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巴塔哥尼亚一个紧凑、监测良好的地区的冰冻圈质量在几个世纪的时间尺度上是如何反应的，巴塔哥尼亚是一个拥有复杂的新近纪山脊俯冲和年轻火山活动的地区。冰川均衡调整(GIA)问题是一个重要的问题，对于理解上地幔变形的粘度和时间尺度至关重要。PI团队将尝试对冰和沉积物加载和卸载的均衡响应进行量化和建模。巴塔哥尼亚南部冰原(SPI)下方和周围现代岩石抬升的主要驱动力被解释为小冰期(LIA)峰值推进后的冰川融化。最近的大地测量研究显示了非常快的抬升速度(高达40毫米/年，在SPI周围平均为20毫米/年)。这些速率是现代地质抬升最快的速率；需要低粘度的地幔。在巴塔哥尼亚，一个在晚新生代时期发展起来的不太被理解的板条窗口的存在支持了这样的推测，即在GIA非常快速的区域下面有一个低粘性带。这个团队将使用：(1)区域宽带地震台阵来描绘地壳和上地幔的结构和粘性，并沿着俯冲的南板观察地震活动(目前尚未确定)，来探索推断的GIA的高速率和时空格局的原因；(2)船上反射地震数据和沉积岩芯，以对冰川槽(现在的峡湾状湖泊)中沉积的年轻前冰川和冰下沉积物进行成像和定年，目的是确定冰的几何形状和沉积沉积物的体积随时间变化的目的；(3)新的空中冰山序列测绘和测年，以确定SPI沿其两个最大出口冰川的时变空间几何形状；(4)改进了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.