The MAGIC Experiment: A Combined Seismic and Magnetotelluric Deployment to Investigate the Structure, Dynamics, and Evolution of the Central Appalachians

Abstract The eastern margin of North America has undergone multiple episodes of orogenesis and rifting, yielding the surface geology and topography visible today. It is poorly known how the crust and mantle lithosphere have responded to these tectonic forces, and how geologic units preserved at the surface related to deeper structures. The eastern North American margin has undergone significant postrift evolution since the breakup of Pangea, as evidenced by the presence of young (Eocene) volcanic rocks in western Virginia and eastern West Virginia and by the apparently recent rejuvenation of Appalachian topography. The drivers of this postrift evolution, and the precise mechanisms through which relatively recent processes have modified the structure of the margin, remain poorly understood. The Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) experiment, part of the EarthScope USArray Flexible Array, consisted of collocated, dense, linear arrays of broadband seismic and magnetotelluric (MT) stations (25–28 instruments of each type) across the central Appalachian Mountains, through the U.S. states of Virginia, West Virginia, and Ohio. The goals of the MAGIC deployment were to characterize the seismic and electrical conductivity structure of the crust and upper mantle beneath the central Appalachians using natural-source seismic and MT imaging methods. The MAGIC stations operated between 2013 and 2016, and the data are publicly available via the Incorporated Research Institutions for Seismology Data Management Center.

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Surface Geology of Jebel Rawdah, Oman Mountains

GeoArabia ◽

10.2113/geoarabia0303401 ◽

1998 ◽

Vol 3 (3) ◽

pp. 401-414 ◽

Cited By ~ 2

Author(s):

M.G. Salah Abou Sayed ◽

Mohamed A. Mersal

Keyword(s):

Volcanic Rocks ◽

Normal Faults ◽

Crust And Upper Mantle ◽

Vertical Movements ◽

Oman Mountains ◽

Shearing Deformation ◽

A Minor ◽

Two Stages ◽

Semail Ophiolite ◽

Surface Geology

ABSTRACT Jebel Rawdah is a west-northwest to east-southeast trending, post-obduction fold located at the western edge of the Hatta Zone of the Northern Oman Mountains. The main syncline plunges about 5 kilometers to the northwest and it is flanked to the west by a minor anticline. The outcrops in the area consist of: (1) allochthonous Semail Ophiolite, consisting of slices of oceanic crust and upper mantle, together with the Haybi Complex of volcanic rocks and associated metamorphics; (2) the parautochthonous Sumeini Group consisting of shelf edge and slope carbonates and clastics; and (3) the post-obduction neoautochthonous clastics and carbonates of the Qahlah, Simsima and Muthaymimah formations (Maastrichtian to Early Tertiary). Two stages of folding were detected in the Jebel Rawdah area. The older folds affect the allochthonous rocks and result from shearing deformation along the westward extension of the Hatta Zone. The younger deformation is manifested in drape folds in the neoautochthonous rocks which was caused by differential vertical movements of fault blocks in the underlying allochthonous rocks. Three sets of faults were observed: (1) northwest-southeast trending vertical to steeply-dipping scissor faults; (b) reverse faults which form flower structures; and (c) northeast-southwest trending normal faults. Field observations, biostratigraphic studies and petrographic examination suggest three stages in the development of the stratigraphic units in Jebel Rawdah. The first stage occurred during the Early Maastrichtian when the Oman Mountains emerged and were subsequently exposed to subaerial erosion. In the second stage a transgression occurred during the gradual subsidence of the area which led to the deposition of the Qahlah Formation in a fluviatile to shallow-marine environment, and the overlying Simsima in a shallow shelf setting. In the final Tertiary stage the Muthaymimah Formation was deposited in a subsiding basin and slope setting.

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STRUCTURE OF THE CRUST AND MANTLE LITHOSPHERE ACROSS THE CENTRAL APPALACHIANS AND IMPLICATIONS FOR TOPOGRAPHIC EVOLUTION AND EOCENE VOLCANISM

10.1130/abs/2017ne-291307 ◽

2017 ◽

Author(s):

Maureen D. Long ◽

◽

Margaret H. Benoit

Keyword(s):

Mantle Lithosphere ◽

Central Appalachians ◽

Topographic Evolution

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Electrical Conductivity Structure of the Crust and Upper Mantle Along the Profile Maqên-Lanzhou-Jingbian in the Northeastern Margin of the Qinghai-Tibet Plateau

Chinese Journal of Geophysics ◽

10.1002/cjg2.776 ◽

2005 ◽

Vol 48 (5) ◽

pp. 1293-1306 ◽

Cited By ~ 16

Author(s):

Ji TANG ◽

Yan ZHAN ◽

Guo-Ze ZHAO ◽

Qian-Hui DENG ◽

Ji-Jun WANG ◽

...

