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Continental fragment

A continental fragment, also known as a microcontinent in some contexts, is a discrete piece of continental lithosphere that has detached from a larger continental mass through tectonic extension and breakup, typically remaining connected via thinned crust in early stages or becoming fully isolated and surrounded by oceanic lithosphere.^[1] These fragments are characterized by continental crustal thickness (often 10–30 km or more), distinct from the thinner oceanic crust, and they play a key role in plate tectonics by influencing subduction dynamics and continental margin evolution.^[1] Unlike full continents, such as Zealandia—which spans 4.9 million km² and maintains coherent geological provinces—continental fragments are smaller and often result from inherited structural weaknesses that facilitate rifting.^[2] The formation of continental fragments primarily occurs in subduction settings where rotational stresses from trench retreat and slab dynamics exploit pre-existing weak zones in the lithosphere, such as ancient suture lines or rheological contrasts with viscosity differences of at least one order of magnitude.^[1] This process is enhanced by narrow weak zones (e.g., ~66 km wide) that promote efficient extension, leading to back-arc basin development and partial detachment from the parent continent.^[1] In divergent settings, fragments can also arise from failed rifts or spreading center jumps, as seen in passive continental margins where oceanic crust intrudes between separating blocks.^[1] Notable examples include the Seychelles microcontinent in the Indian Ocean, which separated from the Indian plate during the breakup of Gondwana around 65–84 million years ago and is now fully surrounded by oceanic crust; the Jan Mayen microcontinent in the North Atlantic, formed during Cenozoic rifting between Greenland and Norway; and the Corsica-Sardinia block in the Mediterranean, a fragment still linked to Europe via extended crust.^[1] Other instances, such as the Lomonosov Ridge in the Arctic Ocean, represent elongated fragments that transect oceanic basins, preserving ancient continental signatures amid polar ice.^[3] These features highlight the fragmented nature of continental evolution, contributing to global tectonics, resource potential (e.g., hydrocarbons), and paleogeographic reconstructions.^[3]

Definition and Characteristics

Definition

A continental fragment is a piece of continental crust that has rifted off from a larger continental mass, often initially remaining connected via thinned crust and potentially becoming a fully isolated block surrounded by oceanic crust. These fragments often manifest as landmasses, elevated plateaus, or submerged features within ocean basins.^[4]^[1] To understand continental fragments, it is essential to distinguish continental crust from oceanic crust: the former is thicker, averaging 30 to 50 kilometers, less dense at about 2.7 g/cm³, and composed primarily of felsic rocks such as granite, while oceanic crust is thinner at 5 to 10 kilometers, denser at around 2.9 g/cm³, and dominated by mafic basaltic rocks. This compositional difference allows continental fragments to "float" higher in the mantle compared to surrounding oceanic material, often leading to their emergence as topographic highs.^[5]^[6] The term "continental fragment" is partly synonymous with "microcontinent," with the latter specifically denoting fully isolated blocks surrounded by oceanic crust, while fragments may include those still connected via thinned continental lithosphere. Continental fragments are typically smaller than full continents but larger than typical oceanic islands or seamounts, with areas often ranging from 10,000 to 100,000 km².^[1]^[4] Their continental affinity is confirmed by diagnostic rock types like granite and a crustal thickness intermediate between oceanic and main continental values.^[5] In scale, continental fragments are comparable to island groups or seamount chains but differ in their geological origin and composition, primarily forming through rifting that separates them from parent continents.^[1]

