf and upper slope. The main components of TMFs are prograding outer shelf–upper slope strata which are constructed largely of foresets comprising debris-flow units. They are commonly capped by topsets that may include subglacially deposited tills (Fig. 1f). Mass-wasting deposits, gullies and channels may also occur in conjunction with or within the TMFs.

Submarine gullies are small-scale, confined channels on the order of tens of metres depth that form one of the most common morphological features of high-latitude continental slopes. Gully morphology varies in width, incision depth, length, sinuosity, branching order, shelf-incision, cross-sectional shape and gully spacing, with six distinct gully signatures recognized on high-latitude continental slopes (Gales et al. 2013a, b). Here we analyse the morphology of slope gullies off Halley and Filchner troughs in the southern Weddell Sea (Fig. 1a–f).

Trough-mouth fans (TMFs) are large depocentres of glacially influenced sediments formed at the mouths of some glacially carved cross-shelf troughs (Vorren et al. 1989). They develop in front of ice streams grounded at, or near to, the shelf edge, which transported large volumes of glacigenic sediment to the outer shelf and upper slope. The main components of TMFs are prograding outer shelf–upper slope strata which are constructed largely of foresets comprising debris-flow units. They are commonly capped by topsets that may include subglacially deposited tills (Fig. 1f). Mass-wasting deposits, gullies and channels may also occur in conjunction with or within the TMFs.

Ploughing by deep keels of floating icebergs is a common feature of high-latitude continental margins. Icebergs that have calved from glaciers or ice sheets produce a range of seafloor signatures, including linear to curvilinear grooves, rounded pits and ploughmarks terminating in sediment ridges. The dimensions and patterns of iceberg ploughmarks vary with iceberg size, water depth, local current, tide and wind conditions, seafloor sediment and past glacial history. The outer shelf and upper continental slope of the southern Weddell Sea is extensively ploughed by icebergs, and three different types of iceberg ploughmarks are recognized. The first signature is small grounding pits which occur over a wide area of the upper slope to water depths of c. 720 m (white arrow in Fig. 1a). The grounding pits have a mean depth of 8 m and a mean diameter of 280 m. The pits appear to be distributed randomly, with the highest intensity occurring in water depths of 410–670 m.

The South Sandwich Islands and associated seamounts constitute the volcanic arc of an active subduction system situated in the South Atlantic. We introduce a map of the bathymetry and geological setting of the South Sandwich Islands and the associated East Scotia Ridge back-arc spreading centre that consists of two sides: side 1, a regional overview of the volcanic arc, trench and back-arc, and side 2, detailed maps of the individual islands. Side 1 displays the bathymetry at scale 1:750 000 of the intra-oceanic, largely submarine South Sandwich arc, the back-arc system and other tectonic boundaries of the subduction system. Satellite images of the islands on side 2 are at scales of 1:50 000 and 1:25 000 with contours and main volcanological features indicated. These maps are the fi rst detailed topological and bathymetric maps of the area. The islands are entirely volcanic in origin, and most have been volcanically or fumarolically active in historic times. Many of the islands are ice-covered, and the map forms a baseline for future glaciological changes caused by volcanic activities and climate change. The back-arc spreading centre consists of nine segments, most of which have rift-like morphologies.

The Drake Passage is an oceanic gateway of about 850 km width located between South America and the Antarctic Peninsula that connects the southeastern Pacific and the southwestern Atlantic oceans and is an important gateway for mantle flow, oceanographic water masses, and migrations of biota. This gateway developed within the framework of geological evolution of the Scotia Arc. As a consequence of this and subsequent submarine processes, this region shows a varied physiography. The new detailed map in the Drake Passage region is mainly founded on a compilation of precise multibeam bathymetric data obtained on cruises between 1992 and 2014, and covers the area between parallels 52ºS and 63ºS and meridians 70ºW and 50ºW. The new map that we present is based in a DTM with 200 m cell resolution of the seafloor in Drake Passage that permits identification of the main seafloor features and the map includes additional useful geological information. This work constitutes an international cooperative effort and is part of IBCSO project (International Bathymetric Chart of the Southern Ocean), under the SCAR umbrella.

