Grenville Province and Monteregian carbonatite and nepheline syenite distribution related to rifting, collision, and plume passage. Geology , 36 , — Casey, M. Strain accommodation in transitional rifts: extension by magma intrusion and faulting in Ethiopian rift magmatic segments. In Yirgou, G. Geological Society special publication , pp. Cloos, H. Geologische Rundschau , 30 Zwischenheft 4A , — Corti, G. Coexisting geodynamic processes in the Sicily Channel.
Coward, M. Continental extensional tectonics. Geological Society special publication Albert M. Quennell volume , pp. Crane, K. Heat flow and hydrothermal vents in Lake Baikal, U.
Crowell, J. Sedimentation along the San Andreas Fault, California. In Dickinson, W. Society of Economic Paleontologists and Mineralogists special publication 19, pp. Davis, G. In Howell, D. Derer, C. The Upper Rhine Graben: basin geometry and early syn-rift tectono-sedimentary evolution.
Dewey, J. Plate tectonics and the evolution of the British Isles. Journal of the Geological Society of London , , — Transtension in arcs and orogens. International Geology Review George A.
Thompson Symposium volume , 44 , — Dickinson, W. The basin and range province as a composite extensional domain. Thompson Symposium volume , 44 , 1— Durand, L. The Mediterranean basins: Tertiary extension within the Alpine Orogen. Einsele, G. Berlin: Springer, Vol. Evans, D. London: The Geological Society of London.
Eyidogan, H. Seismological study of normal faulting in the Demirci, Alasehir and Gediz earthquakes of —70 in western Turkey: Implications for the nature and geometry of deformation in the continental crust. Geophysical Journal of the Royal Astronomical Society , 81 , — Faulds, J. Accommodation zones and transfer zones: the regional segmentation of the Basin and Range Province. Felton, A.
Paleolimnological evidence for the onset and termination of glacial aridity from Lake Tanganyika Tropical East Africa. Palaeogeography Palaeoclimatology Palaeoecology , , —, doi Frostick, L. The East African rift basins.
In Selley, R. Sedimentation in the African rifts. Geological Society special publication 25, pp. Gans, P. An open-system, two-layer crustal stretching model for the eastern Great Basin. Tectonics , 6 , 1— Graham, S. Characteristics of selected petroleum source rocks Xianjiang Uygur autonomous region, Northwest China. American Association of Petroleum Geologists Bulletin , 74 , — Gregory, J. Contributions to the physical geography of British East Africa.
The Geographical Journal , 4 , — Harding, T. Graben hydrocarbon plays and structural styles. Pre-existing sediments are downfaulted into the graben. The third stage is accompanied by significant extension and by more uprise of the asthenosphere. The latter causes doming of the crust which is evident along the E. African rift system, but is variably devloped. New sediments are deposited within the graben as a result of erosion of the uplifting sides of the graben.
So there are both pre-rift and syn-rift sediments within the developing rift valley, but sediments on the flanks are progressively erodied away. Note the complex normal-faulting within the rift valley itself. The fourth stage Fig. New basaltic oceanic crust is formed.
Finally, sea-floor spreading takes over as the ocean basin widens. The rift sedimentary sequence is buried beneath younger marine sediments. Note : on this diagram the sediments at the continental margin are shown as not very thick. This is because the model is based on the East African Rift System, which does not have a great deal of subsidence associated with rifting. However, other rifted continental margin sequences are very different, with thick sedimentary sequences.
The real situation at passive continental margins is shown in Fig. This is typical of a number of crustal cross-sections across the continental shelf of the eastern Atlantic seaboard of North America, projected down to 30 km -- based largely on gravity and magnetic evidence, plus some seismic profiles -- and some extrapolation from land geology based on deep drill holes.
The critical point is the huge thicknesses of Mesozoic and Tertiary sediments, here shown as almost 15 km, but in other cross-sections this can be even thicker. Note that at the bottom of this pile are volcanics and volcanogenic sediments, and evaporites, which most likely are shallow water. Also, massive carbonate reef structures, which must also be shallow water, but also must indicate progressive subsidence.. In many sections of the continental shelf off this eastern seaboard of the USA there is a major coast-parallel magnetic structure, possibly a major intrusion.
But its age is unknown. Rift Terminology. Continental Rift: elongate tectonic depression with which the entire lithosphere has been modified in extension. Rift System: Tectonically interconnected series of rifts.
Modern Rift: A rift that is teconically or magmatically active. Paleorift: A dead or dormant rift. Failed Arm: Branch of a triple junction not developed into an ocean basin. Aulacogen: Paleorift in ancient platform that has been reactivated by compressional deformation. Active Rifting: Rifting in response to thermal upwelling of the asthenosphere.
Passive Rifting: Rifting in response to remote stress field. Rifting structures are often good sites for mineralisation. This arises for three reasons:. These sediments hold vast amounts of inter-granular salt water brines. As the sediments compact, these brines are expelled and can move laterally for large distances until they move up the rift faults.
Having been buried deep the brines get hot, and can be very corrosive. So en route they can dissolve considerable amounts of metals. Lillie, New York, W. Norton and Company, pp. Like other continents, North America has thick crust, compared to the thin crust beneath the adjacent Atlantic and Pacific oceans.
In the western part of the continent, divergent plate boundary forces are beginning to rip the continent apart, forming the Basin and Range Province and its adjacent eastern arm, known as the Rio Grande Rift.
National Park Service sites in this region showcase block-fault mountains and volcanic features forming as the thick crust stretches and cracks apart, releasing magma from below. Similar, but much older, layers are found in NPS sites in the Keweenawan Rift of the Lake Superior region, where divergent plate boundary forces tried, unsuccessfully, to rip the North American continent apart 1.
Lillie, Wells Creek Publishers, 92 pp. Where tectonic plates move away from one another the lithosphere thins. The underlying asthenosphere rises and expands like a hot-air balloon, elevating a broad region. If the plate is capped by thick continental crust, the resulting continental rift zone rises high above sea level. It is similar to the East African Rift, where volcanic materials and sedimentary layers deposited by rivers and lakes partially fill rift valleys.
Prominent planar surfaces fault escarpments along range fronts are evidence that the region continues to rip apart—erosion would smooth them out if the fault movement stopped. Earthquakes, fault-block mountains, and volcanism at Guadalupe Mountains National Park and Bandelier and White Sands national monuments are consequences of the ongoing continental rifting. Left image Lava Beds landscape. Credit: Photo by Robert J. Right image Feature labels.
Click on arrows and slide left and right to see labels. The east side of the Teton Range is a steep fault escarpment rising from the adjacent basin Jackson Hole. Left image Grand Teton Range. Credit: NPS photo. The topography of the Basin and Range Province and Rio Grande Rift reveals the full range of characteristics of a continental rift zone.
First, much of the region—particularly the northern portion—is well above sea level. There the whole landscape is moving upward, with the ranges rising a little faster than the adjacent basins.
For example, the floor of a basin in Wyoming, Jackson Hole, is 6, feet 1, meters above sea level, while the adjacent Teton Range rises to over 13, feet 4, meters. But in the southern part of the province, where rifting is more advanced, elevations are generally lower—much of the floor of Death Valley in eastern California is below sea level! Layers of sand, mud and gravel deposited by rivers and lakes, along with lava flows and other volcanic materials, fill rift valleys as they form.
But sometimes the valley floors move downward much faster than these layers can fill them. A long, narrow fissure in the Earth marking a zone of the lithosphere that has become thinner due to extensional forces associated with plate tectonics.
Continental rifts are thousands of kilometers in length and hundreds of kilometers in width, and they are associated with normal faults and with grabens. We could talk until we're blue in the face about this quiz on words for the color "blue," but we think you should take the quiz and find out if you're a whiz at these colorful terms.
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