The quake occurred 165 kilometres northeast of Santiago del Estero and 960 kilometres northwest of Buenos Aires, the USGS said.
The earthquake took place at 11.32pm local time and was 577 kilometres deep.
The reading was based on the open-ended Moment Magnitude scale, now used by US seismologists, which measures the area of the fault that ruptured and the total energy released.
A measurement of six or higher indicates a strong quake, seven a major quake and eight a great quake.