大别山含柯石英榴辉岩区—一个晚太古代的超高压变质带

安徽碧溪岭岩体的锆石U-Pb年龄为2774±24Ma。它显示大别山的含柯石英榴辉岩可能形成于晚太古代。榴辉岩多硅白云母的Ar-Ar等时线年龄(662±13Ma)也同样限定其退变质作用的上界年龄在寒武纪。同位素年代学结果与该类榴辉岩严格产出在由大别群组成的太古宙地块中的地质特征一致。我们相信,大别山含柯石英榴辉岩变质地区可能是一个晚太古代的超高压变质带。大别山地区在中生代三叠纪时期处于南秦岭构造带的东延部分。大别群以及赋存其中的含柯石英榴辉岩共同遭受晚期的区域动力变质事件。作者分别测得斜长片麻岩白云母Ar-Ar等时线年龄为192.6±3.8Ma,榴辉岩中低角闪岩相普通角闪石Ar-Ar坪年龄230.7±4.6Ma。它们代表大别群片麻岩和榴辉岩两种原始变质岩的印支期改造年龄。     

大别山英山和熊店榴辉岩单颗粒锆石SHRIMP U-Pb年代学研究

报道了对大别山高压-超高压带河南罗山熊店和湖北英山蜜蜂尖两地榴辉岩单颗粒锆石SHRIMP U-Pb原位(in-situ)定年结果.英山超高压榴辉岩年龄有4组:(773±20) Ma,(730±16) Ma,(461±7) Ma和(262±6) Ma,其中以(461±7) Ma占绝对优势.熊店高压榴辉岩有3组年龄:(449±14) Ma,(307±14) Ma和(216±4) Ma.两地榴辉岩中均存在约450 Ma的早古生代奥陶纪年龄,它们均具有极低的Zr含量(9×10-6～19×10-6).结合熊店榴辉岩样品具有类似于MORB的微量元素特征和εNd值(450 Ma时为+6.56),说明该古生代年龄应代表古生代洋壳和岛弧物质俯冲经高压-超高压变质作用的产物.由于奥陶纪高压-超高压事件的年龄同时出现在英山和熊店榴辉岩中,且熊店榴辉岩中清楚地记录了三叠纪高压-超高压事件,表明大别高压-超高压带北界无论是在奥陶纪或三叠纪时均应在熊店榴辉岩以北的桐柏-商城断裂.     

大别-苏鲁造山带大理岩中榴辉岩包体的锆石U-Pb年龄及其地质意义

大别-苏鲁造山带大理岩中榴辉岩包体的锆石有两种类型，为变质增生锆石和变质重结晶的残留碎屑锆石。变质增生锆石和完全变质重结晶锆石都具有较低的U、Th含量和Th/U比值，且给出两组变质年龄，分别为240.9±4.8~25.1±3.1 Ma和223.7±4.2~226.0±3.9 Ma。年龄为240.9±4.8~245.1±3.1 Ma的变质锆石的生长对应于板块俯冲过程中高压榴辉岩相变质作用期间的流体活动，而223.7±4.2~226.0±3.9 Ma的变质锆石的生长可能对应了板块折返早期的流体活动。这些年龄同样可以很好地用来限定其寄主大理岩的变质演化历史。     

大别山岳西碧溪岭地区片麻状斜长花岗岩锆石U-Pb年龄

在大别造山带,出露大量的片麻状花岗岩,其岩性主要为片麻状花岗闪长岩、片麻状二长花岗岩、片麻状斜长花岗岩以及少量的片麻状英云闪长岩,现已确认它们与超高压变质岩石之间存在侵入接触关系。岳西碧溪岭地区的片麻状斜长花岗岩位于榴辉岩体的南部,其单颗粒锆石U－Pb同位素年龄表明,该岩体侵位时代为晋宁期（861±58Ma）,并于海西期（318±14Ma）曾遭受一次强烈的变质热事件改造。这对大别山超高压变质带的形成和折返机制的认识将提供重要的信息。     

柴北缘超高压带中锡铁山榴辉岩的变质时代

锡铁山地体位于柴北缘超高压变质带的中部, 是柴北缘超高压变质带的重要组成部分。该地体由花岗质片麻岩、泥质片麻岩和相对较少的榴辉岩透镜体组成。大部分榴辉岩都经历了不同程度的后生合晶和角闪岩相退化变质改造。虽然近年来进行了大量的锆石U-Pb年代学研究,但榴辉岩相高压-超高压变质的时代一直存在争议,并且以前对锡铁山榴辉岩相变质时代的认识一直与相邻的绿梁山、鱼卡和其东部的都兰等地区的超高压变质年龄有明显的冲突。本文通过锡铁山榴辉岩锆石U-Pb年代学的研究,获得榴辉岩相变质锆石的²⁰⁶Pb/²³⁸U加权平均年龄为433±3Ma,与鱼卡地区榴辉岩的形成年龄一致,代表大陆俯冲时期的高压-超高压变质年龄。该研究对进一步了解锡铁山榴辉岩地体的变质演化和大陆地壳深俯冲有重要意义。     

柴北缘野马滩超高压榴辉岩中副片麻岩夹层的锆石U-Pb定年及其地质意义

榴辉岩与围岩的变质程度和变质年龄研究是超高压竞质地体形成机制研究的关键.已有研究表明,柴北缘野马滩榴辉岩和围岩副片麻岩共同经历了超高压变质作用,榴辉岩的变质年龄为458±7Ma,但有关副片麻岩的变质时代存在争议,从而制约了本区超高压变质地体形成机制的讨论.本文选择新发现的野马滩超高压榴辉岩中的副片麻岩夹层进行详细的年代学和地球化学研究.锆石的阴极发光图象显示所选锆石具有清晰的核.边结构,为典型的变质碎屑锆石特征.LA-ICP-MS定年方法获得锆石核部原岩形成年龄为大于1000Ma,边部变质事件年龄为458±6Ma.该年龄与紧邻的超高压榴辉岩的变质年龄一致,指示二者形成于同一地质事件.岩石地球化学研究表明,片麻岩的原岩为形成于陆缘环境的含泥硅质岩.综合榴辉岩与片麻岩原岩形成构造背景、变质程度及产状关系,提出野马滩榴辉岩与围岩属"原地"关系,可能形成于陆壳的深俯冲作用.     

南大别山碧溪岭榴辉岩加里东期 Ar-Ar年代学信息

笔者曾尝试把热液矿床流体包裹体 Ar- Ar定年技术应用于碧溪岭超高压变质榴辉岩石榴子石流体包裹体定年研究 , 并获得了石榴子石流体包裹体 Ar- Ar等时线年龄～ 450Ma.为了探索这个年龄信息的地质意义 , 继续开展了更广泛的研究工作 , 结果表明,加里东期年龄信息也记录于碧溪岭其他榴辉岩露头的石榴子石流体包裹体中 , 它们的 Ar- Ar年龄谱和等时线非常相似 ; 而碧溪岭榴辉岩体中的花岗片麻岩之角闪石和黑云母的 Ar- Ar年龄谱平坦 , 其等时线年龄分别为 (275± 18) Ma和 (273± 4) Ma, 明显早于当前主流学术观点的超高压峰期变质年龄 240～ 220 Ma.这些 Ar- Ar年龄将有助于进一步认识大别-苏鲁地区超高压变质作用历史.     

