A Study Of Kongur Shan Extensional System In The Eastern Pamir, China Using Quaternary Thermochronology

The Kongur Shan extensional system lies in the northeastern margin of Pamir in Xin Jiang which is the most active in tectonics and one of best areas for the Quaternary research. This system is one of the faults accommodating east-west extension in the Pamir. Robinson et al.(2010) proposed that the rapid in cooling begun at～2Ma,with a constant exhumation rate(4.2mm/a) over the last 7Ma. But the exhumation rate and its process are not constrained from the Quaternary, especially late Quaternary. The thesis attempts to make use of the different themochronology methods to constrain the variations of the exhumation rate and cooling rate of the Quaternary,especially late Quaternary in the Kongur Shan. It's also a focused topic of tectonic thermochronology.Based on pevious work,I take the samples from～3300m to～4800m in Bulunkou Muscovite, biotite and Zircon minerals selected from the gneiss for ⁴⁰Ar/³⁹Ar and (U-Th)/He dating. I also carry out a preliminary study of luminescence dating of schist, gneiss and quartz, trying to explore and test the Quartz OSL-thermochronology.1) The results of biotite ⁴⁰Ar/³⁹Ar thermochronology in gnesis suggest that ⁴⁰Ar/³⁹Ar ages are during 1.63-1.34Ma. The average exhumation rate calculated by age-elevation relationship is about 3.9mm/a, accordant with the viewpoint of Robinson et al.(2010) that exhumation rate is constant since 7-8Ma, about 4.2mm/a.2) The ages of Zircon (U-Th)/He thermochronology are between 0.5-0.7Ma, The average exhumation rate calculated by the age-elevation relationship are 4.7mm/a during 0.7-0.6Ma,and 7.6mm/a during 0.6-0.5Ma.Compared with the biotite ⁴⁰Ar/³⁹Ar results, the exhumation rate may increase since the mid-Quaternary, which is inconsistent with Robinson et al.(2010).3) The mineral pair results of the sample P05T75 show that the cooling rate is 31℃/Ma during 2.38-1.34Ma, and 190℃/Ma during 1.34-0.5Ma. the results of P05T70 show that the cooling rate is 172℃/Ma in1.66-0.7Ma. It indicates that the cooling rate has been an increasing trend since at least 1.66Ma.4) Thermochronology of OSL,IRSL and TL shows that: a) There is no OSL singal in quartz veins. Though the OSL signal of the fine-grained quartz of schist and gnesis is weak, they have typical TL peak and OSL decay curve of quartz; b) The natural OSL signal strength of the fine-grained quartz of the samples generally increases with elevation; c) The equivalent dose of the fine-grained quartz of the different disks in the same sample measured by SAR disperses, and there is a serious problem of signal accumulation in the SAR method cycle. But the SMAR method overcomes the problem of signal accumulation. The equivalent dose of the fine-grained quartz measured by SMAR increases with elevation; d) The results of the IRSL of fine-grained poly minerals show that IRSL equivalent dose measured by SMAR increases with elevation.