地质作用深度测算中的问题

迄今为止,地质作用的深度通常是用压力除以密度来计算的。这种方法只在假设岩石处于静止的液体状态下才是正确的。然而,实际上从浅部地壳直至地幔深处的岩石都是固体状态而不是液体状态,且粘性系数随浓度递增。实测数据表明,地下水平压应力总是大于垂直压应力,说明构造力在量值上超过重力。所以,在地壳中进行地质作用深度的测算必须把岩石看作是固体并依据固体物理理论。因此,吕古贤等在文献〔１６〕中提出的深度测算方法（１     

Pressure State in Deep Crust and Formation Depth of UHP Metamorphic Rocks

INTRODUCTIONSincethediscoveryofeclogiteswithcoesiteanddia mondinclusionsrelatedtothecontinent continentcollision orogenyenvironment,theultrahigh pressuremetamorphism(UHPM )intheDabie Suluhasarousedgreatinterestinmanygeologists (Liouetal .,1994 ;Xuetal.,1992 ) .Experimentalstudieshaveprovedthatsuchmineralsasdia mond ,coesiteandomphaciteoccurredat 2 - 5GPa (andatthecorrespondingtemperatures) (Stevenetal.,1982 ;MirwaldandMasonne ,1980 ) .However,itdoesnotmeanthatthemetamorphicrockscanbe…     

重力和构造力在地壳中的作用

本文对于“上覆岩石重力数值等同于静水压力数值”的认识提出了新的看法，地壳中应力场Ｔ可以看成是一个静水压力Ｐ和一个差应力σ的复合、则静水压力Ｐ是由重力附加静水压力ＰＲ和构造力附加静水压力ＰＳ两者叠合而成，而不仅仅是来自上覆岩石的总重量，有限元模型计算表明，在同样外力条件下，从挤压变形带，剪切变形带到引张变形带中的各带构造附加静水压力值呈降低变化，即ＰＣ〉ＰＺｈ〉Ｐｔ，因而构造附加静水压力得造成局部静     

大别-苏鲁构造带三叠纪碰撞缝合线的位置

大别－苏鲁构造带内超高压（UHP）和高压（HP）变质岩石的分布和不同构造岩石单位间的关系表明, 三叠纪中朝与扬子克拉通碰撞及超高压和高压变质岩石形成时的古缝合线, 位于大别地块的北缘, 沿八里畈－磨子潭－晓天一线展布, 在苏鲁地区, 五莲－烟台断裂代表被强烈改造了的古缝合线的位置.大别山北部霍山县与岳西县交界地区以及舒城、桐城和潜山县交界地区UHP和HP单位岩石的大面积分布, 说明水吼－五河断裂不是UHP和HP榴辉岩相岩石的北限, 因而, 不代表缝合线位置, “南大别”与“北大别”地体的划分地质意义是不明确的.同时, 大别山北部的镁铁质及超镁铁质岩石块体群, 包括变形的方辉橄榄岩、纯橄榄岩组合及未变形的辉石岩、角闪辉石岩和辉长岩组合, 前者与榴辉岩相岩石有相同的变形变质及几何学特征, 后者是燕山期侵入体（123~130Ma）, 因此, 不是“变质蛇绿混杂岩”, 也不代表三叠纪陆－陆碰撞时期古缝合线.强调指出, 准确地鉴别三叠纪碰撞缝合线位置, 是正确理解UHP和HP岩石形成及折返动力学过程的关键.      

Some petrogenetic aspects of Fe2O3: FeO ratio in igneous rocks

The "oxidation ratio" of igneous rocks (F = Fe₂O₃:FeO) depends on the partial pressure of oxygen during crystallization and therefore, in part, on depth of crystallization. For this reason F increases in the order: deep intrusives, dike rocks, extrusives, pyroclastics. Also, in general, F increases with increasing silica content, although there are exceptions. As it is not always easy to distinguish intrusive rocks from extrusive ones, or extrusives from pyroclastics, it is proposed that the oxidation ratio be used as a criterion of fades of igneous rocks. --F. E. Ingersoll.     