Keyword(s):

Electrical Conductivity ◽

Upper Mantle ◽

Tibet Plateau ◽

Crust And Upper Mantle ◽

Conductivity Structure ◽

Qinghai Tibet Plateau

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Evolution of deep mantle sourced carbonated melt in the mantle lithosphere

10.5194/egusphere-egu2020-13055 ◽

2020 ◽

Author(s):

Guoliang Zhang

Keyword(s):

Rare Earth ◽

Field Strength ◽

Rare Earth Elements ◽

Lithospheric Mantle ◽

High Field ◽

Volcanic Rocks ◽

Mantle Lithosphere ◽

High Field Strength ◽

Alkali Basalts ◽

Deep Mantle

Deep sourced magmas play a key role in distribution of carbon in the Earth&#8217;s system. Oceanic hotspots rooted in deep mantle usually produce CO2-rich magmas. However, the association of CO2 with the origin of these magmas remains unclear. Here we report geochemical analyses of a suite of volcanic rocks from the Caroline Seamount Chain formed by the deep-rooted Caroline hotspot in the western Pacific. The most primitive magmas have depletion of SiO2 and high field strength elements and enrichment of rare earth elements that are in concert with mantle-derived primary carbonated melts. The carbonated melts show compositional variations that indicate reactive evolution within the overlying mantle lithosphere and obtained depleted components from the lithospheric mantle. The carbonated melts were de-carbonated and modified to oceanic alkali basalts by precipitation of perovskite, apatite and ilmenite that significantly decreased the concentrations of rare earth elements and high field strength elements. These magmas experienced a stage of non-reactive fractional crystallization after the reactive evolution was completed. Thus, the carbonated melts would experience two stages, reactive and un-reactive, of evolution during their transport through in thick oceanic lithospheric mantle. We suggest that the mantle lithosphere plays a key role in de-carbonation and conversion of deep-sourced carbonated melts to alkali basalts. This work was financially supported by the National Natural Science Foundation of China (91858206, 41876040).

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Global and regional waveform tomography with massive datasets: new insights into the structure and evolution of the continents

10.5194/egusphere-egu2020-5010 ◽

2020 ◽

Author(s):

Sergei Lebedev ◽

Nicolas Luca Celli ◽

Andrew J. Schaeffer

Keyword(s):

Large Scale ◽

Seismic Imaging ◽

Mantle Xenoliths ◽

Mantle Lithosphere ◽

Surface Wave Dispersion ◽

Crust And Upper Mantle ◽

Global Comparison ◽

Archean Crust ◽

Cratonic Mantle ◽

Waveform Tomography

Waveform inversion was introduced in global seismic imaging in the early days of seismic tomography, in the beginning of the 1980s. Thanks to the continual improvements in the data sampling and methodology since then, waveform tomography has been getting more and more effective in extracting structural information from seismic records and producing detailed 3D models of the Earth&#8217;s crust and upper mantle. Today, tomography&#8217;s original problems relating to the large-scale Earth structure have been solved: the structure at the scale of thousands of kilometres is remarkably consistent across recent global models. Resolution of the imaging is now at hundreds of kilometres, the scale of tectonic units and major tectonic and magmatic processes. This has opened a new chapter for waveform tomography. It now fuels discoveries on the structure of individual cratons, evolution of cratons in general, origins of intraplate volcanism, plume-lithosphere interactions and other processes. &#160;&#160;In continents, high-resolution tomography can now map the deep boundaries of different tectonic blocks with useful accuracy.&#160; A global comparison with geological data shows that, as a rule, Archean crust is underlain by thick (180-250 km), cratonic mantle lithosphere. This mantle lithosphere is likely to be of the Archean age as well, as often evidenced by mantle xenoliths. Where Archean crust is unexposed (covered by sediments), its presence can be inferred from the presence of the cratonic mantle lithosphere, imaged by tomography. A growing number of previously unknown cratons in different continents are now being discovered by waveform tomography. The lateral extent of other cratons, hypothesized previously, can now be established.The lithosphere of most known cratons has been remarkably stable since its Archean formation, thanks to its compositional buoyancy and mechanical strength. In some instances, however, cratonic lithosphere is known to have been eroded. This is inferred from the existence of the thick lithosphere in the past, as evidenced by diamondiferous kimberlites, and its absence at present, as evidenced by &#160;seismic imaging. Waveform tomography of continents now reveals more and more occurrences of this process and offers new insights into its mechanisms.ReferencesCelli, N.L., S. Lebedev, A.J. Schaeffer, C. Gaina. African cratonic lithosphere carved by mantle plumes. Nature Communications, 11, 92, doi:10.1038/s41467-019-13871-2, 2020.Schaeffer, A. J., S. Lebedev. Global heterogeneity of the lithosphere and underlying mantle: A seismological appraisal based on multimode surface-wave dispersion analysis, shear-velocity tomography, and tectonic regionalization. In: "The Earth's Heterogeneous Mantle," A. Khan and F. Deschamps (eds.), pp. 3&#8211;46, Springer Geophysics, doi:10.1007/978-3-319-15627-9_1, 2015.Steinberger, B., E. Bredow, S. Lebedev, A. Schaeffer, T. H. Torsvik. Widespread volcanism in the Greenland-North Atlantic region explained by the Iceland plume. Nature Geoscience, 12, 61&#8211;68, doi:10.1038/s41561-018-0251-0, 2019.

