Journal of Petrology Advance Access originally published online on February 25, 2005
Journal of Petrology 2005 46(6):1155-1201; doi:10.1093/petrology/egi013
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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
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
RECEIVED NOVEMBER 12, 2003; ACCEPTED JANUARY 14, 2005
Post-collisional magmatism in the southern Iberian and northwestern African continental margins contains important clues for the understanding of a possible causal connection between movements in the Earth's upper mantle, the uplift of continental lithosphere and the origin of circum-Mediterranean igneous activity. Systematic geochemical and geochronological studies (major and trace element, Sr–Nd–Pb-isotope analysis and laser 40Ar/39Ar-age dating) on igneous rocks provide constraints for understanding the post-collisional history of the southern Iberian and northwestern African continental margins. Two groups of magmatic rocks can be distinguished: (1) an Upper Miocene to Lower Pliocene (8·2–4·8 Ma), 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 including basanites and alkali basalts to hawaiites and tephrites. Mafic samples from the Si–K-rich group generally show geochemical affinities with volcanic rocks from active subduction zones (e.g. Izu–Bonin and Aeolian island arcs), whereas mafic samples from the Si-poor, Na-rich group are geochemically similar to lavas found in intraplate volcanic settings derived from sub-lithospheric mantle sources (e.g. Canary Islands). The transition from Si-rich (subduction-related) to Si-poor (intraplate-type) magmatism between 6·3 Ma (first alkali basalt) and 4·8 Ma (latest shoshonite) can be observed both on a regional scale and in individual volcanic systems. Si–K-rich and Si-poor igneous rocks from the continental margins of southern Iberia and northwestern Africa are, respectively, proposed to have been derived from metasomatized subcontinental lithosphere and sub-lithospheric mantle that was contaminated with plume material. A three-dimensional geodynamic model for the westernmost Mediterranean is presented in which subduction of oceanic lithosphere is inferred to have caused continental-edge delamination of subcontinental lithosphere associated with upwelling of plume-contaminated sub-lithospheric mantle and lithospheric uplift. This process may operate worldwide in areas where subduction-related and intraplate-type magmatism are spatially and temporally associated.
KEY WORDS: post-collisional magmatism; Mediterranean-style back-arc basins; subduction; delamination; uplift of marine gateways
* Corresponding author. Present address: Geological Institute, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark. E-mail: sduggen{at}geol.ku.dk
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