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1.
The rockmagnetic and palaeomagnetic signal in pyrrhotite bearing limestones of different contact-metamorphic settings were investigated related to intrusions ranging from small sills to large magmatic complexes. Magnetic susceptibility, the pyrrhotite/magnetite ratio and thermal modelling serve as an investigative tool to define three metamorphic zonations: a contact zone of a mixed magnetic assemblage and low susceptibilities, a pyrrhotite bearing transitional zone, where full thermoremanent magnetisations (TRMs) are acquired due to temperatures above the Curie temperature of pyrrhotite (Tc,po), and a marginal zone containing pyrrhotite and magnetite generated at temperatures below Tc,po. The fact that TRMs can consist of independent pTRMs is successfully tested by modified Thellier experiments. It is shown that a metamorphic environment with low fluid circulation provides a scenario for the recording of independent pTRMs. Multicomponent behaviour of the NRM residing in samples from the transitional zone can therefore be interpreted as a continuous record of Earth magnetic field variations.  相似文献   

2.
对采自河南嵩县祁雨沟7号角砾岩筒的黄铁矿样品进行了详细的磁化率随温度变化特征研究，加热的最高温度为700℃，结果表明黄铁矿受热分解最终生成磁黄铁矿.黄铁矿通过两个可能的途径转变为磁黄铁矿：一个是黄铁矿颗粒首先经表面吸附氧的氧化转变为磁铁矿，随温度升高新生成的磁铁矿与黄铁矿晶格中挥发出的硫进一步反应转变为磁黄铁矿；另一可能途径是黄铁矿直接脱硫转变为磁黄铁矿，此反应为磁黄铁矿的主要来源.氩气环境下加热过程中，从约380℃开始即有磁铁矿生成，但直到约535℃才有磁黄铁矿的生成.在535℃～560℃的加热过程中生成的磁黄铁矿居里温度不稳定，直到加热至高于约560℃时才生成居里温度稳定的磁黄铁矿.氩气环境下，黄铁矿受热生成的磁性矿物的类型仅受最高温度的控制，与高温段的滞留时间无明显关系，而其生成量同时受最高温度和高温段滞留时间的控制.  相似文献   

3.
Rock magnetic investigations of Permo-Carboniferous carbonate sediments from two areas on Spitsbergen are described, conducted to identify the carriers of the NRM in these rocks. Since microscopic and magnetic separation techniques could not profitably be applied, the nature of magnetic minerals was investigated by thermal demagnetization of the NRM and decay of saturation isothermal remanence (Irs) during heating to 600°C, as well as by the distribution of the median destructive fields of the NRM and observation of magnetic susceptibility after subsequent heatings. The results show that the NRM of these limestones resides mainly in magnetite, but creation of magnetic pyrrhotite and of fresh magnetite is observed during heating to 600°C. Presence of sulphides indicates that magnetite is an oxidation product of pyrite or of non-magnetic pyrrhotite. Examination of rock magnetic properties of limestones leads to the conclusion that most of the magnetite in the rocks of the Bellsund area is of detrital origin, whereas the rocks at Festningen contain magnetite derived from pyrite probably during an early stage of the diagenetic process.  相似文献   

4.
Magnetic properties related to thermal treatment of pyrite   总被引：5，自引：0，他引：5  
Detailed rock magnetic experiments were conducted on high-purity natural crystalline pyrite and its products of thermal treatments in both argon and air atmospheres. In argon atmosphere (reducing environment), the pyrite is altered by heating to magnetite and pyrrhotite; the latter is stable in argon atmosphere, and has coercive force and coercivity of remanence of ～20 and ～30 mT, respectively. Whereas in air, the pyrite is ultimately oxidized to hematite. First order reversal curve (FORC) diagram of the end product shows that the remanence coercivity of hematite is up to ～1400 mT. The corresponding thermal transformation process of pyrite in air can be simply summarized as pyrite→ pyrrhotite→magnetite→hematite. These results are helpful for understanding of sedimentary magnetism, secondary chemical remanence and meteorolite magnetic properties.  相似文献   

