...
  • 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 >Upper mantle SH- and P-velocity structures and compositional models beneath southern Africa
【24h】

Upper mantle SH- and P-velocity structures and compositional models beneath southern Africa

机译：南部非洲下方的上地幔SH和P速度结构及组成模式

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

We constrain SH and P wave velocity structures in the upper mantle beneath southern Africa, using triplicated phases recorded in the epicentral distance range of 11 degrees-28 degrees for one shallow event. We then explore thermal and compositional models appropriate for explaining the inferred seismic structures in the region. Both SH and P wave data suggest presence of a low velocity zone with velocity reductions of at least -5% for S waves and -2% for P waves beneath a 150 kin thick high-velocity lithospheric lid. Seismic observations also suggest that the P/S ratio is larger (1.88) in the transition zone than in the lithospheric lid (1.70). The inferred P wave velocity jump across the 660-km discontinuity is small (<4%), while the inferred SH wave velocity jump across the discontinuity is comparable to that in the Preliminary Reference Earth Model. The low velocity zone can be explained by a high temperature gradient of 6 degrees C/km or presence of partial melt. Partial melt would require presence of water or other volatile elements in the depth range of the low velocity zone to lower the mantle solidus. The different P/S velocity ratios between the lithospheric lid and the transition zone can be explained by a difference in aluminum content of mantle composition, with values of 1% in the lithospheric lid and 4% in the transition zone, respectively. The inferred P and SH velocity jumps suggest a bulk sound velocity decrease of 3.4% across the 660-km discontinuity. Such a large decrease of bulk sound velocity is possible only if the bulk modulus of perovskite is similar to those of ringwoodite and garnet, a result remained to be confirmed by experimental or theoretical studies. The presence of the low velocity zone with large velocity reductions beneath southern Africa suggests existence of a low-density anomaly beneath the lithospheric lid, which may provide an explanation to the observed localized uplift in the "African Superswell". (C) 2007 Elsevier B.V. All rights reserved.
机译：我们使用在一次浅层事件的震中距范围在11度至28度范围内记录的三重相位，来约束南部非洲下方上地幔的SH和P波速度结构。然后，我们探索适用于解释该地区推断地震构造的热力和成分模型。 SH波和P波数据均表明存在低速带，在150 kin厚的高速岩石圈盖下，S波的速度降低至少-5％，P波的速度降低至少-2％。地震观测还表明，过渡带的P / S比（1.88）比岩石圈盖（1.70）大。推断出的穿过660公里不连续点的P波速度跳跃很小（<4％），而推断出的穿过不连续点的SH波速度跳跃与初步参考地球模型中的相当。低速区可以用6摄氏度/公里的高温梯度或存在部分熔融来解释。部分熔融将需要在低速区的深度范围内存在水或其他挥发性元素，以降低地幔固相线。岩石圈盖与过渡带之间不同的P / S速度比可以通过地幔成分中铝含量的差异来解释，岩石圈盖中铝的含量分别为1％，过渡带为4％。推断的P和SH速度跳跃表明，在660公里的不连续处，整体声速下降了3.4％。仅当钙钛矿的体积模量与林木和石榴石的体积模量相似时，体积声速的如此大的降低才有可能，其结果仍有待实验或理论研究证实。南部非洲下方低速带速度大幅度降低的存在表明岩石圈盖下方存在低密度异常，这可能解释了在“非洲超潮”中观测到的局部隆升。 （C）2007 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