大别山陆—陆点碰撞和构造超压的形成

依据大别造山带的地质特征及古地磁证据, 提出大陆动力学非规则边界陆-陆点碰撞模型, 采用数值模拟方法, 分析点碰撞所引起的构造应力集中及其影响因素, 探讨构造压力在大别山超高压变质岩形成过程中所起的作用, 推测可能形成的深度范围.研究表明: 在本文的模拟条件下, (1) 大陆碰撞初期产生的构造应力场中的平均压力在碰撞点附近增大了约5~9倍.在边界力为100 MPa的情况下, 构造压力在超高压中所占的比例约为20 %~35 %; (2) 由于有构造压力的作用和影响, 超高压变质岩的形成深度有可能被提升20~35 km; (3) 仅考虑碰撞方式, 不计岩石物性差异和其他因素的影响, 构造应力的影响有限, 静岩压力在超高压变质岩形成过程中仍占据主导地位.      

大别山陆一陆点碰撞和构造超压的形成

依据大别造山带的地质特征及古地磁证据,提出大陆动力学非规则边界陆-陆点碰撞模型,采用数值模拟方法,分析点碰撞所引起的构造应力集中及其影响因素,探讨构造压力在大别山超高压变质岩形成过程中所起的作用,推测可能形成的深度范围.研究表明:在本文的模拟条件下,(1)大陆碰撞初期产生的构造应力场中的平均压力在碰撞点附近增大了约5～9倍.在边界力为100 MPa的情况下,构造压力在超高压中所占的比例约为20%～35%;(2)由于有构造压力的作用和影响,超高压变质岩的形成深度有可能被提升20～35 km;(3)仅考虑碰撞方式,不计岩石物性差异和其他因素的影响,构造应力的影响有限,静岩压力在超高压变质岩形成过程中仍占据主导地位.     

影响地下应力状态的构造作用

成岩成矿的外部条件中压力是很重要的因素。地下岩石所受的压力不仅来自上覆岩石的重力，而且来自构造力和热力及其它力。这些力合成一个三轴不等的应力状态，相当一个以最短轴为半径的球状应力迭加一个差应力。前者影响成岩成矿和变质作用，后者控制岩石变形和组构的变化。通过三维应变应力测量，这两部分力通过计算是可以区分开的，因而这将是建立地下深度测算新方法的一个基础。     

微观结构超压机制与超高压矿物的形成

提出了由岩石及矿物的结构形态、岩石力学性质不同引起的微结构超压机制。对影响结构超压的诸因素(弹性参数、热物理性质)进行了数值模拟实验和定量分析。研究结果表明，结构压力对超高压岩石、矿物的形成具有重要的意义。结构压力随弹性模量差异、围限压力、温度改变量及热膨胀系数差异的增加而增大。在岩石、矿物的弹性模量相差5倍的条件下，结构附加压力可达到静岩压力的45％左右。如果再考虑热膨胀系数不同及降温引起的附加压力，在较一般的情况下，60公里左右深处就有可能具备柯石英等超高压矿物形成的下限压力条件。     

基于毛细管力的有效储层物性下限判别

有效储层物性下限评价对于油气勘探和开发致关重要。本文在回顾前人相关研究方法的基础上,对储层与围岩介质的物性条件进行了研究,认为有效储层物性下限不是绝对的,而是取决于砂岩与围岩介质物性之间的相对关系,并与埋深具有一定的关系。由此提出了一种新的有效储层物性下限判别方法:利用砂岩储层和围岩介质的毛细管力比值判定有效储层物性下限。有效储层临界条件下的毛细管力比值随埋深增加表现出逐渐增大趋势,其物性下限也随埋深具有一定的变化规律。根据该方法在珠一坳陷深部古近系储层中识别出的有效储层与测井解释成果基本吻合。该方法对于优选油气勘探目标具有一定的指导意义。     

