Collaborative Research: Scotia Arc GPS Project (SCARP)

劳弗和达尔齐尔OPP 9526687贝维斯OPP 9530383斯马利OPP 9527529摘要南极是地球上最与世隔绝的大陆。除了南美地区外，它周围都是活跃扩张的海脊。南美洲相对于南极洲的运动是纬向的，以每年约22毫米的速度向左移动，并沿夹在中间的斯科舍板块的边界分布。一个突出但不连续的测深高地被称为斯科舍海脊，它的三面环绕着斯科舍板块。这一特征包括一些从南美和南极大陆分离出来的大陆物质，但其东部的闭合是一组火山活动和地震活跃的岛屿--南桑威奇弧，它与斯科舍板块之间有一个有力地展开的弧后山脊。连接这两个大陆的整个向东闭合的、局部浮现的测深特征被称为斯科舍弧。相对于南美洲和南极洲，D型夹层板块和弧形似乎正在迅速向东移动，从而首次将俯冲系统引入到原本受裂谷限制的南大西洋盆地。这一运动可能是地幔从封闭的太平洋盆地向扩张的大西洋盆地回流的最好证据。尽管如此，斯科舍弧仍然是地球上最不受约束的主要构造系统之一，但它是全球板块运动回路中一个关键而神秘的纽带。这个斯科舍弧形GPS项目(SCRAP)将使用全球定位系统(GPS)来测量南美洲、南极洲和非洲之间的板块运动，以及使用一种新开发的称为多模式占领战略(MOST)的大地测量策略来测量斯科舍弧周围的板块运动。这包括在南美洲和南极洲的少数地点设置永久的GPS接收器，并使用额外的接收器来定位相对于这个持续运行的网络的许多站。南桑威奇群岛的两个季节性占用的站点将连接到南美洲、南极洲和非洲的永久GPS站点，以及福克兰群岛、南乔治亚岛和南奥克尼群岛的中间站点，这些站点将偶尔被英国合作者占用。在最初的三年中，南桑威奇弧的运动将很容易得到解决，利用南极半岛-南设得兰群岛地区的巡回站，应该可以确定布兰斯菲尔德海峡是否正在发生伸展。该项目还将在巴塔哥尼亚/火地岛建立一个相对密集的子网络，并在南极半岛建立一个中等密度的子网络。虽然预计这些子网络的最初三年项目不会达到亚毫米/年的速度分辨率，但该项目将为六至八年后的后续测量奠定必要的基线。后续项目将能够描述发生在斯科舍板块边界上和内部的慢动作和变形。SCRAP的目标是确定：1.南极、南美洲、斯科舍和南桑德维奇板块的相对运动；2.南美洲-斯科舍板块边界带火地岛内的应变分配；3.跨越火山活动的布兰斯菲尔德海槽的伸展速度和现已灭绝的南设得兰群岛火山弧的抬升或下沉速度；4.与我们的英国同事一起，南美洲-非洲框架内的南桑迪奇海沟的回滚速度；这些目标将反过来允许：1.对与布兰斯菲尔德海峡伸展和南极大陆上冰的积累或丧失有关的弹性位移场的大地测量作出重要贡献；2.确定为什么沿斯科舍板块北部边界存在扭压，而沿其南部边界存在转换挤压；3.测试作为全球板块环路误差来源的南极东西之间的运动；以及4.从地幔流动和将被动裂开洋盆转变为俯冲或消失洋盆的可能性方面，评估南桑威奇海沟回滚意味着什么。

Lawver and Dalziel OPP 9526687 Bevis OPP 9530383 Smalley OPP 9527529 Abstract Antarctica is the Earth's most isolated continent. It is surrounded by actively spreading ridges except in the South American sector. The motion of South America with respect to Antarctica is latitudinal and left-lateral at approximately 22 mm per year and is distributed along the boundaries of the intervening Scotia plate. A prominent but discontinuous bathymetric high known as the Scotia Ridge surrounds the Scotia plate on three sides. This feature includes some continental material detached from the South American and Antarctic continents, but its eastern closure is a volcanically and seismically active group of islands, the South Sandwich arc, that is separated from the Scotia plate by a vigorously spreading back- arc ridge. The entire east-closing, locally emergent bathymetric feature joining the two continents, is known as the Scotia arc. The D-shaped Sandwich plate and arc appear to be moving rapidly east with respect to both South America and Antarctica, thereby for the first time introducing a subduction system into the otherwise rift-bounded South Atlantic Ocean basin. This motion may constitute the best evidence for mantle return flow from the closing Pacific Ocean basin to the expanding Atlantic Ocean basin. The Scotia arc is nonetheless one of the most poorly constrained of the major tectonic systems on Earth, yet it is a critical and enigmatic link in global plate-motion circuits. This SCotia ARc GPS Project (SCARP) will use the Global Positioning System (GPS) to measure the plate motions between South America, Antarctica, and Africa, and around the Scotia arc using a newly developed geodetic strategy known as a multimodal occupation strategy (MOST). This involves setting up permanent GPS receivers at a small number of sites in South America and Antarctica, and using additional receivers to position numerous stations relative to this continuously operat ing network. Two seasonally occupied stations in the South Sandwich islands will be tied to permanent GPS sites in South America, Antarctica, and Africa, and to intervening stations in the Falkland, South Georgia, and South Orkney islands that will be occupied on an occasional basis by British collaborators. During the initial three years the South Sandwich arc motion will be easily resolved, and using roving stations in the Antarctic Peninsula- South Shetland Islands area, it should be possible to determine if extension is occurring across Bransfield Strait. This project will also construct a relatively dense subnetwork in Patagonia/Tierra del Fuego, and a moderately dense subnetwork in the Antarctic Peninsula. While achieving sub-millimeter/year velocity resolution in the initial three year project with these subnetworks is not expected, this project will establish the baseline necessary for a follow-on suite of measurements in perhaps six to eight years. The follow-on project will allow characterization of the slow motions and deformations that occur across and within the boundaries of the Scotia plate. The objectives of SCARP are to determine: 1. the relative motions of the Antarctic, South Americal, Scotia and South Sandwich plates; 2. strain partitioning within the South America-Scotia plate boundary zone, Tierra del Fuego; 3. the rate of extension across the volcanically active Bransfield trough and the present rate of uplift or subsidence of the extinct South Shetland Islands volcanic arc; 4. and with our British colleagues, the rate of rollback of the South Sandwich Trench in a South American-African framework; These objectives in turn will allow: 1. An important contribution to a geodetic assessment of the elastic displacement field associated with extension in Bransfield Strait and the accumulation or loss of ice on the Antarctic continent; 2. Determination of why there is transpression along the northern boundary of the Scotia plate and tra nstension along its southern boundary; 3. Testing for motion between East and West Antarctica postulated as a source of error in global plate circuits; and 4. Evaluatation of what the South Sandwich trench rollback means in terms of mantle flow and the potential for transforming a passive rifted ocean basin into a subducting or disappearing ocean basin.