George Guice

Johns Hopkins University

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Daniel R. Viete

Johns Hopkins University

Freya George

University of Bristol

Iain McDonald

Cardiff University

Hannah S.R. Hughes

University of Exeter

Michael R. Ackerson

Smithsonian Institution

Robert Holder

University of Michigan–Ann Arbor

John Faithfull

The Hunterian

Naomi Becker

Los Alamos National Laboratory

Céline Martin

American Museum of Natural History

Joseph Browning-Hanson

Johns Hopkins University

Cooperative Institutions

Johns Hopkins University

Cardiff University

Centre National de la Recherche Scientifique

Universidade de São Paulo

Carnegie Institution for Science

Geological Survey of Finland

American Museum of Natural History

University of the Witwatersrand

Boston College

University of Glasgow

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EVIDENCE OF SUBDUCTION INITIATION RECORDED IN THE DADEVILLE COMPLEX OF ALABAMA

Abstracts with programs - Geological Society of America (2022)

Naomi Becker Freya George George Guice Daniel R. Viete

The Appalachian Mountain range formed from multiple orogen-scale collisional events spanning from the Neoproterozoic to the Devonian. As the Iapetus Ocean began to close, early subduction zone magmatism created forearc lithosphere and volcanic arcs that were subsequently obducted onto Laurentia during the formation of Pangaea. These early magmatic products contain geochemical information that informs our understanding of subduction zone formation and evolution; however multiple collisional events, the emplacement of large (and potentially unrelated) magmatic intrusions, and extreme weathering at the southernmost extent of the Appalachians have made identifying these rocks and reconstructing the history of this portion of the margin notoriously difficult. Fortunately, recent studies of the modern Izu–Bonin–Mariana subduction system have shed new light on the geochemical evolution of subduction initiation and have resulted in the development of new criteria for classifying the first magmatic products of subduction–forearc basalts and boninites. These constraints allow for reassessment of subduction-related rocks throughout the Appalachian margin. Only one potential volcanic arc has been identified in the Southern Appalachians. This hypothesized arc, the Dadeville Complex of Alabama and Georgia, has geochemical signatures associated with subduction zone influence and is considered to have formed during subduction of Iapetan lithosphere underneath or adjacent to the Laurentian margin; however, the exact nature of the complex and its geologic history remains unclear. We apply the new understanding of subduction zone magmatic evolution derived from the Izu–Bonin–Mariana system to the Dadeville Complex to further elucidate its origin. Using whole rock and mineral major- and trace-element geochemistry coupled with detailed petrographic analyses, we have identified forearc basalts and boninites; therefore, we interpret these data to reflect formation of the Dadeville Complex during initial subduction in the Iapetus Ocean.

Forearc

Volcanic arc

Eclogitization

10.1130/abs/2022nc-375252

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Assessing the Validity of Negative High Field Strength-Element Anomalies as a Proxy for Archaean Subduction: Evidence from the Ben Strome Complex, NW Scotland

Geosciences (2018)

George Guice Iain McDonald Hannah S.R. Hughes Denis Schlatter Kathryn Goodenough

The relative depletion of high field strength elements (HFSE), such as Nb, Ta and Ti, on normalised trace-element plots is a geochemical proxy routinely used to fingerprint magmatic processes linked to Phanerozoic subduction. This proxy has increasingly been applied to ultramafic-mafic units in Archaean cratons, but as these assemblages have commonly been affected by high-grade metamorphism and hydrothermal alteration/metasomatism, the likelihood of element mobility is high relative to Phanerozoic examples. To assess the validity of HFSE anomalies as a reliable proxy for Archaean subduction, we here investigate their origin in ultramafic rocks from the Ben Strome Complex, which is a 7 km2 ultramafic-mafic complex in the Lewisian Gneiss Complex of NW Scotland. Recently interpreted as a deformed layered intrusion, the Ben Strome Complex has been subject to multiple phases of high-grade metamorphism, including separate granulite- and amphibolite-facies deformation events. Additional to bulk-rock geochemistry, we present detailed petrography, and major- and trace-element mineral chemistry for 35 ultramafic samples, of which 15 display negative HFSE anomalies. Our data indicate that the magnitude of HFSE anomalies in the Ben Strome Complex are correlated with light rare earth-element (LREE) enrichment likely generated during interaction with H2O and CO2-rich hydrothermal fluids associated with amphibolitisation, rather than primary magmatic (subduction-related) processes. Consequently, we consider bulk-rock HFSE anomalies alone to be an unreliable proxy for Archaean subduction in Archaean terranes that have experienced multiple phases of high-grade metamorphism, with a comprehensive assessment of element mobility and petrography a minimum requirement prior to assigning geodynamic interpretations to bulk-rock geochemical data.

