Thermal regime of the continental lithosphere

Thermally, the lithosphere may be defined as that outer portion of the earth in which heat is transferred primarily by conduction. It generally includes the crust and part of the mantle. The thermal regime of continental lithosphere is determined by many factors including heat flow from the asthenosphere, the vertical and lateral variation of both thermal conductivity and radiogenic heat production, tectonic history, and such superficial processes as climatic history and the shallow hydrothermal regime. From studies of the global heat flow data set, two generalizations regarding continental lithosphere have arisen, namely that: 1) there is a negative correlation between heat flow and tectonic age of continental lithosphere; and 2) the thermal evolution of continental lithosphere is similar to that of ocean basins with the result that the “stable geotherm” is similar in both environments. When continental heat-flow data are studied from a regional rather than a global point of view, considerable doubt arises as to the general applicability of either statement. R. U. M. Rao and his associates have demonstrated that while Precambrian terranes do have demonstrably lower heat flows than, say, Tertiary terranes, the data are not normally distributed and it is not possible to establish a negative correlation between heat flow and age in any rigorous statistical way. The scatter in the relation may be explained in terms of the variations in the duration, intensity and even the sign of continental thermotectonic events in contrast to the simple situation (creation of new oceanic lithosphere at mid-ocean ridges) which prevails in the oceans. The scatter also is partially attributable to the large and laterally variable radiogenic component of heat flow on continents. For a province for which a heat flow-heat production relation has been established, much of the scatter in surface heat flow due to crustal radiogenic heat production versus age is eliminated by determining reduced heat flow (surface heat flow minus radiogenic component) as a function of tectonic age, but much scatter remains, and it is still not possible to establish a heat flux-age relation in a rigorous way. Primarily because of the spatial variability in radiogenic heat production, no single geotherm can be used to characterize the thermal regime of a stable continental terrane. Thus, while some sites on stable continental blocks may have a geotherm fortuitously similar to that for old ocean basins, there is no reason to expect that this will be true generally, and many stable continental terranes will be characterized by geotherms markedly different from the geotherm for old ocean basins.     

辽宁盖县梁屯—矿洞沟碱性正长岩杂岩体的U—Pb和Sm—Nd年龄及其地质意义

辽宁梁屯 -矿洞沟杂岩体主要由辉石正长岩、霓辉正长岩和霓辉角闪正长岩等碱性岩石组成 ,具有全岩 Rb- Sr等时线年龄 186 6± 115 Ma和 ISr=0 .70 4 9的同位素特征 ,是我国目前报道的最古老的碱性正长岩类。本文报道了该岩体的锆石U- Pb和全岩 Sm- Nd同位素测试资料 ,获得了锆石 U- Pb同位素年龄为 185 7± 2 0 Ma、Sm- Nd等时年龄为 1787± 180 Ma、εNd(t) =- 4 .8～ - 5 .0的数据。它们反映出该杂岩体形成年龄的上限为 185 7± 2 0 Ma、下限不小于 1787± 180 Ma,来源于富集地幔物质。基于这些数据并结合区域地质资料分析 ,作者提出了华北地台北缘古元古宙存在有富集地幔储库 ,以及辽河群主体形成于 190 0 Ma以前的认识     

中国南京与美国德克萨斯稻田甲烷排放的比较

Field measurements of methane emission from rice paddies were made in Nanjing, China and in Texas, USA, respectively. Soil temperature at approximately 10 cm depth of the flooded soils was automatically recorded. Aboveground biomass of rice crop was measured approximately every 10 days in Nanjing and every other week in Texas. Seasonal variation of soil temperature in Nanjing was quite wide with a magnitude of 15.3℃ and that in Texas was narrow with a magnitude of 2.9℃. Analysis of methane emission fluxes against soil temperature and rice biomass production demonstrated that the seasonal course of methane emission in Nanjing was mostly attributed to soil temperature changes, while that in Texas was mainly related to rice biomass production. We concluded that under the permanent flooding condition, the seasonal trend of methane emission would be determined by the soil temperature where there was a wide variation of soil temperature, and the seasonal trend would be mainly determined by rice biomass production if there are no additional organic matter inputs and the variation of soil temperature over the rice growing season is small.     

A comprehensive model inter-comparison study investigating the water budget during the BALTEX-PIDCAP period

Summary A comparison of 8 regional atmospheric model systems was carried out for a three-month late summer/early autumn period in 1995 over the Baltic Sea and its catchment area. All models were configured on a common grid using similar surface and lateral boundary conditions, and ran in either data assimilation mode (short term forecasts plus data assimilation), forecast mode (short term forecasts initialised daily with analyses) or climate mode (no re-initialisation of model interior during entire simulation period). Model results presented in this paper were generally post processed as daily averaged quantities, separate for land and sea areas when relevant. Post processed output was compared against available analyses or observations of cloud cover, precipitation, vertically integrated atmospheric specific humidity, runoff, surface radiation and near surface synoptic observations. The definition of a common grid and lateral forcing resulted in a high degree of agreement among the participating model results for most cases. Models operated in climate mode generally displayed slightly larger deviations from the observations than the data assimilation or forecast mode integration, but in all cases synoptic events were well captured. Correspondence to near surface synoptic quantities was good. Significant disagreement between model results was shown in particular for cloud cover and the radiative properties, average precipitation and runoff. Problems with choosing appropriate initial soil moisture conditions from a common initial soil moisture field resulted in a wide range of evaporation and sensible heat flux values during the first few weeks of the simulations, but better agreement was shown at later times. Received September 8, 2000 Revised April 3, 2001     

Lees's topographic correction in heat flow and the geothermal flux in Tasmania

Summary Lees's topographic correction for a simple idealized hill is discussed and extended to a monoclinal structure. It is valuable as giving very simply the order of magnitude of the correction. A number of new measurements of temperature in Tasmanian boreholes has been made and the previous rather high value of over 2 cal/cm² sec for the heat flux has been confirmed. The variation of thermal conductivity through the thickness of a differentiated tholeiite sheet has been measured and found to be in reasonably good agreement with values calculated from chemical and modal analyses.     

