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S D and S 0 for rocks and associated water are compared between Dalradifin metamorphic, younger basic and granitic dioritic rocks. These are largely distinguishable. Waters calculated to have been in equilibrium with granitic-dioritic rocks are similar in composition, and possibly related, to those of late igneous biotites and secondary (uralite) amphiboles of the basic masses However, primary hornblendes have normal, magmatic D which appear to have been preserved through secondary adjustments of S Dvalues. The fluids associated with the Insch and DJ Oui DG Haddo House-Arnage basic masses are mostly isotopically distinct from those of the thermal aureolesc Insch biotite waters could result from mixing, in nearly equal proportions, of igneous and met am orphic fluids. On the primary hornblende S D values hinges the hypothesis that the present Dalradian metasedinentary country rocks have not contributed to the 18 Oenrichraent, which paralleled the previously reported 87Sr-enrichment by an isotopic exchange mechanism (Pankhurst, 1969) c This could have occurred by means of an almost pure CC>2 fluid, resulting from decarbonation of postulated roof-zone calcareous sediments Alternatively, isotopic exchange may have occurred at a lower structural level than at present with subsequent tectonic emplacement of the solid, or nearly solid., mass whilst it was still sufficiently hot to energise formation of wide thermal aureoles in the metasedimentsJ (these were still relatively hot following the regional metamorphic climax). Serpentinisation most likely resulted from low temperature hydration of peridotites by meteoric water as has been generally observed elsexvhere. Most of the Aberdeenshire Newer granitic-dioritic rocks exhibit correlation between 8 0iro and a cation index. VVK This was empirically modified from that proposed by Garlick (1966) which, coincidentally, is formulated in the same manner; (SiO, 58Al) 10 cation. (Garlick employed mono-oxygen cation equivalents thus Si and A1 referred to SiO Fe and Al3O contents rather than the simple cation content. Tie cation index relates well metamorphic mineral oxygen isotopic fractionations and chemical compositions and can be used to examine isotopic equilibriation of associated samples where bulk % 0 and chemical data are available* From these estimates the range of composition of the associated 18 waters are made in the absence of S 0n data. The mineral oxygen isotope data support the concept that all the Caledonian granites probably derived from a common crustal source region of age greater than the Dalradian country rocks (Bell, 1968; Pankhurst, 197. ). Only small granitic bodies, veins and sills did not follow the correlation between % 0 and cation index which may or may not reflect different origins for this material. All larger units of graixitic-dioritic rocks of Aberdeenshire} as mapped by Walsworth-Bell (1971), appear related in origin. These were probably not products of melting of Dalradian rocks but derived from a common source. This conflicts with the interpretation of Walsworth-Bell (1971) as to the origin of foliated, muscovite-bearing granites. Some of the regional metamorphic rocks have suffered from retrogressive isotopic adjustments making oxygen isotopic thermometry impossible for more than hair of the samples. The internally consistent set of oxygen isotopic mineral fractionation expressions, based on theory, experiments and inferences from natural assemblages, as proposed by Bottinga and Javoy (1973, 1975) are adopted. The few presented data, together with those published by other workers (also a small .proportion of the total number of samples analysed) where there is evidence of a faithfully preserved memory of a high temperature equilibrium state, are interpreted in relation to the aluminosilicate polymorphic inversion, and garnet-formation reactions. |
