Abstract:新发现榴辉岩带位于拉萨北东方向,产在青藏高原拉萨地体中东部。观察到的榴辉岩带宽度约500~600m,呈近东西向延伸,已知规模10km以上。榴辉岩为常见的金红石榴辉岩、石英榴辉岩和多硅白云母榴辉岩。榴辉岩的单斜辉石中含硬玉分子变化较大,Jd=16%~44%,但均落于绿辉石成分区间;石榴子石中镁铝榴石(Pyrope)端元组分16%~33%,铁铝榴石(Alm)40%~54%,钙铝榴石(Gross)22%~31%。利用Grt-Omp-Phe和Grt-Omp矿物组合对变质温-压初步估算,获得金红石榴辉岩样品06Y-334的变质p、t分别为2.58GPa、635℃和2.67GPa、730℃,样品06Y-345的t主要在680~780℃区间,样品06Y-336的t主要在640~740℃区间,3个样品获得的结果相近。显微镜观察表明多硅白云母可能为折返阶段的退变质矿物而不属变质峰期的矿物,推测峰期的压力值有可能高于2.67GPa而进入柯石英稳定区间(p>2.8GPa)。石榴子石和绿辉石中出现的一些类似柯石英假象的石英包裹体与这一推断相吻合。以上初步研究结果表明,拉萨地体的榴辉岩带可能是中国境内又一条高压/超高压(?)变质带。

Abstract:位于北中国板块群与南中国板块群之间的中央造山带是中国大陆一条十分醒目而又极其重要的巨型(长达5000km)构造带。中央造山带是经历了大致600Ma的活动历史,和泥盆纪、三叠纪的两次主要碰撞造山以及白垩纪以来的陆内造山过程而构筑成的典型的“复合造山带”。特别是巨型中央超高压变质带及其两期超高压变质作用的发现,揭示了中央造山带的形成还经历了板块会聚边界洋壳/陆壳深俯冲的两次壮观地质事件。位于中央造山带北部的“北中央早古生代造山带”具有“多地体、多岛弧”的地体构架和“多俯冲和多碰撞造山”的动力学作用。研究认为北中央早古生代多地体/岛弧群是冈瓦纳超大陆西侧(或西北侧)陆块/岛弧群的组成部分,其主要的证据是:1北中央寒武系—志留系的过渡性动物群性质反映早古生代古生物区系与始特提斯洋盆海水相通的古地理环境;2北中央诸多蛇绿岩带形成时代>500~540Ma(新元古代-奥陶纪)可作为始特提斯洋盆扩张时限的印证;3多岛弧带为北中央早古生代地体的陆缘增生带,形成于540~450Ma,岛弧带形成自南(外)而北(里)渐新的趋势表明与始特提斯洋盆相连接的弧前小洋盆逐级俯冲的特征;4北中央早古生代多地体/岛弧群的“弧/陆碰撞”及早古生代造山带的形成是中晚泥盆世(420Ma)冈瓦纳超大陆边部古特提斯洋盆初始扩张的产物。研究表明在500~440Ma形成的柴北缘-南阿尔金超高压变质带与始特提斯弧前小洋盆的俯冲继而地体陆壳的深俯冲有关。

Abstract:We have experimentally determined the P-wave velocities of 68 typical UHP metamorphic rock samples among which 31 were collected from the CCSD (Chinese Continental Scientific Drilling) main hole and 37 from the surface outcrops in the Sulu orogenic belt (China) at ambient temperature and hydrostatic confining pressures up to 800 MPa. The velocity-pressure curves can be well described by a simple expression: V(P)=V_0+DP-B_0exp(-kP), where V_0 is the projected velocity at zero pressure if both porosity and cracks were absent; D is the intrinsic pressure derivative of velocity in the linear elastic regime; B_0 is the initial velocity drop caused by the presence of pores and cracks at zero pressure; and k is the decay constant of the velocity drop, which controls the shape of the velocity-pressure curves in the nonlinear poro-elastic regime. The above equation was used by previous workers as an empirical formula to describe the relationship between seismic velocity and confining pressure. Here we show that the equation can be directly derived on a rather general theoretical basis. The derivation has provided a clarification for the physical meaning of each parameter in the equation. It is suggested that henceforth the seismic velocities of rocks should be published in terms of these four parameters rather using tedious tables to list each velocity at each pressure for each sample as done before. The statistical properties of P-wave velocities in the Sulu UHP rocks provide a complete set of basic information for the interpretation of field seismic data from the root zones of continental convergent orogenic belts and modern and ancient subduction zones.

