赞比亚班韦乌卢变质克拉通东北部姆巴拉组碎屑锆石U-Pb年龄和Hf同位素特征

Detrital zircon U-Pb ages and Hf isotopic characteristics of the Mbala Formation in the northeast Bangweulu Metacraton, Zambia

关键词:  班韦乌卢变质克拉通  伊鲁米德构造带  卢费里安构造带  碎屑锆石  古元古代  赞比亚

Key words:  Bangweulu Metacraton  Irumide belt  Lufilian belt  detrital zircon  Paleoproterozoic  Zambia

摘要:

班韦乌卢变质克拉通活动时间和地壳增长问题一直是地质学家关注的焦点。本文通过对班韦乌卢地块中卡帕图地区姆波罗科索群姆巴拉组石英砂岩进行了碎屑锆石U-Pb年代学和Hf同位素研究，结合变质克拉通已有成果获得认识如下：(1)姆巴拉组的形成时间可能介于(1833±22 Ma)～(1712±22 Ma)之间，属于古元古代。(2)姆巴拉组具有丰富的物质来源，其中2728～2602 Ma(峰值为2650 Ma)的物质可能来源于坦桑尼亚克拉通中的花岗岩类、粗面安山岩及流纹岩等岩石。2246～1833 Ma(峰值为1880 Ma)的物质主要来源于班韦乌卢地块中花岗岩类、石英闪长岩及火山岩类等岩石。(3)班韦乌卢变质克拉通的活动时间包括中太古代、新太古代、古元古代和中元古代四个时期，其中古元古代(1870 Ma)为活动的高峰期，涉及范围广泛，可能与哥伦比亚超大陆的演化密切相关。(4)班韦乌卢变质克拉通沉积岩的源区地壳增生除来自古老地壳的再循环物质外，还存在新生地壳的物质。同时，地壳在古太古代-古元古代均实现了增长，其中凯诺兰超大陆聚合时期(2550 Ma)增长最快。在古元古代之前的地壳主增长期与坦桑尼亚克拉通及全球大陆地壳主增长期基本一致。

Abstract:

The activity time and crustal growth of Bangweulu Metacraton have always been the focus of geologists. This paper studied the detrital zircon U-Pb ages and Hf isotopic characteristics of quartz sandstone from the Mbala Formation in Kapatu area. Based on the previous results of Bangweulu Metacraton, the paper has obtained the following understanding: (1) The Mbala Formation might formed between (1833±22 Ma) and (1712±22 Ma), belonging to the Paleoproterozoic. (2) The Mbala Formation is rich in material sources, among which the material of 2728 ~ 2602 Ma (peak age is 2650 Ma) may be derived from granitoids, trachyandesite, rhyolite and other rocks in Tanzania Craton. The material of 2246~1833 Ma (peak age is 1880 Ma) is mainly derived from granitoids, quartz diorite, volcanic rocks and other rocks in the Bangweulu Block. (3) The activity time of the Bangweulu Metacraton includes Middle Archean, Neoarchean, Paleoproterozoic and Mesoproterozoic. The Paleoproterozoic (1870 Ma) was the peak of the activity, which may be closely related to the evolution of the Columbia Supercontinent. (4) In addition to the recycled materials from the ancient crust, the crust accretion in the source area of the Bangweulu Metacraton sedimentary rocks also contains new crust materials. The crust has achieved growth from Paleoarchean to Paleoproterozoic, with the fastest growth in Kenorland Supercontinent convergence (Neoarchean 2550 Ma). Before Paleoproterozoic, the main growth period of the Bangweulu Metacraton is basically the same as the Tanzania Craton and the global continental crust.