Tectonic evolution of the northern Kenyan Rift
Tectonic evolution of the northern Kenyan Rift
复制标题
肯尼亚北部裂谷的构造演化
DOI：
10.1144/gsjgs.149.3.0333
复制
发表时间：
1992
影响因子：
2.7
通讯作者：
F. Karanja
中科院分区：
文献类型：
--
作者：
C. Morley;W. A. Wescott;D. M. Stone;R. M. Harper;S. Wigger;F. Karanja
最近的地质野外工作，火山岩的放射性年龄测定，重力和地震反射调查，大大提高了我们对肯尼亚裂谷北方构造演化的认识。这些数据表明，深，半地堑盆地厚达7公里的图尔卡纳湖西部可能在晚渐新世-早中新世开始。盆地以东倾断层为界，沿着从图尔卡纳湖到埃尔加约陡崖-图根丘陵地区的裂谷西侧。一些裂谷盆地从渐新世到上新世是间歇性活动的，而另一些裂谷盆地只活动了几百万年。一些坳陷盆地可能是在裂谷平静期发育起来的。在图尔卡纳地区，断层的位置随着时间的推移逐渐向东移动。火山作用既先于裂谷作用，又伴随裂谷作用。在图尔卡纳地区，火山活动随着时间的推移向南和向东移动，大约从33 Ma开始（可能比半地堑形成早几百万年），并持续到今天。沿断层的沿着在图尔卡纳地区较大（25-40公里），在肯尼亚南部裂谷向南减小到5-10公里或更小。这种延伸值的模式与深地震折射工作（KRISP）一致，这表明图尔卡纳地区（约20公里）的地壳很薄，在巴林戈湖以南约35公里处变厚。伸展值、地壳减薄、火山活动年龄和向南断裂的时间都指向裂谷向南扩展。
Recent geological fieldwork, radiometric age dating of volcanic rocks, gravity and seismic reflection surveys have considerably refined our understanding of the tectonic evolution of the northern Kenya Rift. These data reveal that deep, half-graben basins up to 7 km thick were initiated west of Lake Turkana probably during Late Oligocene-Early Miocene times. The basins, bounded by easterly dipping faults, trend along the western side of the rift from Lake Turkana to the Elgayo Escarpment-Tugen Hills area. Some rift basins were episodically active from the Oligocene to the Pliocene while others were only active for a few million years. Some sag basins may have developed during periods of rifting quiescence. In the Turkana area the location of faulting gradually shifted eastwards with time. Volcanism both preceded and accompanied rifting. Within the Turkana area, volcanism moved south and east with time, beginning about 33 Ma (probably preceding half graben formation by a few million years) and continued to the present day. Extension along faults is greater in the Turkana area (between 25-40 km) and decreases southwards to probably 5-10 km or less in the southern Kenya rift. This pattern of extension values agrees with deep seismic refraction work (KRISP), which indicates thin crust in the Turkana area (about 20 km) that thickens to about 35 km south of Lake Baringo. The extension values, crustal thinning, age of volcanism and the timing of faulting to the south all point towards a southerly propagation of the rift.