中央碰撞造山带中两期超高压变质作用：来自含柯石英锆石的定年证据

沿中央造山带存在一条巨大的超高压变质带,其西起阿尔金-祁连,往东经秦岭,延至大别苏鲁,全长超过4000 km.柴北缘片麻岩中含柯石英锆石的SIMS离子探针原位微区U-Pb定年获得超高压变质年龄452±1 3.8 Ma,锆石的退变质年龄419±6.7 Ma.SHRIMP U-Pb定年获得秦岭含金刚石片麻岩中锆石的下交点年龄502±45 Ma,上交点年龄1545±100Ma,认为前者代表超高压变质年龄,后者为原岩岩浆锆石年龄;获得榴辉岩锆石的上交点年龄1381±82 Ma和下交点493±170 Ma,认为上交点代表榴辉岩原岩年龄,下交点代表超高压变质年龄;获得江苏东海县青龙山榴辉岩含柯石英等超高压矿物锆石的年龄为441±9 Ma,449±9 Ma,和442±9Ma,平均444±9 Ma,核部含斜长石+磷灰石锆石年龄为761±13 Ma,认为前者代表超高压变质年龄,后者代表榴辉岩原岩结晶年龄.认为中国中部沿中央造山带中存在两期超高压变质作用,第一期为加里东期,第二期为印支期,两期超高压变质事件在时空分布方面是不同的,加里东期超高压变质事件由西部阿尔金-柴北缘延至东部大别-苏鲁,印支期超高压变质事件没有在大别以西发现.认为中央造山带应是一个多期活动的造山带,较早形成罗德尼亚大陆的格林威尔造山运动可能留下了10亿年左右的构造岩浆事件记录,如中央造山带中大量10亿年左右的花岗岩及基性超基性岩类;罗德尼亚大陆之后第一次裂解作用可能发生在8亿年左右;其后早古生代加里东期的洋盆裂开,蛇绿岩和超高压变质岩石的大量出现是一次十分强烈的板块构造事件,从东到西,沿中央造山带均有分布;加里东期造山事件之后印支期沿该造山带又有一次大的板块裂解和俯冲碰撞作用,表现在勉略蛇绿岩洋壳及大别-苏鲁印支期超高压变质带的存在.中央造山带保留和记录了多期裂解、会聚事件,通过对其解剖,不仅可以认识中国大地构造格局和演化,并由此理解全球的大陆漂移、一系列大裂解和大会聚等重大地质事件.     

含柯石英锆石的SHRIMP U-Pb定年:胶东印支期超高压变质作用的证据

苏鲁超高压变质带的形成时代究竟是印支期还是新元古代争议始终很大。对山东胶南地区超高压变质带中超镁铁岩和榴辉岩的锆石激光拉曼、阴极发光和离子探针原位定年的研究获得超高压变质作用发生的时代为印支期。其中超镁铁岩含柯石英锆石的年龄为221±12Ma,该深成岩侵位时代为新元古代(581±44Ma)。此外,锆石中另有约400Ma年龄记录,可能代表岩石形成后另有一期热事件。榴辉岩的下交点年龄为228±29 Ma,与超镁铁岩含柯石英锆石年龄一致,代表超高压变质时代;上交点为中元古代(1821±19Ma),代表原岩年龄,后者与其片麻岩围岩时代相一致,说明榴辉岩是原位俯冲。     

胶东地块东部变质岩锆石U-Pb定年和氧同位素研究

对胶东地块东部高压-超高压变质岩作了系统的锆石U-Ph定年和矿物氧同位素分析,结果对这些变质岩的原岩性质提供了制约。研究得到:(1)区域花岗片麻岩及岩浆锆石普遍不同程度地亏损~(18)O,3个片庥岩样品中岩浆核锆石U-Pb年龄分别为723±36Ma、738±17Ma和744±63Ma,低δ~(18)O值(-0.42～4.14‰)岩浆核锆石说明其原岩为新元古代低δ~(18)O值岩浆岩,石英-石榴石氧同位素温度及少量印支期变质锆石的出现,指示片麻岩与榴辉岩曾经共同经历了印支期超高压变质作用;(2)花岗片麻岩中的榴辉岩原岩年龄有两种,一种是新元古代,其U-Ph年龄为806±79Ma。另一种是古元古代晚期,其 U-Pb年龄为1838±41Ma。这2个榴辉岩的超高压变质年龄分别为229±3Ma和242±21Ma。多数榴辉岩中的变质增生或变质重结晶锆石也具有低δ~(18)O值特征(0.22～3.4‰),指示在榴辉宕相变质作用之前,这些榴辉岩原岩为低δ~(18)O值蚀变岩或低δ~(18)O值基性岩浆岩;(3)大理岩中榴辉岩变质增生锆石δ~(18)O值高达15.9‰,U-Pb年龄为229±4Ma,指示在榴辉岩相变质作用之前,榴辉岩原岩与大理岩一样具有高δ~(18)O值;(4)斜长角闪岩的原岩U-Pb年龄为1719±18Ma,与同时期榴辉岩原岩一起构成扬子板块北缘新元古代岩浆侵位时的裂谷肩部围岩,在三叠纪大陆碰撞时同样受到变质改造。     

