胶南造山带变质作用及其演化

胶南造山带曾经历过五期变质作用，早中元古代麻粒岩相变质作用，以出现紫苏辉石为标志，其变质条件为Ｐ＝１．３５ＧＰａ、Ｔ＝７８７．７℃，属中高压相系，区域中高温变质作用；晋宁期榴辉岩相变质作用，以发育榴辉岩为标志，其变质条件Ｐ≥２．８ＧＰａ、Ｔ＝６０１－１３７５℃，超高压变质作用，榴辉岩围岩的变质条件为Ｐ＝１．１－１．６ＧＰａ、Ｔ＝５６０－６５０℃；晋宁一震是于期的角闪岩相变质作用是胶南造山带最重要的     

南秦岭造山带东段的变质作用研究

近年来,虽然秦岭造山带的研究取得了重要进展,但对于分布广泛的南秦岭地区变质作用的研究非常薄弱。仅在中国变质地质图和陕西省区域地质志中指出,该区的变质作用以佛坪地区为中心发育递增变质带,最高为十字石蓝晶石级,主变质期为海西期。本课题组最近对南秦岭造山带...     

桐柏—大别造山带随县群变质变形作用研究

中新元古代随县群分布于秦岭－大别造山带南部，是一套形成于大陆裂谷环境中的砂页岩－流纹英安质火山碎屑岩建造，并在拉张环境中受到了辉长辉绿岩墙侵入，从新元玳末开始经历了多期变质和变形作用改造，记录了华北与扬子两大陆块及其造山作用的复杂演化历史，以现代变质地质学理论为指导，结合岩石学与构造学，宏观与微观研究，确立了随县群的地质事件序列，其主要有３个变形和变质演化阶段，晋宁期伸展滑脱固态流变，低绿片岩相变     

南苏鲁造山带毛北超高压变质岩体的成因与成矿作用

毛北超高压变质岩体位于苏鲁造山带南部,是由石榴石橄榄岩、榴辉岩、硬玉石英岩和石榴石多硅白云母石英片岩组成的层状岩体.富金红石榴辉岩和富钛铁矿榴辉岩在岩体中呈连续的层状产出,总厚度达200m,深度＞700m,构成了一个大型的钛矿床.岩石学、地球化学和年代学研究表明,毛北岩体的原岩形成在新元古代Rodinia超大陆裂解过程中,基性岩浆经历了强烈的分异结晶作用,形成了由橄榄辉长岩-辉长岩-闪长岩-花岗岩组成的复杂层状侵入体,并在新元古代的全球冰期与高纬度大气降水发生强烈的水-岩交换作用.在印支期的大陆深俯冲过程中,经历了超高压变质作用,其峰期变质温度＞800℃,压力＞4.5GPa,富钛磁铁矿辉长岩转变成了富金红石榴辉岩,形成了超高压变质的钛矿床.     

大别造山带加里东期高压超高压变质作用的确定及其意义

文中综述了对大别造山带高压超高压变质作用形成时代的 3种观点。重点从高压超高压变质作用同位素定年技术、方法的完善与更新和大别造山带早古生代区域地质构造背景两个方面论证了大别造山带加里东期高压超高压变质作用的存在 ,得出了大别造山带高压超高压变质作用主要为加里东期的结论。这一认识对揭示世界一些大型造山带构造演化规律、研究中国加里东期区域构造格局和在大别造山带及邻区寻找金刚石、金红石、各种宝石、金、铜等矿产都有积极的意义。     

苏鲁造山带超高压变质作用及其P-T-t轨迹

基于超高压变质岩的岩石学,特别是超高压矿物生长成分环带、扩散环带和蚀变作用研究,综合前人的岩石学和年代学研究成果,提出苏鲁造山带超高压变质作用峰期发生在1000～1100℃和6—7GPa条件下,俯冲深度相当于200km,形成年代为240～250Ma。在此基础上,重塑了一个包括八期变质作用的P—T—t轨迹,揭示出超高压变质岩经历了三个不同的折返阶段,即从200km到100km深度的快速折返阶段,抬升速率为5km／Ma,冷却速率为10℃／Ma;从100km到30km的快速折返,抬升速率为4km／Ma,或为近等温降压,或为缓慢降温的快速降压过程;从下地壳到近地表的缓慢折返阶段,抬升速率为1km／Ma,但为快速降温过程,冷却速率可达20℃／Ma。     

苏鲁造山带南缘基础地质研究进展

苏鲁造山带南缘发育的超高压变质成因的榴辉岩带是整个中国中部造山带折返抬升最高部位，具有较典型的造山带根部特征。通过区域地质调查工作，查明区内发育岩石地层有新太古代至古元古代东海岩群、中新元古代锦屏岩群和云台岩群，呈一系列北东向和近东西向构造岩块分布，岩石中密集发育晋宁期韧性推覆剪切带和右形走滑韧性剪切带，后期普遍为印支期滑脱韧性剪切带叠加，形成复杂的韧性剪切系统，是阜宁期华北板块南缘地体拼贴B型俯冲碰撞作用、晋宁期华北板块与扬子板块软碰撞作用和印支期扬子板块向华北板块之下A型俯冲碰撞作用的结果。     

苏鲁造山带南缘岩石—地层格架

系统总结了苏鲁造山带南缘区域地质调查工作所取得的进展,将东海杂岩分解为新太古代至古元古代东海岩群和变质侵入岩。东海岩群由毛北岩组、演马场岩组、武强山岩组、虎山岩组和摩天岭岩组构成;变质花岗质侵入岩分为早期面状侵入体和晚期点状侵入体,超基性岩包体分为北西许沟岩带和南东蒋庄-岗尚岩带,变质杂岩呈一系列北东向和近东西向构造岩块分布,超高压变质岩块划分为4个岩片,密集发育晋宁期韧性推覆剪切带,后期普遍为印支期滑脱韧性剪切带叠加,形成复杂的韧性剪切系统。     

豫西东秦岭造山带核部杂岩变质作用研究若干进展

豫西东秦岭造山带核部杂岩的变质作用研究取得了若干重要进展,包括:(1)据同位素年龄将其划分为晋宁变质旋回和加里东一海西变质旋口;(2)按显微结构分析划分矿物的生长历史为二期六个阶段;(3)厘定了若干降压变质反应和等压冷却反应;(4)较为定量地重建了两大旋回的变质作用P—T－t轨迹.上述成果为核部杂岩,乃至整个造山带的地壳演化提供了新的证据.     

陆—陆碰撞造山带中压型变质作用的pT轨迹——以南秦岭佛坪地区为例

依据石榴石的环带特征反演了南秦岭造山带中压型变质作用的pT轨迹，表明石榴石的环带记录了峰期变质前的温压条件递增过程，其最高温度与最大压力一致，这一过程可能与地壳的持续加厚过程相对应。峰期变质以后即出现有构造作用参与的快速抬升过程，pT轨迹表现为ITD型。这一研究可以加深入们的对造山带发生中压型变质作用过程的理解。     

Ultrahigh-pressure metamorphism in the forbidden zone: the Xugou garnet peridotite, Sulu terrane, eastern China

The Xugou garnet peridotite body of the southern Sulu ultrahigh‐pressure (UHP) terrane is enclosed in felsic gneiss, bounded by faults, and consists of harzburgite and lenses of garnet clinopyroxenite and eclogite. The peridotite is composed of variable amounts of olivine (Fo₉₁), enstatite (En_92?93), garnet (Alm_20?23Prp_53?58Knr_6?9Grs_12?18), diopside and rare chromite. The ultramafic protolith has a depleted residual mantle composition, indicated by a high‐Mg number, very low CaO, Al₂O₃ and total REE contents compared to primary mantle and other Sulu peridotites. Most garnet (Prp_44?58) clinopyroxenites are foliated. Except for rare kyanite‐bearing eclogitic bands, most eclogites contain a simple assemblage of garnet (Alm_29?34Prp_32?50Grs_15?39) + omphacite (Jd_24?36) + minor rutile. Clinopyroxenite and eclogite exhibit LREE‐depleted and LREE‐enriched patterns, respectively, but both have flat HREE patterns. Normalized La, Sm and Yb contents indicate that both eclogite and garnet clinopyroxenite formed by high‐pressure crystal accumulation (+ variable trapped melt) from melts resulting from two‐stage partial melting of a mantle source. Recrystallized textures and P–T estimates of 780–870 °C, 5–7 GPa and a metamorphic age of 231 ± 11 Ma indicate that both mafic and ultramafic protoliths experienced Triassic UHP metamorphism in the P–T forbidden zone with an extremely low thermal gradient (< 5 °C km^?1), and multistage retrograde recrystallization during exhumation. Develop of prehnite veins in clinopyroxenite, eclogite, felsic blocks and country rock gneiss, and replacements of eclogitic minerals by prehnite, albite, white mica, and K‐feldspar indicate low‐temperature metasomatism.     

Petrological and geochronological constraints on the formation, subduction and exhumation of the continental crust in the southern Sulu orogen, eastern-central China

Detailed petrological, geochemical and geochronological studies were carried out for the core samples from the Chinese Continental Scientific Drilling Main Hole (CCSD-MH) with a final depth of 5158 m. This borehole has penetrated into an ultrahigh-pressure (UHP) metamorphic slice consisting mainly of eclogites, gneisses, garnet-pyroxenites and garnet-peridotites. Geochemical characteristics indicate that their protoliths are igneous rocks, and occur in a continental rifting tectonic setting. Quartz-, rutile- and ilmenite-rich eclogites from 0 to 710 m occur as alternating layers; the eclogites, together with interlayers of peridotites and gneisses form a layered ultramafic-mafic-acidic intrusion, which was formed by extensive fractional crystallization of basaltic magma in continental environments. The granitic gneisses from 1190 to 1505 m and 3460 to 5118 m show affinity to within-plate granite, whereas the granitic gneisses from 710 to 1190 m and 1505 to 3460 m exhibit characteristics of volcanic-arc granite. Zircon U-Pb dating demonstrates that the magmatic zircon cores, which have relatively high Th/U ratios (mostly > 0.4), from both eclogites and gneisses, yield the same age at c. 788.8 Ma, suggesting that the protoliths of UHP rocks were formed by bimodal magmatism in Neoproterozoic rifting tectonic zones along the northern margin of the Yangtze Plate, in response to the breakup of the supercontinent Rodinia. U-Pb dating of metamorphic zircons with coesite and other eclogite-facies mineral inclusions and with relatively low Th/U ratios (mostly < 0.14) gives similar Triassic ages, which define two main zircon-forming events at 221.1 Ma and 216.7 Ma. We suggest that the older weighted mean age represents the peak-UHP metamorphic event at a pressure of 5.0 GPa (corresponds to ∼ 165 km depth), whereas the younger mean age reflects the UHP/HP retrograde event at a pressure 2.8 GPa (∼ 92 km depth). Therefore, a maximum rate of vertical movement during early exhumation of the UHP rocks from the Sulu orogen would be 17 mm/year, which is quite similar to initial exhumation rates (16 to 35 mm/year) of many UHP terranes in the world.     

