Sm-Nd isotope and trace element evidence for heterogeneous igneous protoliths of Variscan mafic blueschists in the East Krkonoše Complex (West Sudetes,NE Bohemian Massif,Czech Republic)

Granitoid rocks of the southern Menderes Massif, SW Turkey include widespread possibly Ediacaran high-grade granitic orthogneisses and younger (Tertiary) sheets, sills and/or dikes of variably deformed tourmaline-bearing leucogranites. The latter are confined to the immediate footwall of the regional-scale ductile southern Menderes shear zone. Although both sets of granitoid rocks are essentially calc-alkaline and peraluminous, the syn- to post-collisional tourmaline-bearing leucogranites are chemically distinguishable from both the granitoid orthogneisses and from two sets of mostly sodic siliceous dyke rocks. The leucogranites were generated by partial melting induced by shear heating during the waning stages of the Eocene main Menderes metamorphism and associated top-to-the-NNE thrusting along the southern Menderes ductile shear zone, which transported schists northwards over the granitoid orthogneisses of the core Menderes complex. Upward migration and emplacement of leucogranitic melt weakened formerly sheared rocks, so that when thrust-related deformation ceased it facilitated rapid crustal extension along the shear zone. The emplacement of leucogranites, in turn, promoted the reactivation of the southern Menderes shear zone as a top-to-the-SSW extensional feature. Continued extensional deformation affected the leucogranites which became parallel to the shear-zone foliation; local S-C fabrics were also generated. The additional occurrence of less or almost undeformed leucogranites suggests that the latest stages of extension might have induced adiabatic decompressional melting. Hence the leucogranite melt generation and emplacement in the southern Menderes Massif occurred in pulses. Both compressional and extensional processes played key roles in melt generation, emplacement, deformation and exhumation of the massif.

A clear distinction may also be made between the composition of granite-hosted tourmalines and those from metasedimentary schists. Tourmalines from a pebble of uncertain provenance in the Gökçay metaconglomerate plotted with schist-hosted tourmalines, suggesting that it was unlikely to be derived from granitoid gneiss. This crucial piece of evidence suggests that the presence of a major (Pan-African) unconformity at the so-called “core (orthogneiss)-cover (schist)” boundary in the southern Menderes Massif is unnecessary.     

Structures of Syn-deformational Granites in the Longquanguan Shear Zone and Their Monazite Electronic Microprobe Dating

The Longquanguan shear zone is an important structural belt in the North China Craton, separating the underlying Fuping complex from the overlying Wutai complex. This shear zone has experienced three episodes of deformation： the first and main episode is a ductile top-to-ESE shear along the gently northwest-west dipping foliations, while the other two episodes are later collapse sliding. Prolonged granites parallel to the shear foliations make one of the main compositions of the Longquanguan shear zone. These granites experienced deformation to form mylonitic rocks when they emplaced during the first episode of deformation. Structural characters of the granites and their contacts to the country rocks indicate that these granites possibly resulted from in-situ partial remelting by shearing, i.e., they are syn-deformational granites. Monazites in these mylonitic granites are magmatic minerals and their crystallization ages may represent ages of the magmatic events, and also the ages for the main deformation of the Longquanguan shear zone. Monazite electronic microprobe dating were carried on two samples of granite, which gives multiple peak ages, among which 1,846 Ma and 1,877 Ma are the main peak ages for the two samples. These ages represent the main deformation of the Longquanguan shear zone, which is consistent with the main regional geological event at about 1,850 Ma caused by the collision between the Eastern and Western Blocks in North China. The good match between the monazite ages and the corresponding regional tectono-thermal events shows the feasibility and reliability of monazite electronic microprobe dating.     

辽西兴城—台里韧性剪切带北段变形特征

辽西兴城—台里地区发育系列花岗质岩石,强烈构造变形特征均显示其具有韧性剪切带的特点。对剪切带北段进行详细宏微观构造解析,结合岩石变形强度差异性分析、有限应变测量、石英C轴EBSD测试以及古差异应力值估算等研究,结果表明剪切带内花岗质片麻岩和眼球状花岗质片麻岩具有NEE向左行剪切变形特征,变形岩石为S-L构造岩,应变类型属于平面应变,古差异应力值介于30~40 MPa之间。长石-石英矿物温度计以及石英C轴EBSD组构指示剪切带以中低温变形为主,温度在400℃~500℃,属绿片岩相变质,具中-低温韧性剪切带特征。韧性剪切带内普遍存在变形分解现象,弱变形带内岩石残斑含量较高,眼球状构造和S-C组构较为发育;强变形带岩石残斑含量较低,剪切面理较为发育,糜棱面理发育较弱或者不发育。     

