A systematic Sm-Nd isotopic study was carried out for sediments and metasediments of different ages from Mesoproterozoic to early Mesozoic era in southwestern Fu-jian, Eastern Nanling Range. The results show that Nd m...A systematic Sm-Nd isotopic study was carried out for sediments and metasediments of different ages from Mesoproterozoic to early Mesozoic era in southwestern Fu-jian, Eastern Nanling Range. The results show that Nd model age (tDM) and e Nd(t) value of most sediments are closely simi-lar to those of Paleoproterozoic Mayuan Group, indicating that they may mainly be the recycling product of Paleopro-terozoic crustal materials. However, the Nd model age sig-nificantly decreases with a corresponding increase in the e Nd(t) value at Neoproterozoic (ca. 0.8—0.7 Ga) and Late Paleozoic (ca. 0.25 Ga), respectively. This is manifested by prominent vales and apexes on the diagrams of tDM vs. tStr. (stratum age) and e Nd(t) vs. tStr.. The decrease in tDM and the increase in e Nd(t) are explained as a result of the significant incorporation of juvenile crustal materials that originated from depleted mantle due to strong lithospheric extension during both periods. It appears that tectonic magmatism in the Neoproterozoic and the Late Paleozoic is of prominent importance in affecting the geochemical nature of sediments in South China.展开更多
He and Ar isotopic compositions of megacrystal minerals from mantle xenoliths were measured by the technique of vacuum crushing extraction. The used samples were clinopyroxene, garnet and ilmenite in Cenozoic alkaline...He and Ar isotopic compositions of megacrystal minerals from mantle xenoliths were measured by the technique of vacuum crushing extraction. The used samples were clinopyroxene, garnet and ilmenite in Cenozoic alkaline basalts, which were from Nushan in Anhui Province and Yingfengling in Guangdong Province, respectively, and represented materials from the upper mantle in the continental margin of SE China. The results show 3He/4He ratios of 7.99 Ra to 8.58 Ra, consistent with the characteristic ratios of the MORB-type mantle. 40Ar/39Ar ratios vary from 313 to 909, suggesting a binary mixing between the MORB-type mantle and air argons. This may reflect the incorporation of the air argon absorbed in oceanic sediments into the mantle beneath the continental margin by subduction of oceanic plate. This study presents the first report that ilmenite megacrysts contain abundant fluid inclusions and noble gases in the mantle xenoliths.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.40132010 and 40273018).
文摘A systematic Sm-Nd isotopic study was carried out for sediments and metasediments of different ages from Mesoproterozoic to early Mesozoic era in southwestern Fu-jian, Eastern Nanling Range. The results show that Nd model age (tDM) and e Nd(t) value of most sediments are closely simi-lar to those of Paleoproterozoic Mayuan Group, indicating that they may mainly be the recycling product of Paleopro-terozoic crustal materials. However, the Nd model age sig-nificantly decreases with a corresponding increase in the e Nd(t) value at Neoproterozoic (ca. 0.8—0.7 Ga) and Late Paleozoic (ca. 0.25 Ga), respectively. This is manifested by prominent vales and apexes on the diagrams of tDM vs. tStr. (stratum age) and e Nd(t) vs. tStr.. The decrease in tDM and the increase in e Nd(t) are explained as a result of the significant incorporation of juvenile crustal materials that originated from depleted mantle due to strong lithospheric extension during both periods. It appears that tectonic magmatism in the Neoproterozoic and the Late Paleozoic is of prominent importance in affecting the geochemical nature of sediments in South China.
基金supported by The National Natural Science Foundation of China(Grant Nos.49473175,49972062 and 40110104104).
文摘He and Ar isotopic compositions of megacrystal minerals from mantle xenoliths were measured by the technique of vacuum crushing extraction. The used samples were clinopyroxene, garnet and ilmenite in Cenozoic alkaline basalts, which were from Nushan in Anhui Province and Yingfengling in Guangdong Province, respectively, and represented materials from the upper mantle in the continental margin of SE China. The results show 3He/4He ratios of 7.99 Ra to 8.58 Ra, consistent with the characteristic ratios of the MORB-type mantle. 40Ar/39Ar ratios vary from 313 to 909, suggesting a binary mixing between the MORB-type mantle and air argons. This may reflect the incorporation of the air argon absorbed in oceanic sediments into the mantle beneath the continental margin by subduction of oceanic plate. This study presents the first report that ilmenite megacrysts contain abundant fluid inclusions and noble gases in the mantle xenoliths.
