Tectonic mélange at Chunky Gal Mountain, North Carolina

Lacazette, Alfred; Rast, N.

doi:10.1130/spe228-p217

Cited by 9 publications

(12 citation statements)

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“…Block-in-matrix structures consist of blocks of amphibolite, biotite-gneiss, granitic orthogneiss, and calc-silicate clasts ranging from centimeter to kilometer scale, and matrices include mica schist, biotite migmatite, and biotite schist . Previous studies of mélanges in the Blue Ridge [Lacazette and Rast, 1989;Horton et al, 1989;Raymond et al, 1989;Higgins et al, 1988] propose that the mélanges formed during the Taconic accretion of a microcontinent or island arc (the Inner Piedmont terrane/Piedmont zone) onto the Laurentian margin. We propose that a megamélange formed in the western North Carolina Blue Ridge due to the westward subduction of the Inner Piedmont zone beneath the WBR to produce the EBR and central Blue Ridge terranes as part of the Taconic orogeny at circa 460 Ma.…”

Section: Snowbird and Great Smoky Group Lithologiesmentioning

confidence: 99%

“…[35] Lacazette and Rast [1989] describe a ''megamélange'' at Chunky Gal Mountain in the eastern Blue Ridge ($15 km southeast of Winding Stair Gap). Horton et al [1989] classified several central and southern Appalachian terranes as ''disrupted'' containing mélange complexes and more coherent terrane fragments.…”

Section: Snowbird and Great Smoky Group Lithologiesmentioning

confidence: 99%

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Formation of high‐pressure metabasites in the southern Appalachian Blue Ridge via Taconic continental subduction beneath the Laurentian margin

Anderson

Moecher

2009

Tectonics

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Tectonic models that account for the occurrence of eclogite, retrograde eclogite, peridotite, and migmatitic basement gneisses in the southern Blue Ridge invoke closure of a small ocean basin between the eastern Blue Ridge (EBR) and western Blue Ridge (WBR). In this “obducted ophiolite” model, Franciscan‐type, eastward subduction of oceanic crust beneath the Piedmont arc occurred prior to obduction of the arc onto the Laurentian margin. The discovery of kilometer‐scale eclogite bodies near the EBR‐WBR boundary are cited as evidence for obducted ophiolite/accreted island arc models. However, thermobarometric estimates based on mineral chemistry from HP metabasites of the western, central, and eastern Blue Ridge indicate that eclogites and granulites are medium‐temperature type (550–900°C), inconsistent with the obducted ophiolite model. Mid‐ocean ridge basalt subducted beneath continental margins and island arcs rarely reaches temperatures in excess of 550°C. Thermobarometric comparisons of the present study and a reexamination of deep seismic profiles from the Blue Ridge allow for a model of westward subduction of continental material beneath Laurentia during the Taconic orogeny that produced a megamélange now preserved in the central and eastern Blue Ridge tectonic provinces. P‐T paths determined from Blue Ridge HP metabasites are similar to P‐T paths determined previously from Caledonian and Variscan eclogites. Thermobarometric similarities imply a common tectonic history of continental collision, subduction of continental crust to depths of 50–65 km, followed by rapid eduction.

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Section: Snowbird and Great Smoky Group Lithologiesmentioning

confidence: 99%

Section: Snowbird and Great Smoky Group Lithologiesmentioning

confidence: 99%

Formation of high‐pressure metabasites in the southern Appalachian Blue Ridge via Taconic continental subduction beneath the Laurentian margin

Anderson

Moecher

2009

Tectonics

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“…Misra and Keller 1978;McElhaney and McSween 1983;Hatcher et al 1984;Raymond et al 2003;Swanson et al 2005;Peterson and Ryan 2009), fragments in tectonic mélange complexes (e.g. Abbot and Raymond 1984;Lacazette and Rast 1989), and a riftrelated intrusion origin (i.e. the ultramafic rocks are consanguineous with the mafic rocks and represent sill and dike emplacement of fractional crystallization products from a picriticbasaltic magma; Wang and Glover 1997).…”

