A detailed microstructure analysis and LA-ICPMS U-Pb dating have been done for zir- cons of Weishan granite from Hunan Province, South China. The results indicate that the Weishan granite is a multistage batholith for...A detailed microstructure analysis and LA-ICPMS U-Pb dating have been done for zir- cons of Weishan granite from Hunan Province, South China. The results indicate that the Weishan granite is a multistage batholith formed during the late Indosinian-early Yanshanian time. The intruded time of the late Indosinian granite is 211.0±1.6Ma and 215.7±1.9Ma (two samples), whereas that of the early Yanshanian granite is 187.4±3.5Ma and 184.5±5.1Ma (two samples). In combination with other geochronological data for Indosinian rocks of South China and the adjacent region, it is inferred that the late Indosinian granites of South China (especially Hunan Province) are probably formed under extension regime as a consequence of post-collision stress relaxation, which is a spontaneous response to intracontinental thickening attributed to the collision and extrusion of two Indosinian seams, namely Qinling-Dabie and Song Ma. Moreover, it is also deduced that the early Yanshanian granites of Hunan Province could not be directly related with the subduction of Paleo-Pacific plate towards Eurasian continent, and they are most likely derivation of the mid- or lower-crustal materials because of decompressional melting under the continuous extension setting.展开更多
The Linxi Formation occupies an extensive area in the eastern Inner Mongolia in the Central Asian Orogenic Belt （CAOB）. The Linxi Formation is composed of slate, siltstone, sandstone and plant, lamellibranch microfo...The Linxi Formation occupies an extensive area in the eastern Inner Mongolia in the Central Asian Orogenic Belt （CAOB）. The Linxi Formation is composed of slate, siltstone, sandstone and plant, lamellibranch microfossils in the associated strata. Major and trace element data （including REE） for sandstones from the formation indicate that these rocks have a greywacke protolith and have been deposited during a strong tectonic activity. LA-ICPMS U-Pb dating of detrital zircons yield ages of 1801 to 238 Ma for four samples from the Linxi Formation. 425-585 Ma, together with the ~500 Ma age for the metamorphism event previously determined for Northeast China, indicates that their provenance is the metamorphic rocks of Pan-African age that have a tectonic affinity to NE China. A few older zircons with U-Pb ages at 1689-1801 Ma, 1307 1414 Ma, 593-978 Ma are also present, revealing the Neoproterozoic history of NE China. The youngest population shows a peak at ca. 252 Ma, suggesting that the main deposition of the Linxi Formation was at late Permain. Moreover, the ca. 250 Ma zircon grains of all four samples yield weighted mean ^206pb/^238U ages of 250 ± 3 Ma, 248 ± 3 Ma, 249 ± 3 Ma, and 250 ± 2 Ma, respectively. These ages, together with the youngest zircon age in the sample ZJB-28 （ca. 238 Ma）, suggest that the deposition of the Linxi Formation extended to the early Triassic. Combining with previous results, we suggest that the final collision of the Central Asian Orogenic Belt （CAOB） in the southern of Linxi Formation, which located in the Solonker-Xra Moron-Changchun suture, and the timing for final collision should be at early Triassic.展开更多
基金This work was supported by the National Natural Science Foundation of China(Grant No.40372036)the Doctoral Foundation of Ministry of Education of PRC(Grant No.20030284026).
文摘A detailed microstructure analysis and LA-ICPMS U-Pb dating have been done for zir- cons of Weishan granite from Hunan Province, South China. The results indicate that the Weishan granite is a multistage batholith formed during the late Indosinian-early Yanshanian time. The intruded time of the late Indosinian granite is 211.0±1.6Ma and 215.7±1.9Ma (two samples), whereas that of the early Yanshanian granite is 187.4±3.5Ma and 184.5±5.1Ma (two samples). In combination with other geochronological data for Indosinian rocks of South China and the adjacent region, it is inferred that the late Indosinian granites of South China (especially Hunan Province) are probably formed under extension regime as a consequence of post-collision stress relaxation, which is a spontaneous response to intracontinental thickening attributed to the collision and extrusion of two Indosinian seams, namely Qinling-Dabie and Song Ma. Moreover, it is also deduced that the early Yanshanian granites of Hunan Province could not be directly related with the subduction of Paleo-Pacific plate towards Eurasian continent, and they are most likely derivation of the mid- or lower-crustal materials because of decompressional melting under the continuous extension setting.
基金funded by grants from the Chinese Ministry of Science and Technology(Grant No.2013CB429802)National Natural Science Foundation of China(Grant Nos.41390441,41190075, and 41272241)the Chinese Geological Survey(Grant No. 1212011120153)
文摘The Linxi Formation occupies an extensive area in the eastern Inner Mongolia in the Central Asian Orogenic Belt （CAOB）. The Linxi Formation is composed of slate, siltstone, sandstone and plant, lamellibranch microfossils in the associated strata. Major and trace element data （including REE） for sandstones from the formation indicate that these rocks have a greywacke protolith and have been deposited during a strong tectonic activity. LA-ICPMS U-Pb dating of detrital zircons yield ages of 1801 to 238 Ma for four samples from the Linxi Formation. 425-585 Ma, together with the ~500 Ma age for the metamorphism event previously determined for Northeast China, indicates that their provenance is the metamorphic rocks of Pan-African age that have a tectonic affinity to NE China. A few older zircons with U-Pb ages at 1689-1801 Ma, 1307 1414 Ma, 593-978 Ma are also present, revealing the Neoproterozoic history of NE China. The youngest population shows a peak at ca. 252 Ma, suggesting that the main deposition of the Linxi Formation was at late Permain. Moreover, the ca. 250 Ma zircon grains of all four samples yield weighted mean ^206pb/^238U ages of 250 ± 3 Ma, 248 ± 3 Ma, 249 ± 3 Ma, and 250 ± 2 Ma, respectively. These ages, together with the youngest zircon age in the sample ZJB-28 （ca. 238 Ma）, suggest that the deposition of the Linxi Formation extended to the early Triassic. Combining with previous results, we suggest that the final collision of the Central Asian Orogenic Belt （CAOB） in the southern of Linxi Formation, which located in the Solonker-Xra Moron-Changchun suture, and the timing for final collision should be at early Triassic.
