Hydrothermal circulation in oceanic crust along Middle America Trench: insights from numerical modeling

Abstract

Variation of subduction parameters (i.e., plate age and velocity) along trenches show in general a smooth spatial variation. However, despite these gradual changes heat flow measurements show large variations. For example, previous studies show that heat flow direct observations along the Middle America Trench (MAT) range from 14 to 261 mW/m2, without a clear pattern. One of the common hypotheses that can explain such variations is the presence of hydrothermal circulation within the oceanic crust that enters subduction. Here we present modeling results of hydrothermal circulation using finite elements to calculate the flow, temperature and pressure distribution in oceanic crust. We employ PDE2D (www.pde2d.com), a general-purpose finite element program for solving multidimensional partial differential equations, to solve the coupled equations of continuity, Darcy equation, and energy conservation equation in two dimensions. Our model setup incorporates a low permeability sedimentary layer, a high permeability oceanic crust layer and a basal heat source. Modeling results show that hydrothermal circulation is sensitive to the basal source and multiple convection cells are formed within the permeable oceanic basaltic crust. The sedimentary layer located on top of the permeable layer acts as an insulator. Therefore, smooth temperature fluctuations are observed at the surface. We adapted this model setup and incorporate a series of permeable paths in the sedimentary layer that connect the oceanic crust with the ocean bottom. Modeling results show significant changes in the convection patterns for the oceanic crust, and depending on the width of the permeable conduits and basal heat source, high temperature water plume can infiltrate all the way to the ocean bottom. Some models show that these high temperature plumes have a transitory character and they are followed by infiltration of cold seawater into the oceanic aquifer. Our modeling results show that the observed large heat flow variations along oceanic trenches can be attributed to hydrothermal circulation only when permeable pathways connect the permeable upper crust with the ocean.