EVIDENCE FROM THREE ISOTOPIC PROXIES FOR THE ESTABLISHMENT OF HIGH RELIEF BEFORE NEOGENE IN THE UPPER STREAM DRAINAGE OF THE COLORADO RIVER
We collected Neogene fluvial carbonate cements, lacustrine carbonates and volcanic ashes from basin floors of ~1700 m high and mountain ranges of ~3500 m high. X-ray diffraction analysis and cathodoluminescence microscope observation show that the carbonates are mostly in calcite, with a few samples contain a small component of aragonite, and the carbonate did not experience extensive deep and late digenesis. Clumped isotope temperatures, which represent growth temperatures of the carbonates, changed from ~15-30 ̊C in the latest Oligocene to ~5- 9 ̊C in the latest Miocene, and the temperature difference between the high and low elevation sites persisted during the Neogene. The calculated surface water δ18O values and δD values vary between -17 and -13 ‰, and -125 and -94 ‰, respectively, and the isotopic differences between the high and low elevation sites persisted during the Neogene. The three sets of isotopic proxies show that the high relief in the upper drainage of the Colorado River was created before the Neogene, possibly by differential uplift induced by mantle processes.