EVOLUTION OF A SHALLOW HYDROTHERMAL SYSTEM IN THE SIERRA NEVADA BATHOLITH: RECORDS FROM A ZONED, LOW δ18O SKARN IN THE MINERAL KING PENDANT
The emplacement of the quartz-diorite magma was inboard of the primary magmatic locus of the Sierran arc at 109 Ma, and intruded into shallow, cold crustal wallrock. Our results indicate the significant thermal temperature contrast and brittle deformation of the pendant rocks were a key control in the skarn forming system. Three-dimensional field relationships reveal ~ 40 x 106 m3 of garnetite remains after erosion, a mass that is larger than typical garnetite skarns in the Sierra and indicative of an exceptionally vigorous hydrothermal system. Brecciation within the skarn rocks and alteration of the Empire Mountain pluton suggests that a fracture-enhanced permeability network facilitated the extensive infiltration of early surface fluids and permitted the incorporation of metamorphic and magmatic fluids in the formation of massive skarn and later alteration of the pluton. Therefore, the Mineral King skarn pendant represents a well-exposed, unrecognized model for efficiently driving shallow level decarbonation in convergent margin arc settings like those of the North American Cordillera.