Granitoid rocks of the southern Menderes Massif (southwestern Turkey): field evidence for Tertiary magmatism in an extensional shear zone

Recent field campaign in the southern Menderes Massif in southwestern Turkey revealed that the so-called ‘core of the massif’ comprises two distinct types of granitoid rocks: an orthogneiss (traditionally known as augen gneisses) and leucocratic metagranite, where the latter is intrusive into the former and the structurally overlying ‘cover’ schists. These differ from one another in intensity of deformation, degree of metamorphism and kinematics. The orthogneiss display penetrative top-to-the-N–NNE fabrics formed under upper-amphibolite facies conditions during the Eocene main Menderes metamorphism (MMM), whereas foliation and stretching lineation exists in the leucocratic metagranites but are not strongly developed. The leucocratic metagranites show evidence of syn- to post-emplacement deformation in a series of weakly developed top-to-the-S–SSW fabrics formed under lower greenschist-facies (?) conditions. Leucocratic metagranite bodies occur all along the augen gneiss–schist contact in the southern Menderes Massif; they are emplaced as sheet-like bodies into country rocks (previously deformed and metamorphosed during a top-to-the-N–NNE Alpine orogeny) along a ductile extensional shear zone, located between orthogneisses and metasediments, which was possibly active during emplacement. The data presently available indicate that emplacement and associated ductile extensional deformation occurred during Late Oligocene–Early Miocene time. These results confirm previous contentions that there are Tertiary granites in this part of the Menderes Massif.     

Superposition de la tectonique éburnéenne et panafricaine dans les granitoïdes de la bordure nord du craton ouest africain, boutonniére de Zenaga, Anti-Atlas central, Maroc

The Zenaga Inlier shows a comprehensive record of the Eburnian and Pan-African Orogenies. The Eburnian is characterised by high-temperature regional metamorphism and complex magmatism. The early (Azguemerzi) granodiorite has an isotopic mantle signature and was emplaced diapirically during the Eburnian Orogeny causing local thermal metamorphism. The foliation observed in this granitoid is a result of the interference between its primary syn-emplacement foliation and the regional foliation under amphibolite-facies conditions. The northern part of Zenaga has been intruded by the leucocratic granites of Tazenakht. These granites are cut by mylonites and phyllonites, corresponding to the Pan-African shear zones and accompanied with sub-greenschist-facies metamorphism during the Pan-African Orogeny. The deformation was the result of a regional sinistral transpressive event. This study in the northern part of the West African Craton shows the superposition of the Pan-African on the Eburnian Orogeny and the presence of a major fault in the Anti-Atlas.     

河南省西峡—内乡北部元古界与古生界间的构造边界

构造制图和详细的构造解析,在东秦岭造山带核部识别出一个原先未曾注意的元古代变质岩区与古生代变质岩区间的构造边界——军马河-马蹄湾断裂带。实际上,这个构造边界是一个底部韧性变形带,带内发育构造混杂岩、糜棱岩和强直片麻岩。本文阐述了各种几何学特征,它们表明变形是发生在一个缓倾斜的剪切带之上。大量的运动学标志指出,在中生代花岗岩类岩体就位前,再造的元古代变质岩区沿着构造边界向北逆冲于古生代变质岩区之上。     

The Sierra Ballena Shear Zone in the southernmost Dom Feliciano Belt (Uruguay): evolution, kinematics, and deformation conditions

The Sierra Ballena Shear Zone (SBSZ) is part of a high-strain transcurrent system that divides the Neoproterozoic Dom Feliciano Belt of South America into two different domains. The basement on both sides of the SBSZ shows a deformation stage preceding that of the transcurrent deformation recognized as a high temperature mylonitic foliation associated with migmatization. Grain boundary migration and fluid-assisted grain boundary diffusion enhanced by partial melting were the main deformation mechanisms associated with this foliation. Age estimate of this episode is >658 Ma. The second stage corresponds to the start of transpressional deformation and the nucleation and development of the SBSZ. During this stage, pure shear dominates the deformation, and is characterized by the development of conjugate dextral and sinistral shear zones and the emplacement of syntectonic granites. This event dates to 658–600 Ma based on the age of these intrusions. The third stage was a second transpressional event at about 586 to <560 Ma that was associated with the emplacement of porphyry dikes and granites that show evidence of flattening. Deformation in the SBSZ took place, during the late stages, under regional low-grade conditions, as indicated by the metamorphic paragenesis in the supracrustals of the country rocks. Granitic mylonites show plastic deformation of quartz and brittle behavior of feldspar. A transition from magmatic to solid-state microstructures is also frequently observed in syntectonic granites. Mylonitic porphyries and quartz mylonites resulted from the deformation of alkaline porphyries and quartz veins emplaced in the shear zone. Quartz veins reflect the release of silica associated with the breakdown of feldspar to white mica during the evolution of the granitic mylonites to phyllonites, which resulted in shear zone weakening. Quartz microstructures characteristic of the transition between regime 2 and regime 3, grain boundary migration and incipient recrystallization in feldspar indicate deformation under lower amphibolite to upper greenschist conditions (550–400°C). On the other hand, the mylonitic porphyries display evidence of feldspar recrystallization suggesting magmatic or high-T solid-state deformation during cooling of the dikes.     

龙泉关韧性剪切带同变形花岗岩的构造特征及其独居石定年

龙泉关韧性剪切带强变形部位发育一系列平行剪切带走向展布的花岗岩脉体，构造变形特征表明它们可能是同变形花岗岩，是剪切作用下围岩部分熔融的产物。通过独居石电子探针定年，测得龙泉关韧性剪切带的年龄分别为：主变形幕发生于1877～1846Ma，第2个变形幕发生于1812-1782Ma，晚期1725Ma左右又经历了流体活动。龙泉关韧性剪切带的发生、发展与华北克拉通中部带古元古代晚期的变质事件同期，是东、西陆块碰撞的一个主要剪切带。     

Deformation of footwall rock of Phulad Shear Zone,Rajasthan: Evidence of transpressional shear zone

Phulad Shear Zone (PSZ) of Delhi Fold Belt in Rajasthan is a northeasterly striking ductile shear zone with a well developed mylonitic foliation (035/70E) and a downdip stretching lineation. The deformation in the PSZ has developed in a transpressional regime with thrusting sense of movement. The northeastern unit, i.e., the hanging wall contains a variety of rocks namely calc-silicates, pelites and amphibolites and the southwestern unit, i.e., the footwall unit contains only granitic rocks. Systematic investigation of the granites of the southwestern unit indicate a gradual change in the intensity of deformation from a distance of about 1 km west of the shear zone to the shear zone proper. The granite changes from weakly deformed granite to a mylonite/ultramylonite as we proceed towards the PSZ. The weakly deformed granite shows a crude foliation with the same attitude of mylonitic foliation of the PSZ. Microscopic study reveals the incipient development of C and S fabric with angle between C and S varying from 15 ^° to 24 ^°. The small angle between the C and S fabric in the least deformed granite variety indicates that the deformation has strong pure shear component. At a distance of about 1 m away from the PSZ, there is abrupt change in the intensity of deformation. The granite becomes intensely foliated with a strong downdip lineation and the rock becomes a true mylonite. In mesoscopic scale, the granite shows stretched porphyroclasts in both XZ and YZ sections indicating a flattening type of deformation. The angle between the C and S fabric is further reduced and finally becomes nearly parallel. In most places, S fabric is gradually replaced by C fabric. Calculation of sectional kinematic vorticity number ( W_n) from the protomylonitic and mylonite/ultramylonite granites varies from 0.3 ± 0.03 to 0.55 ± 0.04 indicating a strong component of pure shear. The similarity of the geometry of structures in the PSZ and the granites demonstrates that the deformation of the two units is broadly synchronous and the deformation in both the units is transpressional.     

Thrusting and transpressional shearing in the Pan-African nappe southwest El-Sibai core complex,Central Eastern Desert,Egypt

The Wadi El-Shush area in the Central Eastern Desert (CED) of Egypt is occupied by the Sibai core complex and its surrounding Pan-African nappe complex. The sequence of metamorphic and structural events in the Sibai core complex and the enveloping Pan-African nappe can be summarized as follows: (1) high temperature metamorphism associated with partial melting of amphibolites and development of gneissic and migmatitic rocks, (2) between 740 and 660 Ma, oblique island arc accretion resulted in Pan-African nappe emplacement and the intrusion of syn-tectonic gneissic tonalite at about 680 ± 10 Ma. The NNW–SSE shortening associated with oblique island arc accretion produced low angle NNW-directed thrusts and open folds in volcaniclastic metasediments, schists and isolated serpentinite masses (Pan-African nappe) and created NNE-trending recumbent folds in syn-tectonic granites. The NNW–SSE shortening has produced imbricate structures and thrust duplexes in the Pan-African nappe, (3) NE-ward thrusting which deformed the Pan-African nappe into SW-dipping imbricate slices. The ENE–WSW compression event has created NE-directed thrusts, folded the NNW-directed thrusts and produced NW-trending major and minor folds in the Pan-African nappe. Prograde metamorphism (480–525 °C at 2–4.5 kbar) was synchronous with thrusting events, (4) retrograde metamorphism during sinistral shearing along NNW- to NW-striking strike-slip shear zones (660–580 Ma), marking the external boundaries of the Sibai core complex and related to the Najd Fault System. Sinistral shearing has produced steeply dipping mylonitic foliation and open plunging folds in the NNW- and NE-ward thrust planes. Presence of retrograde metamorphism supports the slow exhumation of Sibai core complex under brittle–ductile low temperature conditions. Arc-accretion caused thrusting, imbrication and crustal thickening, whereas gravitational collapse of a compressed and thickened lithosphere initiated the sinistral movement along transcurrent shear zones and low angle normal ductile shear zones and consequently, development and exhumation of Sibai core complex.     

From migmatites to granites in the Pan-African Damara orogenic belt,Namibia

The Swakop River exposes a unique structural section into the root of the Pan-African Damara orogenic belt (DOB) in Namibia formed as a result of collision between the Congo and the Kalahari cratons from ca. 550 to 500 Ma. The Central Zone of the Damara orogenic belt is characterized by amphibolite to granulite facies metamorphism accompanied by intense partial melting. Three tectonic units are defined in the Central Zone based on the proportion and distribution of the granitic fraction, namely (1) a lower unit dominated by diatexites and comprising plutons of homogeneous granites, (2) a middle unit composed by metatexites with mainly a metasedimentary protolith, and (3) an upper unit corresponding to metamorphic rocks with intrusive leucogranitic sills and laccoliths. The increase in the granitic fraction with structural depth is suggesting an increase in the degree of partial melting and implies a relative inefficiency of magma mobility from the source to higher structural levels. The transition from metatexites of the middle unit to diatexites and granites of the lower unit is interpreted as reflecting the former transition from partially molten rocks to a crustal-scale magmatic layer. Mushroom-shaped granitic plutons in the lower unit are consistent with their emplacement as diapirs and the development of gravitational instabilities within the magmatic layer. In the middle unit, granitic veins concordant and discordant to the synmigmatitic foliation localized in structurally-controlled sites (foliation, boudin’s necks, shear zones, fold hinges) indicate that, within the partially molten zone, deformation plays the dominant role in melt segregation and migration at the outcrop scale. Melt migration from the partially molten zone to the intrusive zone is related to the build-up of an interconnected network of dikes and sills with diffuse contacts with the migmatitic hosts in the middle unit. In contrast, the upper unit is characterized by homogeneous leucogranitic plutons in sharp intrusive contact with genetically unrelated host rocks suggest that part of the melt fraction has migrated upward from its source to an intrusive zone.     

辽南金州拆离断层带中花岗质岩石的变形:显微构造、组构与年代学分析

花岗岩(脉)在中下地壳韧性剪切带中普遍发育,如何正确鉴别剪切带中剪切前、剪切期及剪切后花岗岩(脉)以及正确理解剪切过程中构造变形与岩浆作用之间的关系一直是一个重要课题。本文以辽南金州拆离断层带为研究对象,选取中部地壳伸展作用过程中具有不同变形表现的花岗岩(脉)开展宏观-微观构造观察、石英EBSD组构分析及锆石LA-ICP-MS年代学测试等工作,从而进一步丰富构造-岩浆关系判别准则。剪切前花岗岩(脉)多变形强烈且具有后期固态变形叠加在早期高温岩浆组构之上的特点,而剪切期的花岗岩由于侵位的时间不同,岩石的变形程度也会不同。剪切晚期侵入的岩脉遭受了较弱的晶内塑性变形,而剪切早期的岩脉可以显示岩浆流动或结晶后高温至中温固态变形。从组构特点上看,剪切前和剪切期花岗质岩石石英c轴组构大多表现为中高温组构叠加有低温组构的特点。剪切后的花岗质岩石仅发生微弱的晶内变形或未变形而显示低温或无规律的组构特征。对五个典型的样品进行年代学测试,其结果符合相应的期次划分类型。应用宏观构造、显微构造与组构分析,结合年代学测试综合分析,对于辽南变质核杂岩构造-岩浆活动性进行了精细划分,包括134~130Ma初始伸展阶段,130~115Ma峰期伸展与强烈岩浆活动阶段,以及115Ma前后伸展作用结束。     

Study of the Emplacement Mechanism of the Fenghuangshan Granite Pluton and Related Cu-Au Mineralization in Tongling, Anhui Province

The Fenghuangshan Pluton is located in the Tongling polymineral-cluster district in the middle-lower section of the Yangtze metallogenic belt. In tectonic terms, it is in the middle of the Guichi-Fanchang faulted fold bundle of the lower Yangtze Platform fold belt between the Dabie Orogenic Belt and the Jiangnan Massif. Analyses of the structural deformation characteristics of both the contact zone and the interior of the pluton are used to explain its emplacement mechanism. The foliation and lineation of the pluton, consisting of the oriented distribution of dark minerals and xenoliths, mainly concentrate along the margin of the pluton. Toward the center of the pluton, the foliation structure becomes weak, showing intense compression formation at the margin, and reflecting the conformable intrusion of the pluton. The relatively gentle lineation is evidence of a rotatory emplacement mechanism. Relatively steep marginal foliation reflects compression expanding. Affected by the thermal power of the pluton,     

北京云蒙山地区花岗岩穹隆及伸展构造的探讨

北京云蒙山花岗岩为一中生代侵入的花岗岩穹隆,花岗岩穹隆的叶理普遍发育,叶理轨迹基本平行于穹隆的外部边界,并显示出从核部到边部逐渐增强,东南侧明显强于西北侧的特点。变形构造研究显示,花岗岩穹隆的边部及围岩中普遍存在不同层次及不同运动方向的伸展构造。东南侧以具河防口－水峪伸展型韧性剪切带为特征,剪切运动标志显示为从ＮＷ－ＳＥ的正剪切运动,有限应变分析估算其剪切位移量在１０ｋｍ以上,剪切带上部被河防口正     

佳木斯—伊通断裂韧性剪切变形时代及其地质意义

作为郯庐断裂北段主干断裂的佳木斯-伊通断裂（简称佳-伊断裂）,其最早开始活动的时代一直以来都存在争议。为了更好确定其活动时代,对佳-伊断裂昌图段南城水库附近的韧性剪切带展开了详细研究。野外构造解析和显微构造特征显示,剪切带糜棱面理走向北北东-南南西,其上发育北东方向的缓倾拉伸线理,指示该剪切带为逆冲-走滑韧性剪切特征。锆石U-Pb年龄测试结果表明,剪切带中糜棱花岗岩形成在174~173 Ma,该糜棱岩带被后期未变形辉绿岩脉侵入,辉绿岩脉的锆石U-Pb年龄为164 Ma,从而限定该期次韧性变形发生在174~164 Ma之间的中侏罗晚期。取自剪切带糜棱花岗岩内的变形黑云母40Ar/39Ar测试结果表明,糜棱花岗岩在187~166 Ma左右受到了显著的热事件的扰动。这些证据证明,佳-伊断裂在中侏罗晚期发生过显著的左行走滑韧性剪切,结合对东北地区火成岩研究成果的分析,佳-伊断裂中侏罗晚期的韧性变形可能与古太平洋板块向欧亚大陆的俯冲有关,该时期侵位的岩浆活动开始显著受到俯冲引发的挤压应力作用的影响。      

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。     

Anatomy of the Mondoñedo Nappe basal shear zone (NW Spain)

This paper analyses a major shear zone from the Iberian Hercynian belt which forms the basal thrust of the Mondoñedo Nappe. The shear zone developed by ductile deformation under amphibolite facies metamorphic conditions and later by brittle-ductile deformation in greenschists facies. Folds in the shear zone are asymmetric, very tight, 1C or similar class and frequently developing sheath geometries. The sheath folds originated by non-coaxial flow superimposed on earlier irregularities. The fabric of quartzitic rocks in the shear zone changes from bottom to top from ultramylonites through blastomylonitic rocks to non-mylonitic tectonites. c-axis fabrics vary across the shear zone, but show a dominant monoclinic symmetry. The blastomylonitic rocks include the fabrics representing the highest temperatures. The main foliation of the schists results from flattening of an earlier foliation, recording occasional microfolds. The use of different kinematic criteria has allowed an analysis of their validity as well as an assessment of movement direction towards the foreland of the orogen.     

