Latest precambrian (Cadomian) zircon ages, Nd isotopic systematics and P-T evolution of granitoid orthogneisses of the Erzgebirge, Saxony and Czech Republic

Single zircons from two orthogneiss complexes, the Grey Gneiss and Red Gneiss, the lowermost tectonic units in the Erzgebirge, were dated. The grey Freiberg Gneiss is of igneous origin and has a ²⁰⁷Pb/²⁰⁶Pb emplacement age of 550±7 Ma. A quartz monzonite from Lauenstein contains idiomorphic zircons with a mean ²⁰⁷Pb/²⁰⁶Pb age of 555±7 Ma as well as xenocrysts ranging in age between 850 and 1910 Ma. Red gneisses from the central Erzgebirge contain complex zircon populations, including numerous xenocrysts up to 2464 Ma in age. The youngest, idiomorphic, zircons in all samples yielded uniform ²⁰⁷Pb/²⁰⁶Pb ages between 550±9 and 554±10 Ma. Nd isotopic data support the interpretation of crustal anatexis for the origin of both units. _Nd(t) values for the grey gneisses are –7.5 and –6.0 respectively, (mean crustal residence ages of 1.7–1.8 Ga). The red gneisses have a wider range in _Nd(t) values from –7.7 to –2.8 (T _DM ages of 1.4–1.8 Ga). The zircon ages document a distinct late Proterozoic phase of granitoid magmatism, similar in age to granitoids in the Lusatian block farther north-east. However, Palaeozoic deformation as well as medium pressure metamorphism ( 8 kbar/600–650° C) are identical in both gneiss units and distinguish these rocks from the Lusatian granitoids. The grey and red gneisses were overthrust by units with abundant high-pressure relicts and a contrasting P-T evolution. Zircon xenocryst and Nd model ages in the range 1000–1700 Ma are similar to those in granitoid rocks of Lusatia and the West-Sudetes, and document a pre-Cadomian basement in parts of east-central Europe that, chronologically, has similarities with the Sveconorwegian domain in the Baltic Shield.     

Attitudes to prenatal screening,diagnosis and research among pregnant women who accept or decline an alpha-fetoprotein test

The aim of the study was to describe the opinion of pregnant women who had accepted or declined an alpha-fetoprotein (AFP) test, not only on AFP screening in general, but also on whether every pregnant woman should be offered amniocentesis (AC)/chorionic villus sampling (CVS) and an ultrasound scan for fetal malformations. An additional aim was to describe pregnant women's attitudes concerning continued research in the prenatal field. The study was performed as a questionnaire study in two regions over a 1-year period from 1 October 1988 to 30 September 1989. Results are based on answers from 3331 women who had taken an AFP test and 336 women who had declined the offer of a test. A total of 79 per cent of the women thought that an AFP test, 70 per cent that an ultrasound scan for fetal malformations, and 26 per cent that AC or CVS should be offered to all pregnant women. Fifty-nine per cent of the women were positive towards continued research in the prenatal field. Women who had had an AFP test were generally much more positive towards screening and research than women who had declined, who were generally against. Women who had left school without a high school degree were on average more positive towards the screening issues than women who had this degree. In conclusion, the results obtained in this study strongly suggest that women's attitudes are very dependent on how the prenatal screening programme is already organized in their local area.