大陆俯冲过程中的流体

含水矿物矿物稳定性的实验研究和超高压岩石的同位素地球化学研究表明 ,大陆地壳在俯冲过程中 ,随着变质程度的升高和部分含水矿物的相继分解 ,会有流体释放出来。当俯冲深度接近5 0km ,俯冲陆壳岩石中大量低级变质含水矿物 (如绿泥石、绿帘石、阳起石 )会脱水并从俯冲陆壳逸出形成流体流。这一流体流可溶解带走俯冲陆壳内已从云母类矿物逸出的放射成因Ar及部分U、Pb ,并导致w(U) /w(Pb)升高。这一阶段逸出的流体有可能交代、水化仰冲壳楔 ,为其发生部分熔融形成同碰撞花岗岩或加速山根下地壳的榴辉岩化创造条件。在俯冲深度为 5 0～ 10 0km ,变镁铁质岩石中的角闪石相继分解并释放出H2 O。由于变镁铁质岩石在陆壳中所占比例较少 ,因此 ,这一阶段释放的水不能形成大规模的流体流 ,因而不能使体系内的过剩Ar大量散失 ,但足以形成局部循环 ,加速变镁铁质岩石及其互层或邻近围岩的榴辉岩化变质反应。在俯冲深度 >10 0km的超高压变质阶段 ,仅有少量的含水矿物分解 ,而多硅白云母仍保持稳定。这时俯冲陆壳内只可能有少量粒间水存在 ,从而导致俯冲陆壳与周围软流圈地幔不能发生充分的相互作用。     

Partial Melting Processes During Exhumation of Ultrahigh-Pressure Metamorphic Rocks in Dabieshan, China

INTRODUCTIONUptonowthereisinagreementonthetectonic-dynamicbackgroundoftheformationofUHPmetamorphicrocks,i.e.,theUHPMrocksareproductsofobliquecollisionbe-tweentheYangtzeandSinokoreancratonsinIndosinianstage(Jahn,1998lWangandCong,l998,1996;Lietal.,l997,l996iHackeretal.,l996ILiouet.al.,l9961Okay;Sen-gor,l993,CongandWang,l994;Sengor,1993).Buthowthesemetamorphicrocksareformedatmantledepthexhumedbacktothesurfacesorapidlyisstillastandingproblem-TheexhumationofUHPMrocksisacomplextectoni…     

Influence of tectonic overpressure on P–T paths of HP–UHP rocks in continental collision zones: thermomechanical modelling

The principle of lithostatic pressure is habitually used in metamorphic geology to calculate burial/exhumation depth from pressure given by geobarometry. However, pressure deviation from lithostatic, i.e. tectonic overpressure/underpressure due to deviatoric stress and deformation, is an intrinsic property of flow and fracture in all materials, including rocks under geological conditions. In order to investigate the influences of tectonic overpressure on metamorphic P–T paths, 2D numerical simulations of continental subduction/collision zones were conducted with variable brittle and ductile rheologies of the crust and mantle. The experiments suggest that several regions of significant tectonic overpressure and underpressure may develop inside the slab, in the subduction channel and within the overriding plate during continental collision. The main overpressure region that may influence the P–T paths of HP–UHP rocks is located in the bottom corner of the wedge‐like confined channel with the characteristic magnitude of pressure deviation on the order of ～0.3 GPa and 10–20% from the lithostatic values. The degree of confinement of the subduction channel is the key factor controlling this magnitude. Our models also suggest that subducted crustal rocks, which may not necessarily be exhumed, can be classified into three different groups: (i) UHP‐rocks subjected to significant (≥0.3 GPa) overpressure at intermediate subduction depth (50–70 km, P = 1.5–2.5 GPa) then underpressured at depth ≥100 km (P ≥ 3 GPa); (ii) HP‐rocks subjected to ≥0.3 GPa overpressure at peak P–T conditions reached at 50–70 km depth in the bottom corner of the wedge‐like confined subduction channel (P = 1.5–2.5 GPa); (iii) lower‐pressure rocks formed at shallower depths (≤40 km depth, P ≤ 1 GPa), which are not subjected to significant overpressure and/or underpressure.     

