ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00534.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTOver the last decade, techniques from mathematical statistics, multivariate biometrics, non‐Euclidean geometry, and computer graphics have been combined in a coherent new system of tools for the biometric analysis oflandmarks, or labelled points, along with the biological images in which they are seen. Multivariate analyses of samples for all the usual scientific purposes ‐ description of mean shapes, of shape variation, and of the covariation of shape with size, group, or other causes or effects ‐ may be carried out very effectively in the tangent space to David Kendall'sshape spaceat the Procrustes average shape. For biometric interpretation of such analyses, we need a basis for the tangent space that is Procrustes‐orthonormal, and we need graphics for visualizing mean shape differences and other segments and vectors there; both of these needs are managed by the thin‐plate spline. The spline also links the biometrics of landmarks to deformation analysis of curves in the images from which the landmarks originally arose. This article reviews the principal tools of this synthesis in a typical study design involving landmarks and edge information from a mi

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00535.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe evolution of minor structures during the growth of major folds and thrusts, in the Chartreuse district of the French Subalpine thrust belt, shows that each thrust evolved through a phase of distributed faulting, major thrust propagation and displacement, followed by distributed shear modification of the hanging‐wall fold. Microstructural studies suggest that the distributed faulting phases, early and late in the history, were characterized by strain rates limited by diffusive mass transfer processes (c. 10‐15‐10‐16s‐1). Faulting whose rate is limited by DMT is too slow on its own to accommodate the regional time‐averaged shortening rates for the thrust belt as a whole, implying that the slow thrusts operated in tandem with those major, fast thrusts where deformation was primarily cataclastic. Consequently each thrust anticline experienced a displacement rate cycle and an array of thrust anticlines must amplify simultaneously. These interpretations raise important issues for the dynamics of fault populations, the evolution of thrust wedges and the history of fluid migration in t

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00536.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTKolmogorov's model of the distribution of bed thicknesses is assessed by numerical simulations of a sedimentation process, assumed to be a random time‐series of alternating depositional and erosional episodes conformable with a stationary Markov process in a state of equilibrium. The study supports the validity of the main point of the model. The random time‐series process generates a succession of beds with ‘positive’ (preserved) and ‘negative’ (eroded) thicknesses, the frequency distribution of which, f(x), spans the range of positive to negativex‐values. The beds with negative thicknesses are absent in the stratigraphic record, whereby the measured bed thicknesses show a frequency distribution, f*(x|x>0), that is left‐side truncated, cut off at the zero thickness value. The numerical simulations further indicate that f(x) is a ‘composite’ geometrical distribution, whose actual form changes progressively withpd, the probability of sediment deposition relative to erosion. The distribution f(x) invariably has a maximum atx≤0, such that the truncated distribution f*(x) forpd≥0.5 is a simple geometrical distribution regardless ofpdvalue. The f*(x) distribution will appear to be a negative exponential distribution when based on the bed‐thickness data measured in a conventional metric scale. Data sets from four different turbidite successions in the Cenozoic of Japan, each comprising a few thousand beds, show this type of distribution. However, the sandstone‐capping shales in one of the turbidite successions show a truncated Gaussian distribution, attributed to a significant component of non‐turbiditic mud. No universal form of bed‐thickness distribution can be assumed for the Kolmogorov model. The form of bed‐thickness distribution may vary with the type of the depositional process and the charact

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00537.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTPrevious palaeomagnetic results from Tertiary volcanic rocks of Sardinia suggest that the island underwent a quick counterclockwise rotation between 20.5 and 19 Ma. In order to test this hypothesis, a new palaeomagnetic study was carried out on sediments and volcanic rocks with well‐controlled biostratigraphic or radiometric ages younger than the suggested age for the end of the rotation.Unrotated palaeomagnetic directions obtained from the Upper Ignimbrites (radiometric age: 18.5–19.7 Myr) and the Aquitanian tuffs collected in the Anglona region (N Sardinia) would suggest that the rotation ended earlier than 20.5 Myr. The directions found in the volcanics are perhaps the result of secular variation, rather than differential rotation of the Anglona region with respect to surrounding regions.Two sites belonging to the upper ignimbritic unit (SI2) in the Monte Traessu‐Monte Rispisu area (Logudoro region) exhibited a large amount of rotation (D=320.4°,I=60°) which may be age related (radiometric age: 19.9 Myr). Four dikes (radiometric age: 18.3–16.7 Myr) in the Arcuentu volcanic complex (Arburese region) yield results (D=348.4°,I=33.8°) that indicate a further amount of rotation after their emplacement.Stable end‐point directions were successfully isolated from three Upper Burdigalian/Langhian sedimentary sites (biostratigraphic age: 18–15Ma) from the Marmilla and Logudoro regions. Consistent paleomagnetic directions obtained from these sites (D=352°,I=49°) indicate that a small amount of rotation was still to be completed in the Langhian time. This result is consistent with the history of Sardinian volcanism, which did no

