Coesite inclusions are found in kyanite from the Lanshantou eclogite in the Sulu ultrahigh-pressure (UHP) metamorphic belt. This discovery extends the stable region of kyanite to over 2.4 GPa. As an important UHP meta...Coesite inclusions are found in kyanite from the Lanshantou eclogite in the Sulu ultrahigh-pressure (UHP) metamorphic belt. This discovery extends the stable region of kyanite to over 2.4 GPa. As an important UHP metamorphic belt in China, the Sulu eclogite belt is the product of A-subduction induced by strong compression of the Yellow Sea terrane to the Jiaodong-northereastern Jiangsu terrane during the interaction of the Eurasian plate and Palaeo-Pacific plate in the Indosinian. It stretches about 350 km and contains over 1000 eclogite bodies. Most eclogites in this belt belong to Groups B and C in the classification of Coleman et al., and commonly contain kyanite, while the Lanshantou eclogite belongs to Group A and contains coesite. The MgO, CaO and FeO contents in garnet and pyroxene show regular variation from the core to the rim, which reveals the PTt paths of progressive metamorphism during the Early Mesozoic (240-200 Ma) and retrogressive metamorphism during the Late Mesozoic and Cenozoic exhumation.展开更多
The Curie point depth of continental crust can reflect the regional tectonic pattern and geothermal structures. Analysis of magnetism is an efficient way to obtain the Curie point depth on a regional scale. This study...The Curie point depth of continental crust can reflect the regional tectonic pattern and geothermal structures. Analysis of magnetism is an efficient way to obtain the Curie point depth on a regional scale. This study systematically investigated the Curie point depth of Sulu (苏鲁) ultrahigh pressure (UHP) metamorphic belt (33°40'N to 36°20'N and 118°E to 120°E, ca. 60 000 km^2), eastern China using aeromagnetic data. The results show that the Curie point depth of the Sulu region varies from 18.5 to 27 km. The shallowest Curie point depth (ca. 18.5 km) is located in Subei (苏北) subsidence, where the estimated temperature gradient value is about 31.35℃/km, which is comparable with the measured value of 30 ℃/km. In addition, a two-dimensional numerical solution of the heat conduction was used to calculate the temperature field to a depth of 30 km along the profile from Tancheng (郯城) to Lianshui (涟水) with a length of 139 km. The steady state model solved using the finite element method shows that the temperature around the Curie point depth is about 585.36 ℃, which is close to the Curie temperature (580℃) of magnetite at atmospheric pressure. These results provide new insights into the tectonic and continuous thermal structures of the Sulu UHP metamorphic belt.展开更多
Calibration of seismic reflectors appearing in the crust of the Chinese continent sci- entific drilling site can be completed through the correlation studies between direct evidences, such as the drill cores, and geop...Calibration of seismic reflectors appearing in the crust of the Chinese continent sci- entific drilling site can be completed through the correlation studies between direct evidences, such as the drill cores, and geophysical signatures; therefore the interpretation of geophysical data could produce reliable results of crustal structure and composition. On the other hand, there are two Cenozoic volcanoes close to the scientific drilling site; analyzing composition of xenoliths existent in the volcanoes and evaluating their seismic velocities can also offer information about the mantle and lower crust. After the calibration via cores and well-logging data, the seismic re- flectors appearing in the UHP belt can be caused by lithological changes within the UHP rock slice, ductile shearing rock-suites, and later fracture zones. Among these sources, ductile shearing resulted in displacement and detachment of original rock-sheets, producing some rock-interbeds of several hundred meters thick that are named the ductile shearing rock-suites. A suite consists of mylonized gneiss and eclogite slices that underwent shearing, becoming the major mechanism responsible to generate regional strong reflections. The UHP rock-slice is characterized by complicated structures and high density, high seismic velocity and high electri- cal resistivity, its thickness is usually less than 11 km. Velocity and density of the gneiss-layer beneath gradually tend to normal with increasing depth. Based on the xenoliths we can infer that the middle crust contains a lot of gneisses, and the lower crust consists of different granulites. The lithospheric mantle has multi-layer structures and consists mainly of spinal lherzolite and harzburgite, implying late Mesozoic lithospheric thinning. The seismic fabrics with different ori- gins were possible products of different geodynamic processes. For instance, the UHP rock-slice was produced by the UHP metamorphic process and the exhumation of subducted supercrustal rocks after the Triassic collision between the Yangtze and Sino-Korean cratons; whilst the ductile shearing rock-suites resulted from shearing deformation processes during the subduction and exhumation. The normal velocity below the UHP rock-slice was correlated with Mesozoic exten- sion processes in the area. Through careful calibration of seismic reflectors and analyzing xeno- liths, one can find the relationship between the causes of seismic reflectors and corresponding geodynamic processes, offering a new basis for reconstruction of regional dynamic evolution history.展开更多
The Sulu ultra-high pressure(UHP)metamorphic belt in Eastern China is well known as the eastern extension of the Qingling-Dabie orogenic belt formed by subduction and collision between the Sino-Korean and Yangtze crat...The Sulu ultra-high pressure(UHP)metamorphic belt in Eastern China is well known as the eastern extension of the Qingling-Dabie orogenic belt formed by subduction and collision between the Sino-Korean and Yangtze cratons.The main hole of the Chinese Continental Scientific Drilling(CCSD)project is located at the southern segment of the Sulu UHP metamorphic belt(34°25′N/118°40′E),about 17 km southwest of Donghai County.Integrated geophysical investigations using gravity,magnetic,deep展开更多
A wealth of retrogressive microstructures have been discovered from the UHP metamorphic rocks in Dabie orogenic belt, namely, the ultrahigh-pressure (URP) eclogites, jadeite quartzites and kyanite-zoisite-quartz vein....A wealth of retrogressive microstructures have been discovered from the UHP metamorphic rocks in Dabie orogenic belt, namely, the ultrahigh-pressure (URP) eclogites, jadeite quartzites and kyanite-zoisite-quartz vein. The most important are pseudomorphic replacements of UHP minerals like coesite, the corona reaction textures iuduced by solid-solid reactions as well as the corona and symplectites induced by reactions involving fluid. According to the textural relationships the sequence of mineral Paragenesis and the metamorphic stages in the UHP eclogites can be delineated; the mineral geobarothermometry of the various stages of retrograde metamorphism is studied and a clockwise, nearly isothermal decompressive metamorphic PT-trajectory for the UHP eclogites can be reconstructed. In terms of the PT-trajectory the two stage post collision uplirt and exhumation processes are reflected. When the UHP metumorphic rocks extruded to the lower-middle crust partial melting happened which bad in turn caused tke crustal extension and the further exhumation or the UHP metomorphic rocks. Based on the field strain analysis combined with geochronological data a scenario or post collision uplift aud exhumation model is presented.展开更多
The present-day observable tectonic framework of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts in the Dabie-Sulu region was dominantly formed by an extensional process, mostly between 200 and 1...The present-day observable tectonic framework of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts in the Dabie-Sulu region was dominantly formed by an extensional process, mostly between 200 and 170 Ma, following the Triassic collision between the Sino-Korean and Yangtze cratons. The framework that controls the present spatial distribution of UHP and HP metamorphic rocks in particular displays the typical features of a Cordilleran-type metamorphic core complex, in which at least four regional-scale, shallow-dipping detachment zones are recognized. Each of these detachment zones corresponds to a pressure gap of 0.5 to 2.0 GPa. The detachment zones separate the rocks exposed in the region into several petrotectonic units with different P-T conditions. The geometry and kinematics of both the detachment zones and the petrotectonic units show that the exhumation of UHP and HP metamorphic rocks in the Dabie-Sulu region was achieved, at least in part, by non-coaxial ductile flow in the multi-layered detachment zones, and by coaxial vertical shortening and horizontal stretching in the metamorphic units, under amphibolite- to greenschist-facies conditions, and in an extensional regime. All ductile extensional deformations occurred at depths below 10 to 15 km, i.e. below the brittle/ductile deformation transition.展开更多
The Drillhole ZK703 with a depth of 558 m is located in the Donghai area of the southern Sulu ultrahigh-pressure (UHP) metamorphic belt, eastern China, and penetrates typical UHP eclogites and various non-mafic rocks,...The Drillhole ZK703 with a depth of 558 m is located in the Donghai area of the southern Sulu ultrahigh-pressure (UHP) metamorphic belt, eastern China, and penetrates typical UHP eclogites and various non-mafic rocks, including peridotite, gneiss, schist and quartzite. Their protoliths include ultramafic, mafic, intermediate, intermediate-acidic, acidic igneous rocks and sediments. These rocks are intimately interlayered, which are meters to millimeters thick with sharp and nontectonic contacts, suggesting in-situ metamorphism under UHP eclogite facies conditions. The following petrologic features indicate that the non-mafic rocks have experienced early-stage UHP metamorphism together with the eclogites: (1) phengite relics in gneisses and schists contain a high content of Si, up to 3.52 p.f.u. (per formula unit), while amphibolite-facies phengites have considerably low Si content (<3.26 p.f.u.); (2) jadeite relics are found in quartzite and jadeitite; (3) various types of symplectitic coronas and pseud展开更多
Whether the HP and UHP metamorphic rocks of the Dabie-Sulu orogenic belt are of an "in-situ" or "foreign" origin is a long-standing dispute among geologists. Eclogites preserved today in the HP and...Whether the HP and UHP metamorphic rocks of the Dabie-Sulu orogenic belt are of an "in-situ" or "foreign" origin is a long-standing dispute among geologists. Eclogites preserved today in the HP and UHP units constitute merely 5-10%, which are not isolated exotic bodies tectonically intruding into amphibolite facies gneiss, but remnants of once pervasive or widespread eclogite-facies terranes or slabs. The present spatial distribution and forms of the eclogites have resulted from polyphase and progressive deformation and strain partitioning of the HP and UHP slabs. From their formation in deep mantle to their exhumation to the surface, the eclogites have experienced long-term deformation with different strain regimes. The dominant regime responsible for the present spatial distribution and forms of the eclogites is the shear process. The deformation patterns of the eclogites and gneiss matrix also clearly show that the eclogites were metamorphosed in situ. The original distribution area of the eclogites展开更多
Unusual polyphase inclusions of K-feldspar+quartz+titanite+solid salt and K-feldspar+albite+quartz+epidote with textures similar to the other K-feldspar+quartz inclusions were found in omphacite grains from the Sulu u...Unusual polyphase inclusions of K-feldspar+quartz+titanite+solid salt and K-feldspar+albite+quartz+epidote with textures similar to the other K-feldspar+quartz inclusions were found in omphacite grains from the Sulu ultrahigh pressure (UHP) eclogites. One of these inclusions contain square to round solid salt inclusions of KCl-NaCl composition. Such a mineral assemblage within K-feldspar-bearing inclusions hosted by UHP metamorphic phases suggests that (1) potassium granitic melts enriched in Cl components were presented during UHP metamorphism or at the early stage of rapid exhumation of deeply subducted continental slab; (2) they were resulted from reactions between the incoming granitic melts and quartz (or coesite); and (3) solid salt inclusions of NaCl-KCl were derived from dehydration and desiccation of Cl-bearing melts. Our new observations further demonstrate that during the tectonic evolution of UHP rocks, fertile components within deeply subducted continental materials could undergo partial melting, leading to the formation of Cl-bearing potassium granitic melts and substantial migration of fluid-conservative elements (e.g. Ti, Hf) within the UHP slab.展开更多
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...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.展开更多
Two fresh types of eclogites, namely the massive eclogite and foliated eclogite, are dis- cernible in large eclogite bodies surrounded by country rock gneisses from the Dabie Sulu UHP metamorphic zone. They are diffe...Two fresh types of eclogites, namely the massive eclogite and foliated eclogite, are dis- cernible in large eclogite bodies surrounded by country rock gneisses from the Dabie Sulu UHP metamorphic zone. They are different in mineral assemblage, texture and structure at various scales. The massive eclogite has a massive appearance with a metamorphic inequigranular and grano- blastic texture, which consists mainly of nominally anhydrous minerals such as garnet, omphacite, rutile with inclusions of coesite and rare microdiamond. Massive eclogites which formed at the peak UHP metamorphic conditions (~3.1-4.0 GPa, 800~50 ) within the coesite to diamond stability field recorded the deep continental subduction to mantle depths greater than 100 km during the Triassic (-250-230 Ma). The diagnostic UHP minerals, mineral assemblages and absence of notable macro- scopic deformation indicate the peak metamorphic 'forbidden-zone' P-T conditions, an extremely low geothermal gradient (〈7 "C'kma) and low differential stress. The foliated eclogite is composed of garnet+omphacite+rutile+phengite+kyanite+zoisite+talc+nybtite^coesite/quartz pseudomorphs after coesite. It is quite clear that the foliated eclogite bears relatively abundant hydrous mineral, and shows well-developed penetrative foliation carrying mineral and stretching lineation reflecting intense plastic deformation or flow of eclogite minerals. The foliatcd eclogite occurred at mantle levels and recorded the earliest stages of exhumation of UHP metamorphic rocks. At a map scale, the foliated eclogites de- fine UHP eclogite-facies shear zones or high-strain zones. Asymmetric structures are abundant in the zones, implying bulk plane strain or dominant non-coaxial deformation within the coesite stability field. The earliest stages of exhumation, from mantle depths to the Moho or mantle-crust boundary layering, were characterized by a sub-vertical tectonic wedge extrusion, which occurred around 230-210 Ma. The three- dimensional relationship between the massive and foliated eclogites is well displayed a typical 'block-in-matrix' rheological fabric pattern in- dicating the partitioning of deformation and metamorphism in the UHP petrotectonic unit. The existing data support the now widely accepted con- cept of deep continental subduction/collision and subsequent exhumation between the Yangtze and Sino-Korean cratons. The pressure is a constitutive geological variable. The influence of tectonic over- presure on UHP metamorphism is rather limited.展开更多
‘Single shot'laser-ablation split-stream(SS-LASS)technique analyzing unpolished zircon grains makes their thin rims tenable for determination,which thus offers great potential in deciphering the timing of multipl...‘Single shot'laser-ablation split-stream(SS-LASS)technique analyzing unpolished zircon grains makes their thin rims tenable for determination,which thus offers great potential in deciphering the timing of multiple and short-lived episodes of anatexis and metamorphism in deeplysubducted continental crusts.Dominated granitic gneisses in the deeply subducted continental crust undergoing considerable fluid-melt activities persist multistage growth of zircon.Therefore,a comparative study of SS-LASS and laser ablation inductively coupled plasma mass spectrometer(LA-ICP-MS)zircon dating was conducted on the granitic gneisses from the Sulu belt in this study.Zircons mostly show a core-mantle-rim structure with CL-bright rims thinner than 5μm.For LA-ICP-MS dating,relict magmatic zircon cores yield protolith ages of ca.756-747 Ma;whereas the dark mantles record synexhumation anatexis at ca.214 Ma.By contrast,according to the U-Pb dates,trace element features,zircon crystallization temperatures and geological context,SS-LASS zircon petrochronology deciphers three episodes of anatectic events,as follows:(i)the first episode of anatexis at ca.218-217 Ma dominated by phengite-breakdown melting,likely facilitating the exhumation of the UHP slice from mantle depth;(ii)the second episode of anatexis at ca.193–191 Ma indicating part of northern Dabie-Sulu belt was still“hot”because of buried in the thickened orogenic crust at that time;(iii)the third episode of anatexis(ca.162–161 Ma)consistent with the intrusion ages(ca.161–141 Ma)of the Jurassic to Cretaceous granitoids in this orogen,suggesting the initial collapse of the orogenic root of the Sulu belt occurred at Late Jurassic due to the Izanagi plate initially subducting beneath the margin of Eastern Asia.This study sheds new light upon the utilization of SS-LASS petrochronology deciphering multiple anatectic events in the deeply-subducted continental crust and supports us in better understanding the tectonic evolution of Dabie-Sulu Orogen.展开更多
ABSTRACT: A wide variety of tectonic models have been invoked to explain the exhumation of the world's largest ultrahigh pressure (UHP) orogenic belt, the Qinling Dabieshan Sulu belt in China, and its correlat...ABSTRACT: A wide variety of tectonic models have been invoked to explain the exhumation of the world's largest ultrahigh pressure (UHP) orogenic belt, the Qinling Dabieshan Sulu belt in China, and its correlatives in Korea. Most of these models assume that the orogen contains one main collisional suture between the North and South China cratons that collided in the Mesozoic. New field data reveal that this model is too simplistic, and that the collision involved an additional mi- croplate, which initially rifted off the Yangtze craton. This continental microplate was partially sub- ducted beneath an active margin on the North China craton, and subsequently an additional active Andean-style margin developed on the southern margin of the Qinling microplate after collision, leav- ing the near-vertical microplate wedged between the two thickened and thermally softened margins. The thermo-mechanical environment of collision thus left a cold, thick, and buoyant microplate wedged between two easily deformed margins, which acted as power-law creep channels, accommodating rapid buoyancy-driven rise of a 2 000 km long wedge of the subducted microplate, which became intimately involved with the collisional process. An addi- tional segment of the northern Yangtze craton was subducted to ~100 kin, and formed a separate wedge that rose alongside the thermally softened margin of the Qinling mieroeontinent, and was bordered on the south by the recently thermally- softened rift zone where the Qinling mieroeonti- nent broke off the Yangtze eraton between Late Devonian and Permian times. Recognizing the dual active margins in Qinling-Dabieshan-Sulu orogen and the thermally-softened power-law creep channels sheds new light on understanding exhumation of the world's largest ultrahigh pressure belt. We propose that this model is generally applicable to other UHP belts worldwide.展开更多
文摘Coesite inclusions are found in kyanite from the Lanshantou eclogite in the Sulu ultrahigh-pressure (UHP) metamorphic belt. This discovery extends the stable region of kyanite to over 2.4 GPa. As an important UHP metamorphic belt in China, the Sulu eclogite belt is the product of A-subduction induced by strong compression of the Yellow Sea terrane to the Jiaodong-northereastern Jiangsu terrane during the interaction of the Eurasian plate and Palaeo-Pacific plate in the Indosinian. It stretches about 350 km and contains over 1000 eclogite bodies. Most eclogites in this belt belong to Groups B and C in the classification of Coleman et al., and commonly contain kyanite, while the Lanshantou eclogite belongs to Group A and contains coesite. The MgO, CaO and FeO contents in garnet and pyroxene show regular variation from the core to the rim, which reveals the PTt paths of progressive metamorphism during the Early Mesozoic (240-200 Ma) and retrogressive metamorphism during the Late Mesozoic and Cenozoic exhumation.
基金Major State Basic Research Development Program of China ("973" Project, No. 2003CB716506)the National Natural Science Foundation of China (No. 40474025).
文摘The Curie point depth of continental crust can reflect the regional tectonic pattern and geothermal structures. Analysis of magnetism is an efficient way to obtain the Curie point depth on a regional scale. This study systematically investigated the Curie point depth of Sulu (苏鲁) ultrahigh pressure (UHP) metamorphic belt (33°40'N to 36°20'N and 118°E to 120°E, ca. 60 000 km^2), eastern China using aeromagnetic data. The results show that the Curie point depth of the Sulu region varies from 18.5 to 27 km. The shallowest Curie point depth (ca. 18.5 km) is located in Subei (苏北) subsidence, where the estimated temperature gradient value is about 31.35℃/km, which is comparable with the measured value of 30 ℃/km. In addition, a two-dimensional numerical solution of the heat conduction was used to calculate the temperature field to a depth of 30 km along the profile from Tancheng (郯城) to Lianshui (涟水) with a length of 139 km. The steady state model solved using the finite element method shows that the temperature around the Curie point depth is about 585.36 ℃, which is close to the Curie temperature (580℃) of magnetite at atmospheric pressure. These results provide new insights into the tectonic and continuous thermal structures of the Sulu UHP metamorphic belt.
基金supported by Researches of Chinese Continental Scientific Dilling Project,the National Bas ic Research Progam of China(Grant No.2 003CB716505)the Na tional Natural Science Foundation of China(Grant No.40174013)
文摘Calibration of seismic reflectors appearing in the crust of the Chinese continent sci- entific drilling site can be completed through the correlation studies between direct evidences, such as the drill cores, and geophysical signatures; therefore the interpretation of geophysical data could produce reliable results of crustal structure and composition. On the other hand, there are two Cenozoic volcanoes close to the scientific drilling site; analyzing composition of xenoliths existent in the volcanoes and evaluating their seismic velocities can also offer information about the mantle and lower crust. After the calibration via cores and well-logging data, the seismic re- flectors appearing in the UHP belt can be caused by lithological changes within the UHP rock slice, ductile shearing rock-suites, and later fracture zones. Among these sources, ductile shearing resulted in displacement and detachment of original rock-sheets, producing some rock-interbeds of several hundred meters thick that are named the ductile shearing rock-suites. A suite consists of mylonized gneiss and eclogite slices that underwent shearing, becoming the major mechanism responsible to generate regional strong reflections. The UHP rock-slice is characterized by complicated structures and high density, high seismic velocity and high electri- cal resistivity, its thickness is usually less than 11 km. Velocity and density of the gneiss-layer beneath gradually tend to normal with increasing depth. Based on the xenoliths we can infer that the middle crust contains a lot of gneisses, and the lower crust consists of different granulites. The lithospheric mantle has multi-layer structures and consists mainly of spinal lherzolite and harzburgite, implying late Mesozoic lithospheric thinning. The seismic fabrics with different ori- gins were possible products of different geodynamic processes. For instance, the UHP rock-slice was produced by the UHP metamorphic process and the exhumation of subducted supercrustal rocks after the Triassic collision between the Yangtze and Sino-Korean cratons; whilst the ductile shearing rock-suites resulted from shearing deformation processes during the subduction and exhumation. The normal velocity below the UHP rock-slice was correlated with Mesozoic exten- sion processes in the area. Through careful calibration of seismic reflectors and analyzing xeno- liths, one can find the relationship between the causes of seismic reflectors and corresponding geodynamic processes, offering a new basis for reconstruction of regional dynamic evolution history.
文摘The Sulu ultra-high pressure(UHP)metamorphic belt in Eastern China is well known as the eastern extension of the Qingling-Dabie orogenic belt formed by subduction and collision between the Sino-Korean and Yangtze cratons.The main hole of the Chinese Continental Scientific Drilling(CCSD)project is located at the southern segment of the Sulu UHP metamorphic belt(34°25′N/118°40′E),about 17 km southwest of Donghai County.Integrated geophysical investigations using gravity,magnetic,deep
文摘A wealth of retrogressive microstructures have been discovered from the UHP metamorphic rocks in Dabie orogenic belt, namely, the ultrahigh-pressure (URP) eclogites, jadeite quartzites and kyanite-zoisite-quartz vein. The most important are pseudomorphic replacements of UHP minerals like coesite, the corona reaction textures iuduced by solid-solid reactions as well as the corona and symplectites induced by reactions involving fluid. According to the textural relationships the sequence of mineral Paragenesis and the metamorphic stages in the UHP eclogites can be delineated; the mineral geobarothermometry of the various stages of retrograde metamorphism is studied and a clockwise, nearly isothermal decompressive metamorphic PT-trajectory for the UHP eclogites can be reconstructed. In terms of the PT-trajectory the two stage post collision uplirt and exhumation processes are reflected. When the UHP metumorphic rocks extruded to the lower-middle crust partial melting happened which bad in turn caused tke crustal extension and the further exhumation or the UHP metomorphic rocks. Based on the field strain analysis combined with geochronological data a scenario or post collision uplift aud exhumation model is presented.
基金This study was supported by the Key State Basic Research Development Project grant G1999075506the National Natural Science Foundation of China grants 49794041,49972067 and 49772146the former Ministry of Geology and Mineral Resources Project No.9501102.
文摘The present-day observable tectonic framework of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts in the Dabie-Sulu region was dominantly formed by an extensional process, mostly between 200 and 170 Ma, following the Triassic collision between the Sino-Korean and Yangtze cratons. The framework that controls the present spatial distribution of UHP and HP metamorphic rocks in particular displays the typical features of a Cordilleran-type metamorphic core complex, in which at least four regional-scale, shallow-dipping detachment zones are recognized. Each of these detachment zones corresponds to a pressure gap of 0.5 to 2.0 GPa. The detachment zones separate the rocks exposed in the region into several petrotectonic units with different P-T conditions. The geometry and kinematics of both the detachment zones and the petrotectonic units show that the exhumation of UHP and HP metamorphic rocks in the Dabie-Sulu region was achieved, at least in part, by non-coaxial ductile flow in the multi-layered detachment zones, and by coaxial vertical shortening and horizontal stretching in the metamorphic units, under amphibolite- to greenschist-facies conditions, and in an extensional regime. All ductile extensional deformations occurred at depths below 10 to 15 km, i.e. below the brittle/ductile deformation transition.
基金supported by the Chinese National Key Scientific Program--the Chinese Continental Seientitle Drilling Projectthe National Natural Science Foundation of China(NSFC Grant 49772142)1:250000 Regional Geological Survey of the Lianyungang Sheet(I50C002004)of P.R.China and the Laboratory of Continental Dynamics of the Land and Resource Ministry of China
文摘The Drillhole ZK703 with a depth of 558 m is located in the Donghai area of the southern Sulu ultrahigh-pressure (UHP) metamorphic belt, eastern China, and penetrates typical UHP eclogites and various non-mafic rocks, including peridotite, gneiss, schist and quartzite. Their protoliths include ultramafic, mafic, intermediate, intermediate-acidic, acidic igneous rocks and sediments. These rocks are intimately interlayered, which are meters to millimeters thick with sharp and nontectonic contacts, suggesting in-situ metamorphism under UHP eclogite facies conditions. The following petrologic features indicate that the non-mafic rocks have experienced early-stage UHP metamorphism together with the eclogites: (1) phengite relics in gneisses and schists contain a high content of Si, up to 3.52 p.f.u. (per formula unit), while amphibolite-facies phengites have considerably low Si content (<3.26 p.f.u.); (2) jadeite relics are found in quartzite and jadeitite; (3) various types of symplectitic coronas and pseud
基金support from the Major State Basic Research Development Program of China(No:G1999075506)the Ministry of Land and Resources(No.20001010203).
