Rubidium–strontium age-determinations are presented for minerals and whole rocks from the Lewisian, Moinian and Dalradian metamorphic complexes of Scotland and from the Connemara schists of western Ireland. Age data from the Lewisian complex confirm that it was affected by two major periods of metamorphism. Pegmatites associated with the Scourian part of the Lewisian complex are shown to be at least 2460 m.y. old, whereas the Laxfordian metamorphism occured about 1600 m.y. ago. The effect of the Laxfordian metamorphism on the Scourian pegmatites is to produce a scatter of ages in which coexisting potassium feldspars and biotites show the pattern potassium-feldspar age > biotite age. Six biotites, a microcline and a muscovite from the Moine Series have ages in the range 435 to 405 m.y., showing that a widespread Caledonian (sensu stricto) metamorphism affected the Moine Series 420 ± 15 m.y. ago. Two pegmatites from the Knoydart–Morar area yielded muscovites with ages of 740 m.y. and 665 m.y.; asurvey of the geochemical possibilities and consideration of the geological setting of the pegmatites suggest that the Moine sediments in this area are older than 740 m.y. and may have undergone an early metamorphism before this date. Specimens from the Dalradian Series of Perthshire suggest a major metamorphism at 475 ± 15 m.y. ago, interpreted as Lower or Middle Ordovician in age. Two whole-rock and three mineral analyses from the pre-metamorphic Ben Vuroeh granite-gneiss suggest that the intrusion was formed 600 ± 100 m.y. ago and that a partial reconstitution occurred 415 ± 10 m.y. ago. The Ben Vuroch granite complex as a whole appears to have behaved as a closed system with respect to rubidium and strontium during later metamorphism. Three specimens of muscovite and biotite from the Connemara schists of western Ireland have a mean age of 475 m.y.; this finding tends to support the generally supposed contemporaneity of the Dalradian and Connemara metamorphisms. Biotite from the Galway granite has an age of 365 ± 10 m.y., which suggests that this granite may be contemporaneous with other dated Caledonian granites of the British Isles. Four potassium–argon ages support the conclusions on the age of the Laxfordian and Caledonian–Moinian metamorphisms.

The reflectance spectra of combinations of olivine, orthopyroxene, and iron meteorite metal show systematic variations in spectral properties which can be used to constrain many of the physical and chemical properties of the assemblages. The presence of metal most noticeably affects band area ratios, peak:peak and peak:minimum reflectance ratios, and band widths. INTRODUCTIONRemote sensing is one of the most effective means for deriving information about the surface compositions of terrestrial and extraterrestrial targets which are inaccessible to direct sampling. Consequently, it is imperative that the maximum amount of compositional information be derived from such studies. Reflectance spectroscopy is one of the most effective tools in remote sensing, and in order to improve the quality and quantity of information derivable from spectral studies, the spectral reflectance properties of mafic silicate-meteoritic metal mixtures have been examined.These particular assemblages were chosen because accurate, quantitative identification and analysis of these materials have potentially important implications for theories concerning the origin and evolution of the asteroid belt [Galley, 1984[Galley, , 1986 and perhaps the solar system [Bell, 1986;Galley, 1988]. The S-class asteroids are the most abundant group in the inner part of the main asteroid belt [Gradie and Tedesco, 1982]. Their mineralogy, particularly the nature of the metallic phase, is disputed. These objects have been interpreted as being either Copyright 1990 by the American Geophysical Union. Paper number 89JB03409.0148-0227/90/89JB -03409505.00 differentiated objects with affinities to certain "primitive" achondrites [Galley, 1984[Galley, , 1986 Bell and Kell, 1987] or parent bodies for the ordinary chondrites and hence undifferentiated [Anders, 1978; Felerberg et al., 1982]. The competing interpretations are almost exclusively based on differing interpretations of the telescopic spectral data. Important constraints can be placed on early solar system history depending on which interpretation ultimately proves to be correct.The recent identification of probable olivine-and metal-rich asteroids also hinges on correct interpretation of the telescopic spectra [Bell et al., 1984a,b; Cruikshank and Hartmann, 1984]. If these A-class asteroids are differentiated objects, then they are most likely the remnants of once larger planetesimals whose outer layers have been stripped away by impacts to reveal their core-mantle boundaries, and they are mineralogically similar to pallasitc meteorites [Buseck, 1977;Bell et aL, 1984b]. The necessary laboratory spectral studies were undertaken in order to constrain the possible surface mineralogies of these important classes of asteroids.The spectral reflectance properties of the individual end member phases (oilvine, orthopyroxene, and metal) and olivine-orthopyroxene mixtures have been extensively studied. Olivine reflectance spectra in the 0.3-2.6 tam wavelength region show a broad asymmetric absorption feature near i...

Synopsis Review of existing plate tectonic theories of the Lower Palaeozoic development of the north and northwest British Isles leads to the conclusion that ridge-trench impingement theory can be used to integrate all known geological observations within one unified plate tectonic theory for the area. Consideration of the consequences of the progressive impingement of a ridge-transform system with a northwesterly-dipping subduction zone in Arenig time gives explanations for: (a) termination of Dalradian sedimentation in the Arenig; (b) initiation of Barrovian metamorphism at the same time; (c) development and history of the Girvan-Ballantrae complex; (d) initiation of the Highland Boundary Fault as a dextral transform fault in the Arenig; (e) its absence in western Scotland; (f) the postulated presence of a boundary fault southeast of Connemara and perhaps at Pomeroy; (g) the peak of metamorphism (Barrovian and Buchan types) in the Dalradian and associated basic intrusions in the Arenig in both Scotland and Connemara; (h) the development of the Moine Thrust (and related foreland folds and thrusts) also in the Arenig and (i) the origin of the South Mayo trough on oceanic crust. Related events explained by this model include the location of the Donegal batholith, the generally low-grade metamorphism of Donegal and southwest Scotland, the location of the Great Glen Fault and all known faunal province and Ordovician sedimentological data from the Midland Valley and Southern Uplands. It is proposed that this Lower Ordovician sequence of related events be termed the Grampian Orogeny, distinct from the later Caledonian Orogeny, which is tectonically and geographically separate.

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