Accretion Of Oceanic Crust Research Articles

Plume and arc magmatism in the Abitibi subprovince: Implications for the origin of Archean continental lithospheric mantle

Based on eclogitic mantle xenoliths that appear to be the residue of slab melts, it is commonly argued that the formation of distinctive lithospheric keels beneath Archean cratons occurred by the tectonic accretion of oceanic crust. These models are complicated by evident buoyancy of the keels, the varied compositions of the mantle xenolith suite as a whole, and a compositional constraint that a large portion of the keels originated in mantle plume melting events. Resolution of these issues is complicated by the long development history of most cratons (100’s of m.y.) and the multiple cycles of magmatism they represent. In contrast, the single 50 m.y. period of arc volcanism in the Abitibi subprovince, and the immediate onset of orogeny and craton stabilisation, avoids many of these uncertainties. Chemical and isotopic data demonstrate that syn-volcanic to syn-tectonic adakitic Abitibi granitoids were derived via slab melting. Deep seismic reflection profiles image singular slab-like features along the Moho. These are interpreted as the remnants of oceanic slabs emplaced and torn during orogeny. Nonetheless, their presence directly contradicts subcretion models of keel formation because they occupy regions that should correspond to the top of an earlier-formed subcreted keel. Post-adakite shoshonitic granitoids and lamprophyres also attest to the presence of a metasomatised mantle wedge throughout the entire period of Abitibi arc magmatism. Diamond-bearing lamprophyres in the Abitibi and adjacent Wawa subprovince are compositionally equivalent to Paleoproterozoic diamondiferous rocks and characteristic of adakite-generating shallow subduction rather than evidence of pre-existing sub-cratonic keels. Abitibi mantle plume- and subduction-related volcanism also demonstrates the continuous presence of shallow asthenospheric mantle beneath the belt over a 50 m.y. period. Komatiites and then boninites erupted along the central part of the belt, halfway through its evolution, and rifted arc-style volcanism dominated the belt within a few m.y. of orogeny. None of these events are consistent with the development of a progressively thickened continental lithospheric keel. The geodynamic evolution of the Abitibi belt demonstrates a fact recognised in some xenolith studies: the characteristic association of deep keels and Archean cratons was not developed gradually during greenstone belt volcanism. Rather, it was initiated by the coupling of shallow imbricated plume- and arc-related crust with the buoyant residue of mantle plume melting that rose from depths of 80 km to >400 km. Subduction was active along the southern and eastern margin of the Superior Province craton before and after ascent of the Abitibi plume. Renewal of subduction in the Abitibi, as marked by the occurrence of the ∼2716 Ma boninitic volcanic suite, delayed the ascent of the deep keel and its coupling to the composite crust. Final ascent of the plume residue occurred following orogeny and slab loss and may have included entrainment of fragmented slab residue into the rising diapir. The coupling of shallow crust and deep keel occurred soon after and the keel’s presence beneath the subprovince is recognised by Phanerozoic diamond deposits, xenolith chemistry and geophysical data.

Cooling rates in the lower crust of the Oman ophiolite: Ca in olivine, revisited

Debate over the mechanism of accretion of the lower oceanic crust has centered around the gabbro glacier and the sheeted sills models. The thermal profile of the crust, specifically the roles of hydrothermal circulation and cooling rate, is a key component in distinguishing between these two models. Results of this study show no systematic variation of cooling rate with depth in the lower crust of the Khafifah section in the Wadi Tayin massif of the Oman ophiolite. Additionally, very high rates recorded near the base of the crust suggest that hydrothermal circulation plays an important role in the removal of heat throughout the crust. While the conclusions presented here do not rule out the possibility of accretion by gabbro glacier, they do contradict the initial tenet of the gabbro glacier model – convective heat loss by hydrothermal circulation can penetrate to Moho depths and crystallization is not, by necessity, constrained to the upper crust. On the basis of these results it can be concluded that the sheeted sills model is a thermally viable mechanism for accretion of oceanic lower crust.