Key Geological Features

Continental fragments are characterized by their predominantly felsic composition, consisting primarily of rocks such as granites and gneisses, which contribute to their low average density of ~2.7 g/cm³.^[7]^[5] This buoyancy contrasts sharply with the surrounding mafic oceanic crust, which has a higher density of approximately 2.9 g/cm³ and is composed mainly of basalts and gabbros.^[5] Additionally, these fragments possess relatively thick crusts, typically 20–40 km in depth, far exceeding the 5–10 km thickness of oceanic crust.^[7]^[8] Structurally, continental fragments are often delimited by normal faults inherited from initial rifting, which define their boundaries and facilitate their isolation.^[9] These structures may incorporate rift basins filled with sediments, volcanic arcs from associated magmatism, or overlying sedimentary layers up to several kilometers thick.^[10] Due to their lower density and isostatic equilibrium, fragments exhibit notable elevation variations, commonly forming plateaus that rise 1–2 km above the adjacent seafloor, creating shallower bathymetric features compared to typical oceanic depths.^[7] Identification of continental fragments relies on several geophysical and geochemical techniques. Seismic profiling reveals their distinctive crustal thickness and velocity structures, distinguishing them from thinner oceanic layers.^[7] Geochemical analysis detects continental signatures, such as elevated silica content (>65% SiO₂ in felsic rocks) and stable isotope ratios (e.g., Nd and Sr isotopes indicative of ancient crustal sources).^[10] Magnetic anomalies further aid detection by highlighting the presence of continental basement rocks with contrasting magnetic properties to oceanic lithosphere. Recent examples include the 2024 identification of the Davis Strait proto-microcontinent between Greenland and Canada using integrated seismic profiling and gravity data.^[11] The evolutionary stages of continental fragments begin with proto-fragments during early rifting, where extension thins and segments the continental lithosphere.^[10] These progress to mature isolated blocks fully detached and surrounded by oceanic crust, maintaining structural integrity over geological time.^[7] Eventually, many fragments may accrete to other continental margins through tectonic processes, incorporating into larger landmasses.^[10]

Formation Mechanisms

Rifting and Extension Processes

Continental rifting initiates with a phase of initial extension, during which the lithosphere undergoes thinning primarily through the development of normal faults that accommodate extensional deformation and form subsiding rift basins. This stage involves distributed faulting across the continental crust, leading to crustal thicknesses reduced by factors of up to 50% in some systems. As extension progresses, the process transitions to continental breakup, characterized by focused strain and magma intrusion from the asthenosphere, which intrudes the lower crust and eventually forms new oceanic crust at the rift axis. The final drift stage follows successful breakup, where the detached continental fragment becomes isolated as the newly formed plates diverge, often accompanied by thermal subsidence and the onset of seafloor spreading.^[12] The driving forces behind these rifting stages primarily involve mantle plumes and far-field tectonic stresses. Mantle plumes induce upwelling of hot asthenospheric material, which weakens the lithosphere through thermal erosion and magmatic intrusions, thereby localizing extension and enhancing rift propagation; for instance, plumes have been linked to the rapid maturation of rifts like the East African Rift.^[13] Concurrently, far-field stresses arising from distant plate boundary forces, such as slab pull or continental collisions, impose tensional forces that pull the continents apart, with magnitudes up to several tens of teranewtons per meter sufficient to overcome lithospheric resistance in weakened zones.^[13] Analogue and numerical models provide insights into the mechanics of rifting and fragment detachment. Laboratory experiments using scaled brittle-viscous multilayer setups simulate the "unzipping" of continental lithosphere, revealing how pre-existing weaknesses and strain localization lead to progressive rift propagation and fault interactions that mimic natural systems.^[14] Numerical thermo-mechanical models further demonstrate that asymmetric rifting, driven by oblique extension or rheological contrasts, results in differential thinning and the stranding of continental fragments, as seen in simulations of hyper-extended margins where one side experiences greater crustal excision.^[15] Geophysical evidence supports these processes through observations of thinned crust during extension. Gravity anomalies, often negative due to isostatic compensation from crustal unloading, and elevated heat flow patterns (typically 60–90 mW/m² in active rifts) indicate lithospheric thinning and asthenospheric upwelling; for example, in the southern Rio Grande rift, such anomalies align with extension factors of 1.1–1.5, reflecting 10–30% crustal reduction.^[16] In broader contexts, like the East African Rift, integrated seismic and gravity data reveal extension factors of 1.5–3, underscoring the scale of deformation required for fragment isolation.^[13]

