ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00442.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00443.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTSome geological structures have simple geometrical forms and can be analysed using deterministic equations. Examples include alluvial fans and many sedimentary basins. But most geological structures are complex and appear to defy mathematical analyses. Yet in the complexity there is an order. Complex geological structures generally obey fractal statistics. Examples include topography, distributions of earthquakes and faults, and mineral deposits. An unresolved question is whether the fractal order is simply the result of scale invariance or the result of governing equations that yield deterministic chaos. In order to try to answer this question a variety of slider‐block models have been considered. The stick‐slip behaviour of slider‐block models is a simple analogy to earthquakes. A pair of slider‐blocks has been shown to behave chaotically. Models that use many slider‐blocks exhibit self‐organized criticality and generate fractal statistics similar to the statistics of regional

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00444.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00445.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTSince 1975 several high‐resolution seismic‐refraction and reflection surveys have been carried out in western Germany to investigate the structure of the Earth's crust and uppermost mantle. The investigation culminated in the seismic‐refraction survey along the 825 km long central part of the European Geotraverse (EGT) in 1986. This contribution summarizes the main results of the more recent crustal investigations along and around the EGT.The internal crustal structure throughout the area of the Variscides is very complex and changes laterally considerably. Distinct crustal blocks differing in their internal structure can be assigned to geologically defined units of the Variscan and Caledonian orogeny. In spite of local deviations, in general a more or less transparent and low‐velocity upper crust contrasts with a highly reflective lower crust. A subdivision of upper and lower crust by a well‐defined boundary (Conrad discontinuity) is not always seen. Towards the Alps the average velocity of the lower crust is as low as 6.2 km s−1, in contrast to the area north of the Swabian Jura where the velocities above Moho vary between 6.8 and 7.2 km s−1. In Northern Germany, the Elbe line separates the lower crust into two regions with 6.4 km s−1average velocity in the south and 6.9 km s−1in the north.The total crustal thickness under the Variscan part of Germany is fairly constant between 28 and 30 km, except under the Rhine Graben area with 25–26 km and beneath the central part of the Rhenish Massif where an anomalous crustal thickening to 37 km is observed. Under northern Germany the Moho rises to about 26 km depth and the data indicate at least one fault‐like step of 1 km before the crust thickens toward the Ringkobing‐Fyn basement high. The synthesis of seismic velocity structure and petrological information from xenolith studies allows us to propose a mafic composition for the deeper levels of the crust and uppermost mantle which may be valid at least for the central part of the Variscan crust along the European Geotra

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00446.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTDuring the continental rifting the upper mantle was unroofed, and the mantle rocks were transformed into serpentinite at the ocean‐continent transition of the west Galicia margin (Spain). The serpentinite layer, several km thick, extends probably eastwards, beneath the highly thinned continental crust of the margin.The serpentinite layer was recently imaged by seismic reflection. It is discontinuously and deeply layered. As serpentinized peridotite can have densities and seismic velocities comparable to those of the lower continental crust, we suggest that undercrusting by serpentinite can play a part in building the lower seismic crust in highly stretched continental rifted area

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00447.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTThe Ivrea‐Verbano Zone in northern Italy represents a section through the lower continental crust which has been tilted and emplaced into its present position during the Alpine orogeny. Recent and on‐going structurally‐oriented geological mapping in this region is providing new information about the geometry of the complex. The central part of the zone is dominated by a large basic complex (the ‘mafic formation') which is intrusive into the surrounding gneisses. The foliation within the envelope of gneisses is deflected around the intrusive complex as if by ballooning, but in the region south‐west of Monte Capio both units are folded together into a tight to isoclinal steeply plunging fold with an amplitude ofc.10 km. This fold locally inverts the stratigraphy of the layered basic group of the complex, and is thought to be the result of gravitational collapse following intrusion and inflation of a large magma body into the lower crust.Several high‐temperature shear zones have now been traced within the country rock for distances up to 20 km. The geometry of these, and their relationship to the basic complex suggests that at least some of the extensional collapse of the mafic body is related to uplift caused by intrusion of this body.Close parallels can be drawn between the observed structure in the Ivrea‐Verbano Zone (after removing the effects of late, low‐temperature faulting and folding related to emplacement of the rocks into their present position), and those inferred from deep seismic reflection profiling in areas of current extension such as parts of the US Basin and

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00448.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTIn a deep section of the Jurassic Andean arc, coastal Cordillera of northern Chile, south of Antofagasta, basic magmas from a mantle source accreted large masses of crust in an early stage of arc development. These gabbroic intrusions were isochemically metamorphosed at moderate pressures (≤ 5 kbar) and high temperatures (∼ 800°C) into uniform garnet‐absent dino+ortho‐pyroxene gneisses (granulites). Subsequently they were partly transformed into amphibolites (T≤ 700°C) during tectonically controlled access of fluid without major changes in whole rock chemistry. Locally migmatization occurs in the amphibolites. The metamorphic unit was diversified by enduring magmatic activity in the form of chemically distinct gabbroic and quartz dioritic intrusions. Formation and composition of continental crust might be a typical example for the deeper plutonic sections of this continental m

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00449.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTThe crust ≈ 10–20 km under the Eifel is composed of amphibolite‐facies metasediments and meta‐igneous rocks of tonalitic to granodioritic composition; mafic granulites occupy the base of the crust down to a Moho depth between about 29 and 34 km. The meta‐granodiorites and meta‐tonalites have I‐type chemical characteristics and appear to have formed approximately 400 Myr ago by partial melting of a lower crustal source. Amphibolite‐facies metamorphism probably followed within the same orogeny. During the Quaternary, many amphibolite‐facies rocks were subjected to contact heating in crustal magma chambers and/or during transport to the earth's surface. Contact heating is also recorded in radiogenic isotope compositions of minerals from one xenolith. A genetic link between meta‐igneous amphibolites and the deeper crustal mafic granulites can neither be proven nor discounted by the isotope data. If there is a genetic relationship, it requires fractionation of a mafic magma in the lower crust and assimilation of metasediments and separation of a

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00450.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTIn order to constrain interpretations of seismic reflection records more effectively, the seismic properties of a middle crustal section exposed in the Saint Barthélémy Massif have been determined. The massif, transected by a 200 m thick shear zone has been systematically sampled for density measurements and modal analysis has been performed in order to define the spatial variations of physical properties. Seismic velocities (Vp,VS, shear wave birefringence), have been measured on five representative samples to 600 MPa and 600°C simultaneously in the three structural directions (X, Y and Z). For two samples, the experimental data have been compared with calculated values, based on petrofabric analyses. The Lattice Preferred Orientation (LPO) is determined using universal stage, electron channelling microscopy and neutron diffraction goniometry. Using the experimental and calculated velocity data, we establish a lateral homogeneous anisotropic mod

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1992.tb00451.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY