谈早前寒武纪侵入岩定位、变形、变质的同期性

依据鲁西地区早前寒武纪花岗质侵入岩普遍具有塑性流变特征和退化变质特征,以及变质作用和变形作用相协调等现象,认为岩体的侵位与变形、变质是同一期构造岩浆作用形成的,是岩浆就位后逐渐冷凝过程中,在持续应力作用下发生的,与后期的地质构造作用无关;固态岩石只能发生脆性变形和局部的脆韧性变形。并从热力场、动力场和化学场的变化趋势对变形、变质作用的制约因素作了简要分析。     

Structural and tectonothermal evolution of the ultrahigh-temperature Bakhuis Granulite Belt,Guiana Shield,Surinam:Palaeoproterozoic to recent

We constrain the multistage tectonic evolution of the Palaeoproterozoic UHT metamorphic(P=0.9–1.0 GPa,T>1000℃,t=2088–2031 Ma)Bakhuis Granulite Belt(BGB)in Surinam on the Guiana Shield,using large-to small-scale structures,Al-in-hornblende thermobarometry and published fluid inclusion and zircon geochronological data.The BGB forms a narrow,NE–SW striking belt between two formerly connected,~E–W oriented granite-greenstone belts,formed between converging Amazonian and West African continental masses prior to collision and Transamazonian orogeny.Inherited detrital zircon in BGB metasediments conforms agewise to Birimian zircon of West Africa and suggests derivation from the subsequently subducted African passive margin.Ultrahigh-temperature metamorphism may have followed slab break-off and asthenospheric heat advection.Peak metamorphic structures result from layer-parallel shearing and folding,reflecting initial transtensional exhumation of the subducted African margin after slab break-off.A second HT event involves intrusion,at ca.0.49 GPa,of charnockites and metagabbros at 1993–1984 Ma and a layered anorthosite at 1980 Ma,after the BGB had already cooled to<400℃.The event is related to northward subduction under the greenstone belts,along a new active margin to their south.A pronounced syntaxial bend in the new margin points northward towards the BGB and is likely the result of indentation by an anticlinorial flexural bulge of the subducting plate.Tearing of the subducting oceanic plate along this bulge explains why the charnockites are restricted to the BGB.The BGB subsequently experienced doming under an extensional detachment exposed in its southwestern border zone.Exhumation was focused in the BGB as a result of the flexural bulge in the subducting plate and localised heating of the overriding plate by charnockite magmatism.The present,straight NE–SW long-side boundaries of the BGB are superimposed mylonite zones,overprinted by pseudotachylites,previously dated at ca.1200 Ma and 950 Ma,respectively.The 1200 Ma mylonites reflect transpressional popping-up of the BGB,caused by EW-directed intraplate principal compressive stresses from Grenvillian collision preserved under the eastern Andes.Further exhumation of the BGB involved the 950 Ma pseudotachylite decorated faulting,and Phanerozoic faulting along reactivated Meso-and Neoproterozoic lineaments.     

变质作用P—T—t轨迹若干问题评述

着重介绍了目前变质作用P－T─t轨迹研究在变质作用温压确定、变质作用不同阶段时间标定、变质作用动态演化过程的组构标志、变质作用演化热模拟以及变质作用P─T─t轨迹与大地构造环境之间关系等方面所存在的若干问题。     

Tectonometamorphic evolution of the Bohemian Massif: evidence from high pressure metamorphic rocks