Role of Subduction and Plate Relocation

Subduction zones play a pivotal role in the isolation of continental fragments by driving dynamic processes that extend and detach portions of continental crust, particularly through slab pull and rollback mechanisms. Slab pull, exerted by the negative buoyancy of the descending oceanic lithosphere, initiates trench retreat, which in turn induces extension in the overriding plate, often forming back-arc basins where slivers of continental crust can detach along weak zones.^[7] Rollback exacerbates this by causing rotational stresses that localize deformation, leading to the breakup of continental margins in orogenic belts; for instance, in the Mediterranean, rollback of the Apennines slab contributed to the detachment of the Corsica-Sardinia block around 21 million years ago, where back-arc extension reached up to 1,800% in narrow weak zones with viscosity contrasts of at least one order of magnitude.^[7] Plate boundary relocation further facilitates fragment isolation by shifting subduction zones or transform faults, effectively stranding continental blocks in oceanic domains. Jumps in subduction hinges, such as the relocation from the Liguro-Provençal basin to the Tyrrhenian basin approximately 10 million years ago, occur when slab tearing or differential retreat isolates blocks, often inheriting pre-existing structures like ancient sutures that act as reactivation sites for extension.^[7] These relocations contrast with passive rifting by incorporating active subduction forces that amplify isolation through rapid trench migration rates of up to 1.6 cm/year.^[7] In subduction settings, structural inheritance from prior tectonic events significantly influences fragment formation by providing zones of weakness that guide deformation. Weak structures, such as sutures from ancient collisions or rifted margins, lower the viscosity threshold for breakup, enabling delamination where portions of the overriding lithosphere peel away due to slab-induced stresses, or buckling of the subducting slab upon reaching the 660 km discontinuity, which redirects forces to promote upper-plate extension.^[7] System evolution, including slab rotation and tearing, further enhances this by creating asymmetric extension patterns that detach continental slivers, as seen in numerical models where inherited heterogeneities increase fragmentation efficiency by localizing strain in zones as narrow as 66 km.^[7] Numerical models of subduction dynamics demonstrate how these processes amplify continental fragmentation beyond simple extension, with two- and three-dimensional simulations showing that rotational back-arc stresses, combined with a continental indenter, produce basins up to 650 km wide and detach fragments through viscosity contrasts, distinct from the uniform thinning in passive margin rifting.^[7] These models, incorporating realistic rheologies, reveal that slab rollback velocities of 0.6 cm/year and angles of -15° replicate observed fragment isolation, underscoring the role of convergent margins in generating slivers that become isolated microcontinents.^[7]

Historical Context

Involvement in Supercontinent Cycles

Continental fragments play a pivotal role in the supercontinent cycles, which describe the periodic assembly and disassembly of Earth's landmasses driven by plate tectonics. These cycles are closely tied to the Wilson Cycle, a conceptual framework outlining the lifecycle of ocean basins through phases of rifting, drifting, and collision. During the rifting phase, extensional forces fragment supercontinents into smaller continental blocks, initiating the formation of new ocean basins via seafloor spreading. As continents drift apart, these fragments migrate independently, potentially re-accreting during later collision phases when subduction zones converge and orogenic belts form along their margins. The process repeats approximately every 300–500 million years, with fragments serving as the dispersed components that are later reassembled into new supercontinents.^[17] Fragments from the breakup of Rodinia (~1.1–0.75 Ga) were incorporated into Gondwana (~650–530 Ma), which contributed to the formation of Pangea during the late Paleozoic era through successive collisional events. This fragmentation and reassembly reshape continental configurations and influence global environmental dynamics, such as by altering atmospheric CO₂ levels through enhanced weathering during assembly and increased volcanism during breakup, which affects long-term climate variability via changes in ocean circulation and nutrient distribution.^[18]^[19] Over geological timescales, continental fragments function as fundamental building blocks in supercontinent reconstructions, with paleomagnetic evidence revealing their latitudinal drifts and independent motions prior to reassembly. Paleomagnetic studies of rock magnetizations from these isolated blocks demonstrate rapid polar wander paths, indicating that fragments can traverse significant latitudes—sometimes exceeding 30 degrees—during drift phases, which supports models of their role in cyclical continental evolution. This pattern underscores the fragments' persistence as stable cratonic cores that accrete juvenile material, gradually enlarging continents while preserving ancient geological signatures.^[19]^[20] The formation of continental fragments during breakup phases has profound implications for future supercontinent cycles, as these blocks will inevitably converge again under ongoing plate motions. Current tectonic models predict that extroversion—closure of the encircling superocean—will dominate the next assembly, potentially forming Amasia (a merger of Americas, Asia, and Antarctica near the North Pole) or Pangaea Ultima (reuniting around the equator) within 200–250 million years, with existing fragments like Australia and India playing key roles in the convergence. This cyclical process highlights how fragment dispersal today sets the stage for renewed collisional orogeny in the distant future.^[21]

