[Paper Review] Melt-Enhanced Rejuvenation of Lithospheric Mantle: Insights from the Colorado Plateau

Mousumi Roy, Rodrigo Osuna-Orozco+2 more|arXiv (Cornell University)|Dec 12, 2012

High-pressure geophysics and materials78 references6 citations

TL;DR

This paper proposes that melt-infiltration at the lithosphere-asthenosphere boundary thermally and chemically rejuvenates and destabilizes stable cratonic lithosphere, using the Colorado Plateau as a case study. The process, driven by dynamic pressure gradients from plate motion and melt segregation, explains asymmetric magmatism and geophysical contrasts between the plateau's interior and margins, with melt-enhanced weakening enabling lithospheric thinning and convective removal.

ABSTRACT

The stability of the lithospheric mantle beneath the ancient cratonic cores of continents is primarily a function of chemical modification during the process of melt extraction. Processes by which stable continental lithosphere may be destabilized are not well-understood, although destabilization by thickening and removal of negatively-buoyant lithospheric mantle in "delamination" events has been proposed in a number of tectonic settings. In this paper we explore an alternative process for destabilizing continents, namely, thermal and chemical modification during infiltration of metasomatic fluids and melts into the lithospheric column. We consider observations pertinent to the structure and evolution of the Colorado Plateau within the western United States to argue that the physical and chemical state of the margins of the plateau have been variably modified and destabilized by interaction with melts. In the melt-infiltration process explored here, the primary mechanism for weakening and rejuvenating the plate is through thermal effects and the feedback between deformation and melt-infiltration. We speculate on the nature and geometry of a melt-modulated interaction zone between lithosphere and asthenosphere and the seismically-observable consequences of variable melt-infiltration into the margins of regions of thick, stable lithosphere such as the Colorado Plateau and the Archean Wyoming Province within North America.

Motivation & Objective

• To investigate alternative mechanisms for destabilizing stable continental lithosphere beyond delamination.
• To examine how melt-infiltration at the lithosphere-asthenosphere boundary induces thermal and chemical modification in cratonic regions.
• To explain the observed geophysical asymmetries—such as seismic velocity and heat flow gradients—between the Colorado Plateau's interior and its margins.
• To assess the role of dynamic pressure gradients and melt segregation in controlling spatial patterns of magmatism and lithospheric weakening.
• To generalize the melt-infiltration model to other cratonic provinces, including the Wyoming Province and North China Craton.

Proposed method

• Analyzes seismic tomography and receiver function data to map lateral variations in mantle seismic velocities and lithospheric thickness across the Colorado Plateau.
• Uses xenolith geochemistry and thermobarometry to infer the thermal and chemical state of the lithospheric mantle in the plateau interior and margins.
• Models dynamic pressure gradients at the lithosphere-asthenosphere boundary due to North American plate motion relative to the underlying asthenosphere.
• Integrates melt segregation and viscosity reduction feedbacks to simulate how melt infiltration enhances deformation and weakens the lithosphere.
• Compares observed magmatic encroachment patterns with predicted melt-infiltration rates based on upwind/downwind flow dynamics.
• Applies the model to other cratons (e.g., North China, Tanzania) to test its broader applicability to continental interior evolution.

Experimental results

Research questions

• RQ1 How does melt-infiltration at the lithosphere-asthenosphere boundary contribute to the destabilization of stable cratonic lithosphere?
• RQ2 Why are seismic wave speeds slower and heat flow higher at the margins of the Colorado Plateau compared to its interior?
• RQ3 What controls the asymmetric distribution of Cenozoic magmatism around the Colorado Plateau?
• RQ4 How do dynamic pressure gradients and melt segregation interact to promote lithospheric weakening and thinning?
• RQ5 To what extent can melt-infiltration explain the geochemical and geophysical evolution of other cratonic regions like the Wyoming Province and North China Craton?

Key findings

• The Colorado Plateau's interior exhibits fast seismic velocities and low heat flow, indicating thick, cold, and chemically stable lithosphere with low iron-magnesium ratios.
• The margins of the plateau show slower seismic velocities, higher heat flow, and elevated Vp/Vs ratios, indicating thermal and chemical modification by melt-infiltration.
• Magmatic encroachment is most intense in the SW (upwind) sector of the plateau, consistent with higher dynamic pressure and melt-infiltration rates.
• The NE margin, downwind of the plateau, shows minimal magmatic activity, aligning with lower melt-infiltration potential and reduced dynamic pressure.
• Melt segregation and viscosity reduction create a feedback loop that enhances deformation and promotes lithospheric thinning and convective removal.
• The model explains the rejuvenation of the Wyoming Province and other cratons as a result of similar melt-infiltration processes, suggesting a general mechanism for cratonic destabilization.