0000000000230091
AUTHOR
Holger Sommer
showing 11 related works from this author
Reworking of Archaean and Palaeoproterozoic crust in the Mozambique belt of central Tanzania as documented by SHRIMP zircon geochronology
2005
Abstract New SHRIMP zircon ages for high-grade rocks from the Pan-African Mozambique belt (MB) of central Tanzania document reworking of Archaean–Palaeoproterozoic crust during the formation of this Neoproterozoic collisional orogen. Several gneisses and granulites from the Great Ruaha river area yielded late Archaean emplacement ages of 2575–2680 Ma for their magmatic precursors. Core-rim relationships in some zircons revealed new zircon growth during relatively short episodes of granitoid magmatism. Metamorphic zircons, dated at 1925 Ma, provide new evidence for high-grade metamorphism during formation of the Palaeoproterozoic Usagaran mobile belt. Metamorphic rims around magmatic cores i…
SHRIMP zircon ages for post-Usagaran granitoid and rhyolitic rocks from the Palaeoproterozoic terrain of southwestern Tanzania
2005
We report SHRIMP zircon U-Pb ages for post-Usagaran granitic- to granodioritic intrusives and a rhyolitic agglomerate from the Palaeoproterozoic terrain of southwestern Tanzania. This terrain consists of strongly deformed and metamorphosed rocks ascribed to the ca. 2 Ga Usagaran mobile belt, voluminous post-Usagaran granitoids, and minor supracrustal successions. The southeastern part of this terrain is characterized by the occurrence of little deformed and virtually unmetamorphosed rhyolithic, dacitic and andesitic volcanic rocks which overlie the older Usagaran basement. These rocks extruded between 1820 and 1921 Ma, as documented by SHRIMP zircon ages, which are in good agreement with pr…
Neoproterozoic eclogite- to high-pressure granulite-facies metamorphism in the Mozambique belt of east-central Tanzania: A petrological, geochemical …
2017
Abstract This study investigated Neoproterozoic (Pan-African) eclogite- and high-pressure-granulite (E-HPG) facies rocks from the Mozambique belt of east-central Tanzania, collected close to the town of Ifakara and the adjacent Furua area from different tectonic settings, the Palaeoproterozoic Usagaran and the Neoproterozoic Mozambique belt. The studied rocks are E-HPG facies granite- and diorite-gneisses and a meta-gabbroic rock, which are retrogressed to amphibolite- and greenschist-facies conditions. Four different clockwise P-T paths were constructed. The first P-T path for a granodioritic gneiss displays peak metamorphic conditions at ~ 830 °C and ~ 13.0 kbar. The second P-T path for a…
Ultra-high temperature granulite-facies metamorphic rocks from the Mozambique belt of SW Tanzania
2013
Abstract The metamorphic rocks in the Neoproterozoic (Pan-African) Mozambique belt of southwestern Tanzania, around the town of Songea, can be subdivided into one- and two pyroxene bearing charnockitic gneisses, migmatitic granitoid gneisses and amphibolite-facies metapelites. Lower-grade amphibolite-facies rocks are rare and can be classified as sillimanite- and/or garnet-bearing metapelites. Most of the studied charnockitic gneisses show excellent corona textures with large orthopyroxene grains rimmed by clinopyroxene, followed by quartz and well developed garnet rims due to the reaction Opx + Pl = Grt + Cpx + Qtz that formed during isobaric cooling. These and other charnockitic gneisses …
Isothermal decompression history in the “Western Granulite” terrain, central Tanzania: Evidence from reaction textures and trapped fluids in metapeli…
2008
Abstract The Mozambique Belt (MB) of the East Africa Orogen contains large areas of granulite-facies migmatitic gneisses with Archaean and Palaeoproterozoic protolith ages and that were recycled during the Neoproterozoic Pan-African orogeny. The study area is situated along the Great Ruaha River and within the Mikumi National Park in central Tanzania where migmatitic gneisses and mafic to intermediate granulites are interlayered with Neoproterozoic granulite-facies migmatitic metapelites. Mineral textures suggest isothermal decompression, with the peak mineral assemblage comprising Grt–Bt–Ky–Kfs–Pl–Qtz ± Phn ± Ti-Oxide ± melt and amphibolite-facies retrograde assemblage Grt–Bt–Sil–Ms–Kfs–Pl…
Metamorphic petrology and zircon geochronology of high-grade rocks from the central Mozambique Belt of Tanzania: crustal recycling of Archean and Pal…
2003
