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1
Hoffman, Paul F. "Tuzo Wilson and the acceptance of pre-Mesozoic continental drift." Canadian Journal of Earth Sciences 51, no. 3 (March 2014): 197–207. http://dx.doi.org/10.1139/cjes-2013-0172.
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Tuzo Wilson’s well-known pre-1961 opposition to continental drift stemmed from his early experience as a geologist in the Appalachians and the Canadian Shield, which convinced him that orogenesis did not change drastically over geologic time. Conversely, Taylor (in 1910) and Wegener (in 1912) hypothesized that continental drift began in Cenozoic or Mesozoic time. Between 1949 and 1960, Tuzo Wilson with Adrian Scheidegger developed a quasi-uniformitarian model of progressive continental accretion around fixed Archean nuclei. Tuzo abruptly jettisoned this model in 1961 when, under pressure from paleomagnetic evidence for continental drift and a nascent concept of sea-floor spreading, he finally entertained the possibility of pre-Mesozoic as well as younger continental drift. He immediately found it a superior fit to Appalachian and Shield geology, while his uniformitarian conviction remained intact. Tuzo had blinded himself to the evidence for continental drift so long as he confined it to Taylor or Wegener’s conception. In continental drift operating continuously over geologic time, he found a theory he could eagerly accept.
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Thiede, J., A. Altenbach, U. Bleil, R. Botz, P. Mudie, S. Pfirman, and E. Sundvor. "Properties and history of the central eastern Arctic sea floor." Polar Record 26, no. 156 (January 1990): 1–6. http://dx.doi.org/10.1017/s0032247400022695.
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ABSTRACTThe deep eastern Arctic basin between the Lomonosov Ridge and the Eurasian continental margin differs from other ocean basins in the very slow spreading of its floor and unusual depositional environment under perennial sea-ice cover. The recent expedition ARK IV/3 of RV Polar stern for the first time made geoscientific investigations from the northern margin of the Barents Sea north to the Nansen-Gakkel Ridge. Much deeper than most other mid-ocean ridges, this ridge is poorly-surveyed, but has a central valley which in places is deeper than 5.5 km, 1–1.5 km below the basin floors on either side. Heat flow in the central part of the valley is very rapid; both basement rocks and overlying sediments showed unexpectedly the influence of intense and long-term hydrothermal activity. The sediments on the northern and southern flanks of the ridge are slightly calcareous pelagic mud layers alternating with carbonate-free horizons, where up to 40% of the sedimentary section is soft mud clasts. Similar mud aggregates were observed on the surface of the multi-year sea ice, appearing to represent a special type of sediment transport by sea ice in the Transpolar Drift. In contrast to the western Arctic, Fram Strait and the Norwegian-Greenland Sea, gravel is rarely found in sediment cores. Recovered cores indicate that icebergs and sea ice carrying coarse sediment seldom rafted detritus to the study area during the last approximately 300,000 years.
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MKenzie, Dan. "A Geologist Reflects on a Long Career." Annual Review of Earth and Planetary Sciences 46, no. 1 (May 30, 2018): 1–20. http://dx.doi.org/10.1146/annurev-earth-082517-010111.
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Fifty years ago Jason Morgan and I proposed what is now known as the theory of plate tectonics, which brought together the ideas of continental drift and sea floor spreading into what is probably their final form. I was twenty-five and had just finished my PhD. The success of the theory marked the beginning of a change of emphasis in the Earth sciences, which I have spent the rest of my career exploring. Previously geophysicists had principally been concerned with using ideas and techniques from physics to make measurements. But the success of plate tectonics showed that it could also be used to understand and model geological processes. This essay is concerned with a few such efforts in which I have been involved: determining the temperature structure and rheology of the oceanic and continental lithosphere, and with how mantle convection maintains the plate motions and the long-wavelength part of the Earth's gravity field. It is also concerned with how such research is supported.
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Taylor, Brian, Andrew Goodliffe, Fernando Martinez, and Richard Hey. "Continental rifting and initial sea-floor spreading in the Woodlark basin." Nature 374, no. 6522 (April 1995): 534–37. http://dx.doi.org/10.1038/374534a0.
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Makris, J., and A. Ginzburg. "The Afar Depression: transition between continental rifting and sea-floor spreading." Tectonophysics 141, no. 1-3 (September 1987): 199–214. http://dx.doi.org/10.1016/0040-1951(87)90186-7.
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Goodliffe, A. M., and B. Taylor. "The boundary between continental rifting and sea-floor spreading in the Woodlark Basin, Papua New Guinea." Geological Society, London, Special Publications 282, no. 1 (2007): 217–38. http://dx.doi.org/10.1144/sp282.11.
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Farrar, Edward, and John M. Dixon. "Ridge subduction: kinematics and implications for the nature of mantle upwelling." Canadian Journal of Earth Sciences 30, no. 5 (May 1, 1993): 893–907. http://dx.doi.org/10.1139/e93-074.
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Ridge subduction follows the approach of an oceanic spreading centre towards a trench and subduction of the leading oceanic plate beneath the overriding plate. There are four possible kinematic scenarios: (1) welding of the trailing and overriding plates (e.g., Aluk–Antarctic Ridge beneath Antarctica); (2) slower subduction of the trailing plate (e.g., Nazca–Antarctic Ridge beneath Chile and Pacific–Izanagi Ridge beneath Japan); (3) transform motion between the trailing and overriding plates (e.g., San Andreas Transform); or (4) divergence between the overriding and trailing plates (e.g., Pacific – North America). In case 4, the divergence may be accommodated in two ways: the overriding plate may be stretched (e.g., Basin and Range Province extension, which has brought the continental margin into collinearity (and, therefore, transform motion) with the Pacific – North America relative motion); or divergence may occur at the continental margin and be manifest as a change in rate and direction of sea-floor spreading because the pair of spreading plates changes (e.g., from Pacific–Farallon to Pacific – North America), spawning a secondary spreading centre (i.e., Gorda – Juan de Fuca – Explorer ridge system) that migrates away from the overriding plate.Mantle upwelling associated with sea-floor spreading ridges is widely regarded as a passive consequence, rather than an active cause, of plate divergence. Geological and geophysical phenomena attendant to ridge–trench interaction suggest that regardless of the kinematic relations among the three plates, a thermal anomaly formerly associated with the ridge migrates beneath the overriding plate. The persistence of this thermal anomaly demonstrates that active mantle upwelling may continue for tens of millions of years after ridge subduction. Thus, regardless of whether the mantle upwelling was active or passive at its origin, it becomes active if the spreading continues for sufficient time and, thus, must contribute to the driving mechanism of plate tectonics.
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Goričan, Špela, Josip Halamić, Tonći Grgasović, and Tea Kolar-Jurkovšek. "Stratigraphic evolution of Triassic arc-backarc system in northwestern Croatia." Bulletin de la Société Géologique de France 176, no. 1 (January 1, 2005): 3–22. http://dx.doi.org/10.2113/176.1.3.
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Abstract Middle Triassic arc-related extensional tectonics in the western Tethys generated a complex pattern of intra-and backarc basins. We studied volcano-sedimentary successions of subsided continental-margin blocks (Mts. Žumberak and Ivanščica) and of dismembered incomplete ophiolite sequences interpreted as remnants of a backarc basin (Mts. Medvednica and Kalnik) in northwestern Croatia. We dated the successions with radiolarians, conodonts, foraminifers, algae, and sponges. The continental margin experienced a phase of accelerated subsidence in the late Anisian that was approximately coincident with the onset of intermediate and acidic volcanism; pelagic sediments with volcaniclastics accumulated atop subsided carbonate platforms. These relatively shallow basins were later infilled completely by prograding platforms in the late Ladinian-Carnian. In the backarc basin, sea-floor spreading initiated near the Anisian-Ladinian boundary and continued into the late Carnian. Pillow basalts were erupted and interlayered with radiolarian cherts and shales. The studied area was a part of a larger Triassic arc-backarc system preserved in the southern Alps, Alpine-Carpathian Belt, Dinarides, and Hellenides. Volcano-sedimentary successions of Mts. Medvednica and Kalnik are relics of the Meliata-Maliak backarc basin. In comparison to other previously dated oceanic remnants of this system, the longest continuous sea-floor spreading is now documented in one restricted tectonic unit.
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Nelson, Gareth. "A Decade of Challenge the Future of Biogeography." Earth Sciences History 4, no. 2 (January 1, 1985): 187–96. http://dx.doi.org/10.17704/eshi.4.2.c347xp1671w4m0n0.
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According to Croizat's global synthesis, the main biogeographic patterns include trans-Atlantic, trans-Pacific, trans-Indoceanic, Boreal, and Austral. Geological and geophysical theories vary, but agree that sea-floor spreading in the Pacific is different in its effect from that in other ocean basins. The difference allows for radial expansion of the basin and not merely east-west displacement of continental areas. Biogeographic data suggest that bipolar (boreal + austral) distributions are to be reckoned among the results of sea-floor spreading in the Pacific. Data from one group of inshore fishes (family Engraulidae) exemplify this notion and add, as terminal parts of the differentiation of the Pacific Basin, trans-Panama marine vicariance and a collateral occurrence in freshwater of tropical South America. These findings corroborate Croizat's synthesis. They suggest that the critical evaluation of that synthesis will be the main task of biogeography over the next decade. They indicate that within the area of systematics, evaluation will require a cladistic approach and the elimination of paraphyletic groups from classification.
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Boillot, G., and N. Froitzheim. "Non-volcanic rifted margins, continental break-up and the onset of sea-floor spreading: some outstanding questions." Geological Society, London, Special Publications 187, no. 1 (2001): 9–30. http://dx.doi.org/10.1144/gsl.sp.2001.187.01.02.
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Cresswell, G. "Nutrient enrichment of the Sydney continental shelf." Marine and Freshwater Research 45, no. 4 (1994): 677. http://dx.doi.org/10.1071/mf9940677.
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Nutrient-rich waters arrived at the continental shelf at Sydney in late January 1992 in two ways: as an intrusion from the nearby continental slope and as a cold upwelled plume originating several hundred kilometres farther north. With the former, an undercurrent flowed northward on the upper continental slope south of where the nearshore edge of a warm anticyclonic eddy separated from the shelf and curved out to sea. The undercurrent rose onto the floor of the shelf and spread shoreward at least to the 60-m isobath as an intrusion of slope water. The other source of nutrients, the upwelled plume from the north, probably resulted from the East Australian Current spreading onto the shelf and driving an Ekman bottom boundary layer shoreward, where it upwelled to the surface and was then advected southward. Very high values of fluorescence at 20-40 m depth in the plume suggested a significant phytoplankton bloom. The plume was not continuous at the surface for the final 100 km of its passage to Sydney, rather taking the form of 40-km-long 'slugs' moving at -0.3 m s-1. It was, however, continuous beneath the surface. From Sydney it was carried out to sea around the perimeter of the anticyclonic eddy.
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Hoang, Tien Dinh, and Luan Thi Bui. "The mechanism of formation, development and deformation of sedimentary basins in Viet Nam continental shelf." Science and Technology Development Journal - Natural Sciences 1, T5 (November 29, 2018): 278–89. http://dx.doi.org/10.32508/stdjns.v1it5.561.
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The sedimentary basins in area of Việt Nam continental shelf are located along the deep fault systems between the folded Indochinese block and Việt Băc-Hoa Nam platform and with the transitional zone. Is means that the zone attenuated continental crust. Due to that extruction of the Indochinese block toward the SoustEast which wrenched in right, in addition, due to the appearance of the thermal anomaly, producing the activity of Bien Dong seafloor spreading axis and drift of Australian–New Guinea plate toward Nord-East, induced some geodinamic factors to form many sedimentary basins in margins of Biển Dong Sea, such as: rift, pressure, extension, vertical slide cliff, horizontal displacement and wrench. These geodinamic factors created favourable conditions to form, develop and deform the sedimentary basins in Việt Nam continental shelf, followed the pull- apart type mechanism. But each sedimentary basin had its type of mechanism which depended on the concrete place of its basin from the Indochinese block and the thermal anomaly in Bien Dong Sea. Beside, itsformed condition for gas hydrate accumulations in some basins.
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Todd, B. J., and I. Reid. "The continent–ocean boundary south of Flemish Cap: constraints from seismic refraction and gravity." Canadian Journal of Earth Sciences 26, no. 7 (July 1, 1989): 1392–407. http://dx.doi.org/10.1139/e89-119.
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A seismic-refraction survey providing deep crustal structural information on the continent–ocean boundary south of Flemish Cap on the east coast of Canada was carried out using large air-gun sources and ocean-bottom seismometers. The seismic-refraction results and gravity modelling suggest that thinned continental crust extends 25 km seaward of the shelf break. The transition from continental to oceanic crust with a main crustal layer p-wave velocity of 7.3 km/s extends seaward over 100 km to the south. One refraction profile with thin (~4 km) oceanic crust was probably shot on, or very near, the trace of a fracture zone. Previous plate reconstructions have suggested that Cretaceous-age sea-floor spreading south of Flemish Cap occurred as a series of short spreading segments offset by transform fauits, or by asymmetric rifting between Iberia and Flemish Cap. This study suggests that an oblique shear margin may have formed south of Flemish Cap. possibly as a result of transcurrent motion between Flemish Cap and Iberia.
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Wilson, Robert W., Knud Erik S. Klint, Jeroen A. M. Van Gool, Kenneth J. W. McCaffrey, Robert E. Holdsworth, and James A. Chalmers. "Faults and fractures in central West Greenland: onshore expression of continental break-up and sea-floor spreading in the Labrador – Baffin Bay Sea." Geological Survey of Denmark and Greenland (GEUS) Bulletin 11 (December 5, 2006): 185–204. http://dx.doi.org/10.34194/geusb.v11.4931.
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The complex Ungava fault zone lies in the Davis Strait and separates failed spreading centres in the Labrador Sea and Baffin Bay. This study focuses on coastal exposures east of the fault-bound Sisimiut basin, where the onshore expressions of these fault systems and the influence of pre-existing basement are examined. Regional lineament studies identify five main systems: N–S, NNE–SSW, ENE–WSW, ESE–WNW and NNW–SSE. Field studies reveal that strike-slip movements predominate, and are consistent with a ~NNE–SSW-oriented sinistral wrench system. Extensional faults trending N–S and ENE–WSW (basement-parallel), and compressional faults trending E–W, were also identified. The relative ages of these fault systems have been interpreted using cross-cutting relationships and by correlation with previously identified structures. A two-phase model for fault development fits the development of both the onshore fault systems observed in this study and regional tectonic structures offshore. The conclusions from this study show that the fault patterns and sense of movement on faults onshore reflect the stress fields that govern the opening of the Labrador Sea – Davis Strait – Baffin Bay seaway, and that the wrench couple on the Ungava transform system played a dominant role in the development of the onshore fault patterns.
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Myers, Robert A., and David J. W. Piper. "Seismic stratigraphy of late Cenozoic sediments in the northern Labrador Sea: a history of bottom circulation and glaciation." Canadian Journal of Earth Sciences 25, no. 12 (December 1, 1988): 2059–74. http://dx.doi.org/10.1139/e88-191.
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The seismicstratigraphy of the upper 1 km of sediment in the northern Labrador Sea has been determined from the examination of about 26 000 line kilometres of seismic profiles. Four key reflectors (A to D) have been correlated with Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) holes and range in age from mid-Pliocene to approximately mid-Pleistocene. Ten seismic facies have been distinguished and are interpreted as resulting from slope progradation, turbidite deposition in channels and on the basin floor, and widespread contourite deposition.Tertiary sediments are predominantly hemipelagic or contourite, but in the mid-Pliocene, turbidite deposition began in the northeast Labrador Basin, which might reflect either Greenland glaciation or lowering of sea level. At the same time, widespread erosion and buildup of drift deposits indicate that there was an intensification of bottom-water circulation, probably reflecting high-latitude cooling. This was followed by a return to less dynamic conditions as increased sea-ice cover reduced bottom-water generation in high-latitude seas. A turbidite deep-sea fan developed off Hudson Strait in the Early Pleistocene. In the mid- and late Quaternary, there was a major increase in the supply of turbidites from the Labrador margin, accompanied by the development of an extensive channel system on the continental margin. This was a consequence of glacial ice sheets extending to the top of the continental slope and discharging sediment directly to deep water.
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Healy, D., and N. J. Kusznir. "Early kinematic history of the Goban Spur rifted margin derived from a new model of continental breakup and sea-floor spreading initiation." Geological Society, London, Special Publications 282, no. 1 (2007): 199–215. http://dx.doi.org/10.1144/sp282.10.
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Ghods, A., and J. Arkani-Hamed. "Interpretation of the satellite magnetic anomaly of the Nova Scotia marginal basin." Canadian Journal of Earth Sciences 35, no. 2 (February 1, 1998): 162–74. http://dx.doi.org/10.1139/e97-095.
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Satellite magnetic anomaly maps show well-defined negative anomalies over some deep sedimentary marginal basins, such as the Nova Scotia marginal basin. A possible explanation would be the thermal demagnetization of the oceanic upper crust due to thermal blanketing by the sediments and the oceanic lower crust and uppermost mantle due to subsidence into hotter regions beneath. We examine this possibility by computing the thermoviscous remanent magnetization of the oceanic lithosphere beneath the Nova Scotia basin using a detailed thermal evolution model which takes into account the continental rifting, sea-floor spreading, and subsequent subsidence. It is concluded that the thermal demagnetization is not sufficient to explain the entire observed negative magnetic anomaly over the basin; it contributes ~40% to the anomaly. We suggest that a major part, ~60%, of the anomaly arises from the particular location of the early Mesozoic oceanic lithosphere beneath the basin, which has a relatively weaker bulk remanent magnetization compared with a highly magnetic continental crust in the west and north and the strong magnetic oceanic lithosphere of the Cretaceous Quiet Zone in the east.
