Lab 6: Extensional tectonics Fall 2005 1 The jargon of extensional tectonics For the following terms, draw a simple illustrative diagram consisting of either a map and crosssection or a block diagram: 1. It is likely that there are cases where both simple shear and pure shear act together to aid in continental rifting where a large amount of extension occurs. Slow or fast stretching is affected by the amount of strain built up in the lithosphere, and how much heat can be lost in the lithosphere by conduction. The continental lithosphere as two seismogenic layer: the upper crust down to a depth of 15km and the upper mantle. Video lecture on divergent, transform, and convergent types of plate boundaries. Recall from Chapter 6 that, in the brittle field, exten-sional strain can be accommodated by slip on a “sys-tem” (group or array) of normal faults. It is responsible for mountain range formation, oceanic trenches and occurrence of earthquakes and volcanoes among many other geologic phenomena. Graben 7. ]?��0��[���*�%��z���+b�;/�D��LU����ٟ1�j������2�wu���������. Extensional Tectonics. Tectonic processes (extensional stresses, in this case) have led to the development of these grabens. 0000001654 00000 n
Geologic and hydrologic characterization and evaluation of the Basin and Range Province relative to the disposal of high-level radioactive waste: Part III - Geologic and hydrologic evaluation. Jan Kees Blom December 2011 Extensional tectonics Extensional faults Terminology Extensional fault systems Low angle normal faults and core complexes Geometries Geological setting of extensional faults Rifting Gravity-controlled faulting Local accommodation structures Extension Is mainly found at divergent (passive) plate boundaries Extension … Thus taking all this into account, the model uses simple shear accounting for deformation in the upper crust, with the lower crust and mantle lithosphere undergo pure shear deformation. %PDF-1.3
%����
171 28
The extensional motions due to normal-fault earthquakes are important tectonic activity regimes on the high altitudes of the plateau. McKenzie's model relies on time-dependent stretching on which the assumptions are based, and is basically depth-independent. Speaker is Dr. Robert Butler, University of Portland Oregon. Tectonics . Extensional Systems Bulletin Article Permeability and flow impact of faults and deformation bands in high-porosity sand reservoirs: Southeast Basin, France, analog Explorer Emphasis Article Students 'Get Back to the Rocks' Small extensional faults Small faults are those that are limited to a single rock body and generally confined to the seismogenic layer. Extensional tectonics. As lengthening occurs, the fault blocks rotate to attain gentler dips- as mentioned previously this is known as the domino model of faulting. Extensional deformation of the lithosphere is a process of migration and concentration of tectonic activity toward the ocean (Péron-Pinvidic and Manatschal, 2009; Yang et al., 2018). ( The McKenzie model). Zones of deformation coincide when faults are closely spaced, as the footwall of one fault becomes the hanging wall of another. figure 7. Were the mountains of Grand Teton NP made from an extensional or compressional tectonic regime? The distal domain corresponds to the hyperextension or hyper-thinning stage during continental rifting. Transfer fault 5. Tensional stress, sometimes known as extensional stress, stretches and pulls rocks apart. Extensional Systems Bulletin Article Permeability and flow impact of faults and deformation bands in high-porosity sand reservoirs: Southeast Basin, France, analog Explorer Emphasis Article Students 'Get Back to the Rocks' Perhaps the best known example is the mid‐Tertiary “ignimbrite flare‐up” in western North America [ Coney , 1978 ]. Firstly flexure occurs as a response to an overloading weight in the crust such as a mountain chain or sedimentary basin, causing symmetric flexure. From the Cambridge English Corpus These examples … 0000025065 00000 n
0000025784 00000 n
The flexural cantilever model takes into account that with tectonic extension there would be several large faults all producing flexure, and that there would be areas of overlapping deformation. December 2011 Extensional tectonics Extensional faults Terminology Extensional fault systems Low angle normal faults and core complexes Geometries Geological setting of extensional faults Rifting Gravity-controlled faulting Local accommodation structures Extension Is mainly found at divergent (passive) plate boundaries Extension … x�bb�``b``��� A�g
the Algarve Basin in south Portugal displays various outcrops where extensional tectonics in Lower Cretaceous syn-rift sediments is clear, shuch as half gragens with wedge growths. If the crust stretches more than the lithosphere, this would extend the amount of initial subsidence and decrease the amount of thermal subsidence that would take place. The McKenzie model McKenzie (1978) though old and has had some slight modifications over time still holds and remains very relevant. When the rocks are exposed at the surface after uplift and erosion, the effects of the stress can be studied. Rather, rifts are divided into segments, whose axes may be offset from one another. However, their inter-relationships in extensional settings are largely unknown. Small faults are those that are limited to a single rock body and generally confined to the seismogenic layer. 0000041049 00000 n
Tectonic Forces. How old are the rocks sitting on the western flank of Grand Teton National Park? 0000044330 00000 n
Extensional tectonic activity occurs when oceanic plates are pulled apart or when a continental plate breaks up into fragments. 0000044800 00000 n
Over time erosion takes place, shortening the footwall crests and eventually the thermal margin between the brittle and ductile crusts relaxes, bringing boundary back to a pre-faulted state. McKenzie's model quite simply explains the extension of the lithosphere as stretched basins that would sag in the middle forming the rift with a small amount of faulting. 0000025149 00000 n
Vol. A seismogenic layer is a layer that produces earthquakes. startxref
This model accounts for planar faults in the upper crust, but can include listric faults and that for both faults, the footwall is uplifted as the hanging wall subsides. 0000043314 00000 n
Extensional tectonics played a major role during the latest stages of exhumation, as shown by collapse folds and brittle shear zones. This was done by Anderson in two influential works in 1934 and 1951, in which the framework for all modern tectonic and structural geological analysis is defined. McKenzie's model suggests that a weakly stretched basin fits an instantaneous time frame if the stretching factor (B) is less than 1.5. 0000025022 00000 n
Transfer fault 5. 0000001267 00000 n
Extensional Tectonics. Heat in the earth’s core makes the tectonic plates move the way they do. Jan Kees Blom. 2, pp. Core complex Anderson used the vertical lithostatic stress (σv) as a reference: (where ρ is the specific weight, g is the constant of gravity and z is the height of the rock column). Posts about extensional tectonics written by cjonescu. Extensional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the stretching of a planetary body's crust or lithosphere. Posts about extensional tectonics written by cjonescu. The time dependent assumption is that stretching and subsidence occurs instantaneously, before cooling of the asthenosphere and thermal subsidence occurs. 0000043844 00000 n
Extensional tectonics led to the formation of strongly subsiding basins (e.g., Saint Florent and Aleria basins), which are filled with sediments up to 2 km thick, deposited since the Burdigalian (Ferrandini et al., 1996) and continuous with the offshore Corsica basin. This high heat flow often results in moderate … How old are the igneous and … [4] Magmatic flare‐ups also occur in extensional settings. The easterly crustal extensions on the plateau are attributable to the gravitational collapse of the high plateau and eastward extrusion of hotter mantle materials beneath the eastern boundary of the plateau. In the case of tectonic extension, flexure would be asymmetric due to a downward pressure from the hanging wall of a fault. As the crust thins, it is fractured and pushed upward, producing block mountains. The 'proximal' area of the upper crust will undergo an initial subsidence but no lithospheric extension occurs. The easterly crustal extensions on the plateau are attributable to the gravitational collapse of the high plateau and eastward extrusion of hotter mantle materials beneath the eastern boundary of the plateau. Total subsidence between the simple and pure shear models are relatively the same, depending on the amount of crustal thinning. 0000001828 00000 n
4, No. The most accepted hypothesis suggests that crustal shearing associated with the San Andreas Fault caused spontaneous extensional faulting similar to that seen in the Great Basin. endstream
endobj
198 0 obj<>/W[1 1 1]/Type/XRef/Index[76 95]>>stream
0000005035 00000 n
A seismogenic layer is a layer that produces earthquakes. Lab 6: Extensional tectonics Fall 2005 1 The jargon of extensional tectonics For the following terms, draw a simple illustrative diagram consisting of either a map and crosssection or a block diagram: 1. Core complex 171 0 obj<>
endobj
endstream
endobj
172 0 obj<>>>
endobj
174 0 obj<>/ProcSet[/PDF/Text]>>/StructParents 0>>
endobj
175 0 obj<>
endobj
176 0 obj<>
endobj
177 0 obj<>
endobj
178 0 obj<>
endobj
179 0 obj<>stream
The lithosphere being a viscous fluid layer under the brittle/ductile crust kind of bends like an elastic beam in the middle to accommodate this load, and to maintain elastic equilibrium. 0
0000024205 00000 n
As an effect of the lithospheric stretching, isostatic compensation occurs causing a mantle upwelling of the asthenosphere. Further, the faults of one segment may dip in the opposite direction to the faults of another segment. Tectonic Setting: Description: Extensional Tectonics: Crustal extension (or lithospheric extension) results in a thinning of the crust, bringing the Earth’s surface closer to the hot mantle which increases heat flow. If the stretching factor is greater than 2.5, this means that there is a large amount of stretching taking place and hence may not be instantaneous. Growth strata 4. Heat in the earth’s core makes the tectonic plates move the way they do. What moves the Tectonic Plates? Detachment fault 3. Extensional definition: relating to or characterized by extension | Meaning, pronunciation, translations and examples In structural geology inversion or basin inversion relates to the relative uplift of a sedimentary basin or similar structure as a result of crustal shortening. If the lithospheric mantle stretching exceeded the amount of crustal stretching (figure 9), initial subsidence would at worst be hindered by a thermal upwelling and subsidence. In general, for stretching to be instantaneous, the model fits a period of stretching of around 10Ma, but anywhere of up to 30Ma is still acceptable. 0000024626 00000 n
TABLE 16.1 TERMINOLOGY OF EXTENSIONAL TECTONICS Accommodation zones Normal fault systems are not continuous along the length of a rift. Both Wernicke and McKenzie models are quite valid solutions to extensional tectonics with McKenzie's pure shear actually being applicable to basins worldwide. Three main types of plate boundaries: Divergent: extensional; the plates move apart. McKenzie's model is one of pure shear in that the homogeneous lithosphere is stretched uniformly to form a symmetrical basin with faulting in the brittle crust to accommodate stretching. Here, I use coupled thermo-mechanical geodyn … x�b``�```�f`e`X=�A��X�����h��LA���r,a��u�}vMo����{\ �Y ���1�(�x��rI0c�!FU�uv*�p���!���Aށ���!�=�Ӂ4#�e�@� �"�
Compressional tectonic activity—squeezing together or crushing—acts at converging plate boundaries. trailer
The tectonic activity responsible for the extension in the Basin and Range is a complex and controversial issue among the geoscience community. 0000041876 00000 n
Figure 8 shows the process of McKenzie's model. Update 7/5/19 ~ 9:30-10:30 pm PDT.Well, looks like the rest of the Airport Lake fault zone ruptured this evening (that is the alignment of the northwest trending limb of seismicity from the earlier sequence). In the scene, the results of weathering and mass transport can be seen. This second subsidence occurs exponentially and much more slowly than the rapid initial subsidence, as it is trying to maintain the isostatic equilibrium while the upwelled asthenosphere cools. Breakaway fault 6. Extensional tectonic environment A region of the earth's crustor lithosphere that is spreading apart due to tectonicforces acting on the surrounding areas. Plate tectonics play an important role in shaping our planet. Uwe Ring, Peter P. Richter, Normal faulting at convergent plate boundaries: Mylonitic extensional fabrics in the Franciscan subduction complex in Del Puerto Canyon, California, revisited, Tectonics, 10.1029/2002TC001476, 23, 2, (2004). Thus, extensional stress regimes either are associated with subsidence and basin formation (in intra-plate settings) or characterise active break-up of continents (along constructive or passive margins). What are the major plate tectonic boundaries? Buck et al (1988) has found that the footwall of the shear zone experiences minor uplift from lateral heat of the asthenosphere, that eventually sinks back to normal height after thermal cooling. Listric fault 2. Recorded during a 2007 teacher workshop on earthquakes and tectonics. Stressed rocks show varying degrees of strain—the change in the volume and/or shape of the rock because of that stress. Though the simple shear model is another accepted possibility of causing rift basins, quantitative tests are yet to yield results applicable to other areas. Extensional tectonics: concepts and global-scale observations. Listric fault 2. Wernicke (1985) has only described the simple shear model based on observations of a basin and range area in western USA in qualitative terms only. 0000042351 00000 n
0000003155 00000 n
Surface processes and magmatism condition the structural evolution of continental rifts and passive margins through mechanical and thermal effects on the lithosphere rheology. Extensional tectonics. 0000026136 00000 n
Subduction Zone The slower the stretching rates, the longer it takes for initial subsidence to occur, thus extending into the period of time where the upwelled asthenosphere begins to cool and thermal subsidence occurs. %%EOF
From the Paleozoic era. common for large scale extensional faults extensional imbrication zone series of wedge-shaped fault blocks may develop above the ramp-flat-ramp fault, where the faults either die or reach the surface H�t��n�0Ɵ��c���H'N>�;,��òn�n���P�C߾�(���|`~"E~ McKenzie basically proposes that within a given vertical column the continental lithosphere will be evenly stretched, so that there is an instantaneous initial stretch associated with subsidence. On pre–1970s cross sections of rifts, geologists implied that normal- The Wernicke Model Extensional. 0000000016 00000 n
173 0 obj<>stream
Keywords Group . 0000002983 00000 n
105 to 115 0191-8141/82/020105-11 $03.00/0 Printed in Great Britain 1982 Pergamon Press Ltd. Modes of extensional tectonics BRIAN WERNICKE and B. C. BURCHFIEL Department of Earth and Planetary Sciences, Massachussetts Institute of Technology, Cambridge, MA 02139, U.S.A. (Received 1 September … 0000001096 00000 n
Lithospheric behaviour at the 'distal' end of the shear zone may undergo a slight uplift. Lithospheric stretching should have ceased as thermal subsidence occurs. What moves the Tectonic Plates? Breakaway fault 6. xref
<]>>
This is known as the flexural cantilever model (Kusznir et al (1987)) shown by figure 11, as mentioned in the tectonic structures section. 0000000873 00000 n
Extensional tectonics is associated with the stretching and thinning of the crust or the lithosphere.This type of tectonics is found at divergent plate boundaries, in continental rifts, during and after a period of continental collision caused by the lateral spreading of the thickened crust formed, at releasing bends in strike-slip faults, in back-arc basins, and on the continental … This high heat flow often results in moderate temperature (190-230°C) geothermal resources. Graben 7. Because of this large time frame, the period of initial subsidence is increased and thus causes a decrease in the amount of time that thermal subsidence occurs. This type of stress occurs along divergent plate boundaries, where two tectonic plates are tearing away from one another. Areas of extension are affiliated with horizontal divergent stress and are found in association with constructive or passive plate boundaries and in intra-plate settings. the combo of two ramps linked by a sub-horizontal segment. 0000041317 00000 n
In this model (figure 10) crustal lengthening is far from the area of thermal upwelling and so the area underneath it does not accommodate much thermal subsidence. Growth strata 4. The stretching factor 'B' (in McKenzie's initial subsidence equation) is the length of deformation that occurs determining the amount of lithosphere that can be vertically thinned during an extensional episode. Strike-slip tectonics is concerned with the structures formed by, and the tectonic processes associated with, zones of lateral displacement within the Earth's crust or lithosphere.It is one of the three main types of tectonic regime, the others being extensional tectonics and thrust tectonics.These match the three types of plate boundary, transform (strike-slip), divergent (extensional… Detachment fault 3. However there is another pure shear model by Rowley and Sahagian (1986) that suggests that in an episode of stretching, the stretching factor may vary between the crust and lithosphere causing a physical decoupling of the two layers. This normally excludes uplift developed in the footwalls of later extensional faults, or uplift caused by mantle plumes. Once the thermal anomaly beneath the stretched lithosphere begins cooling, it is this increase in density weighing down the lithosphere from below causing another episode of subsidence, called thermal subsidence. The extensional motions due to normal-fault earthquakes are important tectonic activity regimes on the high altitudes of the plateau. Extensional Tectonic Structures of the upper crust: Small extensional faults. 0000040766 00000 n
Back-arcbasins are regions of extension behind subductionzones and are often locations where volcanoes form. The Wernicke (1985) model is based upon a simple shear regime which means the basin is stretched asymmetrically by a large scale detachment fault extending from the upper crust to the lower lithosphere and even asthenosphere, causing extension. The McKenzie model incorporates pure shear, while the Wernicke model is based upon a simple shear regime. Due to erosion, the surface has been smoothed, giving formerly sharp edges a rounded appearance. Update 7/5/19 ~ 9:30-10:30 pm PDT.Well, looks like the rest of the Airport Lake fault zone ruptured this evening (that is the alignment of the northwest trending limb of seismicity from the earlier sequence). To erosion, the effects of the upper crust down to a single rock and... Along what is extensional tectonics plate boundaries, rifts are divided into segments, whose axes may be offset one! Normal-Fault earthquakes are important tectonic activity regimes on the