A review of crust/upper mantle structure in the Precambrian areas of Australia and implications for Precambrian crustal evolution
A review of crust/upper mantle structure in the Precambrian areas of Australia and implications for Precambrian crustal evolution
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DOI：
10.1016/0301-9268(88)90063-0
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发表时间：
1988-10
影响因子：
3.8
通讯作者：
B. Drummond
中科院分区：
文献类型：
--
作者：
B. Drummond
澳大利亚大陆西部三分之二的地区都是前寒武纪岩石。在地震学上，这一地区的特点是负的地壳运动走时残差，表明厚，冷构造层。尽管在一些克拉通内沉积盆地中存在广泛的地台盖层和古生代地壳改造，但前寒武纪地壳可大致分为太古代和元古代活动带和元古代移动的带。西太平洋板块有一个25-35公里厚的双层地壳，在最低地壳中观测到的速度范围为6.8-7.2 km s-1。莫霍面是一个明显的特征，其速度对比度大于1.0 km s−1。在Yilgarn地块南部的垂直反射探测器获得了有记录的剖面，其中有许多横向不连续但明显的反射，特别是在下地壳层，特别是集中在两个地壳层和莫霍面之间的边界周围。地震反射和速度与主要的长英质地壳一致，镁铁质透镜体占地壳最低层的20-35%，变质程度从上地壳到中地壳的麻粒岩到石榴麻粒岩，甚至地壳底部的榴辉岩。25 km深度以下的速度几乎总是> 7.0 km s-1，在地壳最低处达到7.4-7.6 km s-1;这样的速度是辉长岩（玄武岩）板下的特征。莫霍面的速度对比度< 1.0 km s− 1，比莫霍面的速度对比度小。垂直反射探头的记录剖面显示了一个高反射率的地壳，在折射模型和垂直反射的分布中，地震层之间没有相关性。前寒武纪和元古宙地区地壳的对比特征有利于前寒武纪地壳演化的构造模型，其中主要是长英质的前寒武纪原地壳被构造改造和底侵，产生元古宙地壳。简单的两层原地壳在这个过程中变得更加复杂。大量板块下的引入，特别是在壳幔边界附近，使地壳增厚，破坏了莫霍面的特征。它叠加了地壳的反射特征，因此反射带现在与地壳层之间的边界不相关。下地壳中的速度是高的，这是由于下板。
The western two thirds of the Australian continent are underlain by Precambrian rocks. Seismically, this region is characterised by negative teleseismic travel-time residuals indicating a thick, cold tectosphere. Despite extensive platform cover and Phanerozoic crustal reworking in a few intracratonic sedimentary basins, the Precambrian crust can be classified broadly into Archaean and Proterozoic cratons and Proterozoic mobile belts. The Archaean cratons have a two-layered crust 25–35 km thick, with observed velocities in the lowermost crust in the range 6.8–7.2 km s−1. The Moho is a distinct feature with a velocity contrast of > 1.0 km s−1. Vertical reflection probes in the southern Yilgarn Block yielded record sections that have numerous, laterally discontinuous but distinct reflections, especially in the lower crustal layer, that are especially concentrated around the boundary between the two crustal layers and the Moho. The seismic reflections and velocities are consistent with a predominantly felsic crust, with mafic lenses constituting 20–35% of the lowermost crust, and with the metamorphic grade ranging from granulite in the upper to middle crust to garnet granulite and even eclogite at the base of the crust.The Proterozoic mobile belts and cratons a have multi-layered crust 45–50 km thick. Velocities below 25 km depth are almost always > 7.0 km s−1, and reach 7.4–7.6 km s−1in the lowermost crust; velocities such as these are characteristic of gabbroic (basaltic) underplate. The velocity contrast is < 1.0 km s−1at the Moho, which is less distinct than in Archaean terranes. Record sections from vertical reflection probes show a highly reflective crust with no correlation between seismic layers in the refraction models and the distribution of vertical reflections.The contrasting character of the crust in Archaean and Proterozoic provinces favours a tectonic model for the evolution of Precambrian crust in which predominantly felsic Archaean protocrust was tectonically reworked and underplated to produce Proterozoic crust. The simple two-layered protocrust became more complicated in the process. The introduction of vast amounts of underplate, especially near the crust/mantle boundary, thickened the crust and destroyed the character of the Moho. It overprinted the reflection character of the crust so that the bands of reflections now do not correlate with the boundaries between the crustal layers. The velocities in the lower crust are high because of the underplate.