Collaborative Research: Solid Earth Response of the Patagonian Andes to Post-Little Ice Age Glacial Retreat

该项目的目标是了解地球如何在巴塔哥尼亚的一个紧凑的、监测良好的地区对几个世纪的时间尺度上的冰冻圈质量不平衡作出反应，巴塔哥尼亚是一个复杂的新第三纪山脊俯冲和年轻火山活动的地区。冰川均衡调整问题是认识上地幔粘性和变形时间尺度的重要问题。PI团队将尝试量化和模拟冰和沉积物加载和卸载的均衡响应。 南巴塔哥尼亚冰原（SPI）下方和周围现代岩石隆起的主要驱动力被解释为小冰期（LIA）高峰期后的冰损失。最近的大地测量研究表明，隆起速度非常快（高达40毫米/年，SPI周围平均约20毫米/年）。这些速率是现代最快的地质隆升速率;需要低粘度地幔的速率。在巴塔哥尼亚，存在一个在晚新生代时期发展起来的有点不太了解的板状窗口，这支持了一种推测，即低粘度区位于GIA非常迅速的区域之下。该团队将探索高速率的原因和推断的GIA的时空模式，使用：（1）区域性宽频地震台阵，用以描绘地壳和上地幔的结构和粘滞性，并观测地震活动（目前尚未确定）沿着俯冲的南方板块;（2）船载反射地震数据和沉积物岩心，对沉积在冰川槽中的年轻的冰前和冰下沉积物进行成像和定年（现在类似峡湾的湖泊）由前进的冰雕刻而成，其目标是确定冰的几何形状和沉积物的体积;（3）对陆上冰碛序列进行新的测绘和测年，以确定SPI沿着其两个最大出口冰川的时变空间几何形状;（4）改进冰川和固体地球响应的地球物理模型。

The goal of this project is to understand how the Earth responds to a cryospheric mass imbalance ona time scale of centuries in a compact, well-monitored region of Patagonia, a region of complex Neogene ridge subduction and youthful volcanism. The problem of glacial isostatic adjustment (GIA) is an important problem and critical to understanding the viscosity and time-scales of deformation in the upper mantle. The PI team will try to quantify and model the isostatic response to ice and sediment loading and unloading. A primary driver of modern rock uplift beneath and surrounding the Southern Patagonia Icefield (SPI) is interpreted to be ice loss following the peak advances of the Little Ice Age (LIA). Recent geodetic studies reveal remarkably rapid uplift rates (up to 40 mm/yr and averaging ~20 mm/yr around the SPI). These rates are the fastest modern geologic uplift rates; ones that demand a low viscosity mantle. In Patagonia, the presence of a somewhat poorly understood slab window that developed during Late Cenozoic time supports speculation that a low-viscosity zone underlies the region where GIA is veryrapid.This team will explore the causes of high rates and spatial-temporal pattern of the inferred GIA using: (1) a regional broadband seismological array to delineate the crustal and upper mantle structure and viscosity and observe seismicity (currently undefined) along the subducting Austral slab; (2) shipboard reflection seismic data and sediment cores to image and date the young pro- and subglacial sediments deposited in the glacial troughs (now fiord-like lakes) carved by advancing ice with a goal of defining both the geometry of ice and volume of deposited sediment through time; (3) new mapping and dating of the subaerial morainal sequence to define the time-varying spatial geometry of the SPI along its two largest outlet glaciers; and (4) improved geophysical models of glacier and solid earth responses.