Do you think its possible electric discharges occur within the Earth? With electric discharges, there is a possibility of plasmoids, which will concentrate energy enough for fusion.
I am not familiar with the research on this so I will give my opinion. There are varying levels of conductivity ranging from desert surfaces, liquid bodies and the molten core. Theory says that the earth’s magnetic field arises from the interaction of rotation, internal electrical currents and other forces. The normally occurring electrical currents are so diffuse that plasmoids probably don’t exist. Extraordinary events like earthquakes can release concentrated energy through piezoelectric effects by friction and the breaking of rocks. Plasmoids might occur then but I don’t know how it could be proven.
The most concentrated natural electrical currents that I know of are lightning strikes. I’ve read that very energetic lightning is present around some erupting volcanoes. There can be high energy radiation and interesting chemical reactions but I am not aware of anyone suggesting that nuclear reactions happen.