15Ma以来海陆记录的轨道-构造尺度东亚季风的演化以及西北内陆的干旱化

EAST ASIAN MONSOON EVOLUTION AND ARIDIFICATION OF NORTHWEST CHINA VIEWED FROM LAND AND SEA ON THE TECTONIC-ORBITAL TIME SCALE SINCE 15Ma

通过对比分析中国内陆、南海和西北太平洋15Ma以来的构造和气候记录,本文探讨了构造和轨道尺度上东亚季风和西北内陆的干旱化历史.构造尺度上,在中中新世以来全球变冷的格局下,东亚冬季风逐步增强.而东亚夏季风表现出从10Ma开始逐渐减弱,4Ma再次增强的阶段性变化.我们推测在11.16～7.00Ma,由于青藏高原向东北方向的扩张,导致高原东北缘和西秦岭之间可能存在水汽通道,夏季风降水可以通过水汽通道到达青藏高原的东北缘.7～8Ma之后水汽通道可能全部关闭,加上全球变冷和夏季风的减弱,西北内陆全面干旱,同时高原东北缘的隆升也提供了粉尘物源,风尘开始大面积堆积.2.75Ma以来,在冰期-间冰期旋回上,夏季风变化领先冬季风约30ka,分析表明冬季风与北极冰盖的强迫联系紧密,而夏季风同时受到高纬冰盖和低纬过程的驱动.

Through compiling and analyzing the paleoclimatic and tectonic records from East Asia since 15Ma, the results suggest the East Asian Winter Monsoon gradually strengthened consisting with global cooling. Asian Summer Monsoon progressively weakened from 10Ma and strengthen again since 4Ma. We speculated there was a water passage between eastern margin of the Tibetan Plateau and western Qinling Mountain during the period of 11.16Ma to 7.00Ma. The Asian Summer Monsoon precipitation could travel a long distance to the northeastern margin of the Tibetan Plateau through the passage. Subsequently, the water passage entirely closed after 8-7Ma resulted from the sustained eastward expansion of the Tibetan Plateau during the Late Miocene. In addition, global cooling and weakening summer monsoon promoted the dry climate in Northwest China and widespread aeolian dust accumulation. In the glacial-interglacial cycles, Asian Summer Monsoon led East Asian Winter Monsoon by 30ka in phase relationship since 2.75Ma. This could suggest that the East Asian Winter Monsoon was dominated by the Northern Hemisphere ice volume, while the Asian Summer Monsoon was forced by the combined effects of the Northern Hemisphere ice volume and low latitude processes.