Multibeam data from the southern Weddell Sea, Antarctica show three submarine slides on the upper slope of the Crary Fan, a large Trough Mouth Fan offshore from the glacially calved Filchner cross-shelf trough. These slides are the first Quaternary examples to be documented on an Antarctic Trough Mouth Fan and provide evidence for rarely observed submarine mass wasting on the Antarctic continental margin. Their occurrence contrasts many other previously glaciated continental margins, where mass wasting is common. All submarine slides head at the shelf edge (~500 m water depth), with two styles of mass wasting observed. The first style is characterised by a complex and wide (~20 km long) headwall, with a relief of 60 m and coverage of ~800 km2. Large, tabular slabs are observed down slope of the headwall. Two slides follow the second style of mass wasting. This style is characterised by a small, narrow and steep scarp at the shelf edge with increasing slide width (maximum 6 km) down slope. No large sediment deposits or lobes are observed down slope of these slides, although this may be limited by data extent. The large-scale differences in slide occurrence along the Antarctic continental margin suggest a significant variation in slope and sedimentary processes, environmental characteristics and/or glacial dynamics. It is likely that the slides are influenced by failure of weak layers within the subsurface, which may have been affected by rapid sediment transport and mass flow generation at the shelf edge, as indicated by widespread debris flow deposits observed in subbottom profiler data on the Crary Fan.

The obvious reason for writing an Editorial at the start of this particular issue is to celebrate 150 years since the first publication of Geological Magazine. This is a long and continuous record of service to the scientific community and contribution to the geosciences. All those people who have been associated with the publication of the journal can be proud of it. I would especially like to acknowledge the efforts of the production teams over the years: behind the academic work of authors, referees and the editors stands a dedicated group of publishing staff, who ensure that the high publication standards of the journal are maintained. Thanks are also due to the authors who have contributed to papers in Geological Magazine to date. It is a daunting prospect to think of exactly how many different scientists have co-authored papers in the journal since 1864, and what combinations of evolution and revolution our science has seen in that time.

New multibeam bathymetric data from the southeastern Weddell Sea show significant differences in surface morphology of the outer continental shelf and slope between two adjacent cross-shelf troughs. These are the Filchner Trough and a smaller trough to the east we refer to as the ‘Halley Trough’. Multibeam bathymetric data, acoustic sub-bottom profiler and seismic data show major differences in the incidence and morphologies of submarine gullies, channel systems, submarine slides and iceberg scours, and in sediment deposition. These large-scale differences suggest significant variation in slope and sedimentary processes and in the environmental setting between the two troughs, leading to much greater deposition at the mouth of the Filchner Trough. Bedforms, including a terminal moraine and scalloped embayments on the outer shelf of the Halley Trough provide insight into the relative timing and extent of past ice-sheet grounding and point to grounded ice near to the shelf edge during the Late Quaternary. The new data reveal two large-scale submarine slides on the upper slope of the eastern Crary Fan, a trough mouth fan offshore from the Filchner Trough. Both slides head at the shelf edge (~ 500 m water depth), with the largest slide measuring 20 km wide and with an incision depth of 60 m. Multibeam and seismic data show elongate slabs on the seafloor surface of the mid-slope. The lack of a discernible sedimentary cover suggests that they were generated after the Last Glacial Maximum (LGM). This is unusual because post-LGM submarine slides are very rare on the Antarctic continental margin, and to our knowledge, no other post-LGM slides have been documented on an Antarctic trough mouth fan. Because the slides occur on a part of the continental slope where the deposition of glacial debris was greatest, we speculate that weaker, unconsolidated sedimentary layers within the subsurface are important for slide initiation here.

Understanding of Cretaceous plate motions, and closure of the global plate circuit, is hampered by the "Cretaceous Normal Superchron” (CNS) between 120 and 84 Ma, an interval of very stable geomagnetic field that produced no magnetic striping over the ocean floor. This coincided with eruption of several oceanic large igneous provinces (LIPs), huge outpourings of magma (> 100,000 km3) that created vast regions of volcanic and related rocks (Coffin and Eldholm, 1993), concentrated in time in what is called a superplume event, and associated with a global episode of plate reorganisation (Matthews et al., 2012). Lack of sea floor magnetic striping during the CNS has complicated the task of reconstructing plate motions in detail, leaving large uncertainties in the relative positions of continents, oceans, and the LIPs they bear. Perversely, prolonged stability of the geomagnetic field at these times means that sea floor magnetic striping, which is normally used to reconstruct plate motions, does not form when changes in plate motions can be at their greatest. 123 million years ago, one of the largest LIPs in Earth history was erupted in the palaeo-Pacific Ocean (Chandler et al., 2012; Taylor, 2006) at the beginning of the CNS, the 5 million km2 Ontong Java-Nui super-plateau (OJN; 2/3 the area of Australia). Shortly afterwards, as a result of the changes in palaeo- Pacific plate configuration associated with its formation, it is thought to have split into at least three component parts that are recognised today (e.g. Fig. 1) (Taylor, 2006), the Ontong-Java, Manihiki and Hikurangi plateaus (Fig. 1). 105 million years ago, still within the CNS, a global reorganisation of plate motions, associated with mountain building events on continental margins, was triggered by changes in subduction along the Gondwana margin in the vicinity of West Antarctica (Matthews et al., 2012). Matthews et al. (2012) presented two hypotheses for this to account for global plate reorganisation: 1)

