江苏东海超高压榴辉岩的热导率及对大陆科学钻探研究的意义

对采自江苏东海毛北地区(中国大陆科学钻探先导孔附近) 的新鲜榴辉岩样品进行了岩石热导率的测定, 初步查明了该区榴辉岩热导率随矿物组成的变化关系, 探讨了岩石结构特征和温度变化对热导率的影响.本次所测东海超高压榴辉岩的热导率介于3.2 2 2~ 3.716Wm-1·K-1之间并随岩石中2种主要矿物的相对含量比而变化, 随着榴辉岩中石榴石对绿辉石体积比(V_Grt/V_Omp) 的增加而降低, 近似的函数关系满足K =3.76 7- 0.18× (V_Grt/V_Omp).岩石中矿物分布的不均匀性和面状构造的发育对榴辉岩热导率的影响较大, 由此产生的热导率各向异性可达近10 %.温度是影响热导率的另外一个重要因素.结合本次的实测资料和相应的热导率-温度关系, 建立了东海地区榴辉岩热导率随温度的变化关系方程K (T) =1/ (7.85×10-2 +6.95×10-4 ×T), 根据这一方程并结合东海地区的地热梯度资料推算了榴辉岩热导率随5 0 0 0m钻孔深度的变化关系, 推测东海地区科学钻探施工至5 0 0 0m深度时, 榴辉岩的热导率将比地表平均降低2 4%.该成果为钻探测井资料的解释以及该区地热结构模型的建立提供了重要依据和约束资料.      

中国大陆科学钻探主孔自然放射性测井及其解释

为了认识江苏东海超高压变质带上地壳岩石自然放射性的垂向分布特征, 榴辉岩退变质程度对放射性元素浓度的影响, 以及放射性产热率对地温梯度的影响, 利用中国大陆科学钻探(CCSD) 主孔100~5000m自然放射性测井(自然伽马和自然伽马能谱) 资料统计了CCSD主孔各类岩石的自然放射性强度和铀、钍、钾元素的浓度, 计算出产热率曲线.自然伽马, 铀、钍、钾浓度和产热率从蛇纹岩到榴辉岩、角闪岩、副片麻岩、正片麻岩依次增大.随着榴辉岩退变质程度的增强, 其铀、钍、钾元素的浓度值逐渐增大.CCSD主孔自然放射性的垂向分布特征主要受岩性控制, 自然放射性随深度增加有增强趋势.产热率与自然伽马测井值之间有很好的线性关系, 在高放射性岩层的上部, 地温梯度会出现较强扰动和低值异常.      

利用超高压变质岩的P波速度估算地下岩石的热导率

岩石热导率是了解地球内部热传导过程的重要参数之一, 但热导率的测量在室内和野外都比较复杂.如何利用容易获得的岩石物理参数(如超声波速度) 来估算岩石的热导率就显得非常重要.通过对中国大陆科学钻探(CCSD) 主孔655件样品热导率和超声波速度的相关分析, 把样品分为新鲜榴辉岩、退变质榴辉岩、副片麻岩和正片麻岩4类, 并分别建立了利用岩石P波速度估算热导率的计算方程.回归计算表明, 榴辉岩热导率和P波速度之间的相关性较大, 相关系数在0.7左右, 片麻岩显示的相关系数比较小, 在0.4~0.5之间.鉴于样本数量较大, 这种结果足以表明热导率和P波速度之间可以用给定的线性关系来表达.为了检验获得的方程, 在CCSD主孔中选取典型的岩性单元, 利用测得的P波速度估算相应的热导率, 结果显示估算值和实测热导率平均值非常接近, 表明利用P波估算岩石热导率的方程是可行和实用的, 为本区和相似地区大地热流和热结构计算提供了热导率的计算方法和依据, 因而具有重要的岩石物理学和地球物理意义.      

