|
|||||
|
|
| 大别山北部榴辉岩的Sm-Nd年龄测定及其对麻粒相退变质时间的制约 | |
| 引用本文： | 刘贻灿,李曙光,郑永飞,徐树桐,江来利,陈冠宝,吴维平,江博明,张宗清.大别山北部榴辉岩的Sm-Nd年龄测定及其对麻粒相退变质时间的制约[J].地球化学,2001,30(1):79-87. |
| 作者姓名： | 刘贻灿 李曙光 郑永飞 徐树桐 江来利 陈冠宝 吴维平 江博明 张宗清 |
| 作者单位： | 1. 中国科学技术大学地球和空间科学系;安徽省地质科学研究所 2. 中国科学技术大学地球和空间科学系, 3. 安徽省地质科学研究所, 4. 法国雷恩大学 |
| 基金项目： | 国家自然科学基金项目! (49794041和 40033010)，国家重点基础研究发展规划项目! (G1999075503)，安徽省地质矿产局资助项目 |
| 摘 要： | 报道了大别山北部三个榴辉岩样品的矿物 Sm- Nd等时线年龄，它们分别为 (210± 6) Ma或 (214± 6) Ma、 (208± 38) Ma和 (208± 4) Ma。氧同位素研究表明，这些样品中的石榴子石与绿辉石之间处于氧同位素平衡状态，因此，该 Sm- Nd等时线定年结果可靠。本区榴辉岩的高压麻粒岩相退变质阶段的冷却年龄为 210 Ma左右；榴辉岩的钕同位素初始比ε Nd(t)(两个样品一个为－ 10左右，另一个为－ 2)基本上表现为陆壳岩石特征，可能类似于南部超高压带中的榴辉岩，为印支期扬子陆壳俯冲变质成因。它们的全岩δ 18O值较低，为＋ 2.4‰～＋ 3.6‰，可能指示其原岩同大别山南部超高压带中榴辉岩一样，在板块俯冲之前，经受过高温地表水热液蚀变。年代学结果表明，大别山北部榴辉岩在 230～ 210 Ma期间经历的是一等温或升温过程，这与大别山南部含柯石英榴辉岩在这一时期的快速冷却过程形成强烈对比，这对理解俯冲陆壳中不同构造岩片折返过程的差异有重要意义。 |
| 关 键 词： | 榴辉岩 麻粒岩 变质作用 扬子陆壳俯冲 大别山 钐－钕同位素年龄 氧同位素 |
| 文章编号： | 0379-1726(2001)01-0079-09 |
| 修稿时间： | 2000年4月28日 |
Sm-Nd dating of eclogites from Northern Dabie Mountains and its constraints on the timing of granulite-facies retrogression |
|
| LIU Yi- can,LI Shu- guang,XU Shu- tong,JAHN Bor- Ming,ZHENG Yong- fei,ZHANG Zong- qing,JIANG Lai- li,CHEN Guan- bao,WU Wei- ping.Sm-Nd dating of eclogites from Northern Dabie Mountains and its constraints on the timing of granulite-facies retrogression[J].Geochimica,2001,30(1):79-87. | |
| Authors: | LIU Yi- can LI Shu- guang XU Shu- tong JAHN Bor- Ming ZHENG Yong- fei ZHANG Zong- qing JIANG Lai- li CHEN Guan- bao WU Wei- ping |
| Institution: | LIU Yi- can1,2,LI Shu- guang1,XU Shu- tong2,JAHN Bor- Ming3,ZHENG Yong- fei1,ZHANG Zong- qing4,JIANG Lai- li2,CHEN Guan- bao2,WU Wei- ping2 |
| Abstract: | Sm-Nd and oxygen isotope ratios of garnet and omphacite fromeclogites in North Dabie Mountains were measured along with their petrological features. Unlike coesite-bearing eclogites in South Dabie Mountains which underwent amphibolite-facies retrogression, the eclogites in North Dabie Mountains suffered granulite-facies overprinting. Relationship between the δ18O values of the eclogite minerals suggests oxygen isotope equilibrium fractionation, corresponding to the Sm-Nd isotope equilibrium between the minerals according to comparability between O and Sm-Nd diffusivities. The δ18O values of whole-rocks for the eclogites are + 2. 4‰ to + 3.6‰, indicating that the eclogites underwent the hydrothermal alteration of high-temperature surface water prior to the subduction of the Yangtze continental plate. The Sm-Nd isotope ages for the three samples of eclogites are identical with 210 Ma and they are interpreted to represent the cooling ages in the retrogressive stage of granulite-facies metamorphism. The initial ratios of Nd isotope for the eclogites are negative with εNd(t) = - 10 (two samples) and-2 (one sample), implying that they were derived from the subducted Yangtze continental crust like the eclogites in South Dabie. There is the isothermal or temperature rise history from 230 to 210 Ma for the eclogites in North Dabie, which is in contrast to that of the eclogites in South Dabie. This places important constraint on exhumation processes of the eclogites in northern and southern Dabie blocks. |
| Keywords: | eclogite Sm- Nd isotope age granulite- facies retrogression Yangtze continental crustal subduction Dabie Mountains |
| 本文献已被 CNKI 万方数据 等数据库收录！ | |