Jurassic dykes of western Dronning Maud Land (Antarctica) form a minor component of the Karoo large igneous province. An extensive local dyke swarm intrudes Neoproterozoic gneisses and Jurassic syenite plutons on the margins of the Jutulstraumen palaeo rift in the Svedrupfjella region. The dykes were intruded in three distinct episodes (~204, ~176 and ~170 Ma). The 204 Ma dykes are overwhelmingly low-Ti, olivine tholeiites including some primitive (picritic) compositions (MgO >12 wt.%; Fe2O3 >12 wt.%; Cr >1000 ppm; Ni >600 ppm). This 204 Ma event precedes the main Karoo volcanic event by ~25 Ma, so any correlations to the wider province are difficult to make. However, it may record the earliest phase of rift activity along the Jutulstraumen. The 176 Ma dyke event is more intimately associated with the two syenite plutons. The dykes are alkaline (basanite/tephrite) and were small-degree melts from an enriched, locally derived source and underwent at least some degree of interaction with a syenitic contaminant. This ~176 Ma dyke event is widespread elsewhere in the Karoo (southern Africa and Dronning Maud Land). Later-stage (170 Ma) felsic (phonolite-comendite) dykes intrude the 176 Ma basanite-tephrite suite and represent the last phase of magmatic activity in the region.

The Jurassic Karoo large igneous province (LIP) of Antarctica, and its conjugate margin in southern Africa, is critical for investigating important questions about the relationship of basaltic LIPs to mantle plumes. Detailed aerogeophysical, structural, anisotropy of magnetic susceptibility (AMS), geochronological and geochemical investigations completed under the British Antarctic Survey’s MAMOG project have provided some of the answers. Across most of the area, magma volumes were small compared to those in southern Africa. Jurassic dikes intruding the Archean craton are sparse and the Jutulstraumen trough, a Jurassic rift, is interpreted, from aerogeophysical data, as largely amagmatic. The largest volumes of magma were emplaced along the margin of the craton and close to the Africa-Antarctica rift. Although dikes were emplaced by both vertical and horizontal flow, overwhelmingly magmas in Dronning Maud Land were locally derived, and not emplaced laterally from distant sources. Basaltic magmatism was protracted in Dronning Maud Land (several dike emplacement episodes between ~206 and 175 Ma), and the small magma volumes resulted in highly diverse magma compositions, including picrites and ferropicrites interpreted to have been derived from hot mantle in a mantle plume. The protracted magmatism before the locally ~177 Ma flood lava eruptions, and evidence for a radiating dike swarm, favor a model of mantle plume incubation for 20-30 million years before flood lava eruption.

The magma types belonging to the Gondwana large igneous province can be divided into two categories based on, respectively, their primitive mantle-like and fractionated Sm/Yb and Sr/Zr values, different Sr and Nd isotopic trends, and geographic affinity to the Weddell and Limpopo triple junctions. In the new grouping, the Ferrar magmas, the Karoo Central Area magmas, and the Kirwanveggen-Sembberget magmas from Dronning Maud Land are viewed as three major magmatic lineages generated at the Weddell triple junction. These Weddell group magmas were produced by voluminous low-pressure partial melting of possibly subduction-modified upper mantle and tended to be laterally transported over long distances. The Limpopo group magmas include the Karoo high-Ti magma types and various low- Ti types from Lebombo, Vestfjella, and Heimefrontfjella. They represent magmas that were produced at high pressure from an eclogite-bearing mantle source below the Kaapvaal craton. The distribution of the Limpopo group magmas was mainly confined within the rift valleys of the Limpopo triple junction. The chemically distinctive magma types probably reflect heterogeneities in the Weddell and Limpopo magma sources and lithospheric level differentiation within Archean (Limpopo group) and younger lithospheric terranes.

