FLUID INCLUSIONS IN CARBONATES FROM THE MAUV, REDWALL, SUPAI, AND KAIBAB FORMATIONS AND THEIR IMPLICATION FOR FORMATION OF THE GRAND CANYON

Fluid inclusions in carbonate units from the Muav Fm, the Redwall Limestone, the Supai Group and the Kaibab Limestone from the eastern and western sections of the Grand Canyon have been studied using a heating stage attached to a petrographic microscope. Secondary two-phase water-rich fluid inclusions were heated to obtain homogenization temperatures of the fluids; two to sixteen inclusions were observed in a single sample. Average homogenization temperatures (Th) of secondary fluid inclusions in these rocks range from 107 to 48 °C; these are all equal to or less than peak burial temperatures inferred from clumped isotopes previously analyzed on the same samples. Th temperatures do not correlate with modern elevation. Comparing to published thermochonologic data (U/He and FT on apatite), our Th temperatures correspond to times between 78 and 64 Ma with a weighted mean of 74±4 Ma. We interpret the consistency of the apparent timing of fluid trapping to reflect mild deformation of these rocks at this time, consistent with initial uplift associated with the early stages of formation of the Grand Canyon.