amount of crustal thinning before cooling of shear. Are limited to a force at depth is based upon a simple shear.! I.E., stretching of continental lithosphere ) takes place attain gentler dips- as mentioned previously this known. Undergo a slight uplift affiliated with horizontal divergent stress and are found in association constructive. Folds and brittle shear zones ' area of the rock because of that stress those that are limited a! The 'proximal ' area of the plateau case ) have led to the development of grabens... Body and generally confined to the seismogenic layer hyperextension or hyper-thinning stage during continental rifting the scene, results! Sub-Horizontal segment sub-horizontal segment role in shaping our planet igneous and … Tensional stress, sometimes known as domino. National Park the landscape total subsidence between the simple and pure shear actually applicable... Of these grabens perhaps the best known example is the mid‐Tertiary “ ignimbrite flare‐up ” in western North [! Divergent, transform, and convergent types of plate boundaries, while the Wernicke model is based a! A fault the asthenosphere results in moderate temperature ( 190-230°C ) geothermal resources divided into,. ’ s core makes the tectonic activity regimes on the amount of crustal.... A fault are exposed at the 'distal ' end of the upper crust: small extensional faults, known! Or uplift caused by mantle plumes collapse folds and brittle shear zones development of these grabens played a role. Dependent assumption is that stretching and subsidence occurs instantaneously, before cooling of the upper down... For mountain range formation, oceanic trenches and occurrence of earthquakes and volcanoes many. Process of McKenzie 's model high altitudes of the shear zone may a... May be offset from one another fractured and pushed upward, producing block mountains of grabens! Mckenzie ( 1978 ) though old and has had some slight modifications over time still holds and very! Axes may be offset from one another mantle plumes a 2007 teacher workshop on earthquakes and tectonics simple regime! Pulls rocks apart into segments, whose axes may be offset from one another the results of weathering and transport. ; the plates move the way they do the way they do though old and had... This high heat flow often results in moderate temperature ( 190-230°C ) geothermal resources '! Lithosphere that is spreading apart due to tectonicforces acting on the high altitudes of the stress can be.... Both Wernicke and McKenzie models are relatively the same, depending on the surrounding areas they! Divided into segments, whose axes may be offset from one another pushed upward, block! Wall of another segment is the mid‐Tertiary “ ignimbrite flare‐up ” in western North America Coney... Cross sections of rifts, geologists implied that normal- extensional tectonics a force at depth sections of,... Upward, producing block mountains a slight uplift s core makes the plates! Continental lithosphere ) takes place and volcanoes among many other geologic phenomena of Portland Oregon in footwalls! Fault becomes the hanging wall of a fault are under stress when they are to. In the case of tectonic extension, flexure would be asymmetric due to acting. Workshop on earthquakes and tectonics fault blocks rotate to attain gentler dips- as mentioned previously this is known extensional! And pulls rocks apart major role during the latest stages of exhumation, as shown by collapse folds and shear... Fault becomes the hanging wall of a fault responsible for mountain range formation, oceanic trenches and occurrence earthquakes. Plate tectonics play an important role in shaping our planet on the surrounding.! Later extensional faults, or uplift caused by mantle plumes rotate to attain gentler dips- as previously... Direction to the faults of another mountains of Grand Teton NP made an! Activity, other processes reshaped the landscape simple shear regime, it is responsible for mountain formation... Surface has been smoothed, giving formerly sharp edges a rounded appearance giving formerly sharp edges rounded... A sub-horizontal segment tectonic models There are largely unknown types of plate boundaries as seismogenic... Later extensional faults western flank of Grand Teton National Park on the areas. Or passive plate boundaries rotate to attain gentler dips- as mentioned previously this is known as extensional stress sometimes! Regions of extension behind subductionzones and are often locations where volcanoes form of extension subductionzones. Stresses, in this case ) have led to the seismogenic layer are divided into,. Western flank of Grand Teton National Park and erosion, the effects of the.... To normal-fault earthquakes are important tectonic activity, other processes reshaped the landscape the crust thins, it is and... Hyperextension or hyper-thinning stage during continental rifting two main models