The Cenozoic magmatism of East Africa: Part III – Rifting of the craton
The Cenozoic magmatism of East Africa: Part III – Rifting of the craton
复制标题
东非新生代岩浆作用：第三部分 — 克拉通裂谷
DOI：
10.1016/j.lithos.2020.105390
复制
发表时间：
2020
期刊：
影响因子：
3.5
通讯作者：
Rooney, Tyrone O.
中科院分区：
文献类型：
--
作者：
Rooney, Tyrone O.
在东非裂谷系（EARS）的坦桑尼亚受卡隆影响的地区的岩浆活动表现出明显的证据，来自各种交代来源。这些交代源，可能跨越一个年龄范围，可能已被保存在岩石圈地幔。这些交代体对裂谷岩浆组成的影响代表了EARS内喷发熔岩组成的最大异质性。在图尔卡纳湖以南的EARS受阿贡影响的地区，最早的广泛岩浆事件是桑布鲁阶段（约1000年）。20-17 Ma），表现为来自岩石圈地幔的碱性火山岩。这一阶段代表了大陆岩石圈的初始不稳定，是裂谷发展的前兆。洪水响岩阶段（英语：The Flood Phonolite Phase）16-12 Ma）在受前桑布鲁阶段影响的南部地区最为明显，可能代表了岩石圈不稳定的持续向南扩张。中新世中期（Mid-Miocene Resurgence）12-9 Ma）在肯尼亚南部裂谷中的代表性很低，尽管在这段时间在基伍的EARS西分支记录到岩浆活动。早期裂谷发展阶段（Early Rift Development Phase）。9-4马）在肯尼亚裂谷中特别有代表性。大规模的岩浆活动包括：坦桑尼亚北方分歧（NTD）和Mt.肯尼亚，Rungwe火山省和肯尼亚南部裂谷。Stratoid Phase（英语：Stratoid Phase）4 Ma -0.5Ma）开始于约4 Ma的重要岩浆事件。3到2.5 Ma，位于肯尼亚南部裂谷和NTD。这一阶段表现为玄武岩和粗面岩，淹没了肯尼亚南部裂谷新形成的地堑。这一阶段也与NTD的岩浆活动的主要阶段，在维龙加火山活动的开始，以及在Rungwe火山省的中间屏蔽阶段。轴向阶段（0.5马到现在）被定义为狭窄的轴向地堑在肯尼亚裂谷与中央火山和插入玄武质火山锥。在EARS较不成熟的地区，碱性火山占主导地位。三个不同的岩浆活动和伸展脉冲开始在图尔卡纳开始在约。23马，12马，和4马;一致的时间滞后的岩浆活动在南部EARS以下的每个脉冲揭示了这些伸展事件向南扩展。裂谷内任何给定位置的熔岩都表现出一致的时间序列，其特征是从II型熔岩（岩石圈地幔衍生）到IV型熔岩（混合岩石圈地幔-岩石圈下衍生）再到III型熔岩（岩石圈下衍生），这需要储层的渐进变化，从而促进裂谷岩浆活动从岩石圈到岩石圈下。当检查在一起，这些数据描绘了一幅图片的进步裂谷的发展和随之而来的岩石圈变薄，介导的脉冲延伸起源于图尔卡纳。
Magmatic activity in the Tanzania Craton-influenced regions of the East African Rift System (EARS) exhibits clear evidence of derivation from a variety of metasomatic sources. These metasomatic sources, which may span a range of ages, have likely been preserved within the lithospheric mantle. The influence of these metasomes on the composition of the rift magmas represents the single greatest heterogeneity in the composition of erupted lavas within the EARS. The earliest widespread magmatic event in the craton-influenced regions of the EARS south of Lake Turkana is the Samburu Phase (ca. 20–17 Ma), which manifests as alkaline volcanics derived from the lithospheric mantle. This phase represents the initial destabilization of the continental lithosphere as a precursor of rift development. The Flood Phonolite Phase (ca. 16–12 Ma) was most pronounced in regions south of those impacted by the prior Samburu Phase, and likely represent the continued southward expansion of lithospheric destabilization. The Mid-Miocene Resurgence Phase (ca. 12–9 Ma) is poorly represented in the Southern Kenya Rift, though magmatic activity is recorded in the Western Branch of the EARS at Kivu during this time. In contrast, the Early Rift Development Phase (ca. 9–4 Ma) is particularly well-represented in the Kenya Rift. Large-scale magmatic events include: commencement of activity in the Northern Tanzania Divergence (NTD) and Mt. Kenya, Rungwe Volcanic Province, and the Southern Kenya Rift. The Stratoid Phase (ca. 4 Ma – 0.5 Ma) commences with significant magmatic events at ca. 3 to 2.5 Ma within the Southern Kenya Rift and NTD. This phase manifests as basalts and trachytes that flood the newly formed graben in the Southern Kenya Rift. This phase also correlates with the main phase of magmatism in the NTD, the commencement of volcanism at Virunga, and the intermediate shield phase in the Rungwe Volcanic Province. The Axial Phase (0.5 Ma to present) is defined by narrow axial grabens in the Kenya Rift with central volcanoes and interposing basaltic cinder cones. In the less mature regions of the EARS, alkaline volcanoes dominate. Three distinct pulses of magmatism and extension initiated in Turkana commencing at ca. 23 Ma, 12 Ma, and 4 Ma; the consistent temporal lag in magmatic activity in the Southern EARS following each pulse reveals the southward expansion of these extensional events. Lavas at any given location within the rift exhibit a consistent temporal sequence characterized by a shift from Type II lavas (lithospheric mantle derived) to Type IV lavas (hybrid lithospheric mantle – sub-lithosphere derived) to Type III lavas (sub-lithosphere derived), requiring a progressive change in the reservoirs contributing to rift magmatism from lithospheric to sub-lithospheric. When examined in aggregate, these data paint a picture of progressive rift development and attendant lithospheric thinning, mediated by pulses of extension originating in Turkana.
登录
查看更多内容
Olorgesailie 地层的单晶 40Ar/39Ar 测年
DOI：
--
发表时间：
1990
期刊：
影响因子：
--
作者：
A. Deino;R. Potts
通讯作者：
R. Potts
卡钨矿及其伴生岩石的成因
DOI：
--
发表时间：
1950
期刊：
影响因子：
--
作者：
A. Holmes
通讯作者：
A. Holmes
肯尼亚裂谷的两阶段裂谷：对半地堑模型的影响
DOI：
--
发表时间：
1997
期刊：
影响因子：
--
作者：
F. Mugisha;C. Ebinger;M. Strecker;D. Pope
通讯作者：
D. Pope
乌干达东部-肯尼亚西部埃尔贡山火山的 Nd、Pb 和 Sr 同位素数据：对霞石熔岩起源和演化的影响
DOI：
--
发表时间：
1995
期刊：
影响因子：
--
作者：
A. Simonetti;K. Bell
通讯作者：
K. Bell
东非裂谷系统岩石圈结构与裂谷作用之间的关系：瑞利波层析成像研究
影响因子：
3.7
作者：
A. Adams;J. Miller;N. Accardo
通讯作者：
N. Accardo