A Vestige of Earth's Oldest Ophiolite

A sheeted-dike complex within the approximately 3.8-billion-year-old Isua supracrustal belt (ISB) in southwest Greenland provides the oldest evidence of oceanic crustal accretion by spreading. The geochemistry of the dikes and associated pillow lavas demonstrates an intraoceanic island arc and mid-ocean ridge-like setting, and their oxygen isotopes suggest a hydrothermal ocean-floor-type metamorphism. The pillows and dikes are associated with gabbroic and ultramafic rocks that together make up an ophiolitic association: the Paleoarchean Isua ophiolite complex. These sheeted dikes offer evidence for remnants of oceanic crust formed by sea-floor spreading of the earliest intact rocks on Earth.

Inherited arc signature in Ediacaran and Early Cambrian basins of the Ossa-Morena Zone (Iberian Massif, Portugal): Paleogeographic link with European and North African Cadomian correlatives

Geochemical data from clastic rocks of the Ossa-Morena Zone (Iberian Massif) show that the main source for the Ediacaran and the Early Cambrian sediments was a recycled Cadomian magmatic arc along the northern Gondwana margin. The geodynamic scenario for this segment of the Avalonian-Cadomian active margin is considered in terms of three main stages: (1) The 570–540 Ma evolution of an active continental margin evolving oblique collision with accretion of oceanic crust, a continental magmatic arc and the development of related marginal basins; (2) the Ediacaran–Early Cambrian transition (540–520 Ma) coeval with important orogenic magmatism and the formation of transtensional basins with detritus derived from remnants of the magmatic arc; and (3) Gondwana fragmentation with the formation of Early Cambrian (520–510 Ma) shallow-water platforms in transtensional grabens accompanied by rift-related magmatism. These processes are comparable to similar Cadomian successions in other regions of Gondwanan Europe and Northwest Africa. Ediacaran and Early Cambrian basins preserved in the Ossa-Morena Zone (Portugal and Spain), the North Armorican Cadomian Belt (France), the Saxo-Thuringian Zone (Germany), the Western Meseta and the Western High-Atlas (Morocco) share a similar geotectonic evolution, probably situated in the same paleogeographic West African peri-Gondwanan region of the Avalonian-Cadomian active margin.

Termination of a fossil continent-ocean fracture zone imaged with three-dimensional seismic data: The Chain Fracture Zone, eastern equatorial Atlantic

Abstract We describe the first three-dimensional imaging of the termination of a continent-ocean fracture zone (COFZ), the Chain Fracture Zone, located offshore of the Niger Delta. The COFZ marks the abrupt transition between extended continental crust, comprising multiple half-graben, and oceanic crust that has a pervasive seafloor-spreading fabric. It preserves a history of continent-continent shearing followed by oceanic crust accretion and continent-ocean shearing during the inception of Atlantic rifting. The termination is marked by steeply dipping faults with sigmoidal planform and thrusts that probably formed as a result of continent-continent or continent-ocean shearing. These are crosscut by the seafloor-spreading fabric that formed during the subsequent phase of oceanic crust accretion. The accreted oceanic crust is cut by listric and planar faults that curve in the direction of the COFZ, where they terminate. The transition from continental to oceanic crust across the COFZ is sharp and resolvable to ∼100–200 m. Complexes of lava flows emanate from volcanoes along the COFZ, bifurcating and trifurcating down the volcano flanks. The volcanoes are 2–5.5 km wide and 1.4 km in height relative to adjacent oceanic crust and were injected at the COFZ, probably as the spreading center migrated along it.

EXPERIMENTAL HYDROUS PARTIAL MELTING OF HARZBURGITE AT SHALLOW PRESSURES: IMPLICATIONS ON HYDROUS LATE-STAGE MAGMATIC PROCESSES WITHIN THE MANTLE/CRUST TRANSITION OF THE OCEANIC LITHOSPHERE

EXPERIMENTAL HYDROUS PARTIAL MELTING OF HARZBURGITE AT SHALLOW PRESSURES: IMPLICATIONS ON HYDROUS LATE-STAGE MAGMATIC PROCESSES WITHIN THE MANTLE/CRUST TRANSITION OF THE OCEANIC LITHOSPHERE

A Preliminary Study of Depth Distribution of Crystal Size within the Gabbro Layer of the Oceanic Crust

AbstractCurrent oceanic crustal accretion models at a fast spreading ridge predict at least an order of magnitude difference in the cooling time between the upper and lower gabbros. As a consequence, lower gabbros of the oceanic crust could have grown larger crystals on average than the upper gabbros as seen from the field observations at the Oman Ophiolite.

Thermal models of oceanic crustal accretion: Linking geophysical, geological and petrological observations

Models of oceanic crustal accretion should be able to reproduce both petrological and geological observations from ophiolites and geophysical observations from active spreading ridges. We have developed thermal models of crustal accretion at fast spreading ridges that incorporate petrological variation and allow for a variable vertical distribution of crystallization. Including petrological variation has a major effect on the distribution of melt within the crust and the consequent interpretation of model results in terms of geophysical observables. In particular, the narrow melt lens imaged by seismic reflection surveys can be produced by the presence of large‐scale compositional stratification within the crust, such as that observed in the Oman ophiolite. Controlling the vertical distribution of crystallization allows a range of crustal accretion mechanisms to be tested, including the many sills and gabbro glacier models. Both gabbro glacier and many sills models can broadly match the geophysical observations, but the preferred model is a hybrid, where the uppermost 25% or more of the lower crust forms in a gabbro glacier and the lowermost 25% or more of the lower crust forms by crystallization in situ. The success of all models is dependent on the strength and distribution of hydrothermal cooling.

Geology and tectonic evolution of Palaeoproterozoic basins of the eastern Capricorn Orogen, Western Australia

Abstract The Palaeoproterozoic Yerrida, Bryah, Padbury, and Earaheedy Basins extend for about 700 km along the northern margin of the Yilgarn Craton and are part of the Capricorn Orogen. The basins developed between ca. 2.2 and 1.8 Ga, recording periods of sedimentation, volcanism, rifting, accretion and passive-margin tectonism. The oldest is the 2.17 Ga Yerrida Basin, which began as an intracontinental sag within which siliciclastics and evaporites accumulated. At about 2.0 Ga convergence of the Yilgarn Craton and the Glenburgh terrane closed an oceanic arm, resulting in the accretion of oceanic crust and plateaux onto the Yilgarn margin and the western side of the Yerrida sag basin. This accretion produced the Narracoota Formation, which together with the clastic and chemical (banded iron-formation) sedimentation that followed, forms the Bryah Basin. Continuing collision resulted in the establishment, around 1.96 Ga, of the Padbury foreland basin, developed on top of the Bryah Basin rocks. The ca. 1.83 Ga convergence and collision of the Pilbara and Yilgarn Cratons (Capricorn Orogeny), resulted in deformation of the Bryah–Padbury Basins and orogenic uplift with coarse clastic sedimentation accompanied by the eruption of flood basalts into the Yerrida Basin. To the east of the collision zone, and possibly postdating collision, a passive margin was present. Sedimentation along it consisted of clastic and chemical sediments (granular iron-formation), which form the Earaheedy Basin. During the ca. 1.79 Ga Yapungku Orogeny, due to the convergence of the North Australian and Western Australian cratons, the northern margin of the Earaheedy Basin was deformed (Stanley Fold Belt). This last deformation event concludes the Palaeoproterozoic history of the eastern Capricorn Orogen basins.

Structure of Mesozoic oceanic crust in the vicinity of the Cape Verde Islands from seismic reflection profiles

Multichannel seismic reflection profile data have been used to determine the internal structure of Mesozoic oceanic crust in the vicinity of the Cape Verde islands. The data show the oceanic crust to be characterized by both dipping and sub-horizontal reflectors. Several lines of evidence argue against the reflectors being scattering artifacts arising, for example, from rough basement topography. Instead, the reflectors are attributed to tectonic and magmatic processes associated with the accretion of oceanic crust at the Mid-Atlantic Ridge. The upper crust shows variable reflectivity due to both dipping and sub-horizontal events. We interpret the dipping reflectors, which have been identified on both ridge-normal and ridge-parallel profiles, as sub-surface expressions of normal faults that formed at or near the Mid-Atlantic Ridge. There is no evidence that the faults are caused by loading of the oceanic crust by either the Cape Verde islands or their associated topographic swell. Some faults, however, can be traced into the overlying sediments suggesting they may have been re-activated since their formation at the ridge. The origin of the sub-horizontal reflectors is not as clear. We believe them to be boundaries of different igneous lithologies, such as that between basalts and gabbros. The lower crust is highly reflective in some areas, whereas in others only a few dipping and sub-horizontal reflectors are observed. Some of the dipping reflectors can be traced into the upper crust, suggesting they are also normal faults. Others, however, appear to be confined to the lower crust. The sub-horizontal, discontinuous, reflectors about 2.0–2.5 seconds two-way travel time below the top of oceanic basement are attributed to the Moho.

Abrupt axial variations along the slow to ultra-slow spreading centers of the northern North Fiji Basin (SW Pacific): Evidence for short wave heterogeneities in a back-arc mantle

This study presents results of surveys conducted along the slow to ultra-slow spreading axis of the Northern North Fiji Basin (NNFB), including the Hazel Holmes, Tripartite and South Pandora Ridges, and the newly discovered Futuna and North Cikobia spreading centers. Spreading segments along these axes display highly contrasted axial morphologies, ranging from a rift valley to a prominent axial high. In some places, abrupt inversions of topography are observed between neighboring segments. Detailed analyses of bathymetry and backscatter maps reveal that axial highs are spotted with numerous coalescent volcanoes forming features ranging from irregular terrains to well-organized ridges. The volcanic edifices are distributed over a wide neovolcanic zone, which corresponds to the axial relief, suggesting on important contribution of volcanism to the relief construction. Comparisons between various ridge-shaped segments reveal that axial volcano-tectonic patterns are directly related to the local magma production and delivery, in a context of tectonic extension related to plate divergence, and suggest that coalescent volcanoes are fed from multiples short-lived and unconnected magma lenses. In the competition between horizontal and vertical accretion of oceanic crust, the spreading centers of the NNFB represent a special case where lava production is locally high enough and spreading rate is low enough to allow prominent axial highs to develop. The along axis morphologic variability is related to intermittent volcanic activity that may result from rapid temporal and spatial variations in the distribution of upper mantle convection cells below accretion centers, superimposed on the regional thermal anomaly located under the whole basin.

Lower crustal granulite xenoliths from the Pannonian Basin, Hungary. Part 1: mineral chemistry, thermobarometry and petrology

Lower crustal granulite xenoliths have been found in Pliocene basaltic tuffs at two newly discovered localities in the western Pannonian Basin. Most of them are mafic meta-igneous rocks, among which garnet-rich lithologies are common. In general, clinopyroxene, garnet and plagioclase, with minor ilmenite and scapolite dominate their mineralogy. Several are amphibole-bearing, which is interpreted as evidence for a recent metasomatic event in the lower crust beneath the Pannonian Basin. Meta-sedimentary granulite xenoliths have also been identified in the region for the first time. Their mineralogy is characterised by the absence of clinopyroxene combined with a high proportion of Al-rich phases, especially plagioclase and garnet together with subordinate spinel, sphene, rutile, orthopyroxene and quartz. One sample contains biotite and several contain graphite. Thermobarometric results indicate temperatures and pressures of 800–950 °C and 8–15 kbar for all xenolith types, considerably higher than for most granulite xenoliths from other regions of Phanerozoic Europe. Given that the Pannonian Basin is currently underlain by thin crust (25–30 km thick), the pressure estimates indicate that the crust must have been considerably thicker (40–50 km) prior to the Tertiary collapse in the region. The higher pressures recorded for the meta-igneous xenoliths thus suggest that they formed at (or before) a time when the crust was thicker, i.e. pre-Tertiary. A composite meta-igneous/meta-sedimentary xenolith provides direct evidence for interaction between sediments (or metasediments) and the magmas that gave rise to the meta-igneous granulites, indicating that the metasediments are at least as old as the meta-igneous granulites. The protoliths of the meta-igneous xenoliths had primitive mafic to slightly evolved tholeiitic liquid compositions. They are dominated by LREE-depleted compositions that resemble those of mid-ocean ridge basalts. Such compositions are rare in lower crustal xenolith suites. They are also very low in large ion lithophile elements such as K and Rb, but relatively enriched in Ba and Pb. A few slightly LREE-enriched meta-igneous xenoliths are also K and Rb depleted. In contrast, the meta-sedimentary granulites are strongly LREE enriched, but have very variable LILE contents. One possible explanation for the unusual compositions is a process of subduction–accretion of oceanic crust beneath the continental crust, rather than basaltic underplating.

Crustal accretion under northern Iceland

Successful models of oceanic crustal accretion should be consistent with both geochemical and geophysical observations from active mid-ocean ridges as well as those from ophiolite sections. The major element concentrations of a set of basalt and picrite samples from the Krafla and Theistareykir volcanic systems of the Northern Volcanic Zone of Iceland show two distinct trends. The compositional variation in samples with MgO>9.5 wt% can be explained by addition/removal of a wehrlitic cumulate, while the major element variability in samples with 5–9.5 wt% MgO is dominated by gabbro removal. The results of thermobarometry based on the composition of the samples and the crystals found within them show that crystallisation took place at a range of temperatures (1160–1350°C) and pressures (<0.3–0.9 GPa) in the crust and uppermost mantle under Krafla and Theistareykir. The geochemical results are consistent with crustal accretion models where crystallisation takes place over a range of depths in the crust and uppermost mantle (<10–30 km). The geochemical observations allow estimates of the composition, mineralogy, pressure and temperature of material in the crust and shallow mantle under northern Iceland to be made and these estimates can be used to predict the seismic velocity of the material at the ridge axis. These P-wave velocity estimates are in agreement with the results of a seismic survey of the ridge axis at Krafla. The presence of temperatures of over 1000°C and magma chambers at depths greater than 10 km in the Icelandic crust cannot be ruled out using the available geophysical data from the Icelandic rift zones. Therefore both the geochemical and geophysical observations are consistent with models where crustal accretion takes place at a range of depths under northern Iceland.

Kerguelen Plateau crustal structure and basin formation from seismic and gravity data

We use multichannel seismic data, gravity, and subsidence modeling, in conjunction with plate reconstructions, to evaluate the crustal origin and composition of the Kerguelen Plateau. Predominantly oceanic crust of the southern and parts of the central Kerguelen Plateau appears to include continental fragments related to the breakup of India and Antarctica; these fragments may have been metamorphosed during emplacement of the main plateau. The upper crust is basaltic, the middle crust is intrusive mafic rock and intruded continental crust, and the lower crust is a plagioclase‐rich metamorphic rock. The Labuan Basin crust is predominantly oceanic with stranded Kerguelen Plateau fault blocks. High‐density lower crust in the Labuan Basin is probably composed of serpentinized peridotites formed during slow rifting and spreading. Plate reconstruction models indicate opening between eastern Broken Ridge and southern Kerguelen Plateau at ∼90 Ma, heralding the formation of the Labuan Basin and Diamantina Zone; crustal attenuation and slow accretion of oceanic crust continued until the Australian and Antarctic plates separated at CI8 time (∼40 Ma). Plate reconstructions of the free‐air gravity field indicate that the Naturaliste Plateau fits against Antarctica and that Elan Bank and India were juxtaposed until ∼110 Ma. Both Naturaliste Plateau and Elan Bank are probable microcontinents. A ∼1 km positive residual depth anomaly in the oceanic basins adjacent to the plateau, along with the positive geoid anomaly centered beneath the northern Kerguelen Plateau, imply that the lithosphere is partially dynamically supported by an upwelling hot asthenosphere of the Kerguelen hot spot.

Crustal structure, accretionary processes and rift propagation: a gravity study of the intermediate-spreading Valu Fa Ridge, Lau Basin

The Valu Fa Ridge is an intermediate‐spreading (full rate of 60 mm yr−1) ridge located in the Lau Basin. In 1995 this ridge was surveyed using a multidisciplinary, geophysical approach to image crust and upper mantle structure, with the aim of investigating the processes of oceanic crustal accretion in a back‐arc tectonic environment. As part of this experiment a network of gravity profiles was acquired, together with seismic, magnetic, swath bathymetry and controlled‐source electromagnetic data. Presented in this paper are the results of forward modelling of a subset of the acquired gravity profiles, two oriented ridge‐perpendicular and one ridge‐parallel, using the preferred seismic models of Turner . (1999) as a basis of initial model construction. In addition, the gravity data set in its entirety has been used to calculate the mantle and residual mantle Bouguer anomalies with the aim of investigating variability in crustal structure, both density and layer thickness, and the nature of the underlying upper mantle. Of particular interest are the overlapping spreading centre between the Central and Northern Valu Fa Ridges, where seismic modelling implies a generally thickened crust and a magma chamber located beneath the overlap basin rather than separate chambers supplying each ridge, and the propagating rift tip and associated basin‐bounding pseudo‐fault. Modelling results suggest that the pre‐ and post‐rift crusts have different compositional origins, with lower densities required > 12 km off‐axis to fit the observed free‐air gravity anomaly. The locations of the transitions into regions of lower density correspond with those of Turner . (1999) derived from seismic modelling, which in turn correspond in location to the rift‐related pseudo‐fault identified by Wiedicke & Collier (1993). Calculation and interpretation of the mantle and residual mantle Bouguer anomalies also confirms the lower off‐axis densities and indicates a general increase in crustal thickness northwards towards the overlapping spreading centre between the Central and Northern Valu Fa Ridge segments. The presence of thicker crust, corresponding to a region of negative mantle and residual mantle Bouguer anomaly, implies that the region surrounding the overlapping spreading centre has been in the recent geological past, or is presently, the site of an increased magma supply. The residual mantle Bouguer anomaly also reveals features related directly to off‐axis lateral variation in density and layer thickness, associated with the southward propagation of the Valu Fa Ridge into the Havre Trough. Modelling of the north–south variation in crustal thickness along‐axis shows that the anomaly trend can be explained simply by thicker crust beneath each of the Valu Fa Ridge segments and the overlapping spreading centre between the Northern and Central Valu Fa Ridges. The observation of segment‐centred crustal thickening is consistent with models of ridge segmentation that suggest that melt influx is located towards segment centres and that segment length is controlled by the maximum lateral extent to which this melt can flow ( Macdonald . 1988 ; Tolstoy . 1993 ). However, the overlapping spreading centre remains anomalous from these models in that it also appears to be associated with thicker crust and an increased melt supply.

The Archean Dongwanzi ophiolite complex, North China craton: 2.505-billion-year-old oceanic crust and mantle.

We report a thick, laterally extensive 2505 +/- 2.2-million-year-old (uranium-lead ratio in zircon) Archean ophiolite complex in the North China craton. Basal harzburgite tectonite is overlain by cumulate ultramafic rocks, a mafic-ultramafic transition zone of interlayered gabbro and ultramafic cumulates, compositionally layered olivine-gabbro and pyroxenite, and isotropic gabbro. A sheeted dike complex is rooted in the gabbro and overlain by a mixed dike-pillow lava section, chert, and banded iron formation. The documentation of a complete Archean ophiolite implies that mechanisms of oceanic crustal accretion similar to those of today were in operation by 2.5 billion years ago at divergent plate margins and that the temperature of the early mantle was not extremely elevated, as compared to the present-day temperature. Plate tectonic processes similar to those of the present must also have emplaced the ophiolite in a convergent margin setting.

Along-strike variations in the thermal and tectonic response of the continental Ecuadorian Andes to the collision with heterogeneous oceanic crust

Oblique to strike geological segmentation in the Andean chain has been previously recognised at various scales and is commonly attributed to changes in the convergence vectors of the oceanic and continental plates, as well as the upperplate expressions of differing along-strike subducted slab age, strength and composition. We present new white mica and biotite 40 Ar/ 39 Ar and zircon and apatite fission-track data from several traverses across the Cordillera Real of Ecuador in the northern Andes that reveal distinct along-strike differences in the timing of accelerated crustal cooling during the Cenozoic. The data record elevated cooling rates from temperatures of V380‡C during V65^55 and V43^ 30 Ma from all sampled regions of the Cordillera Real and at V15 Ma and since V9 Ma in the northern Cordillera Real. Each cooling period was probably driven by exhumation in response to the accretion and subduction of heterogeneous oceanic crust. Elevated cooling rates of up to V30^20‡C/Myr were initiated during the Palaeocene and Eocene^early Oligocene along the entire contemporaneous margin of Ecuador and were driven by the accretion of the oceanic Pallatanga Terrane and Pin ‹ on^Macuchi Block, respectively, onto northwestern South America. Both of these geological provinces originated at the southern parts of the leading and trailing boundaries of the Caribbean Plateau and accreted onto the margin during the approximately northeastward migration of the Plateau into its current position. Within Ecuador the development of higher topography and elevated cooling rates of up to 50‡C/Myr at V15 Ma and since V9 Ma are restricted to the region north of 1‡30PS and is situated above the postulated subducted flatslab section of the aseismic Carnegie Ridge. Plate convergence rate calculations suggest the Carnegie Ridge collided with the Ecuador Trench at V15 Ma, which caused the pre-existing coastal provinces to displace to the northeast, subsequently driving extension and marine ingressions in southern Ecuador and compression and uplift in northern Ecuador. fl 2001 Elsevier Science B.V. All rights reserved.