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Kumarapeli, P. Stephen, Greg R. Dunning, Hillar Pintson, and Jim Shaver. "Geochemistry and U–Pb zircon age of comenditic metafelsites of the Tibbit Hill Formation, Quebec Appalachians." Canadian Journal of Earth Sciences 26, no. 7 (July 1, 1989): 1374–83. http://dx.doi.org/10.1139/e89-117.
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Metafelsites in Waterloo area, Quebec, represent the only known silicic volcanic rocks in the predominantly basaltic Tibbit Hill Formation. Low-grade metamorphism accompanied by hydration and albitization has converted the felsic volcanic rocks mainly to muscovite–quartz–albite schists. The volcanic parent of these metafelsites was formed partly as lava flows and partly as tuffs. The principal compositional type was a comendite. A component of intermediate rocks is also present but its extent is undetermined and probably minor. U–Pb zircon studies of the metafelsites have yielded a reliable age of [Formula: see text]. This Early Cambrian age is probably representative of the age of the Tibbit Hill Formation as a whole.The Tibbit Hill Formation accumulated at one of the clearest examples of a RRR (rift–rift–rift) triple junction–the Sutton Mountains triple junction–of the continental rift system formed as a prelude to the opening of the Iapetus Ocean. Its volcanic rocks are products of the youngest major episode of rift-related volcanism known from the continental margin of Laurentia. The volcanic event may have occurred as a harbinger of the onset of sea-floor spreading at the Sutton Mountains triple junction.
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Storey, Bryan C., Alan P. M. Vaughan, and Teal R. Riley. "The links between large igneous provinces, continental break-up and environmental change: evidence reviewed from Antarctica." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 104, no. 1 (March 2013): 17–30. http://dx.doi.org/10.1017/s175569101300011x.
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ABSTRACTEarth history is punctuated by events during which large volumes of predominantly mafic magmas were generated and emplaced by processes that are generally accepted as being, unrelated to ‘normal’ sea-floor spreading and subduction processes. These events form large igneous provinces (LIPs) which are best preserved in the Mesozoic and Cenozoic where they occur as continental and ocean basin flood basalts, giant radiating dyke swarms, volcanic rifted margins, oceanic plateaus, submarine ridges, and seamount chains. The Mesozoic history of Antarctica is no exception in that a number of different igneous provinces were emplaced during the initial break-up and continued disintegration of Gondwana, leading to the isolation of Antarctica in a polar position. The link between the emplacement of the igneous rocks and continental break-up processes remains controversial. The environmental impact of large igneous province formation on the Earth System is equally debated. Large igneous province eruptions are coeval with, and may drive environmental and climatic effects including global warming, oceanic anoxia and/or increased oceanic fertilisation, calcification crises, mass extinction and release of gas hydrates.This review explores the links between the emplacement of large igneous provinces in Antarctica, the isolation of Antarctica from other Gondwana continents, and possibly related environmental and climatic changes during the Mesozoic and Cenozoic.
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Morvan, Mathieu, Pierre L'Hégaret, Xavier Carton, Jonathan Gula, Clément Vic, Charly de Marez, Mikhail Sokolovskiy, and Konstantin Koshel. "The life cycle of submesoscale eddies generated by topographic interactions." Ocean Science 15, no. 6 (November 22, 2019): 1531–43. http://dx.doi.org/10.5194/os-15-1531-2019.
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Abstract. Persian Gulf Water and Red Sea Water are salty and dense waters flowing at intermediate depths in the Gulf of Oman and the Gulf of Aden, respectively. Their spreading pathways are influence by mesoscale eddies that dominate the surface flow in both semi-enclosed basins. In situ measurements combined with altimetry indicate that Persian Gulf Water is stirred in the form of filaments and submesoscale structures by mesoscale eddies. In this paper, we study the formation and the life cycle of intense submesoscale vortices and their potential impact on the spreading of Persian Gulf Water and Red Sea Water. We use a primitive-equation three-dimensional hydrostatic model at a submesoscale-resolving resolution to study the evolution of submesoscale vortices. Our configuration idealistically mimics the dynamics in the Gulf of Oman and the Gulf of Aden: a zonal row of mesoscale vortices interacting with north and south topographic slopes. Intense submesoscale vortices are generated in the simulations along the continental slopes due to two different mechanisms. First, intense vorticity filaments are generated over the continental slope due to frictional interactions of the background flow with the sloping topography. These filaments are shed into the ocean interior and undergo horizontal shear instability that leads to the formation of submesoscale coherent vortices. The second mechanism is inviscid and features baroclinic instabilities arising at depth due to the weak stratification. Submesoscale vortices subsequently drift away, merge and form larger vortices. They can also pair with opposite-signed vortices and travel across the domain. They eventually dissipate their energy via several mechanisms, in particular fusion into the larger eddies or erosion on the topography. Since no submesoscale flow clearly associated with the fragments of Persian Gulf Water was observed in situ, we modeled Persian Gulf Water as Lagrangian particles. Particle patches are advected and sheared by vortices and are entrained into filaments. Their size first grows as the square root of time: a signature of the merging processes. Then, it increases linearly with time, corresponding to their ballistic advection by submesoscale eddies. On the contrary, without intense submesoscale eddies, particles are mainly advected by mesoscale eddies; this implies a weaker dispersion of particles than in the previous case. This shows the potentially important role of submesoscale eddies in spreading Persian Gulf Water and Red Sea Water.
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Schulte, Daniel O., Uwe Ring, Stuart N. Thomson, Johannes Glodny, and Hamish Carrad. "Two-stage development of the Paparoa Metamorphic Core Complex, West Coast, South Island, New Zealand: Hot continental extension precedes sea-floor spreading by ∼25 m.y." Lithosphere 6, no. 3 (June 2014): 177–94. http://dx.doi.org/10.1130/l348.1.
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Goswami, A., P. L. Olson, L. A. Hinnov, and A. Gnanadesikan. "OESbathy version 1.0: a method for reconstructing ocean bathymetry with generalized continental shelf-slope-rise structures." Geoscientific Model Development 8, no. 9 (September 3, 2015): 2735–48. http://dx.doi.org/10.5194/gmd-8-2735-2015.
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Abstract. We present a method for reconstructing global ocean bathymetry that combines a standard plate cooling model for the oceanic lithosphere based on the age of the oceanic crust, global oceanic sediment thicknesses, plus generalized shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to develop a methodology for reconstructing ocean bathymetry in the geologic past that includes heterogeneous continental margins in addition to abyssal ocean floor. First, the plate cooling model is applied to maps of ocean crustal age to calculate depth to basement. To the depth to basement we add an isostatically adjusted, multicomponent sediment layer constrained by sediment thickness in the modern oceans and marginal seas. A three-parameter continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Parameters of the shelf-slope-rise structures at active and passive margins are determined from modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and central Atlantic, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth to basement, ocean bathymetry with an isostatically adjusted multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.
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Wynn, Jeffrey C. "Titanium geophysics: The application of induced polarization to sea‐floor mineral exploration." GEOPHYSICS 53, no. 3 (March 1988): 386–401. http://dx.doi.org/10.1190/1.1442472.
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Titanium is abundant in the Earth's crust, but it can be economically extracted from only a limited group of minerals, principally rutile [Formula: see text] and ilmenite [Formula: see text], both found mainly in fossil beach‐complex placer deposits. Both minerals have only a weak magnetic susceptibility, insufficient to permit correlation between magnetic surveys and known titanium‐rich deposits. However, ilmenite shows an unusually strong induced‐polarization (IP) response, whereas the IP response of rutile is relatively weak. IP spectral signatures for ilmenite acquired in laboratory and field settings are also distinctly different from those of other polarizing materials, for instance pyrite. A nonfloating, towed‐streamer IP system was designed and deployed in surveys off the coasts of Virginia and Georgia. When the cable lies on the sea floor, calculations indicate that only about 8 percent of the injected current actually finds its way into the underlying sediment. Partly because of this high transmitted‐current to injected‐current ratio, a stationary‐streamer IP noise envelope of about 2–4 milliradians (mrad) phase shift and a towed‐streamer noise envelope of 4–6 mrad were measured. Two surveys were undertaken, one of which covered about 30 traverse km of the Atlantic continental shelf (ACS) and crossed two vibracore sites where geologic control could be obtained. Many IP anomalies were observed, with some ranging as high as 20+ mrad; about one‐third of the shallow bathymetric lows (probable paleochannels) showed anomalous IP results. Modeling suggests that these anomalies may have been caused by significant heavy‐mineral placer bodies containing as much as 20 percent ilmenite. Identification of an anomaly in towed‐streamer (conventional IP) mode data will probably be posibble only if the deposit contains more than 1 to 2 weight percentage of ilmenite. Attempts to use the spectral IP method to identify ilmenite directly with the marine IP streamer in a stationary sampling mode gave equivocal results. Although the spectral IP method appears to work well on land, in the marine application the ilmenite was present in only small quantities at the vibracore sites investigated, and the resulting weak signal was partially masked by the noise present in the IP measurement. To make spectral measurements, the streamer must be positioned accurately over a polarizing source. This task is difficult, because the deposits tend to be made up of numerous discrete, kilometer‐long bodies, perhaps no more than 50 m wide and usually only 5 to 15 m thick. Such deposits cannot be adequately tested by a vibracore survey designed to sample every 300 or 1000 m, even if the survey is augmented with a high‐resolution seismic profile. This work suggests that the large IP response of ilmenite may permit rough quantification of sea‐floor placer mineral sources from a shipborne platform while the ship is in motion. Polarizing mineral species might even be identified by using spectral IP measurements. Applications of the technology to identifying other marine mineral deposits, such as smokers at ocean‐floor spreading centers and cobalt‐rich manganese crusts, are logical extensions of this research.
