Low-Temperature Thermochronlogy using Luminescence Signals from K-feldspar: A Case Study along the San Andreas Fault, California

Abstract:

The framework for treating luminescence signals within quartz as leaky and saturating thermochronometers has been put on a sound theoretical footing but requires further empirical exploration of kinetic mechanisms. Expanding treatment of K-feldspar as a low-temperature OSL thermochronometer is desirable as it exhibits higher luminescence sensitivity and often saturates at higher radiation doses than does quartz. This study considers thermal charge eviction dynamics for the IRSL sensitive trap within K-feldspar for different cooling rates and various present-day temperatures. Arrhenius parameters are calculated, and a simple kinetic model is used to predict the thermal evolution of the main IRSL trap in typical geologic settings. Effective closure temperature is found to be lower than 50 ºC for samples cooling at 10 ºC/Ma. Such low temperatures make K-feldspar luminescence thermochronology a promising complement to apatite (U-Th)/He techniques, which exhibit closure temperatures of about 60-80 ºC for the same cooling rate. We examine the various luminescence signals from K-feldspar within recently-exhumed bedrock samples from an uplifted block within the San Bernardino Mountains in southern California, USA. These signals suggest a recent decrease in topographic relief for the Yucaipa Ridge Block.