Pan-African pressure-temperature evolution of the Merelani area in the Mozambique Belt in northeast Tanzania
详细信息 查看全文
- 作者：S. Muhongo ; P. Tuisku ; Y. Mtoni
- 关键词：Landmines ; Mineral exploration industry ; Metal detection
- 刊名：Journal of African Earth Sciences
- 出版年：1999
- 出版时间：August 1999
- 年：1999
- 卷：29
- 期：2
- 页码：353-365
- 全文大小：1220 K
文摘
The bedrock of the Merelani area in the Mozambique Belt in northeast Tanzania was multiply deformed and metamorphosed in Pan-African (Neoproterozoic) times. The first metamorphic event took place at the granulite grade and later the rocks suffered retrogression during isobaric cooling (IBC) at the amphibolite grade. Thermobarometric data from the Merelani gneisses indicate temperatures in the range 670–610°C and pressures of 6.5–6.0 kbar. Isobaric cooling is exemplified by late, post-tectonic growth of kyanite porphyroblasts at the expense of sillimanite in graphitic paragneisses as well as by garnet zoning in the same rock. Further retrogression was due to hydration along shear zones and faults. This led to the alteration of forsterite, enstatite and pargasite into serpentine minerals. Crystallisation of vanadiferous zoisite (tanzanite) in hydrothermally altered rocks took place at this late stage when XH2O = 0.5 in calcsilicate rocks.
These findinds, combined with the textural and thermobarometric data from the Uluguru Mountains and the Furua area, suggest that the IBC P-T path was prominent in the metamorphic evolution(s) of the Pan-African Mozambique Belt rocks in Tanzania. This was most probably caused by addition of igneous rocks (underplating) at the initial stage of the formation of the granulite-facies rocks in the belt: followed by their residence and coolingin the middle and upper crustal levels. The slight decompression during this stage could be explained by either extensional or transtensional deformation. Finally, the Merelani rocks, like those in the Uluguru Mountains, were rapidly exhumed.