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首页> 外文期刊>South African Journal of Geology: Being the Transaction of the Geological Society of South African: Syndie die Verhandelinge van die Geologiese Vereniging van Suid-Afrika >THE GEOLOGY AND STRUCTURE OF THE MASVINGO GREENSTONE BELT AND ADJACENT GRANITE PLUTONS FROM GEOPHYSICAL DATA, ZIMBABWE CRATON
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THE GEOLOGY AND STRUCTURE OF THE MASVINGO GREENSTONE BELT AND ADJACENT GRANITE PLUTONS FROM GEOPHYSICAL DATA, ZIMBABWE CRATON

机译：津巴布韦克拉通地球物理数据显示的马斯文戈格林斯通带和邻近花岗岩块的地质构造

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摘要

The structure and subsurface configuration of the Masvingo Greenstone Belt (MGB) in the Zimbabwe Craton (ZC), were investigated using aeromagnetic and gravity data. Gravity data from 158 new and 202 old gravity stations were combined to produce a Bouguer gravity map covering the greenstone belt and surrounding granites. The greenstone belt and ultramafic complexes are characterised by Bouguer gravity highs, whereas the granitic terrain are lows, with the lowest values over the post-volcanic plutons. Gravity modelling, constrained by surface geology and density measurements, was carried out on a profile crossing the greenstone belt. The modelling results indicate a depth extent of around 6 km for the dense greenstone belt with a thickness of about 8.5 km for the adjacent younger granite plutons, which are significantly less dense. Granite-greenstone contacts along the profile are near-vertical. Magnetic maps compiled from the Zimbabwe Geological Survey national aeromagnetic data set show the bulk of the greenstone belt to have low magnetic anomaly values, but with high magnetic anomaly values along its northern and western margins over ultramafic units and banded iron formations. The younger granites generally have higher magnetic anomaly values compared to both the greenstone belt and the older gneisses. In particular, a pronounced east-northeast-trending broad magnetic high is observed over the Charumbira pluton, and its edges mark the boundaries with the greenstone belt to the north, and the Limpopo belt to the south; with the latter characterised by low magnetic values. Several linear, small amplitude magnetic lows, which are mostly due to faults, trend northwest to southeast: and north to south, with some revealing an apparent dextral movement. Derivative maps for both gravity and magnetic data bring out some of the linear features and the edges of the greenstone belt and granite plutons. Shallow and deep depth slices of the magnetic field allow separation of high and low frequency anomalies; such as the east-northeast-trending Limpopo dyke swarm of Karoo age. The information obtained from modelling, derivative maps and depth slicing suggest a trough-shaped configuration for the MGB, which is consistent with other known greenstone belts on the ZC and elsewhere. This information is consistent with an intracratonic, extensional rift environment for emplacement of the greenstone belt.
机译：使用航磁和重力数据研究了津巴布韦克拉通（ZC）中Masvingo绿岩带（MGB）的结构和地下构造。合并了158个新重力站和202个旧重力站的重力数据，生成了布格重力图，其覆盖了绿岩带和周围的花岗岩。绿岩带和超镁铁质复合体的特征是布格重力高，而花岗岩地势低，在火山后岩体中值最低。受地表地质和密度测量限制的重力模拟是在穿过绿岩带的剖面上进行的。模拟结果表明，致密的绿岩带的深度约为6 km，相邻的较年轻的花岗岩岩体的厚度约为8.5 km，而后者密度明显较低。沿剖面的花岗岩-绿岩接触几乎是垂直的。根据津巴布韦地质调查局国家航空磁数据集编制的磁图显示，绿岩带的大部分磁异常值较低，但沿超镁铁质单位和带状铁矿构造的北，西边缘的磁异常值较高。与绿岩带和较老的片麻岩相比，较年轻的花岗岩通常具有较高的磁异常值。特别是，在Charumbira岩体上观察到了明显的东西向的大磁高，其边缘标志着北部的绿岩带和南部的林波波带的边界。后者的特点是磁值低。几个线性的，小振幅的磁低点主要是由断层引起的，其趋势是从西北向东南：从北向南，其中一些表现出明显的右旋运动。引力和磁场数据的导数图显示出一些线性特征以及绿岩带和花岗岩岩体的边缘。磁场的浅层和深层可以分离高频和低频异常;例如Karoo时代的东西方趋势林波波河堤群。从建模，导数图和深度切片获得的信息表明，MGB呈槽形，这与ZC和其他地方的其他已知绿岩带一致。该信息与克拉通内部的裂谷环境相吻合。

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