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Origin of potassic postcollisional volcanic rocks in young, shallow, blueschist-rich lithosphere

Science Advances ◽

10.1126/sciadv.abc0291 ◽

2021 ◽

Vol 7 (29) ◽

pp. eabc0291

Author(s):

Yu Wang ◽

Stephen F. Foley ◽

Stephan Buhre ◽

Jeremie Soldner ◽

Yigang Xu

Keyword(s):

Temporal Trend ◽

Volcanic Rocks ◽

Continental Collision ◽

Mantle Lithosphere ◽

Source Regions ◽

Himalayan Belt ◽

Potassic Rocks

Potassium-rich volcanism occurring throughout the Alpine-Himalayan belt from Spain to Tibet is characterized by unusually high Th/La ratios, for which several hypotheses have brought no convincing solution. Here, we combine geochemical datasets from potassic postcollisional volcanic rocks and lawsonite blueschists to explain the high Th/La. Source regions of the volcanic melts consist of imbricated packages of blueschist facies mélanges and depleted peridotites, constituting a new mantle lithosphere formed only 20 to 50 million years earlier during the accretionary convergence of small continental blocks and oceans. This takes place entirely at shallow depths (<80 km) without any deep subduction of continental materials. High Th/La in potassic rocks may indicate shallow sources in accretionary settings even where later obscured by continental collision as in Tibet. This mechanism is consistent with a temporal trend in Th/La in potassic postcollisional magmas: The high Th/La signature first becomes prominent in the Phanerozoic, when blueschists became widespread.

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Abiotic Factors Influencing Deer Browsing in West Virginia

Northern Journal of Applied Forestry ◽

10.1093/njaf/23.1.20 ◽

2006 ◽

Vol 23 (1) ◽

pp. 20-26 ◽

Cited By ~ 13

Author(s):

Tyler A. Campbell ◽

Benjamin R. Laseter ◽

W. Mark Ford ◽

Richard H. Odom ◽

Karl V. Miller

Keyword(s):

West Virginia ◽

Abiotic Factors ◽

Woody Species ◽

Surface Shape ◽

Relative Importance ◽

Deer Browsing ◽

Mature Forest ◽

Central Appalachians ◽

Factors Influencing ◽

Forested Ecosystem

Abstract We present a comparison of woody browse availability and white-tailed deer (Odocoileus virginianus) use among clearcut interiors, skidder trail edges, and mature forest and an evaluation of the relative importance of aboitic factors in predicting browsing pressure within regenerating clearcuts in the central Appalachians of West Virginia. We sampled 810 1-m2 plots in or adjacent to nine regenerating clearcuts (8–19 ha) during the summer of 2001. Availability and use of woody browse did not differ between clearcut interior and skidder trail plots for any species observed. Plots in the adjacent mature forest had less woody browse availability and higher utilization. Overall use of available woody browse in clearcuts was >15%. Combining all woody species, elevation (wI = 0.618) and distance to mature forest (wI = 0.379) were more important than landform index, plot surface shape, aspect, and slope in predicting deer browsing pressure in regenerating clearcuts. We believe that without management activities aimed at reducing deer browsing, in many parts of this region the ability of forest managers to regenerate stands will be jeopardized and the forested ecosystem will be compromised.

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