Igneous petrogenesis and tectonic setting of granitic rocks from the eastern Blue Ridge and Inner Piedmont, Alabama Appalachians

Drummond, Mark S.; Neilson, Michael J.; Allison, David T.; Tull, James F.

doi:10.1130/0-8137-1191-6.147

Cited by 14 publications

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“…La edad de las migmatitas y del granito Cozahuico en la zona de contacto entre los complejos cristalinos es congruente con la edad leonardiana (Weber, 1997) de la Formación Matzitzi como unidad de traslape en el área de Metzontla. Además, la relación discordante entre milonitas de la falla de Caltepec y la Formación Matzitzi, aunque plegada pero sin deformación cristaloplástica, implica un tasa de exhumación muy rápida de la zona de cizalla dúctil, lo cual es consistente con la coexistencia de foliaciones magmática y de estado sólido (e.g., Miller y Paterson, 1994) en el granito Cozahuico, y la preservación como fase metaestable de epidota magmática (e.g., Drummond et al, 1997) tanto en el granito como en los neosomas graníticos. 40 Ar/ 39 Ar y detalles del procedimiento analítico, así como los espectros de edades aparentes correspondientes, se presentan en la Tabla 3 y en la Figura 9, respectivamente.…”

Section: Geocronología: Edad Del Granito Cozahuico Migmatitas Y De Lunclassified

La falla de Caltepec: raíces expuestas de una frontera tectónica de larga vida entre dos terrenos continentales del sur de México

Elı́as-Herrera

Ortega-Gutiérrez

Sánchez‐Zavala

et al. 2005

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ResumenEn este trabajo se discuten las características geológicas de la falla de Caltepec, una zona de cizalla de larga vida con dirección norte-sur y mecanismo transpresional derecho que separa a los terrenos Zapoteco al oriente y Mixteco al poniente al nivel de sus basamentos metamórfi cos (complejos Oaxaqueño y Acatlán). Los excelentes afl oramientos (área de Caltepec) que exponen completamente el contacto en una anchura variable entre 2 y 6 km revelan una actividad tectonomagmática y metamórfi ca del Pérmico temprano relacionada con la yuxtaposición de los complejos cristalinos durante la consolidación de Pangea, y registran también períodos múltiples de reactivación mesozoicos, cenozoicos y probablemente hasta recientes. Con base en la cartografía geológico-estructural detallada y estudios petrográfi cos, geocronológicos e isotópicos, se determinó un rango de edad de 275.6−270.4 Ma para el evento de cizalla dúctil en la zona de falla mediante fechamientos U-Pb en circones de un leucosoma anatéctico y granito sintectónico (granito Cozahuico). Se establece también una estructura en semifl or con su cima en posición casi vertical y su base cabalgada hacia el poniente con desplazamientos indeterminados. Las relaciones iniciales de 87 Sr/ 86 Sr (0.70435-0.70686) y edades modelo Sm-Nd (T DM ) (1.0-1.6 Ga) para el granito Cozahuico y el leucosoma indican un origen por mezcla magmática entre corteza local proterozoica y una componente de manto empobrecido. La edad leonardiana de la cobertura discordante (Formación Matzitzi) y una edad de enfriamiento 40 Ar/ 39 Ar (moscovita) de 268.6 Ma para un esquisto de mica milonítico en la base de la cabalgadura, implica tasas altas de enfriamiento (~180°C/Ma) y levantamiento durante el Pérmico. Por otro lado, el registro sedimentológico adyacente indica reactivación tectónica intensa durante el Cretácico Inferior, Paleógeno y Neógeno a lo largo de la falla de Caltepec, alternando con periodos de estabilidad tectónica relativa durante el Triásico, Jurásico y Cretácico medio. La orientación paralela de las fallas de Caltepec y Oaxaca, distante decenas de kilómetros al oriente de la primera, se interpreta como partes de un sistema estructural sincrónico y dinámicamente acoplado que ha estado liberando alternadamente los esfuerzos tectónicos asociados con la ruptura de Pangea y la evolución del margen del Pacífi co del sur de México desde el Jurásico hasta el Holoceno en esta región.Palabras clave: Falla mayor, límite de terrenos, Complejo Acatlán, Complejo Oaxaqueño, México meridional.

