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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 Bushmanland Group supracrustal succession, Aggeneys, Bushmanland, South Africa: Provenance, age of deposition and metamorphism
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The Bushmanland Group supracrustal succession, Aggeneys, Bushmanland, South Africa: Provenance, age of deposition and metamorphism

机译：南非布什曼兰，Aggeneys，布什曼兰组超前演替：起源，沉积时代和变质作用

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摘要

The central portion of the structurally complex and poly-metamorphosed Namaqua Province of western South Africa is underlain by a series of pelitic and psammitic metasediments, termed the Bushmanland Group, which is host to world class Broken Hill-type Pb-Zn-Cu-Ag deposits at Aggeneys. Geochemical, U-Pb SHRIMP zircon geochronology and Sm-Nd isotopic determinations of the metasediments at Aggeneys were undertaken to determine the age and nature of the provenance, as well as to confine the age of deposition of the Bushmanland Group in this area. The metasediments were derived from moderately-weathered granodiorites to granites, or their volcanic equivalents, with similar to 2.65 to similar to 2.25 Ga Sm-Nd T-DM model ages. Mixed sources are likely from the geochemical signatures of the metasediments as well as the varied detrital zircon ages, with two main age groupings present of similar to 2.12 to similar to 1.97 Ga and similar to 1.88 Ga to similar to 1.64 Ga. The upper part of the succession has a narrower compositional range and was derived from a more mafic provenance than the basal portion. The provenance is likely to have been a combination of similar to 1.8 Ga Gladkop Suite granitic gneisses found to the west and the similar to 2.1 to similar to 1.9 Ga intrusive and volcanosedimentary rocks of the Richtersveld Subprovince to the northwest. The metasediments were deposited in a passive margin setting and underwent extensive reworking in addition to recycling. The time of deposition of the Bushmanland Group is constrained between the age of the youngest detrital zircon (similar to 1.64 Ga) and the onset of the regionally extensive Kibaran Orogeny at similar to 1.2 Ga. Metamorphic overgrowths and runs on detrital zircons record two distinct events, the similar to 1.21 to similar to 1.18 Ga Kibaran Orogeny, characterised by extensive granitic magmatism, peak D-2 deformation and peak upper amphibolite facies grade M-2 metamorphism, and the more ubiquitous similar to 1.04 to similar to 1.01 Ga Namaquan Orogeny characterised by weaker M-3 metamorphism.
机译：南非西部纳马夸省结构复杂且多变质的中心部分被一系列的胶质和叠层变质沉积物称为布什曼兰群，该群是世界一流的破碎山型Pb-Zn-Cu-Ag的宿主。在Aggeneys存放。进行了地球化学，U-Pb SHRIMP锆石年代学和Aggeneys沉积物沉积物的Sm-Nd同位素测定，以确定该物源的年龄和性质，以及限制该地区Bushmanland群的沉积年龄。这些变质沉积物是从中等风化的花岗闪长岩到花岗岩或其火山等价物的，年龄与2.65至2.25 Ga Sm-Nd T-DM模型年龄相似。混合来源可能来自变质沉积物的地球化学特征以及不同的碎屑锆石年龄，存在两个主要年龄组，分别类似于2.12至1.97 Ga和类似于1.88 Ga至1.64 Ga。演替的组成范围较窄，其起源于基部。出处可能是类似于在西部发现的1.8 Ga Gladkop Suite花岗岩片麻岩和类似于2.1的相似物（类似于西北的Richtersveld子省的1.9 Ga侵入岩和火山沉积岩）的组合。这些变质沉积物被沉积在一个被动的边际环境中，除了回收外还进行了广泛的返工。 Bushmanland组的沉积时间受最年轻的碎屑锆石年龄（约1.64 Ga）和区域广泛​​的Kibaran造山带开始（约1.2 Ga）的限制。变质的过度生长和在碎屑锆石上运行记录了两个不同的事件，类似于1.21类似于1.18 Ga Kibaran造山带，其特征是广泛的花岗岩浆作用，峰D-2变形和峰顶角闪岩相M-2级变质作用，并且更普遍地类似于1.04到1.01类似于Ga Namaquan造山运动是由于M-3变质能力较弱。

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