中国大陆科学钻探主孔100～2000m岩石热导率及其各向异性：对研究俯冲带热结构的启示

系统研究了中国大陆科学钻探工程主孔100～2000米岩石的热导率和生热率特征。初步研究了岩石热导率随矿物组成的变化关系、岩石热导率的各向异性及其影响因素。主孔2000米的岩心热导率介于1．873～4．062Wm^-1K^-1之间，平均热导率2．967Wm^-1K^-1。整体上热导率出现的频率主峰分布在2．8～3.0Wm^-1K^-1。榴辉岩热导率随着其退变质程度的增加而降低，新鲜榴辉岩热导率集中分布于3．6～3．7Wm^-1K^-1，角闪石化榴辉岩的热导率分布在3．1～3.2Wm^-1K^-1，强退变的榴辉岩热导率分布于2．4～2．5Wm^-1K^-1。片麻岩热导率主要分布于2．8～3.0Wm^-1K^-1。从垂向上看，主孔100～735米主要由榴辉岩组成，热导率整体比较大，平均3.265Wm^-1K^-1；1200～1600米主要以花岗质片麻岩为主，热导率比其它层位偏低，平均2．755Wm^-1K^-1。通过对面理发育的样品进行测试，东海地区各类岩石的热导率具有较明显的各向异性。榴辉岩和片麻岩热导率的各向异性平均值分别为4、66％和22．99％，超基性岩的热导率平均值为3．322Wm^-1K^-1，各向异性16．08％。岩石热导率在垂直于面理的方向上具有最小值，在平行于面理的方向上具有最大值。上述资料对超高压地体热结构特征的研究提供了重要数据基础。     

中国大陆科学钻探主孔0~2000 m榴辉岩的退变质过程

中国大陆科学钻探主孔位于大别-苏鲁这条典型的超高压变质带上，孔内0-2000m的岩心中，各种榴辉岩占到50％以上。榴辉岩大多经历了不同程度的退变质。依据榴辉岩中主要矿物绿辉石和石榴石的退变质程度，0-2000m榴辉岩的退变质过程可分为2个大阶段，4个亚阶段：第一大阶段(又分为轻微退变质、部分退变质)、第二大阶段(又分为退变质和强退变质)。总的退变质趋势是：石榴石逐渐被韭角闪石或黑云母 绿帘石替代；绿辉石逐渐被角闪石 钠长石后成合晶替代，硬玉(1d)含量逐渐减少，并部分转化为霓辉石。榴辉岩在退变质过程中所经历的温压条件为：峰期变质温度为697-831℃，压力3．0Gpa左右；部分退变质阶段温度为629-776℃，压力1．2-1．6Gpa；退变质阶段温度为550-650℃，压力O．5-0．7Gpa；强退变质阶段温度为300-400℃，压力0．30-0．35Gpa。综合岩石、矿物及形成温压条件等特征，推断榴辉岩的折返过程经历了两个大阶段：第一大阶段是近等温降压的快速折返(榴辉岩在此期间经历了第一大阶段的退变质)，第二大阶段是降温降压的缓慢抬升(榴辉岩继而经历了第二大阶段的退变质)。绿辉石的完全退变质，既是划分榴辉岩两大退变质阶段的标志，同时也是区分两大折返阶段的标志。     

桂北豆乍山岩体放射性地球化学特征及其干热岩资源潜力研究

对桂北豆乍山岩体钻孔样品进行了放射性生热元素含量、岩石密度和岩石热导率测试。结果显示该岩体花岗岩U平均含量为17.49×10~(-6),Th平均含量为27.54×10~(-6),K_2O平均含量为4.64%,放射性生热率平均值6.46μW/m~3,高于地壳平均值及大部分华南其他岩体的放射性生热率值;岩石密度平均在2.57 g/cm~3左右,与世界范围内花岗岩密度的平均值大致相同;岩石热贡献率主要来自Th和U的放射性衰变热,而U的贡献率相对更高。研究区岩石热导率平均为3.389 W/mK,与目前已知的花岗岩热导率平均值相近。通过本文及周边其他岩体的研究结果,结合前人资料,推断豆乍山岩体所在的苗儿山地区,乃至桂北地区的地幔热流值低于地壳热流值贡献,属于"热壳冷幔"型岩石圈热结构。根据豆乍山岩体放射性生热元素和生热率的优势,认为其干热岩开发潜力较大,可对其进行进一步干热岩评价工作。     

超高压榴辉岩退变质作用对岩石磁化率的影响

系统测量了中国大陆科学钻探(CCSD) 主孔10 0~ 2 0 0 0m超高压榴辉岩的磁化率及其各向异性, 并进行了相应的岩石学和矿物学分析.研究结果表明, 不同退变质程度榴辉岩的磁化率特征具有明显差别: 新鲜-弱退变质榴辉岩对应超高压榴辉岩相, 平均体积磁化率κ=1.4× 10-3SI, 磁化率各向异性度Pj=1.0 9, 磁性载体主要是顺磁性矿物石榴子石和绿辉石; 中等-强退变质榴辉岩对应角闪岩相, κ =5.1× 10-3SI, Pj=1.2 0, 磁性载体主要是退变质所产生的磁铁矿和钛铁矿-钛磁铁矿; 完全退变质榴辉岩对应绿帘角闪岩相-绿片岩相, κ =1.3× 10-3SI, Pj=1.08, 磁性载体主要来自顺磁性矿物角闪石、绿帘石、黑云母等.该研究为超高压变质岩石地区磁异常的解释提供了基础数据和重要的科学约束, 同时也为大陆深俯冲峰期变质岩石和折返阶段岩石退变质程度提供了磁化率鉴别特征.      

中国大陆科学钻探主孔100~2000 m测井磁化率和磁三分量分析

对比分析了中国大陆科学钻探(CCSD)主孔100~2 000 m测井磁化率与岩心样本磁化率的测量结果,二者具有较好的一致性。测井磁化率统计结果表明CCSD主孔100~2 000 m超高压变质岩的磁化率从高至低依次为:蛇纹岩、石英榴辉岩、金红石榴辉岩、正片麻岩、退变质榴辉岩、多硅白云母榴辉岩、副片麻岩、绿泥石角闪岩、角闪岩。由CCSD主孔100~2 000 m磁三分量测量数据得到磁异常的△BZ、△BH和△BT值,结合前人所做的岩石学研究分析发现:主孔530~575 m的磁异常主要由岩石的金红石矿化、钛磁铁矿化和磁铁矿化引起,604~643 m和652~678 m的磁异常主要由岩石的蛇纹石化引起;钻孔中岩层的磁化率对磁三分量异常起着主要的决定作用,高磁化率岩层都表现出较大的磁三分量异常。     

磁化率和密度对中国大陆科学钻探主孔100～2000 m岩石类型的判别

为查明磁化率和密度对于中国大陆科学钻探工程(CCSD)主孔100~2000m岩性的响应和判别特征,利用SPSS10.0统计分析软件进行了判别分析.研究结果显示,岩石的密度和体积磁化率主要受岩性的控制.采用迫入法建立全模型,对CCSD主孔100~2000m井段岩心的岩性判别率达84.8%.其中,蛇纹石化橄榄岩、正片麻岩、副片麻岩、榴辉岩、角闪岩和退变质榴辉岩的判别率分别为100%、87.1%、89.7%、89.6%、96.7%和63.7%.该研究表明,密度和磁化率可以为超高压变质岩石的岩性鉴别和区分提供定量约束,有利于地球物理探测成果和测井资料的准确解析.同时,本文也是SPSS统计分析软件在超高压变质岩石类型判别方面的一个应用实例,对于其他岩石类型的判别分析具有借鉴意义.     

