ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00660.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.tb00662.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.tb00663.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe North Tyrrhenian–Northern Apennines post‐collisional system (NTAS) has been analysed on the basis of marine reflection profiles and bibliographic sources with the aim of providing an up‐to‐date geotectonic and evolutive framework consistent with structural data. The continental rifting began to affect the most internal (western) side of the system in the middle (?)‐upper Miocene, while the most external (eastern) zones were touched by rifting only in Pleistocene times. The birth and development of extensive, asymmetric basins took place with a progressive speeding up of rifting towards the external sectors.A diachronous, regionally extended and eastward rejuvenating unconformity, recognizable within the Neogene–Quaternary basins, marks the passage from the syn‐rift to the post‐rift tectonic regime. While the first is everywhere dominated by extension, the second one produces vertical movements. Reflection terminations related to this unconformity are interpreted in terms of vertical tectonic component. Three zones that experienced different post‐rift vertical movements are thus recognized in the NTAS: subsidence in the North Tyrrhenian deep water region; tectonic stability or alternation of moderate subsidence and uplift in the continental shelf and western Tuscany, strong uplift in eastern Tuscany.The updated structural data demonstrate that the NTAS upper crust is crosscut by both Tyrrhenian‐dipping and Apennine‐dipping low‐angle detachment planes, above which the upper crustal blocks rotated and experienced extensional transport along two opposite directions: to the west and to the east, respectively. The coexistence of opposite‐dipping crustal surfaces bears two fundamental implications for the NTAS geodynamics. First it stresses the importance of the anti‐Apennine transfer faults, since they separate crustal blocks of opposite extension polarity. Secondly, it testifies that the extension tectonics not only re‐utilized former crustal thrust planes, but also gave origin to new significant E‐ and NE‐dipping detachment planes.Plan and crossview geometries of faults, together with considerations on the role of the metamorphic core complexes, point to an interpretation of the NTAS structure that is more consistent with the ‘anastomosing shear’ model rather than the 'sim

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00664.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTIn the volcanic sequence of the Betic Ophiolitic Association (BOA) volcanic structures and textures are preserved in spite of being metamorphosed to the edogite facies. The original quenched glassy margins of the pillows and lava flows are still recognizable by the darker colour, fine‐grained textures and scarcity of phenocrysts. The BOA eclogitized pillows have chemical compositions very similar to the basalts enriched in LIL elements erupted nowadays at the mid‐oceanic ridges. Magmatism which generated the BOA most likely began under continental rift conditions at the Triassic‐Jurassic boundary and continued under ocean‐floor extensional conditions during the lower and middle Jurassic. In age and petrological characteristics this magmatism is equivalent to that of the western Tethys ophiolites. During the Late Cretaceous, due to the collision of African and Iberian Plates, the BOA ophiolites were subducted and underwent a metamorphism in the eclogite fades whose climax in the Lugros outcrop can be estimated at 650–700°C and a

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00665.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTRecent tectonic models of the Alpine‐Carpatho‐Pannonian region (ALCAPA) assume a large eastward shift of the Transdanubian Range domain, in the Cenozoic. Since palaeomagnetism is one of the most powerful tools in solving geodynamic processes, the authors present an approach to the escape problem by using all available and relevant palaeomagnetic data. This data set demonstrates consistency with models put forward by geologists for Jurassic and older ages. From the mid‐Jurassic on the Northern Calcareous Alps (NCA) did not share the rotations of the Transdanubian Range domain and of the Southern Alps. After individual movements from Neocomian to Miocene, the Transdanubian Range domain must have drifted northward in the mid‐Miocene up to the Southern margin of the Northern Calcareous Alps, before starting the escape in the geologists' def

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00666.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe regional stress field in the northern North Sea (offshore western Norway) has been studied through the acquisition and analysis of directions of maximum horizontal compression (s̀H) as extracted from borehole breakouts and from earthquake focal mechanism solutions.The results indicate that the regional stress field is dominated by NW‐SE compression, with good consistency between shallow borehole breakouts (2–5 km depth) and deeper earthquakes (10–25 km depth). The broad spatial consistency in stress direction indicates that the main stress field is related to factors of primarily plate tectonic origin, and the results are in good agreement with the western Europe trend found in earlier investigations.The Tampen Spur region in the northern North Sea has been subjected to particularly complex deformation, with two dominating fault directions trending NW‐SE and NE‐SW. From Tampen Spur in the west to the Sogn graben in the east an anomalous stress field is indicated, with NE‐SW oriented maximum horizontal compressions. This anomaly is clearly seen both in the borehole breakout data and in the earthquake data. Possible sources for this anomaly are discussed, and include postglacial uplift and/or lateral variations in the physical properties

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00667.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTResearch was undertaken to establish the present coastal dynamics of the area south of Espinho, Portugal, with special emphasis on the migration inland of beaches and the retreat of cliffs during at least the last century.Besides the Holocene units (the Silvalde‐ParamostijucaFormation, 2310 ± 80 yr BP to 500 ± 80 yr BP, and the Cortegaca Beach Formation, 6850 ± 60 yr BP to 950 ± 80 yr BP), a Pleistocene unit (the Maceda Beach Formation, 29, 600 ± 690 yr BP to 14300 ± 160 yr BP) with trunks ofPinus sylvestriswas recognized. The Cortegaca Beach Formation comprises a truncated podzol profile, the Al horizon dating from 3490 ± 60 yr BP to 950 ± 80 yr BP. The study and the dating of the Pleistocene and the Holocene formations suggest a model of evolution related to sea‐level fluctuations and neotectonics, during the interval between 29,000 ± 690 yr BP and the post‐XVth century (Little Ice Age).The final purpose of the research is to apply the results to the prediction of the coastal zone evolution, and particularly to influence policy with respect to coastal zone management. This policy must take into account the inland migration of the beaches and the cliff retreat as a consequence of the natural dynamics of the earth that cannot be arrested or con

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00668.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTBecause of the occurrence of very large observed overpressure in a well located in SE Asia, numerical modelling has been undertaken to evaluate evolution of the sediments. The intensity of the excess pressure, close to lithostatic pressure, and the likely relation to induced, open‐fracture anomalies, as well as evidence of large fluid transfers, all lead to the suggestion that the tectonic regime is related to the generation of high excess pressure. To verify this hypothesis, a 2D fluid‐flow/compaction model (GEOPETTI) was used to test whether high excess pressure could be obtained without considering the effect of lateral stresses. While high excess pressures are possible, even if undercompaction is the only process considered, the distribution of fluid pressure with depth does not correspond to that observed, and the migration of fluids cannot be reproduced because of the extremely low permeability of the sediments. Accordingly, the model has been modified so that the effect of lateral stresses can be investigated through: (1) the value of the fracturing coefficient which controls the maximum overpressure that it is possible to generate; (2) the sensitivity of the system to a possible compressive event, which could squeeze the sediments laterally so that the rate of fluid expulsion would be greater than if the fluids were driven only by the mechanical load of sediments. Finally, the role of faulting or fracturing is discussed as a possible mechanism responsible for the upward transfer of fluid which can lead to anincreaseof excess pressure at depths shallower than the depth where excess pressure was first generated, a mechanism also leading to high excess pressure. Moreover, this mechanism allows for a good reproduction of observed excess pressure distributi

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00669.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTLevelling measurements carried by Osservatorio Vesuviano over Vulcano Island (North Sicily) since June 1976 show a complex history of small but significant vertical movements which took place after the ‘Patti earthquake’ of 15/4/1978. Three phases can be identified in the time history of ground deformation: (I) co‐seismic subsidence of the northern part of the Island with respect to the southern part, followed by (II) transient inflation of the central region surrounding ‘La Fossa’ volcano, and finally (III) deflation and subsidence to stationary values greater than phase I. Large variations in temperature and gas content of magmatic origin were also detected in fumaroles along the crater rim of ‘La Fossa’. The coincidence in time of the earthquake with the start of the deformation history, the proximity of the event to Vulcano Island and the favourable mechanism (right lateral) and orientation (NNW) of the fault strike, suggest that the earthquake triggered the observed deformation. Among the plausible models, one seems particularly able to reproduce the amplitude and time evolution of the geodetic data, in a manner consistent with the geochemical observations. According to this model the earthquake, while generating a compressive stress field in the quadrant of Vulcano Island, induced at first a relative coseismic subsidence of the northern part of the island, accompanied by a large increase of the mean stress within a magma chamber at ∼ 6.5 km depth. Volatile fluids were then released from the top of the magma chamber and migrated towards the surface following the enhanced pressure gradient. As a result fluid pressure diffusion around the magma chamber induced a local transient uplift of ground that vanished after exhaustion of the overpressure at the source, and finally left a permanent dislocation deformation, possibly amplified by the post‐seismic relaxation of the earthquake deviatoric stress. This interpretation is qualitatively consistent with the one suggested by

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1995.tb00670.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY