Multistage Extension and Age Dating of the Xiaoqinling Metamorphic Core Complex,Central China

Abstract There are two extensional systems in the Xiaoqinling metamorphic core complex (XMCC). One is the detachment fault system developed along the peripheries of the XMCC, which extended in an ESE-WNW direction and whose upper plate moved towards the WNW. The other extensional system includes the retrograde shear zones and normal faults developed within the XMCC, which represent the collapse of the XMCC. Ar-Ar and K-Ar dating shows that the extension of the detachment fault system continued from 135 to 123 Ma, i.e. in the late stage of its evolution at about 127 Ma. The collapse represented by the extensional system within the XMCC was operative during 120–106 Ma, and its main activity occurred about 116 Ma ago. These suggest that the XMCC experienced two extensional stages in its evolution, i.e., the syn-orogenic regional extension and post-orogenic collapse extension.

Extension of the Louzidian Metamorphic Core Complex and Development of Supradetachment Basins in Southern Chifeng,Inner Mongolia,China

The Louzidian metamorphic core complex (LMCC) in southern Chifeng is located on the northern margin of the North China craton. Structural analyses of the LMCC and its extensional detachment system indicate that the LMCC experienced two-stage extension. The ductile regime experienced top-to-northeast shearing extension and the brittle detachment fault underwent top-down-outwards slipping. Between these two stages, a semi-ductile regime recorded the transition from ductile to brittle. The hanging wall of the detachment fault is similar to those classic supradetachment basins in western North America. Analyses of provenance and paleocurrent directions in the basins show that there were two filling stages. In the early stage, materials came from the southwest margin of the basin and the hanging wall of the detachment system and were transported from southwest to northeast; while in the late stage, deposits were derived from the footwall of the detachment fault and transported outwards to the two sides of the core complex. Since the filling period of the basins is from the late Jurassic to the late Cretaceous and it is coeval with the extension, the two filling stages reflect the two-stage history of the detachment fault. The large-scale late Jurassic underplating in the deep crust of the Chifeng area led to thickening and heating of the middle-upper crust and trigged the extension at depths and volcanism on the surface. In the early Cretaceous the upper plate of the detachment fault moved northeastwards and sediments were transported from southwest to northeast, while in the late Cretaceous the core complex was uplifted rapidly, the original basin was separated by the uplifted core, and lower-plate-derived debris was deposited in the adjacent upper-plate basins of the detachment fault. Evidentially, the development of the supradetachment basins were controlled by the extension and in turn the fillings in the basins recorded information of the extension, which has provided new evidence for kinematic interpretation of the Louzidian core complex.

Application of General Shear Theory to the Study of Formation Mechanism of the Metamorphic Core Complex:A Case Study of Xiaoqinling in Central China

The kinematic vorticity number and strain of the mylonitic zone related to the detachment fault increase from ESE to WNW along the moving direction of the upper plate of the Xiaoqinling metamorphic core complex (XMCC) and the geometry of quartz c-axis fabrics changes progressively from crossed girdles to single girdles in the same direction. Therefore, pure shear is dominant in the ESE part of the XMCC while simple shear becomes increasingly important towards WNW. However, the shear type does not change with the strain across the shear zone, thus the variation of shear type is of significance in indicating the formation mechanism. The granitic plutons within the XMCC came from the deep source and their emplacement was an active and forceful upwelling prior to the detachment faulting. The PTt path demonstrates that magmatism is an important cause for the formation of the XMCC. The formation mechanism of the XMCC is supposed to be active plutonism and passive detachment. Crustal thickening and magmatic doming caused necking extension with pure shear, and magmatic heating and doming resulted in detachment extension with simple shear and formed the XMCC.