5.
Low-field variation of magnetic susceptibility was investigated on a collection of several hundreds specimens of various minerals and rocks using the KLY-4S Kappabridge. The measurement is fully automated, being executed in 21 distinct fields ranging from 2 to 450 A/m (in one frequency of 875 Hz). The measurement is rapid, 7 min per specimen, so that large collections of specimens can be investigated. The results can be processed both graphically and mathematically. For the latter processing, parameters of two kinds were introduced. One characterizes the susceptibility change with field, the other one characterizes the field in which the susceptibility no longer obeys the Rayleigh law and starts becoming more complex.The results were evaluated statistically. Remarkable differences were revealed between individual minerals and between some rock types. For example, the field variation of susceptibility of pyrrhotite is in general an order of magnitude larger than that of titanomagnetite. The susceptibility increase in pyrrhotite starts at the field an order of magnitude lower than that of titanomagnetite. Low-field variation of susceptibility then appears as an interesting phenomeon that helps in the identification of magnetic minerals and in some cases also in assessing the compositional variation of them.  相似文献   

6.
In order to better constrain the extent to which common sulfide minerals will retain their osmium isotopic composition subsequent to crystallization, we have conducted experiments to quantify the diffusion behavior of osmium in pyrite and pyrrhotite. Experiments consisted of either (1) isothermal soaking of diffusion couples consisting of natural pyrite or pyrrhotite crystals packed against powdered Os-bearing Fe-sulfide or (2) ‘relaxation’ of initially high near-surface osmium concentrations produced in the latter experiments (pyrite only). Osmium penetration into samples was characterized by depth profiling using Rutherford backscattering spectroscopy (RBS) (pyrite) or electron microprobe analyses across sectioned run products (pyrrhotite). Results of the first type of diffusion experiment involving pyrite show only limited osmium penetration into sample surfaces, with the extent of penetration uncorrelated with run duration. Images of pyrite samples using atomic force microscopy show roughening of initially smooth surfaces as a consequence of step formation and suggest that osmium incorporation into the near-surface occurred by solute uptake during step growth and not by volume diffusion. Prolonged (1000+ h) ‘relaxation’ experiments revealed no additional osmium penetration into pyrite surfaces and based on the depth resolution for RBS, a maximum diffusion coefficient of 2.5×10−23 m2/s at 500°C was calculated. Experiments involving pyrrhotite over the temperature range of 950–1100°C showed extensive osmium uptake and osmium concentration gradients that conform with Fickian diffusion behavior. We found that pyrrhotite Fe/S could be varied by changes in the composition of the starting material and osmium source and over the range of Fe/S produced in experiments (molar Fe/S=0.83–0.90), we observed no systematic variation in the osmium diffusion coefficient. Diffusion coefficients measured parallel to the a crystallographic axis were on average 1.4× higher than values measured parallel to c and regression of the c-axis data yielded the Arrhenius relation:
The application of these diffusion data to simple models of diffusive exchange during static or polythermal time–temperature histories is used to assess the conditions under which radiogenic osmium will be retained. During isothermal annealing, calculations indicate that the cores of millimeter-sized spherical pyrrhotite crystals undergoing diffusive exchange with an external osmium reservoir will have their initial compositions perturbed in ≤0.5 Ma at temperatures exceeding 400°C. Pyrite undergoing the same process at 500°C requires in excess of 10 Ma before crystal cores are affected. The relatively short ‘core retention’ time-scales for pyrrhotite indicates that this mineral may be prone to isotopic resetting following relatively brief crustal thermal events, thus possibly accounting for the scatter that commonly occurs in Re–Os isochrons generated from massive sulfide samples. Calculated closure temperatures (Tc) for osmium exchange in pyrrhotite yielded values of 300–400°C for grain sizes ranging from 10 to 1000 μm. These values of Tc are similar to those calculated for Ar retention in biotite, and considerably lower than for Sr in apatite and plagioclase, for example. Such low closure temperatures for pyrrhotite suggest this mineral will date the final stage in the cooling of a magmatic system and possibly be susceptible to open system osmium exchange in the presence of late-stage hydrothermal fluids. This latter result infers that caution be applied when interpreting elevated initial osmium isotopic ratios as a product of crustal assimilation at the magmatic stage.  相似文献   

7.
Thermal effects related to burial and hydrothermal alteration leads to chemical remanent magnetization (CRM). We present an experimental study of CRM production by heating claystones at 95 °C. A vertical magnetic field of 2 mT was applied to the claystones during heating and the evolution of the remanence during heating in air is monitored intermittently for up to four months. Solid fragments (9 to 26 g) of claystones are included in a Teflon holder that is placed in the oven under a controlled atmosphere. Newly formed grains acquire a CRM and a thermoviscous magnetization (TVRM), both being parallel to the applied magnetic field. CRM is related to the amount of newly formed grains that pass the critical volume during the reaction. To measure the acquired remanence, the claystones are first cooled in a zero magnetic field and then measured using a 2G SQUID magnetometer.In the frame of the research programme on the feasibility of radioactive waste disposal in a deep geological formation, we investigate the magnetic transformation of Mont Terri Lower Dogger claystones (Switzerland) due to thermal imprinting at 95 °C. We simulate the dehydration that occurs in the walls of galleries after excavation when interstitial water evaporates and rehydration when the galleries are refilled allowing water to move towards dehydrated zones. During dehydration, the remanence gains one order of magnitude at the beginning of the experiment and then it follows a linear rate of 0.23 ± 0.07 mA m− 1/day between 3 and 14 days. The magnetic susceptibility increases by a few percent. The increase of the remanence and of the magnetic susceptibility stops after 15 days. Mass monitoring indicates that interstitial water evaporates when remanence and magnetic susceptibility stabilizes. During rehydration, the remanence increases again whilst magnetic susceptibility drops by a few percent. After 20 days, the remanence during rehydration follows a rate of 0.42 ± 0.15 mA m− 1/day. By contrast, when rehydration takes place later, after 66 days, the rate is much lower (0.09 ± 0.04 mA m− 1/day). Low temperature investigation of magnetic properties indicates an initial magnetic assemblage of magnetite and pyrrhotite. Newly formed magnetite and hematite carry the remanence. We propose that magnetite is formed at the expense of pyrite. Hematite results from the progressive oxidation of newly formed magnetite. Our results suggest the possibility that any claystones that pass the oil window can be remagnetized due to the unique action of temperature.  相似文献   

8.
Dunite samples from a borehole drilled in the platiniferous concentrically-zoned Kondyor Massif are studied by electron spin resonance (ESR). The spectrum profiles, relative intensities I, and volume magnetic susceptibilities κ are analyzed. These values experience strong irregular variations, sometimes by an order of magnitude, in the upper and medium parts of the column, at depths from 100 to 400 m; and the variations decay at greater depths. The magnetic properties of the samples are determined by iron (II) ions in the olivine lattice and by iron (III) ions in the magnetite and pyrrhotite microphases and in the products of breakdown of the solid solution: chromiferous magnetite, chromoferrite, etc. The I and κ values are directly related: κmax = 27.8 × 10−3 SI units, κmin=2.63 × 10−3 SI units, and κmean = 12.7 × 10−3 SI units. The maximum κ values are found in the zones with elevated contents of magnetite and pyrrhotite particles, and the minimum ones, in zones with few medium and small clusters with Fe3+ ions. The uneven distributions of solid solutions and magnetic phases over depths are suggested to be related to the disturbances in the conditions of crystallization.  相似文献   

9.
The possibility that the parent body of the SNC meteorites is Mars implies that the magnetic properties of these meteorites may provide evidence concerning ancient Martian magnetic fields. EETA 79001 possesses a weak, very stable primary magnetization, the properties of which are consistent with its acquisition in an ambient magnetic field either during the meteorite's formation or during the severe shock event later in its history. The samples of ALHA 77005 studied possessed no measurable primary magnetization: the observed remanence appears to be a viscous magnetization acquired in local laboratory fields. The magnetic carriers in the meteorites are fine-grained magnetite and a lower Curie point mineral, probably titanomagnetite or pyrrhotite, present to the extent of less than 0.1% by weight. Estimates of the strength of the magnetizing field for EETA 79001 are in the range 1–10 μT.  相似文献   

10.
The Neuro Fuzzy System (NFS) is a hybrid algorithm that combines fuzzy logic with neural networks. Since it can be used as a pattern recognition technique, we explore its potential to characterize the major lithological units encompassed by the first 512 m of the Colombian stratigraphic well Saltarin 1A (Guayabo and León Formations). Thus, we employ the NFS to infer the magnetic remanence S-ratio using bulk magnetic susceptibility (κ), κ-normalized saturation isothermal magnetization (SIRM κ) and/or volume of shale (Vsh) obtained from a gamma-ray log. The best results in terms of their corresponding Root Mean-Square Error (RMSE) values, throughout most of the upper Guayabo Formation, where magnetite seems to be an important magnetic phase, are attained with logκ and SIRM κ as input variables. Beyond 350 m downcore, the quality of the inference decreases over the León Formation, characterized by a significant presence of pyrrhotite. However, the extra input variable Vsh adjusts the inferred S-ratio to their experimental counterparts throughout this formation suggesting that the early diagenesis process that led to the formation of dispersed clay in these samples was also responsible for the formation of pyrrhotite. Hence the inclusion of manifold input data increases the ability of the net to predict S-ratio in complex geological settings with a sequence of changing lithologies, varying amounts and types of magnetic minerals, and different distributions of mineral grain sizes. In case these variables do not properly infer the actual S-ratio data, the extent of the different lithostratigraphic units would be still identifiable in some cases by the uneven quality of the correlation observed between inferred and experimental values.  相似文献   

