Geologic evidence for thin-skinned deformation in the east Gogebic range
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The Gogebic iron range extends from northwestern Wisconsin into northern Michigan. The eastern end of the Gogebic range lies roughly forty miles east of Ironwood, Michigan. Recent geologic mapping in this area indicates that Archean and Early Proterozoic rocks underwent multiple periods of deformation. This study focuses primarily on the initial, D1, period of deformation as observed in the western part of the map area. Here, structural data indicate that bedding was folded about fold axes that plunge gently to the northeast. Well developed axial planer foliation strikes east-northeast and dips southeast. None of these features occur in underlying Archean greenstones and gneissic rocks. Rather, gneissic foliation strikes consistently northwest and dips southwest, thus indicating that a decollement fault must separate structures in Early Proterozoic rocks from underlying Archean basement. This deformation occurred during the Penokean orogeny. It was caused by collision of the Wisconsin Magmatic Terranes with a continental foreland to the north along the Niagara suture.Keywords:
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Research Article| October 01, 1964 Geologic Evolution of the Beartooth Mountains, Montana and Wyoming. Part 4. Relationship Between Precambrian and Laramide Structures in the Line Creek Area CLARENCE J CASELLA CLARENCE J CASELLA Villanova University, Villanova, Pa Search for other works by this author on: GSW Google Scholar GSA Bulletin (1964) 75 (10): 969–986. https://doi.org/10.1130/0016-7606(1964)75[969:GEOTBM]2.0.CO;2 Article history received: 29 Jan 1964 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation CLARENCE J CASELLA; Geologic Evolution of the Beartooth Mountains, Montana and Wyoming. Part 4. Relationship Between Precambrian and Laramide Structures in the Line Creek Area. GSA Bulletin 1964;; 75 (10): 969–986. doi: https://doi.org/10.1130/0016-7606(1964)75[969:GEOTBM]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Line Creek area is at the eastern margin of the Beartooth Mountain block, Montana and Wyoming. The range front here changes in trend from due north to N. 45° E. The Precambrian rocks of the range were uplifted and thrust toward the Bighorn basin during Laramide time, over-turning Paleozoic and later strata. The sedimentary rocks at Line Creek were folded about steep, nonparallel axes.The Precambrian rocks include migmatites, granitic gneisses, metasedimentary rock, and ultra-mafic and mafic intrusions. The Archean history is one of sedimentation, folding, igneous intrusion, metamorphism, and granitization which ended 2750 million years ago. All rocks were later intruded by felsic Laramide porphyry. In the core of the range the crystalline rocks preserve open folds trending north to N. 20° E. Small-scale structures show that during granitization at Line Creek a large synform developed, the axis of which trends N. 45° E.The division of the map area into three subareas within which fabric directions are consistent results from the analysis of the penetrative fabric. The three subareas are: a north-central subarea of north-northeast-trending folds; a central subarea of northeast-trending folds which includes the Line Creek synform; and a southeast area of mainlv east-trending folds. Most folds plunge west to southwest at shallow angles. A causal relationship between the northeast-trending folds and the boundary fault is implied by the proximity and parallelism of the two. The northeast-trending Laramide boundary fault follows trends established during the granitization episode.In Precambrian and overturned Paleozoic rocks steep fractures parallel the trends of the range core and also Precambrian dikes. Fractures at the range front indicate that after their formation gravity spreading was not an important process. Planar shear zones dip westward at moderate angles and southeastward at steep angles. They lie in a position predicted by a theory of vertical uplift.Steep folds in the overturned sedimentary rocks bordering the range have resulted from Laramide thrusting of the two oblique-trending boundary fault segments. An area of northeast-southwest compression occurs where the segments join. Horizontal slip took place along the N. 45° E.-trending segment of the frontal thrust during the last stages of Laramide uplift when a large east-west tear fault developed at the northeast corner of the Beartooth Range. This slippage caused stretching along the mountain front and formed two gaps in the sedimentary palisades that mantle the range. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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A structurally simple, 35‐km‐thick, north facing stratigraphic succession of Late Archean to Middle Proterozoic rocks is exposed near the Montreal River, which forms the border between northern Wisconsin and Michigan. This structure, the Montreal River monocline, is composed of steeply dipping to vertical sedimentary rocks and flood basalts of the Keweenawan Supergroup (Middle Proterozoic) along the south limb of the Midcontinent rift, and disconformably underlying sedimentary rocks of the Marquette Range Supergroup (Early Proterozoic). These rocks lie on an Archean granite‐greenstone complex, about 10 km of which is included in the monocline. This remarkable thickness of rocks appears to be essentially structurally intact and lacks evidence of tectonic thickening or repetition. Tilting to form the monocline resulted from southward thrusting on listric faults of crustal dimension. The faults responsible for the monocline are newly recognized components of a well‐known regional fault system that partly closed and inverted the Midcontinent rift system. Resetting of biotite ages on the upper plate of the faults indicates that faulting and uplift occurred at about 1060 +/−20 Ma and followed very shortly after extension that formed the Midcontinent rift system.
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Remapping of upper Proterozoic and Cambrian rocks in the northern Bannock Range south and east of Pocatello, Idaho, indicates a polyphase deformation history characterized by both shortening and extension. Map-scale folds and faults, related to shortening in the transition zone between the Idaho-Wyoming thrust belt and the hinterland to the west, are present, but have been offset and rotated along superimposed normal faults. The oldest structure evident is the north-trending, east-vergent Rapid Creek fold. This fold involves upper Proterozoic and Cambrian strata in the hanging wall of the Putnam thrust fault. The fold is truncated by east-striking subvertical faults that are inferred to be coeval tear faults. Fold and fault geometries suggest the Rapid Creek fold formed over a footwall ramp, whose location may have been controlled by basement normal faults related to Proterozoic rifting. Further evidence of Mesozoic uplift lies in the sub-Neogene unconformity on Cambrian rocks in the Pocatello area, compared to areas of the thrust belt 15 km (9.3 mi) to the northeast, where similar tuffaceous strata rest on Triassic limestones, indicating 7 km (4.3 mi) of pre-Neogene erosion near Pocatello.
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Research Article| December 01, 1988 Basement beneath the Blue Ridge and Inner Piedmont in northeastern Georgia and the Carolinas: A preserved, Late Proterozoic, rifted continental margin PAUL D. FAVRET; PAUL D. FAVRET 1Department of Geology, University of South Carolina, Columbia, South Carolina 29208 Search for other works by this author on: GSW Google Scholar RICHARD T. WILLIAMS RICHARD T. WILLIAMS 2Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996-1410 Search for other works by this author on: GSW Google Scholar Author and Article Information PAUL D. FAVRET 1Department of Geology, University of South Carolina, Columbia, South Carolina 29208 RICHARD T. WILLIAMS 2Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996-1410 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1988) 100 (12): 1999–2007. https://doi.org/10.1130/0016-7606(1988)100<1999:BBTBRA>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation PAUL D. FAVRET, RICHARD T. WILLIAMS; Basement beneath the Blue Ridge and Inner Piedmont in northeastern Georgia and the Carolinas: A preserved, Late Proterozoic, rifted continental margin. GSA Bulletin 1988;; 100 (12): 1999–2007. doi: https://doi.org/10.1130/0016-7606(1988)100<1999:BBTBRA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Seismic reflection, magnetic, and gravity data from the Blue Ridge and Inner Piedmont of Georgia, North Carolina, and South Carolina indicate that southern Appalachian basement contains two sets of steeply dipping normal faults that bound rotated and tilted blocks. The predominant faults strike about N35°E, subparallel to the axis of the orogen, whereas the oblique set strikes about N10°W. Vertical offsets of as much as 1.3 km across individual N10°W-striking faults have been observed on seismic profiles. Regionally, the pattern is probably similar to normal faults in Precambrian rocks exposed in the Adiron-dacks or along other rifted margins. The initial age of faulting was Late Proterozoic, 570 m.y. or older, inferred from comparison of seismic reflectors in the eastern Blue Ridge and Inner Piedmont with stratigraphy along the Great Smoky thrust. Basement beneath the western portion of the Inner Piedmont in South Carolina and northeastern Georgia has been stable at least since the Middle Triassic and did not reactivate during the Mesozoic breakup of Pangea,based on the absence of crosscutting relationships between basement faults and the Brevard zone reflection.Basement structure related to rifting may partially explain the focal mechanisms of regional earthquakes. The oblique fault set is consistent with well-constrained north-south-striking, subvertical nodal planes obtained for many basement earthquakes in the Valley and Ridge of eastern Tennessee. Valley and Ridge earthquakes in southwestern Virginia are consistent with reactivation of the faults that strike parallel to the orogen. We suggest that the basement structures survived Phanerozoic orogeny because Alleghanian continental collision was interpreted in the southern Appalachians, so that convergence between Laurentia and Gondwana stopped about the time their respective lithospheres came into contact. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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Only fragmentary direct information is available on the basement complex of the Southern Peninsula of Michigan because of limited and poorly distributed basement drill holes. This has encouraged the use of geophysical methods, primarily gravity and magnetic, to study the Precambrian formations. A basement configuration map prepared from magnetic depth estimates and basement drill tests confirms that the basement surface under the Southern Peninsula has the form of an oval depression reaching a maximum depth of more than 15,000 ft (4.5 km) below sea level on the western shore of Saginaw Bay. A basement topographic high is associated with the Howell anticline and a roughly north-south-striking basement trough plunges into the basin from the common boundary point of Indiana, Ohio, and Michigan. Aeromagnetic and Bouguer gravity anomaly maps, together with isotopic dates of samples obtained from basement drill holes and extrapolation of known Precambrian geologic trends, indicate that four basement provinces underlie the Southern Peninsula. The Penokean province can be traced geophysically from Lake Michigan into the Southern Peninsula, where it is characterized by east-southeast-striking geophysical anomalies. Central and southwestern Michigan is underlain primarily by felsic rocks correlating with the Central province. Basement rocks in southeastern Michigan strike north-northeast and are interpreted to be metamorphosed intrusive and extrusive rocks and mafic and felsic gneisses of the Grenville province. The Grenville front strikes south-southwest from Sagi aw Bay to west of the Howell anticline and from there due south to the Michigan Ohio boundary. A Keweenawan rift zone characterized by mafic intrusive and extrusive rocks and by uplifted gneisses transects all of the provinces and extends from Grand Traverse Bay to southeastern Michigan. Another subparallel ancient rift zone may be present in southwestern Michigan. These zones were formed during an episode of crustal extension in Keweenawan time. Subsequent deformation of the sedimentary rocks within the basin generally has been associated with movement along lines of basement weakness apparently related to the rift zone and Penokean structural trends.
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The region of southwestern Montana and east-central Idaho, north of the Snake River plain and east of the Idaho batholith, has been affected by a complex sequence of orogenic events from the Proterozoic through Holocene time. Deposition of Proterozoic Belt Supergroup rocks and rocks of similar age in east-central Idaho occurred in basins that were clearly fault controlled. Many of these faults were reactivated repeatedly at later times and controlled or affected the development of younger tectonic features. This study encompasses the entire width of the Sevier orogenic belt in this part of the Cordilleran fold and thrust belt. The thrust belt comprises several major eastward-transported thrust plates that are successively younger to the east. These plates juxtapose distinct stratigraphic packages that were deposited in eugeoclinal, miogeoclinal, and continental platform settings. As a consequence, the thrust plates can be distinguished on the basis of facies and thickness distribution as well as, to some extent, structural style. In southwest Montana, Sevier-type structures overlap with, and butt against, basement-involved Laramide structures. The extension of southwest Montana basement trends into Idaho suggests that this overlap may extend into east-central Idaho. Superimposed on these older structures are mid-Tertiary to Holocene normal faults that formed present-day basins and ranges. Many of these are reactivated older fault zones, some of which can be shown to have Precambrian ancestry. The region has excellent oil and gas potential, because reservoir and source rocks and trapping mechanisms are all clearly present. However, an understanding of the effect of overlapping tectonic elements is necessary to predict accurately where favorable rock packages are preserved. End_of_Article - Last_Page 941------------
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The Rocky Mountain system extends from the Liard River, B. C., to Santa Fe, New Mexico, and is the dominant geological feature within the seven-state Rocky Mountain section. Five tectonic divisions based on the present structural position of the Precambrian crystalline basement exist within the system and the adjacent eastern area. The divisions are: Canadian shield; thinly covered shield; area of locally exposed basement; area of deeply buried basement; and the area where the basement is no longer recognizable. End_Page 785------------------------------ Precambrian rocks exposed over large areas of Canada collectively form the Canadian shield. The exposed basement is bounded in Alberta and Saskatchewan by overlying sediments. The surface upon which the overlying sedimentary rocks were deposited is warped into a major syncline the steeper limb of which lies in or near the disturbed belt of Alberta and Montana and along the Rocky Mountain front. In this syncline the basement is covered by a relatively thin veneer of sediments except for local areas such as the Williston basin. Petroleum accumulation in the area of thin sedimentary cover is controlled more by stratigraphic than by structural factors. The area of local exposure of the Precambrian basement includes the Southern Rockies, the Wyoming basin, and part of the Middle Rocky Mountain province. Prior to deformation the basement was thinly covered by sediments. Anticlinal mountain ranges and deep local intermontane basins characterize the region. The site of deformation was localized by the Pennsylvanian structural history. Petroleum accumulation is largely controlled by geologic structure. The Precambrian basement was deeply depressed beneath the troughs existent in central Utah, western Wyoming, eastern Idaho, western Alberta, and eastern British Columbia during late Precambrian and early Paleozoic time. Deformation of the troughs created the overthrust belt characterized by repetition of the sedimentary sequence in overthrust fault plates. Absence of Precambrian basement rocks in the thrust plates suggests that faulting is localized in the sedimentary sequence. Accumulation of petroleum have been negligible in this division. The Precambrian basement complex is no longer recognizable in the areas of batholithic intrusion in Idaho, Montana, and British Columbia. The development of granite and granite gneiss in the Idaho batholith, age 100 MY, modified the pre-existing rocks, and substituted a new floor for subsequent geologic history. Lineaments of primary significance are superimposed across the tectonic divisions. The lineaments have complex geologic histories in which transverse movement was probably important. The prominent lineaments are: Rocky Mountain trench, Montana lineament, Wyoming lineament, and the Walker lineament, all of which separate regions of differing geology. Volcanically derived materials of Cenozoic age are widely spread across the Rocky Mountain system, and reflect igneous activity of great magnitude. Extensive tectonic adjustment took place by means of normal and reverse faulting both during and subsequent to the deposition of the volcanic products. The extent and magnitude of the late Cenozoic faulting are as yet incompletely understood. Critical discrimination should be made between fault systems of different ages. End_of_Article - Last_Page 786------------
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The name Falls is given to a northeast-trending zone of diverse geologic features that can be traced northeastward from the Idaho batholith in the Cordilleran miogeocline of the United States, across thrust belt structures and basement rocks of west-central and southwestern Montana, through the cratonic rocks of central Montana, and into southwesternmost Saskatchewan, Canada. The zone is well represented in east-central Idaho and west-central Montana where geologic mapping has outlined northeast-trending, high-angle faults and shear zones that: (1) extend more than 150 km (93 mi) from near Salmon, Idaho, northeastward toward Anaconda, Montana; (2) define a nearly continuous zone of faulting that shows recurrent movement from middle Proterozoic to Holocen time; (3) controlled the intrusion and orientation of some Late Cretaceous to early Tertiary batholithic rocks and early Tertiary dike swarms; and (4) controlled the uplift and orientation of the Anaconda-Pintlar Range. Recurrent movement along these faults and their strong structural control over igneous intrusions in this region suggest that northeast-trending faults represent a fundamental tectonic feature of the region. Figure Geologic features that are similar to those mapped in the Salmon-Anaconda region are present to the southwest and the northeast. In central Idaho, these structures include numerous northeast-trending faults and pronounced topographic lineaments that cut across the southern part of the Idaho batholith, and a northeast alignment of Tertiary igneous rocks that cut the Idaho batholith and adjacent rocks. East and southeast of the Anaconda-Pintlar Range, subparallel, high-angle faults and topographic lineaments are present in the Highland, Pioneer, Ruby, and Tobacco Root Mountains. High-angle faults may have in part controlled the orientation of the northeast-elongate Boulder batholith. Northeast-trending structures are not easily traced across the thrust belt of western Montana or across he Lewis and Clark line. In the central Montana plains, northeast of the disturbed belt, however, a broad zone of colinear, northeast-trending structures is present, and includes: parallel, buried basement highs that in part controlled depositional patterns of some Paleozoic and Mesozoic sedimentary rocks; major physiographic features, such as the remarkably straight, 175-km (109-mi) long segment of the Missouri River, and equally long, buried river channels in southwestern Saskatchewan; a northeasterly alignment of highly differentiated igneous rocks and a belt of ultrabasic intrusions and related diatremes; End_Page 1350------------------------------ and a well-defined pattern of northeast-trending gravity and aeromagnetic anomalies underlying this part of central Montana and southwesternmost Saskatchewan. Taken together, all these geologic features define a broad, northeast-trending zone at least 150 to 200 km (93 to 125 mi) wide and more than 1,000 km (620 mi) long. The zone is approximately colinear but not demonstrably continuous with the well-exposed boundary in eastern Saskatchewan and Manitoba between the Archean Superior and the Proterozoic Churchill provinces of the Canadian Shield. This boundary is also characterized by: high-angle faults, shear zones, and topographic lineaments; pronounced linear gravity and magnetic anomalies; igneous intrusions; and fault controlled depositional patterns and mineralization. That the Great Falls lineament is controlled by a similar Precambrian boundary between the Archean Wyoming province of southwestern Montana and early Proterozoic terrane to the north is speculative; however, the geologic features found along the Great Falls lineament share many common characteristics with features present along the Archean-Proterozoic boundary in Canada. End_of_Article - Last_Page 1351------------
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ABSTRACT The Bridger Range is a relatively small (25 mi. long; 40 km), north-trending uplift of Archean metamorphic rocks and Proterozoic through Mesozoic sedimentary rocks. The Bridger Range is unique in that it overlaps the boundaries of four major tectonic provinces that have combined to produce the overall structure of the Northern Rocky Mountains. These tectonic provinces are: 1) the Middle Proterozoic Belt Basin; 2) the Sevier fold and thrust belt, which mimics the shape of the former Belt Basin; 3) the Laramide foreland province of basement-involved deformation; and 4) the Basin and Range province. These provinces span the Middle Proterozoic rifting of western North America through the culmination of compressional mountain building during the Sevier and Laramide orogenies, to the present phase of crustal extension. In a broad sense, the Bridger Range records a mega-Wilson cycle of continental margin evolution. Asa result of having so many different styles of deformation superimposed at one locality, the Bridger Range contains numerous examples of reactivated faults, folded thrust sheets, and overlapping structural families. The Pass fault in the central Bridger Range marks the structural juxtaposition of Proterozoic sedimentary rocks, the LaHood Formation, against Archean basement rocks to the south. This fault was active as a normal fault along the south margin of the Belt Basin between 1.45 Ga. - 850 Ma. ago, and was the site of further movement during the Paleozoic as evidenced by sedimentary facies changes adjacent to the fault. During the Paleocene the Pass fault and other northwest-trending faults in the Bridger Range were reactivated as high-angle, oblique-slip, lateral thrust ramps along the transverse fault zone of the Helena salient. Subsequently, the basement-cored ancestral Bridger anticline developed during the Laramide orogeny in latest Paleocene to earliest Eocene time and was thrust about 1.8 mi. (3 km) eastward over the western flank of the Crazy Mountains Basin. Finite strain analysis helps to distinguish between the thin-skinned (Sevier) and thick-skinned (Laramide) compressional events. Finally, the modern valley and range landscape began to form through crustal extension perhaps as early as the mid-Oligocene (base of the Renova Formation), but certainly by the Late Miocene (base of the Sixmile Creek Formation). The west limb and crest of the ancestral Bridger anticline was down-dropped to form the Gallatin Valley, which filled with up to 6500 ft. (2000 m) of Late Cenozoic clastic detritus, leaving the east limb standing high as the modern Bridger Range. Thus, the Bridger Range is a perched basement wedge of Archean and Proterozoic rocks overlain by steeply east-dipping Paleozoic-Mesozoic strata.
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