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

这个项目的目标是了解地球如何在几个世纪的时间尺度上对巴塔哥尼亚一个紧凑、监测良好的地区的冰冻圈质量失衡做出反应，巴塔哥尼亚是一个复杂的新近纪脊俯冲和年轻火山活动的地区。冰川均衡调整问题是理解上地幔黏度和变形时间尺度的一个重要问题。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）下面和周围的现代岩石隆起的主要驱动力被解释为小冰期（LIA）高峰推进后的冰损失。最近的大地测量学研究表明，隆起速度非常快（在SPI附近高达40毫米/年，平均约为20毫米/年）。这些速度是现代地质隆升速度最快的；那些需要低粘度地幔的。在巴塔哥尼亚，人们对晚新生代发育的板块窗知之甚少，这支持了人们的猜测，即在GIA非常迅速的地区下方有一个低粘度带。该团队将探索高速率的原因和推断GIA的时空模式，使用：(1)区域宽带地震阵列来描绘地壳和上地幔结构和粘度，并观察沿俯冲的南板块的地震活动（目前未定义）；(2)利用船载反射地震数据和沉积物岩心，对冰川推进形成的冰槽（现在的峡湾样湖泊）中沉积的年轻冰前和冰下沉积物进行成像和定年，以确定冰的几何形状和沉积沉积物的体积；(3)对陆地层序进行新的制图和定年，以确定其两个最大出海口冰川沿线SPI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.