Insights into the tectonostratigraphic setting of the Southern Appalachians during the Blountian tectophase from an integrated geochemical analysis of magmatic phenocrysts in the Ordovician Deicke K-bentonite

Herrmann, Achim D.; Haynes, John T.; Robinet, Richard M.; Konzett, Jürgen; Emerson, Norlene R.

doi:10.1016/j.lithos.2021.106301

Cited by 5 publications

(21 citation statements)

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“…The late Aptian-early Albian age of the Cloverly Formation and associated bentonites overlaps with the early stages of Idaho magmatism west of the 0.706 Sr isopleth, a position supported by bentonite whole-rock data [11] where a complex amalgamation of arc terranes and adjoining basins began to dock with Laurentia [7]. The Cloverly bentonite zircon population (Figure 5) includes xenocrysts whose Mesoproterozoic inherited ages match those in the Northern Atlanta Lobe (NAL) of the Idaho batholith [46] whereas younger Early Cretaceous to Middle Jurassic inherited ages match parts of the Blue Mountain Province and associated island arcs [57].…”

Section: Zircon Autocrysts Antecrysts and Xenocrysts And Migrating Magmatismmentioning

confidence: 67%

“…These distally deposited ash beds have the potential to serve as a robust source of geochronologic and geochemical data that track the evolution of their magmatic source terranes. Bentonite eruptive ages and whole-rock geochemistry have previously been used to identify the tectonic setting of coeval magmatic rocks in various settings across the globe (for example, [2][3][4]) and refine accretionary events at convergent plate boundaries [5] and more detailed study of bentonite phenocrysts has been used for stratigraphic correlation [6] and to infer magmatic processes [7]. Prior studies typically have sampled bentonites that formed during a limited time interval of only a few million years and so long-term changes in tectonic setting and the magmatic process that ultimately led to eruption of tephra have not been considered.…”

Section: Introductionmentioning

confidence: 99%

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Tracking 40 Million Years of Migrating Magmatism across the Idaho Batholith Using Zircon U-Pb Ages and Hf Isotopes from Cretaceous Bentonites

et al. 2021

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Cretaceous strata preserved in Wyoming contain numerous large bentonite deposits formed from the felsic ash of volcanic eruptions, mainly derived from Idaho batholith magmatism. These bentonites preserve a near-continuous 40 m.y. chronology of volcanism and their whole-rock and mineral chemistry has been used to document igneous processes and reconstruct the history of Idaho magmatism as emplacement migrated across the Laurentian margin. Using LA-ICP-MS, we analyzed the U-Pb ages and Hf isotopic compositions of nearly 700 zircon grains from 44 bentonite beds from the Bighorn Basin, Wyoming. Zircon populations contain magmatic autocrysts and antecrysts which can be linked to the main pulses of the Idaho batholith and xenocrysts ranging from approx. 250 Ma to 1.84 Ga from country rocks and basement source terranes. Initial εHf compositions of Phanerozoic zircons are diverse, with compositions ranging from −26 to nearly +12. Based on temporal trends in zircon ages and geochemistry, four distinct periods of plutonic emplacement are recognized during the Mid- to Late Cretaceous that follow plutonic emplacement across the Laurentian suture zone in western Idaho and into western Montana with the onset of Farallon slab shallowing. Our data demonstrate the utility of using zircons in preserved tephra to track the regional-scale evolution of convergent margins related to terrane accretion and the spatial migration of magmatism related to changes in subduction dynamics.

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Section: Zircon Autocrysts Antecrysts and Xenocrysts And Migrating Magmatismmentioning

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Tracking 40 Million Years of Migrating Magmatism across the Idaho Batholith Using Zircon U-Pb Ages and Hf Isotopes from Cretaceous Bentonites

et al. 2021

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“…Durango and Madagascar (MAD) apatites were used as secondary standards. Additional sample processing and analytical details were reported by Herrmann et al [27]. The results of the LA-ICP-MS analyses used for the training set are tabulated in online Appendix A.…”

Section: La-icp-ms Analysis Of Apatite Phenocrysts To Establish the Training And Testing Datasetsmentioning

confidence: 99%

“…First, different experimental setups for the analysis can lead to offsets in absolute values of the different elements. This has been shown to be an issue for Ordovician Kbentonites before [5,27]. In particular, problems of accurately quantifying Cl and F concentrations in geological samples, including apatites, using EPMA has been well documented [33,34].…”

