Showing papers on "Gondwana published in 2011"

Geological Evolution of Antarctica

Abstract: Preface Acknowledgements 1. Crustal development: the craton Crustal development: the transantarctic mountains Crustal development: 2. Weddell sea - Ross sea region Crustal development: 3. Gondwana break-up Crustal development: the Pacific margin Cenozoic palaeoenvironments Index.

Assembly and breakup of the core of Paleoproterozoic-Mesoproterozoic supercontinent Nuna

Abstract: Idealized conceptual models of supercontinent cyclicity must be tested against the geologic record using pre-Pangean reconstructions. We integrate tectonostratigraphic records and paleomagnetic data from Siberia, Laurentia, and Baltica to produce a quantitative reconstruction of the core of the Nuna supercontinent at 1.9–1.3 Ga. In our model, the present southern and eastern margins of Siberia juxtapose directly adjacent to, respectively, the arctic margin of Laurentia and the Uralian margin of Baltica. Consistent tectonostratigraphic records of the three cratons collectively indicate the history of Nuna9s assembly and breakup. According to this reconstruction, the late Mesoproterozoic transition from Nuna to Rodinia appears to have been much less dramatic than the subsequent late Neoproterozoic transition from Rodinia to Gondwana.

Palaeozoic–Mesozoic history of SE Asia

Abstract: SE Asia comprises a collage of Gondwana-derived continental blocks assembled by the closure of multiple Tethyan and back-arc ocean basins now represented by suture zones. Two major biogeographical boundaries, the Late Palaeozoic Gondwana–Cathaysia divide and the Cenozoic-Recent Australia–Asia divide (Wallace Line) are present. Palaeozoic and Mesozoic evolution involved the rifting and separation of three collages of continental terranes from eastern Gondwana and the opening and closure of three successive ocean basins, the PalaeoTethys (Devonian–Triassic), Meso-Tethys (Permian–Cretaceous) and Ceno-Tethys (Late Triassic–Cenozoic). This led to the opening and closing of ocean gateways and provision of shallow-marine and terrestrial land bridges and stepping-stones for biotic migration. The SE Asia core (Sundaland) comprises a western Sibumasu block, an eastern Indochina–East Malaya block, and the Sukhothai Island Arc terrane between. The Jinghong, Nan-Uttaradit and Sra Kaeo sutures represent the Sukhothai closed back-arc basin. The Palaeo-Tethys is represented by the Changning-Menglian, Chiang Mai/Inthanon and Bentong-Raub suture zones. The West Sumatra and West Burma blocks were accreted to the Sundaland core in the Late Permian– Early Triassic. SW Borneo and/or East Java–West Sulawesi are now identified as the missing ‘Argoland’ that separated from NW Australia in the Jurassic and accreted to SE Sundaland in the Cretaceous. SE Asia is located at the zone of convergence between the ESE moving Eurasia Plate, the NE moving Indian and Australian Plates and the ENE moving Philippine Plate (Fig. 1). SE Asia and adjoining regions comprise a complex collage of continental blocks, volcanic arcs, and suture zones that represent the closed remnants of ocean basins (including back-arc basins). The continental blocks of the region were derived from the margin of eastern Gondwana as three successive continental strips or collages of continental blocks that separated in the Devonian, Early Permian and Triassic– Jurassic and which then assembled during the Late Palaeozoic to Cenozoic to form present day East and SE Asia (Metcalfe 2005). Global, regional and local Palaeozoic–Mesozoic tectonic evolution resulted in changes to continent– ocean configurations, dramatic changes in relief both on land and in the seas, and changes in palaeo-ocean currents, including the opening and closing of oceanic gateways. The significant effect on ocean circulation caused by ocean gateway closure/ opening is well documented (e.g. Von der Heydt & Dijkstra 2006, 2008). The changes in continent– ocean, land–sea, relief, and ocean current patterns are fundamental factors leading to both global and regional climate-change and to important changes in biogeographical patterns. Changes in biogeographical barriers and bridges caused by geological evolution and consequent climate-change have also influenced the course of migration, dispersal, isolation and evolution of biota, both globally and in SE Asia. This paper provides an overview of the tectonic framework, and Palaeozoic and Mesozoic geological evolution and palaeogeography of SE Asia and adjacent regions as a background to and to underpin studies of the Indonesian Throughflow Gateway and the distribution and evolution of biota in the region. Geological and tectonic framework of SE Asia and adjacent regions Mainland East and SE Asia comprises a giant ‘jigsaw puzzle’ of continental blocks, volcanic arc terranes, suture zones (remnants/sites of destroyed ocean basins) and accreted continental crust (Figs 2 & 3). From: Hall, R., Cottam, M. A. & Wilson, M. E. J. (eds) The SE Asian Gateway: History and Tectonics of the Australia–Asia Collision. Geological Society, London, Special Publications, 355, 7–35. DOI: 10.1144/SP355.2 0305-8719/11/$15.00 # The Geological Society of London 2011. Continental blocks of SE Asia The principal continental blocks located in mainland SE Asia (Fig. 2) have been identified and established over the last two decades (e.g. Metcalfe 1984, 1986, 1988, 1990, 1996a, 1998, 2002, 2006) and include the South China block, the Indochina–East Malaya block(s), the Sibumasu block, West Burma block and SW Borneo block (Fig. 3). More recently, the West Sumatra block has been established outboard of Sibumasu in SW Sumatra (Barber & Crow 2003, 2009; Barber et al. 2005) and a volcanic arc terrane is now identified, sandwiched between Sibumasu and Indochina–East Malaya (Sone & Metcalfe 2008). A series of smaller continental blocks are identified in eastern (maritime) SE Asia and these were accreted to the mainland core of SE Asia in the Mesozoic– Cenozoic. The continental terranes of SE Asia and adjacent regions are here categorized into six types based on their specific origins, times of rifting and separation from Gondwana, and amalgamation/ accretion to form SE Asia. These are discussed below and the suture zones between them are described separately. Continental blocks derived from Gondwana

