中国沉积学的今后发展:若干思考与建议

出露于北京西山房山岩体南北两侧的官地杂岩,主要由正片麻岩、斜长角闪岩组成,局部具混合岩化特征。对官地杂岩的形成时代及出露原因一直存在很大的争议。一种观点认为官地杂岩形成时代为太古宙,出露于中生代早期的区域伸展体制下,另一种观点则认为官地杂岩是中新元古界或古生界泥质变质岩,在房山岩体侵位过程中发生接触变质作用的产物。研究表明,官地杂岩是一套正片麻岩,其中的锆石核部为岩浆成因,而外部普遍发育较窄的浅色边。SHRIMP II锆石铀铅年龄测定获得锆石的一致曲线与不一致曲线上交点年龄值为(2 521 ±20) Ma,代表了新太古代的岩浆结晶年龄,从而证明官地杂岩原岩形成于新太古代。构造分析表明,官地杂岩与上覆中元古代蓟县系至早古生代地层间为剥离断层接触关系,并为房山岩体侵位和改造,证明是一个形成于房山岩体侵位前的变质核杂岩构造。但房山岩体的侵位并未对锆石的岩浆年龄和变质年龄产生明显影响。     

北京西山房山岩体西北部强变形带的成因新解

北京西山房山岩体西北缘不对称发育一条弧形塑性强变形带,前人根据岩体东南部组构缓倾和岩体内部强应变分布特征提出岩浆斜向底辟侵位模式(王人镜等,1990;张吉顺和李志中,1990)。本文在前人研究的基础上,对房山岩体的组构进行系统观测,研究了西北缘固态塑性强变形带地质特征,着重探讨了岩体侵位时围岩热结构状态。文章认为岩浆同侵位固态塑性强变形带的形成需要早期岩浆进入准固态-固态和后期岩浆膨胀动力这两个必要条件。房山岩体西北部的强变形带是由于岩体侵位时西部围岩的温度较低,岩浆较早进入准固态-固态,后期岩浆侵位时膨胀动力双重因素造成的,提出了围岩热结构状态是房山岩体不对称的固态塑性强变形带的控制因素,而不是岩浆斜向底辟侵位的结果。这一研究成果不仅较合理地解释了房山岩体强变形带不对称发育特征,而且对研究同类花岗质岩体的定位机制有一定启示意义。     

云蒙山变质核杂岩抬升过程中伸展拆离和岩浆底辟联合作用的证据

北京地区云蒙山变质核杂岩在白垩纪阶段抬升的早期,伴随着沿四合堂剪切带由北向南的拆离滑脱和大型花岗闪长岩的垂向侵位,晚期变形发生在花岗闪长岩岩基周边及其邻近围岩中,形成云蒙山剪切带,并伴随大量同构造的花岗岩和伟晶岩岩脉灌入。剪切带中所有的岩脉都随时间发生了不同程度的变形,较老的岩脉形成紧闭的圆柱状褶皱,枢纽与剪切带的线理和面理接近平行。岩脉与剪切带中L-S组构的平行化作用主要是由于这种转动的结果。岩脉的成分和长英指数随它们的变形程度发生变化,说明持续的岩浆分异作用与韧性剪切变形是同时发生的。云蒙山剪切带由岩浆底辟引起的上盘岩石重力所驱动,并不断得到同构造侵位岩脉的补充,起到存储和不断改造侵位岩脉的作用。早期伸展体制下形成的四合堂剪切带局部遭受云蒙山剪切带的改造或复合。该地区的岩石、构造和同构造岩脉的变形几何学和运动学证据表明,太古宙结晶基底的抬升是下部岩浆底辟与上部地壳伸展拆离共同作用的结果。     

医巫闾山中—晚侏罗世构造变形与同构造花岗岩的耦合关系

晚中生代期间医巫闾山地区经历了早期的高温韧性变形和晚期的低温脆韧性变形,并最终形成了变质核杂岩。该变质核杂岩中发育多个中-晚侏罗世花岗岩体,通过分析花岗岩体的岩浆组构及围岩中变形组构的特点,确定该期次的岩浆活动与高温韧性变形同时发生,且这些岩体就位于中部地壳的高温韧性剪切带内。岩浆就位的过程包括三个阶段：部分熔融与垂向运移阶段(D1)、水平运移阶段(D2)和固态变形阶段(D3)。尖砬子岩体的主量、微量元素分析结果显示岩浆为埃达克质岩浆,并具有过铝质和由钙碱性向高钾钙碱性过渡的特点。岩石的Th/U比值和碱性组分含量较高,Mg、Cr、Fe2OT3含量较低,岩浆锆石εHf(t)值=-29.5～-23.3、TDM2=2.51～2.18 Ga。这些特点指示岩浆来源于古老的华北陆块下地壳的部分熔融,表明岩浆具有从地壳深部向地壳浅部运移的过程。中-晚侏罗世岩体的产出形态、岩浆组构及磁组构的优选方位,表明岩浆在就位于中部地壳的过程中受到围岩剪切作用的控制,发生强定向的水平流动,形成了NE-SW向延伸最长、垂向最短的扁纺锤状岩浆房。对比中-晚侏罗世和早白垩世两期同构造岩浆就位机制,发现岩浆就位机制与围岩构造环境关系密切。同为下地壳部分熔融并向浅部运移的两期岩浆活动,岩浆就位机制差异很大：中-晚侏罗世岩浆就位于中部地壳的强剪切部位,就位过程中岩浆以侧向流动为主、气球膨胀作用为辅;早白垩世岩浆就位于浅部地壳的弱剪切部位,岩浆以气球膨胀作用和底辟作用为主。岩浆就位过程中不但受到围岩剪切作用的控制,岩浆房的扩张也会挤压围岩,使围岩叶理的产状发生变化,进而影响对构造性质的判断。     

房山变质核杂岩基底拆离断层韧性剪切变形构造及环境分析

在房山岩体南北缘出露有太古代(基底) 官地杂岩, 官地杂岩与上覆盖层不同地层之间发育一条基底韧性拆离断层.宏观及微观尺度上拆离断层运动学标志均指示SE; 剪切带内发育区域动力变质作用下的矿物组合角闪石-斜长石及硅值较高的白云母, 对其进行电子探针分析, 计算出拆离断层韧性剪切变形的温压条件为: 温度492~555 ℃, 压力0.33 Gpa左右, 达到低角闪岩相.按正常的静岩压力计算, 该韧性剪切作用发生于地表以下12.9 km左右, 代表了中地壳韧性流变的变形环境.野外观察发现房山侵入体与官地杂岩及该韧性剪切带间均呈明显的侵入接触关系, 在侵入岩体南北边缘有大量的片麻岩等捕虏体, 沿杂岩的片麻理或韧性构造面理, 发育大量的石英二长闪长岩脉, 岩脉成分与房山岩体一致, 因此该韧性剪切带的形成应早于房山岩体侵位.如对房山岩体的侵入和改造进行复原和恢复, 该韧性剪切带代表了早期的伸展作用, 可能与房山伸展穹隆体的韧性变形同期.      

东北地区新开岭－科洛杂岩变形规律与成因

新开岭－科洛杂岩位于中国东北地区的嫩江－黑河构造带中,其变形规律与成因一直是制约东北地区乃至邻区构造演化的关键问题之一.据详尽的野外调查,系统分析了岩石宏观糜棱面理、矿物拉伸线理、“A”型褶皱、不对称褶皱、眼球状旋转构造和显微书斜式、眼球状旋转等构造样式.构造解析及运动学分析反映杂岩带两侧整体分别向NW及SE向的伸展滑脱特征;杂岩带内黑云斜长片麻岩及侵入糜棱岩中的闪长玢岩锆石U-Pb（LA-ICP-MS）定年及区域对比研究结果显示,其韧性变形变质作用时代为中侏罗世（167 Ma）,变质峰期时限为170~163 Ma,中侏罗世晚期（163 Ma）暴露于地表.新开岭－科洛杂岩具上盘盖层、拆离韧性剪切带及下盘核杂岩3层式结构特征.核内为大面积分布的花岗岩类,地层时代远比核外地层偏新,并无“古老”的变质岩;拆离韧性剪切带变形温度约400~500℃,其变质强度达绿片岩相,后期发生明显退变质作用.新开岭－科洛岩浆核杂岩主要是在岩浆底侵、花岗岩岩体强力侵位引起地壳隆升的伸展构造背景下形成.      