中国大陆科学钻探主孔100-2000m岩心的磁化率各向异性及其地质意义

在常温常压条件下获得了中国大陆科学钻探(CCSD)主孔331块岩心的磁化率各向异性(AMS)数据,并建立了主孔100—2000m的体积磁化率和AMS连续剖面。数据统计分析显示,主孔100—2000m岩心的磁化率(κ)介于1．05×10-4SI和0．12SI之间,几何平均值为1．855×10-3SI;磁化率各向异性度(Pj)介于1．04和2．10之间,几何平均值为1．155。该井段出露的主要岩石类型有榴辉岩、退变质榴辉岩、角闪岩、正片麻岩、副片麻岩和蛇纹石化橄榄岩,它们的垂向分布特征控制着磁化率剖面的变化。主孔的超高压变质岩石在折返过程中普遍经历了强烈的角闪岩相退变质作用的改造。其磁化率特征也发生相应的改变。蛇纹石化橄榄岩具有很高的磁化率(8．58×10-2SI)和各向异性度(1．335)。这主要源于橄榄岩蛇纹石化过程中产生的大量磁铁矿。榴辉岩、退变质榴辉岩和角闪岩代表榴辉岩从新鲜到完全退变质的三个阶段,它们的磁化率和磁化率各向异性度分别为榴辉岩(1．28×10-3SI、1．077)、退变质榴辉岩(3．19×10-3SI、1．206)、角闪岩(1．02×10-3SI、1．104)。正片麻岩的磁化率和各向异性度分别为5．34×10-3SI和1．167。副片麻岩的磁化率和各向异性度分别为3．46×10-4SI和1．150。对58个变形岩石的AMS测试结果显示,其磁化率椭球体的主轴方向与岩石组构基本一致,即最大磁化率主轴κ1平行矿物线理,最小磁化率主轴κ3垂直岩石面理。同时,这些变形岩石的AMS椭球体多呈现明显的压扁状特征,反映超高压变质岩石在折返过程中处于强烈挤压变形的构造应力环境,为苏鲁超高压变质板片的挤出折返模式提供了佐证。该研究成果也为超高压变质岩石地区磁学研究、地球物理调查和测井成果的解释提供了重要的实验约束。     

热流和岩石生热率关系的研究

通过花岗岩体和中下地壳剖面岩石生热率的研究,显示出花岗岩体内生热率的分布至多样性;华北下地壳变质岩的生热率介于0.2-0.4μW/m³之间,其对热流的热贡献较小;地壳岩石生热率总体上是深度不连续的递减函数。中国东南地区出露着大面积的中生代花岗岩体,实测热流和岩石生热率没有得出可信的线性关系。结合对现有热流省资料的认识,提出了对热流和岩石生热率关系的新看法,解释了以往线性关系的不稳定性,估算出正常陆壳厚度的热流下限应为29.5mW/m²。     

The distribution of radiogenic heat production as a function of depth in the Sierra Nevada Batholith, California

Geochemical analyses and geobarometric determinations have been combined to create a depth vs. radiogenic heat production database for the Sierra Nevada batholith, California. This database shows that mean heat production values first increase, then decrease, with increasing depth. Heat production is 2 μW/m³ within the 3-km-thick volcanic pile at the top of the batholith, below which it increases to an average value of 3.5 μW/m³ at 5.5 km depth, then decreases to 0.5–1 μW/m³ at 15 km depth and remains at these values through the entire crust below 15 km. Below the crust, from depths of 40–125 km, the batholith's root and mantle wedge that coevolved beneath the batholith appears to have an average radiogenic heat production rate of 0.14 μW/m³. This is higher than the rates from most published xenolith studies, but reasonable given the presence of crustal components in the arc root assemblages. The pattern of radiogenic heat production interpreted from the depth vs. heat production database is not consistent with the downward-decreasing exponential distribution predicted from modeling of surface heat flow data. The interpreted distribution predicts a reasonable range of geothermal gradients and shows that essentially all of the present day surface heat flow from the Sierra Nevada could be generated within the 35 km thick crust. This requires a very low heat flux from the mantle, which is consistent with a model of cessation of Sierran magmatism during Laramide flat-slab subduction, followed by conductive cooling of the upper mantle for 70 m.y. The heat production variation with depth is principally due to large variations in uranium and thorium concentration; potassium is less variable in concentration within the Sierran crust, and produces relatively little of the heat in high heat production rocks. Because silica content is relatively constant through the upper 30 km of the Sierran batholith, while U, Th, and K concentrations are highly variable, radiogenic heat production does not vary directly with silica content.     

中国大陆科学钻探主孔揭示的大陆地壳生热模型

本文对大陆科学钻探主孔149块岩心样品进行了系统的岩石放射性生热元素 U、Th 和 K 的含量测试,同时结合该井浅部井段前人的实测数据,揭示了上地壳5km 生热率的垂向分布。结果显示,以1650m 为界,上下两段生热率均随深度呈增加趋势,与正常地壳生热率特征不同,显示出超高压变质带独特的生热率垂向变化特征。结合地壳的岩性分布,建立了苏鲁超高压变质带地壳的生热模型。该模型中,地壳厚32km,其中上地壳0～10km,由超高压变质岩片组成,按岩性又详细分为8层,生热率变化在0.49～1.73μWm~(-3)。中地壳10～20km,由片麻岩组成,生热率为生热率1.51μWm~(-3)。下地壳20～32km为麻粒岩,生热率0.31μWm~(-3)。整个地壳热流约31mw/m~2,其中上地壳12mW/m~2。上地壳厚度和热流分别占整个地壳的31%和39%。与华北和下扬子地壳生热模型相比,上地壳热流整个地壳热流的比例最低。这表明,苏鲁超高压变质带,作为中朝与扬子板块俯冲-碰撞的产物,其地壳生率垂向分布与正常大陆地壳(华北、下扬子)相比,具有显著的不同。     

An analysis of heat index over Naples (Southern Italy) in the context of European heat wave of 2003

Two strong heat waves in the summer of 2003 determined elevated heat discomfort conditions all across the Western Europe. In this context, the analysis of hourly Heat Index values in the city of Naples (Southern Italy) showed prolonged heat discomfort conditions during the second half of June 2003 and from the second half of July 2003 up to the first week of September 2003, resulting in highest mortality rate for persons 75 years or more.     

On the radiogenic heat production of igneous rocks

Radiogenic heat production is a physical parameter crucial to properly estimating lithospheric temperatures and properly understanding processes related to the thermal evolution of the Earth. Yet heat production is, in general, poorly constrained by direct observation because the key radiogenic elements exist in trace amounts making them difficulty image geophysically. In this study, we advance our knowledge of heat production throughout the lithosphere by analyzing chemical analyses of 108,103 igneous rocks provided by a number of geochemical databases. We produce global estimates of the average and natural range for igneous rocks using common chemical classification systems. Heat production increases as a function of increasing felsic and alkali content with similar values for analogous plutonic and volcanic rocks. The logarithm of median heat production is negatively correlated(r~2=0.98)to compositionally-based estimates of seismic velocities between 6.0 and 7.4 km s~(-1), consistent with the vast majority of igneous rock compositions. Compositional variations for continent-wide models are also well-described by a log-linear correlation between heat production and seismic velocity. However, there are differences between the log-linear models for North America and Australia, that are consistent with interpretations from previous studies that suggest above average heat production across much of Australia. Similar log-linear models also perform well within individual geological provinces with~1000 samples. This correlation raises the prospect that this empirical method can be used to estimate average heat production and natural variance both laterally and vertically throughout the lithosphere. This correlative relationship occurs despite a direct causal relationship between these two parameters but probably arises from the process of differentiation through melting and crystallization.     

Heat flow and the structure of Precambrian lithosphere

Studies of heat flow from Precambrian terrains have demonstrated three empirical relationships; a temporal relationship between heat flow and tectonic age, a spatial pattern between heat flow and the proximity of Archean cratons, and a temporal relationship between heat flow and the age of lithosphere stabilization. In the first relationship, heat flow is inversely related to tectonic age. The second pattern is characterized by low heat flow from Archean cratons and Proterozoic terrains adjacent to cratonic margins (pericratonic terrains), and higher heat flow from Proterozoic terrains that are more than a few hundred kilometers from a craton. In the third pattern, heat flow decreases as the age of stabilization of the lithosphere increases. A number of interpretations of Precambrian heat flow have been offered to explain one or more of these relationships. The simple cooling of a thermal boundary layer predicts essentially no change in heat flow in terrains older than 1.5 Ga, and therefore does not likely provide a comprehensive framework for the interpretation of Precambrian heat flow. By contrast, two other interpretations, (1) thicker lithosphere beneath Archean terrains than beneath Proterozoic terrains, and (2) greater heat production in Proterozoic crust than in Archean crust, when combined with the special structural configuration of sutures, can both contribute to the spatial and temporal heat flow distributions. Xenolith thermobarometry constraints on lithospheric temperatures, however, limit the contribution of age-dependent crustal heat production, and therefore at least part of the heat flow distributions derive from variations in lithosphere thickness.     

