蛇绿岩中的花岗质岩石成因类型与构造意义

花岗质岩石在蛇绿岩的岩石组合中只占很小部分（通常＜10％），但是对于蛇绿岩的成因研究，特别是对蛇绿岩形成和演化过程的精确年龄测定，具有重要的意义。简要回顾了蛇绿岩中花岗质岩石的研究历史。近年来的研究表明，蛇绿岩中的花岗质岩石不仅包括直接由大洋玄武质岩浆结晶分异形成的花岗质岩石，即传统意义上的大洋斜长花岗岩，还包括蛇绿岩在形成、演化过程中本身形成的和侵入的花岗质岩石。根据成因，可以将这些花岗质岩石分为 4类：结晶分异型花岗岩、剪切型花岗岩、俯冲型花岗岩和仰冲型花岗岩。系统地综述了它们的地球化学特征以及形成的构造背景。     

吉林省夹皮沟花岗岩—绿岩带成因模式探讨

通过对夹皮沟绿岩带层序、岩石成因以及叠加其上的变质变形作用特征的研究,认为绿岩带形成于硅铝壳的扩张环境;英云闪长岩—奥长花岗岩成分的花岗质片麻岩是在大陆或大陆边缘的挤压环境下,由变质镁铁质火山岩经部分熔融侵位的深成花岗质岩石。由此,提出夹皮沟花岗岩—绿岩带的裂谷成因模式。     

太古宙花岗质岩石中暗色包体类型及地质意义

华北陆台北缘广泛分布着太古宙花岗质岩石(英云闪长质-奥长花岗质-花岗质片麻岩),按成因它们可分为:受变质花岗岩(古深成侵入体)、碱性交代花岗岩及深熔花岗岩。这些岩石中广泛分布着暗色包体,按成因及来源可以分为:深源火成岩包体、围岩包体及深熔同     

河北遵化英云闪长质(灰色)片麻岩及其成因

从迁西群角闪岩相至麻粒岩相的变质岩石中可以识别出一套具英云闪长质—奥长花岗质片麻岩。这种浅色的英云闪长质岩石和暗色的基性变质岩在野外构成清楚的“双峰式”岩浆分布特征。根据岩石的结构构造及化学成分可以把英云闪长质（灰色）片麻岩分成:（中性）斜长岩、斑点状英云间长岩、中—细粒英云闪长质、奥长花岗质片麻岩、（富钾）花岗质片麻岩及含榴英云闪长质片麻岩。其中以英云闪长质、奥长花岗质片麻岩最为多见。     

花岗质岩石中铁质球粒的成因探讨

本文从晶体化学和热力学的角度,对产于花岗质岩石中铁质球粒的成因进行了探讨。作者认为,这些铁质球粒完全有可能是地内成因的产物,而不一定都是人们通常所认为的地外物质。球粒内部的铁质核可能是含铁矿物在变质过程中的还原产物,也可能是含铁玄武质基底岩石中的残留铁,还可能是侵位并同熔基底岩石的含铁玄武岩浆中的自然铁。随着花岗质岩浆的演化,逐渐形成Fe→FeO→Fe3O4的反应系列,从而导致以自然铁为核心,方铁矿和磁铁矿为壳层的球状颗粒的产生。花岗质岩石中铁质球粒的数量与特征取决于花岗质岩浆源区的物质成分、岩浆的氧逸度及岩浆温度的变化规律等因素。     

花岗质岩石形成过程中稀土元素分馏特征

本文评述了花岗质岩石的起源、演化及成岩后的各种地质地球化学作用对其轻稀土和重稀土元素分馏的影响,说明了稀土元素分馏和富集的一般趋势及目前常用的研究花岗质岩石成因的地球化学模型的局限性,分析评估了花岗质岩石成因、演化与内生及地表次生富集作用形成稀土矿床的制约因素。     

云开隆起区花岗质岩石同位素定年及其构造意义

云开地区广泛出露以花岗质岩石为主体的变质杂岩,其周缘为浅变质的新元古代云开群所环绕,彼此间呈断层接触。花岗质岩石普遍遭受韧性流变改造,形成麻状、眼球状和条带状等有序变形组构,长期以来,对这套花岗质岩石的成因和形成时代存在不同的看法,从而制约了对云开地...     

东海超高压变质带花岗质片麻岩的岩石学及其成因特征

东海地区的花岗质岩石主要由二长花岗质片麻岩、角碱长花岗质片麻岩和霓石二长花岗质片麻岩组成。根据该类岩石区域产状、化学成分、稀土和微量元素特征,结合前人理论和实验资料,确定研究区花岗质片麻岩是由云母片麻岩类岩石,在超高压变质作用峰期(M2)及近等温减压初期阶段(M3),于相对富水流体体系中经深熔作用而成。该项研究对于深入探讨苏鲁超高压变质带变质作用-岩浆作用相互间的成因关系及其动力学过程有着重要的科学意义     

尚店油田影响储层的主控地质因素分析

通过对尚店油田的构造和沉积环境的分析,对比不同储层岩石类型和储层展布特征,分析了不同储层的宏观特征和微观特征以及不同储层在组成、结构、构造、四性、地震剖面上的不同反映,以及不同储层的成因和特点,指出岩石组构对油气采出的影响。由于储层成因的不同,引起岩石组构和微观特征的不同,这些不同在今后油田开发中尤其是老油田目前产量入不敷出的情况下应引起重视,可为今后油田实施开发措施和制定开发方案提供科学依据。     

定结地区韧性剪切带变形特征与糜棱岩研究

定结地区位于喜马拉雅造山带中段 ,发育有多方向、多尺度、多层次、多期次的韧性剪切带。在剪切带中 ,各种韧性变形组构极为丰富 ,表明剪切带岩石的变形主要为韧性变形机制所致。变形岩石类型为花岗质糜棱岩、长英质糜棱岩和硅质糜棱岩 ;由于岩石受糜棱岩化作用程度的不同 ,在韧性剪切带中发育糜棱岩化岩石、初糜棱岩、糜棱岩及超糜棱岩 ;剪切带岩石的变形温度为 2 0 8～ 5 5 9℃。     

Neogene basin development around Söke-Kuşadası (western Anatolia) and its bearing on tectonic development of the Aegean region

The AMS study has been performed on various types of the basement – Variscan granitic and surrounding – Mesozoic sedimentary rocks in the Velká Fatra Mountains, Tatric Superunit of the Central Western Carpathians. The Velká Fatra Mts. provides good opportunity for AMS study because of composite S-type and I-type granite character of pluton and clear relations to Mesozoic sedimentary rocks in the cover and nappe positions. The granitic massif consists of the three types of weakly magnetic peraluminous granites (350 – 340 Ma in age), ranging from two-mica granites to biotite granodiorites in composition and carrying accessory monazite and ilmenite; whereby they resemble common S-type and/or Ilmenite Series granite. This pre-existing granitic body was intruded by relatively young (304 Ma old) metaluminous to subaluminous, strongly magnetic (due to magnetite) tonalitic intrusion of the I-type and/or Magnetite Series granite. In all S-types investigated as well as in the I-type tonalite body, the magnetic fabrics are not uniform, but slightly variable within a body and differing from body to body. The magnetic fabrics in all granitic rocks can be classified as mostly magmatic in origin, only subordinately affected by ductile deformation. The Alpine overprint of the magnetic fabric of the Variscan granite frequent in the central areas of the Central Western Carpathians was only weak in the Velká Fatra Mts. and the magnetic fabrics of these granites thus mostly comprise the original Variscan magmatic fabrics. On the other hand, in the marginal parts of the Velká Fatra Mts. the magnetic fabrics in granites are locally conformable to the deformational magnetic fabrics in surrounding sedimentary rocks (Mesozoic in age) thus indicating at least local effects of the Alpine deformation. The magnetic fabrics in Mesozoic sedimentary rocks covering the crystalline basement are partially (Cover Formation) to entirely (Nappe Units) deformational in origin.     

Fabric evidence for granodiorite emplacement with extensional shear zones in the Variscan Gredos massif (Spanish Central System)

Three granitoid bodies in the central part of the Gredos massif (Spanish Central System batholith) are tabular, around 1 km in thickness, and intruded into a migmatitic middle crust during the D3 deformation phase of the Variscan Orogeny. Petrologically, they are composed of Bt-granodiorite and Crd-monzogranite, and they show varying abundance of large (cm-scale) feldspar megacrysts. A detailed study of the shape preferred orientation (SPO) magmatic fabric defined by these megacrysts, together with a kinematic analysis of the structures due to interactions between them, and the measurement of quartz c-axis fabrics in migmatites and granitoids, suggests that granitic magma and country rocks were mechanically coupled during deformation. The emplacement took place along large-scale, extensional shear zones active during the first stages of the D3 phase. The shape of the SPO ellipsoids varies from constrictional at the centre of the granitic bodies, to flattening or even oblate at their external contacts with the migmatitic host rocks. The favoured interpretation of this spatial fabric variation is the overprinting of the emplacement fabrics by a constrictional tectonic regime associated with the growth of tabular magma chambers along extensional detachments, followed by shear zone development commonly at the top of the granitic bodies. The entire structure was later folded during the last stages of the D3 phase.     

玲珑花岗岩体的变形磁组构特征及其与金矿的关系

本文利用磁组构的方法对玲珑花岗岩体的磁组构特征及其与金矿的关系进行研究.玲珑岩体的磁化率各向异性度P的平均值为1.2872,具有典型的构造变形成因特点;磁面理围绕其西北侧的北截花岗闪长岩展布,倾角平缓;磁线理呈SW向近水平展布.玲珑岩体的变形磁组构的特征表明玲珑岩体的变形磁组构是由于后期侵入的北截郭家岭花岗闪长岩体侵入造成的.研究还发现除了断裂的控矿作用以外,位于玲珑岩体内部和边缘的金矿和磁化率各向异性间存在密切的空间对应关系.金矿往往位于磁化率各向异性度P值高的区域,而磁化率各向异性度P值低的区域金矿很少.     

AMS record of brittle dilation,viscous-stretching and gravity-driven magma ascent in area of magma-rich crustal extension (Vosges Mts., NE France)

Orogenic compression-related fabrics (~340–335 Ma) were reworked during regional extensional deformation (~328–325 Ma) in a large anatectic crustal domain of the Central Vosges (NE France). The extension was first accommodated by brittle dilation affecting vertically anisotropic high-grade rocks associated with emplacement of subvertical granitic sheets. The AMS fabric of granitoids is consistent with highly partitioned transtensional deformation marked by alternations of flat and steep foliations and development of orthogonal lineations. This deformation passes to top-to-the-southwest ductile shearing expressed in southerly migmatitic middle crust. The AMS fabric revealed moderately west-dipping foliations bearing subhorizontal NNW–SSE-trending lineations and predominantly plane strain to prolate shapes. This fabric pattern is interpreted as a viscous response of stretched partially molten crust during continuous ductile extension. Vertical ascent of voluminous granites and stoping of the upper crust occurs further south. This gravity ascent triggered by extension leads to development of south-dipping AMS foliations, south-plunging lineations and oblate fabrics in various crustal granites. Vertical shortening related to ascent of these (~325 Ma) granitoids and persistent N–S stretching is responsible for reworking and remelting of originally vertical compression-related fabric in roof supracrustal granites (~340 Ma) and development of highly prolate fabrics in these rocks. This work shows that the finite shape of AMS fabric ellipsoid is highly sensitive to both strain regime and superpositions of orthogonal deformation events.     

花岗质岩石的交代结构构造及其成因意义

交代结构构造在花岗岩的结构构造中占有重要地位,它们的出现与花岗岩形成过程的挥发组分有关。本文详述了花岗质岩石中主要造岩矿物的各种交代结构构造的特点及其在不同阶段结构变化系列。花岗岩的交代结构可分为二种成因类型。混合交代和岩浆交代类型,二者在交代结构的表现上有所不同,并可形成一系列交代结构演化系列,它们大致与变质作用经混合岩化作用发展成为岩浆结晶作用的阶段相符合,可分为下列几种主要交代结构类型:由变质作用的镶嵌结构变为混合岩化作用的交代镶嵌和镶嵌交代结构并通过片麻交代结构发展成为岩浆交代的半自形交代结构,后     

Tectonic imprints within a granite exposed near Srinagar,Rajasthan, India

Partial melting in the middle to lower crustal level produces melts of granitic composition during orogeny. Thrusts play a vital role in their exhumation after consolidation of these granitic melts. In this paper we focus on one such granite along the eastern margin of the Delhi Fold Belt (DFB) rocks near Srinagar, Rajasthan, India. This is the first report of granite within the area and holds a key stratigraphic position in the entire rock package. The said granite is found to be intrusive to the DFB metasediments as well as their basement popularly known as the Banded Gneissic Complex (BGC). We disentangle the deformation fabrics seen within the granite and associated DFB metasediments, suggesting that subsequent to emplacement and consolidation, the granite has co-folded along with the country rocks. Three deformational events could be identified within the DFB metasediments namely, D_1D, D_2D and D_3D. The peak metamorphism was achieved in the D_1D event. The granite magma is generated and emplaced late syn-kinematic to D_1D and thereafter is deformed by D_2D and D_3D producing D_1G and D_2G structural fabrics. These compressive deformations resulted in the collapse of the basin; the combined package of DFB rocks and the granite was thrusted eastwards over the basement rocks. The tectonic transport direction during thrusting is suggested eastwards from our structural analysis. Transverse faults developed perpendicular to the length of the granite have led to partitioning of the strain thereby showing a heterogeneity in the development of fabric within it.     

