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首页> 外文期刊>Journal of African earth sciences >Age of ferroan A-type post-tectonic granitoids of the southern part of the Keimoes Suite, Northern Cape Province, South Africa
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Age of ferroan A-type post-tectonic granitoids of the southern part of the Keimoes Suite, Northern Cape Province, South Africa

机译：南非北开普省Keimoes套房南部南部的亚铁A型后构造花岗岩时代

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摘要

The granitoids of the Keimoes Suite represent part of a complex group of late Mesoproterozoic intrusions of granodioritic to potassic granite composition that occupy an outcrop belt striking approximately NW-SE to the immediate west of Upington, Northern Cape Province, South Africa. The intrusions are believed to mark the contact between the Kaapvaal Craton and the Namaqua Sector of the Namaqua-Natal Province. Published geological, geochemical and geochronological knowledge of the Keimoes Suite is poor in general, with most data restricted to the central portion of the outcrop belt. In this contribution new ages and geochemical data for three granitoids of the southeastern Keimoes Suite in the Putsonderwater - Van Wykspan area, the Klip Koppies, Gemsbokbult and a member of the Kleinbegin Subsuite, are presented. All three intrusions show petrological and geochemical characteristics that agree well with literature data for the central and northern outcrop portions of the Keimoes Suite. They are weakly foliated to unfo-liated, medium- to coarse-grained ferroan, alkali-calcic late- to post-tectonic A-type biotite granitoids intruded within a collisional within-plate tectonic setting. Zircon U-Pb SHRIMP ages for the intrusion of the three granitoids are within error of one another at ca. 1100 Ma. Marked differences between the three granitoids include the abundance and age of inherited zircons and Sm-Nd isotope systematics. With an ε_(Nd(t)) value of 1.83, the Gemsbokbult Granite is dominantly sourced from partial melting of material with a mantle derivation with a minor crustal component. The other two intrusions, on the other hand, show a strong crustal source component, as indicated by ε_(Nd(t)) values of -2.03 for the Klip Koppies Granite and -8.46 for the Kleinbegin Granite. The Keimoes Suite granitoids provide important clues as to the timing and tectonic evolution of the western margin of the Kaapvaal Craton at its junction with the Proterozoic Namaqua Sector of the Namaqua-Natal Province. A contribution to these melts from the host rocks, the ～1.24-1.30 Ga Areachap Group volcanic belt is traced through the presence of inherited zircon cores of this age that is particularly evident in the Klip Koppies Granite. Inheritance also reflects the major tectono-magmatic events which affected the western margin of the Kaapvaal Craton during Mesoproterozoic times, with the bulk of the inheritance in the zircon populations due to peak metamorphism and partial melting caused by continental collision between the Kaapvaal Craton and the Kakamas Terrane and Bushmanland Subprovince to the west at approximately 1.18-1.2 Ga. Post 1.1 Ga ages reflect isotopic disturbance due to a later collisional event to the west at ～1.08 Ga and subsequent exhumation of the western margin of the Kaapvaal Craton.
机译：Keimoes Suite的花岗岩代表了晚中生代侵入的花岗闪长岩到钾质花岗岩组成的复杂群的一部分，这些群占据了一条露头带，该露头带撞击约NW-SE到南非北开普省Upington的西面。入侵被认为标志着Kaapvaal Craton与Namaqua-Natal省的Namaqua地区之间的接触。通常，有关Keimoes套件的地质，地球化学和地质年代学知识很少，大多数数据仅限于露头带的中心部分。在这项贡献中，介绍了Putsonderwater-Van Wykspan地区东南的Keimoes Suite的三种花岗岩的新时代和地球化学数据，Klip Koppies，Gemsbokbult和Kleinbegin套房的一名成员。这三个侵入岩都显示出岩石学和地球化学特征，与Keimoes套件中部和北部露头部分的文献资料非常吻合。它们被弱叶化为侵入板内构造环境中侵入的未成叶的，中粒度至粗粒度的亚铁，碱钙的晚至构造后的A型黑云母花岗岩。三种花岗岩侵入的锆石U-Pb SHRIMP年龄彼此之间的误差大约为1。 1100毫安。三种花岗岩之间的显着差异包括遗传锆石和Sm-Nd同位素系统学的丰度和年龄。 Gemsbokbult花岗岩的ε_（Nd（t））值为1.83，主要来自部分熔融的材料，地幔衍生的地壳成分较小。另一方面，另外两个侵入显示出强大的地壳源分量，如Klip Koppies花岗岩的ε_（Nd（t））值为-2.03，Kleinbegin花岗岩的为_8.46。 Keimoes Suite花岗岩类提供了有关Kaapvaal Craton西边缘与纳马夸-纳塔尔省元古代纳马夸地区交界处的时间和构造演化的重要线索。 〜1.24-1.30 Ga Areachap Group火山带对这些融化的贡献来自于该年龄的遗留锆石核，这在Klip Koppies花岗岩中尤为明显。继承也反映了在中元古代时期影响卡普瓦勒克拉通西部边缘的主要构造岩浆事件，锆石种群的大部分遗传归因于卡普瓦瓦尔克拉通和卡卡马斯之间的大陆碰撞而导致的高峰变质和部分融化。 Terrane和Bushmanland省次于西约1.18-1.2 Ga。1.1 Ga时代反映了同位素扰动，这是由于后来在〜1.08 Ga发生了向西的碰撞事件，并随后挖掘了Kaapvaal Craton的西缘。

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