Cross-sectional diagram depicting horst and graben structure and behavior typical of the Basin and Range province. Source:  

Contexts in source publication

Context 1

... North Cache Valley (NCV) is underlain by the western portion of the Idaho Thrust belt, which formed in the Sevier orogeny, active from late Jurassic to the late Eocene, 140 - 70 million years ago (m.y.) ( Figure 2) (Grubbs & Van Der Voo, 1976). During the compressional Sevier orogeny, folding and faulting of the predominantly Paleozoic marine sediments occurred along the western edge of the North American plate as the oceanic Farallon plate was subducted at a shallow angle; creating a zone of deformation stretching from central British Columbia to southeastern California. As the North American plate moved further west, the subduction angle of the underlying Farallon plate changed, starting a period of mountain building known as the Laramide orogeny, lasting from the late Cretaceous (70-80 m.a.) to the early/late Eocene (35-55 m.a.), resulting in the formation of the Rocky Mountains (Liu, 2008). Basin and Range extension began in the early Eocene, approximately 45 m.a., and continues to the present. The province is characterized by repeating sequences of paired normal faults (i.e. graben forming), accommodating the extensional forces and stretching the area to double that of its original width. These paired normal faults allow for the formation of successive series of valleys and mountains. The valleys, or graben, move downward in relation to the mountains, or horsts (Figure 3). As these extensional forces and mechanics thin the continental crust, it may be predicted that the crust would subside. This is not the case however, as the northern Basin and Range remains relatively high above sea level. This is possibly the result of long term subduction of the Farallon plate beneath the North American plate, effectively buoying the continental crust and helping to keep it floating higher on the mantle. Another theory suggests the higher elevation may be the result of the Yellowstone Hot Spot emplacing buoyant asthenosphere underneath the northern section of the Great Basin. The The Basin Because North Cache and the Cache Valley Range NCV Valley is extension is a located northward (NCV) began at is the underlain trending in convergence the valley by early the located of Eocene, western structurally in portion approximately southeastern distinct of the Idaho and Idaho 45 active m.a., Thrust (Figure 1). and provinces, belt, continues which It is it situated formed is to influenced the in at present. the the Sevier confluence by many The orogeny, province forces of several active and is geologic from characterized processes late terrains that Jurassic by may repeating on to influence the the northeastern late sequences the Eocene, occurrence extent of paired 140 of of the normal 70 sources Basin million faults and of years geothermal Range (i.e. ago graben Province (m.y.) energy forming), (Figure 2) where and accommodating the secondary Basin (Grubbs and sources & Range the Van extensional of meets Der permeability. Voo, the forces Sevier 1976). Crust and orogenic During stretching that was belt the and compressional the deformed area Rocky to and Mountains. double Sevier shortened that orogeny, The of during its juncture original folding the of Sevier these width. and faulting provinces orogeny These of paired has is the characterized predominantly been normal reshaped faults by seismic Paleozoic allow and stretched for activity marine the formation by and sediments Basin clusters of and of successive occurred Range hot springs along extension series (Sbar the of western et to valleys al., form 1972). edge and the of mountains. mountains the North bounding The American valleys, the plate or NCV graben, as on the the move oceanic east downward and Farallon west. in plate The relation border was subducted to of the the mountains, Basin at a and shallow or Range horsts angle; with (Figure 3). creating the Rocky a As zone Mountains these of deformation extensional and the forces stretching Colorado and from mechanics Plateau central runs thin British from the southwestern continental Columbia to crust, Montana southeastern it may to be southern California. predicted Nevada As that the and the North crust displays American would high subside. plate levels moved of This seismicity is further not the west, in case comparison the however, subduction to as adjacent the angle northern of areas the underlying Basin (Figure 4). and Range This Farallon area remains plate is commonly changed, relatively referred starting high above to a as period the sea Intermountain level. of mountain This is Seismic possibly building Belt the known (ISB) result as and of the long the Laramide seismicity term subduction orogeny, may indicate lasting of the that Farallon from the the Rocky plate late Cretaceous beneath Mountains the are (70-80 North still m.a.) rising American to with the plate, early/late respect effectively to Eocene the Basin (35-55 buoying and m.a.), Range the continental resulting province in (Smith the crust formation & and Sbar, helping of 1974; the to Rocky Parsons, keep Mountains it 1995). floating The (Liu, higher potential 2008). on the impacts mantle. of Another mountain theory building suggests forces at the the higher scale of elevation a geothermal may prospect be the result are discussed of the in Yellowstone the following Hot sections. Spot emplacing buoyant asthenosphere underneath the northern section of the Great Basin. Because the NCV is located at the convergence of structurally distinct and active provinces, it is influenced by many forces and processes that may influence the occurrence of sources of geothermal energy and secondary sources of permeability. Crust that was deformed and shortened during the Sevier orogeny has been reshaped and stretched by Basin and Range extension to form the mountains bounding the NCV on the east and west. The border of the Basin and Range with the Rocky Mountains and the Colorado Plateau runs from southwestern Montana to southern Nevada and displays high levels of seismicity in comparison to adjacent areas (Figure 4). This area is commonly referred to as the Intermountain Seismic Belt (ISB) and the seismicity may indicate that the Rocky Mountains are still rising with respect to the Basin and Range province (Smith & Sbar, 1974; Parsons, 1995). The potential impacts of mountain building forces at the scale of a geothermal prospect ...