Abstract:北苏鲁莒南—岚山头—日照—桃行—仰口—荣成—威海一带榴辉岩的围岩经历了强烈角闪岩相退变质作用的改造,峰期超高压矿物组合已完全被后期退变矿物组合所取代。锆石微区阴极发光图像和矿物包体激光拉曼测试研究结果表明,132件不同类型岩石(包括榴辉岩、斜长角闪岩、正片麻岩、副片麻岩、大理岩、蓝晶石英岩、云母片岩和钙镁硅酸盐类变质岩等)锆石中,普遍隐藏以柯石英为代表的超高压矿物包体。此外,在南苏鲁东海及其邻区的地表露头和一系列钻孔岩心的锆石中,也普遍发现以柯石英为代表的超高压矿物包体。该项研究成果表明,在苏鲁地体由榴辉岩及其围岩的原岩所组成的陆壳岩石(约320km×20km×5km)曾发生过巨量物质深俯冲—超高压变质的壮观地质事件。

Abstract:榴辉岩型钛矿床是重要的钛矿床类型之一。苏鲁超高压榴辉岩中的钛成矿作用以金红石型钛矿床为主,其中金红石以变质矿物中的包裹体、晶间颗粒或脉状形式出现。富钛石榴子石是金红石包裹体出溶的初始矿物。岩石地球化学研究表明,有利于金红石成矿的榴辉岩为高钛榴辉岩,其源岩为富钛基性岩。利用红外显微镜对金红石进行的流体包裹体研究表明,金红石中主要存在三类流体包裹体,即型H2O溶液包裹体、型CO2-H2O包裹体和型CH4包裹体,其中I型原生和假次生流体包裹体和型流体包裹体反映出的压力范围为0.6~1.3GPa,与榴辉岩角闪岩相退变质作用的压力相当,说明与这类金红石形成有关的变质流体源于榴辉岩退变质作用所释放的水。苏鲁地区超高压榴辉岩是华南—华北板块碰撞的结果,巨量陆壳物质俯冲—折返形成了多样式的高压—超高压岩石,与此同时也发生了以金红石为主要矿石矿物的钛成矿作用。综合矿物学、岩石学、地球化学等研究,我们提出大陆板块汇聚边界的钛成矿作用应该经历了原岩的初始富集、陆壳物质俯冲过程中钛的成矿作用、俯冲板块折返过程中钛的成矿作用和流体阶段的金红石成矿作用四个主要成矿阶段。

Abstract:本文利用电子探针分析了中国大陆科学钻探工程主孔各种类型榴辉岩中金红石的Nb、Cr和Zr含量。Zack等(2002)的金红石Nb-Cr图解表明榴辉岩的原岩均为镁铁质岩,但不同类型榴辉岩具有不同的地球化学特征,即:1金红石榴辉岩、石英榴辉岩、角闪岩和钛铁矿榴辉岩中金红石的Nb和Cr含量大致相同,主孔中上述榴辉岩中金红石的Nb、Cr含量与区域上小焦金红石矿区金红石榴辉岩中金红石的Nb、Cr含量基本相同。总体来讲,区域和主孔榴辉岩中金红石以低Nb为特征,反映它们的原岩为镁铁质岩石。2蓝晶石多硅白云母榴辉岩中金红石具最高的Nb和Cr含量,其Nb和Cr均值分别为720×10-6和712×10-6,多硅白云母榴辉岩中金红石比金红石榴辉岩、石英榴辉岩、角闪岩和钛铁矿榴辉岩中金红石富集Cr。利用Zack等(2004)提出的金红石地质温度计,计算得出金红石榴辉岩的金红石形成温度介于608~746℃,石英榴辉岩的金红石温度介于629~680℃,钛铁矿榴辉岩金红石的形成温度介于629~704℃,蓝晶石多硅白云母榴辉岩的金红石形成温度为600℃,角闪岩的金红石形成温度为629℃。一种可能的解释是,榴辉岩在折返过程中退变质作用明显,流体活动强烈,导致金红石中Zr扩散丢失,金红石中Zr含量不同程度地受到角闪岩相退变质过程中再平衡作用的影响,致使计算的温度偏低。