Significant Geological Events

One of the earliest significant geological events involving continental fragments occurred during the breakup of the supercontinent Columbia (also known as Nuna) between approximately 1.6 and 1.2 Ga in the Paleoproterozoic Era. Recent studies suggest a stepwise process associated with rifting and voluminous volcanism from large igneous provinces, dispersing key proto-cratons including Laurentia, Baltica, Ukrainian, North China, and Kalahari, forming isolated continental blocks that would later reassemble into younger supercontinents.^[22] In the Neoproterozoic Era, the rifting and breakup of Rodinia around 750 Ma scattered numerous continental fragments later incorporated into Gondwana; peri-Gondwanan terranes like Avalonia, with arcs active from 750 to 500 Ma and originating from the Gondwana margin, rifted away ~490 Ma. This event, linked to the emplacement of large igneous provinces such as the ~825 Ma Guibei-Willouran LIP and ~800 Ma Suxiong-Xiaofeng LIP, initiated the dispersal of such blocks across the widening Iapetus Ocean.^[23]^[24] The Phanerozoic breakup of Pangea from 200 to 150 Ma, triggered by the Central Atlantic Magmatic Province (CAMP) at ~201 Ma, represented a major episode of fragmentation, separating Laurasia and Gondwana while isolating smaller blocks along the nascent Atlantic margins. The closure of Paleo-Tethys in the Late Triassic (~230 Ma) accreted Cimmerian continental fragments—derived from northern Gondwana—to the southern Eurasian margin amid subduction and collision dynamics.^[25]^[26] Cenozoic events further highlight fragment isolation, including the India-Eurasia collision around 50 Ma, which closed the Neo-Tethys Ocean and incorporated Indian continental slivers into the Himalayan orogen, while ongoing rifting in the East African Rift System—particularly in the Afar region since the late Oligocene—has begun separating new fragments like the Danakil microplate through magma-rich extension.^[27]^[28] These episodes are evidenced by fossil distributions revealing biogeographic affinities between fragments and parent landmasses (e.g., Gondwanan flora in Avalonia) and U-Pb zircon dating that constrains assembly-breakup timelines, such as ~750 Ma ages in Rodinia-derived blocks linking them to original cratons.^[29]^[30]

Notable Examples

Fragments from Pangaea and Earlier Supercontinents

The breakup of the supercontinent Pangaea, which began around 200 million years ago during the Late Triassic, resulted in the dispersal of various continental fragments, including larger blocks and microcontinents that retained Precambrian basement rocks. These fragments, often isolated by rifting and subsequent seafloor spreading, provide key evidence for reconstructing ancient plate configurations. Among the notable Pangea-derived examples are the Iberian Peninsula and the Seychelles microcontinent, each exhibiting distinct geological signatures of their Gondwanan origins within the assembled Pangaea.^[31]^[32] The Iberian Peninsula represents a major continental fragment that rotated counterclockwise during the early stages of Pangaea's disassembly, separating from the North American craton along the opening Bay of Biscay around 126 million years ago in the Early Cretaceous. This motion, driven by extension between Eurasia and Iberia, preserved Variscan orogenic belts formed during the Late Paleozoic assembly of Pangaea from earlier Gondwanan and Laurentian margins. Seismic and paleomagnetic data confirm its role as a bridge between Gondwanan and Laurasian elements, with crustal thicknesses averaging 30-40 km indicative of stable continental lithosphere.^[32]^[33] The Seychelles microcontinent, covering approximately 50,000 km², is a classic example of a granitic fragment rifted from the eastern margin of Gondwana during the Jurassic breakup of East Gondwana, but isolated as a distinct block around 65 million years ago amid the northward drift of India. Its core consists of Archean to Neoproterozoic granites and gneisses, exposed on islands like Mahé, overlain by Deccan-related volcanics, with seismic refraction studies revealing a continental crustal thickness of 30-33 km featuring high-velocity lower crust. This structure underscores its preservation as an "in situ" Gondwanan sliver amid the Indian Ocean's expansion.^[34]^[35]^[36] Fragments from earlier supercontinents, predating Pangaea's assembly around 300 million years ago, include Avalonia and Mauritia, which were incorporated into Pangaea but later dispersed. Avalonia, a peri-Gondwanan terrane rifted from the northern margin of Gondwana during the Late Neoproterozoic to Early Paleozoic, comprises Cambrian-Ordovician volcanic arcs and sedimentary basins now distributed across southern Britain, Ireland, Newfoundland, and parts of New England. Its drift across the Iapetus Ocean led to accretion to Laurentia by the Devonian, with paleomagnetic and faunal evidence confirming its Gondwanan affinity through shared peri-Gondwanan trilobite assemblages.^[37]^[38] Mauritia, a reconstructed microcontinent in the Indian Ocean, detached from the Madagascar-India nexus between 61 and 83 million years ago during the final stages of Gondwanan fragmentation inherited from Pangaea's breakup. Identified through marine magnetic anomalies and fracture zone analysis, it consists of Archean crustal slivers now underlying volcanic islands like Mauritius and Réunion, with paleomagnetic data placing its components adjacent at around 750 million years ago along Rodinia's margins. Recent zircon geochronology from hotspot lavas supports its ancient continental basement, dating to 2,500-3,000 million years.^[39]^[40]^[41]^[42] Recent seismic investigations post-2020 have affirmed the continental nature of submerged blocks like the Gulden Draak Knoll, a small fragment off Western Australia rifted from East Gondwana during the Jurassic-Cretaceous breakup phase that contributed to Pangaea's disassembly. Wide-angle seismic data reveal middle-to-lower crustal velocities of 6.0-7.2 km/s, diagnostic of thinned continental lithosphere, with the knoll positioned southwest of the Naturaliste Plateau in reconstructions of greater India-Australia separation. These findings, integrating gravity and tomographic models, highlight how such slivers preserve rift inheritance in oceanic settings.^[43]^[44]