11.
福建三明地区被污染土壤的磁学性质及其环境意义   总被引：44，自引：8，他引：36       下载免费PDF全文
对福建三明某钢铁厂和火电厂附近的污染表土样品进行了多参数的岩石磁学测试分析,包括χ T曲线、磁滞回线、等温剩磁获得曲线等. 三明地区污染表土中的磁性矿物有磁铁矿、赤铁矿和磁黄铁矿. 样品中磁性矿物的平均粒度较粗,为较大的准单畴,甚至多畴,粒度明显大于成土作用所产生的磁性颗粒. 粗粒的磁铁矿颗粒是污染物的主要磁性组分. 虽然磁化率测量可以作为一种简单、快速而且廉价的检测污染土壤的方法,但同时辅以必要的岩石磁学测量将有利于提取更多的污染信息. 对于低磁化率的污染土壤,亚铁磁性硫化物的存在可以作为土壤可能被污染的证据之一.  相似文献   

12.
Pyrrhotite bearing metamorphic limestones have recently experienced an increasing relevance in paleomagnetic research. Simple univectorial remanences document the metamorphic uplift, whereas more complex multicomponent pTRMs may constrain its age. For a successful application of the latter, it is important to estimate the degree of magnetic interactions to ensure the additivity of individual pTRM segments. We therefore have subjected the sized dispersed suite (<5-250 μm) of TTE pyrrhotite to FORC analysis and compared the result with remanence-based parameters like the ΔM or the irreversible susceptibility. This is used as a basis to evaluate the response of marly limestone samples from regionally metamorphic areas (Bourg d’Oisans, France) and contact-metamorphic aureoles (Elba, Italy; Skye, Scottland; Manaslu area, Nepal) to these techniques. The results show that the techniques are able to estimate the nature and - to a certain degree - the intensity of the magnetic interaction. The different dominant magnetic states of the assemblage can also be unravelled as well. Based on the remanence measurements of the TTE samples, a relationship between grain-size and the irreversible susceptibility is established in order to estimate the mean grain-size fraction in natural particle distribution.  相似文献   

13.
Summary The hysteresis properties of synthetic samples with very low contents of hematite, pyrrhotite, greigite and admixtures of magnetite and hematite in a diamagnetic matrix have been studied. The diamagnetic matrix used was sodium chloride (NaCl). The contents of the magnetic minerals varied for hematite from 0.5 to 6 wt%, for pyrrhotite from 0.02 to 0.2 wt% and for greigite from 0.02 to 0.6 wt%. Diamagnetic contributions to the magnetization curves can be distinguished in the measured samples. We observed a non-linear dependence of coercivity and saturation magnetization upon increasing contents of hematite as a result of effects of both the diamagnetic matrix and the hematite content. Only the saturation remanence which is measured in a zero magnetic field has a linear dependence on the hematite concentration. The shape of the hysteresis curves of admixtures of magnetite and hematite are probably caused by magnetostatic interactions.  相似文献   

