Problems with the magmatic model for the origin of the Hall Canyon muscovite granite pluton, Panamint Mountains, California

Mahood et al. (1996) described zoning patterns of mineral, rock, and isotopic compositions in the Hall Canyon pluton (Fig. 1) in a ~800 m vertical cross-section of the top of a supposed magma chamber. On the basis of these patterns upper and lower zones of the pluton are alleged to form from two different source rocks and crystallize from two different magmas, although the lower and upper zones are gradational to each other. These investigators also suggest that a third magma has been injected a sills in the bottom of the upper zone in the form of mushes before the upper zone was totally crystallized. The greater thickness (600+ m) of the lower granodiorite zone supposedly permits convection which results in a nearly constant composition. The lesser thickness and nearly constant temperature of the upper granite zone (150-180 m) are posited to prevent convection and allow the upper zone to be fractionated, causing gradational chemical and mineralogical changes from bottom to top. The emplacement of this pluton was suggested to be by stoping of overlying Precambrian metasediments.