Collaborative Research: Scotia Arc GPS Project (SCARP)

摘要南极洲是地球上最孤立的大陆。除了南美洲部分外，它被积极扩张的山脊所包围。南美洲相对于南极洲的运动是纬向和左向的，每年约22毫米，并沿斯科舍板块的边界分布。一个突出但不连续的深海高地被称为斯科舍脊，它在三面围绕着斯科舍板块。这个特征包括一些从南美和南极大陆分离出来的大陆物质，但它的东部闭合是一个火山和地震活跃的岛屿群，即南桑威奇弧，它被一个大力扩张的弧后脊与斯科舍板块分开。整个东闭的，局部出现的，连接两个大陆的水深特征，被称为斯科舍弧。相对于南美洲和南极洲而言，d型夹层板块和弧形似乎正在迅速向东移动，从而首次将一个俯冲系统引入了裂谷边界的南大西洋盆地。这一运动可能是地幔从闭合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，斯科舍弧是地球上主要构造系统中约束最弱的一个，但它是全球板块运动回路中关键而神秘的一环。这个SCotia ARc GPS项目（SCARP）将使用全球定位系统（GPS）来测量南美洲、南极洲和非洲之间以及SCotia ARc周围的板块运动，使用一种新开发的大地测量策略，称为多模式占领策略（MOST）。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连续运行的网络的许多站点。南桑威奇群岛的两个季节性站点将与南美洲、南极洲和非洲的永久GPS站点以及福克兰岛、南乔治亚岛和南奥克尼岛的中间站点联系起来，这些站点将偶尔被英国合作者占用。在最初的三年里，南桑威奇弧的运动将很容易解决，并且利用南极半岛-南设得兰群岛地区的流动站，应该有可能确定是否正在跨越布兰斯菲尔德海峡。本项目还将在巴塔哥尼亚/火地岛建设一个相对密集的子网，在南极半岛建设一个中等密集的子网。虽然预计在最初的三年项目中，这些子网络无法实现亚毫米/年的速度分辨率，但该项目将为接下来的6到8年的一系列测量建立必要的基线。后续项目将对斯科舍板块边界内外发生的缓慢运动和变形进行表征。SCARP的目标是确定：1。南极、南美、斯科舍和南三明治板块的相对运动；2. 火地岛南美-斯科舍板块边界带的应变划分；3. 横跨火山活动的布兰斯菲尔德海槽的延伸速度和已灭绝的南设得兰群岛火山弧目前的上升或下沉速度；4. 与我们的英国同事一起，在南美-非洲框架下，南桑威奇海沟的退缩速度；这些目标反过来将允许：对与布兰斯菲尔德海峡扩展和南极大陆冰的积累或损失有关的弹性位移场的大地测量评估的重要贡献；2. 确定斯科舍板块北部边界的挤压和南部边界的拉伸的原因；3. 对被假定为全球板块电路误差来源的东西南极洲之间运动的测试；和4。评估南桑威奇海沟回滚对地幔流动的意义，以及将被动裂陷海洋盆地转变为俯冲或消失海洋盆地的潜力。

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.