Behaviour of strontium in subsurface calcium chloride brines: Southern Israel and Dead Sea rift valley

Calcium chloride brines are, as a rule, relatively rich in strontium, but the enrichment is usually limited and is found to be related to the concentration of calcium. The limiting mechanisms were evaluated as a model which comprises simple interactions between minerals and solutions. Based on the known ranges of strontium concentration in minerals, mineral solubilities and partition coefficients of strontium (both poorly known in certain cases), six fields of $\text{Sr}\text{Ca}$ molar ratios were defined in terms of participating minerals and processes: (a) 0.38?1.56 × 10^{? 3} by dolomitization of calcite; (b) 1.5?2.2 × 10^{? 2} due to dolomitization of aragonite; (c) 0.4?1.4 × 10^{? 2} as a result of solution-reprecipitation of calcite; (d)0.12?0.20 through transformation of aragonite to calcite; (e)0.10?0.60 through equilibrium of the pair calcite-strontianite; and (f)0.01?0.08 by equilibrium with gypsum and celestite.The model was applied to the analysis of two groups of brines from southern Israel which are originated in the coastal plain (group C) and in the rift valley (group R). The low $\text{Mg}\text{Ca}$ ratios of both water groups point to dolomitization as the main subsurface modifying process. $\text{Sr}\text{Ca}$ ratios of brines belonging to group C are consistent with dolomitization of aragonitic surface sediments at the beginning of their evolution. Brines of group R bear evidence to a similar pathway at the beginning of their evolution, but most of them were further affected by interaction with limestone.     

In vitro screening for endocrine disruptive activity in selected South African harbours and river mouths

Various waterborne anthropogenic contaminants disrupt the endocrine systems of wildlife and humans, targeting reproductive pathways, among others. Very little is known, however, regarding the occurrence of endocrine disruptive activity in South African freshwater ecosystems, and coastal ecosystems have not been studied in this regard. In a first attempt to investigate endocrine disruptive activity in South African coastal waters, surface water samples collected from harbours, river mouths and estuaries in three metropolitan municipalities, eThekwini (which includes Durban), Nelson Mandela (specifically Port Elizabeth Harbour) and City of Cape Town, were screened for (anti) oestrogenicity and (anti)androgenicity using recombinant yeast bioassays. Moreover, levels of the female hormone 17β-(o)estradiol (E2) were determined in all samples, as well as a selection of hydrocarbons in the eThekwini samples. A high proportion of samples collected from eThekwini were oestrogenic, whereas none from Port Elizabeth Harbour and only a single river mouth sampled in the City of Cape Town were oestrogenic. E2 was detected in all the samples tested, but at higher concentrations at the eThekwini and City of Cape Town localities than Port Elizabeth Harbour. In addition, the recombinant yeast assays revealed that anti-androgenicity was widespread, being detected in the majority of samples screened apart from those representing Port Elizabeth Harbour. Conversely, no anti-oestrogenic or androgenic activity was detected. Anti-androgenicity did not associate with hydrocarbon loads, providing evidence that other anti-androgens were responsible for the observed activity. The present data suggest potential reproductive disruption in marine and estuarine fauna inhabiting the eThekwini and City of Cape Town regions.     

东天山伊吾二叠纪花岗质杂岩体的锆石定年、地球化学及其构造意义

伊吾花岗质杂岩体主要由二长花岗岩和碱长花岗岩构成。锆石LA-ICP-MS U-Pb定年分析得到二长花岗岩和碱长花岗岩的侵位年龄分别为284.6±1.4Ma和284.0±1.1Ma。结合地质证据,此年龄表明该杂岩体形成于碰撞之后的二叠纪早期挤压-伸展转折阶段。岩石学、地球化学和同位素等方面的对比研究表明这两种岩石为同一岩浆演化的产物。与二长花岗岩相比,碱长花岗岩表现为硅、碱的含量较高,而铝的含量较低;富Th、U、Nb、Ta,贫Sr、P、Ti、Sm;DI和Rb/Sr升高,Nb/Ta和Zr/Hf下降,从二长花岗岩到碱长花岗岩表现出连续分异演化的趋势。计算得到二长花岗岩和碱长花岗岩的模式年龄(t_(DM))分别为693Ma和763Ma,ε_(Nd)(t)分别为+4.53和+4.64,(~(87)Sr/~(86)Sr)_i分别为0.703858和0.703855,表现出高ε_(Nd)(t)低(~(87)Sr/~(86)Sr)_i的特征。这些特征表明,伊吾岩体的岩浆来自新元古代时从亏损地幔分离出来的初生地壳源区。二长花岗岩岩浆是这种初生地壳岩浆演化的产物,而碱长花岗岩形成于二长花岗岩母岩浆经斜长石、磷灰石、钛铁氧化物、榍石、独居石、褐帘石和锆石等矿物分离结晶后的残留岩浆。