Tectonic history of the western Tethys since the Late Triassic

Abstract: The tectonic history of the western Tethys since the Late Triassic is illustrated through a set of computer-generated plate reconstructions, which are based on a rigorous plate motions model of this region. The model is constrained by the Atlantic plate kinematics and on-land geologic evidence and defines 13 tectonic phases, spanning the time interval from the late Ladinian (230 Ma) to the present. The kinematics associated with the Late Triassic western Tethyan rifts produced the detachment of a large composite fragment from the northern margin of Gondwana. It can be considered as the eastern propagation of the central Pangea breakup. During the Early Jurassic these rift zones became inactive, while new zones of extension formed along the southern margin of Eurasia, the eastern margin of Iberia, and within the rifted northern Gondwana fragment itself. Plate motions associated with the first two extensional centers can still be considered as an eastern branch of the central Atlantic plate kinematics. Conversely, the kinematic parameters of the latter rift result from the composition of the Euler rotation describing the central Pangea breakup and the Euler pole of closure of the paleo–Tethys ocean. The Late Triassic–Early Jurassic rifting phases determined the formation of a number of independent microplates at the interface between Africa and Eurasia. Starting from the Early Cretaceous, convergence between Africa and Eurasia triggered further deformation within the dispersed continental fragments and the formation of backarc basins at the active margins, ultimately leading to an increase in the number of tectonic elements that were moving independently in the western Tethyan region during the Late Cretaceous and the Cenozoic. The proposed tectonic evolution of the western Tethys area is compatible with both global-scale plate kinematics and geological constraints from on-land data observed across the present-day mosaic of displaced terranes surrounding the Mediterranean region.

Geology of the Caucasus: A Review

Abstract: Th e structure and geological history of the Caucasus are largely determined by its position between the still- converging Eurasian and Africa-Arabian lithospheric plates, within a wide zone of continental collision. During the Late Proterozoic-Early Cenozoic, the region belonged to the Tethys Ocean and its Eurasian and Africa-Arabian margins where there existed a system of island arcs, intra-arc rift s, back-arc basins characteristic of the pre-collisional stage of its evolution of the region. Th e region, along with other fragments that are now exposed in the Upper Precambrian- Cambrian crystalline basement of the Alpine orogenic belt, was separated from western Gondwana during the Early Palaeozoic as a result of back-arc rift ing above a south-dipping subduction zone. Continued rift ing and seafl oor spreading produced the Palaeotethys Ocean in the wake of northward migrating peri-Gondwanan terranes. Th e displacement of the Caucasian and other peri-Gondwanan terranes to the southern margin of Eurasia was completed by ~350 Ma. Widespread emplacement of microcline granite plutons along the active continental margin of southern Eurasia during 330-280 Ma occurred above a north-dipping Palaeotethyan subduction zone. However, Variscan and Eo-Cimmerian-Early Alpine events did not lead to the complete closing of the Palaeozoic Ocean. Th

