The Guanshan Fauna, a soft-bodied fauna intermediate between the Chengjiang Fauna and the Kaili Fauna and also the Burgess Shale Fauna stratigraphically, consists of trilobites, trilobitoides, Tuzoia, Vetulicola, Pale...The Guanshan Fauna, a soft-bodied fauna intermediate between the Chengjiang Fauna and the Kaili Fauna and also the Burgess Shale Fauna stratigraphically, consists of trilobites, trilobitoides, Tuzoia, Vetulicola, Paleoscolex, brachiopods and sponges. The discovery and research of this fauna is of great significance in understading the 'Cambrian Explosion' and the evolution of early life. The occurrence of vetulicoliids from the Guanshan Fauna not only adds new members to the taxonomic list, but also provides new information to the evolution of this animal group. This paper describe Vetulicola gantoucunensis Luo, Fu et Hu sp. nov. from the Lower Cambrian Wulongqing Formation in the Kunming area. Also presented are the amended description of Vetulicola and the comparisons with related genera within Vetulicoliids. The affinity, distribution, as well as evolution of vetulicoliids are discussed.展开更多
Anhua-Xupu fault belt plays a very important role in the formation of Xuefeng Mountains. The fault belt shows an arc-structure extruding towards NW. Fault rocks, microstructures and homogeneous temperature (concentrat...Anhua-Xupu fault belt plays a very important role in the formation of Xuefeng Mountains. The fault belt shows an arc-structure extruding towards NW. Fault rocks, microstructures and homogeneous temperature (concentrated around 160℃) of fluid inclusions in the quartz veins shows that the fault belt mainly underwent shallow brittle deformation and the highest-grade dynamic metamorphic rock is mylonitized sericite phyllite. The ESR (Electron Spin Resonance) dating from the quartz veins in the fault rocks shows that the fault belt underwent two intense fluid movement stages at Yanshanian (156.9~136.2Ma, 119.8~90.6Ma); moreover not only the occurrence and microstructures but also the homogeneous temperature of the quartz veins developed in that two stages show obvious diversity, which can prove that there exists the reversion period of Mesozoic extension and compression movement of Xuefeng mountains between these two stages .展开更多
A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. Key features of the new scale are outlined, how it was constructed, and how it can be furt...A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. Key features of the new scale are outlined, how it was constructed, and how it can be further improved. The accompanying International Stratigraphic Chart, issued under auspices of the International Commission on Stratigraphy (ICS), shows the current chronostratigraphic scale and ages with estimates of uncertainty for all stage boundaries. Special reference is made to the Precambrian part of the time scale, which is coming of age in terms of detail, and to the Neogene portion, which has attained an ultra-high-precision absolute-age calibration.展开更多
An analysis of trace elements and isotopic geochemistry suggest that the ore-forming materials of gold deposits in the Jiaodong granite-greenstone belt have multiple sources, especially the mantle source. Seismic wave...An analysis of trace elements and isotopic geochemistry suggest that the ore-forming materials of gold deposits in the Jiaodong granite-greenstone belt have multiple sources, especially the mantle source. Seismic wave, magnetic and gravity fields show that the crust-mantle structure and its coupling mechanism are the fundamental dynamic causes for the exchange and accumulation of materials and energy in the metallogenic system. Considering the evolution history of the structural setting, the tectono-metallogenic dynamics model of the area can be summarized as follows: (1) occurrence of the greenstone belt during the Archean-Proterozoic-the embryonic form of Au-source system; (2) stable tectonic setting in the Paleozoic-an intermittence in gold mineralization; (3) intensive activation and reformation of the greenstone belt in the Mesozoic-tectono-mineralization and tectono-diagensis; (4) posthumous structural activity in the Cenozoic-destruction of orebodies in the later stage. In the middle and late Indosinian, the Tancheng-Lujiang fault zone cut deeply into the upper mantle so that the ore-bearing fluids migrated to higher layers through the crust-mantle interaction, resulting in alteration and mineralization.展开更多
Calcimicrobialites, which could be correlated to the layer 27 in Meishan section according to the Hindeodus parvus, occur abruptly on the end-Permian mass extinction boundary in South China. Microbialites mainly distr...Calcimicrobialites, which could be correlated to the layer 27 in Meishan section according to the Hindeodus parvus, occur abruptly on the end-Permian mass extinction boundary in South China. Microbialites mainly distribute on the top of reef facies or shallow carbonate platforms, thin- ning into deep facies. All the microbialites discovered are composed of micrite and coarse crystal digitate carbonate or patch carbonate. Microfossils usually dominate in the micro- bialites, and small gastropods, bivalves and ostracodes can also be found. This fossil assemblage represents a simple but particular remanent biota after the end-Permian mass ex- tinction on the top of reefs or shallow carbonate platforms. Abrupt occurrence of microbialites above the mass extinction boundary is the ecological response to the end-Permian global event in reef or shallow carbonate facies. Many studies have been done on the Permian-Triassic boundary and event in deep water facies sections or middle to lower shelf facies sections. However, the calcimicrobialites in South China are mainly located above reef facies or shallow carbonate plat- form facies. It will surely be helpful for people to know more about the different responses in different depths of ancient marine environment during the transition between Permian and Triassic by the study of petrology, palaeontology and palaeoecology of the calcimicrobialites.展开更多
U-Pb ages of zircon,monazite and xenotime from the Kude and the Sajia leucogranites in the Sajia dome of the North Hima- layan tectonic unit are measured using TIMS method. The results show that the magma emplacement ...U-Pb ages of zircon,monazite and xenotime from the Kude and the Sajia leucogranites in the Sajia dome of the North Hima- layan tectonic unit are measured using TIMS method. The results show that the magma emplacement ages for the Kude and the Sajia leu- cogranite are 27.5±0.5 and 14.4±0.2 Ma,respectively. Combined with published U-Pb data from the North Himalayan leu- cogranites,the time-span for the formation of the North Himalayan leucogranites is updated from 27.5 to 10 Ma,instead of previous 15 to 10 Ma.According to the U-Pb ages,the petrogenesis for the North Himalayan leucogranites can be constrained.It is suggested that the North Himalayan leu- cogranites have variety in their petrogenesis.展开更多
Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample ...Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample derived from the early lower crust of the North China craton.It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes,however, is contained in the granulite. These processes include the addition of mantle material, crustal remelting,metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842±40Ma, except few ages of 3097-2824 Ma and 2489-2447Ma. The zircons with ages older than 2447Ma have high εHr(up to+18.3) and high Hf model age (2.5-2.6Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εHr of the zircons with early Proterozoic U-Pb age vary around zero, but two have high εHr up to+9.2-+10.2, indicating mantle contribution during the collision and assembly between the Eastern and Western blocks in the early Proterozoic that resulted in the amalgamation of the North China craton.展开更多
The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is ju...The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is just a maximum estimation because some parts of the ELIP were not recognized or dismembered and destroyed during the Triassic to Cenozoic tectonism. In this paper, the chemostratigraphical data of the Zongza block, the Garze-Litang belt and the Songpan-Garze block suggest that the Late Permian basalts in these areas have remarkable similarities to the ELIP basalts in petrography and geochemistry. Flood basalts in the Sanjiangkou area are composed of the lower part of the low-Ti (LT) tholeiite and the upper part of the high-Ti (HT) tholeiite, which is the same as the flood basalts on the western margin of the Yangtze craton. Flood basalts in the Zongza and Songpan-Garze areas, which are far from the Yangtze craton, consist of HT tholeiite only. This is the same as the flood basalts within the Yangtze craton. Therefore we argue that these contemporary basalts all originated from the Emeishan mantle plume, and the ELIP could have a significant westward extension with an outcropped area of over 500,000 km2. This new scenario shows that the LT tholeiite occurs on the western margin of the Yangtze craton, while the HT tholeiite overlying the LT basalts occupies the whole area of the ELIP.展开更多
Eclogites from orogens often show strong plastic deformation and high hydroxyl content. We have studied the correlation between crystallographic preferred orientations of garnet and omphacite from natural eclogites wi...Eclogites from orogens often show strong plastic deformation and high hydroxyl content. We have studied the correlation between crystallographic preferred orientations of garnet and omphacite from natural eclogites with their hydroxyl contents using the electron back-scat- tered diffraction technique. The results show: 1) Omphacite has typical L-type or SL-type crystrallographic preferred orientations, that is, [001] is distributed in a girdle in the foliation plane with a maximum parallel to lineation; (010) is distributed in a girdle normal to the lineation with a maxi- mum parallel to the foliation plane, suggesting a shear dominant deformation regime. Omphacite fabrics do not vary significantly with hydroxyl content, although the hy- drous component may cause lower flow strength. 2) Hy- droxyl can influence significantly flow properties of garnet in eclogite. Garnets behave as rigid bodies under low tempera- ture and dry conditions. Grain boundary processes will dominate the deformation and lower the flow strength of garnet under high water fugacity conditions. Garnets show no crystallographic preferred orientation in both cases. These results may have important implications for a better understanding of deformation mechanisms and associated fluid activities during deep subduction and exhumation processes.展开更多
High-pressure mafic granulites, occurring as lenses within gneisses and quartzite in the central segment of the Himalayan orogen, were dated using SHRIMP U-Pb technique. 13 analyses out of a total of 15 are plotted al...High-pressure mafic granulites, occurring as lenses within gneisses and quartzite in the central segment of the Himalayan orogen, were dated using SHRIMP U-Pb technique. 13 analyses out of a total of 15 are plotted along a concordia line and yield a mean 206Pb/238U age of 17.6 0.3 Ma. This age indicates adiabatic decompression and a metamorphic event associated with rapid uplift of granulites in a tectonic environment resulted from the collision between India and Eurasia, synchronous with large-scale thrusting, extension, detachment as well as emplacement of leu-cogranite. One analysis gives a 206Pb/238U age of 29.5 0.4 Ma that is interpreted to represent the timing of the final closure of the Neo-Tethys. Another age is 1991 26 Ma that represents the age of the protolith of the granulites. In sum-mary, dating results show that granulites in this area under-went multiphase metamorphism and complex geological evolution.展开更多
The Late Caledonian to Early Hercynian North Qilian orogenic belt in no rthwestern China is an elongate tectonic unit situated between the North China p late in the north and the Qaidam plate in the south. North Qili...The Late Caledonian to Early Hercynian North Qilian orogenic belt in no rthwestern China is an elongate tectonic unit situated between the North China p late in the north and the Qaidam plate in the south. North Qilian started in the latest Proterozoic to Cambrian as a rift basin on the southern margin of North China, and evolved later to an archipelagic ocean and active continental margin during the Ordovician and a foreland basin from Silurian to the Early and Middle Devonian. The Early Silurian flysch and submarine alluvial fan, the Middle to L ate Silurian shallow marine to tidal flat deposits and the Early and Middle Devo nian terrestrial molasse are developed along the corridor Nanshan. The shallowin g upward succession from subabyssal flysch, shallow marine, tidal flat to terre strial molasse and its gradually narrowed regional distribution demonstrate that the foreland basin experienced the transition from flysch stage to molasse stag e during the Silurian and Devonian time.展开更多
U-Pb zircon dating by LA-ICP-MS andSHRIMP for one olivine pyroxenite yields complex agepopulations including Mesozoic ages of 97-158 Ma and 228 ±8.7 Ma, Early Paleozoic ages of 418—427 Ma, Paleoprotero-zoic age ...U-Pb zircon dating by LA-ICP-MS andSHRIMP for one olivine pyroxenite yields complex agepopulations including Mesozoic ages of 97-158 Ma and 228 ±8.7 Ma, Early Paleozoic ages of 418—427 Ma, Paleoprotero-zoic age of 1844±13 Ma, Neoarchean age of 2541 ± 54 Ma andmiddle Archean age of 3123 ± 4.4 Ma. The 97—158 Ma and228 ± 8.7 Ma zircons show typical igneous oscillatory zona-tion in CL images, suggesting two episodes of magmaticevents. Overlapping of the 97-158 Ma ages with that ofgranulite xenoliths indicates that the Mesozoic granu-lite-facies metamorphism was induced by heating from thebasaltic underplating at the base of the lower crust. Bothprocesses lasted at least from about 158 to 97 Ma. Ages of 418--427 Ma could be records of the subduction of Mongoliaoceanic crust under the North China craton. Ages of 1.84 Ga, 2.54 Ga and 3.12 Ga correspond to the three importantcrust-mantle evolutionary events in the North China craton,and imply preservation of Precambrian lower crust in thepresent-day lower crust.展开更多
The granulitic xenoliths discovered in the late Cretaceous basaltic rocks from Tuoyun basin, western Xinjiang Province contain the assemblage of Opx + Cpx + Pl ± Grt ± Qtz ± Kfs. Mineral chemistry, petr...The granulitic xenoliths discovered in the late Cretaceous basaltic rocks from Tuoyun basin, western Xinjiang Province contain the assemblage of Opx + Cpx + Pl ± Grt ± Qtz ± Kfs. Mineral chemistry, petrochemistry and zircon U-Pb ages from the xenoliths have been reported in the paper. Petrogenesis, the lower crustal nature and the mantle-crust interaction reflected by the granulites are discussed as well. Tuoyun granulites are mainly mafic with few intermediate components, and represent the magmatic products underwent granulite-facies metamorphism in lower crustal condition. Equilibrium temperature and the maximum pressure estimates of the granulites are 910 ± 35℃ and 13.5 × 108 Pa respectively, indicating that the crust beneath southwestern Tianshan had the thickness of less than 44 km and high geotherm (e.g. > 80 mW/m2) when the host magma erupted. During their formation, the fractional crystallization of olivine, pyroxene, plagioclase and ilmenite, plagioclase accumulation and the contamination of felsic components or fluid metasomatism processes had happened. Metamorphic zircon U-Pb age of 253 Ma may record the crust-mantle interaction caused by the orogenic root delamination beneath the southwestern Tianshan.展开更多
Detailed three-dimensional structural studies indicate that the Bixiling area, Dabie massif, central China shows the deepest exposed levels of the orogenic wedge formed during the Triassic Yangtze -Sino-Korean contine...Detailed three-dimensional structural studies indicate that the Bixiling area, Dabie massif, central China shows the deepest exposed levels of the orogenic wedge formed during the Triassic Yangtze -Sino-Korean continental collision. New 1 : 10 000 scale structural mapping, combined with detailed petrological analysis in this area, has enabled us to accurately distinguish structures related to the Triassic continental collision from those related to post-collisional deformation in the ultrahigh pressure (UHP) metamorphic unit. The collisional or compressional structures include the massive eclogite with a weak foliation, foliated eclogite or UHP ductile shear zones, as well as upper amphibolite facies shear zones, whereas the post-collisional deformation is characterized by a regionally, flat-lying foliation containing stretching lineations and common reclined folds. The former is present exclusively in the eclogite lenses and their margins, representing orogenic thickening or syn-collisional events, while the latter was best occurred on variable scales under amphibolite facies conditions, showing sub-vertical, extreme shortening and ductile thinning of the metamorphic rock stack. The eclogite facies tectonites that have a marked fabric discordance to the penetrative amphibolite facies extension flow fabric are common. It is emphasized that an extensional tectonic setting following the collision-orogenic thickening stage was, at least partly, responsible for exhumation of the UHP metamorphic rocks in the Dabie massif. A new tectonic evolution model is proposed for the UHP metamorphic belt on the scale of the Dabie massif. The Bixiling area thus provides a window, from which the dynamic processes concerning the formation and exhumation of the UHP rocks can be observed. Regional studies in the Dabie Mountains have confirmed this interpretation.展开更多
Glaucophane in Shuangjiang area, West Yunnan Province, supplies a chance for studying south segment of Lancangjiang tectonic zone. But people are at odds as to whether two stage glaucophane exists or not, glaucophane...Glaucophane in Shuangjiang area, West Yunnan Province, supplies a chance for studying south segment of Lancangjiang tectonic zone. But people are at odds as to whether two stage glaucophane exists or not, glaucophane is the result of dynamic metamorphism later, or indicates a high P/T metamorphic belt when Paleozoic Tethys Sea closed. Authors discover in a recent research that there is only one stage glaucophane in Shuangjiang area, and three blueschist belts are distributed near N S tending, and glaucophane in Shuangjiang area is related to the eastward subduction of Changning Menglian basin.展开更多
Sediments of carbonate gravity flows and terrigenous debris turbidites, and normal bathyal deposits were found at the Shaiwa Section, Ziyun County, Guizhou Province, southwestern China. Through grain size analysis of...Sediments of carbonate gravity flows and terrigenous debris turbidites, and normal bathyal deposits were found at the Shaiwa Section, Ziyun County, Guizhou Province, southwestern China. Through grain size analysis of some typical sediments at this section, the changing patterns of the grain parameters and the grain size cumulations were recovered. Results show that the study area was deposited under turbidite control during the Late Permian period, which we also recognized at the outcrop section upon sedimentary characteristics of the sediments. In addition, fossils are abundant in the Upper Permian of the Shaiwa Section, including radiolarians, sponge spicules, bivalves, brachiopods, ammonoids and trace fossils. Radiolarians and siliceous sponge spicules are typical deep water assemblages. Bivalves are dominated by genera of Hunanopecten and Claraia , both showing deep water living characteristics. Ammonoids are composed of planktonic types, showing characteristics of smooth and flat shells. Brachiopods are dominated by a small and thin shelled assemblage, which are commonly flat in shape and usually of slight ornamentations on shells. In addition, trace fossils found at the Shaiwa Section are also common types of deep water facies. Thus, the fossil evidence of the Shaiwa Section also suggests a deep water environment, possibly from the bathyal slope to the basin margin facies, of the studied area during the Late Permian period.展开更多
There are two models of ultrahigh pressure metamorphism (UHPM) zone in Dabie: the model of under thrusting returning which even arrives at the mantle and the superimposed model of tectonics in the crust. There are tw...There are two models of ultrahigh pressure metamorphism (UHPM) zone in Dabie: the model of under thrusting returning which even arrives at the mantle and the superimposed model of tectonics in the crust. There are two points of view in the argument about formation depth of ultrahigh pressure metamorphism: (1) the depth can be calculated by hydrostatic equation; (2) the high pressure was composed of gravity, tectonic and other forces instead of merely gravity force. Some misunderstandings of mechanical conceptions presented in the paper showing the hydrostatic viewpoints should be open to question. The main conceptions are: (1) the confining pressure was only formed by gravity, and the differential stress was only formed by tectonic force; (2) the differential stress is not big enough to lead to form ultrahigh pressure metamorphism; (3) once tectonic overpressure goes beyond the limited strength of rocks the tectonic force would disappear and the rocks would be broken or rheomorphied at the same time. A short discussion in basic mechanics is made in this paper for a perfect process for discussing the argument.展开更多
In the Central Orogenic Belt, China, two UHP metamorphic belts are discriminated mainly based on a detailed structural analysis of the Kanfenggou UHP metamorphic fragment exposed in the eastern Qinling orogen, and tog...In the Central Orogenic Belt, China, two UHP metamorphic belts are discriminated mainly based on a detailed structural analysis of the Kanfenggou UHP metamorphic fragment exposed in the eastern Qinling orogen, and together with previous regional structural, petrological and geochronological data at the scale of the orogenic domain. The first one corresponds to the South Altun North Qaidam North Qinling UHP metamorphic belt. The other is the Dabie Sulu UHP and HP metamorphic belts. The two UHP metamorphic belts are separated by a series of tectonic slices composed by the Qinling rock group, Danfeng rock group and Liuling or Foziling rock group etc. respectively, and are different in age of the peak UHP metamorphism and geodynamic implications for continental deep subduction and collision. Regional field and petrological relationships suggest that the Kanfenggou UHP metamorphic fragment that contains a large volume of the coesite and microdiamond bearing eclogite lenses is compatible with the structures recognized in the South Altun and North Qaidam UHP metamorphic fragments exposed in the western part of China, thereby forming a large UHP metamorphic belt up to 1 000 km long along the orogen strike. This UHP metamorphic belt represents an intercontinental deep subduction and collision belt between the Yangtze and Sino Korean cratons, occurred during the Paleozoic. On the other hand, the well constrained Dabie Sulu UHP and HP metamorphic belts occurred mainly during Triassic time (250-220 Ma), and were produced by the intracontinental deep subduction and collision within the Yangtze craton. The Kanfenggou UHP metamorphic fragment does not appear to link with the Dabie Sulu UHP and HP metamorphic belts along the orogen. There is no reason to assume the two UHP metamorphic belts as a single giant deep subduction and collision zone in the Central Orogenic Belt situated between the Yangtze and Sino Korean cratons. Therefore, any dynamic model for the orogen must account for the development of UHP metamorphic展开更多
The studies on stromatolites occurring in the Mesoproterozoic Tieling Formation, Zhoukoudian, Beijing indicate that the thickness of bright-dark lamina pairs in the stromatolites shows periodic variations, which are i...The studies on stromatolites occurring in the Mesoproterozoic Tieling Formation, Zhoukoudian, Beijing indicate that the thickness of bright-dark lamina pairs in the stromatolites shows periodic variations, which are inter- preted as monthly and seasonal rhythms. On the basis of the S-shaped stromatolites, some preliminary paleo-astronomic parameters have been obtained as follows: In the late Meso- proterozoic (1000 Ma ago) there were at least 516±20 d, 12.9 ±0.5 months per year, 40 d per month and at most 16.99± 0.66 h per day, and paleo-obliquity of the ecliptic was 29.2°— 30.6°.展开更多
基金the joint project between the Yunnan Institute of Geological Sciences the Shenzhen Palaeontological Museum the Natural Science Foundation of Yunnan Province(2002D0033Q).
文摘The Guanshan Fauna, a soft-bodied fauna intermediate between the Chengjiang Fauna and the Kaili Fauna and also the Burgess Shale Fauna stratigraphically, consists of trilobites, trilobitoides, Tuzoia, Vetulicola, Paleoscolex, brachiopods and sponges. The discovery and research of this fauna is of great significance in understading the 'Cambrian Explosion' and the evolution of early life. The occurrence of vetulicoliids from the Guanshan Fauna not only adds new members to the taxonomic list, but also provides new information to the evolution of this animal group. This paper describe Vetulicola gantoucunensis Luo, Fu et Hu sp. nov. from the Lower Cambrian Wulongqing Formation in the Kunming area. Also presented are the amended description of Vetulicola and the comparisons with related genera within Vetulicoliids. The affinity, distribution, as well as evolution of vetulicoliids are discussed.
基金This study was financially supported by China National Science Foundation Grant No.40334037SINOPEC key project.
文摘Anhua-Xupu fault belt plays a very important role in the formation of Xuefeng Mountains. The fault belt shows an arc-structure extruding towards NW. Fault rocks, microstructures and homogeneous temperature (concentrated around 160℃) of fluid inclusions in the quartz veins shows that the fault belt mainly underwent shallow brittle deformation and the highest-grade dynamic metamorphic rock is mylonitized sericite phyllite. The ESR (Electron Spin Resonance) dating from the quartz veins in the fault rocks shows that the fault belt underwent two intense fluid movement stages at Yanshanian (156.9~136.2Ma, 119.8~90.6Ma); moreover not only the occurrence and microstructures but also the homogeneous temperature of the quartz veins developed in that two stages show obvious diversity, which can prove that there exists the reversion period of Mesozoic extension and compression movement of Xuefeng mountains between these two stages .
文摘A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. Key features of the new scale are outlined, how it was constructed, and how it can be further improved. The accompanying International Stratigraphic Chart, issued under auspices of the International Commission on Stratigraphy (ICS), shows the current chronostratigraphic scale and ages with estimates of uncertainty for all stage boundaries. Special reference is made to the Precambrian part of the time scale, which is coming of age in terms of detail, and to the Neogene portion, which has attained an ultra-high-precision absolute-age calibration.
基金This study is supported jointly by the National Natural Science Foundation of China(No.40172036)"the Key Project of Science and Technology Research"(No.01037)+1 种基金the“Trans-century Training Program for Outstanding Talents”Fund sponsored by the Ministry of Educationthe National Important Basic Research and Development Planning Program(No.1999043206).
文摘An analysis of trace elements and isotopic geochemistry suggest that the ore-forming materials of gold deposits in the Jiaodong granite-greenstone belt have multiple sources, especially the mantle source. Seismic wave, magnetic and gravity fields show that the crust-mantle structure and its coupling mechanism are the fundamental dynamic causes for the exchange and accumulation of materials and energy in the metallogenic system. Considering the evolution history of the structural setting, the tectono-metallogenic dynamics model of the area can be summarized as follows: (1) occurrence of the greenstone belt during the Archean-Proterozoic-the embryonic form of Au-source system; (2) stable tectonic setting in the Paleozoic-an intermittence in gold mineralization; (3) intensive activation and reformation of the greenstone belt in the Mesozoic-tectono-mineralization and tectono-diagensis; (4) posthumous structural activity in the Cenozoic-destruction of orebodies in the later stage. In the middle and late Indosinian, the Tancheng-Lujiang fault zone cut deeply into the upper mantle so that the ore-bearing fluids migrated to higher layers through the crust-mantle interaction, resulting in alteration and mineralization.
基金the National Natural Science Foundation of China(Grant Nos.40232025 and 40325004).
文摘Calcimicrobialites, which could be correlated to the layer 27 in Meishan section according to the Hindeodus parvus, occur abruptly on the end-Permian mass extinction boundary in South China. Microbialites mainly distribute on the top of reef facies or shallow carbonate platforms, thin- ning into deep facies. All the microbialites discovered are composed of micrite and coarse crystal digitate carbonate or patch carbonate. Microfossils usually dominate in the micro- bialites, and small gastropods, bivalves and ostracodes can also be found. This fossil assemblage represents a simple but particular remanent biota after the end-Permian mass ex- tinction on the top of reefs or shallow carbonate platforms. Abrupt occurrence of microbialites above the mass extinction boundary is the ecological response to the end-Permian global event in reef or shallow carbonate facies. Many studies have been done on the Permian-Triassic boundary and event in deep water facies sections or middle to lower shelf facies sections. However, the calcimicrobialites in South China are mainly located above reef facies or shallow carbonate plat- form facies. It will surely be helpful for people to know more about the different responses in different depths of ancient marine environment during the transition between Permian and Triassic by the study of petrology, palaeontology and palaeoecology of the calcimicrobialites.
文摘U-Pb ages of zircon,monazite and xenotime from the Kude and the Sajia leucogranites in the Sajia dome of the North Hima- layan tectonic unit are measured using TIMS method. The results show that the magma emplacement ages for the Kude and the Sajia leu- cogranite are 27.5±0.5 and 14.4±0.2 Ma,respectively. Combined with published U-Pb data from the North Himalayan leu- cogranites,the time-span for the formation of the North Himalayan leucogranites is updated from 27.5 to 10 Ma,instead of previous 15 to 10 Ma.According to the U-Pb ages,the petrogenesis for the North Himalayan leucogranites can be constrained.It is suggested that the North Himalayan leu- cogranites have variety in their petrogenesis.
文摘Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample derived from the early lower crust of the North China craton.It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes,however, is contained in the granulite. These processes include the addition of mantle material, crustal remelting,metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842±40Ma, except few ages of 3097-2824 Ma and 2489-2447Ma. The zircons with ages older than 2447Ma have high εHr(up to+18.3) and high Hf model age (2.5-2.6Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εHr of the zircons with early Proterozoic U-Pb age vary around zero, but two have high εHr up to+9.2-+10.2, indicating mantle contribution during the collision and assembly between the Eastern and Western blocks in the early Proterozoic that resulted in the amalgamation of the North China craton.
文摘The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is just a maximum estimation because some parts of the ELIP were not recognized or dismembered and destroyed during the Triassic to Cenozoic tectonism. In this paper, the chemostratigraphical data of the Zongza block, the Garze-Litang belt and the Songpan-Garze block suggest that the Late Permian basalts in these areas have remarkable similarities to the ELIP basalts in petrography and geochemistry. Flood basalts in the Sanjiangkou area are composed of the lower part of the low-Ti (LT) tholeiite and the upper part of the high-Ti (HT) tholeiite, which is the same as the flood basalts on the western margin of the Yangtze craton. Flood basalts in the Zongza and Songpan-Garze areas, which are far from the Yangtze craton, consist of HT tholeiite only. This is the same as the flood basalts within the Yangtze craton. Therefore we argue that these contemporary basalts all originated from the Emeishan mantle plume, and the ELIP could have a significant westward extension with an outcropped area of over 500,000 km2. This new scenario shows that the LT tholeiite occurs on the western margin of the Yangtze craton, while the HT tholeiite overlying the LT basalts occupies the whole area of the ELIP.
基金supported by the National Natural Science Foundation of China(Grant No.40172068)the Ministry of Science and Technology of China(Grant No.2003CB716506)the US National Science Foundation(Grant No.EAR#0003631).
文摘Eclogites from orogens often show strong plastic deformation and high hydroxyl content. We have studied the correlation between crystallographic preferred orientations of garnet and omphacite from natural eclogites with their hydroxyl contents using the electron back-scat- tered diffraction technique. The results show: 1) Omphacite has typical L-type or SL-type crystrallographic preferred orientations, that is, [001] is distributed in a girdle in the foliation plane with a maximum parallel to lineation; (010) is distributed in a girdle normal to the lineation with a maxi- mum parallel to the foliation plane, suggesting a shear dominant deformation regime. Omphacite fabrics do not vary significantly with hydroxyl content, although the hy- drous component may cause lower flow strength. 2) Hy- droxyl can influence significantly flow properties of garnet in eclogite. Garnets behave as rigid bodies under low tempera- ture and dry conditions. Grain boundary processes will dominate the deformation and lower the flow strength of garnet under high water fugacity conditions. Garnets show no crystallographic preferred orientation in both cases. These results may have important implications for a better understanding of deformation mechanisms and associated fluid activities during deep subduction and exhumation processes.
基金supported by the Geological Survey Program with a Scale of 1:250000 in the Unmapped Area of the Qinghai-Tibetan Plateau,the China Bureau of Geological Survey
文摘High-pressure mafic granulites, occurring as lenses within gneisses and quartzite in the central segment of the Himalayan orogen, were dated using SHRIMP U-Pb technique. 13 analyses out of a total of 15 are plotted along a concordia line and yield a mean 206Pb/238U age of 17.6 0.3 Ma. This age indicates adiabatic decompression and a metamorphic event associated with rapid uplift of granulites in a tectonic environment resulted from the collision between India and Eurasia, synchronous with large-scale thrusting, extension, detachment as well as emplacement of leu-cogranite. One analysis gives a 206Pb/238U age of 29.5 0.4 Ma that is interpreted to represent the timing of the final closure of the Neo-Tethys. Another age is 1991 26 Ma that represents the age of the protolith of the granulites. In sum-mary, dating results show that granulites in this area under-went multiphase metamorphism and complex geological evolution.
基金TheresearchissponsoredbytheNationalNaturalScienceFoundationofChina (No .4 9972 0 78)
文摘The Late Caledonian to Early Hercynian North Qilian orogenic belt in no rthwestern China is an elongate tectonic unit situated between the North China p late in the north and the Qaidam plate in the south. North Qilian started in the latest Proterozoic to Cambrian as a rift basin on the southern margin of North China, and evolved later to an archipelagic ocean and active continental margin during the Ordovician and a foreland basin from Silurian to the Early and Middle Devonian. The Early Silurian flysch and submarine alluvial fan, the Middle to L ate Silurian shallow marine to tidal flat deposits and the Early and Middle Devo nian terrestrial molasse are developed along the corridor Nanshan. The shallowin g upward succession from subabyssal flysch, shallow marine, tidal flat to terre strial molasse and its gradually narrowed regional distribution demonstrate that the foreland basin experienced the transition from flysch stage to molasse stag e during the Silurian and Devonian time.
文摘U-Pb zircon dating by LA-ICP-MS andSHRIMP for one olivine pyroxenite yields complex agepopulations including Mesozoic ages of 97-158 Ma and 228 ±8.7 Ma, Early Paleozoic ages of 418—427 Ma, Paleoprotero-zoic age of 1844±13 Ma, Neoarchean age of 2541 ± 54 Ma andmiddle Archean age of 3123 ± 4.4 Ma. The 97—158 Ma and228 ± 8.7 Ma zircons show typical igneous oscillatory zona-tion in CL images, suggesting two episodes of magmaticevents. Overlapping of the 97-158 Ma ages with that ofgranulite xenoliths indicates that the Mesozoic granu-lite-facies metamorphism was induced by heating from thebasaltic underplating at the base of the lower crust. Bothprocesses lasted at least from about 158 to 97 Ma. Ages of 418--427 Ma could be records of the subduction of Mongoliaoceanic crust under the North China craton. Ages of 1.84 Ga, 2.54 Ga and 3.12 Ga correspond to the three importantcrust-mantle evolutionary events in the North China craton,and imply preservation of Precambrian lower crust in thepresent-day lower crust.
基金supported by the National Natural Science Foundation of China(Grant Nos.40273001,40425002)the EYTP(Grant No.2003-119).
文摘The granulitic xenoliths discovered in the late Cretaceous basaltic rocks from Tuoyun basin, western Xinjiang Province contain the assemblage of Opx + Cpx + Pl ± Grt ± Qtz ± Kfs. Mineral chemistry, petrochemistry and zircon U-Pb ages from the xenoliths have been reported in the paper. Petrogenesis, the lower crustal nature and the mantle-crust interaction reflected by the granulites are discussed as well. Tuoyun granulites are mainly mafic with few intermediate components, and represent the magmatic products underwent granulite-facies metamorphism in lower crustal condition. Equilibrium temperature and the maximum pressure estimates of the granulites are 910 ± 35℃ and 13.5 × 108 Pa respectively, indicating that the crust beneath southwestern Tianshan had the thickness of less than 44 km and high geotherm (e.g. > 80 mW/m2) when the host magma erupted. During their formation, the fractional crystallization of olivine, pyroxene, plagioclase and ilmenite, plagioclase accumulation and the contamination of felsic components or fluid metasomatism processes had happened. Metamorphic zircon U-Pb age of 253 Ma may record the crust-mantle interaction caused by the orogenic root delamination beneath the southwestern Tianshan.
基金This study is supported by the National Natural Science Foundation of China (No. 49972067) the Major State Basic Research Development Program (No. G1999075506).
文摘Detailed three-dimensional structural studies indicate that the Bixiling area, Dabie massif, central China shows the deepest exposed levels of the orogenic wedge formed during the Triassic Yangtze -Sino-Korean continental collision. New 1 : 10 000 scale structural mapping, combined with detailed petrological analysis in this area, has enabled us to accurately distinguish structures related to the Triassic continental collision from those related to post-collisional deformation in the ultrahigh pressure (UHP) metamorphic unit. The collisional or compressional structures include the massive eclogite with a weak foliation, foliated eclogite or UHP ductile shear zones, as well as upper amphibolite facies shear zones, whereas the post-collisional deformation is characterized by a regionally, flat-lying foliation containing stretching lineations and common reclined folds. The former is present exclusively in the eclogite lenses and their margins, representing orogenic thickening or syn-collisional events, while the latter was best occurred on variable scales under amphibolite facies conditions, showing sub-vertical, extreme shortening and ductile thinning of the metamorphic rock stack. The eclogite facies tectonites that have a marked fabric discordance to the penetrative amphibolite facies extension flow fabric are common. It is emphasized that an extensional tectonic setting following the collision-orogenic thickening stage was, at least partly, responsible for exhumation of the UHP metamorphic rocks in the Dabie massif. A new tectonic evolution model is proposed for the UHP metamorphic belt on the scale of the Dabie massif. The Bixiling area thus provides a window, from which the dynamic processes concerning the formation and exhumation of the UHP rocks can be observed. Regional studies in the Dabie Mountains have confirmed this interpretation.
