摘要:

AbstractJoints and faults were studied in Mesozoic and Avonian strata along 35 km of coast between Ogmore‐by‐Sea and Lavernock Point, Glamorgan, South Wales. Observations on joint and fault planes were recorded at 22 localities (i.e. approx. 750 stations), an analysis of which suggests the following. In the Mesozoic strata systematic joint patterns of tectonic origin exist with principal azimuths at 340°, 200° and 280°, with the more complex patterns characteristic of Triassic sequences, whilst a System of orthogonal microjoints (striking at 280°–190°) representa perhaps the earliest formed fractures in the Mesozoic strata. The joints in general formed early in the deformation of the area, whilst joints and faults can both be ascribed to a general northsouth compressive force. A study of fracture patterns in Avonian basement reveals a close similarity of trend, but there is little visible evidence to indicate much basement influence on cover

ISSN:0072-1050    

DOI:10.1002/gj.3350090201

出版商:John Wiley&Sons Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractThe geological features of igneous, metamorphic and sedimentary rocks comprising the Precambrian of England and Wales suggest formation in one or more Precambrian orogenic cycles. They are now interpreted in terms of plate tectonics. Evidence for Late Proterozoic plate subduction in the Mona Complex of Anglesey is suggested by the association of pillow lavas, cherts, high P/T metamorphic rocks and by the occurrence of gabbros and serpentinites with similar features to rocks believed to comprise the oceanic crust. Precambrian rocks in England and South Wales include calc‐alkaline plutonic complexes (Malvern and Johnston Complexes), calc‐alkaline lavas (Uriconian and Charnian) and basic and intermediate intrusions of tholeiitic affinity (dykes in the plutonic complexes and granophyric diorites in Charnwood Forest). The features of these rocks indicate formation in a continental margin setting and this is consistent with features of the Rushton Schist and Primrose Hill “gneiss” which suggest that they predate the Late Proterozoic orogenic activity. This evidence is consistent with plate tectonic models involving oceanic plate subduction below the Mona Complex from an ocean to the northwest, or from a small ocean basin southeast of the complex. The Warren House lavas show some affinities to ocean floor basalts and are problematic with regard to the Precambrian history of t

ISSN:0072-1050    

DOI:10.1002/gj.3350090202

出版商:John Wiley&Sons Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractA total field magnetic anomaly contour map of the continental margin west of Ireland is described by reference to geological structure previously established by seismic reflection profiling. The western Irish Mainland Shelf, Porcupine Seabight Trough and Porcupine Ridge were previously defined as major north‐south elements in the structure of the margin. Each is readily distinguished on the magnetic anomaly contour map. To the north these features terminate against, or merge with, the east‐west Slyne Ridge. A pronounced change in the magnetic anomaly pattern at about 53°N suggests that the southern limit of this Ridge coincides with a major geological discontinuity extending from near the coast of Ireland to the continental slope, some 320 km to the west.The magnetic anomaly contour map gives general support to the idea that the Slyne Ridge and Porcupine Ridge represent submerged blocks of marginal continental crust, and that the Porcupine Seabight Trough is founded upon crust significantly different in chara

ISSN:0072-1050    

DOI:10.1002/gj.3350090203

出版商:John Wiley&Sons Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractThe Borrowdale Volcanic rocks of Kentmere have been reinvestigated. A previous structural interpretation (Mitchell 1929) involving Caledonian isoclines superimposed upon pre‐Caradocian NNE trending folds is shown to be incorrect; neither set of structures exist. The geometry of the major structural elements in the area, the Nan Bield Anticline and the Caledonoid cleavage, is described. Evidence is adduced which suggests that the anticline was formed in pre‐Caradocian time as a large open fold trending approximately E‐W. Its present geometry and that of the Wren Gill Monocline result from the superimposition of the regional end‐Silurian cleavage obliquely and inhomogeneously across this pre‐existing fold.The volcanic succession is divided into four compositionally and petrographically defined formations. In upward sequence these are the Nan Bield and Wren Gill formations (andesitic lavas and tuffs), Kentmere Formation (mainly dacitic pryoclastic rocks) and the Garbourn Formation (andesites and dacites), totalling over 2800 m. It is thought that much of this succession was deposited sub

ISSN:0072-1050    

DOI:10.1002/gj.3350090204

出版商:John Wiley&Sons Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractAn account is given of the use of square array resistivity techniques to derive an apparent resistivity section down the length of Holy Island (Anglesey). Possible interpretations of this section in terms of the distribution of true resistivity with depth are given and discussed briefly in relation to proposed geological structure.

ISSN:0072-1050    

DOI:10.1002/gj.3350090205

出版商:John Wiley&Sons Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractSemipermeable membranes are necessary conditions for the realisation of equilibrium open systems in the Earth's crust. Membraneless cases, as at the boundary Earth‐Atmosphere, are rather exceptional. The application of the D. S. Korzhinskii's thermodynamics of open systems to mineral equilibria in rocks may be justified only if the perfect mobility of components is proved independently viz: by means other than the analysis of mineral paragenesis alon

ISSN:0072-1050    

DOI:10.1002/gj.3350090206

出版商:John Wiley&Sons Ltd    

年代:1974

数据来源: WILEY

摘要:

AbstractCarbonate units occur in varying numbers in the fine‐grade members of the alluvial fining‐upwards cyclothems present in the Lower Old Red Sandstone of the Anglo‐Welsh outcrop. They closely resemble contemporary soil‐carbonates (calcretes) and hence show that the local Siluro‐Devonian climate was relatively hot with a comparatively low seasonal rainfall. Compared with contemporary calcretes, the units suggest that sites on the alluvial plains were denied river‐borne sediments for periods each in the general order of 104years. The pedogenic interpretation of the carbonate units, developed in the light of the behaviour of rivers today, leads to alternative models for the geomorphology of the Siluro‐Devonian alluvial plains and for their gross subsurface structure. Geomorphologically, the plains at any instant presented depositionally active and inactive areas in juxtaposition. Under some circumstances the relief was provided only by alluvial ridges. Under others, relief was afforded by valley sides and perhaps river terraces, in addition to ridges. Knowledge of the character of the Lower Old Red Sandstone in vertical sequence leaves as plausible three alternative gross structures for the alluvial pile beneath the plains. They differ chiefly in the lateral variability and connectedness of the palaeosols and place hitherto unavailable limits on the three‐dimensional character of

ISSN:0072-1050    

DOI:10.1002/gj.3350090207

出版商:John Wiley&Sons Ltd    

年代:1974

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350090208

出版商:John Wiley&Sons Ltd    

年代:1974

数据来源: WILEY