Timing of metamorphism and deformation in the Swat valley, northern Pakistan:Insight into garnet-monazite HREE partitioning

New metamorphic petrology and geochronology from the Loe Sar dome in the Swat region of northern Pakistan place refined constraints on the pressure, temperature and timing of metamorphism and deformation in that part of the Himalayan orogen. Thermodynamic modelling and monazite petrochronology indicate that metamorphism in the area followed a prograde evolution from ～525 ± 25 ℃and 6 士 0.5 kbar to ～610 ± 25 ℃ and 9 士 0.5 kbar, between ca. 39 Ma and 28 Ma. Partitioning of heavy rare earth elements between garnet rims and 30-28 Ma monazite are interpreted to indicate coeval crystallization at peak conditions. Microtextural relationships indicate that garnet rim growth post-dated the development of the main foliation in the area. The regional foliation is folded about large-scale N-S trending fold axes and overprinting E-W trending folds to form km-scale domal culminations. The textural relationships observed indicate that final dome development must be younger than the 30-28 Ma monazite that grew with garnet rims post-regional foliation development, but pre-doming-related deformation. This new timing constraint helps resolve discrepancy between previous interpretations,which have alternately suggested that N-S trending regional folds must be either pre-or post-early Oligocene. Finally, when combined with existing hornblende and white mica cooling ages, these new data indicate that the study area was exhumed rapidly following peak metamorphism.

Coal Deformation, Metamorphism and Tectonic Environment in Xinhua, Hunan

This article discusses in detail chemical composition, molecular structure, microstructure phenomena, estimate of the palaeo-stress, paleo-temperature and the strain rate to deepen the knowledge for the correlation of coal deformation and metamorphism with structural environment in Xinhua Hunan by coal quality analysis, XRD and SEM methods, which provide dependable theoretical foundation for coal resource exploitation and utilization. The results show that 1) d002 value of six coal samples is from 3.36 to 3.39 nm, coal resolved itself into aphanitic graphite with the increase of coal rank during coalification, which is characterized by graphite flakes, and the crystallite size is from 50 nm to 250 nm;A certain degree of 3R-structure content is increases and the crystallite size is extend with the coalification process, but RH-structure content is decreased;2) the tectonic environment of research area belongs to the ductile-brittle deformation, which was characterized by low temperature, low stress, high strain rate;3) Tianlongshan magmatic intrusion provided heat source, its side-extrusion made the molecules structure of coal ordering, distance between layers decreased, finally it caused the formation of aphanitic graphite.

^(40)Ar/^(39)Ar Dating of Deformation Events and Reconstruction of Exhumation of Ultrahigh-Pressure Metamorphic Rocks in Donghai, East China

Recent investigations reveal that the ultrahigh-pressure metamorphic (UHPM) rocks in the Donghai region of East China underwent ductile and transitional ductile-brittle structural events during their exhumation. The earlier ductile deformation took place under the condition of amphibolite facies and the later transitional ductile-brittle deformation under the condition of greenschist facies. The hanging walls moved southeastward during both of these two events. The 40Ar/39Ar dating of muscovites from muscovite-plagioclase schists in the Haizhou phosphorous mine, which are structurally overlain by UHPM rocks, yields a plateau age of 218.0±2.9 Ma and isochron age of 219.8Ma, indicating that the earlier event of the ampibolite-facies deformation probably took place about 220 Ma ago. The 40Ar/39Ar dating of oriented amphiboles parallel to the movement direction of the hanging wall on a decollement plane yields a plateau age of 213.1±0.3 Ma and isochron age of 213.4±4.1 Ma, probably representing the age of the later event. The dating of pegmatitic biotites and K-feldspars near the decollement plane from the eastern Fangshan area yield plateau ages of 203.4±0.3 Ma, 203.6±0.4 Ma and 204.8±2.2 Ma, and isochron ages of 204.0±2.0 Ma, 200.6±3.1 Ma and 204.0±5.0 Ma, respectively, implying that the rocks in the studied area had not been cooled down to closing temperature of the dated biotites and K-feldspars until the beginning of the Jurassic (about 204 Ma). The integration of these data with previous chronological ages on the ultrahigh-pressure metamorphism lead to a new inference on the exhumation of the UHPM rocks. The UHPM rocks in the area were exhumed at the rate of 3-4 km/Ma from the mantle (about 80-100 km below the earth's surface at about 240 Ma) to the lower crust (at the depth of about 20-30km at 220 Ma), and at the rate of 1-2 km/Ma to the middle crust (at the depth of about 15 km at 213 Ma), and then at the rate of less than 1 km/Ma to the upper crust about 10 km deep at about 204 Ma.