北京怀柔长园花岗杂岩体岩石学和构造变形特征及其地质意义

本文描述北京北部燕山地区怀柔长园杂岩体及围岩构造变形迹象 ,并对其成因进行了初步分析。认为中、晚侏罗世时期构造应力场的变化是杂岩体内岩石构造变形的主要因素 ,并以此为根据为该地区燕山期构造 岩浆事件序列的建立提供部分证据。     

云南禄丰鸡街杂岩体中碱性超基性岩地球化学特征及成因探讨

本文总结了位于川滇裂谷带南段，滇中地区罗茨碱性超基性岩杂岩体群成员之一－鸡街杂岩体中碱性超基性岩的主要元素、过渡金属元素、大离子亲石元素、稀土元素和同位素地球化学特征；进而从原始岩浆确立、岩浆源岩模拟以及岩浆结晶分异作用等方面讨论了杂岩体中这类岩石的成因。     

河北锥子山复式深成杂岩体岩石谱系单位的建立及就位机制

作者在１：５万区调填图中，应用岩石谱系单位的理论、方法、将著名的锥子山复式深成杂岩体进行了解体。建立了黄土坎超单元，南大天超单元，焦家沟超单元和围场超单元，构成锥子山超单元组合。并从岩体内部组构，变形空间展布和区域构造特征分析，提出了岩体就位的底辟机制，破火山口塌陷机制及岩墙扩展机制。     

漳州侵入杂岩体与尖尾山火山杂岩的时序及成因关系

本文从杂岩体和火山杂岩产出的地质构造环境、活动时序、岩石序列、演化规律、微量元素及锶同位素等方面讨论它们的成因联系。认为是在相同构造环境下,同期、同源岩浆在演化的不同阶段先后喷出和侵入的产物。     

On the role of diapirism in the, segregation, ascent and final emplacement of granitoid magmas

Only bodies of magma with a high crystal content and partially molten (crustal) country rocks can ascend as diapirs; once such an envelope is pierced, the diapiric ascent of the pluton is arrested by the high viscosity of a solid aureole. Deformation by shortening of the carapace of these bodies may lead to the expulsion of a magma with a relatively low crystal content, which may then continue ascent via fractures and dykes.

The details of the mechanisms of granitoid magma segregation are still unknown, but it appears that many magmas hegin their ascent through the crust as mushes with at least 50% melt, and that such magmas are rheologically able to ascend through a thickness of crust. This ascent mechanism explains the dearth of structures attributable to the ascent of granitoids, in contrast to the abundance of structures that developed during their final emplacement.

When a magma becomes too crystalline (melt < 25%) to continue its ascent via dykes, it is immobilised. At approximately this stage, a hydrous magma may become saturated with water and release fluids into the aureole, making it particularly susceptible to deformation. Magma that continues to arrive at this level is also immobilised, and the pluton grows as a ballooning diapir. These characteristically deform themselves and their aureoles by bulk shortening.

Magmas that are able to ascend to shallow depths, largely by virtue of lower water contents and higher initial temperatures, tend to become finally accommodated by such brittle processes as stoping and cauldron subsidence. High level intrusions lend to be tabular, are also fed by dykes or conduits, and assemble in tabular batholiths.     

用接触变质作用标志初步判别北京房山岩体的岩浆侵位机制

近同心状房山岩体接触变质晕中变斑晶-基质关系与变质作用P-T轨迹样式的结合可以区分岩浆底劈式侵位与气球膨胀式侵位机制.例如,该房山岩体南侧接触变质晕中的下马岭组泥质变质岩的变斑晶-基质关系显示强烈的面状压扁应变变形,其变质作用P-T轨迹具等压加热趋势,综合前人成果估算该岩体4个依次侵位的岩石单元的最终就位岩浆结晶深度彼此近于一致,倾向于认为该岩体的岩浆侵位机制为气球膨胀式.      

Tin-tungsten mineralization around the Cannibal Creek diapir,northeastern Australia: implications for exploration

Diapiric intrusion of the Cannibal Creek Granite into the metasediments of the Palaeozoic Hodgkinson Province, Queensland, formed a distinct and discrete set of aureole structures. The intensity of the aureole deformation increases towards the contact, and consists of a set of crenulations with mesoscopic folds, and a schistose cleavage within 500 m of the contact. The foliations in general parallel the intrusive contact, and are continuous with a foliation in the granite. Tin and tungsten mineralization is associated with this diapir. Mined at present as alluvials, the tin was probably originally derived from veins above cupolas of the pluton. Recognition of the structures formed by the intrusion of this diapiric granitoid can be useful in exploration. Assuming that aureole foliations are parallel to the contact in section, flat-lying foliations will indicate the location of the crestal region of a subsurface diapir. Careful mapping of aureole structures can identify areas where tin-tungsten mineralization is most likely to be found.     

