Edge-driven convection (EDC) forms in the upper mantle at locations of lithosphere thickness gradients, e.g., craton edges. In this study we show how the traditional style of EDC, a convection cell governed by the cold downwelling below an edge alternates with another style of EDC, in which the convection cell forms as a secondary feature with a hot asthenospheric shear flow from underneath the thicker lithosphere. These alternating EDC styles produce episodic lithosphere erosion and decompression melting. Three-dimensional models of EDC show that convection rolls form perpendicular to the thickness gradient at the lithosphere-asthenosphere boundary. Stagnant-lid convection scaling laws are used to gain further insight in the underlying physical processes. Application of our models to the Moroccan Atlas mountains region shows that the combination of these two styles of EDC can reproduce many of the observations from the Atlas mountains, including two distinct periods of Cenozoic volcanism, a semicontinuous corridor of thinned lithosphere under the Atlas mountains, and piecewise delamination of the lithosphere. A very good match between observations and numerical models is found for the lithosphere thicknesses across the study area, amounts of melts produced, and the length of the quiet gap in between volcanic episodes show quantitative match to observations.

We studied the effect of increased water content on the dynamics of the lithosphere-asthenosphere boundary in a postsubduction setting. Results from numerical mantle convection models show that the resultant decrease in mantle viscosity and the peridotite solidus produce small-scale convection at the lithosphere-asthenosphere boundary and magmatism that follows the spatially and temporally scattered style and volumes typical for collision magmatism, such as the late Cenozoic volcanism of the Turkish-Iranian Plateau. An inherent feature in small-scale convection is its chaotic nature that can lead to temporally isolated volcanic centers tens of millions of years after initial continental collision, without evident tectonic cause. We also conclude that water input into the upper mantle during and after subduction under the circum-Mediterranean area and the Tibetan Plateau can account for the observed magmatism in these areas. Only fractions (200-600 ppm) of the water input need to be retained after subduction to induce small-scale convection and magmatism on the scale of those observed from the Turkish-Iranian Plateau.

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Earth's continental crust is stabilized by crustal differentiation that is driven by partial melting and melt loss: Magmas segregate from their residuum and migrate into the upper crust, leaving the deep crust refractory. Thus, compositional change is an integral part of the metamorphic evolution of anatectic granulites. Current thermodynamic modelling techniques have limited abilities to handle changing bulk composition. New software is developed (Rcrust) that via a path‐dependent iteration approach enables pressure, temperature and bulk composition to act as simultaneous variables. Path‐dependence allows phase additions or extractions that will alter the effective bulk composition of the system. This new methodology leads to a host of additional investigative tools. Singular paths within pressure–temperature–bulk composition (P–T–X) space give details of changing phase proportions and compositions during the anatectic process, while compilations of paths create path‐dependent P–T mode diagrams. A case study is used to investigate the effects of melt loss in an open system for a pelite starting bulk composition. The study is expanded upon by considering multiple P–T paths and considering the effects of a lower melt threshold. It is found that, for the pelite starting composition under investigation, open systems produce less melt than closed systems, and that melt loss prior to decompression drastically reduces the ability of the system to form melt upon decompression.

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