Search

Ion probe U-Pb dating of different age domains within detrital zircons, distinguished using cathodoluminescent images, has been applied to three metasedimentary gneiss samples from the Jannelsepan, Copperton and Kenhardt Formations in the Areachap and Kakamas Terranes of the Namaqua-Natal Province. The Areachap Group samples yielded largely coherent ages which are considered to reflect the age of extrusion of the surrounding, volcanic rocks. These are 1275 ± 7 Ma for the Jannelsepan Formation at Boksputs (with a component at -1301 Ma) find 1282 ± 45 Ma for the Copperton Formation at Prieska Copper Mines. Direct dates of volcanic rocks in these formations in the literature are 1241 ± 12 Ma for the Jannelsepan Formation at Upington and 1285 ± 14 Ma for the Copperton Formation. The Kenhardt Formation sample contained three age domains. Concordant zircon cores dated at 1568 ± 23, 1351 ± 24 and 1296 ± 14 Ma reflect the presence of older crustal material in the Kakamas Terrane, whereas another six cores are coeval with the main, oscillatory zoned phase, dated at 1194 ± 7 Ma. This is the age of the magmatic rocks from which this metasedimentary sample was derived. The identity of the Areachap Group as defined in the 1980s has been questioned on the grounds that the Boven Rugseer Shear Zone is a terrane boundary that cuts across the Areachap Group. This work shows that the Jannelsepan and Copperton Formations, which crop out to the north and south of this shear zone, both formed in the interval -1.30 to -1.24 Ga. Published geochemical data show that these formations have a common origin as arc-related volcanosedimentary sequences containing volcanic massive sulphide ore deposits. Furthermore the Pb and sulphur isotopic data point to very similar sources of mineralization in the Areachap Mine (Jannelsepan Fn) and Prieska Copper Mines (Copperton Fn). We conclude that the integrity of the Areachap Group as originally defined rests on very strong evidence. The new data are compatible with a tentative plate tectonic model for the region. The -1.57 Ga Kakamas fragment and the juvenile -1.3 Ga Areachap Arc are envisaged as minor crustal blocks in a major ocean basin bounded by the major Bushmanland continental block and the Kaaien-Kheis-Kaapvaal block. The Wilgenhoutsdrift Group formed at the same time as the Areachap Group in a back-arc or rift setting on the margin of the Kalahari Craton, from which it derived Palaeoproterozoic and Archean sedimentary material. Assembly of fill the terranes by collision following closure of the major ocean basin gave rise to a collision-related cycle of D1-D2 deformation, metamorphic events and migmatisation at different localities between 1194 ± 23 and 1158± 7 Ma. A much later thermal event originating in the mantle affected the whole region at -1.1 Ga, leading to extensive magmatism, D3 deformation and local migmatisation. [ABSTRACT FROM AUTHOR]

T cell-mediated immune responses are thought to play an important role in the pathogenesis of anti-neutrophil cytoplasmic antibody- (ANCA-) associated vasculitides (AAV). CD4 + T cells can be divided into subsets depending on their expression of chemokine receptors. In this study, different CD4 + T cell populations in patients with AAV were analysed and compared to healthy blood donors as well as therapy controls. 18 patients with active AAV, 46 in remission, 21 healthy controls (HBD), and 15 therapy controls (TC) were enrolled. CD4 + T cells were divided into Th1, Th2, and Th17 cells and further subdivided into naïve, central memory, effector memory, and effector cells. Regulatory T cells were also analysed. Concentrations of cytokines and chemokines produced by the respective CD4 + T cell subset in plasma from 33 of the patients were measured by ELISA and compared to HBD. Clinical data were collected on all patients. CCL20 concentrations and percentages of Th17 cells ( p = 0.019) were elevated in AAV patients compared to HBD. AAV patients had lower percentages of naïve CD4 + T cells ( p = 0.0016) and a corresponding increase in proportion of effector memory CD4 + T cells when comparing to HBD ( p = 0.027). Therapy controls showed similar results as AAV patients. In this study, we found that CD4 + T cell phenotype distribution is altered in AAV patients, in line with previously published work. However, no differences were found between AAV patients and TC, stressing the importance of treatment impact on this kind of studies.