Context 2

... North Cache Valley (NCV) is underlain by the western portion of the Idaho Thrust belt, which formed in the Sevier orogeny, active from late Jurassic to the late Eocene, 140 - 70 million years ago (m.y.) ( Figure 2) (Grubbs & Van Der Voo, 1976). During the compressional Sevier orogeny, folding and faulting of the predominantly Paleozoic marine sediments occurred along the western edge of the North American plate as the oceanic Farallon plate was subducted at a shallow angle; creating a zone of deformation stretching from central British Columbia to southeastern California. As the North American plate moved further west, the subduction angle of the underlying Farallon plate changed, starting a period of mountain building known as the Laramide orogeny, lasting from the late Cretaceous (70-80 m.a.) to the early/late Eocene (35-55 m.a.), resulting in the formation of the Rocky Mountains (Liu, 2008). Basin and Range extension began in the early Eocene, approximately 45 m.a., and continues to the present. The province is characterized by repeating sequences of paired normal faults (i.e. graben forming), accommodating the extensional forces and stretching the area to double that of its original width. These paired normal faults allow for the formation of successive series of valleys and mountains. The valleys, or graben, move downward in relation to the mountains, or horsts (Figure 3). As these extensional forces and mechanics thin the continental crust, it may be predicted that the crust would subside. This is not the case however, as the northern Basin and Range remains relatively high above sea level. This is possibly the result of long term subduction of the Farallon plate beneath the North American plate, effectively buoying the continental crust and helping to keep it floating higher on the mantle. Another theory suggests the higher elevation may be the result of the Yellowstone Hot Spot emplacing buoyant asthenosphere underneath the northern section of the Great Basin. The The Basin Because North Cache and the Cache Valley Range NCV Valley is extension is a located northward (NCV) began at is the underlain trending in convergence the valley by early the located of Eocene, western structurally in portion approximately southeastern distinct of the Idaho and Idaho 45 active m.a., Thrust (Figure 1). and provinces, belt, continues which It is it situated formed is to influenced the in at present. the the Sevier confluence by many The orogeny, province forces of several active and is geologic from characterized processes late terrains that Jurassic by may repeating on to influence the the northeastern late sequences the Eocene, occurrence extent of paired 140 of of the normal 70 sources Basin million faults and of years geothermal Range (i.e. ago graben Province (m.y.) energy forming), (Figure 2) where and accommodating the secondary Basin (Grubbs and sources & Range the Van extensional of meets Der permeability. Voo, the forces Sevier 1976). Crust and orogenic During stretching that was belt the and compressional the deformed area Rocky to and Mountains. double Sevier shortened that orogeny, The of during its juncture original folding the of Sevier these width. and faulting provinces orogeny These of paired has is the characterized predominantly been normal reshaped faults by seismic Paleozoic allow and stretched for activity marine the formation by and sediments Basin clusters of and of successive occurred Range hot springs along extension series (Sbar the of western et to valleys al., form 1972). edge and the of mountains. mountains the North bounding The American valleys, the plate or NCV graben, as on the the move oceanic east downward and Farallon west. in plate The relation border was subducted to of the the mountains, Basin at a and shallow or Range horsts angle; with (Figure 3). creating the Rocky a As zone Mountains these of deformation extensional and the forces stretching Colorado and from mechanics Plateau central runs thin British from the southwestern continental Columbia to crust, Montana southeastern it may to be southern California. predicted Nevada As that the and the North crust displays American would high subside. plate levels moved of This seismicity is further not the west, in case comparison the however, subduction to as adjacent the angle northern of areas the underlying Basin (Figure 4). and Range This Farallon