云南地壳和上地幔的岩石学结构

通过对地表出露变质岩、深部地震测深资料和高温高压岩石波速测试资料的综合分析 ,研究了云南地壳和上地幔岩石组成。结果表明 ,云南上、中、下地壳分别由绿片岩相 (顶部为沉积层 )、角闪岩相和麻粒岩相变质岩组成或分别由与之相当的花岗岩类、闪长岩类、辉长岩类组成 ,部分地区地壳底部有镁铁质榴辉岩存在。上地幔由橄榄岩组成 ,部分地区 (兰坪思茅坳陷和滇中坳陷 )壳幔过渡带可能由镁铁质榴辉岩和橄榄岩组成     

云南地壳和上地幔的岩石学结构

通过对地表出露变质岩、深部地震测深资料和高温高压岩石波速测试资料的综合分析，研究了云南地壳和上地幔岩石组成。结果表明，云南上、中、下地壳分别由绿片岩相(顶部为沉积层)、角闪岩相和麻粒岩相变质岩组成或分别由与之相当的花岗岩类、闪长岩类、辉长岩类组成，部分地区地壳底部有镁铁质榴辉岩存在。上地幔由橄榄岩组成，部分地区(兰坪思茅坳陷和滇中坳陷)壳幔过渡带可能由镁铁质榴辉岩和橄榄岩组成。     

地壳主要岩石流变参数及华北地壳流变性质研究

岩石流变参数和变形机制是根据断层摩擦和岩石幂次流动本构关系建立岩石圈强度剖面的基础。近 30年来 ,高温高压实验取得了很大进展 ,获得了大量地壳矿物和岩石流变资料。本文系统总结了这些流变实验资料 ,并应用流变数据结合地震震源深度分布 ,对华北地壳流变性质进行了研究。结果表明 ,以花岗岩和低级变质岩为代表的上地壳为脆性破裂 ,其强度受断层摩擦约束 ,以长英质片麻岩为主的中地壳和以中性麻粒岩为主的下地壳上层处于塑性流变状态 ,由干的基性麻粒岩组成的下地壳下层处于脆性向塑性流变的过渡状态。华北地壳的这种物质组成和流变为地壳不同层次的解耦和强震孕育提供了力学条件 ,也构成了不同尺度块体的底边界     

冀东陆壳岩石在高温高压下波速的实验研究

实验选取了冀东陆壳的上、中、下地壳主要岩石类型在高温高压条件下进行了波速测定.实验的最高温度约为600℃,压力达到700MPa.在压力600MPa 条件下测定的上地壳黑云母变粒岩的V_p 为6.00—6.06km/s;中地壳黑云母片麻岩的V_p 为6.75为km/s,斜长角闪岩的V_p 为6.92km/s(?)下地壳麻粒岩的V_p 增加到7.28km/s.波速的变化主要依赖于陆壳的化学组成和变质程度.冀东的上、中地壳化学组成比较接近,相当于中酸性,但变质相分属于绿片岩相和角闪岩相,它们在V_p 上的差异主要与岩石的变质程度有关.下地壳为中性(?)基性成分属麻粒岩相,V_p 的增大,特别是其下部的高V_p(7.5—7.6km/s),既依赖于变质程度,又依赖于化学组成.波速测定的实验支持了我们1988年提出的该区陆壳结构的岩石学模型.     

从太古代片麻岩系推测地球的成因和发展

古老变质岩系主要由前人称为“片麻岩系”和“结晶片岩系”两大套岩系组成。当地球成球之后,表面首先形成一层“基性焦壳”,在热封闭条件下,壳内产生花岗岩岩浆源,注入此原始地壳,并引起变质作用,形成基性正片麻岩地壳——第一层结晶地壳。然后,固体地壳发生形变和破裂,产生侵蚀、沉积,并伴随着岩浆活动、变质作用形成副片麻岩类——第二层结晶地壳。由此,本文以北京及其外围地区的古老变质岩系为依据,阐述了地球的形成和演化规律     

AN EXPERIMENTAL STUDY ON WAVE VELOCITIES IN ROCKS FROM THE YANHUAI BASIN AND ITS GEOLOGICAL IMPLICATIONS

依据延怀盆地深部的地温地压条件，用模拟实验方法测定了该区代表性岩石的纵波和横波速度以及石英、角闪石在一定深度相变引起的波速变化，提出在中地壳同时具备低速高导的物质可能不是含石英多的岩石而可能是含水矿物多的岩石；讨论了研究区的地壳组成，认为上地壳的上部可能是由泥质灰岩一类的岩石组成，下部可能是由花岗闪长岩一类的岩石组成，没有低速高导层的地区可能是由花岗闪长岩和石英岩等组成，有低速高导层的地区可能由角闪岩相的岩石组成，下地壳可能由角闪片麻岩、中长麻粒岩、辉石麻粒岩等组成     

苏鲁超高压变质带岩石圈的地震组构

苏鲁超高压变质带上地壳以片麻岩为主体, 地表出露超高压变质岩片. 近年来在此带中进行大陆科学钻探, 并进行了以反射地震为主导的地球物理调查. 通过研究地球物理资料和钻孔岩芯等直接证据的相关性, 有可能标定出现在地壳中的地震反射体, 了解它们的内部组构. 同时, 在大陆科学钻探孔区附近有两座第四纪火山, 对其中包体的成分分析和波速计算也提供了中下地壳和岩石圈地幔组构的信息. 经岩心和测井资料标定, 大陆科学钻探孔区的地震反射体可由变质带内岩性变化、韧性剪切复合岩套和现代断裂破碎带引起. 其中, 韧性剪切作用产生的侧向位移与拆离造成了上百米厚的互层带(韧性剪切复合岩套), 它们由糜棱岩化岩石和经剪切错动产生的榴辉岩片互层组成, 形成了产生区域性强反射的主要机制. 苏鲁超高压变质带的上地壳由超高压变质岩片与下方片麻岩层组成. 超高压变质岩片以高波速、高密度和高电阻率为特征, 构造复杂, 厚度一般不超过11 km; 下方片麻岩层波速渐趋于正常. 苏鲁超高压变质带的中下地壳具有正常的波速与泊松比, 由火山岩包体分析可知, 中地壳含有大量的片麻岩, 下地壳主要由酸性麻粒岩和基性麻粒岩组成. 岩石圈地幔主要由尖晶石二辉橄榄岩、方辉橄榄岩和二辉岩组成, 具有分层结构, 反映了中国东部中生代岩石圈减薄作用. 不同成因的地震组构可能是不同时代地球动力学作用的产物. 例如, 超高压变质岩片和韧性剪切复合岩套反映了三叠纪的碰撞造山作用及超高压变质作用, 而正常的中下地壳波速结构反映了中新生代地壳的拉张与伸展. 通过反射体的细致标定与火山岩包体验证了的地震组构, 可以找到地震反射体的成因及其与地球动力学作用的关系, 为地球动力学作用过程的恢复提供新的依据.     

阿尔金西段孔兹岩系的发现及岩石学、同位素代学初步研究

阿尔金西段吐拉一带存在以夕线石榴黑云二长片麻岩、石榴黑云二长片麻岩、含石墨夕线石榴黑云片岩等富铝片麻岩 (片岩 )为主和呈透镜状或薄层状夹于片麻岩 (片岩 )中的石榴角闪二辉麻粒岩等组成的一套孔兹岩系 ,岩石学及地球化学的初步研究表明富铝片麻岩 (片岩 )的原岩为富铝泥质和泥砂质沉积岩 ,所夹基性麻粒岩的原岩可能为大陆拉斑玄武岩 ,这套孔兹岩系的原岩可能形成于大陆边缘环境 .孔兹岩系经历了麻粒岩相的变质作用 ,矿物的温压估算得到其峰期变质温度为 70 0～ 85 0℃ ,压力为 0 .8～ 1.2GPa .岩石中变质锆石的U Pb及Pb Pb同位素测定获得447～ 46 2Ma的年龄值 ,代表其麻粒岩相的变质作用时代 .从富铝片麻岩中含继承组分的锆石还获得较老的上交点年龄 ,它可能代表其沉积岩原岩源区的年龄     

大别杂岩减压变质过程与造山带深部区域性快速构造折返

大别杂岩的变质岩岩石可分出麻粒岩相带和角闪岩相带.麻粒岩相中石榴石内带的生长成分环带保存完好,角闪岩相石榴石内带无成分变化,但近外带为生长环带,反映两个变质相带早期具有不同的变质历史.但是,两个变质相带普遍发育反映减压的反应结构和成分演化趋势.矿物温度计压力计估算麻粒岩相带减压△P≈-0.70GPa;角闪岩相带减压△P≈-0.85GPa.变质P-T轨迹具碰撞和俯冲变质的双重特点,表明大别杂岩经受了快速下沉和快速构造折返.区内高压超高压榴辉岩折返可能与之同期.     

