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Paper No. 133-11
Presentation Time: 4:45 PM

GEOCHEMICAL PROGRESSION IN LAVAS AND SHALLOW INTRUSIVES OF THE APPALACHIAN–CALEDONIAN LEKA OPHIOLITE COMPLEX, NORWAY


BECKER, Naomi A.1, BROWNING-HANSON, Joseph1, HOLDER, Robert M.2, NELSON, Wendy R.3, BURGESS, Jerry L.1 and VIETE, Daniel R.4, (1)Earth and Planetary Sciences, Johns Hopkins University, 301 Olin Hall, 3400 N Charles St, Baltimore, MD 21211, (2)Department of Earth & Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, (3)Towson University, Towson, MD 21252, (4)Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21211

Igneous stratigraphy described from drilling and dredging campaigns in the Izu-Bonin-Mariana (IBM) forearc exhibit geochemical trends linked to evolution of magma chemistry during initiation and establishment of a modern subduction zone1. The volcanic section of the forearc progresses up-section from forearc basalts (FAB) to transitional lavas (island arc tholeiites) and then boninites, reflecting increasing influence from subduction zone processes with time1. Similar volcanic stratigraphy has been identified for ophiolites, suggesting origination in ancient forearcs, potentially in association with subduction initiation1. This study investigates the major- and trace-element geochemical characteristics and spatial relationships of lavas and shallow intrusives from the Cambro-Ordovician Leka Ophiolite Complex (LOC), Norway, at the northernmost end of the Appalachian–Caledonian orogenic system.

Discrimination diagrams using Th-Nb and Ti-V trace-element systematics indicate that the LOC contains all the principal magmatic components identified in the IBM model2–4. Spatially, the FAB samples occur at the lowest stratigraphic level of the ophiolite complex, in close proximity to faults that separate the crustal section of the LOC from the mantle section. Up-section from the FAB, compositions change to predominantly island arc tholeiites and boninites, reflecting volcanic progression identical to the IBM forearc. Application of the IBM model to additional ophiolite complexes along the Appalachian–Caledonian orogenic system can facilitate correlation of subduction zone geochemical progression along the >5000 km former Iapetan margin and may assist in identification of samples representing subduction initiation. Guided by this geochemical approach, precise geochronologic constraints on the temporal and spatial evolution of subduction initiation in the Iapetus may provide insights into drivers of global-scale tectonic rearrangements.

(1) Stern et al., 2012, Lithosphere, 4(6)

(2) Pearce and Reagan, 2014, Geosphere, 15(4)

(3) Saccani, 2015, Geoscience Frontiers, 6.

(4) Shervais, 1982, Earth and Planetary Science Letters, 59(1).

Session No. 133

T8. From Rodinia to Pangea: Evolution of the Appalachian-Caledonian Orogen I
Wednesday, 28 October 2020: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol 52, No. 6
doi: 10.1130/abs/2020AM-353768
© Copyright 2020 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.
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