Physical properties of a horizon of a white hole and a Kruskal wormhole

The possible application of a Rindler type reference frame for studies of physical processes near the horizons of black and white holes is considered. New similar reference frames inside black and white holes in the region T of a Kruskal wormhole are introduced.     

Gamma-ray bursts as a result of the interaction of a shock from a supernova and a neutron-star companion

A supernova explosion in a close binary system in which one of the components is a compact magnetized object (neutron star or white dwarf) can form a narrow “tail” with length l _t ～10⁹ cm, width h _t ～10⁸ cm, and magnetic field B _t ～10⁶, due to the resulting shock wave flowing around the magnetosphere of the compact object. The energy released by the reconnection of magnetic field lines in this tail can accelerate electrons to relativistic speeds (γ≈10⁴), creating the conditions required for powerful synchrotron radiation at energies from hundreds of keV to several MeV, i.e., for a gamma-ray burst (GRB). The duration of this radiation will depend on the power of the shock that forms during the supernova. If the shock is not sufficiently powerful to tear off the magnetosphere tail from the compact object, the duration of the GRB will not exceed l _t /V _A ≤1 s, and the conditions necessary for an “afterglow” at softer energies will not arise. If the shock is more powerful, the tail can be torn from the magnetosphere, forming a narrow ejection, which is perceived in its relativistic motion toward the observer(Γ～10⁴) as an afterglow whose duration grows from tens of seconds at gamma-ray energies to tens of days in the optical. This may explain why afterglows are observed only in association with long GRBs (T ₉₀>10 s). Very short GRBs (T ₉₀<0.1 s) may be local, i.e., low-power, phenomena occurring in close pairs containing compact, magnetized objects, in which there is again an interaction between the magnetosphere of the compact object and a shock wave, but the shock is initiated by a flare on the companion, which is a red-dwarf cataclysmic variable, rather than by a supernova.     

Coupled consolidation of a porous medium with a cylindrical or a spherical cavity

This paper presents a theoretical approach to analyse coupled, linear thermoporoelastic fields in a saturated porous medium under radial and spherical symmetry. The governing equations account for compressibility and thermal expansion of constituents, heat sink due to thermal dilatation of water and thermal expansion of the medium, and thermodynamically coupled heat–water flow. It has been reported in the literature that thermodynamically coupled heat–water flows known as thermo-osmosis and thermal filtration have the potential to significantly alter the flow fields in clay-rich barriers in the near field of a underground waste containment scheme. This study presents a mathematical model and examines the effects of thermo-osmosis and thermal-filtration on coupled consolidation fields in a porous medium with a cavity. Analytical solutions of the governing equations are presented in the Laplace transform space. A numerical inversion scheme is used to obtain the time-domain solutions for a cylindrical cavity in a homogeneous or a non-homogeneous medium. A closed form time-domain solution is presented for a spherical cavity in a homogeneous medium. Selected numerical solutions for homogeneous and non-homogeneous media show a significant increase in pore pressure and displacements due to the presence of thermodynamically coupled flows and a negligible influence on temperature. © 1998 John Wiley & Sons, Ltd.     

