青藏高原东北缘玛雅雪山晚第四纪冰川发育的气候和构造耦合  

Climate-tectonics coupling effect on Late Quaternary Glaciation in the Mayaxue Shan,Gansu Province

作　　者：刘蓓蓓[1] 张威[2] 崔之久[1] 刘亮[2] 

机构地区：[1]北京大学城市与环境学院,北京100871 [2]辽宁师范大学城市与环境学院,辽宁大连116029

出　　处：《冰川冻土》2015年第3期701-710,共10页Journal of Glaciology and Geocryology

基　　金：国家自然科学基金项目(41271093;41230743)资助

摘　　要：青藏高原东北缘的玛雅雪山(海拔4 447 m)保存着确切的第四纪冰川遗迹.野外地貌调查与光释光测年方法相结合,确认玛雅雪山晚第四纪主要经历3次冰川作用:第Ⅰ组冰碛时代为新冰期;第Ⅱ组冰碛物年龄为(23.2±1.0)ka,其上覆泥石流年龄为(2.9±0.3)^(2.3±0.1)ka,上层土壤年龄为(3.6±0.2)ka,对应于深海氧同位素2阶段(MIS 2)的末次冰盛期(LGM);第Ⅲ组冰碛年龄为(42.6±1.9)^(45.7±3.0)ka,属于末次冰期中冰阶,对应MIS 3中期.采用最新综合因子法计算玛雅雪山现代冰川物质平衡线为海拔4 605 m.依据冰川地貌形态,计算末次冰期平衡线为海拔3 800 m.通过庄浪河阶地的拔河高度及各级阶地的年代,以河流的下切速率代表玛雅雪山的抬升速率,计算得到末次冰期中期以来玛雅雪山抬升了50~60 m.利用玛雅雪山周边的达里加山和太白山冰川漂砾的10Be数据近似代表流域侵蚀速率,推算出玛雅雪山剥蚀速率大约为29 mm·ka-1,推断MIS 3以来流域的剥蚀量为1~2 m.综合末次冰期中期以来的构造抬升量和剥蚀量,恢复末次冰期中期时的流域高度为海拔4 200 m,平衡线高度为海拔3 750 m.研究结果显示:研究区在MIS 3时,流域平均高度已经在平衡线之上,在流域平均高度到主峰之间冰川开始积累,发育冰川.结合其他环境指标综合推断,玛雅雪山晚第四纪冰川的发育是气候和构造耦合的产物.The Mayaxue Shan,of which the main peak is 4 447 m,located at the northeast of Tibetan Plateau,is a key site for discussing the relationship between climate and tectonics. According to field investigation and optically stimulated luminescence（ OSL） dating,it is considered that there were three Late Quaternary Glaciations. The first one was Neoglaciation. The second one was regarded as the Last Glacial M aximum（ LGM）,corresponding to marine isotope stage（ M IS） 2,in viewof the till and debris flowsediment consisted of soils having the age of（ 23. 2 ± 1. 0） ka,（ 2. 9 ± 0. 3）-（ 2. 3 ± 0. 1） ka and（ 3. 6 ± 0. 2） ka,respectively. The third one was assigned to M IS 3 as indicated by the OSL date of（ 42. 6 ± 1. 9） ka,（ 45. 7 ± 3. 0） ka. The equilibrium line altitude（ ELA） is calculated to be 4 605 m a. s. l. at present; and that at last glacial cycle was 3 800 m a. s. l.according to geomorphology features. It is concluded that the M ayaxue Shan has uplifted 50- 60 m since the last glacial cycle according to the observation in the Zhuanglang River,based on the idea that terrace undercutting rate equals to the mountain uplifting rate. According to exposed ^10Be ages of the boulders on Dalijia Shan and Taibai Shan nearby,the erosion rate is believed to be 29 mm ·ka^-1. Adopting this erosion rate,it is calculated that the erosion amount of 1- 2 m in the research region. Considering these uplift and erosive rates,the watershed height may be recovered to be 4 200 m,higher than the ELA（ 3 750 m） during the middle stage of last glacial cycle,demonstrating that glacier developed in the mountain. Combined with other environmental indexes,it is believed that Late Quaternary Glaciation in the M ayaxue Shan was climate-tectonics coupling product.

关 键 词：玛雅雪山 冰期系列 平衡线 气候和构造 

分 类 号：P534.63[天文地球—第四纪地质学]