Collaborative Research: Investigating the Role of Mantle Metasomatism and Melt-Rock Interaction During Evolution of Continental Lithosphere Mantle

The oldest parts of tectonic plates on Earth are found in the interiors of continents, usually far from plate boundaries. These so-called “cratonic” portions of continental plates are thicker than average and remain stable for billions of years, resisting internal deformation. Cratons are usually surrounded by younger tectonic plate material, added on through the processes of accretion and collision.

However, there is geologic evidence that in some locations the thick cratonic interior portion of continental plates has been destabilized and removed (e.g., the North China Craton and the southwest U.S.). A fundamental question is: why are some cratonic regions able to be deformed/removed while others are stable for billions of years? More specifically, what conditions are needed to weaken and prime the interior of a continental tectonic plate for destabilization?

To investigate this question, this project will use southwest North America as a natural laboratory to explore the role that magmas infiltrating through continental plates may play in destabilizing cratons. The study area has an extensive Cenozoic volcanic history that shows that a period of voluminous magma-infiltration (triggered by the removal of subducting oceanic crust of the Farallon plate from the base of the North American continent) preceded a dramatic destabilization of the interior part of southwest North America, leading to thinning of the plate and deformation characteristic of the present-day Basin and Range Province.

A key feature of this study is to combine information on the chemistry of the volcanic rocks with laboratory experiments on magma moving through rock samples and numerical models of the flow of magma inside a porous material. All of these approaches are necessary to arrive at a process-oriented understanding of how magma might (a) move through continental tectonic plates and (b) modify the plate as it moves.

Our goal is to test the hypothesis that magma-infiltration may play an important role in the weakening and destabilization of the cratonic interiors of continental plates. The team (two female and one male) represents scientists at various career stages and forges a connection between two important minority-serving institutions within the southwestern US.

Within the theory of plate tectonics, constraints for the timescales of the dynamic process of continental lithospheric mantle weakening and removal are generally lacking. By reassessing the relationship between age and geochemical data, in particular isotopic and trace element abundances, we propose a reinterpretation for the relationship between volcanism and tectonism in southwest North America.

The work here will test the hypothesis that the key processes that preconditioned the southwest North America lithosphere for destabilization took place after arc-related magmatism, and before and during the ignimbrite flare-up: namely, regional-scale hydration and metasomatism associated with the amagmatic period of flat/shallow angle subduction of the Farallon plate beneath SWNA. In this project, we test this hypothesis through detailed space-time-composition analyses of volcanic rock geochemical data and through two suites of high-pressure multianvil petrologic experiments.

Both efforts will inform numerical experiments designed to investigate the effects of CLM/melt interaction and/or in situ melting on ascending melt compositions and rheology of the CLM. Geochemical analysis will consist of data mining of the NAVDAT database as well as new sample collection, of particular importance is a critical gap in the available data set is represented by Laramide volcanic rocks in the continental interior, specifically in southern New Mexico.

The two suites of multianvil experiments will investigate (1) the diffusion of trace elements across the melt-rock interface and determine the relevant diffusion constants; and (2) the role of metasomatized CLM in generating in situ melting at the melt-rock interface. Numerical experiments will use the data combined from the geochemical and multianvil datasets to build fluidized flow models for melt-rock interactions that address both thermal and chemical disequilibrium conditions building from 1D to 3D porous flow models.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.