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。     

长乐-南澳断裂带晚中生代岩浆活动 与变质-变形关系

长乐-南澳断裂带是东南沿海地区陆内强烈变质-变形带。带内沉积岩、火山岩和早白垩世的钙碱性角闪石黑云花岗岩和花岗闪长岩都已发生可达角闪岩相的变质和石英-长石相韧性剪切变形。鉴于高温矿物和强烈韧性变形多出现在深成岩附近;远离深成岩,变质和变形就逐渐减弱,故本文认为,至少有一部分变质变形的热源是由岩浆提供的。韧剪组构和糜棱质花岗岩是在岩浆侵位的晚期或长乐-南澳断裂带左旋走滑时,在中地壳部位同时形成的,长乐断裂带中花岗岩的组构记录了一期同走滑变形的岩浆作用,“软变形”作用。据此,长乐-南澳带内花岗岩的形成是受走滑剪切应力和岩浆热双重制约的,是在走滑过程中实现的。其动力来源可能与晚中生代的太平洋板块沿日本中央构造线—台湾纵谷带朝东亚陆缘的斜向俯冲有关。     

Complex and imitation tectonites from the Kosciusko Pluton,Snowy hiountains,New South Wales

Abstract

Comparative fabric studies of the Kosciusko granodiorite and its country rocks reveal that apparent similarities in petrology and megascopic fabric can be very deceptive if no proper integration with microfabric investigations is attempted. Thus it may be shown that the granodiorite is locally an “imitationtectonite”, simulating the tectonic megafabric of the country rocks where frictional drag, due to viscous flow along its walls, was considerable. The isoclinally folded metasediments of the country rock have been subject to various crossed strains with B ⊥ B′ = B″. Their characteristic cross-girdle microfabric (due to penecontemporaneous folding and flattening with stretching mainly in b = A′ along two sets of equivalent (O k l) slip planes but also in a = A along the strain-slip cleavage of the fold fabric and a complementary set of (h O l) planes) is preserved in the internal fabric of a completely granitized xenolith, but no trace of it is encountered in the granitic host-rocks. Bodily rotation of the xenolith over 60° or more is further evidence of the emplacement of the granitic rocks by viscous flow. Explanations for the occurrence of flat quartzite rods in a: by differential stretching of competent beds in b and a, or by crystallization in a semi-solid medium subject to tension in a, arise from the multiple-scale fabric comparison of the country rocks and the granodiorites.     

A new approach to modeling perpendicular fabrics in porphyritic plutonic rocks using the finite element method

A growing body of field evidence indicates that hypersolidus fabrics preserved in syntectonic plutons are likely to have formed in highly crystallized ‘rigid sponge’ magma. This paper demonstrates that such magma could be idealized as a rheological solid and that the development of non-coaxial fabrics in plutonic rocks can very conveniently be modeled in the framework of solid mechanics. Using the finite element method (FEM), we modeled two strain regimes of small magnitudes (plane-strain horizontal simple shear with the shear strain γ of up to 0.30 and plane-strain pure shear of up to 15% shortening) superposed onto vertically oriented and variously spaced elastic phenocrysts set in the viscoelastic matrix. In the simple shear regime, the phenocrysts slightly rotate toward the shear plane, while the principal strain directions in the matrix are instantaneously oriented at an angle of about 45° or less to the phenocryst fabric. Simple shear thus can only lead to the formation of oblique phenocryst and matrix fabrics. By contrast, the vertical phenocryst fabric is maintained in the pure shear regime, and a new horizontal fabric can develop almost instantaneously in the matrix even for small amounts of superposed shortening (5% shortening after 10 ky in our model). We conclude that such a mechanism can easily produce perpendicular hypersolidus fabrics in plutonic rocks and that only a very short time span (first thousands of years) is required to develop magmatic fabric in a pluton for ‘normal’ rates (10⁻¹⁵ to 10⁻¹³ s⁻¹) of tectonic deformation.