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Kent, D. V., and G. Muttoni. "Modulation of Late Cretaceous and Cenozoic climate by variable drawdown of atmospheric <i>p</i>CO<sub>2</sub> from weathering of basaltic provinces on continents drifting through the equatorial humid belt." Climate of the Past Discussions 8, no. 5 (September 13, 2012): 4513–64. http://dx.doi.org/10.5194/cpd-8-4513-2012.
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Abstract. The small reservoir of carbon dioxide in the atmosphere (pCO2) that modulates climate through the greenhouse effect reflects a delicate balance between large fluxes of sources and sinks. The major long-term source of CO2 is global outgassing from sea-floor spreading, subduction, hotspot activity, and metamorphism; the ultimate sink is through weathering of continental silicates and deposition of carbonates. Most carbon cycle models are driven by changes in the source flux scaled to variable rates of ocean floor production. However, ocean floor production may not be distinguishable from being steady since 180 Ma. We evaluate potential changes in sources and sinks of CO2 for the past 120 Ma in a paleogeographic context. Our new calculations show that although decarbonation of pelagic sediments in Tethyan subduction likely contributed to generally high pCO2 levels from the Late Cretaceous until the Early Eocene, shutdown of Tethyan subduction with collision of India and Asia at the Early Eocene Climate Optimum at around 50 Ma was inadequate to account for the large and prolonged decrease in pCO2 that eventually allowed the growth of significant Antarctic ice sheets by around 34 Ma. Instead, variation in area of continental basaltic provinces in the equatorial humid belt (5° S–5° N) seems to be the dominant control on how much CO2 is retained in the atmosphere via the silicate weathering feedback. The arrival of the highly weatherable Deccan Traps in the equatorial humid belt at around 50 Ma was decisive in initiating the long-term slide to lower atmospheric pCO2, which was pushed further down by the emplacement of the 30 Ma Ethiopian Traps near the equator and the southerly tectonic extrusion of SE Asia, an arc terrane that presently is estimated to account for 1/4 of CO2 consumption from all basaltic provinces that account for ~1/3 of the total CO2 consumption by continental silicate weathering (Dessert et al., 2003). A negative climate-feedback mechanism that (usually) inhibits the complete collapse of atmospheric pCO2 is the accelerating formation of thick cation-deficient soils that retard chemical weathering of the underlying bedrock. Nevertheless, equatorial climate seems to be relatively insensitive to pCO2 greenhouse forcing and thus with availability of some rejuvenating relief as in arc terranes or thick basaltic provinces, silicate weathering in this venue is not subject to a strong negative feedback, providing an avenue for sporadic ice ages. The safety valve that prevents excessive atmospheric pCO2 levels is the triggering of silicate weathering of continental areas and basaltic provinces in the temperate humid belt. Increase in Mg/Ca ratio of seawater over the Cenozoic may be due to weathering input from continental basaltic provinces.
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Pattillo, J., and P. J. Nicholls. "A TECTONOSTRATIGRAPHIC FRAMEWORK FOR THE VULCAN GRABEN, TIMOR SEA REGION." APPEA Journal 30, no. 1 (1990): 27. http://dx.doi.org/10.1071/aj89002.
Full textAbstract:
The Vulcan Graben is a northeast trending intracratonic rift system developed in response to Late Jurassic-Early Cretaceous break-up of the Australian northwest continental margin. A depositional sequence study was undertaken of the Vulcan Graben and the surrounding area, incorporating regional well and seismic data. From this a tectonostratigraphic framework has been established. Three megasequences are defined in relation to the Callovian rift episode; Pre-rift (pre-Callovian), Syn-rift (Callovian to Valanginian) and Post-rift (Valanginian to Present Day), each consisting of a number of discrete depositional sequences. This study has clarified the structural and stratigraphic evolution of the region, enabling development of dynamic depositional models. These models constrain the vertical and lateral facies distribution across the region, thus providing a powerful basis for petroleum exploration, including prediction of reservoir, seal and source rocks.Significantly, while Late Jurassic rifting was initiated in the Late Callovian, imprinting a NE-SW oriented grain, a second major tectonic episode occurred in the Kimmeridgian trending ENE-WSW, which generated the dominant regional structural architecture. Recognition of this Kimmeridgian event has considerable impact on the successful delineation of structural plays within the region and provided significant control on syn-rift facies distribution and consequently stratigraphic play potential within the Vulcan Graben. Stratigraphic and structural relationships clearly indicate that rifting ceased in the middle Valanginian, followed by post- rift thermal subsidence and consequent transgression and inundation of the Vulcan Graben. The intra-Valanginian event represents a regional disconformity rather than a major tectonic unconformity and defines the boundary between the syn- and post-rift megasequences. This is consistent with the revised Valanginian date for the onset of sea-floor spreading in the Argo Abyssal Plain.A revised lithostratigraphic nomenclature is proposed for the region which complements the resolution achieved by depositional sequence mapping.
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SUNAL, GÜRSEL, and OKAN TÜYSÜZ. "Palaeostress analysis of Tertiary post-collisional structures in the Western Pontides, northern Turkey." Geological Magazine 139, no. 3 (May 2002): 343–59. http://dx.doi.org/10.1017/s0016756802006489.
Full textAbstract:
Fingerprints of the opening of the Western Black Sea Basin and collision of Pontides and Sakarya Continent along the Intra-Pontide suture can be traced in the area between Cide (Kastamonu) and Kurucaşile (Bartin) in northern Turkey, along the southern coast of the Black Sea. The Western Black Sea Basin is an oceanic basin opened as a back-arc basin of the northward-subducting Intra-Pontide Ocean. Basement units related to this opening are represented by Lower Cretaceous and older units. The first arc magmatism related to this subduction began during Turonian times. Coeval with this magmatism, back-arc extension affected the region and caused development of horst-graben topography. This extensional period resulted in the break-up of continental crust and the oceanic spreading in the Western Black Sea Basin during Late Santonian times. During the Late Campanian–Early Maastrichtian period, the Sakarya Continent and Pontides collided and arc magmatism on the Pontides ended. After this collision, the Western Pontides thickened, imbricated and developed a mainly N-vergent foreland fold and thrust belt character since Late Eocene–Oligocene times. The palaeostress directions calculated from thrust faults of this foreland fold and thrust belt are 4.6°/156.6° for σ1, 6.4°/66.1° for σ2, and 83.2°/261.9° for σ3. The nature of the imbrication indicates that it was a northward prograding foreland system connected to a floor thrust (detachment) fault at the bottom. Field observations on curved slickenfibres support the theory that the thrust faults of this imbricated structure have transformed to oblique thrusts and strike-slip faults over time.
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Kent, D. V., and G. Muttoni. "Modulation of Late Cretaceous and Cenozoic climate by variable drawdown of atmospheric <i>p</i>CO<sub>2</sub> from weathering of basaltic provinces on continents drifting through the equatorial humid belt." Climate of the Past 9, no. 2 (March 4, 2013): 525–46. http://dx.doi.org/10.5194/cp-9-525-2013.
Full textAbstract:
Abstract. The small reservoir of carbon dioxide in the atmosphere (pCO2) that modulates climate through the greenhouse effect reflects a delicate balance between large fluxes of sources and sinks. The major long-term source of CO2 is global outgassing from sea-floor spreading, subduction, hotspot activity, and metamorphism; the ultimate sink is through weathering of continental silicates and deposition of carbonates. Most carbon cycle models are driven by changes in the source flux scaled to variable rates of ocean floor production, but ocean floor production may not be distinguishable from being steady since 180 Ma. We evaluate potential changes in sources and sinks of CO2 for the past 120 Ma in a paleogeographic context. Our new calculations show that decarbonation of pelagic sediments by Tethyan subduction contributed only modestly to generally high pCO2 levels from the Late Cretaceous until the early Eocene, and thus shutdown of this CO2 source with the collision of India and Asia at the early Eocene climate optimum at around 50 Ma was inadequate to account for the large and prolonged decrease in pCO2 that eventually allowed the growth of significant Antarctic ice sheets by around 34 Ma. Instead, variation in area of continental basalt terranes in the equatorial humid belt (5° S–5° N) seems to be a dominant factor controlling how much CO2 is retained in the atmosphere via the silicate weathering feedback. The arrival of the highly weatherable Deccan Traps in the equatorial humid belt at around 50 Ma was decisive in initiating the long-term slide to lower atmospheric pCO2, which was pushed further down by the emplacement of the 30 Ma Ethiopian Traps near the equator and the southerly tectonic extrusion of SE Asia, an arc terrane that presently is estimated to account for 1/4 of CO2 consumption from all basaltic provinces that account for ~1/3 of the total CO2 consumption by continental silicate weathering (Dessert et al., 2003). A negative climate-feedback mechanism that (usually) inhibits the complete collapse of atmospheric pCO2 is the accelerating formation of thick cation-deficient soils that retard chemical weathering of the underlying bedrock. Nevertheless, equatorial climate seems to be relatively insensitive to pCO2 greenhouse forcing and thus with availability of some rejuvenating relief as in arc terranes or thick basaltic provinces, silicate weathering in this venue is not subject to a strong negative feedback, providing an avenue for ice ages. The safety valve that prevents excessive atmospheric pCO2 levels is the triggering of silicate weathering of continental areas and basaltic provinces in the temperate humid belt. Excess organic carbon burial seems to have played a negligible role in atmospheric pCO2 over the Late Cretaceous and Cenozoic.
