400 square kilometres of eastern Aberdeenshire have been surveyed, using magnetic surveying and shallow level drilling, to supplement outcrop mapping. This has shown the existence of the following metasedimentary series in this area: (a) Migmatitic series - sillimanite/fibrolite and garnet bearing metasediments, often migmatitic and with abundant small granite intrusions. (b) Ellon series - cordierite, garnet, andalusite and sillimanite/ fibrolite metasediments. (c) Collieston series - andalusite and cordierite metasediments. Detailed chemical, mineralogical and petrographical studies of these metasediments have shown that these rocks may have originated in the following manner. An initial episode of regional metamorphism led to the development of cordierite, garnet and andalusite in the metasediments. Compositions considered suitable for the development of cordierite are shown to be present within the metasediments of the Migmatitic Series and it is proposed that the absence of cordierite in these rocks is explicable in terms of the higher pressures which prevailed in the Migmatitic Series during the regional metamorphism. The climax of the regional metamorphism was followed by a local rise in temperature, the sillimanite overprint of Chinner (1966), which brought the rocks in the Ellon and Migmatitic Series into the sillimanite/fibrolite stability field, and in addition produced anatexis in the Mignatitic Series. The rocks of the Collieston Series were unaffected by this later, essentially thermal event. The boundaries between the different series are considered to be metamorphic, there being no evidence of a structural break. Following the climax of metamorphism but, before the final episode of metamorphism and folding, basic magma was emplaced to produce a large complex intrusion, previously considered to consist of two separate masses, at Arnage and Haddo House. The magnetic and drilling surveys have greatly modified the pre-existing boundaries of this Arnage/Haddo basic intrusion. In particular, this mass is found to extend as a one kilometre wide zone, seven kilometres south from the previously known limits. The basic rocks consist of cumulates, norites and diorites. The intrusion is bounded by an aureole with cordierite and sillimanite in the metasediments in the inner aureole and cordierite and andalusite in the outer aureole. Chemical and structural evidence indicates considerable differences between the Arnage/Haddo and Belhelvie intrusions, and the disposition of all the "younger" basic intrusions of north east Scotland in an antiformal structure is questioned. The amphibolites of this area', with one exception, possess chemical compositions and exhibit trends of chemical variation closely akin to basic igneous rocks thus, they are considered to be of igneous origin. The one amphibolite of possible sedimentary origin is diopside bearing and very calcareous. On the basis of field relations and textures an "older" and "younger" series of amphibolitised rocks is considered to be present but the age of many of these amphibolites is indeterminate. In addition it has not been found possible to distinguish between the two series on the basis of chemical compositions. Some of the amphibolites along the margins of the Arnage/Haddo intrusion are considered to represent sheared off portions of this mass. Pyroxene occurs in amphibolites found within the inner aureole of Arnage/Haddo whilst cummingtonite occurs in the outer aureole. Diorite veins are also occasionally found within some of the amphibolites in the aureole and are also shown to have developed in response to the physical conditions within the aureole. The absence of garnet in the amphibolites within the Ellon and Collieston series is thought to be due to 1) the low pressures which prevailed during the regional metamorphism and 2) the lack of amphibolites of appropriate composition. The restricted occurrence of garnet in the amphibolites within the Migmatitic Series is thought to be due solely to the unfavourable compositions of most amphibolites. The Al6+ content of the calciferous amphiboles can be related to the pressure of crystallisation.

This thesis concerns certain of the granitic rocks that are seen in the area of south-central and eastern Aberdeenshire. The western limit to the area of this study has been taken as the western termination of the Hill of Pare, this point representing a discontinuity of sorts. The area is very poorly exposed and the rocks themselves are variable from the median granites of Streckeissen's (1973) classification to almost pure hornblende rocks and follow the 'typical' calc-alkaline trend. Mapping work has been extensive (at least 250 km.2) and field relations are discussed. The area has been subdivided into various Units defined on the basis of hand specimen characteristics and geographic separability. Further, the visible field relations and certain other characteristics lead to the possible definition of Groups of units and the suggestion that more than one genetic sequence is represented. These Units, Groups of units and possible genetic sequences are studied statistically using major element geochemical data and some condensation of information is attempted using certain statistical averaging techniques. Through statistical analysis it has been possible to discriminate at the 100% level between the various Groups and the possibility of the application of such techniques to other Caledonian Granites could perhaps lead to a better understanding of the observed variation and complexity than is presently available.

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.

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Normal fault zones play a fundamental role in the development of sedimentary basins and in the migration and trapping of hydrocarbons. The idealised geometry of an isolated post-sedimentary normal fault (Barnett, 1987, Walsh & Watterson, 1989) existing conceptual models that describe the process of fault growth and linkage in brittle systems (Childs et al, 1995; Cartwright et al, 1996; Childs et al, 1995, 1996b; Huggins et al, 1995), where fault planes composed of many overstepping segments are linked by areas of complex deformation called relay ramps, are generally accepted. Relay zones can trap significant volumes of hydrocarbon or act as leakage points, thus understanding the style of fault linkage, which strongly influences the location of hydrocarbon tops and reservoir compartmentalisation, is vital for any petroleum system.

