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Study of shear wave velocities in the Lewisian Metamorphic Complex of NW Scotland
Başlık:
Study of shear wave velocities in the Lewisian Metamorphic Complex of NW Scotland
Yazar:
Ali, Mubarik, author.
ISBN:
9780438052826
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (313 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Advisors: J. Hall.
Özet:
This study of the shear wave velocity distribution in the Lewisian metamorphic complex of Sutherland, NW Scotland, reveals the value of shear waves in imposing constraints in modelling the composition of rocks. The study is made on data of the "LUST" seismic refraction line which crosses a major lineament separating distinct rock units and for which the P-wave interpretation was already available. The data from two end-shots and two intermediate shots into 90 detectors were digitised at 100 Hz frequency, decoded, and processed for the recovery of the shear wave signal from strongly overlapping noise. The picked data gave smooth time-distance graphs without any clear indication of vertical discontinuities. The data were interpreted by ray-tracing techniques aimed to produce a continuous variation that best fitted the data. The interpretation defines velocity and Poisson's Ratio down to 3 km depth and shows dominant vertical and lateral variations related respectively to closing cracks and compositional changes. The vertical increase of velocity (rapid in the first kilometre of depth) is analysed in terms of the crack models of O'Connell and Budiansky (1974) and Toks8z et al (1976), and indicates water saturation of substantially cracked rocks (crack-density decreases 0.6 to 0.07). The lateral sheaf wave velocity variation shows very good correlation with the lateral lithology. The Vs of quartzofeldspathic gneisses of the Northern Belt appears (3.59 +/- 0.02 km/s, sigma = 0.235 +/- 0.005) lower than that of the pyroxene-granulites (3.65 +/- 0.02 km/s, sigma = 0.270 +/- 0.005) of the Central Belt. In the transition zone (Claisfearn and Foindle) velocity decreases progressively with the increased retrogression northwards (average VS = 3.61 +/- 0.02 km/s, sigma = 0.240 +/- 0.005) and reaches minimum on the granites of Laxford Front (3.55 +/- 0.02 km/s, sigma = 0.224 +/- 0.005).Modelling of the composition of these rocks with the use of effective velocities (VP, VS) of essential minerals shows the critical role of quartz, pyroxene and amphibole. The rise of quartz content at the expense of pyroxene and amphibole, and/or the replacement of pyroxene by amphibole reduce velocities. It is predicted from the attempted variational trends of minerals that the content of quartz and k-feldspar increases northwards in the Northern Belt, This may be due to an increase of pegmatitic material. The prediction of high amphibole content near Loch Inchard implies the presence of concealed amphibolitic body correlating approximately with a zone of exposed amphibolites. There is no indication of existence of pyroxene-granulites in detectable amounts at shallow depth. In the retrogressed rocks, south of Loch Laxford, it appears that there is a progressive replacement of pyroxene by amphibole and increase of quartz northwards. The quantitative modelling of lithology and velocities demonstrates clearly the potential significance of VS in improving the correlation of elastic properties with composition of rocks.
Notlar:
School code: 0547
Tüzel Kişi Ek Girişi:
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684428.1) | 684428-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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