Anatexis,Deformation and Exhumation Mechanism for UHP Metamorphic Rocks:A Case Study in the North Qaidam and South Altyn UHP Terrane,Western China

Objective In recent years,hydrous silicate melts by dehydrationdriven in situ partial melting constrained from experiments and natural rocks have been increasingly recognized in UHP rocks,indicating partial melting of UHP slab.Partial melting of UHP metamorphic rocks can dramatically affect the rheology of deeply subducted crust and thus play a crucial role in accelerating the exhumation of UHP slabs.

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

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.

CENOZOIC COLLISIONAL DEFORMATION AND LITHOSPHERE TECTONIC EVOLUTION OF THE EASTERN HIMALAYAN SYNTAXIS

The Eastern Himalayan Syntaxis (EHS) is one of the strongest deformation area along the Himalayan belt resulted from the collision between Indian plate and the Eurasian plate since 50～60Ma, and has sensitivity tracked and preserved the whole collisional processes. It should depend on the detail geological investigations to establish the deformational accommodate mode, and the uplift history, to elucidate the deep structure and the crust\|mantle interaction of the EHS. The Namjabarwa metamorphic complex indented into the Gangdise arc along the sinistral Pai shear fault and the dextral Aniqiao shear fault on the both sides of the Great Canyon of Yalung Zangbo river since the collision of the NE corner of the Indian plate and the Eurasian Plate at 60～70Ma [1] . The distance between Yarlung Zangbo suture and Bangong—Nujiang suture is shortened more 120km in the EHS area than that of the Lhasa block.

Precise Timing of Caledonian Structural Deformation Chronology and Its Implications in Southeast Qilian Mountains, China

The middle Qilian orogenic belt and Lajishan orogenic belt, both of which were formed in the Caledonian, strike NW-SE direction across southeast Qilian Mountains and their basement consists of pre-Caledonian metamorphic rocks with lozenge-shaped ductile shear zones in the crystalline basement. The blunt angle between the conjugated ductile shear zones ranges from 104° to 114°, indicating approximate 210° of the maximum principal stress. The plateau ages of muscovite ^40Ar/^39Ar obtained from the mylonitized rocks in the ductile shear zones of Jinshaxia-Hualong-Keque massif within the middle Qilian massif are （405.1±2.4） Ma and （418.3±2.8） Ma, respectively. The chronology data confirm the formation of ductile shear zones in the Caledonian basement metamorphic rocks during the Caledonian orogeny. Furthermore, on the basis of basement rock study, precise timing for the closing of the Late Paleozoic volcanic basin （or island-arc basin） and Lajishan ocean basin is determined. This provides us a new insight into the closing of ocean basin in the structural evolution of orogenic belt.

MESOZOIC REGIONAL METAMORPHISM IN WESTERN HILLS,BEIJING,CHINA:A REVIEW

Mesozoic regional metamorphism took plaee in Western Hills of Beijing, China, in which platformal and diwa struetural layers were involved. In Zhoukoudian, south of Western Hills, there was low-amphibolite facies in the Triassie as staurolite and kyanite zones were confined to decollements: with decroue in the temperature and pressure in the Jurassic,greenschist facies appeared when chloritoid and andaulusite rones were formed extensively.Intraformational folds and bedding-parallel ductile shear zones are common in Zhoukoudian where regional metamorphism is relatively strong. These phenomena are seldom seen in diwatype orogens and deserve further tesearch in the future.

基于改进切线角理论的十堰市变质岩滑坡预警阈值研究

十堰市地形地貌复杂,地层岩性多变,变质岩广泛分布,区内滑坡灾害多发。为减轻滑坡灾害带来的严重危害,实现滑坡灾害的准确预警,基于改进切线角理论,结合累积加速度及累积加加速度,选取十堰市4个已发生破坏的变质岩滑坡地表位移监测数据。通过绘制其T-t曲线、累积加速度-时间曲线、累积加加速度-时间曲线,分析得到了十堰市变质岩滑坡蠕滑阶段的综合划分结果。确定临滑预警阈值判据为:T-t曲线切线角大于等于80°、累积加速度大于0,并且增长保持较大正值、累积加加速度大于0,且连续增长或保持高值。研究成果对十堰市变质岩滑坡的监测预警工作具有重要意义,同时也可为其他类型滑坡的监测预警阈值研究提供参考。

滇中地区戌街石墨矿矿体特征及区域找矿

云南牟定戌街晶质石墨矿矿体赋存于早元古代普登岩组,经历古元古代末期、青白口纪晚期的变质变形。区内圈定2条具工业意义的细晶-微晶石墨矿、细晶-粗粉晶石墨矿矿体,矿石为石墨白云母片岩型、石墨白云母石英片岩型,工业矿平均品位4.68ω%。为区域(沉积)白云母片岩-白云母石英片岩组合变质型矿床;对戌街石墨矿的成因分析、地质勘查及指示滇中地区区域找矿有较为明显的意义。

Precise timing of the Early Paleozoic metamorphism and thrust deformation in the Eastern Kunlun Orogen

In Dulan County, Qinghai Province NW China, the arc volcanic sequences in the northern side of the Central Fault of the East Kunlun were metamorphosed progressively from upper greenschist facies in the south to epidote-amphibolite facies in the north. High-angle thrust deformation was developed synchronously with the peak metamor-phim and superimposed with later low-angle striking-slip deformation. Zircon U-Pb dating yields a concordant age of (448±4) Ma for the metavolcanics. Syn-kinematic hornblende and muscovite separated from the high-angle thrusting belt give 40Ar-39Ar plateau age of (427±4) Ma and 408 Ma, respectively. These results precisely constrain the timing of the closure of early Paleozoic volcanic basin (Proto-Tethys) over the eastern portion of the East Kunlun Orogen, and the thrust tectonic slice had a cool rate of ca. 9°C/Ma.

Extensional deformation of post ultrahigh-pressure metamorphism and exhumation process of ultrahigh-pressure metamorphic rocks in the Dabie massif,China

A detailed tectonic analysis demonstrates that the present observed regional tectonic configuration of the ultrahigh-pressure metamorphic terrane in the Dabie massif was mainly formed by the extension processes of the post-Indosinian continent-continent oblique collision between the Sino-Korean and Yangtze cratons and ultrahigh-pressure metamorphism (UHPM). The configuration is characterized by a regional tectonic pattern similar to metamorphic core complexes and by the development of multi-layered detachment zones. On the basis of the identification of compressional and extensional fabrics, it is indicated that the exhumation and uplift of ultrahigh-pressure (UHP) metamorphic rocks from the mantle depth to the surface can be divided into at least three different decompression retrogressive metamorphism and tectonic deformation stages, in which the subhorizontal crustal-scale extensional flow in the middle-lower crust under amphibolite facies conditions is an important geodynamic process in the exhumation of UHP metamorphic rocks. Moreover, the extensional flow is probably driven by delamination and magmatic underplating of thickened lithospheric mantle following the continental oblique collision.

Sequence of Ductile Shear Zones in UHP Metamorphic Province with in Dabie Massif,China

Structural studies in the Dabie massif show that distribution of strain is extremely heterogeneous and illustrates the pattern of deformation partitioning in the ultra high pressure (UHP) metamorphic province on all scales. Based on the field structural analysis along with microstructural observation, at least five widespread episodes of ductile shear zone systems are identified by using geometric, kinematic and rheological indicators and they constitute a shear zone sequence in the UHP metamorphic province within the Dabie massif (DM), China. Each shear zone system, for example, the UHP eclogite facies shear zone system in the sequence, exhibits its own features including geometric styles, mineral assemblages, metamorphic pt conditions and deformation regimes during the formation of such shear zone system. Detailed macro and micro scopical features of different episodes of the shear zones are given with respect to mechanism of strain localization and deformation partitioning. The tectonic significance during the creation and exhumation of the UHP metamorphic rocks is evaluated briefly, as well. It is argued that the ductile shear zones in the UHP metamorphic province play an important role in the Dabie mountain building geodynamic process.

Deep-seated large-scale toppling failure in metamorphic rocks：a case study of the Erguxi slope in southwest China

Deep-seated large-scale toppling failure presents unique challenges in the study of natural slope deformation process in mountainous regions.An active deep-seated toppling process was identified in the Erguxi slope located in southwest China,which affected a large area and damaged critical transportation infrastructure with the volume of the deforming rock mass exceeding 24×10~6 m^3.It poses significant risks to the downstream Shiziping Hydropower Station by damming the Zagunao River.Field investigation and monitoring results indicate that the deformation of the Erguxi slope is in the advanced stage of deep-seated toppling process,with the formation of a disturbed belt but no identifiable master failure surface.It was postulated that the alternating tensile and shear strength associated with the hard/soft laminated rock strata of metasandstone and phyllite layers preclude the development of either a tensile or shear failure surface,which resulted in the continuous deformation and displacement without a catastrophic mass movement.The slope movement is in close association with the unfavorable geological conditions of the study area in addition to the construction of transportation infrastructure and the increase of the reservoir level.On the basis of the mechanism and intensity of the ongoing toppling deformation,a qualitative grading system was proposed to describe the toppling process and toevaluate the slope stability.This paper summarized the field observation and monitoring data on the toppling deformation for better characterizing its effect on the stability of the Erguxi slope.The qualitative grading system intends to provide a basis for quantitative study of large-scale deep-seated toppling process in metamorphic rocks.