电测深在榆中盆地地热勘查中的应用

:榆中盆地地热异常区 ,处于区域性地热背景之上 ,具有深源热机制。应用电测深推断盆地基底构造、盖层结构 ,其中部断阶带基底隆升 ,断裂构造发育 ,储、盖层具备 ,是地热赋存有利部位。由电测深曲线极小值视电阻率圈定出热异常的范围、导热构造 ,为地热评价、开发提供依据     

The thermal regime of the Northeastern-German Basin from 2-D inversion

The thermal regime and the distribution of heat flow at the base of sedimentary basins is fundamental to the understanding of the process of basin evolution and the associated mobilization and migration of hydrocarbon and other fluids. For the Northeastern-German sedimentary basin, available information on structure, temperature, and thermal properties along a seismic DEKORP reflection profile allow high resolution 2-D forward and inverse simulations. This approach is attractive in situations where much information is available, if only with considerable uncertainty. In particular, this allows to introduce “soft” information into the analysis. In our case, forward simulations yield initial a priori estimates of the parameters while inversion calculations yield a posteriori estimates of the parameters and their uncertainty. The a priori parameters as well as their assumed uncertainty are input for a Bayesian parameter estimation scheme. In respect to the Northeastern-German sedimentary basin, the inverse analysis postulates a significant and characteristic a posteriori variation of thermal conductivity of the Zechstein unit along the entire profile as well as a generally large a posteriori thermal conductivity of the (pre-Permian) basement in the northern part of the basin. For inverse calculations, we used two alternative scenarios: One assumes the thermal conductivity of the Zechstein unit to be homogeneous along the profile while the other allows a lateral variation. A posteriori heat flow across the base of the model varies from 40 to 60 and 50 to 65 mW m⁻² for models in which values for thermal conductivity and radiogenic heat generation rate were either based on literature values or direct measurements, respectively.     

中国东南地区岩石生热率分布特征

基于５００余块岩石样品的生热率实测值和前人的研究成果，本文系统地分析了中国东南地区不同时代、不同岩性和不同大地构造单元岩石生热率的分布特征，揭示出华南沉积区地层在晚元古代一寒武纪和侏罗纪出现两次生热率高峰，花岗岩具有异常高的生热率背景。岩石生热率以粤中－赣南为核心，向外扩展呈下降趋势；政和－大埔断裂带西侧生热率明显高于东侧火山岩出露区；扬子沉积区明显低于华南区。按区域岩石生热率分布可以划分为三个区：南区生热率背景值超过２．８μＷ／ｍ３，东区介于２．１～２．８μＷ／ｍ３，北区普遍低于２．１μＷ／ｍ３。岩石生热率分布在一定程度上反映了区域基底生热元素的丰度和岩浆活动的强度。     

Retrograde mineral reactions: a heat source in the continental crust?

Chemical reactions of water with silicates are strongly exothermic. Therefeore, retrograde metamorphism is also a strongly exothermic process and thus a potentially powerful heat source. Depending on the time scale its contribution to the terrestrial heat flow can be equivalent to, or even exceed, that of radioactive decay. During hydration mafic rocks and gneisses liberate 60 J/cm³ for each weight percent H₂O they bind. It is argued that retrograde reactions constitute relatively short-lived, single or repeated episodes during crustal cooling, and that they can influence, or even strongly perturb, the geotherm during thousands to a million years. The thermal effects involved are non-trivial; they should be considered in interpretations of heat flow measurements. They could constitute the main heat source for hydrothermal mineralisations not connected with magmatic intrusions and possibly contribute to the thermal development of sedimentary basins. These effects are large enough to be one of the possible explanations for the difference between the predicted and measured heat flows at the KTB site.The authors share the work on this article equally. The order of names, therefore, is purely alphabetical.