feo mgo

lower mantle

piston cylinder

gpa gpa

bulk modulus

pressure gpa

high pressure

pressure raman

Physics of the Earth and Planetary Interiors

We revise the high pressure, high temperature phase diagram of CaCO 3  using Raman spectroscopy in conjunction with laser heated diamond anvil cell experiments. We confirm numerous aspects of earlier studies, including a recent X-ray diffraction study about the stability field of CaCO 3 -VII. Our Raman results show that CaCO 3 -VII is stable in the lower mantle at a depth of 690–1010 km. Our DFT calculations show that the phase transition from aragonite to CaCO 3 -VII at     ≈    25 GPa and from CaCO 3 -VII to post-aragonite at     ≈    40 GPa are accompanied by density changes of 2% and 3.5%, respectively. Shear sound velocities change by 9% and −12% across the transitions, respectively. Hence, a sufficient amount, at least locally, of CaCO 3  in the Earth’s mantle can be detectable by an increase of the shear velocity at 690 km and a decrease of the shear velocity at 1010 km depths.

CaCO3 phase diagram studied with Raman spectroscopy at pressures up to 50 GPa and high temperatures and DFT modeling