文摘Whether the HP and UHP metamorphic rocks of the Dabie-Sulu orogenic belt are of an "in-situ" or "foreign" origin is a long-standing dispute among geologists. Eclogites preserved today in the HP and UHP units constitute merely 5-10%, which are not isolated exotic bodies tectonically intruding into amphibolite facies gneiss, but remnants of once pervasive or widespread eclogite-facies terranes or slabs. The present spatial distribution and forms of the eclogites have resulted from polyphase and progressive deformation and strain partitioning of the HP and UHP slabs. From their formation in deep mantle to their exhumation to the surface, the eclogites have experienced long-term deformation with different strain regimes. The dominant regime responsible for the present spatial distribution and forms of the eclogites is the shear process. The deformation patterns of the eclogites and gneiss matrix also clearly show that the eclogites were metamorphosed in situ. The original distribution area of the eclogites
基金supported by the SinoProbe Project (SinoProbe-2-6)the National Natural Science Foundation of China (41073024 and 40872048)
文摘Unusual polyphase inclusions of K-feldspar+quartz+titanite+solid salt and K-feldspar+albite+quartz+epidote with textures similar to the other K-feldspar+quartz inclusions were found in omphacite grains from the Sulu ultrahigh pressure (UHP) eclogites. One of these inclusions contain square to round solid salt inclusions of KCl-NaCl composition. Such a mineral assemblage within K-feldspar-bearing inclusions hosted by UHP metamorphic phases suggests that (1) potassium granitic melts enriched in Cl components were presented during UHP metamorphism or at the early stage of rapid exhumation of deeply subducted continental slab; (2) they were resulted from reactions between the incoming granitic melts and quartz (or coesite); and (3) solid salt inclusions of NaCl-KCl were derived from dehydration and desiccation of Cl-bearing melts. Our new observations further demonstrate that during the tectonic evolution of UHP rocks, fertile components within deeply subducted continental materials could undergo partial melting, leading to the formation of Cl-bearing potassium granitic melts and substantial migration of fluid-conservative elements (e.g. Ti, Hf) within the UHP slab.
基金supported by the National Natural Science Foundation of China(Nos.90814006,91214301)the Natural Science Foundation of Shandong Province(No.ZR2009EQ002)+1 种基金the Foundation of the Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Minerals(No.DMSM201005)the National Key Basic Research Development Program (973Program) of China(No.2012CB723104)
文摘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.
基金supported by the National Natural Science Foundation of China(Nos.40372094 and 49972067)
文摘Two fresh types of eclogites, namely the massive eclogite and foliated eclogite, are dis- cernible in large eclogite bodies surrounded by country rock gneisses from the Dabie Sulu UHP metamorphic zone. They are different in mineral assemblage, texture and structure at various scales. The massive eclogite has a massive appearance with a metamorphic inequigranular and grano- blastic texture, which consists mainly of nominally anhydrous minerals such as garnet, omphacite, rutile with inclusions of coesite and rare microdiamond. Massive eclogites which formed at the peak UHP metamorphic conditions (~3.1-4.0 GPa, 800~50 ) within the coesite to diamond stability field recorded the deep continental subduction to mantle depths greater than 100 km during the Triassic (-250-230 Ma). The diagnostic UHP minerals, mineral assemblages and absence of notable macro- scopic deformation indicate the peak metamorphic 'forbidden-zone' P-T conditions, an extremely low geothermal gradient (〈7 "C'kma) and low differential stress. The foliated eclogite is composed of garnet+omphacite+rutile+phengite+kyanite+zoisite+talc+nybtite^coesite/quartz pseudomorphs after coesite. It is quite clear that the foliated eclogite bears relatively abundant hydrous mineral, and shows well-developed penetrative foliation carrying mineral and stretching lineation reflecting intense plastic deformation or flow of eclogite minerals. The foliatcd eclogite occurred at mantle levels and recorded the earliest stages of exhumation of UHP metamorphic rocks. At a map scale, the foliated eclogites de- fine UHP eclogite-facies shear zones or high-strain zones. Asymmetric structures are abundant in the zones, implying bulk plane strain or dominant non-coaxial deformation within the coesite stability field. The earliest stages of exhumation, from mantle depths to the Moho or mantle-crust boundary layering, were characterized by a sub-vertical tectonic wedge extrusion, which occurred around 230-210 Ma. The three- dimensional relationship between the massive and foliated eclogites is well displayed a typical 'block-in-matrix' rheological fabric pattern in- dicating the partitioning of deformation and metamorphism in the UHP petrotectonic unit. The existing data support the now widely accepted con- cept of deep continental subduction/collision and subsequent exhumation between the Yangtze and Sino-Korean cratons. The pressure is a constitutive geological variable. The influence of tectonic over- presure on UHP metamorphism is rather limited.
基金supported by National Natural Science Foundation of China(Nos.42072228,42102060,41902036,41572182)China Postdoctoral Science Foundation(No.2021M692983)+4 种基金the Chinese Ministry of Education(No.BP0719022)the Most Special Fund(Nos.MSFGPMR02-3,MSFGPMR30)Open funds from the State Key Laboratory of Geological Processes and Mineral ResourcesChina University of Geosciences(Nos.GPMR201703,GPMR201704 and GPMR201903)the Fundamental Research Funds for National University(No.CUG-G1323511572)。
文摘‘Single shot'laser-ablation split-stream(SS-LASS)technique analyzing unpolished zircon grains makes their thin rims tenable for determination,which thus offers great potential in deciphering the timing of multiple and short-lived episodes of anatexis and metamorphism in deeplysubducted continental crusts.Dominated granitic gneisses in the deeply subducted continental crust undergoing considerable fluid-melt activities persist multistage growth of zircon.Therefore,a comparative study of SS-LASS and laser ablation inductively coupled plasma mass spectrometer(LA-ICP-MS)zircon dating was conducted on the granitic gneisses from the Sulu belt in this study.Zircons mostly show a core-mantle-rim structure with CL-bright rims thinner than 5μm.For LA-ICP-MS dating,relict magmatic zircon cores yield protolith ages of ca.756-747 Ma;whereas the dark mantles record synexhumation anatexis at ca.214 Ma.By contrast,according to the U-Pb dates,trace element features,zircon crystallization temperatures and geological context,SS-LASS zircon petrochronology deciphers three episodes of anatectic events,as follows:(i)the first episode of anatexis at ca.218-217 Ma dominated by phengite-breakdown melting,likely facilitating the exhumation of the UHP slice from mantle depth;(ii)the second episode of anatexis at ca.193–191 Ma indicating part of northern Dabie-Sulu belt was still“hot”because of buried in the thickened orogenic crust at that time;(iii)the third episode of anatexis(ca.162–161 Ma)consistent with the intrusion ages(ca.161–141 Ma)of the Jurassic to Cretaceous granitoids in this orogen,suggesting the initial collapse of the orogenic root of the Sulu belt occurred at Late Jurassic due to the Izanagi plate initially subducting beneath the margin of Eastern Asia.This study sheds new light upon the utilization of SS-LASS petrochronology deciphering multiple anatectic events in the deeply-subducted continental crust and supports us in better understanding the tectonic evolution of Dabie-Sulu Orogen.
基金supported by the National Natural Science Foundation of China (Nos.91014002,40821061,40802045)the Science Foundation of Shandong Province,China (No.Q2008E03)+1 种基金the Special Financial Grant from China Postdoctoral Science Foundation (No.201104495)Ministry of Education of China (No.B07039)
文摘ABSTRACT: A wide variety of tectonic models have been invoked to explain the exhumation of the world's largest ultrahigh pressure (UHP) orogenic belt, the Qinling Dabieshan Sulu belt in China, and its correlatives in Korea. Most of these models assume that the orogen contains one main collisional suture between the North and South China cratons that collided in the Mesozoic. New field data reveal that this model is too simplistic, and that the collision involved an additional mi- croplate, which initially rifted off the Yangtze craton. This continental microplate was partially sub- ducted beneath an active margin on the North China craton, and subsequently an additional active Andean-style margin developed on the southern margin of the Qinling microplate after collision, leav- ing the near-vertical microplate wedged between the two thickened and thermally softened margins. The thermo-mechanical environment of collision thus left a cold, thick, and buoyant microplate wedged between two easily deformed margins, which acted as power-law creep channels, accommodating rapid buoyancy-driven rise of a 2 000 km long wedge of the subducted microplate, which became intimately involved with the collisional process. An addi- tional segment of the northern Yangtze craton was subducted to ~100 kin, and formed a separate wedge that rose alongside the thermally softened margin of the Qinling mieroeontinent, and was bordered on the south by the recently thermally- softened rift zone where the Qinling mieroeonti- nent broke off the Yangtze eraton between Late Devonian and Permian times. Recognizing the dual active margins in Qinling-Dabieshan-Sulu orogen and the thermally-softened power-law creep channels sheds new light on understanding exhumation of the world's largest ultrahigh pressure belt. We propose that this model is generally applicable to other UHP belts worldwide.