No description available.

The eruptive sequences linked to the Cumbre Nueva Collapse of La Palma’s Taburiente volcano provide ideal material for a study that integrates field volcanology, geochronology, lava petrology and whole rock magmatic geochemistry. Lavas exposed in Taburiente’s El Time region and on the post-collapse Bejenado volcano bracket the collapse and record this period’s magmatic processes. Their integrated study allows us to reconstruct how a collapse interacted with the magma supply system. By studying the same lava flows using multiple techniques that address successively deeper parts of the magma supply we present an unusually well-constrained interpretation of the processes at depth. Results of field and 40Ar/39Ar geochronological study indicate that the collapse (≈530 ka) ended a typical period of volcanic re-surfacing at Taburiente’s Paleo-Cumbre Nueva Rift. It was followed by focused volcanism within the collapse structure producing the Bejenado volcano. This was a major, rapid, volcanic episode that included explosive phreatomagmatic activity as well as of voluminous, effusive lava emplacement. Its physical volcanology was in part controlled by magmatic evolution, with products ranging from basanites to tephri-phonolites. Petrological study indicates that dynamic collapse-related processes took place within the magma reservoir system throughout this period, in reservoirs located in the lithospheric mantle. Reservoir processes included the disruption of cumulates, super-saturated crystallisation of feldspar and clinopyroxene, mixing between primitive and evolved magmas, and assimilation of amphibole-bearing lithologies. Whole rock elemental and isotope (Sr, Nd, Pb) geochemistry results indicate that most of Bejenado’s eruptive products were hybrids between two magma batches with contrasting source signatures in a major ongoing reservoir process. The more primitive of these batches had an unusually depleted isotope signature for La Palma lavas, while the more evolved, HIMU-dominated, magma had high incompatible element contents. The unusual depleted signature indicates that the collapse affected the deepest part of the magma-supply system.

Ras ed Dom and Abu Dom are two anorogenic ring-complexes, of Triassic age, emplaced into the Precambrian gneisses of the central Bayuda Desert in northern Sudan. The two complexes are closely similar lithologically and are composed of early-formed subaluminous syenites, and later peralkaline syenites and granites. The intrusions are emplaced as sub-volcanic stocks and ring-dykes and both complexes are partly girdled by acid cone-sheet swarms. Minor occurrences of acid volcanic rocks are also present. Ras ed Dom is a striking example of a migrating ring-complex, and in it the focus of magmatism migrated eastwards, and declined in strength, with time. Field relations indicate that the sequence early syenite -> alkali syenite -> alkali granite constitutes a recurrent fractionation Series in the complexes. The early syenites occasionally contain early-formed plagioclase, but in general the suite is typically hypersolvus. Feldspar bulk compositions cluster close to Or38 Ab62, and the most calcic composition (An 7 mol%) is from an early syenite. Pyroxenes in the subaluminous units are zoned from cores of ferrohedenbergite to rims of aegirine-augite, and are enclosed within later ferroedenite. Amphiboles in the peralkaline rocks range from ferrorichterite through arfvedsonite compositions to riebeckite. Late aegirine typically replaces alkali amphibole, especially in the granites. Aenigmatite is an additional mafic phase in some of the syenites . Minor late albite is common in the peralkaline rocks. The principal cryptic variation in the mafic phases is the substitution of Na and Fe{sup]3+ for Mg, Ca and Fe[sup]2+. Major element variation in the rocks supports the proposed fractionation sequence, and it is apparent that the main changes with fractionation are enrichment in SiO[sub]2 and Fe[sub]2O[sub]3 relative to FeO, together with an increase in alkalinity due to A1[sub]2O[sub]3 depletion relative to the alkalies. Relations to alkali-rich analogues of the 'granite system' confirm a magmatic origin, and trends in terms of SiO[sub]2 - A1[sub]2O[sub]3 - (Na[sub]2O + K[sub]2O) suggest that fractionation of alkali-feldspar is the major process in the evolution of the rock-series. Major depletions in Sr and Ba support this hypothesis, as does the variation in Rb/Sr ratios. In common with other alkaline provinces the Bayuda rocks exhibit strong enrichment in incompatible elements such as Zr, Nb, Rb, Y and the LREE group. Concentrations are highest in the granites and this may reflect in part the overprinting by late sodic residual fluids. Partial REE trends are characterised by LREE enrichment, and are consistent with a cogenetic origin for the rocks. The parental melt is believed to have been similar in composition to the early syenites, and is considered to have been generated by lower crustal partial melting. Ras ed Dom and Abu Dom, together with some eighteen or so similar ring-complexes in the Bayuda area, belong to the Younger Granite Association which occurs widely throughout the Sudan, and shows many features in common with the Nigerian Younger Granite province.