Characteristics of Metamorphic Rock Magnetic Fabrics in the Nyalam Area of the Southern Tibet and Its Geological Significance, China

This paper reports Precambrian rock magnetic fabrics in the Nyalam area of southern Tibet. The analytical results of magnetic fabrics show that the values of H are high （〉 10% in general）, so the ductile deformations of the Precambrian rock are strong. The orientation of the maximum principal stress inferred from the minimum magnetic susceptibility is nearly S-N, NE-SW and NW-SE. The Flinn diagram of the magnetic fabrics show that the strain pattern is oblate and constrictional type. Magnetic foliation of great majority of rock samples is well developed and the magnetic lineation is poor and the magnetic susceptibility ellipsoid is flattened. The magnetic lineation of the minority rock samples is well developed and the magnetic foliation is poor and the magnetic susceptibility ellipsoid is prolate. According to the geological field and the magnetic fabrics, there are 3 times tectonic stress field in SN directed extruding, NW-SE directed extruding, NW-SE directed extension. It shows that the Nyalam area has undergone process the orientation of SN, NW-SE nappe structure and NW-SE directed extension structure. The change of tectonic stress is reflected by the field characteristics of the Precambrian rock magnetic fabrics that is the direct responding result of the arc-continental, continent-continental collision between the India and Asian continents in the late part of the Late Cretaceous to Late Eocene and subsequently shifted to intra-continental convergent, the plateau uplifting and extension structure stage since the Late Eocene.

New Recognition of Spiral-shaped Porphyroblast Inclusion Trails From Orogenic Belts: an Effective Means to Determine History of Early Deformation and Metamorphism——With Lancang Metamorphic Belt of Western Yunnan as an Example

1 A Method of Determining Early Deformation and Metamorphism History in Orogenic Belts Porphyroblast inclusion trails from orogenic belts represent early-formed foliations composed of oriented metamorphic minerals preserved in rocks in the processes of porphyroblast growth (i.e. progressive and retrogressive metamorphism). Since they were studied in the 1920s, such inclusion trails have been recognized as products of syntectonic rotation due to progressive ductile deformation, which may be used as a known

Tonian–Ediacaran Tectonometamorphic History of the Sa'al Complex,Sinai(Egypt):Implications for the Tectonostratigraphic Framework of the Northern Arabian–Nubian Shield

The Sa'al Metamorphic Complex(SMC;southern Sinai)encompasses the oldest arc rocks in the Arabian–Nubian Shield,comprising two non-consanguineous metavolcanic successions(the Agramiya Group and the Post-Ra'ayan Formation)separated by the metasediments of the Ra'ayan Formation.It experienced three distinct deformational events(D_(1)–D_(3))and two low-medium grade regional metamorphic events(M_1–M_(2)).The Agramiya Group and the Ra'ayan Formation experienced all tectonometamorphic events(D_1–D_(3)and M_(1)–M_(2)),whereas the Post-Ra'ayan volcanic rocks were only affected by the D_(3)and M_(2)events.D_(1)is an extensional event and is connected to the late Rodinia break-up(~Tonian;900–870 Ma).The M_(1)metamorphism variably affected the older Agramiya Group,the rhyolitic tuffs experiencing lower to upper greenschist facies conditions and the basic and intermediate volcanic rocks undergoing amphibolite facies metamorphism.The Ra'ayan Formation metasediments experienced upper greenschist to amphibolite facies metamorphism.The upper greenschist facies M_(2)affected the youngest Post-Ra'ayan volcanic rocks and other stratigraphic successions.The compressive D_(2)and D_(3)events were coeval with the accretion of dismembered terranes in the assembly of Gondwana.D_(2)can be linked to the Tonian–Cryogenian arc-arc assembly(~880–760 Ma;in Elat and Sinai),whereas D_(3)and the accompanying M_(2)is constrained to 622–600 Ma(Ediacaran).