Post-Pangaea and Modern Microcontinents

Following the breakup of Pangaea around 200 million years ago, subsequent tectonic processes in the Cenozoic era led to the formation of several microcontinents through rifting and extension of continental margins. These post-Pangaea fragments often exhibit thinned continental crust surrounded by oceanic lithosphere, resulting in partial or near-total submergence. Notable examples include the Jan Mayen Microcontinent, which detached during the separation of the North Atlantic margins.^[2]^[45] In the North Atlantic, the Jan Mayen Microcontinent spans 400–450 km in length and up to 310 km in width, isolated between the Norway Basin and the Kolbeinsey Ridge. It formed through two phases of Cenozoic rifting: an initial breakup from the Norwegian and East Greenland margins around 55–53 million years ago, accompanied by subaerial volcanism and seaward-dipping reflectors, followed by final isolation between 24 and 21.5 million years ago as the Ægir Ridge was abandoned in favor of the Kolbeinsey Ridge. The microcontinent's crust reaches thicknesses of 15–25 km, with Eocene plateau basalts and later intrusive complexes reflecting hotspot influence from the Iceland plume.^[45]^[46]^[45] Oceanic plateaus like the Azores Plateau and Broken Ridge also incorporate continental fragments amid volcanic edifices. The Azores Plateau, in the North Atlantic, features isolated blocks of continental crust embedded within predominantly oceanic lithosphere formed by the Azores hotspot, with rifting episodes from about 20 million years ago enhancing its fragmented structure. Similarly, Broken Ridge in the Indian Ocean rifted from the Kerguelen Plateau between 118 and 79 million years ago as part of the Kerguelen Large Igneous Province, with final separation along the Southeast Indian Ridge after 43 million years ago; its elevated bathymetry preserves thinned continental slivers up to 20 km thick beneath volcanic cover.^[47]^[48]^[48] Submerged examples include the Davis Strait proto-microcontinent and the Gilbert Ridge. The Davis Strait proto-microcontinent, identified in 2024 between Greenland and Baffin Island, consists of 19–24 km thick continental crust that failed to fully detach around 58–49 million years ago during a plate reorganization event; ongoing bathymetric and seismic studies reveal its isolation within the Davis Strait High, bounded by transform faults. In the equatorial Pacific, the Gilbert Ridge (or Seamount Complex) in the Tasman Sea detached from the southern Lord Howe Rise around 79–77 million years ago during Gondwana's fragmentation, forming a submerged block of continental affinity approximately 200 km long with seamounts marking rift-related volcanism.^[49]^[49]^[50] These modern microcontinents remain tectonically active, with ongoing subsidence and minor seismicity.^[51]

