SHOCK ATTENUATION, WASTE SHOCK HEAT AND RELATED HYDROTHERMAL EFFECTS IN CENTRAL UPLIFTS: EVIDENCE FROM MANICOUAGAN

Hydrothermal systems in impact structures arise from three main sources of heat: (1) impact melt; (2) central uplift rocks that have been elevated from depth and (3) waste shock heat. The relative contributions of these sources depend on location within a given structure, as well as crater dimensions. In the central uplift of the 90 km rim-diameter Manicouagan impact structure of Canada, I attempt to differentiate thermal effects due to exhumation of previously buried anorthositic rocks, which have been virutally instantly elevated due to exacavation and modification stage processes, versus heat from shock. Given negligible structural disruption of central uplift units at Manicouagan, the elevated isotherms remain subhorizontal, or at least parallel to one another, whereas the waste heat contribution defines hemispherical zones about the projectile contact region, with higher temperatures being realized nearer the core of the uplift. The latter contribution is dependent on the maximum shock realized and the shock attenuation rate. Differentiation between these two heat sources (exhumed warm footwall and waste shock heat) is sought by characterizing associated hydrothermal effects in the anorthositic host rocks. These effects are manifest in zeolite development, the distribution, volume and mineralogy of which is defined across the uplift structure.