摘要
从浙东、闽东南的早白垩世“双峰式火山岩”和“复合岩体”中选择了有代表性的玄武岩和角闪辉长岩,分离出钛-磁铁矿,进行Re-Os同位素分析。角闪辉长岩的γo_s(130Ma)为-83．7～-47．1,其(^(187)Os/^(188)Os)_i过低,为0．0667和0．0205这低得不合理的(^(187)Os/^(188)Os)_i表明成岩之后Re-Os体系可能受到扰动,某些地质过程导致外加Re的进入,使岩石的^(187)Re/^(188)Os比值偏高、(^(187)Os/^(188)Os)_i及γo_s(t)值偏低。玄武岩的γo_s(130Ma)=21．4～267．8,其(^(187)Os/^(188)Os)_i为0．1531～0．4639。Re-Os、Sm-Nd同位素及微量元素地球化学研究表明,早白垩世玄武岩浆不是来自富集地慢,而是来自亏损的地幔源区,在其演化过程中经受了地壳岩石和熔体的混染。晚中生代时期,东南沿海“大陆弧”下的地幔可能不是富集的岩石圈地幔,具有亏损特性,因而是软流圈地幔。
The representative basalts and hornblende gabbros samples have been selected from early Cretaceous ＂bimodal volcanics＂ and ＂composite plutons＂ from eastern Zhejiang and southeastern Fujian provinces of southeastern coast of China. We separated the FeTi oxide concentrates in them and analyzed their Re-Os isotopic compositions. The γos （130Ma） of two hornblende gabbros are - 83.7 and -47.1 with unreasonable low initial （^187 Os/^188 Os） ratios of 0. 0667 and 0. 0205. The extremely low initial （^187 Os/^188 Os） ratios indicated that some geological processes have disturbed their Re-Os system and it is likely that a recent Re gain after emplacement caused their higher ^187 Re/^188 Os and lower（ ^187 Os/^188 Os）; and γos（t） . In contrast, the basalts yielded reasonable γos（130Ma） values from 21.4 to 267.8, with initial （ ^187 Os/^188 Os） ratios of 0. 1531 - 0. 4639 . Combined Re-Os, Sm-Nd isotopic and trace element geochemical studies indicate that the early Cretaceous basaltic magmas might be derived from depleted rather than enriched mantle source, and may have been contaminated by crustal rocks and melts. During late Mesozoic, the sub-arc mantle from southeastern coast of China should be depleted asthenospheric rather than enriched lithospheric mantle.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第2期407-413,共7页
Acta Petrologica Sinica
基金
国家自然科学基金项目(批准号40273017和40221301)
南京大学成矿作用国家重点实验室资助项目的研究成果之一。
