A combined study using LA-ICP-MS U-Pb dating, Hf isotopes, trace elements and the Ti-in-zircon geothermometer was carried out on zircons from the metamorphosed basic-ultrabasic rocks in the metamorphic basement of the...A combined study using LA-ICP-MS U-Pb dating, Hf isotopes, trace elements and the Ti-in-zircon geothermometer was carried out on zircons from the metamorphosed basic-ultrabasic rocks in the metamorphic basement of the Cathaysia Block, southwestern Zhejiang Province. The formation and metamorphic ages of the rocks from the metamorphic basement of the Cathaysia Block were determined based on zircon U-Pb geochronology. The age for the magmatic crystalline zircons from the protolith is about 1.85 Ga. The ε Hf (t) values of the older zircons were from ?7 to ?3, with two-stage model Hf ages (T DM2 LC ) of about 2.9 to 3.4 Ga, indicating that the source material was derived from anatexis and recycling of the Archean crust. The newly formed metamorphic zircons yielded U-Pb ages of 260–230 Ma. The metamorphic temperature calculated using the Ti-in-zircon geothermometer ranged from 610 to 720°C, consistent with the results from petrographic observations, indicating that the Cathaysia Block experienced an amphibolite facies metamorphism during the Indosinian. Results from this study provided an important timeframe for the tectonic evolution in South China and the Southeast Asia during the Late Permian and Early Triassic times.展开更多
A combined study of zircon LA-ICP-MS U-Pb dating, trace elements and Hf isotope was carried out for gneissic granite from the Sanzhishu area in Jingning, SW Zhejiang Province. Nearly all the zircons separated from the...A combined study of zircon LA-ICP-MS U-Pb dating, trace elements and Hf isotope was carried out for gneissic granite from the Sanzhishu area in Jingning, SW Zhejiang Province. Nearly all the zircons separated from the granite exhibited oscillatory zoning and high Th/U ratios (>0.1). The REE profile showed a pronounced positive Ce anomaly, negative Eu anomaly and an enrichment of HREE, which are typical characteristics of magmatic zircon. Thirteen concordant or nearly concordant analytical data yielded a weighted mean 207Pb/206Pb age of 1860±13 Ma (MSWD=0.084), representing the formation age of the granite. The magmatic zircons had negative εHf(t) values of -15.6 to -10.0 and two-stage Hf model ages of 3.1 to 3.4 Ga, indicating that the granites were formed by reworking of ancient crust. The major- and trace-element data indicate that the gneissic granites are metaluminous high-K calc-alkaline rocks and exhibit the same geochemical characteristics as aluminous A-type granites, implying the emplacement of the granite in a post-orogenic extensional tectonic setting. We conclude that the Pa-leoproterozoic crustal reworking event in the Cathaysia Block of South China marked the transition from assembly to break-up of the Columbia supercontinent.展开更多
基金the National Natural Science Foundation of China (Grant No. 40372094)the Opening Foundation of State Key Laboratory of Continental Dy-namics, Northwest University (Grant No. 06LCD12)the project of Land and Resources Bureau of Zhejiang Province (Grant No. 2004005)
文摘A combined study using LA-ICP-MS U-Pb dating, Hf isotopes, trace elements and the Ti-in-zircon geothermometer was carried out on zircons from the metamorphosed basic-ultrabasic rocks in the metamorphic basement of the Cathaysia Block, southwestern Zhejiang Province. The formation and metamorphic ages of the rocks from the metamorphic basement of the Cathaysia Block were determined based on zircon U-Pb geochronology. The age for the magmatic crystalline zircons from the protolith is about 1.85 Ga. The ε Hf (t) values of the older zircons were from ?7 to ?3, with two-stage model Hf ages (T DM2 LC ) of about 2.9 to 3.4 Ga, indicating that the source material was derived from anatexis and recycling of the Archean crust. The newly formed metamorphic zircons yielded U-Pb ages of 260–230 Ma. The metamorphic temperature calculated using the Ti-in-zircon geothermometer ranged from 610 to 720°C, consistent with the results from petrographic observations, indicating that the Cathaysia Block experienced an amphibolite facies metamorphism during the Indosinian. Results from this study provided an important timeframe for the tectonic evolution in South China and the Southeast Asia during the Late Permian and Early Triassic times.
基金Supported by National Natural Science Foundation of China (Grant No. 40873004)Special Funds for National Scientific Research of Commonweal Industries+3 种基金the Ministry of Land and Resources of China (Grant No. 2008110015)Opening Foun-dation of State Key Laboratory of Continental DynamicsNorthwest University (Grant No. 06LCD12)the Project of Land and Resources Bureau of Zhejiang Province (Grant No. 2004005)
文摘A combined study of zircon LA-ICP-MS U-Pb dating, trace elements and Hf isotope was carried out for gneissic granite from the Sanzhishu area in Jingning, SW Zhejiang Province. Nearly all the zircons separated from the granite exhibited oscillatory zoning and high Th/U ratios (>0.1). The REE profile showed a pronounced positive Ce anomaly, negative Eu anomaly and an enrichment of HREE, which are typical characteristics of magmatic zircon. Thirteen concordant or nearly concordant analytical data yielded a weighted mean 207Pb/206Pb age of 1860±13 Ma (MSWD=0.084), representing the formation age of the granite. The magmatic zircons had negative εHf(t) values of -15.6 to -10.0 and two-stage Hf model ages of 3.1 to 3.4 Ga, indicating that the granites were formed by reworking of ancient crust. The major- and trace-element data indicate that the gneissic granites are metaluminous high-K calc-alkaline rocks and exhibit the same geochemical characteristics as aluminous A-type granites, implying the emplacement of the granite in a post-orogenic extensional tectonic setting. We conclude that the Pa-leoproterozoic crustal reworking event in the Cathaysia Block of South China marked the transition from assembly to break-up of the Columbia supercontinent.
