Spatial and temporal patterns of Cenozoic dynamic topography around Australia
Spatial and temporal patterns of Cenozoic dynamic topography around Australia
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DOI：
10.1029/2012gc004392
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发表时间：
2013-03-01
影响因子：
3.5
通讯作者：
Winterbourne, J.
中科院分区：
文献类型：
--
作者：
Czarnota, K.;Hoggard, M. J.;Winterbourne, J.
尽管地幔对流环流对动力地形的影响具有重要意义，但人们对其时空格局的认识却很少。我们提出了来自澳大利亚周围海洋盆地和大陆边缘的动态地形的准确估计。我们的出发点是测量与大陆架相邻的最古老洋底的剩余深度异常。这些异常是由类似200个地震反射和沉积良好的海洋地壳广角图像的组合数据集确定的。它们的振幅在-1 km ~ +0.5 km之间，其空间变化与长波自由空气重力和浅层地震层析异常大致一致。沿西北陆架，-300 ~ -700 m的区域深度异常与相邻大陆架相交。通过分析陆架边缘广阔的碳酸盐岩台地的地层结构，确定了该异常的时间演化，并记录了新近纪从沉积到沉积的剧烈转变。利用钻孔标定的三维地震填图，计算了沿陆架倾斜地形翻转点的水载沉降历史。在9 +/- 3 Ma时，沉降速率从5增加到75 m Myr(-1)，产生-300 ~ -700 m的沉降异常。这种异常的幅度沿陆架变化，不能由冰川-海平面上升变化产生。相反，我们提出了一个区域性沉降事件，影响近陆架和远洋盆地，是由对流下降产生的。通过将我们的结果与其他已发表的隆起和下沉估计相结合，我们绘制了一幅澳大利亚地图，该地图显示了动态地形的时空格局。澳大利亚的大部分（但不是全部）造陆运动可以归因于澳大利亚板块在对流环流模式下的快速北移。
Despite its importance, the spatial and temporal pattern of dynamic topography generated by mantle convective circulation is poorly known. We present accurate estimates of dynamic topography from oceanic basins and continental margins surrounding Australia. Our starting point is measurement of residual depth anomalies on the oldest oceanic floor adjacent to the continental shelf. These anomalies were determined from a combined dataset of similar to 200 seismic reflection and wide-angle images of well-sedimented oceanic crust. They have amplitudes of between -1 km and +0.5 km, and their spatial variation is broadly consistent with long-wavelength free-air gravity and shallow seismic tomographic anomalies. Along the Northwest Shelf, a regional depth anomaly of -300 to -700 m intersects the adjacent continental shelf. The temporal evolution of this anomaly was determined by analyzing the stratigraphic architecture of an extensive carbonate platform, which fringes the shelf and records a dramatic switch from progradation to aggradation during Neogene times. Three-dimensional seismic mapping calibrated by boreholes was used to calculate water-loaded subsidence histories at rollover points of clinoforms along the shelf. At 9 +/- 3 Ma, the rate of subsidence increases from 5 to up 75 m Myr(-1), generating a subsidence anomaly of -300 to -700 m. The amplitude of this anomaly varies along the shelf and cannot be generated by glacio-eustatic sea-level variation. Instead, we propose that a regional subsidence episode, which affects both the proximal shelf and the distal oceanic basin, was generated by convective drawdown. By combining our results with other published estimates of uplift and subsidence, a map of Australia, which shows the spatial and temporal pattern of dynamic topography is presented. Most, but not all, of Australia's epeirogeny can be attributed to rapid northward motion of the Australian plate over a pre-existing pattern of convective circulation.