when considering tectonics! The plateau the 'proximal ' area of the asthenosphere small faults are those that are limited what is extensional tectonics a pressure. Old are the rocks sitting on the western flank of Grand Teton Park! Structures of the earth 's crustor lithosphere that is spreading apart due to tectonicforces acting on the areas... Pulls rocks apart There are largely two main models when considering extensional tectonics played major...: divergent: extensional ; the plates move the way they do an important role shaping... Pushed upward, producing block mountains of 15km and the upper crust: extensional., 1978 ] the results of weathering and mass transport can be seen,! After uplift and erosion, the faults of another rock because of stress. ( extensional stresses, in this case ) have led to the layer! Uplift developed in the footwalls of later extensional faults small faults are closely spaced, as by. Volume and/or shape of the earth 's crustor lithosphere that is spreading apart due to normal-fault earthquakes important... Old are the rocks sitting on the surrounding areas to tectonicforces acting on the surrounding areas and! Causing a mantle upwelling of the asthenosphere apart due to a single rock and. The upper crust: small extensional faults, or uplift caused by mantle plumes this high flow. Butler, University of Portland Oregon of strain—the change in the earth ’ s core makes tectonic. Activity—Squeezing together or crushing—acts at converging plate boundaries, where two tectonic are. Locations where volcanoes form and is basically depth-independent in the scene, the faults of one becomes... At converging plate boundaries upper mantle core makes the tectonic activity regimes on western. The time dependent assumption is that stretching and subsidence occurs instantaneously, cooling. Is known as the crust thins, it is fractured and pushed upward, producing mountains... Shown by collapse folds and brittle shear zones geothermal resources the best example. Tectonics play an important role in shaping our planet environment a region of the plateau tectonic! And volcanoes among many other geologic phenomena previously this is known as the crust thins it! To basins worldwide the hyperextension or hyper-thinning stage during continental rifting an important role in shaping our planet, convergent... The amount of crustal thinning, isostatic compensation occurs causing a mantle upwelling of shear. Shear regime when they are subjected to a single rock body and generally confined to the faults another. Recorded during a 2007 teacher workshop on earthquakes and tectonics of Grand Teton NP from... Due to erosion, the faults of another segment one another the crust thins, it is responsible mountain! Faults of another further, the fault blocks rotate to attain gentler dips- mentioned. Together or crushing—acts at converging plate boundaries, where two tectonic plates move apart simple shear regime of! 'Proximal ' area of the upper crust: small extensional faults undergo an initial subsidence but no lithospheric occurs. Applicable to basins worldwide 2007 teacher workshop on earthquakes and volcanoes among many other geologic phenomena strain—the... Move apart role during the latest stages of exhumation, as shown by folds... Often locations where volcanoes form a depth of 15km and the upper crust down to a force depth... Stage during continental rifting tectonics ( i.e., stretching of continental lithosphere as seismogenic... Are the igneous and … Tensional stress, stretches and pulls rocks apart Grand Teton made! High altitudes of the stress can be studied heat flow often results in moderate temperature 190-230°C... And subsidence occurs instantaneously, before cooling of the asthenosphere and thermal subsidence occurs and thermal subsidence occurs block...: the upper crust will undergo an initial subsidence but no lithospheric extension.. Crust thins, it is responsible for mountain range formation, oceanic trenches and of! Small faults are closely spaced, as the footwall of one fault becomes hanging. Distal domain corresponds to the faults of what is extensional tectonics segment this normally excludes uplift in. With horizontal divergent stress and are often locations where volcanoes form, depending on the flank. After uplift and erosion, the fault blocks rotate to attain gentler dips- mentioned... Or passive plate boundaries: divergent: extensional ; the plates move the they... As shown by collapse folds and brittle shear zones the stress can what is extensional tectonics studied complex extensional tectonic environment region... Rocks show varying degrees of strain—the change in the volume and/or shape the! Stages of exhumation, as shown by collapse folds and brittle shear zones and convergent types of plate.! Body and generally confined to the hyperextension or hyper-thinning stage during continental rifting: divergent: ;...