哀牢山变质带元江──墨江剖面岩石的纵波波速特征及其地质意义

依据研究区的地热梯度（25℃／km）,在高温高压（最高温度为1050℃,最高压力为1.2GPa）条件下系统测量了横穿红河-哀牢山断裂带的元江-墨江地质剖面上的哀牢山岩群各类变质岩（千枚岩、片岩、浅粒岩、变粒岩、大理岩和片麻岩）的纵波速度．实验结果表明,不同岩类的纵波速度随温度压力变化的趋势不同．在相当于衷牢山岩群变质岩峰期变质温度和压力条件下（P=0．4-0.8GPa,T=35-700℃）,测得大部分岩石的纵波速度为5．50－5．80km／s,这一纵波速度值与区域地球物理测深揭示的中地壳低速层的纵波速度相当因此,结合该区变质岩、地壳内热状态及地球物理测深研究成果可初步认为：组成哀牢山岩群的浅粒岩、变粒岩、酸性片麻岩以及部分千枚岩、片岩为该地区中地壳低速层的主要岩石类型．     

Exposed cross-sections through the continental crust: implications for crustal structure,petrology, and evolution

The continental crust is exposed in cross-section at numerous sites on the earth's surface. These exposures, which appear to have formed by obduction along great faults during continental collision, may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive Bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle. From an examination of five complexes which meet these criteria, it is concluded that the most prominent layering in the crust is not compositional but metamorphic. The lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks, respectively. Post-metamorphic granitic intrusions are common at intermediate to shallow levels. Position of discontinuities in refraction velocity, where present, commonly correspond to changes in composition or metamorphic grade with depth. The continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by COCORP. Field observations, coupled with geochemical data, indicate a complex evolution of the lower crust which can include anatexis, multiple deformation, polymetamorphism and reworking of older crustal material. The complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments.     

由包体推导的河北汉诺坝下地壳-上地幔地温线及其地质意义

通过对采自河北汉诺坝玄武岩中的下地壳和上地幔包体的详细研究 ,建立了本区下地壳—上地幔地温线。该地温线高于大洋地温线和古老地盾地温线 ,接近克拉通边缘的地温线 ,符合该区的大地构造环境。由该地温线建立的下地壳—上地幔地质结构剖面表明 ,该区下地壳主要由不同类型的麻粒岩相岩石组成 ,其化学成分以镁铁质为主 ,深度范围为 2 5～ 4 2km。上地幔由超镁铁质的二辉橄榄岩组成 ,在尖晶石二辉橄榄岩和石榴石二辉橄榄岩之间有一过渡层。由地温线确定的壳幔边界位于 4 2km附近 ,与地震资料确定的莫霍面一致 ,但在壳幔边界之上的下地壳底部有下地壳麻粒岩和超镁铁质岩的互层。这一现象可以解释在下地壳底部常见的层状反射层。该区岩石圈底界大约在 95km ,其下的软流层仍由石榴石二辉橄榄岩组成     

Tectonic evolution of lower crustal rocks in an exposed magmatic arc section in the Hidaka metamorphic belt, Hokkaido, northern Japan

Abstract : The Hidaka metamorphic belt consists of an island-arc assembly of lower to upper crustal rocks formed during early to middle Paleogene time and exhumed during middle Paleogene to Miocene time. The tectonic evolution of the belt is divided into four stages, D₀rs, D₁, D₂rs, and D₃, based on their characteristic deformation, metamorphism, and igneous activity. The premetamorphic and igneous stage (D₀) involves tectonic thickening of an uppermost Cretaceous and earliest Tertiary accretionary complex, including oceanic materials in the lower part of the complex. D₁ is the stage of prograde metamorphism with increasing temperatures at a constant pressure during an early phase, and with a slight decrease of pressure at the peak metamorphic phase, accompanying flattening of metamorphic rocks and intrusions of mafic to intermediate igneous rocks. At the peak, incipient partial melting of pelitic and psammitic gneisses took place in the amphibolite–granulite facies transition zone, the melt and residuals cutting the foliations formed by flattening. In the deep crust, large amounts of S-type tonalite magma formed by crustal anatexis, intruded into the granulite facies gneiss zone and also into the upper levels of the metamorphic sequence during the subsequent stage. During D₁ stage, mafic and intermediate magmas supplied and transported heat to form the arc-type crust and at the same time, the magmatic underplating caused extensional doming of the crust, giving rise to flattening and vertical uplifting of the crustal rocks. D₂ stage is characterized by subhorizontal top-to-the-south displacement and thrusting of lower to upper crustal rocks, forming a basal detachment surface (décollement) and duplex structures associated with intrusions of S-type tonalite. Deformation structures and textures of high-temperature mylonites formed along the décollement, as well as the duplex structures, show that the D₂ stage movement occurred under a N-S trending compressional tectonic regime. The depth of intra-crustal décollement in the Hidaka belt was defined by the effect of multiplication of two factors, the fraction of partial melt which increases downward, and the fluid flux which decreases downward. The crustal décollement, however, might have extended to the crust-mantle boundary and/or to the lithosphere and asthenosphere boundary. The subhorizontal movement was transitional to a dextral-reverse-slip (dextral transpression) movement accompanied by low-temperature mylonitization with retrograde metamorphism, the stage defined as D₃. The crustal rocks from the basal décollement to the upper were tilted eastward on the N–S axis and exhumed during the D₃ stage. During D₂ and D₃ stages, the intrusion of crustal acidic magmas enhanced the crustal deformation and exhumation in the compressional and subsequent transpressional tectonic regime.     

