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Abstract Continental formation models invoke subduction or plume‐related processes to create the buoyant, refractory character of continental lithospheric mantle (CLM). From similarities in melt depletion, major element composition, modal clinopyroxene, and Os isotope systematics it has been proposed that oceanic mantle lithosphere is the likely protolith to non‐cratonic CLM, however, a direct link between the two has been difficult to ascertain. Using dredged mantle peridotite xenoliths from the Ferrel Seamount, off the west coast of Baja California, Mexico, we show that tectonic isolation of an oceanic plate may lead to formation of non‐cratonic CLM. Ferrel xenoliths are coarse‐grained spinel lherzolite, or rare harzburgite. Bulk‐rock and clinopyroxene trace element compositions reveal two‐stages of melt refertilization following melt depletion, with infiltration by mid‐ocean ridge basalt‐type melts, followed by melt addition from host alkali basalt. Melt depletion correlations with187Os/188Os and highly siderophile element abundances indicate preserved melt depletion and refertilization processes are ancient. From these observations, the Ferrel xenoliths represent lithosphere from the abandoned Pacific‐Farallon ridge. The history of melt depletion, followed by MORB‐melt refertilization is consistent with the peridotites representing oceanic mantle lithosphere that was subsequently incorporated into the Baja‐Guadalupe microplate during “ridge jump.” These peridotites demonstrate that isolation of oceanic lithosphere that is rafted onto a continental margin provides a viable means for producing non‐cratonic CLM. We suggest that continuation of late‐stage, low degree melt refertilization may provide a link between oceanic lithosphere and non‐cratonic CLM and propose a tectonic model to preserve and facilitate this continued evolution.
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Topography and Gravity Reveal Denser Cratonic Lithospheric Mantle Than Previously Thought
Abstract The density structure of the cratonic lithospheric mantle (CLM) remains debated. We suggest that one important reason for which many geodynamic studies favor neutrally buoyant CLM is that they adopted separate reference frames when estimating the isostatic effects of continental and oceanic lithosphere, while instead a globally consistent one should be used. This reflects a misconception that continental crust perfectly balances the surrounding oceanic lithosphere. Using a unified global reference frame with recent constraints on crustal properties and residual topography, we show that assuming neutrally buoyant CLM leads to prominent negative residual topography (∼−1.3 km) and positive residual gravity (∼354 mGal) within cratons relative to oceans, neither of which can be explained by the effects of the convecting mantle. This requires the CLM, especially that with thick keels, to be less compositionally buoyant and denser than previously thought, a conclusion supporting recent observations on CLM deformation.
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- Award ID(s):
- 1554554
- PAR ID:
- 10385505
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 1
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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