Archaean tectonics in the Agnew supracrustal belt,Western Australia

The Agnew supracrustal belt consists of a greenstone sequence (interlayered metabasalt, differentiated gabbroic sills, ultramafic bodies, and black volcanogenic sediment) unconformably overlain by granitoid-clast conglomerate and meta-arkose. The base of the preserved sequence is intruded by grey tonalite with a crudely concordant upper contact, and by small discordant bodies of leucogranite.An early deformation (D1) produced isoclinal folds and a regional penetrative foliation. These structures were probably gently dipping when formed. D2 produced large-scale NNW-trending upright folds, a regional foliation, and a vertical N-trending ductile fault on the west side of the belt. D2 structures indicate a combination of ENE-WSW shortening, and right-lateral shear along the ductile fault. Both D1 and D2 were accompanied by metamorphism under upper greenschist to lower amphibolite facies conditions.The interpreted sequence of tectonic events is (1) deposition of the greenstone sequence on an unknown basement; (2) intrusion of large volumes of tonalite, separating the supracrustal rocks from their basement; (3) erosion of mafic rocks and tonalite to produce the clastic sedimentary sequence; (4) the first deformation; (5) intrusion of small volumes of leucogranite; (6) the second deformation.The bulk of the granitoid rocks were emplaced before the first recognisable deformation. Thus the granitoid magma cannot have been produced by partial melting of previously downbuckled ‘greenstone belt’ rocks, nor can the large-scale upright folds (D2) be a result of forceful emplacement of the magma — two common postulates for Archaean terrains. The D2 folds are closely related to the ductile fault bounding the zone: these structures, which give the present N-trending tectonic belt its form, are the youngest features in the terrain.     

华北东部晚中生代区域伸展背景下同构造花岗岩体的起源与就位

花岗质岩浆的起源、迁移及就位是研究大陆岩石圈流变学特性的重要方面。然而,板内伸展背景下同构造花岗岩体的岩浆来源、就位机制和岩浆流动与区域应力场的关系等问题缺乏系统性的总结。晚中生代期间华北板块东部逐渐变为区域伸展体制,同时中浅部地壳形成一系列的韧性剪切带、变质核杂岩和拆离断层,这些伸展构造往往伴有同剪切变形的花岗岩体。因此,华北东部是系统研究板内伸展背景下同构造花岗岩体的最佳区域。本文选取多个典型的同构造花岗岩体,进行综合分析。通过归纳总结这些同构造岩体的岩石地球化学和年代学资料,发现多数同构造岩体具有多个岩浆源区,且较早就位的中性岩席(单元)往往来自壳幔混合岩浆或新生下地壳的部分熔融,而较晚的酸性岩席(单元)则主要来源于古老下地壳的部分熔融。这一特点反映了同伸展岩体岩浆源区由深至浅的演化规律,也揭示了区域伸展背景下源自地幔的流体和热量是触发地壳部分熔融的重要因素。通过分析岩浆就位过程中围岩和岩体中形成的定向及变形组构,发现华北东部同伸展岩体的就位模式可分为三大类:以扁平岩床或岩基形式就位于中部地壳的水平韧性剪切带内;岩浆以近直立运移的方式形成长轴平行拆离断层的岩基,就位于变质核杂岩核部或拆离断层下盘;岩浆就位于再活化的先存断裂,通过膨胀作用、挤压围岩获得就位空间并使围岩变形,形成类似底辟作用的就位方式。剪切应力和浮力是影响岩浆运移方向的重要力学参数。岩浆自源区上升的过程中浮力起着主要控制作用,就位于韧性剪切带时剪切应力起着控制作用,就位于浅部地壳的脆-韧性过渡带时浮力的作用再次凸显。     

康古尔韧性剪切带变形特征及控矿作用

康古尔韧性剪切带具明显的遥感影像特征和区域重、磁异常变化特征。韧性剪切引起的变质作用表现为强应力下的岩石变质、变形，变质相序从绿片岩相到角闪岩相，变质岩石类型为千枚岩、片岩、变粒岩、糜棱岩及糜校岩化的岩石。韧性剪切变形和塑性流动形成的面理、线理、招皱、韧性断裂等构造形迹十分明显，构成一条东百长1000多千米，南北宽20～30km的狭长线形构造带（强应变带）；它经历了多期次、多种构造作用交替叠加的变化过程，按性质分类属大型平移断裂系统。康古尔韧性剪切带控制着重要的金矿、铜镍矿床及稀有金属等矿产，是新疆东部有重要找矿意义的成矿带。