The Variscan orogenic belt, of which the Bohemian Massif is a part, is typically recognized for its characteristic low pressure, high temperature metamorphism and a large volume of granites. However, there are also bodies of high pressure rocks (eclogites, garnet peridotites and high pressure granulites) which are small in size but widely distributed throughtout the Massif. Initially the high pressure rocks were considered to be relicts of a much older orogenic event, but the increasing data derived from isotopic and geochronological investigations show that many of these rocks have Palaeozoic protoliths. Metamorphic ages from the high pressure rocks define no single event. Instead, a number of discrete clusters of ages are found between about 430 Ma and the time of the dominant low pressure event at around 320–330 Ma.Most of the eclogite and granulite facies rocks are assigned to allochthonous nappes that arrived close to the end of the low pressure event, but before final granite intrusion. The nappes contain a mixture of different units and the relationship between rocks with high pressure relicts and host gneisses with no apparent signs of deep burial is still problematic. Some of the high pressure rocks retain evidence of multiple stages of partial re-equilibration during uplift. Moreover, it can be shown in certain instances that host gneisses also endured a multistage metamorphic development but with a peak event convergent with one of the breakdown stages in the enclosed rocks with high pressure relicts. It thus appears that the nappe units are composite bodies probably formed during episodic intracrustal thrusting. Fluids derived from prograde dehydration reactions in the newly under thrusting slab are taken to be the catalysts that drove the partial re-equilibrations.On the scale of the whole Massif it can be seen within the units with high pressure relicts that the temperature at the peak recorded pressure and that during the breakdown are variable in different locations. It is interpreted that regional metamorphic gradients are preserved for given stages in the history and thus the present day dismembered nappe relicts are not too far removed from their original spatial distribution in an original coherent unit. From the temperature information alone it is highly probable that the refrigerating underthrusting slab was situated in the north-west. However, this north-west to south-east underthrusting probably represents the major 380–370 Ma event and is no guide to the final thrusting that emplaced the much thinned nappe pile with high pressure relicts.Granite genesis is attributed to the late stage stacking, during the final Himalayan-type collision stage, of thinned crust covered by young, water-rich, sediments — erosion products of the earlier orogenic stages. Regional metamorphism at shallow depths above the voluminous granites was followed by final nappe emplacement which rejuvenated the granite ascent in places. Correspondence to: P. J. O'Brien     

渗流影响下岩石损伤和渐进破裂演化过程的数值试验研究

在FLAC-3D软件平台上,开发出岩石破裂过程的渗流-损伤耦合分析程序,对渗流-损伤耦合作用下岩石的裂纹萌生、扩展过程进行模拟研究。分析了在孔隙水压力作用下,含原生裂隙和弱化单元的非均质试件在单轴、三轴加载下的破坏过程,并与非渗流条件下试件在单轴、三轴压缩下的破坏过程相对比,通过动态显示损伤状态、渗流场,并分析应力应变关系、位移图等,对渗流影响下裂隙岩体的损伤和渐进破裂过程进行了研究。     

基于向量式有限元的黏滞阻尼减震结构抗竖向连续倒塌动力反应分析

向量式有限元是以向量力学为基础的一种新的结构分析方法,在处理结构大变形等复杂行为时具有较大的优势。基于向量式有限元理论建立了黏滞阻尼单元,对附加黏滞阻尼器的平面钢框架结构进行了抗竖向连续倒塌动力分析,结合拆除构件法,采用MATLAB编制可以考虑初始变形的瞬时卸载法程序,实现结构在构件拆除前的静力分析和构件拆除后动力分析的全过程统一。研究了阻尼器布置位置和参数在结构抗竖向连续倒塌中的性能需求,以失效点竖向位移时程曲线、梁端转角、动力放大系数和结构塑性铰分布为参考指标,对比分析布置阻尼器前后钢框架结构的抗连续倒塌能力。结果表明向量式有限元是一种研究结构竖向连续倒塌动力响应的有效方法,合理布置阻尼器能够有效控制剩余结构的变形和振动,降低构件内力,减少塑性铰个数,较大地提高结构的抗竖向连续倒塌能力。     

关于巴罗式变质带的最新研究及其对研究秦岭杂岩的意义

本文对苏格兰高地Grampian造山运动中产生的经典巴罗变质带进行了讨论,重点介绍了近年来关于其变质作用的特征及发生机制认识方面的重大变化。强调巴罗变质作用仅发生在整个造山运动过程中的部分时段,纪录了短暂的加热过程,时空上与区域内大规模的双峰式岩浆活动有关。经典的巴罗变质系列并非形成于地壳增厚及其热弛豫,而是代表了中地壳内大规模的接触变质作用。参考经典地区的变质特征,对发育巴罗式变质作用的秦岭杂岩进行了初步对比分析,指出其中与夕线石有关的变质P-T-t轨迹可能是等压冷却过程,而不是等温降压的顺时针演化模式。秦岭杂岩的变质作用时间仍需要进一步准确厘定。结合其它相关地质特征的分析和对比,得出如下推论:巴罗式变质带发育地区的变质作用、混合岩与花岗岩均属于同一动力系统作用的结果,花岗质岩体不是变质作用的原因;基性岩浆可能提供了巴罗式变质作用发生所需要的热能,但不是必要条件;巴罗式变质作用可以发生在正常地壳厚度情况下,不是碰撞构造的标志;伴随热异常的变形过程中产生了变质带的梯度分布(巴罗式变质带)和一些花岗岩,形成类似于底辟的冲起构造。     