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TAKASHIMA, REISHI, HIROSHI NISHI, and TAKEYOSHI YOSHIDA. "Late Jurassic–Early Cretaceous intra-arc sedimentation and volcanism linked to plate motion change in northern Japan." Geological Magazine 143, no. 6 (September 4, 2006): 753–70. http://dx.doi.org/10.1017/s001675680600255x.
Full textAbstract:
The Sorachi Group, composed of Upper Jurassic ophiolite and Lower Cretaceous island-arc volcano-sedimentary cover, provides a record of Late Jurassic–Early Cretaceous sedimentation and volcanism in an island-arc setting off the eastern margin of the Asian continent. Stratigraphic changes in the nature and volume of the Sorachi Group volcanic and volcaniclastic rocks reveal four tectonic stages. These stages resulted from changes in the subduction direction of the Pacific oceanic plate. Stage I in the Late Jurassic was characterized by extensive submarine eruptions of tholeiitic basalt from the back-arc basin. Slab roll-back caused rifting and sea-floor spreading in the supra-subduction zone along the active Asian continental margin. Stage II corresponded to the Berriasian and featured localized trachyandesitic volcanism that formed volcanic islands with typical island-arc chemical compositions. At the beginning of this stage, movement of the Pacific oceanic plate shifted from northeastward to northwestward. During Stage III, in the Valanginian, submarine basaltic volcanism was followed by subsidence. The Pacific oceanic plate motion turned clockwise, and the plate boundary between the Asian continent and the Pacific oceanic plate changed from convergent to transform. During Stage IV in the Hauterivian–Barremian, in situ volcanism ceased in the Sorachi–Yezo basin, and the volcanic front migrated west of the Sorachi–Yezo basin.
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Cawood, Peter A., Chris J. Hawkesworth, Sergei A. Pisarevsky, Bruno Dhuime, Fabio A. Capitanio, and Oliver Nebel. "Geological archive of the onset of plate tectonics." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 376, no. 2132 (October 2018): 20170405. http://dx.doi.org/10.1098/rsta.2017.0405.
Full textAbstract:
Plate tectonics, involving a globally linked system of lateral motion of rigid surface plates, is a characteristic feature of our planet, but estimates of how long it has been the modus operandi of lithospheric formation and interactions range from the Hadean to the Neoproterozoic. In this paper, we review sedimentary, igneous and metamorphic proxies along with palaeomagnetic data to infer both the development of rigid lithospheric plates and their independent relative motion, and conclude that significant changes in Earth behaviour occurred in the mid- to late Archaean, between 3.2 Ga and 2.5 Ga. These data include: sedimentary rock associations inferred to have accumulated in passive continental margin settings, marking the onset of sea-floor spreading; the oldest foreland basin deposits associated with lithospheric convergence; a change from thin, new continental crust of mafic composition to thicker crust of intermediate composition, increased crustal reworking and the emplacement of potassic and peraluminous granites, indicating stabilization of the lithosphere; replacement of dome and keel structures in granite-greenstone terranes, which relate to vertical tectonics, by linear thrust imbricated belts; the commencement of temporally paired systems of intermediate and high dT/dP gradients, with the former interpreted to represent subduction to collisional settings and the latter representing possible hinterland back-arc settings or ocean plateau environments. Palaeomagnetic data from the Kaapvaal and Pilbara cratons for the interval 2780–2710 Ma and from the Superior, Kaapvaal and Kola-Karelia cratons for 2700–2440 Ma suggest significant relative movements. We consider these changes in the behaviour and character of the lithosphere to be consistent with a gestational transition from a non-plate tectonic mode, arguably with localized subduction, to the onset of sustained plate tectonics. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics'.
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Shellnutt, J. Gregory. "Igneous Rock Associations 21. The Early Permian Panjal Traps of the Western Himalaya." Geoscience Canada 43, no. 4 (December 15, 2016): 251. http://dx.doi.org/10.12789/geocanj.2016.43.104.
Full textAbstract:
The Early Permian (290 Ma) Panjal Traps are the largest contiguous outcropping of volcanic rocks associated with the Himalayan Magmatic Province (HMP). The eruptions of HMP-related lava were contemporaneous with the initial break-up of Pangea. The Panjal Traps are primarily basalt but volumetrically minor intermediate and felsic volcanic rocks also occur. The basaltic rocks range in composition from continental tholeiite to ocean-floor basalt and nearly all have experienced, to varying extent, crustal contamination. Uncontaminated basaltic rocks have Sr–Nd isotopes similar to a chondritic source (ISr = 0.7043 to 0.7073; eNd(t) = 0 ± 1), whereas the remaining basaltic rocks have a wide range of Nd (eNd(t) = –6.1 to +4.3) and Sr (ISr = 0.7051 to 0.7185) isotopic values. The calculated primary melt compositions of basalt are picritic and their mantle potential temperatures (TP ≤ 1450°C) are similar to ambient mantle rather than anomalously hot mantle. The silicic volcanic rocks were likely derived by partial melting of the crust whereas the andesitic rocks were derived by mixing between crustal and mantle melts. The Traps erupted within a continental rift setting that developed into a shallow sea. Sustained rifting created a nascent ocean basin that led to sea-floor spreading and the rifting of microcontinents from Gondwana to form the ribbon-like continent Cimmeria and the Neotethys Ocean.RÉSUMÉLes Panjal Traps du début Permien (290 Ma) constituent le plus grand affleurement contigu de roches volcaniques associées à la province magmatique de himalayienne (HMP). Les éruptions de lave de type HMP étaient contemporaines de la rupture initiale de la Pangée. Les Panjal Traps sont essentiellement des basaltes, mais on y trouve aussi des roches volcaniques intermédiaires et felsiques en quantités mineures. La composition de ces roches basaltiques varie de tholéiite continentale à basalte de plancher océanique, et presque toutes ont subi, à des degrés divers, une contamination de matériaux crustaux. Les roches basaltiques non contaminées ont des contenus isotopiques Sr–Nd similaires à une source chondritique (Isr = 0,7043 à 0,7073; eNd (t) = 0 ± 1), alors que les roches basaltiques autres montrent une large gamme de valeurs isotopiques en Nd (eNd (t) = –6,1 à +4,3) et Sr (Isr = de 0,7051 à 0,7185). Les compositions de fusion primaire calculées des basaltes sont picritiques et leurs températures potentielles mantelliques (TP de ≤ 1450°C) sont similaires à la température ambiante du manteau plutôt que celle d’un manteau anormalement chaud. Les roches volcaniques siliciques dérivent probablement de la fusion partielle de la croûte alors que les roches andésitiques proviennent du mélange entre des matériaux de fusion crustaux et mantelliques. Les Traps ont fait irruption dans un contexte de rift continental qui s’est développé dans une mer peu profonde. Un rifting soutenu a créé un début de bassin océanique lequel conduit à une expansion du fond océanique et au rifting de microcontinents tirés du Gondwana pour former le continent rubané de Cimméria et l'océan Néotéthys.
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Long, D. G. F. "Ella Bay Formation: Early Cambrian shelf differentiation in the Franklinian basin, central eastern Ellesmere Island, Arctic Canada." Canadian Journal of Earth Sciences 26, no. 12 (December 1, 1989): 2621–35. http://dx.doi.org/10.1139/e89-223.
Full textAbstract:
Strata of the Lower Cambrian (Atdabanian) Ella Bay Formation reflect progradation and exposure of a rimmed carbonate platform, subject to intermittent introduction of siliciclastic material from an inshore coastal sand belt or fluviodeltaic source. Initial rapid progradation of platformal carbonates was related to late rift subsidence. Stabilization of depositional sites of oolitic and stromatolitic platform marginal carbonates during middle and late Ella Bay times reflects the earliest phase of differential subsidence of the platform and deep-water basin within the Franklinian mobile belt. Carbonate strata landward of the rim accumulated in a protected shelf setting that was for the most part below effective storm wave base. Towards the end of Ella Bay times, the outer rim became emergent as a result of differential rotation along listric faults as the continental margin began to subside in response to early sea-floor spreading. Dissolution of carbonates along the outer rim during this phase led to the development of distinctive breccia-conglomerates as cave and karst fill. Carbonate production in the lagoon became highly restricted as siliciclastics derived from the inshore clastic belt flooded the area. The pronounced change in style between the Ella Bay Formation and overling clastics of the Ellesmere Group, which consists of a thick sequence of northwesterly prograding clastic wedges, may reflect a change to more rapid subsidence as the ocean began to spread. The local unconformity between the Ella Bay Formation and the Ellesmere Group is thus interpreted as a breakup unconformity.
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Devlin, William J., Gerard C. Bond, and Hannes K. Brueckner. "An assessment of the age and tectonic setting of volcanics near the base of the Windermere Supergroup in northeastern Washington: implications for latest Proterozoic – earliest Cambrian continental separation." Canadian Journal of Earth Sciences 22, no. 6 (June 1, 1985): 829–37. http://dx.doi.org/10.1139/e85-088.
Full textAbstract:
Mafic metavolcanics of the Huckleberry Formation in northeastern Washington occur near the base of the Windermere Supergroup, a sequence of immature clastic rocks thought to have been deposited during a rift event associated with the establishment of the early Paleozoic miogeocline of the North American Cordillera. Previously reported K–Ar data from the Huckleberry volcanics yielded a wide scatter of ages, with a preferred age of extrusion of between 827 and 918 Ma, in apparent agreement with the Late Proterozoic (800–900 Ma) age assigned to this rift event based on geologic relations and ages from the youngest rocks unconformably underlying the Windermere Supergroup. Quantitative subsidence analyses that have been recently applied to the post-rift strata of the miogeocline yield ages for the final phases of rifting, which led directly to continental separation and the onset of sea-floor spreading, of 555–600 Ma. A significant problem arises between the older ages for rifting and the younger ages for breakup, since it implies that a rift phase preceding breakup could have spanned more than 200 Ma.This paper presents new geochemical and isotopic data from the same exposures of Huckleberry volcanics analyzed by K–Ar techniques in an attempt to assess their tectonic setting and age of extrusion. Major- and trace-element compositions are found to be consistent with the rift setting previously interpreted for the Windermere Supergroup. Isotopic analyses, although inconclusive with respect to the true age of the Huckleberry volcanics, indicate that the Rb–Sr system has been disturbed subsequent to extrusion of the volcanics, and therefore the K–Ar ages should be considered suspect. Isotopic data that are beginning to emerge from the northern Canadian Cordillera indicate that the Windermere Supergroup may in fact be younger, in closer agreement with the ages for breakup indicated by the subsidence analyses.
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Henriksen, Niels, A. K. Higgins, Feiko Kalsbeek, and T. Christopher R. Pulvertaft. "Greenland from Archaean to Quaternary. Descriptive text to the 1995 Geological map of Greenland, 1:2 500 000. 2nd edition." GEUS Bulletin 18 (November 27, 2009): 1–126. http://dx.doi.org/10.34194/geusb.v18.4993.
Full textAbstract:
The geological development of Greenland spans a period of nearly 4 Ga, from Eoarchaean to the Quaternary. Greenland is the largest island on Earth with a total area of 2 166 000 km2, but only c. 410 000 km2 are exposed bedrock, the remaining part being covered by a major ice sheet (the Inland Ice) reaching over 3 km in thickness. The adjacent offshore areas underlain by continental crust have an area of c. 825 000 km2.
Greenland is dominated by crystalline rocks of the Precambrian shield, which formed during a succession of Archaean and Palaeoproterozoic orogenic events and stabilised as a part of the Laurentian shield about 1600 Ma ago. The shield area can be divided into three distinct types of basement provinces: (1) Archaean rocks (3200–2600 Ma old, with local older units up to> 3800 Ma) that were almost unaffected by Proterozoic or later orogenic activity; (2) Archaean terrains reworked during the Palaeoproterozoic around 1900–1750 Ma ago; and (3) terrains mainly composed of juvenile Palaeoproterozoic rocks (2000–1750 Ma in age). Subsequent geological developments mainly took place along the margins of the shield. During the Proterozoic and throughout the Phanerozoic major sedimentary basins formed, notably in North and North-East Greenland, in which sedimentary successions locally reaching 18 km in thickness were deposited. Palaeozoic orogenic activity affected parts of these successions in the Ellesmerian fold belt of North Greenland and the East Greenland Caledonides; the latter also incorporates reworked Precambrian crystalline basement complexes.
Late Palaeozoic and Mesozoic sedimentary basins developed along the continent–ocean margins in North, East and West Greenland and are now preserved both onshore and offshore. Their development was closely related to continental break-up with formation of rift basins. Initial rifting in East Greenland in latest Devonian to earliest Carboniferous time and succeeding phases culminated with the opening of the North Atlantic Ocean in the late Paleocene. Sea-floor spreading was accompanied by extrusion of Palaeogene (early Tertiary) plateau basalts in both central West and central–southern East Greenland.
During the Quaternary Greenland was almost completely covered by ice, and the present day Inland Ice is a relic from the Pleistocene ice ages. Vast amounts of glacially eroded detritus were deposited on the continental shelves around Greenland.
Mineral exploitation in Greenland has so far encompassed cryolite, lead-zinc, gold, olivine and coal. Current prospecting activities in Greenland are concentrated on gold, base metals, platinum group elements, molybdenum, iron ore, diamonds and lead-zinc. Hydrocarbon potential is confined to the major Phanerozoic sedimentary basins, notably the large basins offshore North-East and West Greenland. While reserves of oil or gas have yet to be found, geophysical data combined with discoveries of oil seeps onshore have revealed a considerable potential for offshore oil and gas.
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Scrutton, Roger A. "The geology, crustal structure and evolution of the Rockall Trough and the Faeroe-Shetland Channel." Proceedings of the Royal Society of Edinburgh. Section B. Biological Sciences 88 (1986): 7–26. http://dx.doi.org/10.1017/s0269727000004437.
Full textAbstract:
SynopsisFrom direct sampling, the deeper Rockall Trough and Faeroe-Shetland Channel are known to have a Tertiary-Quaternary sedimentary sequence up to 3000 m thick, which is in places, particularly in the north, underlain by early Tertiary basaltic volcanic rocks. The seamounts in the Rockall Trough are of basic volcanics of probable Upper Cretaceous age. The eastern shelf areas have a rifted basement of Precambrian-Devonian (-?Carboniferous) age, overlain by Permian + Mesozoic sedimentary rocks that reach 5000 m in thickness in rift basins. Tertiary sediments thicken rapidly from the shelf into deep water. The western shelf areas have extensive early Tertiary basalts from the Faeroe Islands to the southern part of Rockall Bank. A thin Tertiary—Quaternary cover exists and Precambrian basement lies beneath.The pre-Tertiary geology of the deep water areas and the overall crustal structure have been inferred from geophysical investigations. In the Rockall Trough the crust is of oceanic thickness, about 6 km, but it is probably slightly thicker beneath the Faeroe-Shetland Channel. This fact, coupled with the size of the channel compared with other small ocean basins and the knowledge that fully developed oceanic crust exists just outside the mouth of the Rockall Trough, strongly suggests that at least parts of the deep water areas are floored by oceanic crust. However, seismic reflection and magnetic anomaly profiles do not yield observations characteristic of normal oceanic crust.The age of any oceanic crust in the Rockall Trough and Faeroe-Shetland Channel is equivocal. Between 54° and 59° N a succession of largely sedimentary rocks up to 3000 m in thickness occurs between the Tertiary and the acoustic basement. To the north this succession is masked on seismic profiles by early Tertiary basalts but it is probably present; to the south it is interrupted by a series of acoustically opaque basement ridges. With slow sedimentation rates, this succession could extend back to the late Palaeozoic, but with rapid rates, only to the mid-Upper Cretaceous. An age of mid-Lower to mid-Upper Cretaceous for oceanic crust, equal to that of the ocean crust outside the mouth of the Rockall Trough, is accepted here. Although rapid subsidence and infill in Upper Cretaceous time is not characteristic of major shelf basins around Britain, it may be acceptable for the Rockall Trough and Faeroe-Shetland Channel if they are underlain by oceanic crust rather than continental crust.A likely model for the formation of the Rockall Trough and Faeroe-Shetland Channel is of continental rifting and subsidence from late Palaeozoic or earliest Mesozoic to mid-Cretaceous time, then sea-floor spreading in Albian (c.105My)–Santonian (c.85 My) time, accompanied and immediately followed by rapid subsidence and deposition. The Tertiary was heralded by widespread basaltic igneous activity which briefly arrested subsidence, but was largely a period of subsidence without sedimentation keeping pace.
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Johnson, Walter R., Zhen-Gang Ji, and Charles F. Marshall. "STATISTICAL ESTIMATES OF SHORELINE OIL CONTACT IN THE GULF OF MEXICO." International Oil Spill Conference Proceedings 2005, no. 1 (May 1, 2005): 547–51. http://dx.doi.org/10.7901/2169-3358-2005-1-547.
Full textAbstract:
ABSTRACT As steward of the Federal offshore lands known as the Outer Continental Shelf (OCS), the U.S. Department of the Interior (DOI), Minerals Management Service (MMS), is responsible for balancing the Nation's search for commercial oil and gas with protection of the human and marine environments. The MMS regulates the development of mineral resources in an environmentally safe manner by analyzing environmental consequences of the OCS program prior to lease sales or approval of industry's plans. The Oil-Spill Risk Analysis (OSRA) model was developed by the DOI for the analysis of possible oil-spill impact from offshore oil and gas operations. The OSRA model produces statistical estimates of hypothetical oil-spill occurrence and contact from projected OCS operations. The model generates an ensemble of sea surface oil-spill trajectories by initiating thousands of oil-spill simulations at hypothetical spill locations to statistically characterize oil-spill risk in areas of prospective drilling and production and along projected pipeline routes. The hypothetical spills are initiated every day and move at the velocity of the vector sum of the surface ocean currents plus an empirical wind-induced drift of speed equal to 3.5% of the local wind speed, with a wind-speed-dependent direction (Samuels et al., 1982). The model generates oil-spill trajectories by integrating interpolated values of the wind and ocean current fields at intervals short enough to use the full spatial resolution of the ocean current and wind fields. The OSRA model, as applied to the Gulf of Mexico, uses 3-hourly ocean current fields over 7 years (1993–1999) generated by the Princeton Regional Ocean Forecast System (PROFS) (Oey et al., 2004). The PROFS is driven by synoptic winds, heat flux, and river flows. The wind field is based on the European Center for Medium-Range Weather Forecasts surface winds enhanced by observations from meteorological buoys and Coastal-Marine Automated Network stations. The same wind field used to force the ocean model is used to move the oil in the spill trajectories. As an example of environmental assessment, the OSRA model was used to estimate the spreading of oil spills by simultaneously modeling fractions of each spill, referred to as spillets. The spillets were used to calculate additional statistics, in particular, the length of coastline contacted by a large spill. The coastline was divided into equal length segments. Assumptions were made regarding what fraction of the spill (i.e., the number of spillets) that contacted a land segment would constitute a contact larger than the “level of concern.” Sensitivity of the analysis to key assumed parameters, such as the number of spillets and the level of concern, were tested.
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Larsen, L. M., W. S. Watt, and M. Watt. "Geology and petrology of the Lower Tertiary plateau basalts of the Scoresby Sund region, East Greenland." Bulletin Grønlands Geologiske Undersøgelse 157 (January 1, 1989): 1–164. http://dx.doi.org/10.34194/bullggu.v157.6699.
Full textAbstract:
The early Tertiary plateau basalts in East Greenland are situated on a continental margin and were erupted during continental break-up and initiation of sea-floor spreading in the North Atlantic. In the region stretching from Scoresby Sund southward to 69°N 40 000 km2of basalts with an average thickness of 1.5 km have been investigated by measuring and flow-to-flow sampling of 130 profiles, followed by major element geochemical analysis and microprobe analysis, trace element analysis and some Sr isotope data. The basalts rest on Mesozoic sediments in the east and on Precambrian gneiss in the west. Six basalt formations are defined: the Magga Dan, Milne Land and Geikie Plateau Formations form a lower regional sequence erupted in one volcanic episode from sites in the NW part of the region; the Rømer Fjord and Skrænterne Formations form an upper regional sequence erupted in a subsequent volcanic episode in which eruption sites moved SE to centres east of the present Atlantic coast; the Igtertivâ Formation and a coast-parallel dyke swarm formed in a third volcanic episode only recorded at the Atlantic coast. The lavas are essentially flat-lying; a narrow strip along the Atlantic coast is extensively block faulted. Single lava flows are extensive (max. 11 000 km2) and voluminous (max. 300 km3). They are well preserved, with metamorphism of the low zeolite facies. All the lavas and most of the dykes are fractionated tholeiitic basalts with Mg/(Mg+Fe2+) ratios of 0.66-0.39 and TiO2 = 1.2-4.5%. The major part (the 'main basalts', 96% by volume) have Mg ratios of 0.56-0.39, while only 4 vol.% are Mg-rich basalts with Mg ratios of 0.66-0.57. A nephelinitic tuff layer occurs at the base of the second sequence. A few dykes are alkaline. The Mg-rich basalts have microphenocrysts of olivine (FO90-70) and chromite, while the main basalts comprise both aphyric and porphyritic sequences. Phenocrysts of plagioclase (An88-37) are abundant, of olivine (FO80-57) are sparse but ubiquitous, and of augite (FS9-20) sparse and often absent. Groundmass phases are olivine (to FO3737), plagioclase (to An13, augite (to FS62), pigeonite (Fs26-50), titanomagnetite and ilmenite. All rocks contain several per cent fine-grained mesostasis. The phenocrysts frequently show disequilibrium textures and a wide range of compositions within one sample. Extrusion temperatures are calculated to 1280-1110°C, and densities to 2.68-2.78 g/cm3, increasing with fractionation. The volcanic episodes are demonstrated in systematic compositional variations with height in the basalt sequence. Each of the two major episodes started with a variety of lava compositions including Mg-rich basalts, followed by a thick sequence of 'main basalts' showing a systematic decrease of TiO2 and other incompatible elements with height, and ending with a reversal to higher TiO2 values. The third episode is not cyclic, and its products have changed incompatible element ratios. The Mg-rich basalts comprise depleted MORB type basalts, relatively enriched olivine tholeiites, and very enriched tholeiites (Mikis type basalt). Sr isotopes show 87Sr/86Sr ratios of 0.7034 in most basalts and 0.7045 in the Mikis type basalt, while some Si-rich basalts have ratios up to 0.7079. The East Greenland basalts are 'initial rifting' basalts very similar to those in Deccan. The magmas have equilibrated at low pressures in crustal magma chambers. The main basalts have fractionated ol + pl + cpx no matter whether they are aphyric or porphyritic. Simple crystal fractionation can account for sub-trends but not for the complete compositional variation of the main basalts. This is considered as resulting from fractionation in open magma chambers which were repeatedly filled, mixed and tapped. The decrease in TiO2 with height in each volcanic episode indicates increasing magma input rate and shorter residence time in the chamber, while the final reversal indicates the decline and cessation of activity. There is evidence for widespread crustal contamination (1-4%) in the magma chambers of the two lowest formations. Crustal contamination of magmas on the way to the surface occurred sporadically throughout both sequences. One case of magma mixing occurred when a Mg-rich basalt magma invaded the regional main basalt magma chamber. The Mg-rich basalts cannot be directly related to each other or to the main basalts. A petrogenetic scheme is suggested where the Mikis type basalt originated in, or contains an addition from, an undepleted or enriched mantle source. All the other magma types originated in a depleted mantle source by varying degrees and possibly depths of melting. Increasing degrees of melting are indicated for the types nephelinite - enriched olivine tholeiite – main basalt parent – MORB type basalt. The MORB type basalt may also be produced by melting of a residuum. The basalts of the third volcanic episode include another component of mantle or basaltic crust. The three recorded volcanic episodes are related to rifting events during the break-up of the North Atlantic continent, viewed as repeated attempts to straighten out a bend in the original line of opening. The two first rifting events failed while the third for a short while produced oceanic crust. Compared to other regions of the North Atlantic volcanic province the Scoresby Sund basalts are similar to basalts from Kangerdlugssuaq, northern East Greenland, West Greenland, the Faeroes, the Vøring Plateau and some basalts on lceland. The main magma source for the North Atlantic province was similar to that of the lceland hotspot, but enriched subcontinental lithosphere may also have participated in the stage of initial rifting. A correlation for the volcanic episodes throughout East Greenland and the Faeroes is proposed.
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Larsen, Michael, Morten Bjerager, Tor Nedkvitne, Snorre Olaussen, and Thomas Preuss. "Pre-basaltic sediments (Aptian–Paleocene) of the Kangerlussuaq Basin, southern East Greenland." GEUS Bulletin, October 31, 2001, 99–106. http://dx.doi.org/10.34194/ggub.v189.5163.
Full textAbstract:
NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example:
Larsen, M., Bjerager, M., Nedkvitne, T., Olaussen, S., & Preuss, T. (2001). Pre-basaltic sediments (Aptian–Paleocene) of the Kangerlussuaq Basin, southern East Greenland. Geology of Greenland Survey Bulletin, 189, 99-106. https://doi.org/10.34194/ggub.v189.5163
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The recent licensing round in the deep-water areas south-east of the Faeroe Islands has emphasised the continued interest of the oil industry in the frontier areas of the North Atlantic volcanic margins. The search for hydrocarbons is at present focused on the Cretaceous– Paleocene succession with the Paleocene deepwater play as the most promising (Lamers & Carmichael 1999). The exploration and evaluation of possible plays are almost solely based on seismic interpretation and limited log and core data from wells in the area west of the Shetlands. The Kangerlussuaq Basin in southern East Greenland (Fig. 1) provides, however, important information on basin evolution prior to and during continental break-up that finally led to active sea-floor spreading in the northern North Atlantic. In addition, palaeogeographic reconstructions locate the southern East Greenland margin only 50–100 km north-west of the present-day Faeroe Islands (Skogseid et al. 2000), suggesting the possibility of sediment supply to the offshore basins before the onset of rifting and sea-floor spreading. In this region the Lower Cretaceous – Palaeogene sedimentary succession reaches almost 1 km in thickness and comprises sediments of the Kangerdlugssuaq Group and the siliciclastic lower part of the otherwise basaltic Blosseville Group (Fig. 2). Note that the Kangerdlugssuaq Group was defined when the fjord Kangerlussuaq was known as ‘Kangerdlugssuaq’. Based on field work by the Geological Survey of Denmark and Greenland (GEUS) during summer 1995 (Larsen et al. 1996), the sedimentology, sequence stratigraphy and basin evolution of the Kangerlussuaq Basin were interpreted and compared with the deep-water offshore areas of the North Atlantic (Larsen et al. 1999a, b).
