The petrogenesis of leucogranitic dykes intruding the northern Semail ophiolite, United Arab Emirates: field relationships, geochemistry and Sr/Nd isotope systematics   总被引：3，自引：0，他引：3  

Jon Cox  Mike Searle  Rolf Pedersen 《Contributions to Mineralogy and Petrology》1999,137(3):267-287

The Khawr Fakkan block of the Semail ophiolite (United Arab Emirates) exhibits a suite of 10–100 m scale metaluminous to peraluminous granitic intrusions, ranging from cordierite-andalusite-biotite monzogranites to garnet-tourmaline leucogranites, which intrude mantle sequence harzburgites and lower crustal sequence cumulate gabbros. Structural constraints suggest that the subduction of continental sedimentary material beneath the hot proto-ophiolite in an intra-oceanic arc environment led to granulite facies metamorphism at the subduction front and the generation of granitic melts which were emplaced up to the level of the ophiolite Moho. Compositions indicate the analysed granitoids were largely minimum melts that crystallised at variable a _H2O and pressures of 3 to 5 kbar. The LILE (Sr, Rb and Ba) covariation modelling suggests that the granitoids formed largely by the dehydration melting of muscovite rich metasediments. Initial ⁸⁷Sr/⁸⁶Sr ratios of analysed dykes vary between 0.710 and 0.706 at initial ɛ_Nd values of between −6.3 and −0.5. Cogenetic units of a composite sill from Ra's Dadnah yield a Sm-Nd isochron age of 98.8 ± 9.5 Ma (MSWD = 1.18). Geochemical and isotopic characteristics of the analysed granitic intrusions indicate that the subducted continental material was derived from oceanic trench fill (Haybi complex) sediments, preserved as greenschist (Asimah area) to granulite facies (Bani Hamid area) ophiolitic metamorphic sole terranes. The Sr-Nd isotope systematics suggest that hybrid granitic melts were derived from pre-magmatic mixing of two contrasting subduction zone sources. Received: 17 December 1998 / Accepted: 19 July 1999  相似文献   

Geophysical studies of the Atlantic sea floor near 40°N, 24°W,and its relation to King's Trough and the Azores     

Roger Searle 《Marine Geology》1977,25(4):299-320

A detailed survey of a 1°-square of sea floor 100 miles northeast of the Azores has revealed the presence of scarps over 30 km long striking generally 120°, transverse to the regional topographic and magnetic lineations. They are not associated with a major fracture zone. Sedimentation in the area appears to have been by a mixture of pelagic and turbidity-current processes, with a Miocene increase in sedimentation rate probably indicating the subaerial emergence of the Azores Archipelago. Magnetic anomalies were identified along a number of profiles between the survey area and the Mid-Atlantic Ridge crest, and indicate a short period of increased spreading rate from about 12-3 m.y. ago.  相似文献   

Field meeting at Upnor,Kent: Saturday, 20th July, 1946     

D.L. Searle 《Proceedings of the Geologists' Association. Geologists' Association》1947,58(2):125-127

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Restoration of the Western Himalaya： implications for metamorphic protoliths, thrust and normal faulting, and channel flow models     

Michael P. Searle Ben Stephenson James Walker Christian Walker 《《幕》》2007,30(4):242-257

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INTERNATIONAL SYMPOSIUM ON THE KARAKORAM AND KUN LUN MOUNTAINS Kashgar, Xinjiang, China 5-17 June 1992     

M.P. Searle 《地学学报》1992,4(5):531-535

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The structure and origin of the Azores-Biscay Rise, North-east Atlantic Ocean     

R. B. Whitmarsh  A. Ginzburg  R. C. Searle 《Geophysical Journal International》1982,70(1):79-107

Summary. The Azores—Biscay Rise is a roughly linear north-east—south-west trending feature rising 1500–3000m above its surroundings, which extends from about 4°N, 1°30'W towards the Azores. Its south-western termination is near 40°30'N, 21°30'W. About halfway along its length the Rise intersects the WNW-trending King's Trough. In 1978 a set of bathymetric, magnetic, gravity, GLORIA and seismic reflection and refraction data were obtained in the vicinity of the Rise. Together with earlier data these observations suggest that: (1) there has been no substantial post-emplacement tectonic activity, with the possible exception of the construction of some volcanic seamounts at the south-western end of the Rise, and (2) the Rise is underlain by a low-velocity (low-density) lower crust and is in isostatic equilibrium.
The Rise can be convincingly shown to be the eastern half of a pair of ridges formed by abnormal crustal generation at the Mid-Atlantic Ridge crest between the times of anomalies 33 and 24 (76–56 Ma ago). The western counterpart of the Rise includes Gauss and Milne seamounts in the Newfoundland Basin.
Magnetic anomaly 31 passes uninterruptedly across the Rise and therefore hypotheses that the northern part of the Rise was the site of a Cenozoic transform fault or subduction zone are not supported by our data. It is speculated that King's Trough was linked to the North Spanish Trough by an early Cenozoic east—west transform fault across the northern Iberia Abyssal Plain. This plate boundary became inactive about the middle of the Oligocene epoch.  相似文献   

