Oxygen isotope evidence for major fluid flow along the contact zone of the Rum ultrabasic intrusion

Recent studies indicate that the Rum Tertiary ultrabasic intrusion formed in situ, and was not emplaced as a fault-bounded plug. The suggestion that the Main Ring Fault was the primary pathway for the flow of meteoric hydrothermal fluids on Rum is therefore seriously flawed. Oxygen isotope evidence is presented indicating that the contact zone of the intrusion was the major pathway for meteoric fluids during cooling of the pluton. Delta-O-18 depletions of over 12 parts per thousand correlate with hydrothermal alteration assemblages, indicating that the bulk of the interaction with meteoric fluids took place at low temperatures (200-450-degrees-C).