The late Carboniferous quartz dolerite suite of Scotland consists mainly of quartz tholeiites, with subordinate olivine tholeiites and tholeiitic andesites. The low pressure evolution of the magmas was controlled by fractionation of olivine–plagioclase–pyroxene–oxides assemblages from more magnesian compositions and plagioclase–pyroxene–oxides–apatite removal from intermediate compositions. A higher pressure stage dominated by olivine fractionation is suggested by the presence of olivine nodules in a magnesian basalt dyke from Fife.The suite is of high-Fe-Ti type, closely comparable to certain basalts erupted in areas of active lithospheric spreading or “hot spots”, such as Iceland and Hawaii. The ppO2 can be inferred to have been rather higher in the Scottish rocks than in comparative suites, promoting earlier separation of Fe-Ti oxides, with the consequent effects on trace element distribution.Apart from varying degrees of fractionation, chemical variations in the dykes are of three types: rather minor variations along individual dykes, variations across certain thicker dykes, and minor and trace element variations reflecting chemical heterogeneities in the mantle sources. The dykes and sills are inferred to have been fed from a plexus of small, partly independent, magma reservoirs.New trace element data on tholeiitic lavas from the Oslo Rift confirm recently revived suggestions that the Scottish and northern English quartz dolerites are part of a larger province extending into Scandinavia.
The combined water (H2O+) in 30 geochemical standards having known and unknown water contents was determined by an elemental analyzer on 1 day during each of 6 weeks over a period of several months. The analysis of variance of the data measured in the form of a Youden square shows an extremely significant variation due to some unknown cause during the weeks in which the data were obtained. The higher water contents of the first two sets were obtained in the fall season when this area (Reston, Va.) has high and variable humidity, whereas the last four sets were measured during winter months. Humidity, however, was not included as a variable in the design and was not measured.
The first two of three average blanks for H2O+, measured after determining H2O+ contents of about 11 percent for two samples, are noticeably higher than the third average blank. Similarly, the first of two average blanks for H2O+, measured after determining the H2O+ content (4.70 percent) of PCC‐1, is higher than the second. Data for the last 4 weeks were used to calculate the line of regression and the extremely significant correlation coefficient. The line is used to predict suggested revisions of the “best” H2O+ contents of the standards.
Coefficients of variation calculated from the data for the last 4 weeks indicate that there is no severe sampling problem due to the small sample size (20 mg) taken for the determinations. The coefficients follow the general trend of large coefficients for samples containing the least amount of the constituent (BHVO‐1: x̄= 11.76% H2O+; C.V. = 7.3%) and of small coefficients for samples containing the greatest amount (BX‐N: x̄= 11.76% H2O+; C.V. = 0.4%).
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