Accessory phase petrogenesis in relation to major phase assemblages in pelites from the Nelson contact aureole, southern British Columbia

Monazite petrogenesis in the Nelson contact aureole is the result of allanite breakdown close to, but downgrade and therefore independent of, major phase isograds involving cordierite, andalusite and staurolite. The development of garnet downgrade of the staurolite and andalusite isograds does not appear to affect the onset of the allanite-to-monazite reaction but does affect the textural development of monazite. In lower pressure, garnet-absent rocks, allanite breakdown results in localized monazite growth as pseudomorphous clusters. In higher pressure, garnet-bearing rocks, allanite breakdown produces randomly distributed, lone grains of monazite with no textural relationship to the original reaction site. Fluids liberated from hydrous phases (chlorite, muscovite) during garnet formation may have acted as a flux to distribute light rare earth elements more widely within the rock upon allanite breakdown, preventing the localized formation of monazite pseudomorphs. Despite these textural differences, both types of monazite have very similar chemistry and an indistinguishable age by electron microprobe chemical dating (157 ± 6.4 Ma). This age range is within error of isotopic ages determined by others for the Nelson Batholith. Garnet from the garnet, staurolite and andalusite zones shows euhedral Y zoning typified by a high-Y core, low-Y collar and moderate-Y annulus, the latter ascribed to allanite breakdown during garnet growth in the garnet zone. The cause of the transition from high-Y core to low-Y collar, traditionally interpreted to be due to xenotime consumption, is unclear because of the ubiquitous presence of xenotime. Accessory phase geothermometry involving monazite, xenotime and garnet returns inconsistent results, suggesting calibration problems or a lack of equilibration between phases.     

新疆艾维尔沟煤变质作用研究

新疆艾维尔沟矿区是侏罗纪天山褶皱带中的一个小型山间含煤盆地。多项煤变质指标的分析结果表明:该区煤级在横向上分带明显,垂向上煤级突变,煤岩组份中出现热变显微组份,煤晶核指标(La/Lc)大于1,矿区广泛发育热液石英脉和方解石脉,煤层围岩也具有中低温热液蚀变现象。所有这些特征都充分表明,艾维尔沟的煤变质属区域热变质类型。推测其附加热源位于该煤盆地西部,地下水热液的对流为主要热传导方式。矿区及其外围的构造、地层结构、地势、水文等条件均有利于地下水热液循环。     

喜马拉雅造山带中段亚东地区石榴角闪岩的成因：岩石学和锆石U- Pb年代学

喜马拉雅造山带中段出露的基性麻粒岩是理解印度大陆前喜马拉雅期演化历史和新生代碰撞造山作用的理想研究对象。本文对亚东多庆湖地区的石榴角闪岩进行了岩石学、全岩主微量元素地球化学和锆石U- Pb年代学研究,揭示了其原岩类型和新生代的变质作用过程。石榴角闪岩的原岩很可能为新元古代(~890 Ma)的玄武岩,具有E- MORB型岩石的地球化学特征。石榴角闪岩具有三期矿物组合：① 进变质矿物组合可能为石榴子石+角闪石+斜长石+钛铁矿+石英,即石榴子石核部及其中包裹体;② 峰期矿物组合为石榴子石+角闪石+斜长石+黑云母+石英,即石榴子石边部和基质矿物;③ 退变质矿物组合为角闪石+斜方辉石+斜长石+黑云母+石英,包括退变质域和石榴子石边部的后成合晶矿物。矿物温压计和相平衡模拟表明,石榴角闪岩进变质、峰期和退变质条件分别为609~621℃和0. 59~0. 65 GPa、805~845℃和0. 91~1. 04 GPa、825~840℃和0. 61~0. 68 GPa,经历了峰期高压麻粒岩相的变质作用。锆石U- Pb年代学研究表明,石榴角闪岩的峰期变质时间为34. 8~20. 3 Ma,退变质时间为18. 1~17. 7 Ma,可能经历了一个较长期的部分熔融过程。本文研究认为,亚东石榴角闪岩是印度板块向欧亚板块长期俯冲、地壳增厚成因的基性麻粒岩,原岩可能与Rodinia超大陆拼合相关;其以加热埋藏、近等温降压为特征的顺时针P- T轨迹指示了喜马拉雅造山带中段的大喜马拉雅岩系上部构造层位经历了长期持续的地壳增厚和高温麻粒岩相变质作用,以及早中新世(21~17 Ma)相对快速的减压抬升和随后(17 Ma之后)相对缓慢的折返至地表的演化过程。