ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1991.tb00835.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1991.tb00836.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1991.tb00837.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe year 1991 marks the 200th anniversary of the death of Mozart. His last opera,The Magic Flute, was begun, completed and first performed in the year of his death, 1791. The creation of the opera was closely associated with prominent geologists of the time although the work itself is an alchemical drama, deriving more from Hermetic ‘science’ and magic than from the emerging ‘legitimate’ science of

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1991.tb00838.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractVolatile fluxes from Mid Ocean Ridge (MOR) and subaerial volcanism have been estimated or re‐evaluated using several natural tracers‐3He,210Po, SO2‐and chemical ratios of volatile species in lavas and volcanic gases.These estimates confirm the net predominance of anthropogenic fluxes over volcanic fluxes for CO2, SO2and trace metals.They also suggest that, while most of the volatiles transferred during MOR volcanism come from the mantle, volatiles stored at the surface of the Earth supply an appreciable fraction of subaerial fluxes and can be the dominant source for some of them.The surface inventory of volatile species cannot result from steady‐state degassing with constant rate and needs much greater fluxes in the past or other volatile supply processes. This inventory is the result of several of the following processes: capture of the solar nebula and its subsequent partial escape, impact degassing of accreting bodies, and, from Archean to present mantle, degasssing through volcanism and associated phenomena, with recycling into the mantle through sub

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1991.tb00839.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThermal data represent a valuable remote sensing aid in studying crustal evolution. Heat flow (Q) results from the heat loss by the cooling earth and from the heat production (A) of the radiogenic elements brought to the upper crust by magmatic intrusives. Heat flow is often observed to be linearly related to heat production. The slope of this relation, or thermal depth (D), has been used to infer a global upward enrichment in heat‐producing elements. This thermal depth has been equated with the thickness of granites, but such an interpretation has not been confirmed everywhere. The depth to which granitic plutons are rooted can be computed from the inversion of gravity data. It averages 7±2 km and is much smaller than the thermal depth. Granulite facies rocks are assumed to be present in the lower crust on the basis of seismic and geochemical data. These rocks are generally depleted or initially poor in radiogenic elements (U, Th, K). It is suggested that the thermal depth reflects the depth to the depleted layer in continental regions and that it corresponds to the granulitic layer in most places. Worldwide thermal and seismic data support this relationship, although surface heterogeneities introduce complications. Thermal data can therefore be used to constrain the structure of the crust and its evolution through ti

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1991.tb00840.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractResults of palaeomagnetic measurements of a core from Mururoa atoll, French Polynesia, led us to document for the first time the atoll's magnetostratigraphy. Periods of slow aggradation, correlated with sea‐level low‐stands, show that atolls are accurate recorders of sea level fluctuations. The timing and amplitude of sea level fluctuations may be reconstructed on the basis of precise dating of atolls and shallow‐water platforms. Magnetostratigraphy is therefore a first step towards a quantitative calibration of the eustatic records of coral a

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1991.tb00841.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIn this paper, we present an expansion of the model for marine ecosystem collapse at the Cretaceous‐Tertiary boundary presented by Brinkhuis and Zachariasse (1988). A long‐term sea‐level drop at the end of the Cretaceous culminated in a short‐term regressive pulse at K‐T time. Deep‐water production was curtailed, minimizing the vertical advection of nutrients and oxygen in the oceans. Consequently, a productivity crisis developed, which could only be survived by cosmopolitan shallow‐dwellers, and the Oxygen Minimum Zone (OMZ) expanded. No sustained Oceanic Anoxic Event followed the K‐T boundary event, since productivity had dropped to extremely low values. At K‐T time, however, the short‐term expansion of the OMZ, invoked by the combination of minimized oxygen advection and abrupt mass mortality, caused dysoxic conditions even to reach up to the shelves, as can be deduced from sedimentological, chemical and fau

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1991.tb00842.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA recent surge of interest in short‐period fundamental mode Rayleigh waves (Rg) propagation is motivated by their usefulness for structural mapping and estimation of attenuation (Q) properties of the uppermost crust, their importance in scattering studies and as a nuisance (false alarms) in detection seismology. We have investigated Rg phase velocity dispersion characteristics, using recordings from 16 out of 22 subarrays of the NORSAR array of aperture 100 km. The observed phase velocity in combination with a one‐layer and two‐layers model over halfspace models were inverted using a maximum likelihood scheme. In view of the smoothness and simplicity of the dispersion curves, the number of unknowns were limited to three parameters, namely shear velocities and thickness, using a Poisson's ratio of 0.25 for P‐S velocity coupling and density fixed. In the general array siting area the derived low velocity layer has an average thickness of 1.02 km, and the associated shear velocity is 2.82 km s‐1. The underlying model half space appears to be uniform, and its derived shear velocity is 3.55 km s‐1, which is typical of the upper crust. In contrast to other similar studies, no obvious correlation was found with local geology, which mainly consists of Precambrian crystalline rock sequences. Group velocities were calculated from the structural models and compared to the observational ones. The agreement between calculated and observed group velocities was

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1991.tb00843.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe deep seismicity of the Tyrrhenian Sea is analysed using data from a new instrumental catalogue of the seismicity of the Italian area. We use algorithms for the determination of absolute and relative hypocentral locations and for the evaluation of the geometry and coherence of the state of stress within the subducting slab. The structure of the Benioff zone, although simpler than previously indicated, reveals anomalous traits both in the seismicity distribution and in the stress geometry, confirming that standard subduction models cannot be applied in the Tyrrhenian region. The velocity anomaly and the location of few isolated events indicate that the subducted slabs extend to the north along the Apenninic chain approximately to the latitude of the Irpinia region, in Central Italy (˜ 42°N

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1991.tb00844.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY