The Greenland-Iceland Ridge is Continental
Abstract
A simple model for the Greenland-Iceland-Faroe Ridge (GIFR) as excess volcanism on the mid-ocean ridge cannot account for numerous features including the dense lower crust, diffuse shear and extensional deformation in Iceland and continental material in the petrology and geochemistry of Icelandic igneous rocks. These features can be explained by complex Pangaean fragmentation that incorporated continental material in the new ocean. In this model, the NE Atlantic Ocean opened via new rifts that propagated both north and south but were unable to propagate across a ~300-km-wide barrier comprising the Nagssugtoqidian and Caledonian orogens. The ~100 x 300-km block of continental crust that separated the rift tips-the Iceland Microcontinent-together with flanking continental regions on the Greenland and Faroe sides, extended in a distributed, unstable, ductile manner. Stretched, magma-inflated continental crust was capped with magmas in the style of SDRs. Such deformation and magmatism is still ongoing in Iceland. Numerical modeling confirms ductile extension of continental crust can continue for tens of Ma by lower-crustal flow. The lower crust beneath the GIFR comprises magma-inflated continental crust overlain by a ~ 6-8 km thick basaltic upper crust. The crust is not anomalously thick oceanic crust as often assumed. Magmatic production in Iceland today accounts for only 10-15 km, corresponding to the same ~10-km thick production as occurs on the Reykjanes and Kolbeinsey ridges, boosted by partial remelting of the continental lower crust. A largely continental composition of GIFR lower crust can account for multiple cross-disciplinary observations including difficulties in modeling 40 km of melt production, low observed source temperatures and the diachronous chevron ridges of thick crust that flank the Reykjanes Ridge. Other regions of the N Atlantic, S Atlantic and W Indian Ocean also fit this model. Complex breakup likely resulted from far-field extensional stresses tearing apart structurally heterogeneous supercontinents. All oceanic plate boundaries are complex to a greater or lesser degree. Simple, textbook-style boundaries and diffuse deformation zones such as that in the Afar and Gulf of California regions just comprise end members on a continuous spectrum.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T11C..01F
- Keywords:
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- 1021 Composition of the oceanic crust;
- GEOCHEMISTRY;
- 8102 Continental contractional orogenic belts and inversion tectonics;
- TECTONOPHYSICS;
- 8104 Continental margins: convergent;
- TECTONOPHYSICS;
- 8105 Continental margins: divergent;
- TECTONOPHYSICS