秦岭造山带佛坪地区花岗岩类的特征及其意义

通过岩石学和地球化学研究，认为佛坪地区花岗岩类可分为两种不同的成因类型：深熔混合岩化型和陆壳重熔型。它们具有截然不同的野外地质特征和稀土元素地球化学特征，反映造山带不同演化阶段的构造热事件。深熔混合岩化小岩体与晋宁期南秦岭强烈变质变形密切相关；大面积出露的陆壳重熔型岩体则是主造山期地慢上涌引起的垂向加积构造演化的物质反映，对佛坪穹窿的形成和穹窿中心基底结晶杂岩的抬升剥露有重要意义．     

断裂区域变质作用与混合岩化作用、花岗岩化作用研究

本文通过三个实例,讨论了断裂区域变质作用与混合岩化和花岗岩化作用之间的关系,指出: 1) 在断裂区域变质作用地区,中—高级变质岩、混合岩、混合花岗岩构成“三位一体”的岩石共生组合。它们均受断裂构造控制;断裂带在形态上呈带状分布。 2) 混合岩本身分带不明显,未见同心分带现象。 3) 断裂变质带具有双变质带的特征,一般规律是下盘具有挤压特点,出现兰晶石、十字石变质矿物组合的变质岩;上盘具拉张性特征,出现红柱石、硅线石等低压变质矿物组合的变质岩及混合岩;变质岩类的递增分带性不清楚。空间上双变质带彼此平行,且与断裂方向一致。形成时间上,二者同时,或略有先后,一般是先压后张,但仍隶属同一变质幕之内。 4) 由断裂构造作用所导致的双变质带,可以出现于大陆板块内部,也见于活动大陆边缘。     

中祁连地块东段元古宙基底湟源群沉积构造环境

通过对中祁连地块东段元古宙基底湟源群原岩建造及其地球化学特征的研究,认为：湟源群主要由各种千枚岩、片岩、变粒岩、大理岩、石英岩和斜长角闪岩等组成的中浅变质的表壳岩组合;其原岩为一套由陆源碎屑岩、不纯碳酸盐岩、中基性大山岩等组成的火山岩沉积岩组合;湟源群中变质沉积岩系中沉积韵律、沉积条带构造的广泛发育以及浊积层的存在等,指示了其原岩建造具有复理石或类复理石建造的特征;其中变质杂砂岩的地球化学特征类似于大陆岛弧或安底斯岛弧型杂砂岩的特征;湟源群变质中基性火山岩的地球化学特征类似于岛弧或活动大陆边缘的钙碱性火山岩的特征。经综合分析得出,湟源群沉积构造环境可能为陆缘弧后盆地且靠近大陆一侧。     

太行山-恒山太古代古老陆块: 年代学和地球化学制约

太行山-恒山-五台山变质地块的构造热演化和地质年代学研究,以及前寒武纪高压麻粒岩带、五台群金刚库组高压变质泥质岩的发现表明,可能存在太古代末到古元古代初东部陆块、西部陆块之间的碰撞造山带.太行山变质地块北段与恒山变质地块的地质学、地质年代学、构造热演化和地球化学资料对比反映这两个变质地块在华北地台形成演化早期应为同一构造单元,相当于东部陆块的西部活动陆缘.经历了东部、西部陆块碰撞作用而发生构造岩浆活动和变质作用的强烈改造.     

江西慈竹英云闪长岩体及其周围区域变质岩石的成因

慈竹英云闪长岩体位于江西弋阳县南,岩体在平面上呈哑铃状,面积约45平方公里。利用钾氩法测定其同位素地质年龄为477×10~6 年,形成时代属加里东早期。岩体附近为一套区域变质岩石,按变质程度可划分出三个变质带:硅线石黑云母斜长片麻岩带,红柱石二云母片岩带,碳质板岩与石英岩带。英云闪长岩体主要位于硅线石黑云母斜长片麻岩中。从硅线石和红柱石的出现,本区区域变质岩石属于比较典型的高温低压变质带。岩体内部可见到围岩的包体,岩体产状与围岩基本一致,边部具形状奇特的塑性流动构造,岩体周围发育条带状混合岩、褶皱状混合岩和肠状混合岩。岩体分相不清楚,边部具片麻状构造,而内部为致密块状。英云闪长岩与硅线石黑云母斜长片麻岩在矿物组合方面非常相似.区别在于矿物的相对含量有所不同。二者的副矿物成分也相同,均属锆石磷灰石型。镜下观察,组成英云闪长岩的矿物,结晶有一定顺序,交代结构不明显。根据以上特征,初步认为英云闪长岩的形成是在区域变质作用的背景上,在变质程度最深部位由泥质、粉砂质岩石发生深熔作用的结果,开始阶段产生少量的花岗质熔体,当温度进一步升高,终于导致英云闪长质熔体形成,后者向上侵入,但位移的幅度不大。综合各方面证据得到的结论是:慈竹英云闪长岩体属于深熔作用产生的半原地型具流化特征的同褶皱岩体。     

混合岩中锆石的特征是其成因的标志(以鞍本地区为例)

辽宁鞍山本溪地区广泛出露了混合岩类,对其中副矿物锆石的研究表明,混合岩形成时的环境特征良好地反映在锆石的标型特征中。而锆石的特征又表明,鞍山本溪地区的混合花岗岩属原地花岗岩,它的形成是在岩石基本上保持固态的条件下进行的,这时发生着广泛的变质结晶、重结晶和变形作用。锆石的特征还表明本区混合岩化作用前的原岩为一套中酸性火山沉积建造。     

东天山造山带区域变质作用及其构造环境研究

以活动论思想为指导，分析了东天山造山带区域变质作用的基本特征，成因类型，变质岩分带特征和特征矿和的组合的空间分规律，论证了大型断裂构造对区域变作用的同期制约和后期迭加改造作用，阐明了断裂区域变质作用在东天山普遍性以及断裂活动与变质变形，混合容化和花岗岩化作用之间的关系。最后对东天山变质岩带的板块构造环境和多期变质演化规律进行了探讨。     

福建尤溪梅仙地区马面山群变质岩原岩恢复及其与铅锌成矿的关系

通过变质岩产状、矿物组合及组构特征、矿物间的交代关系、典型矿物空间分布特征、岩石化学、稀土元素化学等方面对原岩恢复进行研究。研究结果表明:丁家山铅锌矿区新元古代马面山群变质岩均为副变质岩,其中石英云母系列变质岩的原岩为泥质粉砂岩和粉砂质泥岩,石榴子石绿帘石透辉石系列变质岩原岩为钙质泥岩、钙质泥质粉砂岩、钙质粉砂质泥岩、泥灰岩等富钙质岩类,而大理岩类的变质原岩为钙镁质沉积岩;丁家山铅锌矿为马面山群龙北溪组上段经加里东期区域变质的富钙质沉积岩与燕山期花岗岩发生接触交代作用而形成的矽卡岩型矿床,矿区广泛存在的石榴子石、透辉石、绿帘石等非金属矿物与磁铁矿、磁黄铁矿、黄铁矿、闪锌矿和方铅矿等金属矿物同为接触交代变质作用在不同阶段的产物。     

南祁连党河南山地区鸡叫沟复式岩体岩石地球化学特征及构造环境

通过对党河南山北坡东段鸡叫沟岩体的岩体地质特征和岩石地球化学特征研究,发现该岩体为一加里东期中酸性复式岩体,岩浆活动有4期,依次为岩枝(脉)状产出的辉石闪长岩、辉石正长闪长岩,岩株状产出的(角闪)石英二长岩,岩脉状产出的黑云二长花岗岩和脉状产出的细粒二长花岗岩.第1,2期(石英二长岩锆石U-Pb年龄为455.3±5.6 Ma)构成该复式岩体的主体部分.总体上,4期岩体均富含碱质(碱度率平均为2.72%)、高钾(平均值为4.24%)、贫钛(均小于1.3%),属钾玄岩系列.岩石富集大离子亲石元素和轻稀土元素,具负Eu异常.进一步分析发现,从第1期到第4期,岩石铝质、钾质质量分数渐次升高,稀土总量降低.同时发现前2期、后2期岩体岩石地球化学特征分别大体相似,而且后2期岩体比前2期岩体贫稀土和不相容元素(第4期比第3期尤甚).岩浆演化程度从第1期到第4期逐渐增加,尤其后2期岩浆演化程度很高(DI平均值达95.9).综合判断显示前2期岩体岩浆源岩为基性岩熔融,形成环境为岛弧环境;后2期岩浆原岩为变质沉积岩,形成于造山环境.     

混合岩脉体中的石榴石及其地质意义

混合岩化作用是介于变质作用和典型的岩浆作用的之问的地质作用,其形成的混合岩有基体和脉体两部分组成；脉体的形成机制有四种:石榴石作为脉体的常见变质矿物,只出现在深熔作用形成的脉体中.深熔作用形成的脉体中的石榴石则分为两种,这两种不同的石榴石具有不同的地质特征,对其寄主的岩石具有不同的地质意义.     

Evolution of the Xiaotian-Mozitan fault and its implications for exhumation of Dabie HP-UHP rocks

The Xiaotian-Mozitan fault （XMF） located north of the Dabie orogenic belt separates the North Dabie complex to the south from the Beihuaiyang low-grade metamorphic rocks to the north. It comprises several NW-striking ductile shear zones and brittle faults. The brittle faults obviously overprinted on the ductile shear zones and promoted the development of the volcanic basins in early Cretaceous to the north, which suggests that the brittle faults were normal faults formed in early Cretaceous during doming of the Dabie orogenic belt. The ductile shear zone superposed on the north Dabie gray gneiss, and it is an important channel where the Dabie HP-UHP rocks exhumed. For obtaining new structural constraint on exhumation of the HP-UHP rocks, we present here experimental results on the microstructure, quartz C-axis fabrics and the microprobe analyses of phengite. The ductile shear zone was determined to be formed at a temperature of 600-650 ℃ and pressure of 1.1 GPa by the mineral deformation, microprobe analyses and geobarometry of Si-in-phengite of the mylonite, the results suggest that the mylonite now exposed on the surface experienced an upper amphibolite-facies metamorphism in the lower crust. The mineral stretching lineation varies from horizontal in the east segment to sub-dip in the west. Shear sense indicators from outcrop and thin sections of orientated specimen and quartz C-axis fabrics suggest that the XMF is a sinistral normal fault. The kinematics analysis of the ductile shear zone indicates that the exhumation of Dabie HP-UHP rocks is the results of a SE-directed extrusion and an anticlockwise rotation around its eastern pivot simultaneously.     

Petrology, geochemistry and geodynamics of basic granulite from the Altay area, North Xinjiang, China

The basic granulite of the Altay orogenic belt occurs as tectonic lens in the Devonian medium- to lower-grade metamorphic beds through fault contact. The Altay granulite (AG) is an amphibole plagioclase two-pyroxene granulite and is mainly composed of two pyroxenes, plagioclase, amphibole and biotite. Its melano-minerals are rich in Mg/(Mg Fe^2 ),and its amphibole and biotite are rich in TiO2. The AG is rich in Mg/(Mg Fe^2 ), Al2O3 and depletion of U, Th and Rbcontents. The AG has moderate ∑REE and LREE-enriched with weak positive Eu anomaly. The AG shows island-arc pattern with negative Nb, P and Ti anomalies, reflecting that formation of the AG may be associated with subduction. Geochemical and mineral composition data reflect that the protolith of the AG is calc-alkaline basalt and formed by granulite facies metamorphism having peak P-T conditions of 750℃-780℃ and 0.6-0.7 Gpa. The AG formation underwent two stages was suggested. In the early stage of oceanic crustal subduction, calc-alkaline basalt with island-arc environment underwent granulite facies metamorphism to form the AG in deep crust, and in the late stage, the AG was thrust into the upper crust.     

Detachment within subducted continental crust and multi-slice successive exhumation of ultrahigh-pressure metamorphic rocks: Evidence from the Dabie-Sulu orogenic belt

Although tectonic models were presented for exhumation of ultrahigh-pressure （UHP） metamorphic rocks during the continental collision, there is increasing evidence for the decoupling between crustal slices at various depths within deeply subducted continental crust. This lends support to the multi-slice successive exhumation model of the UHP metamorphic rocks in the Dabie-Sulu orogen. The available evidence is summarized as follows： （1） the low-grade metamorphic slices, which have geotectonic affinity to the South China Block and part of them records the Triassic metamorphism, occur in the northern margin of the Dabie-Sulu UHP metamorphic zone, suggesting decoupling of the upper crust from the underlying basement during the initial stages of continental subduction; （2） the Dabie and Sulu HP to UHP metamorphic zones comprise several HP to UHP slices, which have an increased trend of metamorphic grade from south to north but a decreased trend of peak metamorphic ages correspondingly; and （3） the Chinese Continental Science Drilling （CCSD） project at Donghai in the Sulu orogen reveals that the UHP metamorphic zone is composed of several stacked slices, which display distinctive high and low radiogenic Pb from upper to lower parts in the profile, suggesting that these UHP crustal slices were derived from the subducted upper and middle crusts, respectively. Detachment surfaces within the deeply subducted crust may occur either along an ancient fault as a channel of fluid flow, which resulted in weakening of mechanic strength of the rocks adjacent to the fault due to fluid-rock interaction, or along the low-viscosity zones which resulted from variations of geotherms and lithospheric compositions at different depths. The multi-slice successive exhumation model is different from the traditional exhumation model of the UHP metamorphic rocks in that the latter assumes the detachment of the entire subducted continental crust from the underlying mantle lithosphere and its subsequent exhumation as a whol     

Inconsistent correlation of seismic layer 2a and lava layer thickness in oceanic crust

At mid-ocean ridges with fast to intermediate spreading rates, the upper section of oceanic crust is composed of lavas overlying a sheeted dyke complex. These units are formed by dykes intruding into rocks overlying a magma chamber, with lavas erupting at the ocean floor. Seismic reflection data acquired over young oceanic crust commonly image a reflector known as 'layer 2A', which is typically interpreted as defining the geologic boundary between lavas and dykes. An alternative hypothesis is that the reflector is associated with an alteration boundary within the lava unit. Many studies have used mapped variability in layer 2A thickness to make inferences regarding the geology of the oceanic crust, including volcanic construction, dyke intrusion and faulting. However, there has been no link between the geologic and seismological structure of oceanic crust except at a few deep drill holes. Here we show that, although the layer 2A reflector is imaged near the top of the sheeted dyke complex at fast-spreading crust located adjacent to the Hess Deep rift, it is imaged significantly above the sheeted dykes section at intermediate-spreading crust located near the Blanco transform fault. Although the lavas and underlying transition zone thicknesses differ by about a factor of two, the shallow seismic structure is remarkably similar at the two locations. This implies that seismic layer 2A cannot be used reliably to map the boundary between lavas and dykes in young oceanic crust. Instead we argue that the seismic layer 2A reflector corresponds to an alteration boundary that can be located either within the lava section or near the top of the sheeted dyke complex of oceanic crust.     

郯庐断裂带中生代火山活动与深部过程

郯庐断裂带中生代火山活动主要发生在早白垩世 ,形成了一套以橄榄安粗岩系为主的火山岩。火山岩岩石化学特征、地球化学特征与断裂带外明显不同 ,以富碱富钾、富轻稀土元素为特征 ,具有较高的 ISr值和明显偏低的εNd值 ,表明火山活动不仅与地壳混染有关 ,而且与深部地幔以及断裂带的演化有密切的关系。研究显示该区岩浆起源于地幔底侵、壳幔相互作用下的壳幔过渡带 ,也反映此时的断裂带切入到壳幔边界。     

Syn-deformationP-T paths of Xiaoqinling metamorphic core complex

TheP-T paths of the Xiaoqinling metamorphic core complex (XMCC) have been investigated with the Gibbs method by researching the compositional changing of zoned epidotes which formed during syn-deformation metamorphism. TheseP-T paths indicate that the XMCC had experienced the following thermodynamics processes: firstly, near isobaric falling slightly in temperature in lower crust; secondly, fast decompression and rising in temperature during extensional uplifting to middle crust level; and finally, isobaric falling in temperature in middle crust. The upwelling and emplacement of the deep magma may be a major factor during the uplifting processes of the metamorphic core complex.     

太仓-奉贤断裂基于遥感、重磁数据的构造特征研究

利用遥感影像数据研究太仓-奉贤断裂地貌特征,通过小波多尺度方法对布格重力数据进行分解,并应用重力、航磁数据分析其深部结构,结合前人人工地震及沉积演化历史资料进一步探讨该断裂与古海岸线的关系.布格重力异常显示,该断裂形成NW向的重力梯度带,由北向南依次控制白茆断凹、甪直断凹和松江断凹的东部边界;重力小波细节图表明,该断裂切穿中上地壳到达下地壳,在下地壳太仓-奉贤断裂仍与太仓-陈家镇断裂、昆山-嘉定断裂、青浦-龙华断裂、松江-嘉善断裂和南汇-平湖断裂相交;航磁场揭示该断裂两侧的地质体存在明显的磁性差异.综合重力、航磁及前人资料可知,太仓-奉贤断裂是江苏地区一条重要的隐伏构造断裂,切穿底部基岩至下地壳,构成全新世中期古海岸线.     

与深断裂有关的近断裂变质作用及其成矿体系

根据在乌拉尔和哈萨克斯坦的研究成果，系统论述了近断裂变质作用形成时的大地构造环境和构造条件，及其在地壳和上地幔各深度段中的发育特点和表现形式、近断裂变质带中金属矿化的特点，并讨论了研究近断裂变质作用对非传统型金属矿床成矿预测和找矿的意义。     

Evolution of the Archaean crust by delamination and shallow subduction

The Archaean oceanic crust was probably thicker than present-day oceanic crust owing to higher heat flow and thus higher degrees of melting at mid-ocean ridges. These conditions would also have led to a different bulk composition of oceanic crust in the early Archaean, that would probably have consisted of magnesium-rich picrite (with variably differentiated portions made up of basalt, gabbro, ultramafic cumulates and picrite). It is unclear whether these differences would have influenced crustal subduction and recycling processes, as experiments that have investigated the metamorphic reactions that take place during subduction have to date considered only modern mid-ocean-ridge basalts. Here we present data from high-pressure experiments that show that metamorphism of ultramafic cumulates and picrites produces pyroxenites, which we infer would have delaminated and melted to produce basaltic rocks, rather than continental crust as has previously been thought. Instead, the formation of continental crust requires subduction and melting of garnet-amphibolite--formed only in the upper regions of oceanic crust--which is thought to have first occurred on a large scale during subduction in the late Archaean. We deduce from this that shallow subduction and recycling of oceanic crust took place in the early Archaean, and that this would have resulted in strong depletion of only a thin layer of the uppermost mantle.The misfit between geochemical depletion models and geophysical models for mantle convection (which include deep subduction) might therefore be explained by continuous deepening of this depleted layer through geological time.     

Paleoproterozoic lower crust beneath Nushan in Anhui Province： Evidence from zircon SHRIMP U-Pb dating on granulite xenoliths in Cenozoic alkali basalt

Zircon SHRIMP U-Pb dating was carried out for an intermediate granulite xenolith in Cenozoic alkali basalt from Nushan. The results suggest that the lower crust beneath Nushan may have formed at about 2400—2200 Ma, and have been subjected to granulite-facies metamorphism at 1915 27 Ma. The old age of the Nushan lower crust is consistent with the geochemical similarities between Nushan granulite xenoliths and Archean-Paleoproterozoic granulite terrains in the North China craton, but it is not distinguishable from high-grade metamorphic rocks in the Yangtze craton where such old ages were also reported. Significant Pb-loss occurs in the Nushan zircons, implying important influence of widespread Mesozoic to Cenozoic underplating in East China on the lower crust beneath Nushan.