青藏高原东部当子沟末次冰期冰川演化光释光测年

OSL dating study on the glacial evolutions during the Last Glaciation at Dangzi Valley in the eastern Qinghai-Tibetan Plateau

青藏高原东部横断山脉沙鲁里山北支雀儿山北麓的当子沟,保留了4组末次冰期冰碛垄,每组冰碛垄由若干道小冰碛垄组成,是末次冰期多次冰川波动的理想地貌证据。为恢复该地末次冰期冰川演化历史,从这4组冰碛垄中采集了7个光释光测年样品进行年代测定。等效剂量采用单片再生法(SAR)和标准生长曲线法(SGC)进行测试。年代结果显示:第1～3组冰碛垄形成于22.4-16.5 ka BP,属深海氧同位素2阶段(MIS-2),大致与全球末次盛冰期(LGM)相当。第4组冰碛垄形成于MIS-3。MIS-3冰川规模大于MIS-2。第1～3组9道次一级小冰碛垄表明,约在22.4-16.5 ka BP期间当子沟冰川经历了9次小波动。冰川在稍早于22.4 ka BP达到MIS-2的最大范围,此后规模在波动中逐渐萎缩,可能是冰川对MIS-2后期太阳辐射增强、气温回升的响应。最里侧冰碛垄形成于16.5 kaBP,可能标志着该地冰消期的开始。此后,当子沟冰川大幅快速退缩。冰川融水在最里侧冰碛垄里侧低洼谷地汇集并被阻塞形成当子错。

There are four sets of preserved moraines in Dangzi Valley, located in the southeastern edge of Zhuqing Basin, northern slope of Queershan Mountains, the north branch of the Shaluli Mountains in the Hengduan Mountains, eastern part of Qinghai-Tibetan Plateau. Each set of moraines is composed of several small moraines. These are the perfect geomorphological evidence for multiple glacial fluctuations during the Last Glaciation in this region. To reconstruct the history of glacial evolution during the Last Glaciation, seven optically stimulated luminescence（OSL） samples are collected from these moraines. Equivalent doses（De） are determined using SAR（single aliquot regenerative-dose） and SGC（standardized growth curve） protocols. Internal testing results indicate that these protocols are suitable for De determination. The age results show that the first, second, and third sets of moraines were formed during 22.4-16.5 ka BP, belonging to the Marine Isotope Stage 2 （MIS-2）, approximately equal to the Last Glacial Maximum （LGM）. The fourth set was formed during the MIS-3. These results are in good agreement with the chronology of other sites in the Shaluli Mountains. MIS-3 glacier in this region is bigger than MIS-2 glacier. The existence of nine small moraines in first, second, and third sets indicates that Dangzi Glacier had experienced nine small fluctuations during the period of 22.4-16.5 ka BP. The glacier reached its largest MIS-2 scale a little earlier than 22.4 ka BP. After that, the Dangzi Glacier fluctuated and shrank with time, which is probably the response of the glacier to the increasing solar radiation and the rising temperature during late MIS-2. The most inner moraine was formed at 16.5 ka BP, which may be a sign of onset of local deglaciation. Then, the Dangzi Glacier retreated dramatically and rapidly. Melting water converged into the lower part of the valley and was blocked by the most inner moraine and thus formed the Dan- gzi Lake.