Petrogenesis of UHP metamorphic rocks from Qinglongshan, southern Sulu, east-central China

Five kinds of UHP metamorphic rocks, including eclogite, orthogneiss, paragneiss, schist and quartzite are exposed in the Qinglongshan roadcut, southern Sulu orogenic belt of eastern central China. They comprise metamorphic supracrustal rocks with bimodal volcanic characteristics and continental affinity, and granitic intrusive associations. The preservation of coesite inclusions and/or its pseudomorphs in eclogite and other rocks indicate that they have been subjected to in-situ UHP metamorphism. Four stages of metamorphism were recognized by combining petrographic observations and compositions of minerals from various UHP rocks. Prograde epidote-amphibolite facies, UHP coesite–eclogite facies, post UHP quartz–eclogite facies, and retrograde amphibolite facies assemblages delineate an inferred P–T path with a clockwise trajectory and a retrograde event characterized by the coupling of decompression with a temperature decrease. Garnet porphyroblasts in UHP eclogites display a complex growth zoning and mineral distribution, and record a crucial segment of the prograde and retrograde metamorphic evolution. The preservation of growth zoning in eclogitic and gneissic garnets suggests that the UHP rocks had a short residence time before retrograde metamorphism and a very high uplift rate in order to preserve the prograde growth zoning.     

榴辉岩的地震波性质：对苏鲁超高压变质带地壳成分和折返机制的探讨

本总结了榴辉岩的高温高压弹性波速测量结果,并将其应用于苏鲁超高压变质带地震资料的解释。由于榴辉岩具有高密度和高波速,它们和长英质片麻岩、大理岩、石英岩、角闪岩、麻粒岩、蛇纹石化橄榄岩的界面可以产生强反射。如果俯冲的陆壳物质以榴辉岩与围岩互层的形式在上地幔保留下来,就可能在造山带的上地幔产生地震反射。根据CCSD孔区地震剖面所建立的地壳成分模型表明：苏鲁超高压带地壳浅部的高速层可归因于夹在花岗质片麻岩、副片麻岩、角闪岩等岩石中的榴辉岩和超基性岩;中地壳主要由中酸性片麻岩、斜长角闪岩和副片麻岩组成;下地壳以中基性麻粒岩为主。在该超高压变质带现今的深部地壳,榴辉岩含量很少或几乎没有。因此,折返的超高压变质岩是以构造岩片的形式沿一系列剪切带逆冲并覆盖在正常的中下地壳之上,深部榴辉岩的缺乏可能与下地壳拆沉作用无关。     

超高压变质过程中的元素地球化学行为——CCSD主孔榴辉岩的矿物化学研究

中国大陆科学钻探主孔位于江苏东海县,苏鲁超高压变质带的南部.该钻孔的0～2050m深度获取了六种不同类型的榴辉岩和少量石榴石辉石岩岩心,它们是典型的基性超高压变质岩,为研究大陆深俯冲过程中的元素地球化学行为提供了非常好的样品.本文对各种超高压变质矿物的微量元素成分进行了系统的原位微区分析,结合全岩化学成分和矿物主量元素成分,深入地研究了超高压变质岩的微量元素赋存特征、分配规律、控制因素,及其对变质条件和流体.岩石相互作用的限定意义.结果表明,超高压榴辉岩中的LREE和Sr主要赋存在磷灰石、帘石和单斜辉石中,HREE赋存在石榴石中,Ba、Rb和Cs等LILE赋存在多硅白云母中,Ti、Nb和Ta等HFSE主要赋存在金红石、钛铁矿中,V、Sc、Co和Ni等元素大多赋存在石榴石和单斜辉石中.研究表明,全岩化学成分和矿物组成、及其含量的变化明显控制着超高压矿物的微量元素含量和分布形式.本研究也获得了如下重要的认识超高压变质矿物之间的微量元素分配达到了化学平衡,并具有与地幔榴辉岩矿物之间类似的分配系数,表明榴辉岩的峰期变质温度很可能达到900℃～1000℃.部分高Ti和高Fe-Ti榴辉岩中的石榴石和绿辉石有明显的稀土元素成分环带,表明超高压变质岩经历了快速折返过程.金红石的Zr含量明显受到全岩成分和退变质作用影响,并不仅仅与形成温度有关,不是可靠的温度计.在超临界流体的作用下,榴辉岩中金红石的Nb、Ta发生了明显的分异,导致其Nb/Ta比值增大,由此推测俯冲到地幔深处的大量榴辉岩是地球内部高Nb/Ta比值的物质源区.在榴辉岩的不同程度退变质阶段,参与变质反应的流体具有不同的来源、成分和流体活动规模.     

Metamorphism of the East Sector of the Southern Qinling Orogenic Belt and Its Geological Significance

The east sector of the southern Qinling belt is, lithologically, composed mainly of metapelites,quartzites, marbles and small amount of metabasites and gneisses, whose protoliths are the Silurian, Devonian andless commonly the Sinian and Upper Palaeozoic. They have been subjected at least to two epochs of metamorphism.The early epoch belongs to progressive metamorphism which is centered on high amphibolite-granulite facies in theFuping area and changed outwards into low amphibolite facies (staurolite-kyanite zone), epidote amphibolite facies(garnet zone) and greenschist facies (chlorite and biotite zones), the metamorphic age of which is about 220-260 Ma.This early-epoch metamorphism belongs to different pressure types: the rocks from greenschist to low amphibolitefacies belong to the typical medium-pressure type which shows geothermal gradients of about 17-20℃/km and wasprobably produced by a crustal thickening process related to continental collision, and the high amphibolite-granulitefacies belongs to the low-pressure type which shows geothermal gradients of about 25-38℃/km and was probablyaffected by some magmatic heats. Based on the basic characteristics of the P-T paths of the different facies calculatedfrom the garnet zonations, it can be deduced that the metamorphism of medium-pressure facies series took place dur-ing an imbricated thickening process, rather than during the uplifting process after thickening. The late-epoch meta-morphism belongs to dynamic metamorphism of greenschist facies which is overprinted on the early-epoch meta-morphic rocks and is Yanshanian or Himalayan in age, probably related to intracontinental orogeny.     

Retrogressive Microstructures:A Key to Post Collisional Uplift and Extension Tectonics of Ultrahigh-Pressure Metamorphic Rocks from Dabie Orogenic Belt,China

ThereisanunanimousunderstandingthattheUHPmetamorphisminDabie-SuluareaswasformedduringtheTri-assiccollisioneventbetweentheYangtzeandNorthChinacratons(Congetal.,l994$Zhouetal-,l996;Liouetal.,l994)-Eclogiteisthemostimportantrocktypeamongtheul-trahigh-pressure(UHP)metamorphicrocks.Accordingtotheiroccurrencethereare3typesofeclogites:typeIisen-clavesinultramaficintrusionsandasmembersinthelayeredmafic-ultramaficcomplex(Jahnl998);typeIispodsorlay-ersinthehighlymetamorphicsupracrustals(mainlying…     

苏鲁造山带威海地区石榴角闪岩中“环状”石榴子石的成因

发育特征结构的石榴子石是研究俯冲带矿物演化和元素迁移的理想对象。本文首次报道苏鲁造山带东北端威海地区出露的含"环状"石榴子石的石榴角闪岩,并对其开展了详细的岩相学、矿物化学、锆石SHRIMP U-Pb年代学和变质作用研究。X射线主元素扫面显示,"环状"石榴子石经历了3个阶段生长:最高Ca部分的成核阶段、相对低Ca部分的扩展阶段和最低Ca部分的快速塑形阶段,分别对应M₁、M₂和M₃阶段变质作用,相应的矿物组合为石榴子石高Ca环核部及其矿物包裹体(如角闪石+富Na斜长石+金红石+绿帘石+磷灰石)、石榴子石低Ca环内边及其后成合晶矿物(如角闪石+富Ca斜长石边部+钛铁矿±金红石±磷灰石)和最低Ca石榴子石环外边±角闪石±钛铁矿,未发现超高压变质矿物或假象。传统地质温压计估算出M₁和M₂阶段的变质P-T条件分别为620～740℃/6.8～10.4kbar和705～775℃/5.3～7.1kbar,而M₃阶段可能发生于温度稍高和压力稍低的P-T范围。其中M_...