Intrarift fault fabric, segmentation, and basin evolution of the Lake Malawi (Nyasa) Rift, East Africa
Intrarift fault fabric, segmentation, and basin evolution of the Lake Malawi (Nyasa) Rift, East Africa
复制标题
东非马拉维湖（尼亚萨）裂谷的裂谷内断层结构、分段和盆地演化
作者：
C. Scholz;D. Shillington;L. J. Wright;N. Accardo;J. Gaherty;P. Chindandali
马拉维湖（尼亚萨湖）裂谷位于东非裂谷系（EARS），是研究低应变速率环境下伸展构造系统的理想现代类比对象。这个地震活跃的裂谷包含深700米的马拉维湖，它是世界上最古老和最大的淡水湖之一，拥有地球上最多样化的地方性动物群落之一。现代及重新处理的传统多道地震反射数据受到广角地震实验速度信息的约束，以评估沿550千米长裂谷带的伸展、分段和断层发育时间的变化性。断层几何形状和同裂谷期沉积物填充模式表明，马拉维湖裂谷由三个不对称的裂谷段组成，其间的调节带形态由段边界断层之间的重叠程度控制。大部分伸展发生在盆地边界断层上，广泛分布的伸展仅在一个调节带观察到，在该调节带没有观察到边界断层重叠。构造复原表明这是一个伸展较弱的裂谷系统（约7千米），伸展值从北向南递减，裂谷填充物从北向南变薄，这表明裂谷向南逐渐变新。在马拉维湖裂谷的同裂谷期填充物中没有岩墙侵入、岩床注入或喷出物的证据，尽管湖以北的伦圭岩浆系统的火山负荷及相关沉降可能解释了湖最北部同裂谷期填充物异常厚的原因。最厚的同裂谷期沉积中心（约5.5千米）局限于每个裂谷段边界断层附近10 - 20千米宽的狭窄区域，这表明应变集中在边界断层而非裂谷内断层上。裂谷内构造控制着北部和中部裂谷段的轴向沉积物输送，使沉积物集中在有限区域，导致局部超压和页岩底辟。这种不对称的、受基底控制的地形在裂谷发育早期就已形成。当这种地形被该盆地有充分记录的频繁高振幅水文气候波动叠加时，随时间变化的高度多变的地貌和湖泊形态可能影响了在盆地内进化的多样的地方性动物群。新的地震反射数据，加上广角地震数据和来自钻孔岩芯的年龄约束，提供了迄今为止东非新生代晚期伸展变形最高分辨率的三维视图，并为灾害分析、资源评估以及约束低应变速率、贫岩浆活动裂谷的变形提供了基础。
The Lake Malawi (Nyasa) Rift, in the East African Rift System (EARS), is an ideal modern analogue for the study of extensional tectonic systems in low strain rate settings. The seismically active rift contains the 700-m-deep Lake Malawi, one of the world’s oldest and largest freshwater lakes with one of the most diverse endemic faunal assemblages on Earth. Modern and reprocessed legacy multichannel seismic-reflection data are constrained by velocity information from a wide-angle seismic experiment to evaluate variability in extension, segmentation, and timing of fault development along the 550-km-long rift zone. Fault geometries and patterns of synrift sediment fills show that the Lake Malawi Rift is composed of three asymmetric rift segments, with intervening accommodation zone morphologies controlled by the degree of overlap between segment border faults. Most extension occurs on the basin border faults, and broadly distributed extension is only observed at one accommodation zone, where no border fault overlap is observed. Structural restorations indicate a weakly extended rift system (∼7 km), with diminishing values of extension and thinner rift fill from north to south, suggesting a progressively younger rift to the south. There is no evidence of diking, sill injection, or extrusives within the synrift fill of the Lake Malawi Rift, although the volcanic load of the Rungwe magmatic system north of the lake and related subsidence may explain the presence of anomalously thick synrift fill in the northernmost part of the lake. The thickest synrift depocenters (∼5.5 km) are confined to narrow 10- to 20-km-wide zones adjacent to each rift segment border fault, indicating concentration of strain on border faults rather than intrarift faults. Intrarift structures control axial sediment delivery in the North and Central rift segments, focusing sediment into confined areas resulting in localized overpressure and shale diapirs. The asymmetric, basement-controlled relief was established early in rift development. When overprinted with frequent high-amplitude hydroclimate fluctuations, which are well documented for this basin, the resulting highly variable landscape and lake morphometry through time likely impacted the diverse endemic faunas that evolved within the basin. New seismic-reflection data, augmented by wide-angle seismic data and age constraints from drill core, offer the most highly resolved 3D view to date of latest Cenozoic extensional deformation in East Africa and provide a foundation for hazards analysis, resource assessments, and constraining deformation in a low strain rate, magma-poor active rift.
DOI：
10.1073/pnas.1512864112
发表时间：
2015-12-22
影响因子：
11.1
作者：
Lyons, Robert P.;Scholz, Christopher A.;Blome, Margaret W.
通讯作者：
Blome, Margaret W.
东非低岩浆输入地区的裂谷演化
影响因子：
5.3
作者：
Muirhead, James D.;Wright, Lachlan J.M.;Scholz, Christopher A.
通讯作者：
Scholz, Christopher A.
影响因子：
18.3
作者：
Bastow, Ian D.;Keir, Derek
通讯作者：
Keir, Derek