Chewore Inliers

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The Chewore Inliers ( German  "Chewore enclaves" ) are island-like outcrops of the Young Neoproterpozoic ( pan-African ) deformed Zambezi Belt in the border triangle Zambia - Zimbabwe - Mozambique, surrounded by Phanerozoic sediments of the Zambezi Trench .

In the Chewore inliers , pre-neoproterozoic deformed crustal areas open up, which were only weakly influenced by the folding of the Zambezi Belt. They are therefore of particular importance for understanding the Precambrian geology of the region.

Geographical location

Chewore Mountains
Location of the Zambezi Basin in southern Africa
Position of the Chewore Mountains (marked in red) in the Zambezi river basin

The Chewore Inliers extend over an area of ​​approx. 2000 km², the northern half of which is in the southeast of the Zambian province of Lusaka and the southern half of which is in the Zimbabwean Mashonaland . In contrast to the surrounding unfolded and unmetamorphic sediments of the Zambezi Trench, the crystalline of the Inliers forms relatively heavily reliefed and significantly higher lying terrain, the Chewore Mountains . These are crossed in a breakthrough valley , the Mupata Gorge , by the Zambezi , which forms the natural border between Zambia and Zimbabwe.

Regional geology

The chewores occupy a central position in the east-west striking Zambezi belt. The rocks of the Inliers represent pan-African reclaimed crust of the older Irumide Belt to the north, which is part of the Mozambique Belt , and archaic gneisses of the northern edge of the Zimbabwe Craton. Due to the expansion of the crust from the Younger Permian to the Cretaceous , the Precambrian basement in the immediate vicinity of the Inliers has been lowered by faults and covered by sediments of the appropriate age. The Inliers therefore form a tectonic eyrie .

Terrans, rocks, metamorphoses

The inliers consist of four terrans (regional crust blocks), granulite , quartzite , Zambezi and ophiolite terran. The terrans are different in their rock properties and each have a uniform metamorphic grade, which, however, differs from the other terran.

The ophiolite terrane is the oldest block at 1393 mya and consists mainly of mafic and ultramafic gneisses , which are interpreted as ophiolite (ocean floor pushed onto the mainland) and island arc sequence. Together with the Kadunguri Whiteschist ( white slate ) group, it represents a geosutur (contact zone between earth plates). This suture arose as a result of the accretion of the sequence with the Congo SF Kraton before or during the Neoproterozoic Pan-African orogen formation.

The remaining terranos are dominated by supracrustal ( exposed on the surface of the earth's crust) gneisses and quartzites of various types, into which granitic orthogneiss units (rocks converted from igneous sources), 1083 and 1071 mya, intruded. They were subject to the same tectonic-thermal events, such as the low-pressure / high-temperature metamorphoses in the so-called M1 phase around 1071 to 1068 and finally 943 mya. As a result, the granulite terran was completely recrystallized during a tectonic transport from south to north.

The other terranes recrystallized during the Pan-African metamorphic M2 cycle penetrating around 526 mya under high / medium temperature influences. These processes were accompanied by a tectonic transport with crust thickening running in a north-east to south-west direction. The granulite terran hardly underwent any deformation during the M2 phase. However, shear zones at the edges of this terran have been completely recrystallized.

The orogenic M2 cycle culminated with the merging and rapid uplift of the terrane (clump formation), resulting in a multitude of post-tectonic intrusions, such as pegmatites , around 480 mya. Ductile (plastic) shear processes occurred between the adjacent terrances.

Pan-African supracrustal rocks are absent in the Chewore Inliers.

literature

Individual evidence

  1. ↑ Ben Goscombe, R. Armstrong, JM Barton: Tectonometamorphic Evolution of the Chewore Inliers: Partial Re-equilibration of High-grade Basement during the Pan-African Orogeny . In: Journal of Petrology . tape 39 , no. 7 , 1998, pp. 1347-1384 , doi : 10.1093 / petroj / 39.7.1347 ( oxfordjournals.org [PDF]).
  2. ↑ Karl Hiller, Burkhard Buttkus: Structural style and sedimentary thicknesses in the Zambezi Rift Valley, Zimbabwe - investigation of the potential for hydrocarbons . In: Journal of Applied Geology . tape 42 , 1996, pp. 132-137 .
  3. ↑ Geoffrey Howard, Guy Broucke: Mission Report Reactive Monitoring Mission Mana Pools, Sapi and Chewore Safari Areas (Zimbabwe) 9-15 January 2011. UNESCO, 2011 ( PDF 1.4 MB)
  4. ↑ SP Johnson, GJH Oliver: High f O 2 Metasomatism During Whiteschist Metamorphism, Zambezi Belt, Northern Zimbabwe . In: Journal of Petrology . tape 43 , no. 2 , February 2002, p. 271-290 , doi : 10.1093 / petrology / 43.2.271 ( oxfordjournals.org [PDF]).