Archean versus Phanerozoic oceanic crust formation and tectonics: Ophiolites through time
IMAGE: PLATE TECTONIC PICTURE THAT SHOWS CONTINENT-OCEAN TRANSITION, MID-OCEAN RIDGE SPREADING SYSTEM, PLUME-HEAD WITH OVERLYING OCEANIC PLATEAU, BACKARC SPREADING SYSTEM, FOREARC, AND VOLCANIC ARC SYSTEM. THE VARIOUS OPHIOLITE TYPES AND THEIR ARCHITECTURAL CONSTRUCTIONS HAVE BEEN PLACED IN THE POSITION WHERE THEY ORIGINALLY WERE FORMED. view more
CREDIT: GEOGEO
Archean versus Phanerozoic oceanic crust formation and tectonics: Ophiolites through time
https://doi.org/10.1016/j.geogeo.2021.09.004
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In this article researchers from the University of Bergen, Bergen, Norway and Miami University, Oxford, OH, USA present a global compilation of structural, lithological, and geochemical data on a selection of Archean, Proterozoic and Phanerozoic magmatic complexes, interpreted as ophiolites. Ophiolites, based on Phanerozoic examples, can be classified into subduction-related and subduction unrelated categories. These categories can be further subdivided into several subtypes depending on the proximity to subduction zones, and on sequential development from rifting – drifting to seafloor spreading for the subduction-unrelated category.
From bottom to top ophiolites exhibit a magmatic sequence of ultramafic rocks (upper mantle units), gabbros (layered and isotropic), basaltic dikes and lavas, as well as boninites and felsic dikes and lavas in the subduction-related types. Archean greenstone belts show large variations in their construction, but Eoarchean examples display identical structure and lithology to the Phanerozoic ophiolites, attesting to the operation of seafloor spreading and subduction zone processes in the early Earth's history.
Lithological differences between the Archean and Proterozoic/Phanerozoic ophiolites are demonstrated in the common occurrence of komatiites and felsic rocks, and scarcity of sheeted dike complexes in the former, compared to the opposite situation in those ophiolites that are younger than ca. 2 Ga. Geochemically there is a concomitant decrease in the content of incompatible elements (e.g., Sr, Zr, Y, Nb) and an increase in the content of compatible elements (e.g., Mg, Cr, Ni). In terms of tectonic environment analyzes, the Archean ophiolites are more abundantly subduction-related than those of Proterozoic and Phanerozoic ages. The subduction-dominant Archean oceanic crust (ophiolites) was characterized by accretionary cycle plate tectonics, whereas for those of Proterozoic and Phanerozoic ages, a combination of both accretionary cycle and Wilson cycles plate tectonic processes was operative.
Article reference: Harald Furnes, Yildirim Dilek, Archean versus Phanerozoic oceanic crust formation and tectonics: Ophiolites through time, Geosystems and Geoenvironment, Volume 1, Issue 1, 2022, 100004, ISSN 2772-8838, https://doi.org/10.1016/j.geogeo.2021.09.004.
Keywords: Ophiolites, Construction, Geochemistry, Classification, Plate tectonics
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ISSN 2772-8838
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DOI
CAPTION
Selected stratigraphic columnar sections from ten Archean and seven Proterozoic greenstone belts, seven Phanerozoic ophiolite complexes, and the oceanic in-situ Izu-Bonin-Mariana sequence.
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GeoGeo
CAPTION
Columnar section showing the upper mantle and crustal components of a typical suprasubduction zone ophiolite, illustrated by field photographs. (a) and (b): Banded and folded harzburgite (olivine + orthopyroxene); (c): Layered cumulates of dunite (bright yellow) and dark wehrlite (olivine + clinopyroxene); (d): Layered and folded gabbro; (e): Varitextured gabbro; (f): Gabbro cut by basaltic and felsic intrusions; (g): Sheeted dike complex; (h): Volcanic breccia set in a hyaloclasite matrix; (i): pillow lava; (j): Massive andesitic lava flow; (k): Folded chert layers. Pictures a-c, i (Leka ophiolite, Norway), d (Karmøy ophiolite, Norway), e-h (Solund-Stavfjord ophiolite, Norway, j, k (Mirdita ophiolite, Albania). Key to lettering: Chpyr- chalcopyrite, H/D- Harzburgite/dunite, H- Harzburgite, L- Lherzolite, Opx–veins- orthopyroxenite veins, Pyr- pyrite.
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GeoGeo
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