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00538.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTAt Santa Maria Volcano (New Hebrides island arc), extensive ash and scoria flow deposits overlie the mainly effusive, pre‐caldera cone. Hydromagmatic features characterize these deposits, the composition of juvenile clasts ranges from basalt to acid andesite/dacite (SiO2= 51–63.6%) with a dominant basaltic composition. The stratigraphic position of this pyroclastic series and its spatial distribution around a 8.5 km × 6 km wide caldera provide evidence of a relationship between this series and the caldera formation. In addition, these pyroclastic deposits are co‐genetic to parasitic cones and lava flows developed along faults concentric to the caldera. Both series result from a compositionally layered magma reservoir, the subordinate differentiated magmas being the result of fractional crystallization from the basalts. A model of caldera formation which implies a large hydromagmatic eruption at the central vent and minor magma withdrawal by flank eruptions is proposed. This model emphasizes the importance of mafic hydroclastic eruptions in the caldera forming event and contradicts a model implying only quiet subsidence, a process often proposed for the formation of calderas in island are volcanoes of mainly mafic compo

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00539.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTA structural analysis carried out on the volcanic products of the islands of Salina, Lipari and Vulcano (Aeolian archipelago) points out that the large‐scale tectonic setting is dominated by NW‐SE trending right‐lateral extensional strike‐slip faults and by N‐S to NE‐SW trending normal faults and fractures. This fault pattern generates pull‐apart type structures, developing between different right‐hand overlapping fault segments and a characteristic extensional imbricate fan geometry at the tip of the major strike‐slip faults. All the structures, representing the surface expression of an active crustal discontinuity which controls the evolutionary history of the magmatism of the three islands, are kinematically compatible with a N100°E extension related to a rifting process affect

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00540.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTDirect observation of active emission of fluids and mud from a submarine mud volcano were made for the first time in an extensive field of mud diapirs and mud volcanoes on the Mediterranean Ridge using a video camera towed 2 m above the seafloor in 1800 m of water. This recent research using both long range and deep‐towed sidescan sonar systems indicates also that diapirism and eruption of mud along the crest of the ridge is more common than previously thought. The southwards increase in age of rock fragments carried within the erupted mud supports the hypothesis that the fluid mud becomes overpressured within a southward‐dipping backthrust from the Inner Deformation Front of this accretionary pr

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00541.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTA discussion is given of the impact of normal slant faults on basinal structure, compaction, fluid overpressure development, and thermal effects in sedimentary basins. Faults which are hydraulically closed or open to fluid flow are examined in a dynamical two‐dimensional fluid/ flow compaction model.From this numerical investigation three dominant factors characterize the effects of single and multiple faults with open or closed hydraulic behaviours: (i) there is a difference in excess pressure for fault planes with open or shut hydraulic conditions, but the neighbourhood where the effect of the fault is dominant is fairly localized (to within about half a kilometre or so laterally from the fault plane); (ii) the lateral and vertical motion of sediments between faulted blocks induces a thermal difference prior to, during, and post‐faulting, which can play a role in influencing hydrocarbon generation, migration, and accumulation; (iii) porosity retention and permeability modification by fault development could influence hydrocarbon exploration decisions regarding sealing, migration pathways, and fluid retention.The general patterns of slant fault effects described here should prevail in most geological situations, because the numerical experiments are designed to illuminate sharply the dominant response characteristics within the framework of simplified situati

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00542.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00543.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY