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Fluid activity during exhumation of deep-subducted continental plate

Chinese Science Bulletin 2004年第10期49卷 985-998页

作者： zhengyongfei SchoolofEarthandSpaceSciences UniversityofScienceandTechnol-ogyofChinaHefei230026China(e-mail:yfzheng@***)

It is well known that a great deal of fluid wasreleased during subduction of oceanic crust, resulting in arcmagmatism, quartz veining and metamorphic mineralizationof syn-subduction. In contrast, the process of continentalsubduction is characterized by the relative lack of fluid andthus no arc magmatism has been found so far. During exhu-mation of deep-subducted continental crust, nevertheless,significant amounts of aqueous fluid became available fromthe decomposition of hydrous minerals, the decrepitation ofprimary fluid inclusions, and the exsolution of structuralhydroxyls. This kind of metamorphic fluid has recently at-tracted widespread interests and thus been one of the mostimportant targets in deciphering the geological processesconcerning metamorphism, magmatism and mineralizationin collisional orogens. A large number of studies involvingstable isotopes, fluid inclusions and petrological phase rela-tionships have been accomplished in past a few years withrespect to the mobility and amount of metamorphic fluid inUHP metamorphic rocks from the Dabie-Sulu orogenic *** results demonstrate that the fluid activity during theexhumation of deep-subducted continental crust has the fol-lowing effects: (1) amphibolite-facies retrogression due topervasive fluid flow; (2) formation of HP quartz veins withineclogites due to channelized fluid flow; and (3) partial melt-ing of overlying crustal rocks due to focused fluid flow, pro-ducing syn-exhumation magmatism within the orogenic *** particular, the aqueous fluid released by decompressionexsolution of hydroxyl from UHP minerals is characterizedby low salinity and is capable of resulting in pervasive andchannellized flow. Therefore, the intensive study of fluid ac- tivity during exhumation of UHP metamorphic rocks can notonly provide insight into geodynamic processes that occurred in continental collisional belts, but also shed light on under- standing of crust-mantle recycling and relevant magmatism in subduction

关键词：大陆板快深俯冲含水矿物超高压变质减压剥落流活性结构羟基稳定同位素流包含物岩石

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Genesis of zircon and its constraints on interpretation of U-Pb age

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Chinese Science Bulletin 2004年第15期49卷 1554-1569页

作者： WUYuanbao zhengyongfei SchoolofEarthandSpaceSciences UniversityofScienceandTechnologyofChinaHefei230026China

Zircon U-Pb dating is the most commonly used method for isotopic geochronology. However, it has been a difficult issue when relating zircon U-Pb ages to metamor- phic conditions in complex metamorphic rocks. Much pro- gress has been made in the past decade with respect to the genesis of zircon and its constraints on interpretation of U-Pb age. Three methods have been proposed to link zircon U-Pb age to metamorphic conditions: (ⅰ) internal structure; (ⅱ) trace element feature; (ⅲ) mineral inclusion composition. Magmatic zircon shows typical oscillatory zoning and/or sector zoning, whereas metamorphic zircon has internal structures such as no zoned, weakly zoned, cloudy zoned, sector zoned, planar zoned, and patched zoned ones. Zircons formed in different geological environments generally have characteristic internal structures. Magmatic zircons from different rock types have variable trace element abundances, with a general trend of increasing trace element abundances in zircons from ultramafic through mafic to granitic rocks. Zircons formed under different metamorphic conditions have different trace element characteristics that can be used to relate their formation to metamorphic conditions. It is an effective way to relate zircon growth to certain P-T condi- tions by studying the trace element partitioning between coexisting metamorphic zircon and garnet in high-grade metamorphic rocks containing both zircon and garnet. Pri- mary mineral inclusions in zircon can also provide unambi- guous constraints on its formation conditions. Therefore, interpretation of zircon U-Pb ages can be constrained by its internal structure, trace element composition, mineral inclu- sion and so on.

关键词： U-Pb定年锆石内部结构示踪元素矿物包含物同位素地质年代学

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Zircon U-Pb ages for Wulian granites in northwest Sulu and their tectonic implications

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Chinese Science Bulletin 2003年第4期48卷 379-384页

作者： ZHOUJianbo zhengyongfei 等 ScoolofEarthSciences JilinUniversityChangchun130026China SchoolofEarthandSpaceSciences UniversityofScienceandTechnologyofChinaHetei230026China

The Wulian complex occurring in the north- western part of the Sulu orogen consists of metaigneous and metasedimentary rocks at greenschist-facies. Zircon U-Pb dating for three granite intrusions within it yields concor-dant ages of (672±4), (742±9) and (747±14) Ma, respec-tively. These ages indicate that the granites are the Neopro-terozoic intrusions in the northern margin of the Yangtze plate, and correspond to the magmatic complex at Luzhen-guan in the eastern part of the Beihuaiyang belt in the Dabie orogen. They were tectonic slices scraped off from the Yang-tze plate during Triassic subduction and thus belong to a part of the accretionary wedge of the Yangtze plate subduc-tion. The discovery of extensive Neoproterozoic magmatic rocks in the Wulian area suggests that the suture location between the North China and the Yangtze plates lies north of the Wulian complex.

关键词：锆石 U-Pb测年山东五连组花岗岩苏鲁造山带构造地质

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Position of South China in configuration of Neoprotero- zoic supercontinent

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Chinese Science Bulletin 2004年第8期49卷 751-753页

作者： zhengyongfei SchoolofEarthandSpaceSciences UniversityofScienceandTechnologyofChinaHefei230026China

Configuration and evolution of Neoproterozoic supercontinent and the position of South China within it have been very important targets in earth sciences concerning many forefront topics of general interest. In the common reconstruction of the supercontinent Rodinia, south China was located between Australia and Laurentia, and thus lies in the center of the supercontinent and southeast of Australia, According to the new paleomagnetic and geochronological data for the approx 800 Ma Xiaofeng dyke in Yichang as existing data, Li et al. suggest that Rodinia would probably spread from the equator to the polar region at about 800 Ma, followed by rapid ca. 90 deg C rotation around an axis near Greenland that brought the entire supercontinent to a low-latitude position by ca. 750 Ma. As a result, South China is reinterpreted to be placed adjacent to both Australia and India, with a rapid shift of rotation from a position northeast of Australia and southeast of India at about 800 Ma (Fig. l (a)) to a position northwest of Australia and northeast of India at about 750 Ma (Fig. l(b)). By combining existing paleomagnetic data with their new paleomagnetic data for the Cambrian sediments in the Sichuan Basin, Yang et al. also place South China against northwestern Australia but remote southeast of India at about 755 *** the Paleopangaea reconstruction, South China was placed in northeast of India. In the discussion of relationship between the Rodinia configuration and the snowball Earth event, South China was tentatively placed in northwest of India. In dynamic models of reconstructing the Rodinia assemblage and breakup on the basis of global paleomagnetic data, Powell et al. placed South China in northeast of Australia and thus remote east of India; Meert and Torsvik placed South China in northeast of Australia and northwest of Laurentia, interjacent between two transform faults in its southeast and southwest. Geochemical studies of Zhou et al. suggest that Neoproterozoic magm

关键词：新元古代中国南部地区超大陆布局动态模型磁性岩体锆石探年

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Finding of Neoproterozoic low-^(18)O igneous rocks in the northern margin of the Dabie orogen

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Chinese Science Bulletin 2004年第14期49卷 1536-1538页

作者： zhengyongfei WUYuanbao ZHAOZifu GONGBing SchoolofEarthandSpaceSciences UniversityofScienceandTechnologyofChinaHefei230026China

Examines the occurrence of coeval igneous rocks during the Neoproterozoic age in the northern margin of Dabie orogen. Method used to identify the igneous rock in the surface water signature of China; Investigation on the capability of zircon to preserve O isotope composition under conditions of ultrahigh pressure eclogite-facies metamorphism; Interaction of energy and matter in the earth during the period.

关键词：新元古代低^18O火成岩大别山造山带 U-Pb定年

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Rb-Sr and U-Pb Dating of the Daguzhai and Luobuli Granitic Massifs in South China

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Chinese Journal Of Geochemistry 1992年第2期11卷 97-110页

作者： zhengyongfei SHENWEIZHOU 等 GeochemicalInstitute UniversityofGottingenGoldschmidtstrasse1D－3400GottingenGermany DepartmentofE

Rb-Sr and U-Pb isotopic studies of the two contrasting granite types of the Dauzhai and Luobuli massifs in South China provide new constraints on the interpretation of isotopic age data for plutonic igneous rocks.A Rb-Sr internal isochron age of 146±7Ma for the Luobuli adamelligte is interpreted to represent the age of magma crystallization,whereas the whold-rock Rb-Sr isochron yields an older apparent age of 161±10Ma which is regarded as resulting from contamination processes affecting the petrogenesis of 161±10Ma which is regarded as resulting from contamination processes affecting the petrogenesis of this *** the Daguzhai granite the marked scatter of whole-rock Rb-Sr data in isochron diagram is ascribed to the open sstem behavior of Rb during postmagmatic *** of intital ^87Sr/^86Sr ratio in this granite is indicated in a plot of ^87 Sr versus ^*** autometasomatism has also affected zircon U-Pb system ,resulting in a spread of data along the *** between 165 and *** spread is regarded as indicating the duration the autometasomatism.

关键词：铷-锶年代学铀-铅年代学花岗岩华南地区同位素火成岩

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