20 Petrology, Structural Geology, Geophysics, and Economic Geology

Wednesday, 2 May 2001
1:00 PM - 5:00 PM

A PRELIMINARY U-PB LARAMIDE DATE ON CAVE SPAR, BIG CANYON, GUADALUPE MOUNTAINS, NEW MEXICO, AND POSSIBLE IMPLICATIONS FOR TIME OF UPLIFT OF SOUTHERN ROCKY MOUNTAINS AND OF HYDROCARBON MATURATION/MIGRATION IN THE DELAWARE BASIN

Paper number: 20-1
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

U-Pb dating of a football-sized, hydrothermal, dogtooth spar, calcite crystal lining a small dissolutional cave in Big Canyon, Guadalupe Mountains, New Mexico, USA has given an age of 92.7 Ma (2 std deviation range of 87-98 Ma) for deposition. This upper Cretaceous (early Laramide) date is important because: (1) it implies that there may have been an episode of karstification in the Guadalupe Mountains in the Laramide; (2) it implies that the early Laramide was a time of heating and deeply circulating water; (3) it relates to the possible time of regional uplift above sea level of the Guadalupe Mountains along with the rest of the southern Rocky Mountains, and (4) to a time of possible hydrocarbon maturation and migration into reservoirs on the east side of the Delaware Basin. Variability in carbon isotopes (d13=+1.98 to -6.13 per mil), oxygen isotopes (d18O=-11.42 to -19.01 per mil), and strontium isotopes (87Sr/86Sr=0.708755-0.714463) demonstrates that dramatic fluid changes occurred during crystal growth - perhaps as a result of evolving flow patterns and source waters caused by thermo-tectonic structural changes. This date also coincides with an iridium spike, volcanism, maximum eustatic rise, and a second-order mass extinction of marine invertebrates at the Cenomanian-Turonian (C-T) boundary.