I have been working on the link between tectonics, erosion and climate in the Alborz Mountains, northern Iran during five years of my research at the University of Cambridge.
Knowledge of the temporal and spatial pattern of exhumation and erosion in the Alborz as a part of Alpine - Himalaya orogenic belt is required for understanding the evolution of the adjacent orogenic systems and I made the first comprehensive study of the interaction of erosion, climate and tectonics on this region.
To this effect, the exhumation and erosion pattern in different time scales was investigated, employing thermochronology (apatite fission track and He/U-Th analysis), geomorphic-hydrologic analysis, structural geology and stratigraphy and river gauging station data and observations.
Erosion rate of the orogen on decadal time scale was elucidated by normal straight average and monthly average of suspended sedimentary load data.
Run off, precipitation, stream power, NDVI and lithological index of the area are qualified to analyze and calibrate the role of discharge, climate, vegetation and lithology in erosion.
In this study, using apatite fission track dating I document the first time several episodes of cooling phases and differentiate between them combining geological observations. Post emplacement crystallization and tectonic exhumation have been identified as the main mechanisms govern the cooling history in the area. Quantifying the temporal and spatial development of the Alborz using thermochronological tools necessitates regional knowledge of the mountain belt deformation and erosion history was traced in stratigraphic record. In this respect, I learnt that heterochronism and the differences in intensity of exhumation are characteristic in the mountain belt result in a discontinuous rapid cooling across the range.
The riverine, detrital apatites of Quaternary contain a preserved record of the original source cooling history in the scale of catchment. In this study I identify the age components significantly consistent with the cooling episodes resulted from apatite fission track ages of fully reset samples.
Using the lag time to qualify the exhumation rate I got lower exhumation in NE than the rest of the Alborz, this domain might be described as an escaped deformation zone clustered by partially reset apatite fission track ages.
In this respect, the cooling history deduced from the depositional record monitors timing and rates of exhumation more effectively than local cooling paths detected from surface samples of the mountain belt.
Resolving the timing of deformation across the Alborz Mountains is fundamental to addressing models to constructing the tectonic evolution of this fold and thrust belt. Although many studies highlight the importance of the Arabia-Eurasia collision in driving middle to late Cenozoic deformation (e.g. Berberian and King 1981), the timing of onset of exhumation driven by deformation is crucial to figure out active slip rate and total shortening and how the deformation has been accommodated episodically in a steady compressional collision zone.
I learnt that exhumation and erosion pattern on decadal- million year time scale is governed by the intramountain basins position where the highly localized erosion rates and exhumation focused.
My PhD thesis:
Coupled tectonics, erosion and climate in the Alborz Mountains, Iran, 2008, 219 p.
- Chapter 2: Thermochronometry (Apatite Fission Track – U-Thu / He)
- Chapter 4: Synthesis of stratigraphic and thermochronometric data
- Chapter 5: Decadal erosion rate
- Chapter 6: Decadal erosion rate controls
- Chapter 7: Synthesis and main conclusion
- Appendix