Industry Clusters and Sydney's ITT Sector: northern Sydney as ‘Australia's Silicon Valley’?     

Glen Searle 《The Australian geographer》2005,36(2):145-169

This paper examines the claim that the North Ryde–North Sydney arc is Australia's ‘Silicon Valley’, seeking firstly to identify the empirical validities behind the claim, and secondly to ask how the documented patterns might be explained. The paper evidences the fact that this area indeed provides the pre-eminent site for Australia's information technology and telecommunications (ITT) sector. However, examination of this industry suggests that its expansion in Sydney has been motivated primarily by the increasing centrality of advanced producer services within the high-order business sector. It is Sydney's attributes for multinational business, as opposed to the propulsive dynamics of local clustering per se, which appears to explain the spatial concentration of these activities. Thus, it is the urbanisation economies of Sydney more than the localisation economies of the ITT sector which account for the growth of this sector in the city. Nevertheless, localisation economies are sporadically significant, suggesting that Sydney's ITT sector is to a certain extent a hybrid product of the two types of economies.  相似文献   

The Demise of Place Equity in Sydney's Economic Development Planning     

Glen H. Searle 《The Australian geographer》2002,33(3):317-336

The role of planning in Sydney's economic development since the mid-1970s is explored, focusing on its role in reducing spatial disparities across the region. Planning policies during the period of each State government--Labor (1976-88), Liberal-National (1988-95) and Labor (1995-present)--are reviewed. The paper analyses a hierarchy of factors underlying the relative failure of policies to lessen disparities, notably intra-government failure to produce effective policies, the influence of prevailing ideology, local institutions and political culture, and the wider context of globalisation and the mode of capitalist accumulation. Each of these has been significant in limiting planning's role in addressing uneven development across the region.  相似文献   

Magnetic anomalies in the northeast Atlantic Ocean (35°-50° N)     

J. Verhoef  B. J. Collette  P. R. Miles  R. C. Searle  J. -C. Sibuet  C. A. Williams 《Marine Geophysical Researches》1986,8(1):1-25

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Gloria survey of the east pacific rise near 3.5°S: Tectonic and volcanic characteristics of a fast spreading mid-ocean rise     

Roger Searle 《Tectonophysics》1984,101(3-4)

A long-range, sidescan sonar (GLORIA) survey of an approximately 100-km square area of the East Pacific Rise crest between 3°S and 4°S extends results obtained in the same area by Lonsdale (1977) using Deep-tow. The axial, linear volcano was found to be continuous over a distance of 75 km. The presence of major inward and outward facing fault scarps was confirmed, but the GLORIA data show several distinct differences between the two fault sets. The inward dipping faults are more numerous, more closely spaced, and longer than the outward dipping ones, and their dip-slopes backscatter sound more extensively than those of the outward dipping faults; moreover most of them appear to be formed within 2 km of the axis, whereas the majority of the outward dipping faults begin to develop between 5 and 8 km from the axis. These differences suggest that the two sets of faults have different origins. The horizontal pattern of inward dipping faults is similar to those observed on other mid-ocean rises at all spreading rates, though the lengths and separations of the scarps are slightly, and their throws considerably, less than on slower spreading rises. This common horizontal pattern suggests that inward dipping faults on all rises have a common mode of formation regardless of spreading rate. Horizontal tension is probably the dominant factor, but an additional mechanism is needed to explain the polarization of fault dips that occurs in the region 2–8 km from the axis. The similarity of major fault spacings on the East Pacific Rise to those on slower spreading rises suggests that faulting is invariant in space, rather than time, and that the lithosphere where these faults are formed (about 2 km from the spreading axis) has a similar, small thickness for all spreading rates. This is attributed to the regulating effect of hydrothermal circulation and plate cooling.  相似文献