14.
In Precambrian terrains all regional and most localintensive magnetic anomalies areproduced by magnetite. Monoclinic pyrrhotite isresponsible for some local, but oftenintensive, magnetic anomaly patterns. Both magnetiteand pyrrhotite are affected byhydrothermal alteration processes in various ways,resulting in changes either inabundance or in grain fabric. These changes arerecorded in the magnetic properties ofthe altered rock units and reflected in theiraeromagnetic signatures. Hydrothermalalteration in deformed bedrock zones is commonlycontrolled by structural or tectonicfeatures. Regional high-resolution aerogeophysicalsurveys can be utilized, in bothregional and detailed investigations, to map theoverall geological and tectonic settingor to estimate local changes in magnetic mineralogyand the relative abundance ofradionuclides.Magnetite is most commonly destroyed in alterationprocesses, such as biotitization,carbonation, sulfidization and silicification. Theprogressive destruction of magnetitebegins at grain margins and results first in broken and cracked grain texture and smallergrain size, then progresses to total disappearanceof magnetite. Alteration in magnetite-bearing rock units may be recognized by decreasedmagnetic intensity and by thebroken, disrupted magnetic pattern. The abundance ofmonoclinic pyrrhotite isenhanced by reducing hydrothermal fluids, and typicalcrystal anisotropy is developeddue to tectonic stress.The relative contents of radioelements are changedin the same hydrothermal processesand partly for the same reasons as the ferrimagneticminerals. Potassic alteration oftenresults in elevated K radiation particularly formafic rocks, and then anomalous K/Thratios along local shear or fracture zones may beindicative of gold-bearingmineralization. On the other hand, high U/Th ratioswithin metasedimentary units maypoint out prospects for sulphidization. Althoughvariation of U/Th ratios largely reflectsthe environmental conditions during primarydiagenesis or a later deformational phase,mainly the decrease in Th radiation close tosulphide mineralization seems to beresponsible for the elevated U/Th ratios.  相似文献   

15.
We carried out thermomagnetic susceptibility analyses of fault rocks from core samples from Hole B of the Taiwan Chelungpu Fault Drilling Project (TCDP) to investigate the cause of high magnetic susceptibilities in the fault core. Test samples were thermally and mechanically treated by heating to different maximum temperatures of up to 900 °C and by high-velocity frictional tests before magnetic analyses. Thermomagnetic susceptibility analyses of natural fault rocks revealed that magnetization increased at maximum heating temperatures above 400 °C in the heating cycle, and showed three step increases, at 600 to 550 °C and at 300 °C during the cooling cycle. These behaviors are consistent with the presence of pyrite, siderite and chlorite, suggesting that TCDP gouge originally included these minerals, which contributed to the generation the magnetic susceptibility by thermomechanical reactions. The change in magnetic susceptibility due to heating of siderite was 20 times that obtained by heating pyrite and chlorite, so that only a small fraction of siderite decomposition is enough to cause the slight increase of the susceptibility observed in the fault core. Color measurement results indicate that thermal decomposition by frictional heating took place under low-oxygen conditions at depth, which prevented the minerals from oxidizing to reddish hematite. This finding supports the inference that a mechanically driven chemical reaction partly accounts for the high magnetic susceptibility. A kinetic model analysis confirmed that frictional heating can cause thermal decomposition of siderite and pyrite. Our results show that decomposition of pyrite to pyrrhotite, siderite and, to some extent, chlorite to magnetite is the probable mechanism explaining the magnetic anomaly within the Chelungpu fault zone.  相似文献   

16.
Summary This study is a follow up of the investigation of some magnetic properties and metastability of greigite in samples obtained from Miocene claystones in the Kruné hory (Erzgebirge) Piedmont basins (Bohemia). Three different methods of upgrading the smythite were applied; the magnetic properties of the concentrates are compared. The thermal conversion of smythite sets in at 200°C while greigite converts at 250°C. The first intermediate products to be formed are iron sulphides, marcasite clearly dominating over pyrite and pyrrhotite. Apart from a Fe3+ sulphate with a composition of Fe2(SO4)3, oxidation of these sulphides gives rise to -Fe2O3. The result of the subsequent decomposition of the mentioned sulphate is the formation of -Fe2O3, which retains the sulphate structure. The final product of the thermal decomposition at 800°C is -Fe2O3. In the smythite concentrate the conversion to Fe3+ sulphate and -Fe2O3 is about twice as intensive as in greigite. No direct conversion to -Fe2O3 was found. During the thermal process self-reversals of remanence were observed, in various samples as many as four reversals in the temperature interval from 340 to 590°C. The occurrences of self-reversals of remanence were only observed at high degrees of thermal demagnetization, of the order of 10–2 down to 10–3 in the temperature interval of sulphide origin (below 400°C), and of the order of 10–4 down to 10–6 in the temperature interval of Fe-oxides origin (above 400°C).Presented at the 3rd Conference on New Trends in Geomagnetism, Castle of Smolenice, Czechoslovakia, June 22–29, 1992  相似文献   

