赞比亚东北部班韦乌卢地块泛非期以来构造演化的裂变径迹约束

Constraints of fission track dating after the Pan-African tectonic evolution of the Bangweulu Block,northeastern Zambia

本文利用锆石和磷灰石裂变径迹方法探讨了班韦乌卢地块泛非期以来的主要构造演化时间。为研究班韦乌卢地块的构造活动,本文从班韦乌卢地块中部卡帕图地区的沉积盖层姆波罗科索群的姆巴拉组、萨马组和卡布韦卢马组中采集多件新鲜的岩石样品,并获得5件锆石和2件磷灰石样品裂变径迹分析结果。5件锆石裂变径迹年龄介于575±35~380±22 Ma之间,其峰值年龄组为600~572 Ma和420~390 Ma。2件磷灰石裂变径迹年龄介于59±6~27±4 Ma之间,其峰值年龄组为99~80 Ma和19~11 Ma。它们的峰值年龄组分别对应的主要时代为新元古代的埃迪卡拉纪、早泥盆世、晚白垩世和中新世。对比区域上已有的年龄数据可知,南部非洲地区新元古代的埃迪卡拉纪、早泥盆世和晚白垩世的构造活动是一个区域性的构造事件,仅中新世(19~11 Ma)的构造活动在区域上的表现尚不明确。综合前人成果资料,自泛非构造运动以来,班韦乌卢地块至少经历600~572 Ma、488~441 Ma、420~390 Ma、375~293 Ma、99~80 Ma及19~11 Ma六个构造事件。班韦乌卢地块泛非期以来的构造演化研究程度很低,此次研究成果可为今后在该地区的深入研究提供重要参考。

The main tectonic evolution times of the Bangweulu Block since the Pan-African tectonic activities were studied in this paper using the zircon and apatite fission track methods.The Kapatu is located in the center part of the Bangweulu Block,northeastern Zambia.In order to study the tectonic activities of the Bangweulu Block,fresh rock samples from Mbala,Nsama and Kabweluma Formations of the Mporokoso Group were collected in Kapatu.The five zircon fission track ages are between 575±35 Ma and 380±22 Ma and the ages may be divided into two groups,i.e.600~572 Ma and 420~390 Ma.The two apatite fission track ages are between 59±6 Ma and 27±4 Ma and the ages can be divided into two groups,i.e.99~80 Ma and 19~11 Ma.All four ages groups which respectively correspond to the main periods of the Neoproterozoic Ediacaran,Lower Devonian,Late Cretaceous and Miocene.Compared with the ages from southern Africa,the tectonic activities of Neoproterozoic Ediacaran,Lower Devonian,Late Cretaceous involve a wide area and the tectonic activity during the Miocene(19~11 Ma)is not yet clear.Since the Pan-African tectonic evolution,the Bangweulu Block at least has been affected in 600~572 Ma,488~441 Ma,420~390 Ma,375~293 Ma,99~80 Ma and 19~11 Ma.Since limited data after the Pan-African tectonic evolution of the Bangweulu Block are available,these results provide important information for future work.