Collaborative Research: Energy-Constrained Geochemical Models for Open System Magma Bodies with Anatexis, Replenishment, Magma Mixing and Fractional Crystallization

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Spera EAR-0073932 Existing tools that model the geochemical evolution of open-system magma bodies suffer from several limitations, the most critical of which are lack of accounting of energy-conservation and lack of inclusion of the consequences of wallrock partial melting. A new tool will be developed, called Energy-Constrained Recharge Assimilation Fractional Crystallization (EC-RAFC), that models the geochemical evolution of a magma body-wallrock system. A user-friendly EC-RAFC computer code, written in Visual Basic, will be developed in which energy, mass and species are conserved as magma undergoes, fractional crystallization, magma recharge, and assimilation of partially melted wallrock. Input parameters include thermal and chemical characteristics of the magma body, wallrock, and replenishment magma. The EC-RAFC model will couple phase equilibria and thermochemical constraints by incorporating information from melt productivity functions fa (Ta) and fm(Tm) for user-defined compositions of initial magma, wallrock and replenishment magma. The EC-RAFC computer code will also allow for the development and maintenance of compositionally distinct melt reservoirs within an EC-RAFC magma body, thus enabling application of EC-RAFC to zoned ignimbrites. A critical component of this project is development of code capability that can model melt extraction efficiency that is less than unity so that mass and energy addition can be decoupled. Application of the EC-RAFC simulator to a number of well-documented magmatic systems spanning a range of geologic environments will allow exploration of the potential systematics that exist in the relative roles of fractional crystallization, recharge and assimilation in magma bodies from particular tectonic-magmatic settings (e.g., MOR, continental arcs). This research has the potential to impact the work of the large number of geoscientists who generate and interpret geochemical, geochronological, petrographic and petrologic data from extant and ancient magmatic systems and will parallel the dramatic improvement in the amount and quality of geochemical data describing magmatic systems.