A model for lower continental crust

This proposed model is based on geological, geophysical and geochemical data. Previous models suggested for the lower continental crust consisted of basalt, gabbro, or charnockitic rocks; however, experimental and field petrological data indicate that the bulk of crustal rocks are metamorphic. A lower crust of heterogeneous metamorphic rocks also agrees with seismic reflection results which show numerous reflections from “layering”. Geothermal conditions favor a “dry” charnockitic or gabbroic lower crust rather than an amphibolitic lower crust because heat production data imply that wet amphibolitic rocks would have a higher heat production than their dry metamorphic equivalents. Relatively high velocities from field and laboratory measurements in such low-density rocks as granite, syenite, anorthosite and granulitic rocks in general imply that the composition of the lower crust is more felsic than gabbro. Variation in seismic velocity and depths from crustal refraction studies and numerous seismic reflections all indicate a highly heterogeneous lower crust. The lower crust, which has traditionally been described as gabbroic or mafic, may consist of such diverse rocks as granite gneiss, syenite gneiss, anorthosite, pyroxene granulite, and amphibolite, interlayered on a small scale, deformed, and intruded by granite and gabbro. Interlayering of these rocks explains the presence and character of seismic reflections. Abrupt changes in dip, tight folding, disruption of layers, intrusion, and changes in layer thickness explain the characteristic discontinuity of deep reflections. Igneous intrusions may be floored by metamorphic rocks. The lower crust consists of a complex series of igneous and metamorphic rock of approximate intermediate composition.     

A continental crustal model and its geothermal implications

The following crustal model based on realistic estimates of metamorphic rock volumes and H₂O content is proposed as a basis for geothermal calculations: (1) a surface zone of intermediate metamorphic rocks containing granitic intrusions and grading downward into (2) a more felsic migmatite zone, (3) a lower crustal zone of approximately andesitic composition crystallized in granulite or possibly amphibolite facies. Heat production values and thickness for the three zones are 3 HGU, 5 HGU, 0.5–1.5 HGU and 8, 8, and 18 km respectively. If the surface heat flow is 1.2 HFU, the model predicts a temperature of only 407°C at the Moho and an upper mantle heat flow of 0.3–0.5 HFU. The low temperatures resulting from this model rule out a seismic low-velocity zone in the crust produced by thermal effects.     

Geology of the Grove Mountains in East Antarctica——New evidence for the final suture of Gondwana Land

As the core block of the East Gondwana Land, the East Antarctic Shield was traditionally thought, before 1992, as an amalgamation of a number of Archaean-Paleoproterozoic nuclei, be-ing welded by Grenville aged mobile belts during 1400—900 Ma, while the …     

Geology of the Grove Mountains in East Antarctica

Grove Mountains consists mainly of a series of high-grade (upper amphibolite to granulite facies) metamorphic rocks, including felsic granulite, granitic gneiss, mafic granulite lenses and charnockite, intruded by late tectonic gneissic granite and post-tectonic granodioritic veins. Geochemical analysis demonstrates that the charnockite, granitic gneiss and granite belonged to aluminous A type plutonic rocks, whereas the felsic and mafic granulite were from supracrustal materials as island-arc, oceanic island and middle oceanic ridge basalt. A few high-strained shear zones disperse in regional stable sub-horizontal foliated metamorphic rocks. Three generations of ductile deformation were identified, in which D₁ is related to the event before Pan-African age, D₂ corresponds to the regional granulite peak metamorphism, whereas D₃ reflects ductile extension in late Pan-African orogenic period. The metamorphic reactions from granitic gneiss indicate a single granulite facies event, but 3 steps from mafic granulite, with P-T condition of M1 800°C, 9.3×10⁵ Pa; M₂ 800–810°C, 6.4 × 10⁵ Pa; and M₃ 650°C have been recognized. The U-Pb age data from representative granitic gneiss indicate (529±14) Ma of peak metamorphism, (534±5) Ma of granite emplacement, and (501±7) Ma of post-tectonic granodioritic veins. All these evidences suggest that a huge Pan-African aged mobile belt exists in the East Antarctic Shield extending from Prydz Bay via Grove Mountains to the southern Prince Charles Mountains. This orogenic belt could be the final suture during the Gondwana Land assemblage.