rocks can melt in the mantle part of the earths internal structure.
in what part of the earths internal structure can rocks melt?
mantle
the internal structure of the earth is layered in spherical shells: an outer silicate solid crust, a highly viscous asthenosphere and mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. scientific understanding of the internal structure of the earth is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through the earth, measurements of the gravitational and magnetic fields of the earth, and experiments with crystalline solids at pressures and temperatures characteristic of the earth's deep interior.
structure of the earth
when rocks melt, they do so slowly and gradually because most rocks are made of several minerals, which all have different melting points; moreover, the physical and chemical relationships controlling the melting are complex. as a rock melts, for example, its volume changes. when enough rock is melted, the small globules of melt (generally occurring between mineral grains) link up and soften the rock. under pressure within the earth, as little as a fraction of a percent of partial melting may be sufficient to cause melt to be squeezed from its source. melts can stay in place long enough to melt to 20% or even 35%, but rocks are rarely melted in excess of 50%, because eventually the melted rock mass becomes a crystal-and-melt mush that can then ascend "en masse" as a diapir, which may then cause further decompression melting.
magma