Section: Evaluation Of the ML Models Based On Geochemical Data Of Apatite Phenocrystsmentioning

confidence: 99%

“…[5,14]). More recently, Herrmann et al [27] showed that the Deicke K-bentonite also has multiple layers, and they suggest that this finding can most likely be attributed to the amalgamation of several discrete tephra layers into one stratigraphic horizon as seen today. The type localities and type sections of the Deicke and Millbrig K-bentonites are in the Upper Mississippi Valley (UMV) and are relatively far removed from the Ordovician volcanic centers that produced these ash falls.…”

Section: Evaluation Of the ML Models Based On Geochemical Data Of Apatite Phenocrystsmentioning

confidence: 99%

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Machine Learning Applied to K-Bentonite Geochemistry for Identification and Correlation: The Ordovician Hagan K-Bentonite Complex Case Study

et al. 2021

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Altered tephras (K-bentonites) are of great importance for calibration of the geologic time scale, for local, regional, and global correlations, and paleoenvironmental reconstructions. Thus, definitive identification of individual tephras is critical. Single crystal geochemistry has been used to differentiate tephra layers, and apatite is one of the phenocrysts commonly occurring in tephras that has been widely used. Here, we use existing and newly acquired analytical datasets (electron probe micro-analyzer [EPMA] data and laser ablation ICP-MS [LA-ICP-MS] data, respectively) of apatite in several Ordovician K-bentonites that were collected from localities about 1200 km apart (Minnesota/Iowa/Wisconsin and Alabama, United States) to test the use of machine-learning (ML) techniques to identify with confidence individual tephra layers. Our results show that the decision tree based on EPMA data uses the elemental concentration patterns of Mg, Mn, and Cl, consistent with previous studies that emphasizes the utility of these elements for distinguishing Ordovician K-bentonites. Differences in the experimental setups of the analyses, however, can lead to offsets in absolute elemental concentrations that can have a significant impact on the correct identification and correlation of individual K-bentonite beds. The ML model using LA-ICP-MS data was able to identify several K-bentonites in the southern Appalachians and establish links to K-bentonites samples from the Upper Mississippi Valley. Furthermore, the ML model identified individual layers of multiphase eruptions, thus illustrating very well the great potential of applying ML techniques to tephrochronology.

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New specimens of Cyclocystoides scammaphoris (Echinodermata) from the Upper Ordovician rocks of the American midcontinent with implications for cyclocystoid functional morphology

Kolata

Frank²,

Kaplan³

et al. 2023

J. Paleontol.

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New specimens of Cyclocystoides scammaphoris Smith and Paul, 1982, are here reported from the Upper Ordovician Platteville Formation of northern Illinois, Plattin and Decorah groups of east-central Missouri, and Lebanon Limestone of central Tennessee. These fossils reveal skeletal details that provide insight into the anatomy of cyclocystoids. Of particular significance is a network of channels that likely originate near the center of the central disk and extend along the oral side of the radial plates, bifurcating distally two or three times before entering the radial facets on the proximal surface of each marginal ossicle. From here, the network enters a series of facet canals that extend upward through each marginal ossicle, exiting in a linear row of pores. The canals are very similar in size and distribution to the nerve canals in living echinoderms. The axes of the canals, which number up to 500 in some specimens, and those of the radial ducts project proximally away from the oral surface at an elevation angle of about 25°, apparently forming a network that could have converged within the upper part of the body cavity. This origin and function are made clear by the connection between the channel on each radial plate and the radial facet canal pores within each marginal ossicle.

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Insights into the tectonostratigraphic setting of the Southern Appalachians during the Blountian tectophase from an integrated geochemical analysis of magmatic phenocrysts in the Ordovician Deicke K-bentonite

Cited by 5 publications

References 59 publications

Tracking 40 Million Years of Migrating Magmatism across the Idaho Batholith Using Zircon U-Pb Ages and Hf Isotopes from Cretaceous Bentonites

Tracking 40 Million Years of Migrating Magmatism across the Idaho Batholith Using Zircon U-Pb Ages and Hf Isotopes from Cretaceous Bentonites

Machine Learning Applied to K-Bentonite Geochemistry for Identification and Correlation: The Ordovician Hagan K-Bentonite Complex Case Study

New specimens of Cyclocystoides scammaphoris (Echinodermata) from the Upper Ordovician rocks of the American midcontinent with implications for cyclocystoid functional morphology

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