Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska
Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska
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DOI：
10.1073/pnas.1512549112
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发表时间：
2015-12-08
影响因子：
11.1
通讯作者：
Swartz, John M.
中科院分区：
文献类型：
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作者：
Gulick, Sean P. S.;Jaeger, John M.;Swartz, John M.
侵蚀，沉积物的生产，路由上的构造活动的大陆边缘反映了构造和气候过程，分区这些过程的相对重要性仍然存在争议。阿拉斯加湾保存着雅库塔特地体与北美碰撞的沉积记录。由于沿海圣埃利亚斯造山带的构造会聚在6 My内大致保持不变，因此保存在海上测量扇中的侵蚀沉积物的变化限制了构造物质流入、侵蚀和沉积物输出的预算。地震成像沉积物体积校准年表来自综合大洋钻探计划钻孔显示，侵蚀加速响应北方半球冰川加剧（类似于2.7马），900公里长的测量师通道的开始似乎与此事件。然而，构造流入超过综合沉积物流出的时间间隔2.8-1.2马。在中更新世气候过渡期（1.2-0.7 Ma），准周期（类似于100-ky）冰川周期开始后，体积侵蚀加速。从那时起，侵蚀和搬运的材料造山带已经超过了50- 80%的构造流入。如此快速的净质量损失解释了从暴露日期和绘制的序列外断层模式推断的陆上折返率明显增加。在造山楔响应的时间尺度上（数百万年），1.2-My质量预算的不平衡必须放松回到平衡状态，与构造流入保持平衡。圣埃利亚斯山脉提供了一个关键的例子，说明活跃的造山系统如何对瞬时质量通量作出反应，以及气候驱动的侵蚀过程可能产生的影响，这些侵蚀过程偏离了百万年尺度的平衡。
Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (similar to 2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (similar to 100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2-0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50-80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale.