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1.
大别山超高压榴辉岩带榴辉岩的特征和变质作用 总被引：17，自引：2，他引：17
大别山超高压柯石英榴辉岩带中多处产出含柯石英榴辉岩,岩石中广泛分布柯石英假象。它们产在片麻岩和大理岩中,并有不同的特征矿物组合。与鄂北等地高压型榴辉岩比较,超高压(柯石英)榴辉岩的绿辉石富硬玉组分,而石榴石为一般的富铁铝榴石贫镁铝榴石的石榴石。钙质角闪石和钠钙质冻蓝闪石是超高压(柯石英)榴辉岩中主要的次生角闪石类型。榴辉岩的原岩是陆内拉张过程中形成的广义拉斑玄武岩,它们在中朝一扬子大陆板块汇聚造山的俯冲大地构造背景中,发生渐进变质。变质时地热增温率极低。造山运动后期,榴辉岩随构造运动抬升又经历两阶段迭加变质。 相似文献
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苏北榴辉岩成因类型及其形成条件 总被引：5，自引：0，他引：5
苏北榴辉岩至少存在高压壳源型（Ｈ型）、超高压壳源型（Ｕ型）和幔源型（Ｍ型）三类。其中Ｈ型榴辉岩的石榴石为铁铝榴石,具正环带结构,单斜辉石属低硬玉绿辉石,主要形成于晋宁期低温高压变质条件下的下地壳;Ｕ型榴辉岩含微粒金刚石（？）、柯石英及其假象等,发育放射状胀裂结构和正、反环带结构,石榴石为钙铝榴石,单斜辉石属高硬玉绿辉石,主要形成于印支期高温超高压变质条件下的上地幔;Ｍ型榴辉岩的石榴石属镁铝榴石,形成于晋宁期高温超高压条件下的岩石圈与软流圈交界附近。 相似文献
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苏北榴辉岩成因型及其形成条件 总被引：4，自引：0，他引：4
苏北榴辉岩至少存在高度压壳源型（Ｈ型）、超高压壳源型（Ｕ型）和幔源型（Ｍ型）三类。其中Ｈ型榴辉岩的石榴石为铁铝榴石,具正环带结构,单斜辉石属低硬玉绿辉石,主要形成于晋宁期低温度高压变质条件下的下地壳;Ｕ型榴辉岩含微粒金刚石（？）、柯石英及其假象等,发育放射状胀裂结构和正、反环带结构、石榴石为钙铝榴石、单斜辉石属高硬玉绿辉石,主要形成于印支期高温超高压变质条件下的上地幔;Ｍ型榴辉岩的石榴石属镁铝榴石 相似文献
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中国大陆科学钻探主孔(CCSD-MH)石榴石橄榄岩:一个经历了深俯冲作用的古生代超镁铁质侵入体 总被引：3，自引：1，他引：3
中国大陆科学钻探主孔中的超镁铁岩主要产在603.20～683.53m深度之间。超镁铁岩的上部直接围岩为高Ti-Fe型榴辉岩;内部夹有薄层状含柯石英高镁榴辉岩和厚层状多硅白云母榴辉岩;下部直接围岩为石英榴辉岩和普通榴辉岩。超镁铁岩的主体岩性为石榴石单辉橄榄岩,主要由橄榄石(60%～70%),石榴石(10%～25%),单斜辉石(5%～15%),斜方辉石(1%～5%)和少量金云母和钛铁矿或钛斜硅镁石组成。橄榄石Fo 79～89,其中一些以包裹体形式出现的高MgO橄榄石可能形成较早,主体橄榄石属变质重结晶阶段形成;石榴石以低CaO、高MgO和Cr_2O_3含量高(达3%)为特征,保留较好的进变质成分环带;单斜辉石Na_2O含量达到4%～5%,分为绿辉石和普通辉石类,属变质成因,结合矿物对的温压估算,岩石已经经历超高压变质作用。岩石成分研究表明,石榴石单辉橄榄岩与其顶、底板榴辉岩及其中的榴辉岩夹层有一较大的成分间断,其中MgO含量约相差10%左右,认为超镁铁岩与榴辉岩的原岩不属同一岩浆演化产物。锆石SHRIMP定年表明石榴石单辉橄榄岩原岩时代为古生代346～461Ma,超高压变质作用时代为早中生代220～240Ma。认为CCSD主孔石榴石橄榄岩为古生代的超镁铁质侵入体,在印支期的中国南北板块俯冲折返过程中经历了超高压变质作用。 相似文献
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中国大陆科学钻探主孔1200米构造柱及变形构造初步解析 总被引：31，自引：20，他引：31
在利用成象测井资料准确地恢复岩心空间位置的基础上，建立了位于江苏省东海县毛北村的中国大陆科学钻探主孔岩心1200m精细构造柱。划分了由榴辉岩与超镁铁质岩组成的第一岩性-构造单元及由副片麻岩夹榴辉岩与超镁铁质岩透镜体组成的第二岩性-构造单元，自上而下岩石的面理产状由向东陡倾变为向南东缓倾。第一岩性-构造单元的榴辉岩与超镁铁质岩是毛北榴辉岩杂岩体的组成部分，在榴辉岩中发现以南北向拉伸线理及由北往南的剪切指向为特征的超高压变质岩早期变形举止。位于第二岩性一构造单元下部(770-1130m深度)300多米厚的韧性剪切带是地表出露的毛北韧性剪切带在孔下的延伸，剪切应变及石英组构分析表明，在伴随的退变质角闪岩相一绿帘角闪岩相一绿片岩相的转换过程中，剪切应变由自SE往NW的“逆冲”转为NW向SE的正向滑移。结合钻孔围区地质，重塑了上部由毛北榴辉岩杂岩体与副片麻岩围岩组成的轴面向SE倾斜的同斜倒转褶皱系，以及下部为韧性剪切带的构造模型。钻孔验证了VSP地震反射剖面中850-1200m深度的强反射层与韧性剪切带相吻合。结合苏鲁超高压变质地体的折返构造的研究，提出该构造模型的成因与折返阶段超高压变质地体的斜向上的挤出及后折返阶段的穹隆形成有关。 相似文献
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中国大陆科学钻探工程5000m主孔位于苏鲁超高压变质带南部。该钻孔0～2000m主要由榴辉岩、片麻岩、石榴石橄榄岩和少量片岩和石英岩组成。累积厚度达1000多米的榴辉岩具有不同的矿物组成、不同的矿物含量和不同的全岩化学成分,可划分成富Si的石英榴辉岩、富Ti的金红石榴辉岩、富Al的多硅白云母和蓝晶石榴辉岩、富Mg的双矿物榴辉岩和具有正常玄武岩成分的普通榴辉岩。榴辉岩的原岩包括基性层状侵入岩和变质表壳岩。榴辉岩全岩成分对石榴石和绿辉石中某些化学组分的含量有明显控制,而且直接影响到变质条件估算的准确性。扩散成分环带的广泛发育表明超高压矿物在早期退变质过程中发生了成分再平衡。这一事实以及具有成分生长环带石榴石变斑晶的存在,为榴辉岩形成在更高温度(>940℃)和更高压力(>4.5GPa)条件下提供了有力的证据。 相似文献
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北秦岭松树沟榴辉岩的确定及其地质意义 总被引：9，自引：8，他引：1
松树沟石榴石角闪岩(榴闪岩)呈透镜状产于松树沟超镁铁岩旁侧的斜长角闪岩中,一直以来被认为是形成于接触交代变质或麻粒岩相变质过程。详细岩相学及矿物元素分析,在榴闪岩的基质矿物、石榴石幔部及锆石包体中发现残留的绿辉石,而且石榴石也保存了明显的进变质主、微量元素成分环带,表明松树沟榴闪岩为榴辉岩退变质的产物,至少经历了从角闪岩相到榴辉岩相再到角闪岩相的三阶段顺时针PT演化过程。锆石定年结果得到榴辉岩的变质年龄为500±8Ma,原岩结晶时代为796±16Ma,与秦岭岩群北侧官坡超高压榴辉岩的变质年龄和原岩年龄完全一致,也与北秦岭区域高压-超高压变质时代和原岩的结晶时代一致。表明松树沟榴辉岩与北秦岭造山带已发现的高压-超高压变质岩石一起都应是古生代大陆深俯冲作用的结果,而松树沟超镁铁岩可能是俯冲的大陆板片在折返过程中携带的俯冲隧道中的交代地幔岩。 相似文献
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印度与亚洲大陆新生代碰撞-俯冲形成的喜马拉雅造山带核部由高压和超高压变质岩组成.超高压榴辉岩分布在喜马拉雅造山带西段,由石榴石、绿辉石、柯石英、多硅白云母、帘石、蓝晶石和金红石组成.超高压榴辉岩的峰期变质条件为2.6～2.8GPa和600～620℃,其经历了角闪岩相退变质作用和低程度熔融.超高压榴辉岩的进变质、峰期和退变质年龄分别为～50Ma、45～47Ma和35～40Ma,指示一个快速俯冲与快速折返过程.高压榴辉岩产出在喜马拉雅造山带中-东段,由石榴石、绿辉石、多硅白云母、石英和金红石组成.高压榴辉岩的峰期变质条件为>2.1GPa和>750℃,叠加了高温麻粒岩相退变质作用与强烈部分熔融.高压榴辉岩的峰期和退变质年龄可能分别是～38 Ma和14～17 Ma,很可能经历了一个缓慢俯冲与缓慢折返过程.喜马拉雅造山带两种不同类型榴辉岩的存在表明,印度与亚洲大陆约在51～53Ma碰撞后,印度大陆地壳的西北缘陡俯冲到了地幔深度,导致表壳岩石经历了超高压变质作用,而印度大陆地壳的东北缘平缓俯冲到亚洲大陆之下,导致表壳岩石经历了高压变质作用. 相似文献
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The 5158-m-deep main borehole of the Chinese Continental Scientific Drilling Project (CCSD-MH) penetrated granitic gneisses, paragneisses, eclogites, retrograde eclogites, amphibolites and ultramafic rocks in the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. The CCSD-MH consists of four petro-structural units separated by three SE-dipping ductile shear zones DFa (835-1280 m), DFb (2010-2280 m) and DFc (2920-3225 m), which are correspondent with the regional shear zones in the northern Sulu UHP supracrustal zone. Using the electron backscatter diffraction (EBSD) technique, we investigated the lattice-preferred orientations (LPOs) of omphacite, diopside and quartz in core samples from the CCSD-MH. Omphacite from eclogites and diopside from garnet pyroxenites display very strong LPOs, which are characterized by the maximum concentration of [001]-axes parallel to the lineation and (010)-poles normal to the foliation. Quartz in para- and granitic mylonites/gneisses from the shear zones DFa, DFb and DFc developed multiple slip systems. 40Ar/39Ar dating of biotite in para- and granitic gneisses from the CCSD-MH yields 223-202 Ma, which constrains the formation ages of the quartz high-temperature prism slip systems {m}<a> and {m}[c]. The asymmetric LPOs of omphacite, diopside, olivine and quartz with respect to the structural frame reveal three deformation phases in the Sulu terrane. In the Middle Triassic, the northward subduction of the Yangtze plate to depths > 100 km produced a top-to-the-south shear sense in LPOs of omphacite, diopside and olivine, and a nearly N-S-striking foliation and a subhorizontal N-S-trending lineation in eclogites and ultramafic rocks. In the Late Triassic, the UHP rocks were exhumed to the lower crust and quartz developed high-temperature slip systems with a top-to-the-NW shear sense, which is consistent with the regional SE-dipping foliation and SE-plunging lineation in the ductile shear zones. In the Cretaceous the UHP rocks were exhumed to the middle crust when the migmatization and granitic intrusion formed a NE-striking antiform structure. As a result, the activation of quartz low-temperature basal slip (0001)<a> is characterized by a top-to-the-SE shear sense in the south, but a top-to-the-NW shear sense in the north. 相似文献
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Caledonian eclogite facies shear zones developed from Grenvillian garnet granulite facies anorthosites and gabbros in the Bergen Arcs of western Norway allow direct investigation of the relations between macroscopic structures and crystallographic preferred orientation (CPO) in lower continental crust. Field relations on the island of Holsnøy show that the eclogites formed locally from granulite facies rocks by progressive development of: (1) eclogite adjacent to fractures; (2) eclogite in discrete shear zones (> 2 m thick); (3) eclogite breccia consisting of >80% well-foliated eclogite that wraps around rotated granulite blocks; and (4) anastomosing, subparallel, eclogite facies shear zones 30–100 m thick continuous over distances > 1 km within the granulite terrane. These shear zones deformed under eclogite facies conditions at an estimated temperature of 670 ± 50°C and a minimum pressure of 1460 MPa, which corresponds to depths of >55 km in the continental crust. Detailed investigation of the major shear zones shows the development of a strong foliation defined by the shape preferred orientation of omphacite and by alternating segregations of omphacite/garnet-rich and kyanite/zoisite-rich layers. A consistent lineation throughout the shear zones is defined by elongate aggregates of garnet and omphacite. The CPO of omphacite, determined from five-axis universal stage measurements, shows a strong b-axis maximum normal to foliation, and a c-axis girdle within the foliation plane with weak maxima parallel to the lineation direction. These patterns are consistent with deformation of omphacite by slip parallel to [001] and suggest glide along (010). The lineation and CPO data reveal a consistent sense of shear zone movement, although the displacement was small. Localized faulting of high-grade rocks accompanied by fluid infiltration can be an important mode of failure in the lower continental crust. Field relations show that granulite facies rocks can exist in a metastable state under eclogite facies conditions and imply that the lower crust can host differing metamorphic facies at the same depth. Deformation of granulite and partial conversion to eclogite, such as is exposed on Holsnøy Island, may be an orogenic-scale process in the lowermost crust of collisional orogens. 相似文献
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We present an integrated study of geochemistry, petrofabrics and seismic properties of strongly sheared eclogites from the Chinese Continental Scientific Drilling (CCSD) project in the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. First, geochemical data characterize diverse protoliths of the studied eclogites. The positive Eu- and Sr-anomalies, negative Nb anomaly and flat portion of heavy rare earth elements in coarse-grained rutile eclogites (samples B270 and B295) suggest a cumulate origin in the continental crust, whereas the negative Nb anomaly and enrichment of light rare earth elements in retrograde eclogites (samples B504, B15 and B19) imply an origin of continental basalts or island arc basalts. Second, P-wave velocities (Vp) of three typical eclogite samples were measured under confining pressures up to 500 MPa and temperatures to 700 °C. At 500 MPa and room temperature, the mean Vp reaches 8.50-8.53 km/s in samples B270 and B295 but drops to 7.86 km/s in sample B504, and the P-wave anisotropy changes from 1.7-2.7% to 5.5%, respectively. The pressure and temperature derivatives of Vp are larger in the retrograde eclogite than in fresh ones. Third, the electron backscatter diffraction (EBSD) measurements of the eclogites reveal random crystal preferred orientation (CPO) of garnet and pronounced CPO of omphacite, which is characterized by a strong concentration of [001]-axes sub-parallel to the lineation and of (010)-poles perpendicular to the foliation. The asymmetric CPO of omphacite in sample B270 recorded a top-to-the-south shear event during subduction of the Yangtze plate. The calculated fastest Vp is generally sub-parallel to the lineation, but a different deformation environment during exhumation could form second-order variations in omphacite CPO and affect the Vp distribution in eclogites (e.g., the fastest Vp is at ~ 35° from the foliation in sample B295). Comparison between measured and calculated seismic properties indicates that the CPO of omphacite controls the seismic anisotropy of eclogites at high pressure, and compositional layering and retrograde minerals will increase the anisotropy. Calculated P-wave velocities agree well with velocities measured at 500 MPa and room temperature for fresh eclogites, but much higher than those of retrograde eclogite. As a case study, the laboratory-derived Vp-P and Vp-T relationships were used to estimate P-wave velocities of eclogites and peridotites beneath the Western Superior Province, Canada. The results indicate that besides the fabric-induced anisotropy, the direction dependence of pressure and temperature derivatives of Vp can significantly increase seismic anisotropy of eclogites with depth, which results in eclogites being an important candidate for the seismic anisotropy in the upper mantle. Due to their very high density and velocity, garnet-rich eclogites within peridotite could be detected in seismic reflections in subduction zones. 相似文献
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超高压变质岩提供了研究大陆俯冲隧道中岩石的变形机制和流变差异性的窗口。文章使用电子背散射衍射技术分析了大别山超高压变质带的榴辉岩和长英质片麻岩的显微构造。榴辉岩中的石榴子石基本呈无序分布，绿辉石发育较强烈的晶格优选定向，[001]轴的极密平行或近平行于拉伸线理，(100)面的法线近垂直于面理，退变榴辉岩中角闪石的(100)[001]组构可能继承了绿辉石的晶格优选定向。退变榴辉岩和长英质片麻岩中的石英记录了(0001)低温底面滑移和{1010}中温
柱面滑移，反映了超高压变质岩折返到中地壳的韧性变形；而斜长石的(001)<110>和(010)[100]组构形成于折返到下地壳的角闪岩相变质条件（>600℃）。根据主要矿物的流变律计算了俯冲与折返过程中无水矿物的有效黏度变化。俯冲过程中，钠长石=硬玉+石英的分解反应以及石英-柯石英相变导致长英质片麻岩的有效黏度和密度都显著增高，有利于陆壳深俯冲。但是折返过程中由于温度较高，这两个反应带来的有效黏度变化较小。>80 km深度，石榴子石的流变强度>硬玉>绿辉
石>柯石英，俯冲上地壳的流变由柯石英和硬玉控制，下地壳的流变由绿辉石和石榴子石控制。超高压变质岩流变强度的差异有助于上—下地壳力学解耦，使相对低密度、低黏度的上地壳物质在俯冲隧道内快速折返。 相似文献
15.
Quantitative analysis of the structural evolution of jadeite‐quartzite, a rare ultra‐high pressure (UHP) rock type from the Dabie Mountains of eastern China, sheds light on the formation and evolution of UHP orogenic belts worldwide. Geological mapping of the Shuanghe area, where jadeite‐quartzites crop out, was carried out to determine the spatial relationships between different UHP rocks within this orogen. The deformation mechanisms of jadeite‐quartzite, geodynamical parameters (stress, strain, strain rate), and microstructure including lattice preferred orientation (LPO) were determined from six jadeite‐quartzite samples from the Shuanghe area. LPOs of clinopyroxene (jadeite and omphacite), garnet, rutile and quartz from these jadeite‐quartzite samples are compared with those of three eclogites preserving different degrees of deformation from the Shuanghe area. Microstructural LPOs of jadeite, omphacite, garnet, rutile and quartz were determined using electron backscattered diffraction (EBSD) analysis. Quartz fabrics were largely recrystallized during late, low‐grade stages of deformation, whereas garnet shows no strong LPO patterns. Rutile fabrics show a weak LS fabric along [001]. Jadeite and omphacite show the strongest eclogite facies LPO patterns, suggesting that they may provide important information about mantle deformation patterns and control the rheology of deeply subducted continental crust. Microstructural data show that the jadeite LPO patterns are similar to those of omphacite and vary between L‐ and S‐types, which correlate with prolate and oblate grain shape fabrics (SPO); quartz LPOs are monoclinic. Microstructural analysis using TEM shows that the dominant slip systems of jadeite in one sample are (100)[001], (110)[001] and (1 1 0)1/2[110], while in another sample, no dislocations are observed. Abundant dislocations in quartz were accommodated by the dominant slip system (0001)[110], indicating basal glide and represents regional shearing during the exhumation process. This suggests that dislocation creep is the dominant fundamental deformation mechanism in jadeite under UHP conditions. The protoliths of jadeite‐quartzite, metasedimentary rocks from the northern passive continental margin of the Yangtze craton, experienced the same deep subduction and were deformed under similar rheological conditions as other UHP eclogite, marble and paragneiss. Experimental UHP deformation of quartzo‐feldspathic gneiss with a chemical composition similar to the bulk continental crust has shown that the formation of a jadeite–stishovite rock is associated with a density increase of the host rock similar to the eclogite conversion from basaltic protoliths. The resulting rock can be denser than the surrounding mantle pyrolite up to depths of 660 km (24 GPa). Thus, processes of deep continental subduction may be better‐understood through understanding the rheology and mechanical behaviour of jadeite. Jadeite‐quartzites such as those from the Shuanghe may be exhumed remnants of deeply‐subducted slabs of continental crust, other parts of which subducted past the ‘depth of no return’, and remain in the deep mantle. 相似文献
16.
In order to contribute to a better understanding of exhumation related retrogression processes ultrahigh-pressure (UHP) mafic and ultramafic rocks from the Chinese Continental Scientific Drilling (CCSD) in the Maobei eclogite body of the Sulu ultrahigh-pressure metamorphic belt in eastern China were studied for their magnetofabrics. Variably retrogressed eclogites and serpentinized ultramafic rocks were retrieved from the depth interval of 100 to 1000 m of the borehole. A vein network of irregular shaped veins with a retrograde metamorphic assemblage cuts across the eclogite foliation at both low and high angles. SEM imaging of the eclogites documents that magnetite associated with retrograde pargasitic amphiboles developed around shape-preferred garnet. SEM imaging of the serpentinized ultramafic rocks documents that magnetite rims grew around shape-preferred garnet and that magnetite formed within a mesh texture related to serpentinization. Syn-serpentinization magnetite growth increased bulk susceptibilities, but reduced anisotropy. Maximum susceptibility axes from both eclogites and serpentinized garnet-peridotites trend N-S, i.e. parallel with the stretching lineation as defined by olivine and omphacite grains. This implies that the magnetic fabric mimics the UHP fabric and survived retrogression and that the fabric is inherited from the UHP stage. As a consequence, retrogression was not associated with substantial ductile deformation and the mafic-ultramafic Maobei body behaved as a rigid body within a ductile deforming quartzo-feldspathic matrix during exhumation. Internal strain is restricted to brittle fracturing, associated fluid circulation and vein formation facilitating retrograde reactions in the mafic-ultramafic rocks. 相似文献
17.
Polyphase Deformation of the Weihai-Rongcheng UHP Unit Rocks, NE Sulu： Insights into the Tectonic Evolution of the Dabie-Sulu UHP and HP Belts, China 
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下载免费PDF全文 SUO Shutian ZHONG Zengqiu ZHOU Hanwen YOU Zhendong 《《地质学报》英文版》2007,81(1):42-54
Different scales of structural data reveal a complex deformation history of ultrahigh- pressure （UHP） rocks exposed in the Weihai-Rongcbeng area, NE Sulu （northern Jiangsu-eastern Shandong）, eastern China. Excluding pre-UHP deformations, at least five major sequential deformational stages （D1-Ds） are recognized. The first deformation （DO produced a weak foliation and lineation in massive eclogites. The foliated eclogite with a dominant foliation containing a stretching and mineral lineation was developed during the I）2 deformation. Both the D1 and D2 deformations occurred under UHP metamorphic conditions, and are well preserved in the eclogite bodies. D3 structures which developed shortly after the formation of granulite/amphibolite facies symplectites are characterized by imbricated associations marked by a regional, steeply dipping foliation, compositional layering, eclogite boudinage, isoclinal folds and reverse ductile shear zones. The D3 deformation was accompanied by decompressional partial melting. A regional, gently dipping amphibolite facies foliation and stretching lineation, low-angle detachments, and dome- and arc-shaped structures formed during the D4 deformation stage dominate to some degree the map pattern of the Weihai-Rongcbeng UHP domain. The last stage of deformation （Ds） gave rise to the final exhumation of the UHP rocks. Ds is characterized by development of brittle-dominated high-angle faulting associated with emplacement of large volmnes of undeformed granite plutons and dykes dated at 134-100 Ma. The deformational and metamorphic sequence followed by the UHP rocks in the Weihai-Rongcheng area is similar to that studied in the entire Dabie-Sulu UHP and HP metamorphic belts from microscopic to mapping scale. Based on structural data, combined with available petrographic, metamorphic and geochronological data, a speculative tectonic evolutionary model for the Dabie-Sulu UHP and IIP belts is proposed, involving continental subduction/collision between the Sino-Korean and Yangtze cratons and subsequent polyphase exhumation histories of the UHP and IIP metamorphic rocks. 相似文献
18.
大别山碧溪岭地区超高压变质岩构造分析 总被引：7，自引：1，他引：7
大比例尺 (1∶10 0 0 0 )构造制图及构造分析表明 ,碧溪岭地区超高压变质岩石含有丰富的构造演化历史记录。同碰撞或挤压组构只保留于榴辉岩及其它超高压变质岩透镜体内部 ,表现为高角度网络状超高压剪切带与弱应变透镜体域规律组合格式。前者由面理或糜棱岩化榴辉岩组成 ,后者由块状榴辉岩及石榴橄榄岩组成。碰撞期后伸展构造表现为区域性的假单斜状 ,内部呈低缓角度的网络状强应变带及所环绕的透镜状弱应变域组合格式 ,强应变带的岩石为由榴辉岩退变成的角闪岩相高压片麻岩及部分熔融形成的含榴花岗岩 ,透镜状弱应变域的岩石为弱角闪相改造的榴辉岩及石榴橄榄岩。不同尺度上同碰撞或挤压组构及碰撞期后伸展组构所显示的这种残斑基质流变学结构样式 ,虽然与先期原岩成分、结构、流变学的不均一性有关 ,但主要是多期递进应变分解作用的结果 ,支持榴辉岩“原地”成因模式。依据构造学证据和可利用的岩石学及同位素年代学资料 ,分析了超高压变质岩石的形成及折返过程 ,指出碧溪岭地区超高压变质岩石是在 2 45～ 2 10Ma形成的 ,碰撞期后伸展作用主要发生在 2 0 0～ 170Ma。在超高压变质岩石向地壳表层折返过程中 ,张扭作用可能有重要功能 ,不支持碧溪岭地区遭受过多期超高压变质作用的推论。 相似文献
19.
韧性剪切带中片麻岩和超高压榴辉岩变形特征及其与地震波速各向异性的关系：来自中国大陆科学钻探（CCSD）680～1200米岩心的证据 总被引：12，自引：3，他引：12
中国大陆科学钻探(CCSD)680-1200米区段发育了多个韧性剪切带,带中主要岩石类型包括片麻岩和超高压榴辉岩。片麻岩中的变形石英、面理化榴辉岩中的拉长石榴石和绿辉石的应变轴比都表现为X>Y>Z,Flinn系数分别为0.11-0.27、0.22-0.23和0.23-0.24。随着糜棱岩化作用的增强,变形石英的C轴组构由Z轴极密逐渐向Y轴极密和叶理面上的大圆环带转变。在常温常压下测试了样品的波速,计算出片麻岩Vp和Vs的各向异性分别为30.17％-60.97％和11.52％-35.79％,榴辉岩Vp和Vs的各向异性分别为0.17％-11.19％和2.41％-6.70％。影响各向异性的主要因素有岩石的结构构造、矿物的晶格优选方位(LPO)、形态优选方位(SPO)和定向微裂隙。随着糜棱岩化作用的增强,岩石的P波各向异性逐 渐升高。变形岩石中的黑云母、石英、绿辉石的LPO和SPO是地震波各向异性的主要控制因素。饱水后的片麻岩样品的P波各向异性明显低于干燥片麻岩样品。在东海钻井中的强反射带主要是由于不同岩层之间的波阻抗差异而造成的,榴辉岩/强退变榴辉岩和黑云斜长片麻岩之间的接触界面会产生较强的地震深反射。此外,与LPO相关的地震波各向异性会增强地震波的反射,所以韧性剪切带中的糜棱岩化片麻岩可能是地震反射的良好载体。韧性剪切带中岩石弹性波速度的强各向 相似文献
20.
北苏鲁荣成地区超高压变质带的形成与折返动力学 总被引：1，自引：0，他引：1
山东省荣成地区位于苏鲁高压-超高压变质带的东北部,以花岗质片麻岩、副片麻岩为主,夹有少量的榴辉岩、石榴辉石岩、麻粒岩、超基性岩、石英岩、大理岩和斜长角闪岩等,各类岩石的锆石中普遍含有柯石英包裹体,表明荣成地区岩石曾经历超高压变质作用过程。荣成地区区域构造格架表现为面理产状总体为NNE-SSW走向,向南转为由NE-SW走向,呈弧形展布,倾向SE或SSE,超高压变质岩石由一系列近平行的剪切岩片组成,岩片之间的分界线为一些韧性剪切带,是折返阶段角闪岩相-绿片岩相的产物。结合野外宏观变形现象、显微构造分析以及糜棱岩中石英的优选方位EBSD （electron backscatter diffraction,电子背散射技术）测量结果,可以判断北苏鲁荣成地区韧性剪切带主要形成于中、低温（550~350℃）条件,并具有由NW向SE“斜向正滑”的剪切指向。根据韧性剪切带中所含的榴辉岩透镜体的显微构造和绿辉石与金红石的优选方位的EBSD的研究,重塑超高压变质阶段的流变学特征：绿辉石和金红石都具有高温的滑移系组构模式。横穿苏鲁高压-超高压变质带的地震反射剖面揭示了苏鲁高压-超高压变质带呈厚10km以上的穹形板片,位于苏鲁高压-超高压变质板片下部的荣成及江苏刘山以韧性正断裂系列为主。Ar-Ar测年结果表明,发生这种伸展韧性剪切作用的时间在117~130Ma。位于板片上部的南苏鲁以韧性逆冲性断裂系列为主。基于以上各方面的研究,进一步验证了苏鲁超高压-超高压变质带折返动力学的挤出模式。 相似文献