What can the dihedral angle of conjugate-faults tell us?

Deformation within the upper crust (elastico-frictional regime) is largely accommodated by fractures and conjugate faults. The Coulomb fracture criterion leads us to expect that the average dihedral angle of conjugate-fault sets is expected to be ∼60°. Experiments, however, reveal a significant amount of scatter from this 60° average. The confining pressure under which these rocks are deformed is a contributing factor to this scatter.The Canyon Range syncline, Sevier fold-thrust belt (USA) and the Jebel Bani, Anti-Atlas fold-belt (Morocco) both folded under different depths, within the elastico-frictional regime, by cataclastic flow. Conjugate-fault sets assisted deformation by cataclastic flow. The Canyon Range syncline and the Jebel Bani are used here as natural examples to test the relationship between the dihedral angle of conjugate-faults and confining pressure. Variations is confining pressure are modeled by the difference in depth of deformation and position within the folds.Results from this study show that the dihedral angle increases with an increase in depth and within the hinge regions of folds, where space problems commonly occur. Moreover, the shortening directions based on the acute bisectors of conjugate-faults may not be accurately determined if the dihedral angles are unusually large or small, leading to incorrect kinematic analyses.     

ZEOLITES IN SEDIMENTARY ROCKS, WITH REFERENCE TO THE DEPOSITIONAL ENVIRONMENTS AND ZONAL DISTRIBUTION

The authors have studied alterations of Cenozoic and Mesozoic pyroclastic rocks of Japan, which contain several kinds of zeolites in abundance. This paper summarizes zeolites in sedimentary rocks, with reference to the depositional environments and zonal distribution, by a survey of the literature in addition to the authors’ data. The zonal distribution of zeolites is recognized in buried sedimentary rocks as follows: The zeolites in syngenetic or early diagenetic origin depend strongly upon a specific sedimentary environment. Phillipsite occurs largely in pelagic sediments of the younger geologic age. Analcime is found in saline-lake and terrestrial sediments in a warm, rather arid region, frequently associated with phillipsite, chabazite and natrolite. The zeolites are not influenced by the sedimentary environments but depend upon the depth of burial, i.e., increasing temperature and pressure. Most of clinop- tilolite, mordenite and erionite, forming at a relatively shallow depth, occur only as an alteration product of acidic to intermediate volcanic glass and cement of the post- Jurassic pyroclastic rocks. Laumontite, forming at a greater depth, on the other hand, is widely distributed in the pre-Pliocene various sedimentary rocks.     

地壳的应力状态、构造附加静压力和岩石矿床形成深度的研究

本文对深度计算公式：D=P/d（式中D为深度,P为压力,d为密度）的应用提出质疑。该公式源自一个流体力学原理,即描述静流体中压力与深度关系的帕斯卡原理,所以只适用于流体。如果物质是一种固体,而不是液体或气体,它可以承受剪应力或差应力,则这一公式就不能应用。所有岩石,从出露地表深至核幔边界,都是固体。当外力作用于固体单元上时,固体的应力场存在两部分：均应力和差应力,不论外力是构造力还是重力。而当外力作用于液态物质时,在这个液体应力场中则总是只有均应力而无差应力。地应力测量结果表明,作用于垂直截面上的水平应力通常大于作用于水平截面上的垂直应力,而且越靠近造山带或剪切带,水平应力越大,显示构造力在地壳应力场中起某种主导作用。事实上推动板块运动的力主要是水平的,而非垂直的。地壳中某处的总静压力至少由两部分合成：由构造引起的压力和由重力引起的压力,前者称构造附加静压力。合理计算成岩成矿深度的方法,应该是从总压力中减去构造附加静压力,再除以岩石比重,即D=（P-Pt）/d,式中Pt为构造附加静压力。     

