Geological Society of America

10 D16. Petrology (Posters)

Friday, 20 March 2020
8:00 AM - 12:00 PM
Grand Ballroom A–D

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

Paper number: 10-12
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Naomi Becker Presenting Author
Johns Hopkins University, Baltimore, MD
Joseph Browning-Hanson
Johns Hopkins University, Baltimore, MD
Robert M. Holder
Johns Hopkins University, Baltimore, MD
Wendy Nelson
Towson University, Towson, MD
Jerry Burgess
Johns Hopkins University, Baltimore, MD
Daniel Viete
Johns Hopkins University, Baltimore, MD

Abstract

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 model^2–4. 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).

Geological Society of America Abstracts with Programs. Vol. 52, No. 2

doi: 10.1130/abs/2020SE-344817

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