Very fast Uplifting in the Kongur Shan, NE Pamir during Marine Isotope Stage 5 (MIS 5)

Tuesday, 16 December 2014
Jie Chen, Chunru Liu, Jintang Qin, Huili Yang, Ming Luo, Mingda Huang and Wenqiao Li, State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, China
Understanding the evolution of relief in active regions in response to climate change is of particular importance because of the potential linkages between climate and tectonics, such as in the case of the highly debated late Cenozoic uplift of the Himalayas and Tibetan plateau in relation to the onset of Quaternary Glaciations (Molnar and England, 1990; Whipple et al., 1999).Using paramagnetic centers in quartz measured by electron spin resonance (ESR) has shown a potential to quantify late-stage exhumation rates in the range of about 10 ka to 1 Ma due to their relatively low closure temperatures (Grün et al., 1999). However, successful field case study has rarely been documented. Here, we explore the potential ESR dating to provide multiple-thermochronometers using the Al and Ti center in quartz in the Kongur Shan, NE Pamir, to measure how the landscape of a tectonically active range has responded to a change in climatic conditions at the timescale of Quaternary glacial cycles.

The Kongur Shan is located in NE Pamir, at the western end of the Himalayan-Tibetan orogenic belt, and presents exhumation rates of ~5 mm/a since 7-8 Ma (Robinson et al., 2010). Bedrock samples were collected from an elevation transect (between 3380 m and 4850 m above sea level) across the Kongur Shan normal fault and along the east-flowing Ghez river.

We investigated both the ESR Al center (a hole center located at AlO-) and the Ti center (an electron center: Ti3++e- substituting silicon and stabilized by H+, Li+ in channels near the edge of the silicon-oxygen tetrahedron) in quartz. Our preliminary results show that the quartz Al and Ti centers signals are bright enough for dating. There is a clear age offset between samples from the hanging wall and footwall of the fault, suggesting that the fault is still active. In general, the apparent exhumation rate of the footwall from the ESR Al center is quite similar to that of zircon (U-Th)/He (Thiede et al., 2013), however, there is a clear inflection points on ESR Al center ageā€elevation plots, the apparent exhumation rate increased to ~22 mm/a around ~75 ka, might be caused by a mix of enhanced fluvial and glacial erosion, normal faulting and bulk exhumation during MIS 5.