  We present distinct demarcation of the Bragg glass (BG) to multi-domain
vortex glass (VG) transition line and the eventual amorphization of the VG
phase in a weakly pinned single crystal of the superconducting compound
Ca3Ir4Sn13 on the basis of comprehension of the different yields about the
second magnetization peak (SMP) anomaly in the dc magnetization and the
corresponding anomalous feature in the ac susceptibility measurements. The
shaking by a small ac magnetic field, inevitably present in the ac
susceptibility measurements, is seen to result in contrasting responses in two
different portions of the field-temperature (H, T) phase space of the
multi-domain VG. In one of the portions, embracing the BG to VG transition
across the onset of the SMP anomaly, the ac drive is surprisingly seen to
assist the transformation of the well ordered BG phase to a lesser ordered VG
phase. The BG phase exists as a superheated state over a small portion of the
VG space and this attests to the first order nature of the BG to VG transition.
