坦桑尼亚乌本迪活动带西北部元古宙沉积盆地碎屑锆石U-Pb年龄及其地质意义

U-Pb Age of detrital Ziron and its geological significance in the Proterozoic sediments basin in the northwestern Ubendian belt of Tanzania

坦桑尼亚西北部卡拉戈维-安科连活动带和玛拉嘎拉西台地发育一系列元古宙沉积盆地,由于沉积岩性和变质程度相近,地层层序的界定存在争议。本文通过对原划分的卡盖拉超群和玛拉嘎拉西超群乌哈群上部马攸攸组碎屑锆石铀铅年龄的测试,获得了坦桑尼亚西北部基戈马附近中元古代沉积盆地碎屑锆石207Pb/206Pb年龄集中分布于1 276~1 562 Ma、1 735~2 156 Ma和2 505~2 836 Ma三个年龄区间;坦桑尼亚西北部基戈马附近玛拉嘎拉西台地乌哈群上部马攸攸组碎屑锆石207Pb/206Pb年龄集中分布于735~1 400 Ma、1 793~2 094 Ma和2 554~2 934 Ma三个年龄区间;坦桑尼亚西北部卡雷马附近玛拉嘎拉西台地乌哈群上部的马攸攸组两个样品碎屑锆石U-Pb不一致线上交点年龄分别为2 654±29 Ma和2 671±13 Ma。结合已有的地质资料可以推断坦桑尼亚西北部基戈马附近中元古代沉积盆地沉积时代不早于1 400 Ma;坦桑尼亚西北部基戈马附近玛拉嘎拉西台地乌哈群上部马攸攸组沉积时代不早于735 Ma;坦桑尼亚西北部卡雷马附近乌哈群上部的马攸攸组与基戈马附近的马攸攸组碎屑成分来源存在明显差异,建议重新划分。

Karagwe-Ankolean active zone and Malagarazi platform in northwestern Tanzania are a series of Proterozoic sedimentary basins developed in the later period of the Ubendian belt. Due to the similarity of sedimentary lithology and metamorphism, the definition of stratigraphic sequence is controversial. In this paper,the U-Pb ages from detrial zircons in the upper part of the Manyouo Formation in the upper Uha group in the Kagala supergroup and the Malagasi supergroup were obtained. The detrital zircon 207Pb/206Pb ages are concentrated in the three peak ranges of 1 276~1 562 Ma, 1 735~2 156 Ma and 2 505~2 836 Ma;the 207Pb/206Pb ages from detrital zircon in the manyouo group in the upper Uha group of the Malagarazi platform near Kigoma in northwestern Tanzania are concentrated in the three peak intervals of 735~1 400 Ma, 1 793~2 094 Ma and 2 554~2 934 Ma;the U-Pb ages from two samples detrital zircon in the manyouo group in the upper part of the Uha group on the Malagarazi platform near Kalimain northwestern Tanzania are 2 654 ± 29 Ma and 2 671± 13 Ma. Based on the available geological data, it can be concluded that the sedimentary age of the Mesoproterozoic sedimentary basin near Kigoma in northwestern Tanzania is not earlier than 1 400 Ma;the sedimentary age of the manyouo group in the upper Uha group of the Malagarazi platform near Kigoma in northwestern Tanzania is not earlier than 735 Ma;The manyouo group in the upper part of the Uha group on the Malagarazi platform near kalimais diffrent with the same group near Kigoma, and re-division is recommended.