The Liaonan Metamorphic Core Complex: Constitution, Structure and Evolution

The Liaonan metamorphic core complex （mcc） has a three-layer structure and is constituted by five parts, i.e. a detachment fault zone, an allochthonous upper plate and an supradetachment basin above the fault zone, and highly metamorphosed rocks and intrusive rocks in the lower plate. The allochthonous upper plate is mainly of Neoproterozoic and Paleozoic rocks weakly deformed and metamorphosed in pre-Indosinan stage. Above these rocks is a small-scale supradetachment basin of Cretaceous sedimentary and volcanic rocks. The lower plate is dominated by Archean TTG gneisses with minor amount of supracrustal rocks. The Archean rocks are intruded by late Mesozoic synkinematic monzogranitic and granitic plutons. Different types of fault rocks, providing clues to the evolution of the detachment fault zone, are well-preserved in the fault zone, e.g. mylonitic gneiss, mylonites, brecciated mylonites, microbreccias and pseudotachylites. Lineations in lower plate granitic intrusions have consistent orientation that indicate uniform top-to-NW shearing along the main detachment fault zone. This also provides evidence for the synkinematic characteristics of the granitic plutons in the lower plate. Structural analysis of the different parts in the mcc and isotopic dating of plutonic rocks from the lower plate and mylonitic rocks from detachment fault zone suggest that exhumation of the mcc started with regional crustal extension due to crustal block rotation and tangential shearing. The extension triggered magma formation, upwelling and emplacement. This event ended with appearance of pseudotachylite and fault gauges formed at the uppermost crustal level. U-Pb dating of single zircon grains from granitic rocks in the lower plate gives an age of 130±2.5 Ma, and biotite grains from the main detachment fault zone have ^40Ar-^39Ar ages of 108-119 Ma. Several aspects may provide constraints for the exhumation of the Liaonan mcc. These include regional extensional setting, cover/basement contact, temporal and spatial coupling of extension and magmatism, basin development and evolution of fault tectonites along detachment fault zone. We propose that the exhumation of the Liaonan mcc resulted from regional extension and thinning of crust or lithosphere in eastern North China, and accompanied with synkinematic intrusion of granitic plutons, formation of detachment fault zone, uplifting and exhumation of lower-plate rocks, and appearance of supradetachment basin.

Metamorphic Core Complexes and Its Significance in the Continental Crustal Evolution

Metamorphic core complexes are a basic structural pattern related to extensional tectonics. Several characteristics of different scales of metamorphic core complexes in the Fangshan and Yunmengshan (Beijing) , Zhongtiaoshan (Shanxi) , and Dengfong (Henan) are examined. A three-layer model for metam orphic core complexes is suggested . The conclusion is that metam orphic core complexes are the result of multiphase intracontinental crustal extensions and are an important tectonic pattern. which exposes the basement metam orphic rocks to the ground surface in the intracontinental cover .

Numerical modeling of metamorphic core complex formation:Implications for the destruction of the North China Craton

Widespread magmatism, metamorphic core complexes(MCCs), and significant lithospheric thinning occurred during the Mesozoic in the North China Craton(NCC). It has been suggested that the coeval exhumation of MCCs with uniform northwest-southeast shear senses and magmatism probably resulted from a decratonization event during the retreat of the paleo-Pacific Plate. Here we used two-dimensional finite element thermomechanical numerical models to investigate critical parameters controlling the formation of MCCs under far-field extensional stress. We observed three end-member deformation modes: the MCC mode, the symmetric-dome mode, and the pure-shear mode. The MCC mode requires a Moho temperature of ≥700 ℃ and an extensional strain rate of ≥5 × 10^(-16)s^(-1), implying that the lithosphere had already thinned when the MCC was formed in the Mesozoic. Considering that the widespread MCCs have the same northwest-southeast extension direction in the NCC, we suggest that the MCCs are surface expressions of both large-scale extension and craton destruction and that rollback of the paleo-Pacific slab might be the common driving force.

Structural Analysis of Jianglang Metamorphic Core Complex in Western Margin of yangtze Crston,Sichuan Province

There is a belt of metamorphic core complexes in the western margin of the Yangtze craton . The geological setting of the belt is similar to that of the Cordilleran metamorphic core complexes . A typical one in this belt is the Jianglang metamorphic core complex , which has a configuration consisting of three layers : a core complex consisting of Mesoproterozoic schist sequence . a ductile middle slab consisting of Paleozoic meta- sedimentary -basalt characterized by the development of ' folding layer' and an upper cover consisting of Xikang Group which has suffered both buckling and flattening . A detachment fault developed along the contact boundary between the cover and basement causes the omission of Upper Sinian and Cambrian at the base of cover . A lot of normal ductile shear zones developed in the cover causes the thinning of it . All the features show that the early extension results in the thinning of crust , but the formation of the dome and exposure of basement rocks may be the results of superimposing of the E-W directed contraction and the following southward thrusting during Indosinian to Yanshanian orogeny . Syntectonic plutonism and pervasive thermo - metamor-phism in the cover suggest that the thermal uplift also causes the uplift of the MCC .

FEM simulation of formation of metamorphic core complex with ANSYS software

This study utilizes ANSYS to establish FEM's model of metamorphic core complex,and used thermal-structure analysis to simulate metamorphic core complex's temperature field and stress field.The metamorphic core complex formation mechanism is discussed.The simulation results show that the temperature field change appearing as the earth surface's temperature is the lowest,and the temperature of metamorphic core complex's nucleus is the highest.The temperature field is higher along with depth increase,and the stress field change appearing as the biggest stress occurs in the nucleus.The next stress field occurs at the top of the cover.

The Wulian Metamorphic Core Complex: A Newly Discovered Metamorphic Core Complex along the Sulu Orogenic Belt, Eastern China

Combined with field studies, microscopic observations, and EBSD fabric analysis, we defined a possible Early Cretaceous metamorphic core complex （MCC） in the Wulian area along the Sulu orogenic belt in eastern China. The MCC is of typical Cordilleran type with five elements： （1） a master detachment fault and sheared rocks beneath it, a lower plate of crystalline rockswith （2） middle crust metamorphic rocks, （3） syn-kinematic plutons, （4） an upper plate of weakly deformed Proterozoic metamorphic rocks, and （5） Cretaceous volcanic-sedimentary rocks in the supradetachment basin. Some postkinematic incursions cut across the master detachment fault zone and two plates. In the upper plate, Zhucheng （诸城） Basin basement consists of the Proterozoic Fenzishan （粉子山） Group, Jinning period granite （762–834 Ma）. The s u pr a de tac hme nt ba sin a bo ve the Proterozoic rocks is filled with the Early Cretaceous Laiyang （莱阳） （~135–125 Ma） and Qingshan （青山） groups （120–105 Ma）, as wellas the Late Cretaceous Wangshi （王氏） Group （85–65 Ma）. The detachment fault zone is developed at the base and margin of the superposed basin. Pseudotachylite and micro breccia layers located at the top of the detachment fault. Stretching lineation and foliation are well developed in the ductile shear belt in the detachment faults. The stretching lineation indicates a transport direction of nearly east to west on the whole, while the foliations trend WNW, WSW, and SE. Protomylonite, mylonite, and ultramylonite are universally developed in the faults, transitioning to mylonitic gneiss, and finally to gneiss downward. Microstructure and quartz preferred orientation show that the mylonites formed at high greenschist facies to low greenschist facies as a whole. The footwall metamorphic rock series of the Wulian MCC are chiefly UHP （ultrahigh pressure） metamorphic rocks. Syntectonic rocks developed simultaneously with the Wulian MCC detachment and extension. Geological research has demonstrated that the MCC is associated with small-scale intrusive rocks developing in the vicinity of the detachment faults, for instance, dike. Geochronology results indicate that the denudation of the Wulian MCC occurred at about 135–122 Ma. Its development and exhumation was irrelevant to the Sulu UHP metamorphism zone rapid exhumation during Triassic Period but resulted from the crustal extension of North China Craton and adjacent area.

Oxygen-evolving Activity in Photosystem II Core Complex of Photosynthetic Membrane in the Presence of Native Lipid

The techniques of oxygen electrode polarography and Fourier transform infrared (FT IR) spectroscopy were employed to explore the involvement of digalactosyl diacylglycerol (DGDG) in functional and structural roles in the photosystem II core complex (PSIICC). It was shown that DGDG exhibited the ability to stimulate the oxygen evolution in PSIICC, which was accompanied by the changes in the structures of PSIICC proteins. The results revealed that there existed hydrogen bonding interactions between DGDG molecules and PSIICC proteins. It is most likely that the sites of PSIICC interaction with DGDG are in the extrinsic protein of 33 kDa.