Emplacement History of Pasupugallu Gabbro Pluton, Eastern Ghats Belt, India: a Structural Study

Structural mapping of the Pasupugallu pluton, an elliptical intrusive gabbro-anorthosite body, emplaced into the western contact zone between the Eastern Ghats Mobile Belt and the Archaean East Dharwar Craton, along the east coast of India, reveals concentric, helicoidal and inward dipping magmatic and/or tectonic foliations. We identify a <1 km-wide structural aureole characterized by pronounced deflection of regional structures into margin parallel direction, mylonitic foliations with S-C fabrics, sigmoidal clasts, moderately plunging stretching lineations, non-cylindrical intrafolial folds, and stretched elliptical mafic enclaves in the aureole rocks. Our results suggest that the pluton emplacement is syn-tectonic with respect to the regional ductile deformation associated with the terrane boundary shear zone at the western margin of the Eastern Ghats. We present a tectonic model for the emplacement of the pluton invoking shear-related ductile deformation, rotation and a minor component of lateral expansion of magma. The intrusive activity (1450-800 Ma) along the western margin of the Eastern Ghats can be correlated with the significant event of recurring mafic, alkaline and granitic magmatism throughout the global Grenvillian orogens associated with the continent-continent collision tectonics possibly related to the amalgamation and the breakup of the supercontinent Rodinia.     

Metamorphic Environments around the Cretaceous Kurihashi Pluton in the Kitakami Mountains, NE Japan: in Comparison to the Ganidake Pluton - Kamaishi Skarn Metasomatism

Abstract. Many granitic plutons of Early Cretaceous age are intruded on various scales in the Kitakami Mountains. The stock‐type Ganidake pluton accompanies enormous Fe‐Cu mineralization of the Kamaishi deposits, whereas the Kurihashi pluton accompanies less mineralization. To elucidate the cause of these differences, the metamorphic conditions and redox state of the contact metamorphic aureole around the Kurihashi pluton have been examined by the petrochemical study and gas analysis of the metamorphic rocks. A typical mineral assemblage in the pelitic rocks in the lowest‐grade part is biotite‐muscovite‐chlorite‐quartz‐plagio‐clase‐graphite, which occur more than 2 km away from the contact point with the Kurihashi pluton. Graphite disappears at the 1550 m point, and cordierite and garnet appear in the middle and highest‐grade parts, respectively. A typical mineral assemblage in the tuffaceous rocks in the lower‐grade part is chlorite‐actinolite‐biotite‐quartz‐plagioclase. Actinolite changes into hornblende near to the pluton. The CO₂/CH₄ ratios obtained in measurements by gas chromatography exceeds 100 in the pelitic rocks at the contact point with the pluton. The ratios decrease and become less than 0.1 with distance from the pluton. Equilibrium temperatures calculated from a garnet‐biotite pair in the pelitic rock and a hornblende‐plagioclase pair in the tuffaceous rock are 640d? and 681 d?C at the contact point, respectively. The log?o₂ values among these metamorphic aureoles estimated from the CO₂/CH₄ ratios are slightly lower than the FMQ‐buffer. Redox states of the contact metamorphic aureole are kept in an intermediate condition between oxidized magma of the Kurihashi pluton and graphite‐bearing pelitic country rocks. Judging from these metamorphic conditions around the Kurihashi pluton and from the re‐evaluation of the previous knowledge about contact metasomatism around the Ganidake pluton, the Kurihashi metamorphism has occurred at higher temperatures and dry conditions than the Ganidake metasomatism. These differences in the metamorphic conditions and presence or absence of a large limestone mass around the pluton might be the principal reasons why the Kurihashi pluton accompanies less mineralization and the Ganidake pluton accompanies gigantic Kamaishi skarn mineralization.     

The emplacement of the Late Miocene Monte Capanne intrusion (Elba Island,Central Italy): constraints from magnetic fabric analyses

Anisotropy of magnetic susceptibility (AMS) analysis has been carried out in the thermometamorphic aureole surrounding the Late Miocene Monte Capanne pluton (Elba Island, Central Italy). The identification and separation of the main carriers of the magnetic susceptibility by low-temperature and high-field AMS measurements demonstrate that a correct knowledge of the magnetic fabric is needed in order to use AMS for tectonic interpretations. Magnetic fabric data, combined with structural data from the aureole, and their comparison with data from the pluton itself, were used to constraint the mode of pluton emplacement. Results document an intimate linkage between the magmatic flow pattern and the syn-metamorphic fabrics acquired during pluton emplacement in the host rocks. The magnetic/structural fabric in the aureole rocks is dominated by flattening deformation and no systematic relationship with any regional tectonic feature is observed. These results suggest that local processes induced by magma ascent in the upper crust might have played a primary role in space generation for pluton emplacement in the Tuscan Magmatic Province, suggesting a revaluation of the modes of pluton emplacement during the post-orogenic evolution of the northern Apennine system as a whole.     

地球内部物质、能量交换与资源和灾害

通过对凤凰山岩体接触带的变质与变形特征、显微构造及变形缩短量的计算 ,分析了凤凰山岩体侵位与接触带变形及区域变形的关系。通过接触带变质矿物变形特征的研究 ,揭示了热变质作用与侵位变形的同时性 ;接触带构造变形研究表明 ,岩体周围发育的流变褶皱、韧性剪切带、压溶缝合线等与岩体左旋上升与汽球膨胀侵位有关 ;围岩缩短量的计算结果表明 ,岩体侵位过程造成强烈的围岩缩短是一种强力侵位机制。研究表明 ,凤凰山岩体侵位是在区域NNE向水平左旋剪切应力场作用下完成的。岩体接触带变形是NNE向水平左旋剪切应力与横向推挤的侵位应力联合作用下形成的。     

Conditions of contact metamorphism, Papoose Flat Pluton, eastern California, USA: implications for cooling and strain histories

Abstract Petrological study of highly strained carbonate and pelitic rocks within the contact aureole surrounding the western part of the Papoose Flat pluton yields thermal profiles (plots of metamorphic temperature versus distance) across the aureole that show temperature gradients which are relatively flat and narrow (<100m). The gradients occur close to the contact and indicate a slight decrease in temperature from 500–550°C at the pluton/wall rock contact to 450–500°C at the outer margin of the aureole. One thermal profile across low-strain metasedimentary rocks located in the southern part of the aureole shows that thermal effects from emplacement extend no further than 600 m from the contact. Coexistence of andalusite and cordierite in pelitic rocks of the aureole constrain pressures to <4 kbar. Thermal modelling using an analytical solution of the conductive heat flow equation for a rectangular-shaped pluton reproduces the observed thermal maxima and profile shape. Conductive rather than convective cooling also is supported by isotopic and field evidence for limited fluid flow along the strongly deformed margin of the pluton. Simple thermal models coupled with observed high-temperature deformation features and a measured 90% attenuation of stratigraphic units in the plastically deformed western part of the pluton's aureole indicate that strain rates may have been of the order of 10^-12s^-1. Evidence for episodic heating, such as two distinct generations of andalusite growth in pelites from the aureole, alternatively may indicate a longer heating event and, therefore, slower strain rates. Thermal models also indicate that parts of the pluton still may have been above the solidus during deformation of the pluton margin and aureole.     

Intrusion and contamination of high-temperature dunitic magma: the Nordre Bumandsfjord pluton, Seiland, Arctic Norway

The Caledonian Nappe Complex of Arctic Norway provides rare insights into the interaction between mafic–ultramafic magmas and the deep continental crust. The Kalak Nappe Complex contains >25,000 km³ of mafic igneous rocks, mostly layered gabbros, making up the 570–560 Ma Seiland Igneous Complex. The complex has been intruded by a series of ultramafic magmatic rocks, including the Nordre Bumandsfjord pluton. Field relationships in this pluton show that extremely fluid, dry, relatively Fe-rich (Fo₈₁) dunite magmas intruded a pile of cumulate gabbros, with block stopping and intrusive brecciation. Diking on scales from mm to metres and extensive melting and assimilation of the gabbros attest to high temperatures, consistent with a 2-km-wide granulite-facies contact aureole. Major- and trace-element trends show that the dunites were progressively contaminated by a cpx-rich partial melt of the gabbros, producing a range of lithologies from dunite through lherzolites to wehrlite. Experimental studies of natural samples at 0.8–1 GPa define the dunite solidus at 1,650–1,700 °C. In the average peridotite, contamination has produced a crystallisation interval of ca 400 °C (1,600–1,200 °C); this would provide large amounts of heat for melting and metamorphism and would maintain the fluidity of the magmas to relatively low T, consistent with field relationships. Thermochemical and dynamic modelling demonstrates that the dunitic primary magmas may represent the last melting of a rapidly ascending diapir of previously depleted subducted oceanic lithosphere. The mafic rocks of the Seiland Complex may already have been extracted from this diapir, and the late dikes of the province may reflect melting of the asthenosphere as the diapir spread out beneath the lithosphere. Ultramafic magmas, abundant in the Archean, may still be more common than usually assumed. However, they would only penetrate to the shallow crust under unusually extensional conditions, where ascent could outpace assimilation.