Brazilian Twins Research Articles

The role of sedimentary and tectonic brines in the Damara Orogen, Namibia

Along the southern margin of the Upper Proterozoic Damara Orogen, Namibia, an accumulation of extraordinarily large megacrystalline quartz-dolomite bodies occur. They were emplaced in tectonically controlled positions during an early deformational phase of the Damara Orogeny, where hot nappes were thrust over a fluvial-lacustrine and evaporitic metaplaya sequence (Kamtsas and Duruchaus Formations) which was deposited on the faulted EW-trending continental margin of the Kalahari craton. Individual occurrences of the quartz-dolomite bodies often cover several hundred square meters. Characteristic for the quartz-dolomite bodies is zoning with an outer shell of giant milky quartz crystals, some more than 15 m long along the c-axis, tightly intergrown or twinned (Brazilian twins) with a perfect cleavage parallel to the positive rhombohedral faces {1011}; there is an inner shell of crystalline dolomite and a central pipe of dolomitic breccia. Based on fluid inclusions studies the formation fluids of quartz-dolomite bodies can be related to the mobilization of interstitial fluids and to dehydration and leaching of evaporitic hydrate minerals of the metaplaya sequence. The fluids are characterized by extremely high salinities of up to 68 wt % total salt content. Minimum temperatures of formation, as determined in fluid inclusion studies, ranged from 150 to 250°C. At a later stage CO 2 derived from decarbonatization reactions was dissolved in the fluids. Changes in pressure and temperature led to effervescence and the formation of a quartz stockwork in the surrounding country rock. During the main phase of the progressive Damara Orogeny, the southward advancing accretionary nappe pile of the Khomas trough drove ahead large amounts of tectonometamorphic fluids, characterized by intermediate salinity and high CO 2 contents. When these fluids met with the previously established hypersaline fluid system, large amounts of CO 2 were released due to the mixing of the two fluids; if there is no mixing, each fluid then maintains its salinity and there is no CO 2 degassing. The CO 2 from this mixing is now present as secondary, high-density inclusions not only in the quartz-dolomite bodies but also in the surrounding country rock. Pressure estimations indicate at least 100–600 MPa as a minimum pressure of formation for these inclusions. The remaining aqueous fluid phase has produced local alterations and Cu, Pb, and Au mineralization.

Genetic and environmental determinants of 17 serum biochemical traits in Brazilian twins.

The genetic and environmental effects on the levels of 17 serum biochemical quantitative traits (calcium, phosphorus, glucose, urea nitrogen, uric acid, total protein, albumin, total bilirubin, alkaline phosphatase, lactate dehydrogenase (LDH), glutamic-oxaloacetic transaminase (SGOT), total lipid, cholesterol, triglyceride, alpha-lipoprotein, pre-beta-lipoprotein and beta-lipoprotein) were estimated in 105 pairs of healthy twins of both sexes (57 MZ and 48 DZ) by path analysis. The genotype effect h2 was significant for all traits (P less than 0.001) and its value extended from 0.52 (alpha-lipoprotein) to 0.81 (alkaline phosphatase), whereas environmental effect b2 was significant (P less than 0.05) in only 10 traits of the 17 analyzed, with the maximum value of 0.13 (cholesterol). Correlations between genotypes of paired traits were estimated and, of 136 values, 47 were significant at the 5% levels, thus indicating partial and common genetic mechanisms.

Estimates of the Genetical and Environmental Determinants of Serum Lipid and Lipoprotein Concentrations in Brazilian Twins

Genetic and environmental effects were estimated for six serum lipid and lipoprotein variables (total lipids, cholesterol, triglyceride, and lipoproteins Β, pre- Β and Α) in 105 Brazili

Path analysis of aptitude, personality, and achievement scores in Brazilian twins.

Achievement at school and performance on the Dominoes test, the Differential Aptitude Tests (DAT), and Griéger's Characterological Questionnaire of 45 monozygotic and 46 same-sex dizygotic pairs of twins were analyzed using a new linear model for familial corrrelation. For 14 of the 20 sets of data, the genotype's contribution to the total variance is estimated to be higher than 50%. The effect of common environment seems to be important only for achievement in Arts.

School achievement, intelligence, and personality in twins.

A sample of 47 MZ and 49 DZ pairs of Brazilian twins was investigated in relation to school achievement in six specific areas of study, as well as performance in the test of Dominoes, the Differential Aptitude Tests (DAT) and Grieger's Characterological Qur the school grades obtained in five of the six areas considered, as well as for their general average; the same being true for the results on the indicated measure of general intelligence, six of the eight DAT tests, and two of the characterological elements. There is a clear positive relationship between the grades earned by the twins and their performance in the Dominoes test. Achievement in Portuguese and foreign language correlates positively with DAT's Numerical Ability, Abstract Reasoning, and Clerical Speed and Accuracy. The results show an agreement with previous estimates of the genetic determination of these variables, which is to a certain extenet surprising if we consider the differences in sample sizes, age, and degree of schooling of the subjects, environmental differences, and the dissimilarities which exist between the homes and school systems of USA, Europe, and Brazil.