A protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16 32 μm.This was accomplished by introducing N 2 into ICP to increase the sensitivity.The...A protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16 32 μm.This was accomplished by introducing N 2 into ICP to increase the sensitivity.The obtained U-Pb ages for zircon standards GJ-1,TEMORA and SK10-2 are consistent with the preferred values within about 1% uncertainty (2σ) by simple external calibration against zircon standard 91500.Different data reduction softwares could yield different uncertainties for calculation of U-Pb ages.The commercially available program GLITTER4.4 could apply an improper uncertainty calculation strategy,but it may yield artificial high precisions for single analyses.Our trace element analyses indicate that Si is not an ideal internal standard for zircon when calibrated against the NIST glasses.Calibration against the NIST glasses using Si as an internal standard,a systematic deviation of 10% 30% was found for most trace elements including Zr.However,the trace element compositions of zircon can be accurately measured by calibration against multiple reference materials with natural compositions (e.g.,BCR-2G,BHVO-2G and BIR-1G),or calibration against NIST SRM 610 and using Zr as an internal standard.Analyses of two pieces of GJ-1 demonstrate that it is relatively homogenous for most trace elements (except for Ti).展开更多
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-...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.展开更多
Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comp...Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comparable with that of SHRIMP in both accuracy and precision. The age is also identical to that of the Yinmawanshan gabbro from the Liaodong Peninsula within error. Both the Yongsheng nepheline syenite and the Yinmawanshan gabbro represent the youngest known exposed intrusions in northeastern and even eastern China. The results indicate the Eocene mantle-derived magmatic underplating, and the rapid crustal uplifting of this region since 30 Ma. The analyses also document extremely high LREE concentrations and relatively flat REE patterns for the zircons from the Yongsheng nepheline syenite, which represent a new type of zircon REE pattern.展开更多
The Cretaceous granitoids in the middle and northern Gangdese, Tibet are generally interpreted as the products of anatexis of thickened deep crust genetically associated with the Lhasa-Qiangtang collision. This paper ...The Cretaceous granitoids in the middle and northern Gangdese, Tibet are generally interpreted as the products of anatexis of thickened deep crust genetically associated with the Lhasa-Qiangtang collision. This paper reports bulk-rock major element, trace element and Sr-Nd isotopic data, zircon U-Pb age data, and zircon Hf isotopic data on the Zayu pluton in eastern Gangdese, Tibet. These data shed new light on the petrogenesis of the pluton. Our SHRIMP zircon U-Pb age dates, along with LA-ICPMS zircon U-Pb age dates recently reported in the literature, indicate that the Zayu pluton was emplaced at about 130 Ma, coeval with Early Cretaceous magmatic rocks in other areas of eastern Gangdese (e.g., Rawu, Baxoi areas) and the Middle Gangdese. The Zayu pluton samples lack amphibole and muscovite, and are compositionally characterized by high SiO2 (69.9%–76.8%), K2O (4.4%–5.7%), and low P2O5 (0.05%–0.12%). These samples also have A/CNK values of 1.00–1.05, and are enriched in Rb, Th, U, and Pb, and depleted in Ba, Nb, Ta, Sr, P, Ti, and Eu. These geochemical features suggest that the Zayu pluton samples are metaluminous to slightly peraluminous and are of highly fractionated I-type granite. The Zayu pluton samples have high ? Nd(t) values (?10.9–?7.6) and low initial 87Sr/86Sr ratios (0.7120–0.7179) relative to melts derived from mature continental crust in the Gangdese (e.g., Ningzhong Early Jurassic strongly peraluminous granite). The Zayu pluton samples are heterogeneous in zircon ? Hf(t) values (?12.8–?2.9), yielding ancient zircon Hf crustal model ages of 1.4–2.0 Ga. The data obtained in this study together with the data in the recent literature suggest that the Early Cretaceous granitoids in eastern Gangdese represent the eastward extension of the Early Cretaceous magmatism in the middle Gangdese, and that the Lhasa micro-continent block with ancient basement may extend for ～2000 km from east to west. Zircon Hf isotopic data and bulk-rock zircon saturation temperature (789–821 °C) indicate t展开更多
Although a number of petrographic observations and isotopic data suggest that magma mixing is common in genesis of many granite plutons, it is still controversial whether the mantle-derived magmas were involved in gra...Although a number of petrographic observations and isotopic data suggest that magma mixing is common in genesis of many granite plutons, it is still controversial whether the mantle-derived magmas were involved in granites. We carried out in this study a systematic analysis of in situ zircon Hf-O isotopes for three early Yanshanian intrusions dated at ca. 160 Ma from the Nanling Range of Southeast China. The Qinghu monzonite has very homogeneous zircon Hf-O isotopic compositions, εHf(t) =11.6±0.3 and δ18O=5.4‰±0.3‰. In combination with whole-rock geochemical and Sr-Nd isotopic data, the parental magma of the Qinghu monzonite were likely derived from the partial melting of recently-metasomatized, phlogopite-bearing lithospheric mantle without appreciable crustal contamination. The Lisong and Fogang granites and the mafic microgranular enclaves (MME) within the Lisong granites have a wide range of zircon Hf-O isotopic compositions, with Hf and O isotopes being negatively correlated within each pluton. The Lisong MMEs were crystallized from a mantle-derived magma, similar to the parental magma of the Qinghu monzonite, with small amount of crustal assimilation. The Lisong and Fogang granites were formed by reworking of meta-sedimentary materials by mantle-derived magmas and mixing of the mantle-and sediment-derived melts to varying degrees. It is thus concluded that these two Yanshanian granites in the Nanling Range were formed associated with growth and differentiation of continental crust.展开更多
基金supported by the National Natural Science Foundation of China (GrantNos. 40821061,90914007,40576030 and 90714010)the State Administration of Foreign Expert Affairs of China (Grant No. B07039)the Special Fund for Basic Scientific Research of Central Colleges,China University of Geosciences
文摘A protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16 32 μm.This was accomplished by introducing N 2 into ICP to increase the sensitivity.The obtained U-Pb ages for zircon standards GJ-1,TEMORA and SK10-2 are consistent with the preferred values within about 1% uncertainty (2σ) by simple external calibration against zircon standard 91500.Different data reduction softwares could yield different uncertainties for calculation of U-Pb ages.The commercially available program GLITTER4.4 could apply an improper uncertainty calculation strategy,but it may yield artificial high precisions for single analyses.Our trace element analyses indicate that Si is not an ideal internal standard for zircon when calibrated against the NIST glasses.Calibration against the NIST glasses using Si as an internal standard,a systematic deviation of 10% 30% was found for most trace elements including Zr.However,the trace element compositions of zircon can be accurately measured by calibration against multiple reference materials with natural compositions (e.g.,BCR-2G,BHVO-2G and BIR-1G),or calibration against NIST SRM 610 and using Zr as an internal standard.Analyses of two pieces of GJ-1 demonstrate that it is relatively homogenous for most trace elements (except for Ti).
文摘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.
基金co-supported by the National Natural Science Foundation of China(Grant Nos.40133020 and 40272045)the Chinese Ministry of Science and Technology of China(Grant No.G1999043202)the Chinese Academy of Sciences and the Key Laboratory of Continental Dynamics,Northwest University,the Ministry of Education of China.
文摘Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comparable with that of SHRIMP in both accuracy and precision. The age is also identical to that of the Yinmawanshan gabbro from the Liaodong Peninsula within error. Both the Yongsheng nepheline syenite and the Yinmawanshan gabbro represent the youngest known exposed intrusions in northeastern and even eastern China. The results indicate the Eocene mantle-derived magmatic underplating, and the rapid crustal uplifting of this region since 30 Ma. The analyses also document extremely high LREE concentrations and relatively flat REE patterns for the zircons from the Yongsheng nepheline syenite, which represent a new type of zircon REE pattern.
基金Supported by National Natural Science Foundation of China (Grant Nos. 40572051, 40830317, 40873023, 40672044)National Basic Research Program of China (Grant No. 2009CB421002), Chinese "111" Project (Grant No. B07011)Programme of the Integrated Study of Basic Geology of Qinghai-Tibetan Plateau of the China Geological Survey
文摘The Cretaceous granitoids in the middle and northern Gangdese, Tibet are generally interpreted as the products of anatexis of thickened deep crust genetically associated with the Lhasa-Qiangtang collision. This paper reports bulk-rock major element, trace element and Sr-Nd isotopic data, zircon U-Pb age data, and zircon Hf isotopic data on the Zayu pluton in eastern Gangdese, Tibet. These data shed new light on the petrogenesis of the pluton. Our SHRIMP zircon U-Pb age dates, along with LA-ICPMS zircon U-Pb age dates recently reported in the literature, indicate that the Zayu pluton was emplaced at about 130 Ma, coeval with Early Cretaceous magmatic rocks in other areas of eastern Gangdese (e.g., Rawu, Baxoi areas) and the Middle Gangdese. The Zayu pluton samples lack amphibole and muscovite, and are compositionally characterized by high SiO2 (69.9%–76.8%), K2O (4.4%–5.7%), and low P2O5 (0.05%–0.12%). These samples also have A/CNK values of 1.00–1.05, and are enriched in Rb, Th, U, and Pb, and depleted in Ba, Nb, Ta, Sr, P, Ti, and Eu. These geochemical features suggest that the Zayu pluton samples are metaluminous to slightly peraluminous and are of highly fractionated I-type granite. The Zayu pluton samples have high ? Nd(t) values (?10.9–?7.6) and low initial 87Sr/86Sr ratios (0.7120–0.7179) relative to melts derived from mature continental crust in the Gangdese (e.g., Ningzhong Early Jurassic strongly peraluminous granite). The Zayu pluton samples are heterogeneous in zircon ? Hf(t) values (?12.8–?2.9), yielding ancient zircon Hf crustal model ages of 1.4–2.0 Ga. The data obtained in this study together with the data in the recent literature suggest that the Early Cretaceous granitoids in eastern Gangdese represent the eastward extension of the Early Cretaceous magmatism in the middle Gangdese, and that the Lhasa micro-continent block with ancient basement may extend for ～2000 km from east to west. Zircon Hf isotopic data and bulk-rock zircon saturation temperature (789–821 °C) indicate t
基金Supported by National Basic Research Program of China (Grant No. 2007CB411403)Knowledge Innovation Project of the Chinese Academy of Sci-ences (Grant No. KZCX1-YW-15-2)National Natural Science Foundation of China (Grant No. 40728002)
文摘Although a number of petrographic observations and isotopic data suggest that magma mixing is common in genesis of many granite plutons, it is still controversial whether the mantle-derived magmas were involved in granites. We carried out in this study a systematic analysis of in situ zircon Hf-O isotopes for three early Yanshanian intrusions dated at ca. 160 Ma from the Nanling Range of Southeast China. The Qinghu monzonite has very homogeneous zircon Hf-O isotopic compositions, εHf(t) =11.6±0.3 and δ18O=5.4‰±0.3‰. In combination with whole-rock geochemical and Sr-Nd isotopic data, the parental magma of the Qinghu monzonite were likely derived from the partial melting of recently-metasomatized, phlogopite-bearing lithospheric mantle without appreciable crustal contamination. The Lisong and Fogang granites and the mafic microgranular enclaves (MME) within the Lisong granites have a wide range of zircon Hf-O isotopic compositions, with Hf and O isotopes being negatively correlated within each pluton. The Lisong MMEs were crystallized from a mantle-derived magma, similar to the parental magma of the Qinghu monzonite, with small amount of crustal assimilation. The Lisong and Fogang granites were formed by reworking of meta-sedimentary materials by mantle-derived magmas and mixing of the mantle-and sediment-derived melts to varying degrees. It is thus concluded that these two Yanshanian granites in the Nanling Range were formed associated with growth and differentiation of continental crust.
