ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00235.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00236.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The exhumation of high‐pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures, or the transport of the metamorphic rocks through the overburden. Exhumation cannot be achieved simply by thrusting or strike‐slip faulting. It may be caused by erosion of shortened and thickened crust, but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km. One or more of the following additional mechanisms may be involved.1 Corner flow of low‐viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock, and may explain some occurrences of high‐pressure tectonic blocks in mélange. This process does not, however, appear to be adequate to explain the exhumation of regional high‐pressure terrains.2 Buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings. This is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle, but cannot explain the emplacement of coherent tracts of high‐density metamorphic rock into shallow crustal levels. Some high‐pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low‐density mud or serpentinite.3 Extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high‐pressure terrains. Extension may occur in the upper part of an accretionary wedge thickened by underplating; or it may affect the whole lithosphere in a region of intracontinental convergence, if surface elevation has been increased by the removal of a lithospheric root. In the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the m

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00237.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

According to the theory of heat conduction in a semi‐infinite body, temperature changes at the surface propagate into the subsurface with the amplitude attenuation and time delay that increase with depth. Temperature changes on the earth's surface, reflecting the past climatic history, can thus be evaluated by analysing the curvature they have caused in the present temperature‐depth distribution. As a rule, temperature profiles to depths of 200–300 m record surface temperature trends accurately over the last two centuries or so; deeper holes may reveal climate history farther back but with decreasing resolution.We present several synthetic temperature‐depth profiles to demonstrate the expected signature of past surface temperature changes in the subsurface, the analysis of which may help better identify the climate of the past. Examples of extracted climate recollections from holes in North America and Europe are discussed. While inconspicuous underground records may correspond to the postglacial warming 8–11 kyr ago, reasonably well‐documented borehole logging data have confirmed climate excursions in the past millenium, namely the Little Climate Optimum and the Little Ice Age. Traces of recent warming are generally common in many temperature records, evidencing the temperature rise by 1–2 K over the p

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00238.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

When continental rifting takes place above a hot asthenosphere, pressure‐release melting of adiabatically upwelling mantle may generate large volumes of basaltic melts which subsequently are emplaced at crustal levels and cool. To correctly estimate the heat flow from tectonic subsidence and crustal thinning, it is necessary to account for the melt volumes. A simple physical model of heat flow that incorporates a crustal growth correction on lithospheric extension estimates, as well as the heat in the emplaced magma, has been developed. The principal result is that heat flow may be substantially increased for several million years after rifting, even for a moderately heated asthenospher

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00239.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Creepex, defined as the systematic deviation of the magnitude of a single earthquake from the linear orthogonal regression between local magnitudeMLand coda duration magnitudeMd, calculated for the whole region, is used as a measure of the frequency content of the seismic sources in the Italian region. Predominantly high‐frequency events are found in the two areas of Quaternary tectonic shortening in North‐Central Italy and in the Calabrian Arc. This result, confirmed by two independent statistical tests, is in agreement with the global pattern obtained from the study of the regression between body‐wave magnitude,mb, and surface‐wave magnitudeMs: systematic shift to high frequencies in the energy release of seismic sources located in subduction zones and to low frequencies in zones of spreading. The analysis of the correlation between the patterns of heat flow and of seismic source spectral properties indicates that these source properties, in general, do not reflect thermal conditions in the lithosphere, but rather represent the result of tectonic pr

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00240.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Multichannel seismic reflection data from the Southern Kerguelen Plateau show many dipping basement reflectors associated with volcanic flows. These reflectors are quite similar in their shape to seaward‐dipping basement reflectors observed along volcanic passive margins. On the Kerguelen Plateau the sources are updip of the basement reflectors, in the presently extinct and eroded volcanoes. We suggest that the same source/reflector geometry may also apply to the seaward‐dipping basement reflectors observed along passive margins. We interpret these reflectors to be the result of volcanism on the passive margin which flowed in all directions into the newly created ocean basin at an early spreading st

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00241.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

An interdisciplinary project of ETH Zurich, in collaboration with Turkish universities, is described. The research area of NW Turkey was chosen because it exhibits active crustal movements, pronounced seismicity, elevated heat flow, and characteristic deep groundwater circulation patterns. In order to elucidate the interrelations between these features the collaboration of different specialists is required. Among the disciplines employed are geology, tectonics, seismology, geodesy, hydrogeology, and geothermics.

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00242.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Due to the contrast in thermal conductivity between salt and typical sedimentary formations the presence of salt in various shapes in the sub‐surface can have a significant impact on the sub‐surface temperature distribution and thermal maturation of source rocks.Using a thermal indicator tomography 1‐D modelling system, which deals with salt insertion, the thermal and excess maturity anomalies caused solely by the presence of a salt layer are investigated. Two cases, salt ‘plug’ and ‘lens’, illuminate the different patterns of vitrinite reflectance variation with depth that would be recorded by borehole sampling. Salt can be inserted either as a primary depositional layer or by secondary intrusion at depth.The effects of salt are more dominant on the subsalt layers because:1salt insertion changes the burial paths of subsalt sediments. Thus the compaction‐driven fluid flow of subsalt sediments, and also basement subsidence, are altered;2 iso‐temperature lines are modified by the presence of the salt and the variation depends on the thickness of the salt layer.The model was also designed to estimate the time of salt insertion and the variation of salt thickness in an inverse sense using present day data on temperature with depth and measured thermal indicators. An investigation is given of the degree to which inverse procedures resolve parameters associated with salt insertion. The sensitivity of those parameters

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00243.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The tectonic significance of the Erzincan earthquake of 13 March, 1992 in Eastern Turkey is discussed. The intersection of the North Anatolian and The East Anatolian strike‐slip fault zones has resulted in formation of the Erzincan pull‐apart basin and new seismically active fault branches on its northeastern side. Local concentrations of surface ruptures strike along the most active branches of the North Anatolian fault zone (N300W) for 62 km. They are usually open fractures with northeastern sides uplifted up to 20 cm and rarely with dextral offset up to 10 cm. These secondary ruptures manifest indirectly oblique seismic fault displacement corresponding to the Late Quaternary motion on the fault zone, although at the surface the dextral component has been suppressed relative to the vertical

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00244.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY