Rio Grande Rift (E side of Colorado Plateau): Modern hot springs deposits (calcium carbonate) along a fault on the flanks of the Jemez caldera taken from on the 2005 UNO field trip to the New Mexico Rift. east coast. This architecture of a deformed upper plate above a detachment with a less or differently deformed lower plate below was given the name of 'thin-skinned' tectonics. The basic idea is as follows. much more later. This detachment is part of a metamorphic core complex. Photos from lava lakes in the world: Erta Ale, Nyiragongo, Hawaii, Vanuatu. Metamorphic core complexes and lower crustal flow, associated with extreme extension, more info here. rifts. Continental drift, large-scale horizontal movement of continents relative to one another and to the ocean basins during one or more episodes of geologic time. Continental Rift Features at NPS Sites in the Keweenawan Rift Basalt lava flow rocks in Isle Royale National Park formed when the Keweenawan Rift attempted to rip the North American continent apart 1.1 billion years ago. Influence of previous structure on rift patterns? These deposits are fanglomerates. Detailed guidelines to 42 different volcanoes around the world. What This is part of the rift bounding normal fault (likely with a strike-slip component) that has caused the mountain uplift. and Courtillot model: Orogenic topographic collapse: Intro comment: Ocean basins, and the underlying oceanic crust, are often bordered by continental rocks. Particularly coarse phase of the mafic (basaltic) sill with plagioclase and clinopyroxene grains. edges of rifted continental fragments flanking an oceanic basin that is opening. Africa, for example, will eventually split along the Great Rift Valley system. might be factors that determine the pattern of continental rifting? Rift valley s are sites where a continental landmass is ripping itself apart. Extensive subhorizontal faults are known as detachments (with the upper plate detached from the underlying lower plate). localized interior rift basin (prone to … are all factors that determine the chemical composition of a Suggested reading: Rift Basin Architecture and Evolution by Roy W. Schlische & Martha Oliver Withjack at http://www.ldeo.columbia.edu/~polsen/nbcp/breakupintro.html. Palisades Sill on the west side of the Hudson River, below Peekskill. There is discussion on the role of isostatic rebound and/or lower crustal ductile flow play in the development of the large elongate domal feature. Salton trough, California Triassic grabens seen along the U.S. east coast (described below) are exposed examples of such rifts. The rock basin above is the source of the debris flows that mainly happen during the rare (from a human perspective) and intense rain falls that mobilize debris flows in this part of the world. The diagram to the right attempts show various mechanisms associated with continental extension: Lithospheric thinning (5) Triassic grabens along U.S. episode. Rift tip propagation, Vink models for continental rifting. Image source: http://en.wikipedia.org/wiki/File:CAMP_Magmatism_in_the_context_of_Pangea.jpg . cycle is not followed faithfully - it is much more of a schema. The most prominent example of a continental rift is the East-African Rift Valley and its continuations into the Red Sea and the Gulf of Aden. gravity high - in the interior of the U.S.. Intraplate tectonism: a possible model for Carboniferous basins on the Barents Shelf. The rifting can also be insufficient to trigger seafloor spreading processes, and instead forms a rift basin or basins within continental crust. Some people argued that they started out in a steeper position and then were rotated into a low-angle position, where they were inactive. Elevated geothermal gradients, and magma chambers and recent intrusions all serve to increase the heat flow of the thinned crust leading to such hydrothermal activity. Same field trip, same group as above, but in the recesses of a lava tube from a recent basalt flow from the Mal Pais area of New Mexico. melt, http://www1.eere.energy.gov/geothermal/geomap.html, http://veimages.gsfc.nasa.gov/5188/France.A2003078.1050.500m.jpg. tends to occur along old orogenic axes, so that these become the Note the low angle orientation and low angle truncation of the hanging wall sediments against the fault. However, evidence has accumulated that actively slipping low-angle normal faults occur. and aulocogens (Burke & Dewey (1973) model). The Rio Grande Rift could be considered as part of the larger Basin and Range province on the other side of the Colorado Plateau, which is an area of North American crust with distinctive properties, some of which likely contributed to its being sheltered from Basin And range rifting. There are certainly examples where the Wilson These pyroclastics from explosive volcanism in the past are part of the Basin and Range rift basin that the National Park is centered on. A natural question to ask is what localizes the detachment at a given level? rifts. Evaporite (salt deposits) that occupy the middle part of the Death Valley rift, with alluvial fan deposits across the way on the other side. Schematic diagram of continental rifts (modified from USGS material). This large mafic sill can be traced down to NYC, and is part of the LIP. This would suggest the continents come apart to make new oceanic basins. In the foreground is an alluvial fan in Death Valley (note the person to the right for scale) that consists mainly of debris flow deposits that emanate from the canyon mouth at the apex of the fan. Another rift, the East African Rift Valley, is still in the phase where it forms a graben that is 'trying' to rip East-Africa apart from the rest of Africa. (transtensive): Some better known past continental to form a new mountain belt. Rifting has been pulling Arabia away from the African continent and a new ocean is developing in the Red Sea and the Gulf of Aden. This concept was an important precursor to the development of the theory of plate tectonics, which incorporates it. The area is no longer volcanically active, but was about 38-32 million years ago. If the rifting between East Africa and the rest of the continent continues, a new ocean will eventually be formed here. (modified from USGS). Image showing the footprint of the LIP CAMP. models of continental rifting, http://www.ldeo.columbia.edu/~polsen/nbcp/breakupintro.html, http://visibleearth.nasa.gov/view.php?id=77566, USGS site on the geophysics of Rio Grande Rift, brief summary of the history of the rift by Manley (1984), More info on image from NASA's Visible Earth, http://earthquake.usgs.gov/regional/nca/research/salton/, http://woodshole.er.usgs.gov/project-pages/dead_sea/tectonic.html, http://3dparks.wr.usgs.gov/nyc/mesozoic/mesozoicbasins.htm, http://www.ldeo.columbia.edu/~polsen/nbcp/lipmc.html, http://en.wikipedia.org/wiki/File:CAMP_Magmatism_in_the_context_of_Pangea.jpg, Wikipedia article on European Cenozoic rift system, http://geomaps.wr.usgs.gov/parks/deva/ftdan1.html, https://pubs.usgs.gov/bul/b2004/html/bull2004detachmentfaultrelated_mineraliz.htm, http://maps.unomaha.edu/maher/GEOL3300/week14/rift.html, What A classic case example is the Appalachian orogen (see is observed with modern rifts. Detachments can have areas of 10,000s of square kilometers.When we describe convergent margins the concept of detachments and thin-skinned tectonics will be explored again. Basin analysis: holistic look at a basin and the factors that contributed to its character. So we need to look at continental rifting broadly. the implication is that old rift basin structures underlie passive continental margins such as the east coast of North and South America. There was a significant debate as to the mechanics of such low-angle normal faults (e.g. A careful look will show a fault scarp that displaces these deposits and runs parallel to the mountain front. adjacent diagram). What factors in particular might influence rift basins? The basic idea in the Wilson cycle is that continental rifting It is basically a cycle of oceanic basin opening and closing. One broad example of this is how the Norwegian-Greenland oceanic starting point (but not a simple one) for the Wilson Cycle. Camera lens for scale. Some examples of presently active continental Illustration of the main types of plate boundaries. Schematic image from USGS based on Basin and Range rifting showing the subhorizontal detachment and the position of mineralization in this tectonic context. sedimentary basin formation, and often thermal and igneous activity. Continental rifting is a convenient You may remember from your Physical Geology or Structural Geology course that normal faults have a dip of ≈ 60° and many such faults do. These are often linked to normal faults with more 'standard' dips as evident in the diagram below. The image below is from the park and shows the geologic interpretation of Goat Mountain. As oceanic crust gets older and colder, subduction likely starts and the ocean basin closes, with the bounding continents eventually colliding Extensional detachments as an expression of thin-skinned tectonics: A mini-revolution within plate tectonics was realizing that detachments played an important role in the architecture of plate boundaries, both at convergent and divergent margins. Collettini 2011). For this reason rift zones can have hydrothermal related mineralization and be ore exploration targets. They show a complex and diverse set of patterns, sometimes concentrated, sometimes more diffuse, and localized rifting can occur in what may initially seem unlikely positions - on top of convergent mountain belts for example. What Transtensive releasing covering a good bit of the southwest U.S.. Keweenawan rift and the mid-continent Fanglomerate and other Death Valley rift deposits faulted against mylonitized, brecciated and chloritized (from retrograde metamorphism) basement rocks. bends: will take about