Section: Virginia -Carolinamentioning

confidence: 99%

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

Chew

Staal

2014

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A combination of deep seismic imaging and drilling has demonstrated that the ocean-continent transition (OCT) of present-day, magma-poor, rifted continental margins is a zone of hyperextension characterized by extreme thinning of the continental crust that exhumed the lowermost crust and/or serpentinized continental mantle onto the seafloor. The OCT on present-day margins is difficult to sample, and so much of our knowledge on the detailed nature of OCT sequences comes from obducted, magma-poor OCT ophiolites such as those preserved in the upper portions of the Alpine fold-and-thrust belt. Allochthonous, lens-shaped bodies of ultramafic rock are common in many other ancient orogenic belts, such as the Caledonian – Appalachian orogen, yet their origin and tectonic significance remains uncertain. We summarize the occurrences of potential ancient OCTs within this orogen, commencing with Laurentian margin sequences where an OCT has previously been inferred (the Dalradian Supergroup of Scotland and Ireland and the Birchy Complex of Newfoundland). We then speculate on the origin of isolated occurrences of Alpine-type peridotite within Laurentian margin sequences in Quebec – Vermont and Virginia – North Carolina, focusing on rift-related units of Late Neoproterozoic age (so as to eliminate a Taconic ophiolite origin). A combination of poor exposure and pervasive Taconic deformation means that origin and emplacement of many ultramafic bodies in the Appalachians will remain uncertain. Nevertheless, the common occurrence of OCT-like rocks along the whole length of the Appalachian – Caledonian margin of Laurentia suggests that the opening of the Iapetus Ocean may have been accompanied by hyperextension and the formation of magma-poor margins along many segments.SOMMAIREDes travaux d’imagerie sismique et des forages profonds ont montré que la transition océan-continent (OCT) de marges continentales de divergence pauvre en magma exposée de nos jours, correspond à une zone d’hyper-étirement tectonique caractérisée par un amincissement extrême de la croûte continentale, qui a exhumé sur le fond marin, jusqu’à la tranche la plus profonde de la croûte continentale, voire du manteau continental serpentinisé. Parce qu’on peut difficilement échantillonner l’OCT sur les marges actuelles, une grande partie de notre compréhension des détails de la nature de l’OCT provient d’ophiolites pauvres en magma d’une OCT obduite, comme celles préservées dans les portions supérieures de la bande plissée alpine. Des masses lenticulaires de roches ultramafiques allochtones sont communes dans de nombreuses autres bandes orogéniques anciennes, comme l’orogène Calédonienne-Appalaches, mais leur origine et signification tectonique reste incertaine. Nous présentons un sommaire des occurrences d’OCT potentielles anciennes de cet orogène, en commençant par des séquences de la marge laurentienne, où la présence d’OCT a déjà été déduites (le Supergroupe Dalradien d’Écosse et d'Irlande, et le complexe de Birchy de Terre-Neuve). Nous spéculons ensuite sur l'origine de cas isolés de péridotite de type alpin dans des séquences de marge des Laurentides du Québec-Vermont et de la Virginie-Caroline du Nord, en nous concentrant sur les unités de rift d'âge néoprotérozoïque tardif (pour éviter les ophiolites du Taconique). La conjonction d’affleurements de piètre qualité et de la déformation taconique omniprésente, signifie que l'origine et la mise en place de nombreuses masses ultramafiques dans les Appalaches demeureront incertaines. Néanmoins, la présence fréquente de roches de type OCT tout le long de la marge Calédonnienne-Appalaches de Laurentia suggère que l'ouverture de l'océan Iapetus peut avoir été accompagnée d’hyper-étirement et de la formation de marges pauvres en magma le long de nombreux segments.

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“…Some ultramafic-bearing suites have been interpreted as ophiolitic melanges (Abbott and Raymond, 1984;Lacazette and Rast, 1989). The ultramafic bodies and mafic-ultramafic complexes are commonly interpreted to be fragments of oceanic crust (see Lipin, 1984;Hatcher and others, 1984), but Shaw and Wasserburg (1984) cautioned that they probably have more than one origin.…”

Section: Na2e: Jefferson Terranementioning

confidence: 99%

“…REFERENCES- Abbott and Raymond (1984); Abrams and McConnell (1981); Absher and McSween (1985); Edelman and others (1988); Hatcher (1979); others (1984, 1988); Horton and others (1989a); Lacazette and Rast (1989); Lipin (1984); Neathery and Reynolds (1975); Odom and Fullagar (1973); Rankin and others (1989Rankin and others ( , 1991Rankin and others ( , 1993a; Shaw and Wasserburg (1984); Stow and others (1984); Tull (1978); Wehr (1985); Wones and Sinha (1988) NA2g: POTOMAC COMPOSITE TERRANE TERRANE BOUNDARIES-In Virginia, the Potomac composite terrane, as defined by Drake (1985a), has been thrust along the Mountain Run fault zone onto the True Blue formation (informal name) of Pavlides (1989). This map includes the True Blue in the Jefferson terrane, following the interpretation of Horton and others (1989a), although Pavlides (1989) regards the True Blue as part of Laurentia.…”

Section: Na2e: Jefferson Terranementioning

confidence: 99%

Terranes and overlap sequences in the Central and Southern Appalachians, an expanded explanation for part of the Circum-Atlantic terrane map

Horton¹,

Drake²,

Rankin³

1994

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Tectonic mélange at Chunky Gal Mountain, North Carolina

Cited by 9 publications

References 0 publications

Formation of high‐pressure metabasites in the southern Appalachian Blue Ridge via Taconic continental subduction beneath the Laurentian margin

Formation of high‐pressure metabasites in the southern Appalachian Blue Ridge via Taconic continental subduction beneath the Laurentian margin

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

Terranes and overlap sequences in the Central and Southern Appalachians, an expanded explanation for part of the Circum-Atlantic terrane map

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