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"Crustal accretion and metamorphism in Taiwan, a post-Palaeozoic mobile belt." Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 321, no. 1557 (January 20, 1987): 129–61. http://dx.doi.org/10.1098/rsta.1987.0008.
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Taiwan consists chiefly of Permo-Mesozoic basement unconformably overlain by Cainozoic cover strata; on the east, this complex is juxtaposed along the Longitudinal Valley against the Neogene Coastal Range, the northern extension of the Luzon calc-alkaline arc and intervening fore-arc basin. Accumulation of well-ordered sandstones, shales, limestones and intercalated basaltic units, and outboard argillite melange along the eastern margin of Asia in Permian and early to mid-Mesozoic time was terminated by a major late Cretaceous (85—90 Ma) dynamothermal event that produced the composite basement complex of Taiwan, and also affected much of southeastern China. This basement consists of a westerly Tailuko belt, separated from the easterly Yuli belt by a major fault. The miogeoclinal Tailuko belt is characterized by chloride and biotitic greenschist facies low-pressure assemblages, except in the north where amphibolite facies assemblages are associated with emplacement of remobilized granitic rocks; metamorphic grade increases gradually eastward. The eugeoclinal Yuli belt lacks marble layers and granitic intrusions, and instead contains serpentinite bodies and associated rare highpressure epidote-bearing barroisitic amphibolite tectonic lenses. Tailuko quartzofeldspathic rocks contain mineralogic and geochronologic evidence of Palaeogene and Neogene reheating. Mafic tectonic blocks in the Yuli belt show partial conversion to glaucophanic assemblages; radiometric ages for the blueschist metamorphism are 8-14 Ma. The Cainozoic slate sequence was deposited on the basement complex following renewed Palaeogene rifting. It consists largely of sedimentary strata (and intercalated basalts) laid down on the Asiatic passive margin and seaward in the South China Sea as continental slope deposits. An accretionary wedge was constructed adjacent to the approaching Neogene Luzon arc, marking the non-subducted western margin of the Philippine Sea plate. During Plio-Pleistocene collision of the Luzon arc with the Chinese continental margin, the landward Cainozoic shelf and slope units were imbricated and thrust westward; increased pressure ( P ) and temperature ( T ) during this loading evidently promoted recrystallization of the basement and passive margin cover. Metamorphism ranged from diagenetic and zeolite facies in the Western Foothills to upper greenschist and locally amphibolite facies in the basement complex. No metamorphic hiatus between Mesozoic basement and Cainozoic cover is recognized. The accretionary terrane lying east of the Longitudinal Valley is virtually unmetamorphosed. However, the East Taiwan Ophiolite, occurring as clastic debris and slide blocks in the unmetamorphosed olistostromal, largely Pliocene, Lichi Melange of the Coastal Range fore-arc basin, carries the effects of a mid-Miocene oceanic-ridge recrystallization of actinolite hornfels facies, overprinted by a late Miocene ocean-floor zeolitization. Large portions of the sialic crust making up Taiwan evidently formed approximately in situ , then were deformed and thrust landward during subsequent tectonic events, but far-travelled terranes and allochthonous fragments of oceanic material played an important role in accretion. Recognized and suspected exotics include. (1) Lower or mid-Mesozoic meta-ophiolites, now greenstones, amphibolites and minor serpentinites, previously obducted into the Upper Mesozoic Tailuko belt; amphibolites also occur as enclaves in granitic intrusives 85—90 Ma old; (2) the entire Upper Mesozoic Yuli belt; (3) Mio-Pliocene tectonic blocks of blueschistic meta-ophiolite, emplaced in the east-central part of the Yuli terrane; (4) olistostromal ophiolitic debris (preexisting Miocene oceanic crust of the South China Sea) within the Pliocene Lichi Melange of the Coastal Range; and (5) the Neogene calc-alkaline Luzon arc, which began to collide with Asiatic continental crust in Plio-Pleistocene time. The Cainozoic slate series represents an additional, parautochthonous terrane, which was deposited as the Tertiary miogeoclinal cover along the Asiatic passive margin, and was thrust westward during Plio-Pleistocene arc collision. Among the suspected allochthonous units, Mesozoic amphibolites of both Tailuko and Yuli belts have been identified as of chiefly normal more affinites from their chemical and Nd and Sr isotopic compositions. The clearly oceanic East Taiwan Ophiolite apparently formed along a transform-interrupted spreading centre of the South China Sea marginal basin, based on mineralogic, chemical and isotopic evidence.
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Henriksen, Niels, A. K. Higgins, Feiko Kalsbeek, and T. Christopher R. Pulvertaft. "Greenland from Archaean to Quaternary. Descriptive text to the Geological map of Greenland, 1:2 500 000." GEUS Bulletin, December 29, 2000, 2–93. http://dx.doi.org/10.34194/ggub.v185.5197.
Full textAbstract:
NOTE: This monograph was published in a former series of GEUS Bulletin. Please use the original series name when citing this monograph, for example:
Henriksen, N., Higgins, A., Kalsbeek, F., & Pulvertaft, T. C. R. (2000). Greenland from Archaean to Quaternary. Descriptive text to the Geological map of Greenland, 1:2 500 000. Geology of Greenland Survey Bulletin, 185, 2-93. https://doi.org/10.34194/ggub.v185.5197
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The geological development of Greenland spans a period of nearly 4 Ga, from the earliest Archaean to the Quaternary. Greenland is the largest island in the world with a total area of 2 166 000 km2, but only c. 410 000 km2 are exposed bedrock, the remaining part being covered by an inland ice cap reaching over 3 km in thickness. The adjacent offshore areas underlain by continental crust have an area of c. 825 000 km2. Greenland is dominated by crystalline rocks of the Precambrian shield, which formed during a succession of Archaean and early Proterozoic orogenic events and which stabilised as a part of the Laurentian shield about 1600 Ma ago. The shield area can be divided into three distinct types of basement provinces: (1) Archaean rocks (3100-2600 Ma old, with local older units) almost unaffected by Proterozoic or later orogenic activity; (2) Archaean terraines reworked during the early Proterozoic around 1850 Ma ago; and (3) terraines mainly composed of juvenile early Proterozoic rocks (2000-1750 Ma old). Subsequent geological developments mainly took place along the margins of the shield. During the later Proterozoic and throughout the Phanerozoic major sedimentary basins formed, notably in North and North-East Greenland, and in places accumulated sedimentary successions which reached 10-15 km in thickness. Palaeozoic orogenic activity affected parts of these successions in the Ellesmerian fold belt of North Greenland and the East Greenland Caledonides; the latter also incorporates reworked Precambrian crystalline basement complexes. Late Palaeozoic and Mesozoic sedimentary basins developed along the continent-ocean margins in North, East and West Greenland and are now preserved both onshore and offshore. Their development was closely related to continental break-up with formation of rift basins. Initial rifting in East Greenland in latest Devonian to earliest Carboniferous time and succeeding phases culminated with the opening of the North Atlantic in the late Paleocene. Sea-floor spreading was accompanied by extrusion of Tertiary plateau basalts in both central West and central and southern East Greenland. During the Quaternary Greenland was almost completely covered by ice sheets, and the present Inland Ice is a relic of the Pleistocene ice ages. Vast amounts of glacially eroded detritus were deposited on the continental shelves offshore Greenland. Mineral exploitation in Greenland has so far mainly been limited to one cryolite mine, two lead-zinc deposits and one coal deposit. Current prospecting activities in Greenland are concentrated on the gold, diamond and lead-zinc potential. The hydrocarbon potential is confined to the major Phanerozoic sedimentary basins, notably the large basins offshore East and West Greenland. While proven reserves of oil or gas have yet to be found, geophysical data combined with extrapolations from onshore studies have revealed a considerable potential for offshore oil and gas. The description of the map has been prepared with the needs of the professional geologist in mind; it requires a knowledge of geological principles but not previous knowledge of Greenland geology. Throughout the text reference is made to the key numbers in the map legend indicated in square brackets [ ] representing geological units (see Legend explanation, p. 79), while a Place names register (p. 83) and an Index (p. 87) include place names, geological topics, stratigraphic terms and units found in the legend. The extensive reference list is intended as a key to the most relevant information sources.