Single-zircon geochronology and Nd isotopic systematics of Proterozoic high-grade rocks from the Mozambique belt of southern Tanzania (Masasi area): implications for Gondwana assembly

<p>The Mozambique belt of southern Tanzania is underlain by locally restricted 1100–950 Ma (late Kibaran) granitoid gneisses that were derived from remelting of Archaean continental crust, as suggested by Nd isotopic systematics. These rocks were deformed and metamorphosed during an intense Neoproterozoic (Pan-African) event at around 630 Ma together with tectonically interlayered and widespread 800–650 Ma granitoid gneisses and minor clastic metasediments. The 800–650 Ma granitoids were derived predominantly from Neoproterozoic juvenile melts. There is no evidence for pre-800 Ma deformation. The 630 Ma event led to extensive migmatization in all gneisses and caused local melting. Similarities in age and tectonometamorphic evolution between these rocks and similar gneisses in northern Mozambique and southern Malawi suggest a similar geological evolution. However, distinctly different ages for the peak of metamorphism in Tanzania, Malawi and Mozambique indicate diachronous high-grade events that may be associated with terrane accretion and continental collision during orogenesis and favour the view that East Gondwana was not a coherent block during formation of the Gondwana supercontinent. </p

Early Neoproterozoic magmatism (1000-910 Ma) of the Zadinian and Mayumbian Groups ( Bas-Congo): onset of Rodinia rifting at the western edge of the Congo craton

IF=3.736info:eu-repo/semantics/publishe

A new method for dating impact events – Thermal dependency on nanoscale Pb mobility in monazite shock twins

To test the potential of deformation twins to record the age of impact events, micrometre-scale size mechanical twins in shocked monazite grains from three impact structures were analyzed by atom probe tomography (APT). Shocked monazite from Vredefort (South Africa; ∼300 km crater diameter), Araguainha (Brazil; ∼40 km diameter), and Woodleigh (Australia; 60 to 120 km diameter) were studied, all from rocks which experienced pressures of ∼30 GPa or higher, but each with a different post-impact thermal history. The Vredefort sample is a thermally recrystallised foliated felsic gneiss and the Araguainha sample is an impact melt-bearing bedrock. Both Vredefort and Araguainha samples record temperatures > 900 °C, whereas the Woodleigh sample is a paragneiss that experienced lower temperature conditions (350–500 °C). A combined 208Pb/232Th age for common {12¯2¯} twins and shock-specific (1¯01) twins in Vredefort monazite was defined at 1979 ± 150 Ma, consistent with the accepted impact age of ∼2020 Ma. Irrational η1 [1¯1¯0] shock-specific twins in Araguainha monazite yielded a 260 ± 48 Ma age, also consistent with the accepted 250–260 Ma impact age. However, the age of a common (001) twin in Araguainha monazite is 510 ± 87 Ma, the pre-impact age of igneous crystallisation. These results are explained by the occurrence of common (001) twins in tectonic deformation settings, in contrast to the (1¯01) and irrational η1 [1¯1¯0] twins, which have only been documented in shock-deformed rocks. In Woodleigh monazite, APT age data for all monazite twins [(001), (1¯01), newly identified 102°/ twin], and host monazite are within uncertainty at 1048 ± 91 Ma, which is interpreted as a pre-impact age of regional metamorphism. We therefore are able to further constrain the poorly known age of the Woodleigh impact to <1048 ± 91 Ma. These results provide evidence that Pb is expelled from monazite during shock twin formation at high temperature (Vredefort and Araguainha), and also that Pb is not mobilised during twinning at lower temperature (Woodleigh). Our study suggests that twins formed during shock metamorphism have the potential to record the age of the impact event in target rocks that are sufficiently heated during the cratering process

U-Pb and Pb-Pb zircon ages for metamorphic rocks in the Kaoko Belt of Northwestern Namibia : a palaeo- to Mesoproterozoic basement reworked during the Pan-African orogeny