The evolution of Patagonian climate and vegetation from the Mesozoic to the present

Abstract: In this review, Patagonian phytogeographical patterns are analysed from a global and evolutionary perspective that takes into account aspects from the geology, climatology and plant evolution. The biomes contained within the different climatic belts are inferred through time for the southwestern Gondwana supercontinent on the basis of palaeogeographical reconstructions, climate-sensitive rocks and plant distribution. Some current plant components of Patagonia can be traced back to early Mesozoic times, to the Triassic and Jurassic mesophytic floras. The main features of the Cretaceous and Palaeogene Patagonian floras are described and compared with other Gondwanic areas that shared, at the time, more plant components than they do today. The Neogene floras are analysed in relation to the rise of the Andes and the global climatic cooling, which differentiated the Andean and the Extra-Andean regions, and ended in the modern cool-temperate Andean forest and the arid steppe.

Neoproterozoic geodynamic evolution of SW-Gondwana: a southern African perspective

Abstract: Our current understanding of the tectonic history of the principal Pan-African orogenic belts in southwestern Africa, reaching from the West Congo Belt in the north to the Lufilian/Zambezi, Kaoko, Damara, Gariep and finally the Saldania Belt in the south, is briefly summarized. On that basis, possible links with tectono-stratigraphic units and major structures on the eastern side of the Rio de la Plata Craton are suggested, and a revised geodynamic model for the amalgamation of SW-Gondwana is proposed. The Rio de la Plata and Kalahari Cratons are considered to have become juxtaposed already by the end of the Mesoproterozoic. Early Neoproterozoic rifting led to the fragmentation of the northwestern (in today’s coordinates) Kalahari Craton and the splitting off of several small cratonic blocks. The largest of these ex-Kalahari cratonic fragments is probably the Angola Block. Smaller fragments include the Luis Alves and Curitiba microplates in eastern Brazil, several basement inliers within the Damara Belt, and an elongate fragment off the western margin, named Arachania. The main suture between the Kalahari and the Congo-Sao Francisco Cratons is suspected to be hidden beneath younger cover between the West Congo Belt and the Lufilian/Zambezi Belts and probably continues westwards via the Cabo Frio Terrane into the Goias magmatic arc along the Brasilia Belt. Many of the rift grabens that separated the various former Kalahari cratonic fragments did not evolve into oceanic basins, such as the Northern Nosib Rift in the Damara Belt and the Gariep rift basin. Following latest Cryogenian/early Ediacaran closure of the Brazilides Ocean between the Rio de la Plata Craton and the westernmost fragment of the Kalahari Craton, the latter, Arachania, became the locus of a more than 1,000-km-long continental magmatic arc, the Cuchilla Dionisio-Pelotas Arc. A correspondingly long back-arc basin (Marmora Basin) on the eastern flank of that arc is recognized, remnants of which are found in the Marmora Terrane—the largest accumulation of oceanic crustal material known from any of the Pan-African orogenic belts in the region. Corresponding foredeep deposits that emerged from the late Ediacaran closure of this back-arc basin are well preserved in the southern areas, i.e. the Punta del Este Terrane, the Marmora Terrane and the Tygerberg Terrane. Further to the north, present erosion levels correspond with much deeper crustal sections and comparable deposits are not preserved anymore. Closure of the Brazilides Ocean, and in consequence of the Marmora back-arc basin, resulted from a change in the Rio de la Plata plate motion when the Iapetus Ocean opened between the latter and Laurentia towards the end of the Ediacaran. Later break-up of Gondwana and opening of the modern South Atlantic would have followed largely along the axis of the Marmora back-arc basin and not along major continental sutures.