AN ENORMOUS THRUST NAPPE AND EXTENSIONAL METAMORPHIC CORE COMPLEX NEWLY DISCOVERED IN SINO-MONGOLIAN BOUNDARY AREA

An enormous thrust nappe and a metamorphic core complex of extensional origin have been recently discovered within the Hercynian-Indosinian orogen of Inner Mongolia. Both features are of the Mesozoic age, but the former is older. The thrust nappe strikes WNW-ESE and Proterozoic dolomite was thrust southwards atop strata ranging from the Cambrian to the Triassic in age. The visible displacement of the thrust is ca. 70 km and the deduced one is over 140 km. The metamorphic core complex (mainly mylonites) extends in an N-E direction, forming itself into a dome geometry and lying under an extensional detachment fault. The mylonitic foliation dips gently and the stretching mineral lineation, as a whole, plunges SSE. Various shear sense markers show a normal-sense shear movement. Some significant problems atise from the coexistence of nappe and extensional structures at a postoro-genic stage.

Genesis of the Hongzhen metamorphic core complex and its tectonic implications

The Hongzhen metamorphic core complex is situated in the Yangtze plate to the east of the Dabie oro- genic belt. Its ductile detachment zone in the foot wall overprints on the metamorphic complex of the Proterozoic Dongling Group. The present profile of the ductile shear zone with consistent SW-dipping mineral elongation lineation shows antiform and reversed S-shape from northeast to southwest respectively. Exposure structures, microstructures and quartz C-axis fabric all indicate top-to-SW movement for the ductile shear zone. Recrystallisation types of quartz and feldspar in the mylonites demonstrate that the shear zone was developed under the amphibolite facies condition and at mid-crust levels. The metamorphic core complex formed in the Early Cretaceous with a muscovite plateau age of 124.8±1.2 Ma. Regional NE-SW extension along a SW-dipping, gentle detachment zone was responsible for formation of the core complex. Intrusion of the Hongzhen granite with a biotite plateau age of 124.8±1.2 Ma rendered the ductile shear zone curved, uplifted and final localization of the core complex. The Hongzhen metamorphic core complex suggests that the Early Cretaceous magma- tism in this region took place under the condition of regional extension and the eastern Yangtze plate also experienced lithospheric thinning.

Deformation characteristics and formation mechanism of the Yunmengshan metamorphic core complex

The Yunmengshan metamorphic core complex in the middle part of the Yanshan Fold and Thrust Belt records crust extension processes of the eastern North China Craton during its peak destruction.Development of the metamorphic core complex was controlled by the generally NNE-striking Dashuiyu Shear Zone.The shear zone dips SE and becomes shallower NE-wards,leading to exposures of a ductile shear zone in the southern and middle parts and brittle faults in the northern part.Exposure structures,microstructures,and quartz C-axis fabrics indicate that the ductile shear zone belongs to an extensional shear zone with a top-to-the-SE shear sense.Deformation temperatures of 300–520°C suggest a midcrustal origin for the ductile shear zone.A ductile deformation belt in the footwall of the shear zone is only as wide as 1–3 km,indicating no widespread mid-crustal ductile flow in the region during the deformation.Zircon U–Pb dating of dykes and plutons as well as hornblende and biotite40Ar/39Ar dating demonstrate that the metamorphic core complex originated at 135 Ma and experienced intense shearing of the Dashuiyu Shear Zone,development of the supradetachment basins,and synkinematic intrusion during 135–125 Ma.The metamorphic core complex was subjected to rapid exhumation during 125–114 Ma when the Dashuiyu Shear Zone suffered continuous activity and passive doming.The shear zone and its hanging wall were cut or replaced by a series of brittle faults when they wereuplifted to a brittle regime,showing that exhumation took place in continuous extensional activities.The metamorphic core complex turned into slow exhumation in an extensional regime in the following latest Early Cretaceous.The evolution history suggests that the Yunmengshan metamorphic core complex was developed by the rolling-hinge model,a common formation mechanism for intraplate metamorphic core complexes in the North China Craton,under the continuous NW–SE extension during the Early Cretaceous(135–100 Ma).

