Magma-wallrock interaction in crustal magma chambers (a process known as crustal assimilation) is critical to the thermodynamic and chemical evolution of a magmatic system and formation of many of the most economically important base and precious metal deposits on Earth. Although such generalized model is largely accepted, details on how these interactions take place are relatively poorly characterized. One of the major issues has been the lack of models that integrate mass and energy exchange, thermodynamics and geochemistry. The widely used assimilation-fractional crystallization (AFC) model does not provide any hint on whether its results are thermodynamically feasible or not. These limitations may significantly impact the mass balance of crustal and magma sources in the models, and thus obscure the constraints on the generation and identification of valuable metal deposits.
We propose to explore the petrologic and geochemical impact of magma-wallrock interaction at major intrusive complexes in, for example, Antarctica, United States, and Finland in a multidisciplinary study. Its central part is computational modeling using recently developed energy-constrained equations (Magma Chamber Simulator = MCS). The models add thermodynamic constraints for a multicomponent + multiphase magma body that crystallizes in contact with a crustal wallrock and is recharged with batches of fresh magma. The results of the models will be tested against existing and potentially new geochemical data and state-of-the-art wallrock partial melting experiments. In the experiments, the goal is to melt the wall rock alone, and to melt the wall rock together with the resident magma.
The outlined research plan is first of its kind, combines world-class expertise of different aspects of the issue, and is expected to provide unprecedented insight into the relative contributions of magma and crust to the formation of layered intrusions and associated ore deposits. The results should be of great interest to both academic and non-academic institutions and companies. An expected innovative outcome of the proposed project is that the results of research in the field of petrology and geochemistry are implemented in ore deposit models applicable to ore exploration. For example, mappings of “thermodynamically feasible” magma-wallrock pairs can potentially lead to new discoveries. The project is funded by the Academy of Finland.
More info in our blog: https://blogs.helsinki.fi/jsheinon/