Self-organized pattern evolution on SiO2 surface under low energy Ar-ion irradiation has been investigated extensively at varied ion energies, angles of ion incidence, and ion flux. Our investigations reveal an instability on SiO2 surface in an angular window of 40° ̶ 70° and for a comprehensive range of Ar-ion energies (200-1000 eV). Different topographical features, viz. ripples, mounds, and elongated nanostructures evolve on the surface, depending upon the angle of incidence and ion fluence. The results are compiled in the form of a parametric phase diagram (ion energy versus angle of incidence) which summarizes the pattern formation on SiO2 surface. To understand the evolution of observed patterns, we have carried out theoretical estimation, taking into account the synergetic roles of ion induced curvature-dependent sputter erosion and prompt atomic redistribution. It is shown that irradiation-induced mass redistribution of target atoms plays a crucial role in determining the critical angle of ion incidence for pattern formation on SiO2 under the present experimental conditions, whereas the contribution of curvature-dependent sputtering needs to be considered to understand the existence of the angular window of pattern formation. In addition, ion-beam shadowing by surface features are shown to play a dominant role in the formation of mounds and elongated structures at higher ion fluences.