Abstract:为探讨榴辉岩中磷灰石的矿物化学特征及榴辉岩中某些相关元素的地球化学行为,对中国大陆科学钻探(CCSD)主孔500~540m深度的榴辉岩样品进行了岩石化学及磷灰石的矿物化学分析。这些榴辉岩具有不同的矿物组成和化学成分,并可据此分为上下两段,上段500~530m为正常榴辉岩,下段530~540m为高Ti榴辉岩和高Ti-Fe榴辉岩,其原岩可能为类似于辉长质和苦橄质的基性—超基性岩石。其中的磷灰石成分没有明显差别,均为氟—磷灰石,其富F贫Cl的特征可能是造成榴辉岩中高盐度流体包裹体和全岩高F低Cl的主要原因。磷灰石普遍含有一定的Sr、S、Fe元素,多数还含有Cu、Pb、Zn等元素。榴辉岩中P2O5含量与其F、Cl、Sr、S元素的相关程度表明,磷灰石是榴辉岩中F元素的最主要储存库,也是Sr元素的重要储存库之一,而对于Cl元素则只是部分控制,与S元素则没有相关性。榴辉岩中F、Sr及Cl元素的地球化学行为主要受控于磷灰石,因此,在榴辉岩从进变质—退变质过程中,这些元素的活动性直接受控于磷灰石的稳定性。

Abstract:本文对苏鲁造山带西南端(南苏鲁)的中生代花岗岩采用激光探针等离子体质谱(LA-ICP-MS)方法进行了年代学测定,李埝岩体为122±5Ma(6个测点的加权平均值),抗日山岩体的年龄为119±2Ma(5个测点的加权平均值),这些结果表明,南苏鲁地区的花岗岩主要形成于燕山期,相当于早白垩世。两个花岗岩体中还分别检测出新元古代的锆石,年龄范围为751~639Ma,表明有新元古代的岩石参与了中生代花岗岩的形成。花岗岩与围岩花岗质片麻岩地球化学和Sr-Nd同位素以及锆石特征的对比表明,经历超高压变质的花岗质片麻岩不是中生代花岗岩的主要源岩。花岗岩中存在暗色包体,结合该地区存在大量同时代的幔源岩浆活动,推测壳幔岩浆的混合可能是南苏鲁花岗岩形成的主要方式。

Abstract:江苏东海地区构造上位于苏鲁造山带的西南缘,区内出露新元古代片麻状碱性花岗岩,其特征矿物组合为石英+钾长石+钠-更长石+霓(辉)石、亚铁钠闪石。地球化学上,该套岩石具有富硅(SiO2=73.43%~77.38%)、富碱(ALK=8.19%~9.53%),铁镁比值高[FeO*/(FeO*+MgO)=0.83~0.94],CaO、MgO含量低,富Ga、Y、Zr、Hf,贫Sr、P、Ti,镓铝比值高(104×Ga/Al=2.76~5.15),轻重稀土分馏显著[(La/Yb)N=2.08~17.89],并具有中—强的铕亏损(δEu=0.12~0.66)等特点。在花岗岩成因类型判别图解中,它们均投影在A型花岗岩区,结合岩石具有过碱(AKI=0.99~1.22)和相对贫铝(A/NKC=0.78~0.93)的化学组成特征,表明它们应属过碱性A型花岗岩。在微量元素蛛网图上,这套岩石表现出较明显的Nb、Ta、Ti负异常,保留有先期“弧”岩浆作用产物的地球化学印记,其Y/Nb和Y/Ta值也较高(分别为1.85~9.72和4.71~30.14),在A型花岗岩岩石学亚类判别图解中,它们均投影在产于后造山环境的A2型花岗岩区。根据对矿物化学和全岩地球化学组成及产出动力地质背景的全面分析,表明这套岩石应形成于从碰撞造山转向伸展塌陷(collapse)的最早阶段,而不应是同裂谷阶段岩浆作用(syn-riftmagmatism)的产物。这一认识对于进一步了解新元古代苏鲁造山带的构造演化及深入探讨Rodinia超大陆的裂解机制具有重要意义。

Abstract:在中国大陆科学钻探主孔榴辉岩中发现了重晶石。重晶石以包裹体形式保存在石榴子石中,多为浑圆状,表面积平均约250μm2。通过电子探针测试,重晶石中SrO含量大多超过20%,为锶重晶石,其化学分子式为(Ba0.4836~0.6180Sr0.3787~0.4722Ca0.0064~0.0889)S0.9688~0.9963O4。同时还发现榴辉岩中的石榴子石有柯石英假象,温压条件计算表明该榴辉岩的峰期温压条件为696~730℃,2.9~3.2GPa。电子探针成分测定包裹这些重晶石的石榴子石为峰期变质矿物,这进一步说明重晶石也经历过超高压变质。重晶石通常形成于强氧化和高盐度流体作用的条件下,本文的研究表明超高压变质过程中至少出现了一定范围内的强氧化环境和高盐度流体作用,但其地球动力学意义有待进一步研究。

Abstract:本文样品是采自中国大陆科学钻探(CCSD)主孔的含金红石榴辉岩,在这些样品中常常含有锆石副矿物,锆石可以呈粒间矿物存在,也可以包裹在其他矿物(如石榴子石、金红石)中。背散射电子图像(BSE)显示这些锆石包裹体的亮度较弱,颗粒较小(约10~30μm),发育多晶面,晶体内部结构和成分均匀。采用能谱分析(EDS)方法来测量锆石的元素成分含量,结果表明:1这些锆石具有很高的Hf含量,金红石中达到1.51%~2.45%,石榴子石中为1.77%~2.13%;2Zr/Hf值约为35.92,比一般的基性原岩中的锆石的Zr/Hf值明显要低,这些特征说明它们很可能是形成在超高压条件下的变质锆石。

Abstract:Quartz bar (or needle) exsolutions from clinopyroxenes are considered as one of the diagnostic indicators in the ultrahigh-pressure metamorphism, and were frequently identified from several UHP metamorphic belts in the world. Exsolutions in omphacites in eclogites from the Chinese Continental Scientific Drilling Project main hole (CCSD-MH) and Pre-pilot 1(CCSD-PP1) were studies by using laserRaman and electron microprobe analysis, and numerous parallel quartz bars (or needles) were found. For comparison, omphacites in CCSD eclogites without any quartz exsolution were also analysed. The results indicate that the omphacites with quartz exsolution is supersilicic. Ultrahigh-pressure experiments shown that part of silica can form octahedral coordination structure, if pressure is high enough. It's proposed that decline of pressure will facilitate quartz exsolution. The peak pressure of UHP metamorphism indicated by quartz exsolutions in the CCSD omphacites is much higher than 2.5GPa, which was estimated by the previous researchers based on facies transformation of quartz-coesite and graphite-diamond, suggests that subuduction depth of the Su-Lu UHP metamorphic belts may be greater than commonly recognized 80~120km.

Abstract:Noble gases isotopic compositions of fluid inclusions in major rock-forming minerals in HP-UHP metamorphic rocks collected from the Chinese Continental Scientific Drilling (CCSD) were analysed by using a high vacuum gas mass spectrum. The results show that the ~ 3 He/ ~ 4 He ratios are (0.004~0.775) 10~ -6 , and the corresponding R/R_a are 0.003~0.553; The ~ 40 Ar/ ~ 36 Ar ratios are 316.2~11358.8, much higher than that of the air (295.5). ~ 20 Ne/ ~ 22 N and ~ 21 Ne/ ~ 22 Ne are 9.47~12.4 and 0.026~0.051 respectively, and the respective ~ 134 Xe/ ~ 132 Xe and ~ 136 Xe/ ~ 132 Xe are 0.376~0.484 and 0.324~0.416, all higher than their corresponding values of the air. He-Ar, Ne and Xe isotopic compositions suggest that the ore-forming fluid of the fluid inclusions in the CCSD HP-UHP rocks were composed mainly of crustal fluid and a little air-saturated water, while the mantle-derived fluid was nearly absent. In the fluid inclusions, the He derived predominantly from the crust, the Ar are composed mainly of crustal radiogenic ~ 40 Ar and about one third air Ar. A little amount of Ne and Xe might derive from the mantle. The characteristics of F~ 40 Ar

Abstract:In order to understand seismic response of folded structures, reflection modeling has been performed on various types of fold trains including single-order open folds, close folds and asymmetric inclined folds as well as multi-order folds. The synthetic sections show that, unlike large scale single-order open folds, multi-order folds and inclined folds cannot be correctly imaged by conventional reflection techniques. The reflections from fold limbs tend to be muted, leaving the crests and troughs that merge laterally into pseudo-horizontal reflections. These reflections bear no resemblance to folds but mislead, instead, the presence of subhorizontal reflections. The latter is often interpreted as subhorizontal layering or compositional lamination formed by crustal extension or underplating. The modeling results also suggest that the compositional lamination is not necessarily the sole source of subhorizontal reflections. Complex folded structures due to intensive shortening may also produce such subhorizontal reflections, but the latter are generally more discontinuous laterally and less dense than those caused by simple lamination. Interestingly, the reflections observed in cratons and fold belts are generally laterally shorter and less dense (except in ductile shear zones) than those observed in the extensional regions. This indicates that seismic lamination may correspond to laminated lower crust in extensional regions such as the Basin and Range (USA), but most likely to complex folded structures beneath both ancient and modern fold belts.

Abstract:在不同类型变质岩和超基性岩的造岩矿物(如橄榄石、石榴子石、绿辉石等)中都发现了大小不一的固态出溶体。对大小仅为几个微米的出溶体,利用常规方法,电子探针、拉曼光谱等很难定量地确定它们的化学组分,严重地限制了对这些出溶体的地球化学动力学意义的认识。在最近的一系列研究中,发现榴辉岩中磷灰石含大量的出溶体,这些出溶体是平行于磷灰石C轴出溶的含铁、铜、铅等元素的硫化物。采用扫描电镜能谱分析(EDS)的点分析和线扫描技术,确定出溶体的主要组成元素,然后通过扣除磷灰石对所分析出溶域的贡献,能较准确地确定这些出溶体的化学组分,主要为FeS和FeS2。这些实验结果表明,利用扫描电镜的能谱分析(EDS)技术,通过点分析和线扫描,能够较精确地测量与母矿物之间化学成分差异较大的出溶体的化学组成。本文所提出的处理方法也适用于电子探针。

