Development of luminescence dating using feldspar and its application to river terraces in north piedmont of Chinese Tianshan

Abstract

This study focused on developing luminescence dating procedures for feldspar, and the application of the luminescence dating technique to fluvial terraces of Anjihai River in the northern piedmont of Tian Shan range, China, to evaluate the deformation rate of the Anjihai anticline in the late Quaternary. To develop luminescence dating methods, a low temperature multi-elevated-temperature post-infrared infrared stimulated luminescence (MET-pIRIR) protocol has been proposed for measuring the Holocene samples using K-feldspar. Progressively increasing IR stimulation temperatures from 50 to 170 °C in step of 30°C were used in the protocol. The residual doses for the MET-pIRIR signals were generally less than 1 Gy. This protocol was further simplified to a three-step pIRIR method, with three stimulation temperatures of 110, 140 and 170°C. It has been shown that these new pIRIR methods can be applied successfully to aeolian samples within the Holocene. A high temperature MET-pIRIR dating protocol was initially applied to polymineral fine grains (4-11 μm), recovered from Chinese loess samples collected at Luochuan that accumulated within the last glacial-interglacial period. The MET-pIRIR ages for fine grains were compared with the coarse grain (63-90 μm) K-feldspar MET-pIRIR ages and the coarse grain quartz OSL ages, and the stratigraphic age controls. The results show that the MET-pIRIR protocol can be applied to fine grains from these loess samples without fading correction. A plateau test, termed the De (T, t) plot, was proposed as a self-diagnosing tool for the pIRIR dating protocols. The pattern of the De (T, t) plot was shown to be affected by non-bleachable signal, partial bleaching and anomalous fading effects. The achievement of a plateau in the De (T, t) plot indicates that the non-fading signal has been achieved, and the effects of non-bleachable dose and partial bleaching are negligible. The De (T, t) test was successfully applied to different pIRIR protocols. A series of loess and fluvial sand samples were collected from the north piedmont of Tian Shan range to determine appropriate dating procedures for samples in this area. Luminescence properties of quartz and K-feldspar grains extracted from these samples were investigated. The extent of bleaching for the samples and the reliability of the measured ages were assessed based on equivalent dose distribution and age comparison between chronometers. Optimized dating procedures for samples in north Tian Shan have been proposed. K-feldspar MET-pIRIR dating is recommended for the loess samples, while single aliquot quartz OSL dating is suggested for the fluvial sand samples, after consideration of signal brightness and the extent of signal resetting. The dating procedures proposed above were applied to the deformed fluvial terraces of Anjihai River in the north flank of Tian Shan. Combined with topographic measurements, the deformation rate of the Anjihai anticline was calculated. The average shortening rates of the Anjihai anticline since 3.6 ±0.1, 9.0 ±0.6 and 53.3 ±2.2 ka were calculated to be 1.4 ±0.3, 1.2 ±0.3 and 0.5 ±0.1 mm/a, respectively. It suggests that the northern Tian Shan region was tectonically active during the late Quaternary, especially in the Holocene.