Ultramafic rock

Dharwar Craton

Trace element

10.3390/geosciences8090338

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Citations (21)

EVIDENCE OF SUBDUCTION INITIATION RECORDED IN THE DADEVILLE COMPLEX OF ALABAMA

Abstracts with programs - Geological Society of America (2022)

Naomi Becker Freya George George Guice Daniel R. Viete

10.1130/abs/2022ne-373684

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ARE SERPENTINITES FROM THE GREATER NYC AREA ALL OPHIOLITES? INSIGHT FROM B ISOTOPES AND SPINEL-GROUP MINERALS

Abstracts with programs - Geological Society of America (2023)

Céline Martin George Guice Kennet E. Flores N. Morales George E. Harlow

10.1130/abs/2023am-394616

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SUBDUCTION INITIATION IN THE IAPETUS OCEAN: WHEN, WHERE AND HOW?

Abstracts with programs - Geological Society of America (2022)

Daniel R. Viete Naomi Becker George Guice James L. Crowley

10.1130/abs/2022am-380102

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Polymetamorphism and metastability in Paleozoic schists of the central Appalachian Baltimore Terrane, USA

Lithos (2024)

Freya George Daniel R. Viete George Guice Kayleigh Harvey Stephanie Walker

10.1016/j.lithos.2024.107824

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Spinel-group minerals as a record of magmatic and metamorphic processes: evidence from the highly altered Morro do Onça ultramafic suite, São Francisco Craton (Brazil)

Contributions to Mineralogy and Petrology (2022)

George Guice Joana Reis Magalhães Marco Aurélio Piacentini Pinheiro Raianny Carolini Ramos Ferreira Vinícius T. Meira

Ultramafic rock

10.1007/s00410-022-01901-0

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A c. 1900 Ma Tethyan-type ophiolite in the Penokean Orogen, Pembine, Wisconsin (USA): Insights from the volcanic stratigraphy

Precambrian Research (2023)

George Guice Daniel R. Viete Robert Holder Supratik Roy

Forearc

Geochronology

Orogeny

Volcanic arc

Obduction

10.1016/j.precamres.2023.107223

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The B isotopic signature of serpentine from obducted ophiolites: Mixing of fluids and tectonic implications

Lithos (2023)

Céline Martin Kennet E. Flores George E. Harlow Samuel Angiboust Florent Hodel

Ultramafic rock

10.1016/j.lithos.2023.107275

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Suprasubduction zone ophiolite fragments in the central Appalachian orogen: Evidence for mantle and Moho in the Baltimore Mafic Complex (Maryland, USA)

Geosphere (2021)

George Guice Michael R. Ackerson Robert Holder Freya George Joseph Browning-Hanson

Abstract Suprasubduction zone (SSZ) ophiolites of the northern Appalachians (eastern North America) have provided key constraints on the fundamental tectonic processes responsible for the evolution of the Appalachian orogen. The central and southern Appalachians, which extend from southern New York to Alabama (USA), also contain numerous ultramafic-mafic bodies that have been interpreted as ophiolite fragments; however, this interpretation is a matter of debate, with the origin(s) of such occurrences also attributed to layered intrusions. These disparate proposed origins, alongside the range of possible magmatic affinities, have varied potential implications for the magmatic and tectonic evolution of the central and southern Appalachian orogen and its relationship with the northern Appalachian orogen. We present the results of field observations, petrography, bulk-rock geochemistry, and spinel mineral chemistry for ultramafic portions of the Baltimore Mafic Complex, which refers to a series of ultramafic-mafic bodies that are discontinuously exposed in Maryland and southern Pennsylvania (USA). Our data indicate that the Baltimore Mafic Complex comprises SSZ ophiolite fragments. The Soldiers Delight Ultramafite displays geochemical characteristics—including highly depleted bulk-rock trace element patterns and high Cr# of spinel—characteristic of subduction-related mantle peridotites and serpentinites. The Hollofield Ultramafite likely represents the “layered ultramafics” that form the Moho. Interpretation of the Baltimore Mafic Complex as an Iapetus Ocean–derived SSZ ophiolite in the central Appalachian orogen raises the possibility that a broadly coeval suite of ophiolites is preserved along thousands of kilometers of orogenic strike.

Ultramafic rock

10.1130/ges02289.1

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Citations (9)