The Kaoko Belt belongs to the Neoproterozoic mobile belt system of western Gondwana, whose geodynamic evolution is assumed to have resulted from collision between the Congo Craton (present Africa) and the Rio de la Plata Craton (present South America). Several magmatic intrusion periods can be distinguished in the coastal area of this belt, based on conventional U-Pb, SHRIMP and Pb-Pb evaporation analyses on zircons. The prevailing igneous rock types are of granitic to tonalitic composition. A Palaeoproterozoic terrain with U-Pb magmatic emplacement ages between similar to2.03 and 1.96 Ga may be correlated with the Eburnian event (similar to1.8 to 2.0 Ga), which is widespread in Africa. Additionally, two distinct magmatic events appear to be significant in the southwestern Congo Craton in late Palaeoproterozoic and Mesoproterozoic times, indicated by magmatic ages around 1.77 Ga and between similar to1.52 and similar to1.45 Ga. These two events have so far not been reported from the Dom Feliciano Belt (southeastern Brazil), which is considered to represent the South American counterpart of the Kaoko Belt. Therefore, a possible link of these two belts prior to the Pan-African orogeny (similar to750 to similar to450 Ma) can neither be confirmed nor rejected on the basis of our data.Emplacement ages for several Pan-African granitoids, obtained by U-Pb and SHRIMP analyses, range from similar to730 to similar to655 Ma. The youngest granitoids, representing the last major magmatic activity in that area, were emplaced at similar to550 Ma during a transpressional regime at peak Pan-African temperatures

Tectonic Subdivision of the Prince Charles Mountains: A Review of Geologic and Isotopic Data

The Prince Charles Mountains have been subject to extensive geological and geophysical investigations by former Soviet, Russian and Australian scientists from the early 1970s. In this paper we summarise, and review available geological and isotopic data, and report results of new isotopic studies (Sm-Nd, Pb-Pb, and U-Pb SHRIMP analyses); field geological data obtained during the PCMEGA 2002/2003 are utilised. The structure of the region is described in terms of four tectonic terranes. Those include Archaean Ruker, Palaeoproterozoic Lambert, Mesoproterozoic Fisher, and Meso- to Neoproterozoic Beaver Terranes. Pan-African activities (granite emplacement and probably tectonics) in the Lambert Terrane are reported. We present a summary of the composition of these terranes, discuss their origin and relationships. We also outline the most striking geological features, and problems, and try to draw attention to those rocks and regional geological features which are important in understanding the composition and evolution of the PCM and might suggest targets for further investigations

Samarium–neodymium isotope map of Western Australia

Isotope maps are used to characterize lithospheric architecture through time, to understand crustal evolution and mineral system distributions, and play an increasingly important role in exploration targeting. These Sm-Nd isotope maps of Western Australia (Fig. 1) are based on whole-rock Sm-Nd data for felsic igneous rocks, which provide a window into the middle and lower continental crust, and are used for isotope mapping. Although mafic to intermediate igneous and sedimentary rocks were not used in constructing the contoured isotope maps, Sm-Nd data for those samples are included with those for felsic igneous rocks in the data table

Geochronology of metasedimentary and igneous rocks in the Lamboo Province, Kimberley region: reassessing collisional geodynamic models

ISBN : 978-1-74168-964-8 / ISSN : 1834-2280U–Pb and Lu–Hf isotope data for detrital zircons from metasedimentary rocks of the Lamboo Province have been used to test collisional and intraplate geodynamic models for the Paleoproterozoic development of the Kimberley region. The 1870–1840 Ma turbiditic metasedimentary rocks deposited across the Western, Central and Eastern Zones of the Lamboo Province have remarkably consistent detrital zircon age signatures, with a dominant 1875–1860 Ma age component and a subsidiary c. 2500 Ma age component. These age components have similar Lu–Hf isotope values across all three zones, consistent with a common source for the sedimentary protoliths. The close similarities in provenance suggest that all three zones of the Lamboo Province developed in a continental intraplate setting prior to the 1837–1808 Ma Halls Creek Orogeny, which has previously been considered to represent a collision between an exotic Kimberley Craton and the proto- North Australian Craton. Comparable provenance signatures of coeval metasedimentary rocks across the broader North Australian Craton suggest that assembly of the main craton elements was complete prior to c. 1885 Ma