The Appalachian orogen: A brief summary

Hatcher, Robert D.

doi:10.1130/2010.1206(01)

Cited by 164 publications

(172 citation statements)

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“…The Southern Appalachians are the product of diachronous, largely oblique collision of the North American craton with Africa and a number of continental fragments and island arcs (Hatcher, , 2002(Hatcher, , 2010Hatcher et al, 2007). Closing of various ocean basins took place more or less continuously from the Early Ordovician to the Permian, but deformation was most intense during the Taconic (480-450 Ma), , and Alleghanian (330-260 Ma) orogenies.…”

Section: Geologic Settingmentioning

confidence: 99%

Isostatic compensation for a portion of the Southern Appalachians: Evidence from a reconnaissance study using wide-angle, three-component seismic soundings

Hawman

Khalifa

Baker

2011

Geological Society of America Bulletin

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Wide-angle refl ections generated by fi ve controlled blasts and over 110 timed quarry blasts in the Southern Appalachians were used to test models for isostatic compensation of topog raphy. The profi les cross the Appa lachian gravity gradient and gravity low and sample the highest elevations within the orogen. Migration of P, SV, and SH refl ections suggests that crustal thickness varies from 35 to 39 km within the coastal plain and 37-39 km within the Carolina terrane. It increases northwestward from 40 to 45 km across the Inner Piedmont, and then thickens to 50-52 km along the southeastern fl ank of the Blue Ridge Mountains. Crustal thickness within the Blue Ridge Mountains ranges from 47 to 56 km. Receiver functions for broadband stations GOGA and MYNC show a similar pattern in crustal thickness. Assuming Airy compensation, the correlation between elevation and Moho depth suggests a range of 50-150 kg/m 3 for the density contrast between the crustal root and mantle. The greatest Moho depths are associated not with the tallest peaks, but rather with the broadest portions of the mountain chain. This observation is consistent with regional bending of the lithosphere. However, the planar basement surface suggests that the root either predates Alleghanian thrusting, and therefore is unrelated to the present topography, or formed in response to some other mechanism. Bounds on curvature of the basement surface suggest a lower bound of 30-40 km for the effective elastic thickness of the lithosphere. This is consistent with previous estimates for the southern Appalachians based on analysis of gravity data.

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Section: Geologic Settingmentioning

confidence: 99%

Isostatic compensation for a portion of the Southern Appalachians: Evidence from a reconnaissance study using wide-angle, three-component seismic soundings

Hawman

Khalifa

Baker

2011

Geological Society of America Bulletin

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“…This similarity suggests that a Cambrian age is a possible alternative to Mesoproterozoic deposition of the Jacobsville Sandstone. Given that reverse faults juxtapose rift volcanics with the Jacobsville Sandstone (e.g., the Keweenaw fault), a Cambrian age would imply significant structural reworking of the rift sometime within or after the Cambrian-most likely during one or more phases of Appalachian mountain building (Hatcher, 2010). However, the dramatic structural offset due to Midcontinent Rift fault inversion (up to 5 km; Cannon et al, 1989) does not continue into overlying Paleozoic sediments: current geologic mapping indicates minimal (<100 m) to no offset of Middle Cambrian to Ordovician strata along the reactivated Douglas, Pine, Lake Owen, and Hinckley faults that bound the St. Croix horst southwest of Lake Superior (Boerboom, 2001;Setterholm, 2010;Cannon et al, 1993).…”

Section: Jacobsville Formationmentioning

confidence: 99%

The end of Midcontinent Rift magmatism and the paleogeography of Laurentia

et al. 2017

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Paleomagnetism of the North American Midcontinent Rift provides a robust paleogeographic record of Laurentia (cratonic North America) from ca. 1110 to 1070 Ma, revealing rapid equatorward motion of the continent throughout rift magmatism. Existing age and paleomagnetic constraints on the youngest rift volcanic and sedimentary rocks have been interpreted to record a slowdown of this motion as rifting waned. We present new paleomagnetic and geochronologic data from the ca. 1090-1083 Ma "late-stage" rift volcanic rocks exposed as the Lake Shore Traps (Michigan), the Schroeder-Lutsen basalts (Minnesota), and the Michipicoten Island

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“…Future fi eld studies in this area will help to further constrain the tectonostratigraphy and structural confi guration of the southernmost Brevard fault zone, and mapping in Georgia is needed to delimit the extent and signifi cance of this Blue Ridge window beneath the Dadeville Complex that has been referred to as the Opelika belt (Hibbard et al, 2006) and the Dog River window ( Fig. 1; Higgins and Crawford, 2007;Hatcher, 2010;Steltenpohl et al, 2010aSteltenpohl et al, , 2011Higgins et al, 2011).…”

Section: Discussion and Directions For Future Studiesmentioning

confidence: 97%

“…Based on decades of surface geological studies, correlations of buried rocks with otherwise known features outside of Alabama, and drill-core data, the crust underlying Alabama is recognized as belonging to three fundamental types: 1) Laurentian, 2) peri-Gondwanan, and 3) Gondwanan (Neathery and Thomas, 1975;Hatcher, 1978Hatcher, , 1987Hatcher, , 2010Tull, 1982;Chowns and Williams, 1983;Horton et al, 1984;Tull, 1978Tull, , 1980Tull, , 1982Tull, , 1984Guthrie and Raymond, 1992;Drummond et al, 1994Drummond et al, , 1997Steltenpohl, 2005;McClellan et al, 2005McClellan et al, , 2007Steltenpohl et al, 2008Steltenpohl et al, , 2010a. Our results from comparing regional geophysical data with the surface and subsurface geology indicate clear demarcation of Laurentian crust in roughly the northwestern half of Alabama, and periGondwanan or Gondwanan crust underlying the southeastern quarter.…”

Section: Discussion and Directions For Future Studiesmentioning

confidence: 99%

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et al. 2013

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We dedicate this paper to the memory of coauthor Isidore (Izzy) Zietz, who died at age 93 while this paper was in review. After contributing to the early theoretical foundation for analysis of airborne magnetic surveys, Izzy became a leading advocate for aeromagnetic survey acquisition and interpretation throughout the U.S., combining surveys into regional, state, and national maps, and working with regional geologists in interpreting geophysical anomalies. Like many geologists, we have been energized by Izzy's contagious enthusiasm for using magnetic and gravity anomalies to delineate and characterize major tectonic features. Lessons from working with him on data from Alabama and elsewhere over the years will continue to infl uence our appreciation and understanding of aeromagnetic and gravity anomalies for interpreting the Earth's upper crust."Magnetics is never good, and gravity is even worse!" "…all of it can just be dashed." -Isidore Zietz ABSTRACT Aeromagnetic and gravity data sets obtained for Alabama (United States) have been digitally merged and fi ltered to enhance upper-crustal anomalies. Beneath the Appalachian Basin in northwestern Alabama, broad deep-crustal anomalies of the continental interior include the Grenville front and New York-Alabama lineament (dextral fault). Toward the east and south, high-angle discordance between the northeast-trending Appalachians and the east-west-trending wedge of overlapping Mesozoic and Cenozoic Gulf Coastal Plain sediments reveals how bedrock geophysical signatures progressively change with deeper burial. Highfrequency magnetic anomalies in the Appalachian deformed domain (ADD) correspond to amphibolites and mylonites outlining terranes, while broader, lower-amplitude domains include Paleozoic intrusive bodies and Grenville basement gneiss. Fundamental ADD structures (e.g., the Alexander City, Towaliga, and Goat Rock-Bartletts Ferry faults) can be traced southward beneath the Gulf Coastal Plain to the suture with Gondwanan crust of the Suwannee terrane. Within the ADD, there is clear magnetic distinction between Laurentian crust and the strongly linear, high-frequency magnetic highs of peri-Gondwanan (Carolina-Uchee) arc terranes. The contact (Central Piedmont suture) corresponds to surface exposures of the Bartletts Ferry fault. ADD magnetic and gravity signatures are truncated by the eastwest-trending Altamaha magnetic low associated with the Suwannee suture. Arcuate northeast-trending magnetic linears of the Suwannee terrane refl ect internal structure and Mesozoic failed-rift trends. Geophysical data can be used to make inferences on surface and subsurface geology and vice versa, which has applicability anywhere that bedrock is exposed or concealed beneath essentially non-magnetic sedimentary cover.

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The Appalachian orogen: A brief summary

Cited by 164 publications

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Isostatic compensation for a portion of the Southern Appalachians: Evidence from a reconnaissance study using wide-angle, three-component seismic soundings

Isostatic compensation for a portion of the Southern Appalachians: Evidence from a reconnaissance study using wide-angle, three-component seismic soundings

The end of Midcontinent Rift magmatism and the paleogeography of Laurentia

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