Orogenesis without collision: Stabilizing the Terra Australis accretionary orogen, eastern Australia

Abstract: The Neoproterozoic to end-Paleozoic Terra Australis orogen extended along the Gondwana margin of the paleo–Pacific Ocean, and it now provides a detailed record of orogenic activity and continental stabilization within an ongoing convergent, accretionary plate margin. New geochronological data from end-Paleozoic plutonic and volcanic rocks associated with the Gondwanide orogeny in the New England region of eastern Australia, integrated with information on the nature and timing of associated sedimentation, deformation, and metamorphism, allow resolution of a high-fidelity record of orogenesis. At the end of the Carboniferous, around 305 Ma, convergent margin magmatism, which had been active along the western margin of the New England region, terminated and was followed by a short pulse of regional compressional deformation and metamorphism, marking the commencement of the Tablelands phase of Gondwanide orogenesis. Deformation was almost immediately followed by the onset of clastic sedimentation and local calc-alkaline volcanism, dated at 293 Ma, in the extensional Barnard Basin. Emplacement of the two New England S-type granitic suites, the Bundarra and the Hillgrove suites, along with localized high-temperature, low-pressure metamorphism, was essentially contemporaneous, ranging in age from 296 to 288 Ma, and overlapped in time with I-type magmatism and the switch from regional compression to extension and Barnard Basin rifting. The Hunter-Bowen phase of the Gondwanide orogeny commenced with contractional deformation, resulting in termination of sedimentation in the Barnard Basin and regional deformation and metamorphism across New England and into the Sydney and Gunnedah basins to the west at around 265–260 Ma. Contractional loading of the Sydney and Gunnedah basins resulted in their conversion from extensional to foreland basins, which received ongoing pulses of sediment from the New England orogenic welt until 230 Ma. The Hunter-Bowen phase was associated with widespread I-type plutonism and volcanic activity in New England that ceased around 230 Ma, marking the termination of Gondwanide orogenesis. Orogenesis occurred in an evolving convergent plate-margin setting. S- and I-type magmatic activity ranging in age from ca. 300 to 230 Ma represents a stepping out of arc magmatism from the western margin of New England (prior to 305 Ma) into the preexisting arc-trench gap. There is no evidence that deformation was related to the collision of the convergent margin with a major lithospheric mass, and the widespread development of extensional basins in the eastern third of Australia in the Early Permian indicates control by phenomena acting on a continental scale, probably changing plate kinematics associated with the amalgamation of Pangea.

Progressive Cenozoic cooling and the demise of Antarctica’s last refugium

Abstract: The Antarctic Peninsula is considered to be the last region of Antarctica to have been fully glaciated as a result of Cenozoic climatic cooling As such, it was likely the last refugium for plants and animals that had inhabited the continent since it separated from the Gondwana supercontinent Drill cores and seismic data acquired during two cruises (SHALDRIL I and II) in the northernmost Peninsula region yield a record that, when combined with existing data, indicates progressive cooling and associated changes in terrestrial vegetation over the course of the past 37 million years Mountain glaciation began in the latest Eocene (approximately 37–34 Ma), contemporaneous with glaciation elsewhere on the continent and a reduction in atmospheric CO2 concentrations This climate cooling was accompanied by a decrease in diversity of the angiosperm-dominated vegetation that inhabited the northern peninsula during the Eocene A mosaic of southern beech and conifer-dominated woodlands and tundra continued to occupy the region during the Oligocene (approximately 34–23 Ma) By the middle Miocene (approximately 16–116 Ma), localized pockets of limited tundra still existed at least until 128 Ma The transition from temperate, alpine glaciation to a dynamic, polythermal ice sheet took place during the middle Miocene The northernmost Peninsula was overridden by an ice sheet in the early Pliocene (approximately 53–36 Ma) The long cooling history of the peninsula is consistent with the extended timescales of tectonic evolution of the Antarctic margin, involving the opening of ocean passageways and associated establishment of circumpolar circulation

Full‐fit, palinspastic reconstruction of the conjugate Australian‐Antarctic margins

Abstract: [1] Despite decades of study the prerift configuration and early rifting history between Australia and Antarctica is not well established. The plate boundary system during the Cretaceous includes the evolving Kerguelen–Broken Ridge Large Igneous Province in the west as well as the conjugate passive and transform margin segments of the Australian and Antarctic continents. Previous rigid plate reconstruction models have highlighted the difficulty in satisfying all the available observations within a single coherent reconstruction history. We investigate a range of scenarios for the early rifting history of these plates by developing a deforming plate model for this conjugate margin pair. Potential field data are used to define the boundaries of stretched continental crust on a regional scale. Integrating crustal thickness along tectonic flow lines provides an estimate of the prerift location of the continental plate boundary. We then use the prerift plate boundary positions, along with additional constraints from geological structures and large igneous provinces within the same Australian and Antarctic plate system, to compute “full-fit” poles of rotation for Australia relative to Antarctica. Our preferred model implies that the Leeuwin and Vincennes Fracture Zones are conjugate features within Gondwana, but that the direction of initial opening between Australia and Antarctica does not follow the orientation of these features; rather, the geometry of these features is likely related to the earlier rifting of India away from Australia-Antarctica. Previous full-fit reconstructions, based on qualitative estimates of continental margin overlaps, generally yield a tighter fit than our preferred reconstruction based on palinspastic margin restoration.