176Hf/177Hf isotopes provide information about the behaviour of so-called immobile elements in subduction environments. Early studies of Hf isotopes in subduction zones reached different conclusions regarding the mobility of high-field-strength elements during subduction-related processes. To test the behaviour of Hf during subduction, we have examined the young, intra-oceanic South Sandwich subduction system. Combined 176Hf/177Hf and trace element ratios reveal that Hf may behave as both immobile and mobile, depending upon the exact spatial relationship of the arc volcano to the slab. Throughout most of the arc, magmas show no detectable Hf transfer from the slab to the wedge, perhaps because enrichment of the wedge took place by Hf-deficient, fluid-dominated processes. On the basis of ΔεNd values, which describe the Nd isotope deviation from a local MORB-OIB array, we can discern that northern volcanoes of the arc require a source enriched by fluids that originated from the oceanic crust, whereas southern arc volcanoes have a source modified by a higher proportion of sediment-derived fluids. However, close to the southern slab edge and in rear-arc settings, arc magmas were derived from a source that had undergone Hf addition; we attribute this to element transfer via partial melts from sediment. This implies that Hf mobility from the slab is possible where temperatures are sufficiently high to induce sediment melting rather than fluid generation alone. The implication of this work, for the majority of the arc, is that sediment-derived fluids contribute to magmatism and that sediment-derived melt does not.

New airborne geophysical data reveal subglacial imprints of crustal growth of the Antarctic Peninsula by Mesozoic arc magmatism and terrane accretion along the paleo-Pacific margin of Gondwana. Potential field signatures indicate that the Antarctic Peninsula batholith is a composite magmatic arc terrane comprising two distinct arcs, separated by a >1500 km-long suture zone, similar to the Peninsular Ranges batholith in southern and Baja California. Aeromagnetic, aerogravity and geological data suggest that a mafic Early Cretaceous western arc was juxtaposed against a more felsic eastern arc which, in mid-Cretaceous times, was intruded by highly magnetic tonalitic/granodioritic plutons of island arc affinity. Suturing of the two arcs against the Gondwana margin caused the mid-Cretaceous Palmer Land orogenic event. Convergence and suturing may have been driven by two subduction zones or, alternatively, by a decrease in slab dip, leading to an inboard migration of the arc, as in California.

A suite of mafic dykes from the Underberg region of southern KwaZulu-Natal (South Africa) were intruded at 178 Ma, coincident in age with the major Okavango Dyke Swarm of Botswana, and also coincident with minor Karoo-related intrusions of the northern and central Lebombo. The dykes are all low-Ti-Zr tholeiites, they trend NW-SE and are presumed to continue into the Karoo central area of the Lesotho Highlands. In many respects, the Underberg dykes are similar to the majority of the low-Ti-Zr volcanic and subvolcanic intrusions of the Karoo; however, their 87Sr/86Sr and Nd isotope ratios are either ‘Ferrar-like’ (87Sr/86Sr 0·710; Nd < -3) or transitional between Karoo low-Ti-Zr and Ferrar low-Ti magmas. A potential Ferrar source for at least some of the Underberg dykes is supported by anisotropy of magnetic susceptibility analyses of the dyke suite, which demonstrate absolute flow direction from the SE to the NW, consistent with Gondwana reconstructions. The role of crustal contamination and combined fractional crystallization is also demonstrated to have played a key role in the petrogenesis of the Underberg dykes, involving a local upper crust contaminant. However, the composition of the ‘Ferrar-like’ dykes cannot be easily explained by AFC processes, but they do demonstrate that melting of a lithospheric mantle source enriched to a small degree by subduction-derived fluid was also important.

The chemistry of mafic volcanic rocks and minor intrusions erupted on continents can be used to define sub-continental asthenospheric and lithospheric mantle sources. Data have been collated from Antarctica and the Falkland Islands (adjacent in Gondwana) in order to identify lithospheric mantle sources beneath the continent. The lithosphere-derived magmas include lamproitic and some lamprophyric rocks and end-members in basaltic suites that are interpreted as mixtures of magmas from lithospheric and asthenospheric sources. The lithosphere-derived mafic rocks from Archaean to Middle Proterozoic cratonic and circumcratonic areas of East Antarctica have time-corrected εNd values of −20 to −3. This demands isolation of the LREE-enriched sources within pockets of stable sub-cratonic lithosphere for more than 1 Ga, consistent with the lithosphere thickness up to 250 km imaged by seismic tomography. In contrast, lithosphere-derived mafic rocks from Middle Proterozoic to Early Palaeozoic areas of West Antarctica, Victoria Land and the Falkland Islands that formed the Gondwana continental margin, have time-corrected εNd values of −3.6 to +3.5, implying more recent isolation from asthenosphere. In terms of mantle reservoirs, cratonic and circumcratonic areas trend toward EMI, with EMII possibly being a minor component. In contrast, Gondwana margin areas trend toward EMII, with EMI being, at most, a very minor component.