Abstract:The Nangang-Gaogongdao ductile shear zone is a slice boundary tectonic zone with strong mylonitization, which formed by thrusting from the southeast to the northwest. The main minerals in rock, such as feldspar and biotite et al., had decomposited or altered with different degree, that resulted in compositional variation during ductile deformation. Thereinto, the variation of mobile components in the rock resulted from fluid infiltration, and the variation of immobile components was caused by the volume loss during mylonition. The isocon line slopes are determined by comparing the geochemical compositions of rocks before and after deformation of feldspar or albite quartz schist within the ductile shear zone. The mass balance calculation shows that the volume losses of protomylonite and mylonite during mylonition are 17% and 27% respectively. The mass balance analysis and isocon diagram indication that the loss of SiO_2 is largest, the next is Al_2O_3, and while FeO, CaO and Na_2O lose to different extent, showing that they are mobile components in the rock. MgO located over the isocon line, is the import components. The quartz vein or felsic band in mylonites formed by separation and transfer of SiO_2, Al_2O_3, Na_2O and FeO et al., which resulted from the saussuritization and sericitization of feldspar and the chloritization of biotite during mylonition. The volume loss and component variation during ductile shearing are the important richment mechanism of immobile components, and have the important guidance for researching the mechanism of felsic band and metalogenesis of precious metals deposits.

Abstract:Subduction is one of the important mechanisms for the formation of the high-pressure (HP)-ultrahigh-pressure (UHP) metamorphic belt. The movement rate and strength of a subducted block are important tectonic constraints on its formation and evolution. Studying the formation process of a HP-UHP metamorphic belt by using plate subduction is a useful attempt to study the formation mechanism of the Sulu HP-UHP metamorphic belt and construction of a dynamic model. The most conspicuous tectonic effect of subduction is strong underthrusting of the land surface at the front of a subducted block and the Moho, which results in the formation of a piedmont depression and accretion and thickening of continental crust. Preliminary numerical modeling suggests that the translational rate of a subducted block is broadly positively correlated with the amount and rate of downwarping of a piedmont depression and the amount and rate of downward flexure of the Moho, indicating that they are boundaries of important intracrustal active tectonics. The migration of the tectonic boundary in the interior of a subducted block, as the movement carrier of deep subduction of a HP-UHP metamorphic belt, indirectly reflects the changes in formation process and movement rate of a HP-UHP metamorphic belt. The results of the numerical modeling seem to show that the land surface and Moho is likely to be boundaries of important active tectonics for the study of the formation process of a HP-UHP metamorphic belt and deep subduction. The tectonic stress field in the interior of a subducted block is also an important tectonic factor for constraining and influencing the formation process of a HP-UHP metamorphic belt. Modeling calculation indicates that the intracrustal stress field of a subducted block during subduction is relatively stable and always dominated by compressional stress, while the strength of subduction only affects the magnitude of stress rather than the distribution of stress in the intracrustal stress field.

Abstract:苏鲁-大别造山带是中国东部华北、华南地块之间的大地构造交界带.本文分析研究了我国东部的地震活动性,并根据1918～2005年间苏鲁-大别及其周围地区发生的1000余个地震的震源机制解,系统研究了应力场的区域特征以及华北、华南地壳应力场构造分区,探讨了其动力学来源以及构造运动特征.结果表明,中国东部大陆华北、华南地块地壳现代应力场和构造运动可以归结为太平洋板块和菲律宾海板块与欧亚板块之间相对运动,以及大陆板内区域块体之间相互作用的结果.华北地区受到太平洋板块向欧亚板块俯冲挤压的同时,受到从贝加尔湖经过大华北直到琉球海沟的广阔地域里存在着的统一的、方位为170°的引张应力场的控制.华北地区大地震的震源机制解均反映出震源应力场为ENE向挤压应力和NNW向张应力的共同作用.郯庐断裂带等华北地区的北北东走向的断裂带,表现为右旋走滑的现代构造运动特征.来自台湾纵谷的北西西向挤压应力控制了华南块体直至南北地震带南段东部地域的地壳应力场.本文研究结果表明,将中国东部大陆划分成华北、华南两部分的现代地壳应力场分界线,其西部大致与秦岭带相同,然而在大别及其以东地区则逐渐偏离大地构造带,到北纬30°后向东南偏转,在温州附近的北纬27°左右转为向东延伸,最终穿过东海直至琉球海沟.