...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Magma residence time beneath the Piton de la Foumaise volcano, reunion island, from U-series disequilibria
【24h】

Magma residence time beneath the Piton de la Foumaise volcano, reunion island, from U-series disequilibria

机译：U系列不平衡，留尼汪岛Piton de la Fournaise火山下的岩浆停留时间

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The U, Th and Ba concentrations, U-238-Th-230-Ra-226-Pb-210 and Ra-228-Th-232 disequilibria have been measured in a suite of basalts and oceanites erupted during the last two millennia at Piton de la Fournaise (Reunion Island, Indian Ocean). Most of the variation in the concentration of all three incompatible elements is due to crystal fractionation or accumulation (and incorporation of olivine xenocrysts in the oceanites), but contamination by hydrothermally altered rocks or secondary minerals might explain significant variations in Ba/Th. Basalts with Th contents lower than 2.25 ppm have only been produced in eruptions outside the Enclos Fouque caldera, whereas more evolved basalts are predominantly observed close to the summit craters, inside the Enclos caldera and the rift-zones. The samples have almost uniform Th/U of 3.95, identical Th isotope ratios ((Th-230/Th-232)=0.934) and, therefore, approximately 20% excess of Th-230 over U-238. All analysed samples are in Ra-228-Th-232 radioactive equilibrium, showing the absence of recent (< 30 years) Ra-Th fractionation.Lava flows erupted inside the Enclos caldera and the rift-zones have (Ra-226/Th-230)(0) varying from 1.18 to 1.34, whereas the basalts from craters outside the Enclos caldera and the rift-zones, in addition to the oceanites and the 1945 basalt, have higher (Ra-226/Th-230)(0) around 1.40. This value is assumed to represent that of the deep magma entering the central plumbing system, beneath the Enclos caldera. The evolution through time of (Ra-226/Th-230)(0) is attributed to alternating episodes of near closed-system evolution in one or several, poorly replenished, deep reservoirs, on timescales of the order of 1000 yr, and episodes of increased re-iniection and mixing of the deep magma into older magmas of the previous period. Modelling of such a recent re-injection episode, from 1960 to 1998, suggests a short residence time of about 25 yr and a volume of 0.35 km(3) for the shallow reservoir. At the time of eruption, (Pb-210/Ra-226)(0) in both oceanites and basalts from the Enclos and rift-zones spans a narrow range with a mean value of 0.68, with the exception of the 1945 basalt which has an unusually low ratio of 0.20. The value of 0.68 can be explained by Rn degassing from the shallow magma chamber on a timescale comparable to that deduced from the evolution of (Ra-226/Th-230)(0) in the 1960-1998 period. (c) 2005 Elsevier B.V. All rights reserved.
机译：在过去两千年在皮顿喷发的一系列玄武岩和大洋洲中测量了U，Th和Ba浓度，U-238-Th-230-Ra-226-Pb-210和Ra-228-Th-232不平衡de la Fournaise（留尼汪岛，印度洋）。所有这三种不相容元素的浓度变化大部分是由于晶体分馏或积累（以及在海洋岩中掺入橄榄石异种晶）引起的，但是热液蚀变岩石或次生矿物的污染可能解释了Ba / Th的显着变化。 Th含量低于2.25 ppm的玄武岩仅在Enclos Fouque破火山口外的火山喷发中产生，而在Enclos破火山口和裂谷带附近的山顶火山口附近，主要观察到更多的演化玄武岩。样品的Th / U几乎均匀，为3.95，相同的Th同位素比（（Th-230 / Th-232）= 0.934），因此，Th-230比U-238大约多20％。所有被分析的样品均处于Ra-228-Th-232放射性平衡状态，表明没有最近（<30年）的Ra-Th分馏.Enclos破火山口内爆发的熔岩流和裂谷带具有（Ra-226 / Th- 230）（0）从1.18到1.34不等，而Enclos破火山口和裂谷带之外的火山口中的玄武岩，除了大洋岩和1945年的玄武岩外，其含量更高（Ra-226 / Th-230）（0）大约1.40。假定该值代表进入Enclos破火山口下方的中央管道系统的深部岩浆。 （Ra-226 / Th-230）（0）随时间的演变归因于一个或几个，补充欠佳的深层储层在1000年左右的时间尺度上的近封闭系统演化的交替事件和事件重吸收和深部岩浆混合到前一时期的较旧岩浆中。从1960年到1998年，对这种最近的回注事件进行了建模，结果表明，浅层储层的停留时间较短，约为25年，体积为0.35 km（3）。喷发时，Enclos和裂谷带的大洋洲和玄武岩中的（Pb-210 / Ra-226）（0）范围狭窄，平均值为0.68，但1945年的玄武岩除外0.20的比率异常低。 0.68的值可以解释为，Rn在与1960-1998年期间（​​Ra-226 / Th-230）（0）的演化所推导的时间尺度相当的时间范围内，从浅部岩浆室脱气。 （c）2005 Elsevier B.V.保留所有权利。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号