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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 >Composition and single zircon U-Pb emplacement and metamorphic ages of the Aggeneys granite suite, Bushmanland, South Africa
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Composition and single zircon U-Pb emplacement and metamorphic ages of the Aggeneys granite suite, Bushmanland, South Africa

机译：南非布什曼兰，Aggeneys花岗岩套件的组成和单一锆石U-Pb沉积及变质年龄

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摘要

The central Bushmanland portion of the Namaqua Province of South Africa is underlain by three voluminous suites of granitic gneisses, termed the Achab, Hoogoor and Aroams Gneisses, in the Aggeneys District, the site of major world-class Broken Hill-type Pb-Zn-Cu-Ag deposits. Geochemically the granitic gneisses have similar characteristics with only slight differences in the degree of fractionation present. The gneisses exhibit a predominance of Kibaran magmatic zircon similar to 1.21 to similar to 1.17 Ga ages, which correspond closely to a similar tectono-magmatic event in the Okiep District in Namaqualand to the west and to similar aged granitic gneisses in the Natal Province of the Namaqua-Natal Belt. During this period the Aggeneys District was subjected to peak prograde M-2 amphibolite facies grade metamorphism associated with peak D-2 deformation. This period was characterised by continental collision and accretion throughout the belt. After a 140 m.y. period of tectonic quiescence a discrete tectono-magmatic episode is recorded in U-Pb ages of similar to 1.04 to similar to 1.01 Ga Namaquan Orogeny age from low Th/U metamorphic overgrowths also found in the Okiep District in Namaqualand to the west. Unlike Namaqualand and Natal, however, the Aggeneys District was not subjected to extensive magmatism at this time, and metamorphic conditions did not reach granulite facies grade as it did in Namaqualand. All of the granitic gneisses were included syn- to post-collision over a short time period. As the granitic gneisses are texturally, petrographically and geochronologically similar it is argued that they were coeval. The generally I- to S-type metaluminous to peraluminous nature of all of the granitic gneisses, along with previously published depleted mantle (T-DM) Sm-Nd model ages of between similar to 2.42 and similar to 2.05 Ga, suggests derivation by partial melting of pre-existing similar to 2.0 Ga crust at similar to 1.2 Ga in a continental collision tectonic setting.
机译：南非纳马夸省的布什曼兰中部地区位于阿格尼尼斯地区的三套庞大的花岗岩片麻岩之下，分别称为Achab，Hoogoor和Aroams片麻岩，这是世界一流的主要破碎山型Pb-Zn-铜银沉积物。在地球化学上，花岗岩片麻岩具有相似的特征，但存在的分馏程度仅有微小差异。片麻岩的基巴兰岩浆锆石占主导地位，与1.21相似，与1.17 Ga年龄相似，这与西部纳马夸兰Okiep地区的类似构造-岩浆事件和纳塔尔省纳塔尔省类似的老花岗片麻岩密切相关。纳马夸-纳塔尔带。在此期间，Aggeneys区经历了与峰D-2变形相关的峰级M-2闪石岩相变质。这一时期的特点是整个带大陆性碰撞和增生。 140 m.y.之后在构造静止期，在西纳马夸兰的奥基普地区发现的低Th / U变质过度生长的U-Pb年龄中记录到一个离散的构造岩浆事件，其年龄约为1.04至1.01 Ga Namaquan造山运动年龄。然而，与Namaqualand和Natal不同，Aggeneys区目前没有受到广泛的岩浆作用，并且变质条件没有达到像Namaqualand一样的粒岩相等级。碰撞后到碰撞后的所有短时间内都包含了所有的花岗岩片麻岩。由于花岗片麻岩在质地，岩石学和年代学上相似，因此认为它们是同时代的。所有花岗片麻岩的一般为I型到S型，从金属性到高铝质，再加上以前发表的贫化地幔（T-DM）Sm-Nd模型年龄介于2.42和2.05 Ga之间，表明部分衍生在大陆碰撞构造环境中，类似2.0 Ga的地壳早已融化，类似于1.2 Ga的地壳融化。

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