江苏沉积变质型磷矿构造制约机制与找矿方向

江苏沉积变质型磷矿带位于大别—苏鲁造山带东段,锦屏岩组是带内唯一赋矿地层,因其遭受过多期强烈变形变质作用改造,层序杂乱,勘查难度大。通过对磷矿带内各矿床地质特征的研究,查明区域早期复式褶皱构造控制着带内磷矿体的空间分布、厚度及品位,晚期复式褶皱构造制约着含磷岩系的总体分布;结合区域及各矿区的地球物理资料,建立了覆盖区隐伏磷矿的地球物理勘查模型,认为在面积性重力高异常区内,局部叠加剩余重力高异常,且伴随平缓正磁异常的地段是隐伏磷矿勘查的首选目标;通过钻探进行验证,在此基础上圈定了3处找矿靶区,为后续磷矿勘查指明了方向。

吉林省大横路铜钴矿复杂的沉积-变质变形-热液作用演化过程及其对钴的赋存状态和富集成矿的制约

吉林省白山市大横路铜钴矿为国内少有的沉积-变质变形-热液等多种成因叠加改造的大型钴矿床,是综合研究古元古代造山带钴复杂成矿作用过程的理想地区。目前,有关该矿床中钴的赋存状态、富集迁移规律及复杂的成矿过程等方面的研究十分薄弱。本文采集矿床内典型钻孔样品,通过精细的矿相结构观察、扫描电镜物相分析、X射线元素面扫描和矿物成分定量分析等综合研究,发现大横路铜钴矿床经历了多期多阶段复杂的沉积-变质变形-热液作用,钴主要以Co的独立矿物(硫镍钴矿和辉砷钴矿),类质同象进入富Co黄铁矿和在磁黄铁矿中发育钴镍黄铁矿出溶体等形式存在。该矿床成矿作用分为以下5个阶段:沉积阶段以黄铁矿-磁黄铁矿-黄铜矿呈极细粒包体零星分布为特点;变质变形阶段以硫镍钴矿-磁黄铁矿-黄铜矿组合沿绢云母-黑云母-石英变质千枚理定向分布为特点,变质程度达高绿片岩相;早期热液作用主要沉淀粗大脉状磁黄铁矿及其钴镍黄铁矿出溶体;中期热液作用以条带状自形富Co黄铁矿和硫镍钴矿为标志,该阶段为Co富集成矿的主成矿期;网脉状黄铜矿沉淀对应于最晚期热液作用,同时发育极少量细粒辉砷钴矿。矿体的蚀变类型以硅化、碳酸盐化、钠长石化和绿泥石化为主,次为钾长石化和绢云母化。其中,硅化、铁白云石化和钠长石化蚀变稍早于金属硫化物形成,为金属硫化物的沉淀与富集提供了有利条件;辉砷钴矿的沉淀与钠长石的绿泥石化、钾长石化和绢云母化等蚀变作用关系密切。由此可见,多期多阶段沉积-变质变形-热液事件对Co的迁移-富集起着关键的控制作用,不同的变质变形-热液演化阶段均存在富Co硫化物的沉淀,Co的赋存形式也存在明显差异。富Co黄铁矿和硫镍钴矿为大横路铜钴矿Co最主要的赋存形式。综上所述,在辽-吉古元古造山带形成演化过程中,大横路大型铜钴矿钴的富集成矿经历了沉积-变质变形-多期热液叠加改造的复杂演变过程,可称之为造山型铜钴矿床。原始的沉积作用为钴矿的预富集提供了重要的成矿条件,古元古代造山过程及其伴随的区域变质变形事件对钴的初始活化-迁移起着关键的控制作用,后期热液叠加改造事件主导了钴的迁移-超常富集成矿过程。

Tectonic evolution of the Dabieshan orogen: In the view from polyphase deformation of the Beihuaiyang metamorphic zone

The Beihuaiyang metamorphic zone was formed by the Early Mesozoic collision of the North and South China Blocks. It consisted of the Foziling and Luzhenguan complexes and was thought to have never afforded a deep subduction. A similar feature of the deformation in the Dabieshan UHP metamorphic rocks implies that these different tectonic units share the same geodynamic background. The early stage of deformation can be preserved on account of their relatively shallower subduction than that for UHP rocks. On the basis of an analysis of the geo- logical structure and geochronological results, five deformational stages have been recognized: a D1-Early compressional deformation which represents the continental subduction; a D2-Early exhumation deformation producing a syn-convergence exhumation; a D3-Main deformation, represented by an exhumation deformation with Late Triassic age; a D4-Doming and its margin extensional gravity collapse deformation and finally a D5-regional extensional deformation of Cretaceous that was mostly introduced by the migmatization and plutonism.