17.
Study of the opaque minerals from well No. 7, Krafla, indicates two mineral assemblages: (1) hydrothermally altered igneous minerals and (2) secondary minerals that have precipitated from the geothermal fluid at depths down to 2140 m, and at temperatures up to more than 340°C. Chief amongst the chemically precipitated minerals are pyrite, pyrrhotite and goethite, which is described here for the first time in an Icelandic geothermal drill hole.The geothermal system at Krafla has been periodically disturbed by the influx of volcanic emanations; this article attempts to interpret, by use of thermochemical calculations, the processes affecting the precipitated mineral assemblage.  相似文献   

18.
The central Taupo Volcanic Zone (TVZ) is a region of intense Quaternary rhyolitic volcanism and geothermal activity in the North Island of New Zealand from which about 14,000 km3 of pyroclastics and lavas have been erupted during the last 1.6 Ma. Analysis of aeromagnetic surveys over the TVZ showed the presence of long-wavelength (10 to 25 km) magnetic anomalies which roughly follow the trend of the currently active eastern TVZ, from the north of Lake Taupo to the east of Lake Rotorua. An interpretation of the long-wavelength magnetic anomalies using 3-D magnetic modelling suggests that these anomalies are caused by the magnetic effects of < 3 km thick sequence of volcanic rocks and deeper magnetised bodies within the non-magnetic upper crust (4–7 km depth) beneath the young (age < 0.7 Ma), currently active eastern TVZ. The deep magnetised bodies are interpreted as solidified rhyolitic sub-volcanic plutons that have cooled down to below their Curie temperature.Although the existence of plutonic bodies beneath the TVZ has been postulated prior to this study, this magnetic interpretation result appears to be the first geophysical model of such bodies.  相似文献   

19.
Paleomagnetic, rock magnetic, and sedimentary micro-textural data from an early Miocene mudstone sequence exposed in Okhta River, Sakhalin, Russia, indicate the presence of pyrrhotite and magnetite at different stratigraphic levels. Sites that contain only magnetite have a reversed polarity characteristic remanent magnetization (ChRM) with a low-coercivity overprint, which coincides with the present-day geomagnetic field direction. Pyrrhotite-bearing sites have stable normal polarity ChRMs that are significantly different from the present-day field direction. After correction for bedding tilt, the ChRM data fail a reversals test. However, the normal polarity pyrrhotite ChRM directions become antipodal to the tilt-corrected magnetite ChRM directions and are consistent with the expected geocentric axial dipole field direction at the site latitude after 40% partial unfolding. These data suggest that the pyrrhotite magnetization was acquired during folding and after lock-in of the magnetite remanences. Electron microscope observations of polished sections indicate that fluid-associated halos surround iron sulphide nodules. Pyrrhotite is present in randomly oriented laths in and around the nodules, and the nodules do not appear to have been deformed by sediment compaction. This observation is consistent with a late diagenetic origin of pyrrhotite. Documentation of a late diagenetic magnetization in pyrrhotite-bearing sediments here, and in recent studies of greigite-bearing sediments, suggests that care should be taken to preclude a late origin of magnetic iron sulphides before using such sediments for geomagnetic studies where it is usually crucial to establish a syn-depositional magnetization.  相似文献   

20.
The mean temperature gradient maps from surface down to top basement and down to base Tertiary correspond to the boundaries and internal features of the basin. The Landshut-Neuötting High in Eastern Bavaria is an area of relatively high temperature. The German Eastmolasse part west of this high shows extremely low temperature gradients. In the German Westmolasse area, in addition to a normal Tertiary gradient of about 25°C/km which is assumed to be the Tertiary paleogradient a steep near-surface gradient down to 500–800 m depth is deduced from the present interpretation of the measurements so that due to the southward increasing sediment thickness of the Tertiary in the flat northern margin of the basin there results a higher Tertiary mean gradient than in the south. The intramesozoic gradients are somewhat irregular, but generally tend to increase from north to south. Thus far they compensate to a certain degree the regional trend of the Tertiary gradients so that the mean gradients from surface down to top basement show smaller differences than the mean Tertiary gradients. A slight increase of the Mesozoic temperature gradients as compared with the Tertiary gradients is interpreted by both the lower heat conductivity of the consolidated and carbonate-rich Mesozoic and the northward directed water flow in the Malm karst transporting heat from the deeper southern part of the basin within the Malm karst northward at least since Pliocene time.  相似文献   

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