Tectonostratigraphy of the Lesser Himalaya of Bhutan: Implications for the along-strike stratigraphic continuity of the northern Indian margin

Abstract: New mapping in eastern Bhutan, in conjunction with U-Pb detrital zircon and δ 13 C data, defi nes Lesser Himalayan tectonostratigraphy. The Daling-Shumar Group, 2–6 km of quartzite (Shumar Formation) overlain by 3 km of schist (Daling Formation), contains ~1.8–1.9 Ga intrusive orthogneiss bodies and youngest detrital zircon peaks, indicating a Paleoproterozoic deposition age. The Jaishidanda Formation, 0.5– 1.7 km of garnet-biotite schist and quartzite, stratigraphically overlies the Daling Formation beneath the Main Central thrust, and yields youngest detrital zircon peaks ranging from ~0.8–1.0 Ga to ca. 475 Ma, indicating a Neoproterozoic–Ordovician(?) deposition age range. The Baxa Group, 2–3 km of quartzite, phyllite, and dolomite, overlies the DalingShumar Group in the foreland, and yields ca. 0.9 Ga to ca. 520 Ma youngest detrital zircon peaks, indicating a Neoproterozoic– Cambrian(?) deposition age range. Baxa dolo mite overlying quartzite containing ca. 525 Ma detrital zircons yielded δ 13 C values between +3‰ and +6‰, suggesting deposition during an Early Cambrian positive δ 13 C excursion. Above the Baxa Group, the 2–3 km thick Diuri Formation diamictite yielded a ca. 390 Ma youngest detrital zircon peak, suggesting correlation with the late Paleo zoic Gondwana supercontinent glaciation. Finally, the Permian Gondwana succession consists of sandstone, siltstone, shale, and coal. Our deposition age data from Bhutan: (1) reinforce suggestions that Paleoproterozoic (~1.8–1.9 Ga) Lesser Himalayan deposition was continuous along the entire northern Indian margin; (2) show a likely east ward continuation of a Permian over Cambrian unconformity in the Lesser Himalayan section identifi ed in Nepal and northwest India; and (3) indicate temporal overlap between Neoproterozoic–Paleozoic Lesser Himalayan (proximal) and Greater Himalayan–Tethyan Himalayan (distal) deposition.

Unraveling the New England orocline, east Gondwana accretionary margin

Abstract: [1] The New England orocline lies within the Eastern Australian segment of the Terra Australis accretionary orogen and developed during the late Paleozoic to early Mesozoic Gondwanide Orogeny (310–230 Ma) that extended along the Pacific margin of the Gondwana supercontinent. The orocline deformed a pre‐Permian arc assemblage consisting of a western magmatic arc, an adjoining forearc basin and an eastern subduction complex. The orocline is doubly vergent with the southern and northern segments displaying counter‐clockwise and clockwise rotation, respectively, and this has led to contrasting models of formation. We resolve these conflicting models with one that involves buckling of the arc system about a vertical axis during progressive northward translation of the southern segment of the arc system against the northern segment, which is pinned relative to cratonic Gondwana. Paleomagnetic data are consistent with this model and show that an alternative model involving southward motion of the northern segment relative to the southern segment and cratonic Gondwana is not permissible. The timing of the final stage of orocline formation (∼270–265 Ma) overlaps with a major gap in magmatic activity along this segment of the Gondwana margin, suggesting that northward motion and orocline formation were driven by a change from orthogonal to oblique convergence and coupling between the Gondwana and Pacific plates.