三轴条件下岩石抗剪强度参数线性回归法的修正

岩石三轴强度包络线通常为非线性,通过线性回归法（LRM）获得的抗剪强度参数对围压的变化具有很高的敏感性。为使 LRM能够考虑围压对抗剪强度参数估计的影响,定义了岩石三轴强度围压效应系数,构造一个指数函数表示该系数与围压的关系,并将其引入到 LRM 的修正中,提出考虑围压效应的线性回归分析法（CCPE-LRM）。同时,提出了CCPE-LRM 的合理性检验方法,并定义了距离系数作为指标来表征抗剪强度参数估计值与参数实际值的差异。通过以公开发表文献中多种类型岩石的三轴强度数据为例进行验证分析,结果显示各种岩石的距离系数均较小,CCPE-LRM 获得的抗剪强度包络线紧贴摩尔圆,且近似相切状态。表明通过CCPE-LRM 获得的抗剪强度包络线在一定程度上可以代替理想抗剪强度包络线,该方法估计的抗剪强度参数与理论抗剪强度参数的一致性较高,证明CCPE-LRM 具有较好的适用性。     

Geophysical methods application in groundwater natural protection against pollution

Natural protection against groundwater pollution mostly depends on water-bearing bed coverage with permeable rocks presenting a good or bad pollution intrusion barrier between the surface and subterranean water. Additional positive effects of polluted groundwater self-purification in these zones are visible. Natural protection from surface pollutants primarily depends on natural (geological) factors: (1) presence of poorly permeable rocks; (2) depth, lithology (grain-size distribution), and filtration features of rocks covering groundwater reservoirs; and (3) aquifer depth. In contrast to artesian aquifers, quantitative and qualitative evaluation for natural protection of intergranular aquifers with a free water surface is significantly complicated. In this case, the estimation is possible with the help of a specially developed statistical method, which requires the following elements referring to the zone of aeration: (1) poorly permeable strata depth; (2) filtration features; (3) groundwater level depth; and (4) lithology. For quantitative evaluation, it is necessary to know the time interval for pollution propagating from surface of the terrain to the free water surface. Describe access is particularly useful in the domain of zones of sanitary protection defined around the source of groundwater. This exploration method could be considerably rationalized by geophysical methods application. Various methods are useful, namely: electric mapping and sounding, self-potential method, seismic reflection and refraction methods, gravity and geomagnetic methods, the turam method, and different well-logging measurements (gamma ray, gammagamma, radioactivity log, and thermal log). In the paper, geophysical methods applictations in natural protection against groundwater pollution and appropriate critical analysis are presented. The results of this paper are based on the experience and application of geophysical methods to groundwater studies in Yugoslavia by the author.     

Foreword

Since the discovery of a lot of eclogites with coesite and diamond inclusions related to the continent-continent collision-orogeny environment, the ultrahigh-pressure metamorphism (UHPM) in the Dabie-Sulu has aroused great interest in geologists. Experimental studies have proved that such minerals as diamond, coesite and omphacite etc. formed at pressures 2-5 GPa (and corresponding temperatures). However, it does not mean that by the formation pressure we can directly determine that the metamorphic rocks are the products of a deep-seated subducting plate downward to depths of 100-200 km and then returning to the surface. The calculation method of P/SW (depth=pressure/specific gravity), i.e. the formula of pressure=depth×specific gravity, needs to be thought about again.     

超高压变质作用中水的相变增压

据静水压力梯度计算, 榴辉岩形成深度至少要70km, 含柯石英榴辉岩的形成深度至少要12 0km, 而同时含有柯石英和金刚石的榴辉岩形成深度至少要145km, 超高压变质岩要从如此深的部位折返到地表是不可想象的.大量资料表明水参与了超高压变质作用过程.通过矿物的脱水行为、水的相变和地温曲线等研究, 指出由于存在水的相变增压等多种增压因素, 大大提高了超高压变质作用过程中的地压梯度, 据静水压力计算出的超高压变质岩形成深度只是最大深度, 其形成时的实际深度要比该最大深度小得多.