文摘Glaucophane in Shuangjiang area, West Yunnan Province, supplies a chance for studying south segment of Lancangjiang tectonic zone. But people are at odds as to whether two stage glaucophane exists or not, glaucophane is the result of dynamic metamorphism later, or indicates a high P/T metamorphic belt when Paleozoic Tethys Sea closed. Authors discover in a recent research that there is only one stage glaucophane in Shuangjiang area, and three blueschist belts are distributed near N S tending, and glaucophane in Shuangjiang area is related to the eastward subduction of Changning Menglian basin.
基金the National Natural Science Foundationof China ( Nos. 40172012 and 40232025 ), the Australian Common wealth Government and Deakin University for the award of an Interna tional Postgraduate Research Scholarship (IPRS) to PYQ
文摘Sediments of carbonate gravity flows and terrigenous debris turbidites, and normal bathyal deposits were found at the Shaiwa Section, Ziyun County, Guizhou Province, southwestern China. Through grain size analysis of some typical sediments at this section, the changing patterns of the grain parameters and the grain size cumulations were recovered. Results show that the study area was deposited under turbidite control during the Late Permian period, which we also recognized at the outcrop section upon sedimentary characteristics of the sediments. In addition, fossils are abundant in the Upper Permian of the Shaiwa Section, including radiolarians, sponge spicules, bivalves, brachiopods, ammonoids and trace fossils. Radiolarians and siliceous sponge spicules are typical deep water assemblages. Bivalves are dominated by genera of Hunanopecten and Claraia , both showing deep water living characteristics. Ammonoids are composed of planktonic types, showing characteristics of smooth and flat shells. Brachiopods are dominated by a small and thin shelled assemblage, which are commonly flat in shape and usually of slight ornamentations on shells. In addition, trace fossils found at the Shaiwa Section are also common types of deep water facies. Thus, the fossil evidence of the Shaiwa Section also suggests a deep water environment, possibly from the bathyal slope to the basin margin facies, of the studied area during the Late Permian period.
文摘There are two models of ultrahigh pressure metamorphism (UHPM) zone in Dabie: the model of under thrusting returning which even arrives at the mantle and the superimposed model of tectonics in the crust. There are two points of view in the argument about formation depth of ultrahigh pressure metamorphism: (1) the depth can be calculated by hydrostatic equation; (2) the high pressure was composed of gravity, tectonic and other forces instead of merely gravity force. Some misunderstandings of mechanical conceptions presented in the paper showing the hydrostatic viewpoints should be open to question. The main conceptions are: (1) the confining pressure was only formed by gravity, and the differential stress was only formed by tectonic force; (2) the differential stress is not big enough to lead to form ultrahigh pressure metamorphism; (3) once tectonic overpressure goes beyond the limited strength of rocks the tectonic force would disappear and the rocks would be broken or rheomorphied at the same time. A short discussion in basic mechanics is made in this paper for a perfect process for discussing the argument.
文摘In the Central Orogenic Belt, China, two UHP metamorphic belts are discriminated mainly based on a detailed structural analysis of the Kanfenggou UHP metamorphic fragment exposed in the eastern Qinling orogen, and together with previous regional structural, petrological and geochronological data at the scale of the orogenic domain. The first one corresponds to the South Altun North Qaidam North Qinling UHP metamorphic belt. The other is the Dabie Sulu UHP and HP metamorphic belts. The two UHP metamorphic belts are separated by a series of tectonic slices composed by the Qinling rock group, Danfeng rock group and Liuling or Foziling rock group etc. respectively, and are different in age of the peak UHP metamorphism and geodynamic implications for continental deep subduction and collision. Regional field and petrological relationships suggest that the Kanfenggou UHP metamorphic fragment that contains a large volume of the coesite and microdiamond bearing eclogite lenses is compatible with the structures recognized in the South Altun and North Qaidam UHP metamorphic fragments exposed in the western part of China, thereby forming a large UHP metamorphic belt up to 1 000 km long along the orogen strike. This UHP metamorphic belt represents an intercontinental deep subduction and collision belt between the Yangtze and Sino Korean cratons, occurred during the Paleozoic. On the other hand, the well constrained Dabie Sulu UHP and HP metamorphic belts occurred mainly during Triassic time (250-220 Ma), and were produced by the intracontinental deep subduction and collision within the Yangtze craton. The Kanfenggou UHP metamorphic fragment does not appear to link with the Dabie Sulu UHP and HP metamorphic belts along the orogen. There is no reason to assume the two UHP metamorphic belts as a single giant deep subduction and collision zone in the Central Orogenic Belt situated between the Yangtze and Sino Korean cratons. Therefore, any dynamic model for the orogen must account for the development of UHP metamorphic
文摘The studies on stromatolites occurring in the Mesoproterozoic Tieling Formation, Zhoukoudian, Beijing indicate that the thickness of bright-dark lamina pairs in the stromatolites shows periodic variations, which are inter- preted as monthly and seasonal rhythms. On the basis of the S-shaped stromatolites, some preliminary paleo-astronomic parameters have been obtained as follows: In the late Meso- proterozoic (1000 Ma ago) there were at least 516±20 d, 12.9 ±0.5 months per year, 40 d per month and at most 16.99± 0.66 h per day, and paleo-obliquity of the ecliptic was 29.2°— 30.6°.