Structure, evolution and regional tectonic implications of the Queshan metamorphic core complex in eastern Jiaodong Peninsula of China

The Queshan MCC is an important example of a crustal extensional structure in the eastern Jiaodong Peninsula along the southeastern margin of the NCC in the Early Cretaceous. The MCC is a typical Cordilleran-type core complex with a three-layered structure:(1) the upper plate is constituted by the Cretaceous supradetachment basin and Paleoproterozoic basement;(2) the lower plate comprises the Neoarchean high-grade metamorphic complexes and late Mesozoic granitic intrusions; and(3) the two plates are separated by a master detachment fault. A series of late NEN-oriented brittle faults superimposed on and destructed the early MCC. Petrology, geometry, kinematics, macro- and micro-structures and quartz c-axis fabrics imply that the MCC has a progressive exhumation history from middle-lower to subsurface level(via middle-upper crustal level) under the nearly WNW-ESE regional extensional regime. We present structural and geochronological evidence to constrain the exhumation of the Queshan MCC from ca. 135 to 113 Ma. Based on the comprehensive analysis of the different patterns of extensional structures in the Jiaodong and Liaodong Peninsula, we have defined the Jiao-Liao Early Cretaceou extensional province and further divided the crustal extension of it into two stages: the first stage was the intense flow of the middle-lower crust and the second stage was the extension of the middle-upper crust. Combining the tectonic setting, the lithosphere thinning in the Jiao-Liao Early Cretaceous extensional province can be considered a typical model for the response of crust-mantle detachment faulting under regional extension in East Asia.

Thermal stability of oxygen evolution in photosystem Ⅱ core complex in the presence of digalactosyl diacylglycerol

The influence of digalactosyldiacylglycerol (DGDG), one of the photosynthetic membrane lipids, on heat inactivation of the process of oxygen evolution has been studied in vitro in photosystem Ⅱ(PS Ⅱ) core complex. It was found that the temperature of semi-inactivation of oxygen evolution in the complex increased from 40.0 to about 43.0℃ in the presence of DGDG with 5-min heat treatment in the dark. Furthermore, when PS Ⅱ core complex was incubated for 5 min at 45.0℃, the oxygen evolution in the complex was completely lost, whilst the DGDG-complexed PS Ⅱ core complex still retained a 16% of activity (100% for 25.0℃). In addition, a 1-h incubation at 38.0℃ inactivated absolutely the oxygen evolution for the PS Ⅱ core complex. By contrast, there remained about 20% of activity (zero time for 100%) for the complex in the presence of DGDG under the same condition. These results indicate a new role of DGDG in the protection of PS Ⅱ core complex against the deleterious effects of temperature. It was

Deformation characteristics and genesis of the Waziyu metamorphic core complex in western Liaoning of China

The Waziyu metamorphic core complex is situated at the eastern end of the Yanshan tectonic belt.The NNE-striking detachment ductile shear zone in the core complex lies between the Archean metamorphic basement and Fuxin-Yixian rift basin,dips NW gently,and shows corrugation folds.Exposure structures,microstructures,and quartz C-axis fabrics all indicate top-to-the WNW sense of shear,i.e.,ca.285°,for the shear zone.Estimates of the deformation temperatures(ca.550-250°C) demonstrate its mid-crustal origination and progressive deformation from deep to shallow levels.The northern segment of the shear zone shows relatively weak exhumation with exposures of low-temperature mylonites whereas its middle and southern segments have more intense uplifting with exposures of high-temperature mylonites.Biotite and muscovite 40 Ar/39 Ar ages,U-Pb dating results of zircon from dikes and plutons as well as formation ages of the supra-detachment basin all suggest the formation time of 135-100 Ma for the core complex.The formation was also associated with syntectonic emplacement of the Early Cretaceous Shishan pluton.The western margin of the core complex was truncated by the Sunjiawan-Shaohuyingzi brittle normal fault when it uplifted to shallow crust levels,and finally exhumed to near-surface levels.The core complex was developed by the rolling-hinge model under WNW-ESE extension during the Early Cretaceous peak destruction of the North China Craton.Ductile flow did not appear in the lower plate,therefore not supporting the low-crust gravitational collapse.

Determining the key conditions for the formation of metamorphic core complexes by geodynamic modeling and insights into the destruction of North China Craton

Metamorphic core complex(MCC) is characterized by the exhumation of lower crust over a large-scale detachment fault, providing natural records for tectonic extension. MCCs are widely identified in the North China Craton(NCC), which have been intensively studied on their structural and geological characteristics. Yet, the condition for the formation of MCCs and their link with NCC destruction are still in debate. In this study, we perform numerical simulations to investigate MCC formation under extension, with a focus on the effect of crustal rheologies. Results indicate that three end-member modes of deformation may occur: the metamorphic core complex mode, the detachment fault-uplifting mode and the pure shear mode. Weaker lower crust and stronger upper crust may promote the formation of MCC. In contrast, stronger lower crust(>1.3×1021 Pa s) may prohibit the exhumation of lower crust(detachment fault-uplifting mode), while weaker upper crust(<7.8×1021 Pa s) may fail to develop detachment faults(pure shear mode). Given that cratons typically have a strong crust, we suggest that the lower crust of NCC was weakened prior to extension, which promoted the formation of MCC in a later stage under the back-arc extension.

Isolation and characterization of rod-core complex from the phycobilisome of Anabaena variabilis

THE phycobilisomes (PBSs) of A. variabilis, like most other cyanobacteria and red alage,are hemi-discoidal. They contain various phycobiliproteins such as phycoerythrocyanin(PEC), C-phycocyanin (C-PC) and allophycocyanin (APC), and the energy transfer flowscan be examplified by the following scheme: PEC→C-PC→APC. Although the high resolu-tion crystal structures of PEC, C-PC and APC have been determined by X-ray method,

Syn-deformation P-T paths of Xiaoqinling metamorphic core complex

The \%P_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. These \%P_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.

内蒙古大青山-盘羊山晚中生代-早新生代构造事件及其对华北北缘构造演化的启示

内蒙古大青山和盘羊山位于华北克拉通北缘,其复杂的地质构造对华北克拉通北部中—新生代构造演化具有重要的指示作用。大青山以北的盘羊山逆冲体系,形成于晚二叠世至早三叠世古亚洲洋的闭合,晚侏罗世可能受蒙古-鄂霍次克洋闭合的影响而重新活动。大青山地区发育4期中—新生代变形构造,从老至新依次是:SE-NW向伸展形成的呼和浩特变质核杂岩、NW向逆冲的大青山逆冲体系、以不变形花岗岩为核心的构造穹窿、大青山山前断裂及高角度正断层。发生于约142~132 Ma的SE-NW向伸展,形成于造山增厚地壳的重力垮塌,并形成呼和浩特变质核杂岩和相关的拆离体系。大青山逆冲体系形成于约130~120 Ma,代表造山过程中地壳荷载与板块汇聚的抗衡导致的构造反转,另一可能是古太平洋俯冲的远程效应。自约120 Ma以来,大青山处于一个构造-热松弛期,导致该区约120~90 Ma的冷却事件被广泛记录,并形成以不变形花岗岩(约114 Ma)为核心的穹窿构造;这些事件可能与华北克拉通的峰期破坏相关。大青山山前断裂和相关的高角度正断层开始于始新世,可能是印度-欧亚大陆碰撞和太平洋板块运动方向改变的远程效应所致。古亚洲洋和蒙古-鄂霍次克洋的闭合导致华北克拉通北缘地壳增厚,引发早白垩世造山晚期的垮塌和伸展,形成呼和浩特变质核杂岩。自120 Ma开始,大青山开始受华北克拉通破坏的影响,并形成后造山伸展。新生代,大青山受新特提斯和太平洋构造域的远程影响。