CONTACT METAMORPHISM IN THE RACETRACK VALLEY AREA, DEATH VALLEY NATIONAL PARK, CALIFORNIA, BASED on NASA AIRBORNE VISIBLE/INFRARED IMAGING SPECTROMETER (AVIRIS) DATA

The Racetrack Valley area in western Death Valley National Park is underlain by Paleozoic limestone and dolomite which are intruded by at least five separate (at the surface) Mesozoic quartz monzonite plutons. Data from NASA’s Airborne Visible/Infrared Imaging Spectrometer with 17 m spatial resolution have been processed to examine the distribution of metamorphic minerals with respect to pluton contacts and stratigraphy and structure of the host rocks. Included in the area is the Ubehebe Peak contact aureole which has been the focus of previous remote sensing and petrologic study. The new results accurately replicate mineral distribution in the Ubehebe Peak aureole and outline four other significant aureoles and several smaller areas of contact metamorphism. The remote sensing interpretations are supported by field checking at over 270 sites and by over 1500 field and lab visible/near infrared spectra from those sites in addition to laboratory study using optical microscopy, SEM/EDS, and XRD. In the AVIRIS imagery, contact aureoles are characterized by sequential appearance of tremolite, serpentine (after forsterite), and brucite (after periclase) toward the contact, although the sequence and extent of these zones varies as a function of host rock bulk composition and structural relationships with pluton contacts. Tremolite appears at distances up to 1.5 km from exposed contacts, but is largely restricted to siliceous dolomite units that are typically not more than 50 m thick. Serpentine is limited to within 750 m of apparent contacts; it locally follows stratigraphic control, but is also widely disseminated in dolomite within this zone. This is interpreted to indicate that hydrothermal fluid circulation and metasomatism were most active at this spatial scale. Serpentine distribution generally coincides with bleaching of marbles, which is considered an additional indicator of fluid interaction. Brucite occurs only in dolomite within 200 m of contacts or in roof pendants within plutons. Overall, these results indicate that remotely-sensed and field-based visible/near infrared methods can provide detailed maps of mineral distribution in siliceous dolomite bulk compositions which, in turn, can assist in understanding thermal-mechanical and fluid flow processes in contact aureoles.