Tectonic origin of supra-subduction zone ophiolites from the three-dimensional geochemical structure of the lava pile
Final Report Abstract
Based on >700 new major and trace element analyses, we constructed a 3D geochemical picture of lavas from the Troodos Ophiolite. We showed that there are large and systematic variations in lava chemistry with geographic position. Highly depleted lavas, with a strong subduction zone enrichment in fluid mobile elements occur on the southern margin of the Troodos Ophiolite. Boninites are restricted to the southern margin of the Troodos Ophiolite, and dominate the lava sequence in the southeastern region. Lavas from the northern margin are andesites or dacites, and were derived from a less depleted source, with less subduction component. The lavas from close to the Arakapas Transform Fault were derived from a depleted mantle source which was later enriched in highly incompatible Nb and Th by smalldegree melts. The geographic variations in lava geochemistry show that the Troodos spreading centre was located about 100 km above a former subduction zone which lay to the west of Troodos within the Tethys Ocean during the Cretaceous, before rotation of the Troodos microplate. We found important differences in composition between lavas from Troodos, and those from western Pacific fore-arcs which formed by subduction initiation. Although boninites occur in both locations, lavas with compositions similar to fore-arc basalts are not present in Troodos. Compared to fore-arc lavas formed during 'subduction initiation', all Troodos lavas were derived from a more depleted mantle source, and contain a larger subduction component than back-arc lavas. Based on the comparisons with young lavas from different tectonic settings, as well as regional variations in geochemistry and the position of the Troodos spreading centre relative to the subduction zone, we published a new tectonic model for formation of the Troodos Ophiolite. We propose that Troodos formed in a near-trench location at a rear-arc spreading centre that propagated into arc and fore-arc crust. A presentday analogue is the Southeast Mariana Forearc Spreading Centre in the western Pacific, and lavas from this location have very similar compositions to Troodos lavas. Such tectonic settings are rare on Earth today, but due to their location on the overriding plate, young, buoyant oceanic crust formed in such a setting would be resistant to subduction and destruction. Our model may therefore explain the origin of many other supra-subduction zone ophiolites.
Publications
- 2018. Petrogenesis of boninitic lavas from the Troodos Ophiolite, and comparison with Izu-Bonin-Mariana fore-arc crust. Earth and Planetary Science Letters 498, 203-214
Woelki, D., Regelous, M., Haase, K.M., Romer, R., Beier, C.
(See online at https://doi.org/10.1016/j.epsl.2018.06.041) - 2019. Geochemical mapping of a paleosubduction zone beneath the Troodos Ophiolite. Chemical Geology 523, 1-8
Woelki, D., Regelous, M., Haase, K., Beier, C.
(See online at https://doi.org/10.1016/j.chemgeo.2019.05.041) - 2019. Geochemische Entwicklung des Troodos Ophioliths: Magmengenese in einem Spreizungszentrum über einer Subduktionszone’. Doctoral thesis, Friedrich-Alexander Universität Erlangen-Nürnberg
Woelki, D.
- 2020. Enrichment of H2O and fluid-soluble trace elements in the Troodos Ophiolite: evidence for a near-trench origin. Lithos 356- 357, 105299
Woelki, D., Michael, P., Regelous, M., Haase, K.
(See online at https://doi.org/10.1016/j.lithos.2019.105299)