Propagation of a shear crack in a compressed plane with a circular hole

The problem of the equilibrium of a plane with a circular hole and a shear crack is considered to model failure of an excavation (borehole or circular opening) in rocks weakened by discontinuities (planes of weakness). It is assumed that sliding occurs in a part of the plane of weakness when the Mohr–Coulomb friction criterion is satisfied due to the stress redistribution caused by the excavation. The method of singular integral equations is employed to solve the boundary value problem. Geomechanical problems concerning borehole breakout and rockburst caused by fault-opening interaction are discussed. © 1998 John Wiley & Sons, Ltd.     

Spreading of a NAPL lens in a double-porosity medium

Spreading of a non-aqueous phase liquid (NAPL) denser than water (DNAPL) lens (mound) in the unsaturated zone of double-porosity aquifer above an impervious plane boundary is investigated. The double-porosity aquifer is conceptualized as a fracture network surrounding pervious blocks. Vertical gravity equilibrium is assumed to prevail in each one of the two media, fractures and blocks. Through vertical integration, two coupled partial differential equations for the DNAPL content in each medium are obtained. The mass exchange rate between high- and low-permeability media is considered as a function of NAPL content. The dominant effect is gravity, whereas capillary forces are negligible. Analytical solutions for one-dimensional and axisymmetric problems of mound spreading are obtained.     

Phase space of a two-dimensional model of a Parker dynamo

The dependences of the magnetic-field strength, variations of the magnetic field, and the multipole level on the amplitudes of the α and ω effects are considered using a two-dimensional model for a Parker dynamo in a spherical layer. Calculations have been carried out for both traditional spatial distributions of α and ω and geostrophic regimes obtained from three-dimensional modeling of thermal convection. Two-dimensional distributions of the dynamo-wave velocities in the zone where magnetic field is generated are presented. Comparisons with the solar and planetary dynamos are considered.     

Locating a point on a spherical surface relative to a spherical polygon of arbitrary shape

An algorithm for determining if any given point,P, on the surface of a sphere is located inside, outside, or along the border of an arbitrary spherical polygon,S, is described. The polygon is described by specifying coordinates of its vertices, and coordinates of some pointX which is known to lie withinS. The algorithm is based on the principle that an arc joiningX andP will cross the border ofS an odd number of times ifP lies outsideS, and an even number of times ifP lies withinS. The algorithm has been implemented as a set of FORTRAN subroutines, and a listing is provided. The algorithm and subroutine package can be used with spherical polygons containing holes, or with composited spherical polygons.     

Scattering of a plane wave by a lined cylindrical cavity in a poroelastic half-plane

The focus of this contribution is to develop a complex variable function method to solve the two-dimensional scattering of plane waves by a lined cylindrical cavity in the poroelastic half-plane. The poroelastic half-plane is based on Biot’s dynamic theory, and the governing equations are solved by reduction to three Helmholtz equations. The lining structure can be treated as an elastic material and decoupled into two Helmholtz equations. Here, the large circle assumption is applied to simulate the half-plane boundary. By using appropriate boundary conditions and continuity conditions, the unknown coefficients in the potentials can be determined. Selected numerical results are presented in this paper.     

Bearing capacity of a strip foundation on a sand layer overlying a smooth rigid stratum

The effect of a smooth rigid stratum, located beneath a dense sand layer, on the bearing capacity and settlement of surface and shallow strip footings is investigated using an advanced experimental model. A theoretical analysis is presented for the bearing capacity of surface footings. The results indicate that the bearing capacity reaches a minimum value at a specific sand-layer thickness. Any increase in the layer thickness above this value causes an increase in the bearing capacity up to that corresponding to a continuous media.Notation H= thickness of the sand layer - B= foundation width - N _q and N = bearing capacity factors for a semi-infinite layer - N _qs and N _s= bearing capacity factors for a finite layer - H _o /B= limiting depth - D _r= relative density - = angle of soil internal friction - M= model width - D= depth of surcharge - q= bearing stress, pressure applied on the footing - q _u= bearing capacity - = unit weight of sand