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Post-Collisional Transition from Subduction- to Intraplate-type Magmatism in the Westernmost Mediterranean: Evidence for Continental-Edge Delamination of Subcontinental Lithosphere |
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| Authors: | DUGGEN S; HOERNLE K; VAN DEN BOGAARD P; GARBE-SCHONBERG D |
| Institution: | 1 GEOMAR RESEARCH CENTRE FOR MARINE GEOSCIENCES, DEPARTMENT OF VOLCANOLOGY AND PETROLOGY, WISCHHOFSTR. 1–3, 24148 KIEL, GERMANY 2 IFM–GEOMAR LEIBNIZ INSTITUTE FOR MARINE SCIENCES, DYNAMICS OF THE OCEAN FLOOR, WISCHHOFSTR. 1–3, 24148 KIEL, GERMANY 3 INSTITUTE FOR GEOSCIENCES, UNIVERSITY OF KIEL, OLSHAUSENSTR. 40, 24118 KIEL, GERMANY |
| Abstract: | Post-collisional magmatism in the southern Iberian and northwesternAfrican continental margins contains important clues for theunderstanding of a possible causal connection between movementsin the Earth's upper mantle, the uplift of continental lithosphereand the origin of circum-Mediterranean igneous activity. Systematicgeochemical and geochronological studies (major and trace element,Sr–Nd–Pb-isotope analysis and laser 40Ar/39Ar-agedating) on igneous rocks provide constraints for understandingthe post-collisional history of the southern Iberian and northwesternAfrican continental margins. Two groups of magmatic rocks canbe distinguished: (1) an Upper Miocene to Lower Pliocene (8·2–4·8Ma), Si–K-rich group including high-K (calc-alkaline)and shoshonitic series rocks; (2) an Upper Miocene to Pleistocene(6·3–0·65 Ma), Si-poor, Na-rich group includingbasanites and alkali basalts to hawaiites and tephrites. Maficsamples from the Si–K-rich group generally show geochemicalaffinities with volcanic rocks from active subduction zones(e.g. Izu–Bonin and Aeolian island arcs), whereas maficsamples from the Si-poor, Na-rich group are geochemically similarto lavas found in intraplate volcanic settings derived fromsub-lithospheric mantle sources (e.g. Canary Islands). The transitionfrom Si-rich (subduction-related) to Si-poor (intraplate-type)magmatism between 6·3 Ma (first alkali basalt) and 4·8Ma (latest shoshonite) can be observed both on a regional scaleand in individual volcanic systems. Si–K-rich and Si-poorigneous rocks from the continental margins of southern Iberiaand northwestern Africa are, respectively, proposed to havebeen derived from metasomatized subcontinental lithosphere andsub-lithospheric mantle that was contaminated with plume material.A three-dimensional geodynamic model for the westernmost Mediterraneanis presented in which subduction of oceanic lithosphere is inferredto have caused continental-edge delamination of subcontinentallithosphere associated with upwelling of plume-contaminatedsub-lithospheric mantle and lithospheric uplift. This processmay operate worldwide in areas where subduction-related andintraplate-type magmatism are spatially and temporally associated. KEY WORDS: post-collisional magmatism; Mediterranean-style back-arc basins; subduction; delamination; uplift of marine gateways |
| Keywords: | : post-collisional magmatism Mediterranean-style back-arc basins subduction delamination uplift of marine gateways |
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