Rb-Sr isochron study of the Thorr and Main Donegal Granites, Ireland

A Rb-Sr whole-rock isochron study indicates that the entire Donegal granite suite was emplaced into orthotectonic Caledonian (Dalradian) rocks over a short interval during mid-Silurian to earliest-Devonian times. The Thorr pluton, probably the earliest member of the suite, yields an age of 418 ± 26 Myr and initial 87Sr/86Sr ratio of 0·7055 ± 4, while the latest member, the Main Donegal pluton has an age of 407 ± 23 Myr and initial 87Sr/86Sr ratio of 0·7063 ± 5 (Λ87Rb = 1·42 ± 10−11 yr−1). Errors on both the age and initial Sr isotope ratios incorporate both a priori and geological scatter components and are quoted at the 2-sigma level. The low and restricted range of initial Sr isotope ratios suggests small but significant differences in the composition of the parental granitic magmas which were derived from a low Rb/Sr, low 87Sr/86Sr source.

[1]  D. Hutton.  The structural setting of the main donegal granite; a reply to comments on a recent interpretation , 2007 .

[2]  D. Hutton.  A structural cross-section from the Aureole of the Main Donegal Granite , 2007 .

[3]  P. J. O'Connor.  Radioelement geochemistry of Irish granites , 1981, Mineralogical Magazine.

[4]  N. Gale,et al.  Discussion of a paper by McKerrow, Lambert and Chamberlain on the Ordovician, Silurian and Devonian time scales , 1980 .

[5]  J. Miller,et al.  On the age of the Donegal Granite , 1980, Scottish Journal of Geology.

[6]  R. Cliff,et al.  The evolution of excess argon in alpine biotites — A40Ar-39Ar analysis , 1980 .

[7]  B. Leake,et al.  A revised age for the Donegal granites , 1980, Nature.

[8]  J. Spray,et al.  Petrology and 40Ar/39Ar geochronology of some hellenic sub-ophiolite metamorphic rocks , 1980 .

[9]  R. Harmon,et al.  Oxygen and strontium isotope relationships in the British late Caledonian granites , 1980, Nature.

[10]  G. C. Brown,et al.  Space-time variations in British Caledonian Granites: some geophysical correlations , 1979 .

[11]  D. Titterington,et al.  On the fitting of parallel isochrons and the method of maximum likelihood , 1979 .

[12]  A. B. Blaxland,et al.  Pb isotopic composition of feldspars from Scottish Caledonian Granites, and the nature of the underlying crust , 1979, Scottish Journal of Geology.

[13]  R. Pankhurst.  Isotope and Trace Element Evidence for the Origin and Evolution of Caledonian Granites in the Scottish Highlands , 1979 .

[14]  G. C. Brown,et al.  The initiation and thermal diversity of granite magmatism , 1978, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[15]  James G. Anderson,et al.  Age and origin of the major syenite centers in the Gardar province of south Greenland: Rb-Sr studies , 1978 .

[16]  R. Steiger,et al.  Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmochronology , 1977 .

[17]  C. Stillman,et al.  A Caledonian plate tectonic model , 1976, Journal of the Geological Society.

[18]  R. Pankhurst,et al.  Determination of Rb/Sr and 87Sr86Sr ratios of some standard rocks and evaluation of X-ray fluorescence spectrometry in Rb1bSr geochemistry , 1973 .

[19]  S. Hart,et al.  Realistic use of two‐error regression treatments as applied to rubidium‐strontium data , 1972 .

[20]  M. Atherton,et al.  The Composition and Metamorphic History of some Aluminium Silicate-bearing Rocks from the Aureoles of the Donegal Granites , 1970 .

[21]  J. Miller,et al.  ISOTOPIC AGES OF LATE CALEDONIAN GRANITIC INTRUSIONS IN THE BRITISH ISLES , 1968 .

[22]  Derek York,et al.  Least squares fitting of a straight line with correlated errors , 1968 .

[23]  B. Leake,et al.  The geochronology of the Connemara granites and its bearing on the antiquity of the Dalradian Series , 1966, Quarterly Journal of the Geological Society of London.

[24]  H. Read.  Aspects of Caledonian magmatism in Britain , 1961 .

[25]  H. Read,et al.  THE AUREOLE OF THE MAIN DONEGAL GRANITE , 1960, Quarterly Journal of the Geological Society of London.

[26]  H. Read,et al.  THE MAIN DONEGAL GRANITE , 1958, Quarterly Journal of the Geological Society of London.

[27]  E. Whitten.  The Petrogenetic Significance of the Contact Relationships of the Donegal Granite in Gweedore and Cloghaneely , 1957, Geological Magazine.

[28]  W. S. Pitcher.  The Rosses granitic ring-complex, County Donegal, Eire , 1953 .

[29]  W. S. Pitcher.  The migmatitic Older Granodiorite of Thorr district, Co. Donegal , 1952, Quarterly Journal of the Geological Society of London.