Multiple accretion at the eastern margin of the Rio de la Plata craton: the prolonged Brasiliano orogeny in southernmost Brazil

Abstract: The Neoproterozoic-Eoplalaeozoic Brasiliano orogeny at the eastern margin of the Rio de la Plata craton in southernmost Brazil and Uruguay comprises a complex tectonic history over 300 million years. The southern Brazilian Shield consists of a number of tectono-stratigraphic units and terranes. The Sao Gabriel block in the west is characterized by c.760–690 Ma supracrustal rocks and calc-alkaline orthogneisses including relics of older, c. 880 Ma old igneous rocks. Both igneous and metasedimentary rocks have positive eNd(t) values and Neoproterozoic TDM model ages; they formed in magmatic arc settings with only minor input of older crustal sources. A trondhjemite from the Sao Gabriel block intruding dioritc and tonalitic gneisses during the late stages of deformation (D3) yield an U–Pb zircon age (LA-ICP-MS) of 701 ± 10 Ma giving the approximate minimum age of the Sao Gabriel accretionary event. The Encantadas block further east, containing the supracrustal Porongos belt and the Pelotas batholith, is in contrast characterized by reworking of Neoarchean to Palaeoproterozoic crust. The 789 ± 7 Ma zircon age of a metarhyolite intercalated with the metasedimentary succession of the Porongos belt provides a time marker for the basin formation. Zircons of a sample from tonalitic gneisses, constituting the Palaeoproterozoic basement of the Porongos belt, form a cluster at 2,234 ± 28 Ma, interpreted as the tonalite crystallization age. Zircon rims show ages of 2,100–2,000 Ma interpreted as related to a Palaeoproterozoic metamorphic event. The Porongos basin formed on thinned continental crust in an extensional or transtensional regime between c. 800–700 Ma. The absence of input from Neoproterozoic juvenile sources into the Porongos basin strongly indicates that the Encantadas and Sao Gabriel blocks were separated terranes that became juxtaposed next to each other during the Brasiliano accretional events. The tectonic evolution comprises two episodes of magmatic arc accretion to the eastern margin of the Rio de la Plata craton, (i) accretion of an intra-oceanic arc at c. 880 Ma (Passinho event) and (ii) accretion of the 760–700 Ma Cambai/Vila Nova magmatic arc (Sao Gabriel event). The latter event also includes the collision of the Encantadas block with the Rio de la Plata craton to the west. Collision and crustal thickening was followed by sinistral shear along SW–NE-trending orogen-parallel crustal-scale shear zones that can be traced from southern Brazil to Uruguay and have been active between 660 and 590 Ma. Voluminous granitic magmatism in the Pelotas batholith spatially related to shear zones is interpreted as late- to post-orogenic magmatism, possibly assisted by lithospheric delamination. It marks the transition to the post-orogenic molasse stage. Localized deformation by reactivation of preexisting shear zones continued until c. 530 Ma and can be assigned to final stages of the amalgamation of West Gondwana.

Tectonic escape of a crustal fragment during the closure of the Rheic Ocean: U–Pb detrital zircon data from the Late Palaeozoic Pulo do Lobo and South Portuguese zones, southern Iberia

Abstract: The Pulo do Lobo Zone, which crops out immediately north of the allochthonous South Portuguese Zone in southern Iberia, is classically interpreted as a polydeformed accretionary complex developed along the southern margin of the Gondwanan parautochthon (Ossa–Morena Zone), during the late Palaeozoic closure of the Rheic Ocean. This closure was a major event during the amalgamation of Pangaea. U–Pb laser ablation inductively coupled mass spectrometry dating of detrital zircons from late Palaeozoic Devono-Carboniferous clastic units in the South Portuguese Zone and Pulo do Lobo Zone yield contrasting age populations and attest to the exotic nature of both zones. Detrital zircons from the South Portuguese Zone display populations typical of detritus derived from either Gondwana (Ossa–Morena Zone), or peri-Gondwanan terranes. In contrast, rocks from the Pulo do Lobo Zone contain populations consistent with derivation from Baltica, Laurentia or recycled early Silurian deposits along the Laurentian margin. An example of one such deposit is the Southern Uplands terrane of the British Caledonides. Taken together, these data can be reconciled by a model involving tectonic transport of a crustal fragment that was laterally equivalent to the Southern Uplands terrane between the allochthonous South Portuguese Zone and Gondwana as a result of an early Devonian collision between an Iberian indenter with Laurussia. Supplementary material: U–Pb data tables, concordia diagrams, methods and representative back-scattered electron images are available at http://www.geolsoc.org.uk/SUP18441.