Emerging and Future Fragments

The East African Rift System, particularly in the Afar Depression, represents an active zone of continental extension where the Nubian, Somali, and Arabian plates are diverging, potentially leading to the isolation of a new continental fragment within 5 to 100 million years as a nascent ocean basin forms. GPS measurements indicate extension rates of 1.8 to 2 cm per year across the rift, with higher localized rates up to 3.7 cm per year in magmatic segments like Dabbahu-Manda-Hararo, signaling progression toward breakup. Similarly, ongoing extension in the Red Sea and Gulf of Aden continues to widen the rift separating the Arabian Plate from Africa at rates of 1 to 1.6 cm per year, further refining the boundaries of the already isolated Arabian block through oblique spreading.^[52]^[53]^[54] In the West Antarctic Rift System, current tectonic activity is delineating smaller crustal blocks, including Marie Byrd Land, Thurston Island, and the Ellsworth-Whitmore Mountains, through Cenozoic extension that separates these proto-fragments beneath the ice sheet. GPS networks detect ongoing motion along these boundaries, with heat flux from rifting influencing ice stability but not yet fully isolating new fragments. Iceland serves as a transitional feature in the North Atlantic rift, underlain by snippets of continental crust—a 350 km by 70 km sliver detached from East Greenland in the Early Eocene—embedded within oceanic crust and interacting with the Mid-Atlantic Ridge to produce hybrid magmatic systems.^[55]^[56] Geodynamic models project that continued widening of the North Atlantic, at rates of 2 to 2.5 cm per year, could evolve existing microcontinents like the Rockall Plateau through further margin extension, potentially isolating additional slivers over tens of millions of years. In the longer term, fragments from ongoing rifts may contribute to the assembly of a future supercontinent such as Pangaea Ultima around 250 million years from now, where superplume activity could preserve dispersed pieces amid continental collision.^[57]^[58] Contemporary monitoring relies on GPS networks, which reveal extension rates of 1 to 5 cm per year across these rifts, enabling precise tracking of strain accumulation and rift propagation. These dynamics enhance volcanism by facilitating magma ascent, as seen in Afar's magmatic segments, and may indirectly influence local sea-level changes through crustal subsidence and basin formation, though global effects remain tied to broader plate cycles.^[53]^[59]

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Feb 28, 2013 · The research team believe that this micro-continent, which they have named Mauritia, was split off from Madagascar and India between 61 and 83 ...
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Evolution of the Southwest Australian Rifted Continental Margin ...
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Discovery of a microcontinent (Gulden Draak Knoll) offshore ...
Aug 6, 2025 · This is evident from seismic studies showing slower wave speeds in two distinct regions of the middle to lower crust. We analyzed seismic data ...
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... Jan Mayen Fracture Zone (WJMFZ in Fig. 5). The crustal thickness of the central area of the microcontinent (Fig. 6b) is 15–18 km based on refraction data ...Missing: elevation | Show results with:elevation
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Feb 4, 2019 · Continental rifting and breakup of eastern Gondwana during the Cretaceous separated northern Zealandia from eastern Australia, ...
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Seismic Volcanostratigraphy: The Key to Resolving the Jan Mayen ...
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[54]
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Broken Ridge (BR) and Kerguelen Plateau (KP) are conjugate rifted plateaus in the Indian Ocean separated by the Southeast Indian Ridge. The overlap of BR ...
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The Davis Strait proto-microcontinent: The role of plate tectonic ...
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[57]
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Feb 16, 2017 · Whatever it is called, Mortimer says, studies of Zealandia should help biogeographers to better understand how New Zealand's endemic plants and ...
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Sep 29, 2021 · The data show that extension is tightly focused around the volcanic segments and broadly distributed around those lacking volcanism.
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Current plate motions across the Red Sea - Oxford Academic
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Continental fragments of both plates are currently separated by small ... small blocks defined by the variability in the magnetic anomalies. Read more.
[62]
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The next Pangaea will have pieces missing - ScienceDirect
Sep 17, 2011 · A Pangaea-like supercontinent is forecast to form in 250 million years, but a new model predicts that superplumes rising from hotspots deep in the Earth's ...Missing: fragments | Show results with:fragments
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https://www.nature.com/articles/s41598-025-23264-9