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Section: Geocronología: Edad Del Granito Cozahuico Migmatitas Y De Lunclassified

La falla de Caltepec: raíces expuestas de una frontera tectónica de larga vida entre dos terrenos continentales del sur de México

Elı́as-Herrera

Ortega-Gutiérrez

Sánchez‐Zavala

et al. 2005

BSGM

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“…S u w a n n e e te rr a n e (Russell, 1978;Drummond et al, 1997;Tull et al, 2009;Schwartz et al, 2011). Timing of pluton emplacement in the Alabama eastern Blue Ridge is only beginning to be understood (Russell, 1978;Stowell et al, 1996;Steltenpohl et al, 2005b;Tull et al, 2009;Schwartz et al, 2011).…”

Section: Laurentian Gondwanan P E R I -G O N D W a N A Nmentioning

confidence: 99%

“…The Elkahatchee Quartz Diorite, a premetamorphic batholith (Fig. 2;Tull, 1978;Allison, 1992;Drummond et al, 1994Drummond et al, , 1997, was previously reported to be ca. 490 Ma based on U-Pb isotopic dating of multi-grain aliquots of zircons (Russell, 1978).…”

Section: Laurentian Gondwanan P E R I -G O N D W a N A Nmentioning

confidence: 99%

“…Mueller, 2010, personal commun.). Other eastern Blue Ridge intrusions northwest of the Brevard zone in Alabama are lumped broadly into the Rockford, Bluff Springs, and Almond suites of granite (Deininger et al, 1973;Deininger, 1975;Russell, 1978;Defant, 1980;Defant and Ragland, 1981;Defant et al, 1987;Drummond, 1986;Osborne et al, 1988;Drummond et al, 1997), from which Schwartz et al (2011) recently reported U-Pb zircon dates of ca. 365 Ma, ca.…”

Section: Laurentian Gondwanan P E R I -G O N D W a N A Nmentioning

confidence: 99%

“…The Emuckfaw Group comprises mostly metagraywacke and schist that is intruded by Paleozoic granitoid plutons assigned to the Kowaliga batholith or the suite of sill-like Zana granites (Fig. 2;Russell, 1978;Stoddard, 1983;Bieler and Deininger, 1987;Grimes et al, 1997;Drummond et al, 1997;Steltenpohl, 2005). Russell (1978) reported whole-rock Rb-Sr "errorchron" ages for the Kowaliga and Zana granites within the Silurian and Devonian Periods, respectively, whereas U-Pb analysis of zircons (multi-grain aliquots) gave Middle Ordovician ages.…”

Section: Laurentian Gondwanan P E R I -G O N D W a N A Nmentioning

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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Isotopic Age Constraints and Metamorphic History of the Talladega Belt: New Evidence for Timing of Arc Magmatism and Terrane Emplacement along the Southern Laurentian Margin

McClellan¹,

Steltenpohl²,

Thomas³

et al. 2007

The Journal of Geology

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Talladega belt, southernmost Appalachians, provide insight into the timing and nature of pre-Alleghanian tectonism in this region. Low-grade metasedimentary rocks of the Talladega belt represent the outermost preserved portions of the southern Laurentian margin, thus recording the earliest orogenic events that affected the margin, in addition to later overprinting events. These rocks are structurally overlain by the Hillabee Greenstone metavolcanic sequence, from which metadacite yields an age of ‫4ע074‬ Ma (ion microprobe U-Pb zircon age). Hillabee geochemistry indicates formation in an arc or back-arc setting. We suggest correlation of the Hillabee Greenstone with 460-470-Ma arc-related rocks in the Dahlonega gold belt, which extends along strike with the Hillabee through Georgia and into North Carolina, and interpret the Hillabee as the southernmost volcanic expression of an Early-Middle Ordovician arc that formed outboard of Laurentia. Rocks of the Talladega belt, including the Hillabee, preserve a record of only one Paleozoic dynamothermal metamorphic event. 40 Ar/ 39 Ar dates are consistent with metamorphism following deposition of the youngest biostratigraphically dated unit, the Erin Slate, which contains early Mississippian Periastron plant fossils (360-350 Ma). Muscovite (closure temperature 350Њ-400ЊC) yields internally consistent ages between 334 and 320 Ma. Metamorphism of the Talladega belt, therefore, is constrained to the interval between 360 and 320 Ma. The pre-to synmetamorphic thrust contact between the Hillabee Greenstone and Talladega belt metasedimentary rocks must have formed after deposition of the Erin Slate at 360-350 Ma but before metamorphism of the Talladega belt (no later than ∼320 Ma). We propose that the Ordovician Hillabee-Dahlonega arc terrane first collided with the Laurentian continental margin between 360 and 320 Ma, with variations in timing of deformation and metamorphic character along the collision zone.

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Igneous petrogenesis and tectonic setting of granitic rocks from the eastern Blue Ridge and Inner Piedmont, Alabama Appalachians

Cited by 14 publications

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La falla de Caltepec: raíces expuestas de una frontera tectónica de larga vida entre dos terrenos continentales del sur de México

La falla de Caltepec: raíces expuestas de una frontera tectónica de larga vida entre dos terrenos continentales del sur de México

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Isotopic Age Constraints and Metamorphic History of the Talladega Belt: New Evidence for Timing of Arc Magmatism and Terrane Emplacement along the Southern Laurentian Margin

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