Contrasting rock permeability in the aureole of the Ballachulish igneous complex, Scottish Highlands: the influence of surface energy?
13
Citation
35
Reference
10
Related Paper
Citation Trend
Keywords:
Dalradian
MAJOR objectives of this study have been to define the character of the igneous rocks present; to determine the number of separate igneous complexes, their relative ages, their variations, the relationships of these variations to structure, and the interpretation of their origin; to elucidate the mechanics of intrusion; and to discriminate primary magmatic structures from postconsolidation metamorphic features and to describe and interpret the mineralogic facies as a result of metamorphism.
Cite
Citations (224)
Suites of samples from the type area of the Leven Schist and from localities within the Monadhliath Schists of the Central Highlands have been analysed for major and trace elements and for their Sr isotopes. Petrologically the two schist groups are consistently different: the Leven Schists are muscovite-rich, plagioclase-poor semipelites to pelites, whereas the Monadhliath Schists are a typical ‘Moinian’ semipelite, consisting almost entirely of biotite, sodic andesine and quartz. Equally, consistent geochemical differences between the two include more Nb, Zr, Y and Rb, and less Ca, Sr and Ni in the Leven than the Monadhliath Schists. Ratios of Rb: Sr and of Y to P 2 ,O 5 , Sr and CaO discriminate the Leven from the Monadhliath schists. Factor analyses of the chemical data also serve to distinguish the two suites Rb-Sr isochron studies give 655±f2.5Ma, initial 87 Sr/ 86 Sr = 0.7232±f10, for the Leven Schists, and 486±9Ma, initial "Sr 87 /"Sr 86 = 0.7190±1, for the Monadhliath Schists and also separate the two formations from one another. The 655 Ma age for the Leven Schists is thought to record sedimentation and diagenesis, whereas the 486±9 age for the Monadhliath Schists is probably related to the cessation of Rb and Sr migration at or after the peak of the Grampian orogeny. Their Sr isotopic compositions were also completely different hack to 1300 Ma ago and serve to confirm the lack of any continuity between the Leven and Monadhliath schists. Sets of schists located between the main outcrop areas were also analysed and can be assigned without ambiguity either to the Leven or the Monadhliath schists on the basis of their chemistry. The results of this study imply that the Lower Dalradian Appin Group rests on the Grampian Division unconformably and that the latter is closely related, through its geochemistry, to the Moinian NW of the Great Glen.
Dalradian
Cite
Citations (29)
Dalradian
Laurentia
Yilgarn Craton
Passive margin
Cite
Citations (5)
Abstract Systematic variations in both timing and conditions of metamorphism are observed in the Dalradian rocks of Central Perthshire, Scotland. Early (D2–D3 and syn-D3) relatively low-pressure metamorphism (550 °C, 7 kb) occurs in the Flat belt rocks of the Tay Nappe to the south, and later (post-D3) higher-pressure conditions (550 °C, 9 kb) dominate the Steep belt to the north. The latter appear to be superimposed on earlier low pressure assemblages (chloritoid–biotite) with the pressure increase probably relating to formation of the Tummel Steep Belt, possibly near 460 Ma. This polymetamorphism, in addition to the generally high pressures of Barrovian metamorphism throughout Perthshire, may account for the poor development of the metamorphic zonal pattern in this region compared to the eastern Dalradian.
Dalradian
Cite
Citations (39)
The petrology of the igneous rocks has for the last quarter of a century been established,on a sound quantitative basis, largely as a result of the body of experimental work available on silicate melts. In the field of metamorphism, however, progress has been much less marked, and the difficulties of the laboratory development of stresses comparable with those acting during regional metamorphism must for some time leave our knowledge of the crystalline schists far behind that even of the hornfelses. A quantitative approach, however, is not confined to the experimental side. The introduction of the conceptions of facies and grade raises a new need for exact knowledge of the compositions of the various minerals, both of those constituting the different isophysical assemblages of a given grade, and of the isochemical assemblages representing a given rock under the grade-conditions of the various facies established.
Dalradian
Cite
Citations (42)
Abstract The Monadhliath and Leven Schists are separated north of Glen Roy by some 500m of psammitic rock. Junctions are gradational and conformable, and evidence from sedimentary structures indicates that all three face upwards. The two schists should not be equated, nor should the Monadhliath Schist be included in the Dalradian Supergroup unless the entire Grampian Division is also included.
Dalradian
Conformable matrix
Cite
Citations (7)
Igneous rocks and crystalline schists are often associated with each other in such a manner as to compel the conclusion that either the igneous rocks have been formed out of the schists or the schists out of the igneous rocks. There are other cases in which the two kinds of rock are less intimately related; parallel structure is wanting, the junctions are sharply defined, and there is no evidence of an original mineral gradation. These are examples of the ordinary irregular intrusion of igneous rocks in schists. But there is a third group in which the characters are intermediate. In these rocks, structural parallelism is more or less distinct, and there is often a partial blending of the two kinds of rock at the line of contact; but other indications forbid the belief that the schists have been elaborated out of the associated igneous masses.
Cite
Citations (1)
Abstract Evidence is adduced to relate the published minimum absolute date of — 475 m.y., for the metamorphism of the Connemara Schists, to its correct position in the Lower Palaeozoic stratigraphy of Western Ireland. The metamorphism pre-dates the Didymograptus extensus zone of the Arenig in Connemara and South Mayo and an Upper Cambrian or Tremadocian age is considered likely.
Dalradian
Cite
Citations (59)
Dalradian
Cite
Citations (1)
Synopsis The metamorphism of the Dalradian rocks of Scotland is reviewed and commented on, attention being paid to the nature and spatial distribution of the zones and their significance in PT modelling. Reactions defining Barrovian and Buchan isograds are listed and figured and the importance of textural and chemical disequilibrium discussed. The effect of rock composition on the isograds is examined and a T-X diagram constructed to indicate the probable metamorphic mineral sequence for the average pelitic Dalradian composition. The history of ideas on the genesis of the migmatites is outlined and it is concluded that they may well be polygenetic, and those in the NE may even be of Pre-Caledonian age. The role of oxidation and reduction reactions is briefly mentioned and the late cooling reactions are described, from which it can be seen that the climatic assemblages have often been markedly modified. The pressures and temperatures of the metamorphism, determined from phase considerations are plotted on a PT diagram and compared to the isotope results. Finally, evidence is used to suggest that although the fundamental cause of metamorphism might be a normal heatflow across the mantle/crust boundary and within the tectonic pile, the evidence at the present level indicates some of the metamorphism is due to high level magma and perhaps heat focussing along major structures.
Dalradian
Cite
Citations (92)