New data on the metamorphic petrology and zircon geochronology of high-grade rocks in the central Mozambique Belt (MB) of Tanzania show that this part of the orogen consists of Archean and Palaeoproterozoic material that was structurally reworked during the Pan-African event. The metamorphic rocks are characterized by a clockwise P–T path, followed by strong decompression, and the time of peak granulite facies metamorphism is similar to other granulite terranes in Tanzania. The predominant rock types are mafic to intermediate granulites, migmatites, granitoid orthogneisses and kyanite/sillimanite-bearing metapelites. The meta-granitoid rocks are of calc-alkaline composition, range in age fr…
Archaean and Palaeoproterozoic gneisses reworked during a Neoproterozoic (Pan-African) high-grade event in the Mozambique belt of East Africa: Struct…
2006
Abstract This study presents new zircon ages and Sm–Nd whole-rock isotopic compositions for high-grade gneisses from the Udzungwa Mountain area in the central part of the Mozambique belt, Tanzania. The study area comprises a succession of layered granulite-facies para- and orthogneisses, mostly retrograded to amphibolite-facies. The original intrusive contacts became obscured or severely modified during non-coaxial ductile deformation, and extensive shearing occurred during retrogression. Structures reflecting the early deformational history were mostly obscured when the rocks were transported into the lower crust as documented by severe flattening. Only the fragmented gneisses in the easte…
Igneous petrology, zircon geochronology and geochemistry of multiply emplaced granitoid bodies from the Palaeoproterozoic Usagaran domain in central …
2019
Abstract This study reports igneous petrology, zircon ages and geochemistry for Palaeoproterozoic I-type granitic, granodioritic, Qtz-monzonitic, Qtz-monzodioritic and monzodioritic rocks from the Usagaran domain of southwestern Tanzania. These rocks can be subdivided into three groups according to their age, T-t evolution and geochemistry. The oldest group is made up of amphibolite-facies calcic-alkalic gneisses, ranging in age between ∼1984 and ∼1910 Ma, which have been divided into two subgroups regarding their T-t evolution. The first subgroup shows a constant increase in T, and the second subgroup first shows a decrease in T, followed by an increase in T. The second group consists of a…
SHRIMP ZIRCON AGES AND PETROLOGY OF LOWER CRUSTAL GRANULITE XENOLITHS FROM THE LETSENG-LA-TERAE KIMBERLITE, LESOTHO: FURTHER EVIDENCE FOR A NAMAQUA-N…
2013
Recrystallized zircons extracted from intermediate granulites of the Letseng-la-Terae Diamond Mine in northeastern Lesotho provide evidence that the Tugela Terrane of the Mesoproterozoic high-grade Namaqua-Natal mobile belt may extend ~200 km farther west than previously thought. The rock-forming minerals in the investigated lower crustal granulites contain garnet, clinopyroxene, plagioclase and quartz or garnet, wollastonite, plagioclase and quartz. Calculated values for peak granulite-facies metamorphism are ~13 kbar and ~850°C. Thermal overprint and therein granulite-facies metamorphism occurred during the late Mesoproterozoic and is documented by SHRIMP metamorphic zircon ages of 1018 ±…
Vestiges of the Mesoproterozoic Events in the Neoproterozoic Mozambique Belt: the East African Perspective in the Rodinia Puzzle
2003
Abstract Most of the geological and palaeogeographical models consider the Neoproterozoic supercontinent Gondwana (∼650-550 Ma) as the direct offspring of the disintegrated Mesoproterozoic supercontinent Rodinia (∼1300-750 Ma). One of the main classical sutures along which the dispersing Rodinia fragments were fused into a new supercontinent (Godwana) is identified as the Mozambique belt of East Africa. The calc-alkaline magmatism (∼1200-950 Ma) in northern Mozambique, southern Malawi and southern Tanzania is regarded as the sole evidence for fragmentation of Rodinia, which is traced within this Neoproterozoic orogenic belt. There are no unequivocal Mesoproterozoic (Kibaran) sediments in th…
SHRIMP U–Pb zircon and Sm–Nd garnet ages from the granulite-facies basement of SE Kenya: evidence for Neoproterozoic polycyclic assembly of the Mozam…
2007
The Taita Hills–Galana River region is a key area to demonstrate the polycyclic nature of the Mozambique Belt in SE Kenya. On the basis of petrological and tectonic data, this area is composed of two different granulite-facies terranes, which are separated by the 20–30 km wide Galana Shear Zone. The Taita Hills and adjoining Sagala Hills exhibit a metamorphic overprint at 630–645 Ma, similar to areas in Tanzania. An emplacement age for the magmatic precursor rocks of 850–960 Ma was derived from zircon cores. Sm–Nd garnet–whole-rock analyses give an age of 585 Ma, interpreted as the cooling age after 630–645 Ma metamorphism. Nd crustal residence ages are between 1000 and 1500 Ma. The Galana …