THE STABLE ISOTOPE RECORD IN COUPLED BASIN-DETACHMENT SYSTEMS AS A PROXY FOR PALEOCLIMATE AND PALEOALTIMETRY RECONSTRUCTIONS

The elevation of the Earth’s surface is one of the most important characteristics of continental crust and mantle in that it reflects the distribution of mass and heat inside the Earth, controls drainage patterns and detrital recycling in large-scale river systems, and influences atmospheric circulation and therefore precipitation and climate. During the past decade stable isotope studies have been applied to reconstruct paleoelevation of mountains belt exploiting changes in meteoric water composition in the near-surface record or using silicates from extensional shear zones. Here we extend these approaches by combining multi-proxy, multi-isotope data from extensional mylonite zones and kinematically linked syntectonic basins that record paleotopographic and climatic changes during Cenozoic extension of the western North American Cordillera.

We focus on the Snake Range metamorphic core complex and Sacramento Pass Basin (Nevada, USA) that co-developed as a consequence of Oligocene Miocene extension of the Basin and Range Province.

Collectively, this basin-core complex pair allows us to track Oligo-Miocene meteoric fluid flow at different levels of actively extending crust in a high-topography region. For paleoaltimetry purposes we compare the oxygen and hydrogen isotopic compositions as well as compositional and geochronological information acquired from a distinct proxies (lacustrine carbonate, calcite fault breccia, white mica in detachment mylonites) in the Snake Range to a ~30 Ma lacustrine stable isotope record from a nearby basin in the House Range (UT, USA) whose paleoelevation has been constrained independently through paleobotanical analysis.

To first order, each of the investigated compartments of the paleohydrologic system (lacustrine sediments, brittle faults, footwall mylonite) within the Snake Range metamorphic core complex depict a coherent scenario of very low Oligo-Miocene meteoric d¹⁸O and dD values. When compared to the isotopic composition of lake sediments from the House Range (UT), stable isotope paleoaltimetry of the Snake Range points to locally sourced waters that originated at high elevations in an area with strong relief, most likely forming an Oligocene topographic high within the Cordilleran hinterland.