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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 >Supracrustal gneisses in southern Swaziland: a basaltsandstone assemblage of the upper Mozaan Group deformed in the Neoarchaean
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Supracrustal gneisses in southern Swaziland: a basaltsandstone assemblage of the upper Mozaan Group deformed in the Neoarchaean

机译：斯威士兰南部的Supracrustal片状：莫扎恩集团的基础杆石集合在新立场制造中变形

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This study represents the first detailed field, geochemical and geochronological study of Archaean rock units that crop out along the Ncotshane River in the southern part of Swaziland. These rock units were mapped as Mahamba Gneiss on the geological map of Swaziland (Wilson, 1982). However, field examination indicated that the area consists of a heterogeneous assemblage of ductilely deformed supracrustal rocks (amphibolite and quartzite) and granitoid gneisses intruded by diorite, granite and dolerite. Amphibolites were derived from the metamorphism of tholeiitic basalts characterized by geochemical signatures similar to those of volcanic rocks of the nearby Pongola Supergroup. Quartzites are compositionally similar to sandstones from the Mozaan Group. LA-ICP-MS U-Pb analysis of zircon grains from grey quartzite define source ages of circa 3.35 Ga, 3.16 Ga, 3.04 Ga, 2.98 Ga, 2.91 Ga and 2.83 Ga, similar to, albeit ~40 Ma younger than previous detrital zircon studies of the Mozaan Group. The age of 2.83 Ga is regarded to represent the maximum age of deposition of the grey quartzite precursor, indicating an overlap in time between the deposition of the Mozaan Group and the Central Rand Group of the Witwatersrand Supergroup. A SHRIMP U-Pb age of 2810 ± 5 Ma was obtained for granitic augen gneiss, interpreted as the age of protolith emplacement. Zircons from a granite were dated at 2808 ± 10 and are regarded as xenocrysts sourced from the augen gneiss during partial melting. The chemistry and U-Pb zircon ages suggest that augen gneiss and granite are part of the Mswati granite suite, which consists of post-tectonic plutons that cross-cut all Archaean rock types in Swaziland. All rock units have been subjected to three deformational events (D_1, D_2 and D_3) at amphibolite and retrograde greenschist facies grade. The upper limit for the age of deformation and metamorphism is provided by a U-Pb age of titanite at 2.73 Ga, reflecting crustal reworking of the eastern Kaap
机译：本研究代表了沿斯威士兰南部南部的纳米森河播种的大型岩石单位的第一个详细领域，地球化学和地理学研究。这些岩石单位被映射为斯威士兰地质地图（威尔逊，1982年）的Mahamba片状。然而，现场检查表明该面积由凹道变形的外岩（Amphibolite和石英岩）的异质组合组成，并由二霰毛，花岗岩和潮和毒剂侵入的花岗岩片。倒置倒置的烟雾玄武岩的变质，其特征在于地球化学签名，其类似于附近的Pongola超级的火山岩。石英酯与来自Mozaan组的砂岩合成。 La-ICP-MS U-PB Zircon谷物的灰色石英岩谷物分析Circa 3.35 Ga，3.16 Ga，3.04 Ga，2.98 Ga，2.91 Ga和2.83 Ga，类似于以前的替代Zircon年轻〜40马莫扎南集团的研究。 2.83Ga的年龄被认为是灰色石英石前体的最大沉积年龄，表明莫扎恩集团沉积与Witwatersrand Superrom的中央兰特组之间的重叠。为Granitional Aggen Gneiss获得了2810±5 mA的虾U-PB Age，被解释为促果实施加的年龄。来自花岗岩的锆石以2808±10日期，并被视为在部分熔化期间从Aggen Gneiss提供的XenoCrysts。化学和U-PB锆石年代表明，Aggen Gneiss和Granite是Mswati花岗岩套件的一部分，由后构造钚组成，跨越斯威士兰的所有拱形岩石类型。所有岩石单位都经过两栖动物和逆行绿色植物等级的三个变形事件（D_1，D_2和D_3）。变形和变质年龄的上限由钛铁矿的U-PB年龄在2.73 Ga，反映了东方KAAP的地壳重新加工

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