area remains plate is commonly changed, relatively referred starting high above to a as period the sea Intermountain level. of mountain This is Seismic possibly building Belt the known (ISB) result as and of the long the Laramide seismicity term subduction orogeny, may indicate lasting of the that Farallon from the the Rocky plate late Cretaceous beneath Mountains the are (70-80 North still m.a.) rising American to with the plate, early/late respect effectively to Eocene the Basin (35-55 buoying and m.a.), Range the continental resulting province in (Smith the crust formation & and Sbar, helping of 1974; the to Rocky Parsons, keep Mountains it 1995). floating The (Liu, higher potential 2008). on the impacts mantle. of Another mountain theory building suggests forces at the the higher scale of elevation a geothermal may prospect be the result are discussed of the in Yellowstone the following Hot sections. Spot emplacing buoyant asthenosphere underneath the northern section of the Great Basin. Because the NCV is located at the convergence of structurally distinct and active provinces, it is influenced by many forces and processes that may influence the occurrence of sources of geothermal energy and secondary sources of permeability. Crust that was deformed and shortened during the Sevier orogeny has been reshaped and stretched by Basin and Range extension to form the mountains bounding the NCV on the east and west. The border of the Basin and Range with the Rocky Mountains and the Colorado Plateau runs from southwestern Montana to southern Nevada and displays high levels of seismicity in comparison to adjacent areas (Figure 4). This area is commonly referred to as the Intermountain Seismic Belt (ISB) and the seismicity may indicate that the Rocky Mountains are still rising with respect to the Basin and Range province (Smith & Sbar, 1974; Parsons, 1995). The potential impacts of mountain building forces at the scale of a geothermal prospect are discussed in the following sections. Along the northeastern and eastern edge of the valley are low rolling foothills overlying the base of the Portneuf and the Bear River mountain ranges (Figure 5). These foothills are comprised of Miocene to Pliocene aged, east-northeast dipping Salt Lake formation deposits overlying Cambrian to Ordovician aged carbonates, which have been faulted overtop Neoproterozoic to Cambrian aged Brigham group quartzite (McIntyre and Koenig, 1978). Separating the foothills on the east side of the valley from the Bear River range is a system of inactive, northeast trending, west to southwest dipping normal faults which flatten at shallow depths (Janecke & Evans, 1999). The stratigraphy of the Bear River range consists of marine sedimentary units of Ordovician through Silurian age situated atop large sequences of Cambrian aged carbonates. These in turn are underlain by upper Precambrian and lower Cambrian meta-sedimentary rocks of the Brigham group. Structures found in these mountains are complex, complicated by fold structures such as roll over anticlines to the northeast and east-northeast plunging synclines and anticlines (Janecke and Evans, 1999). The Along Two Portneuf, main the northeastern north-trending Bear River and normal and eastern Bannock fault edge systems mountain of the run valley ranges along are are the low horst east rolling and complexes foothills west flanks bounding overlying of the the the valley NCV base at (Figure 1). of the the base Portneuf of The the and Bannock Bannock the Bear mountain and River Bear range mountain River mountain is made ranges up ranges (Figure 5). primarily (Figure 5). of These the The Precambrian foothills displacement are Scout comprised of Mountain these of faults Miocene member may be to of between Pliocene the Pocatello 2,400 aged, formation. and east-northeast 3,000 meters. This dipping member Subsidiary Salt is characterized Lake faults, formation such by as diamictite deposits those associated overlying featuring with Cambrian angular, the Little silt to Mountain and Ordovician sand sized Horst aged grains complex, carbonates, of quartz run throughout which and feldspar have the been within graben faulted a (McIntyre chloritic overtop or and sericitic Neoproterozoic Koenig, groundmass 1978). to Also Cambrian punctuated present aged is by a large Brigham linear granule structure group to quartzite described boulder (McIntyre ...