Comparison of oceanic crust accretion features with low-velocity and ultralow-velocity spreading

Comparison of oceanic crust accretion features with low-velocity and ultralow-velocity spreading

A recipe for microcontinent formation

Research Article| March 01, 2001 A recipe for microcontinent formation R. Dietmar Müller; R. Dietmar Müller 1University of Sydney, School of Geosciences, Building F05, Sydney, New South Wales 2006, Australia Search for other works by this author on: GSW Google Scholar Carmen Gaina; Carmen Gaina 1University of Sydney, School of Geosciences, Building F05, Sydney, New South Wales 2006, Australia Search for other works by this author on: GSW Google Scholar Walter R. Roest; Walter R. Roest 2Geological Survey of Canada, 615 Booth Street, Ottawa, Ontario K1A 0E9, Canada Search for other works by this author on: GSW Google Scholar David Lundbek Hansen David Lundbek Hansen 3Department of Earth Sciences, University of Aarhus, DK 8200 Aarhus N., Denmark Search for other works by this author on: GSW Google Scholar Geology (2001) 29 (3): 203–206. https://doi.org/10.1130/0091-7613(2001)029<0203:ARFMF>2.0.CO;2 Article history received: 11 Aug 2000 rev-recd: 04 Dec 2000 accepted: 04 Dec 2000 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation R. Dietmar Müller, Carmen Gaina, Walter R. Roest, David Lundbek Hansen; A recipe for microcontinent formation. Geology 2001;; 29 (3): 203–206. doi: https://doi.org/10.1130/0091-7613(2001)029<0203:ARFMF>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyGeology Search Advanced Search Abstract Accreted slivers of continental margins are common in the geologic record, but the processes that lead to their formation are poorly understood. We observe an association of plume-related microcontinent isolation and subsequent long-term asymmetries in oceanic crustal accretion based on four recent examples: the Seychelles in the Indian Ocean, Jan Mayen in the Norwegian-Greenland Sea, and the East Tasman Plateau and the Gilbert Seamount Complex in the Tasman Sea. These microcontinents formed by rerifting of a young continental margin (<25 m.y. old) in the vicinity of a mantle-plume stem, followed by asymmetric seafloor spreading. Two-dimensional numerical stochastic basin modeling suggests that a yield-strength minimum along the landward edge of a rifted margin, thermally enhanced by heating from a mantle plume, may cause a spreading ridge to jump onto this zone of weakness. This action isolates a passive-margin segment. The association of large igneous provinces and microcontinents should be useful for identifying similar events in the geological record. You do not currently have access to this article.

A synthesis of electromagnetic studies in the Lithoprobe Alberta Basement Transect: constraints on Paleoproterozoic indentation tectonics

Electromagnetic surveys of the crust and upper mantle underlying the Western Canada Sedimentary Basin have revealed two conductivity anomalies that are arguably related to Paleoproterozoic tectonic processes, recording a signature diagnostic of euxinic (foreland?) basin succession and perhaps defining a deep-marine transtensional basin. As well, a regionally pervasive electrical anisotropy throughout the crust crosses Proterozoic tectonic boundaries and is aligned in many areas with the regional tectonic fabric (as expressed by aeromagnetic data) created during the final stages of Proterozoic tectonic assembly of western Laurentia. There is also an order of magnitude increase in the upper mantle conductivity underlying Churchill Province Archean crust relative to that underlying the neighbouring Proterozoic crust. The interpretations of the electromagnetic observations are analogous with the Tertiary to modern-day tectonic development of southeast Asia. The foreland basin succession would reflect the closing of the South China Sea and the deep-marine basin may be analogous to the Andaman Sea and North Sumatra basin. Electrical anisotropy may be indicative of the successive lateral accretion of oceanic crust beneath the continental shelf followed by shortening. The enhanced mantle conductivity mechanism is unknown, although it may be associated with metasomatic modification of the subcontinental lithosphere subsequent to collisional thickening and followed by delamination or convective removal of some lithosphere. While the Indo-Eurasian–Laurentia tectonic analogy is incomplete, it is sufficiently compelling in explaining the electromagnetic and other data that it is a useful basis for understanding the Proterozoic assembly of Laurentia.