Basin and Range Extensional Tectonics Near the Latitude of Las Vegas, Nevada
Basin and Range Extensional Tectonics Near the Latitude of Las Vegas, Nevada
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DOI：
10.1130/spe253-p243
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发表时间：
1991-04
期刊：
影响因子：
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通讯作者：
B. Wernicke;G. J. Axen;J. Snow
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文献类型：
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作者：
B. Wernicke;G. J. Axen;J. Snow
位于内华达州拉斯维加斯纬度（约36°N）的盆岭地区非常适合重建新近纪伸展，因为在总体整合的科迪勒拉山脉微地斜内发育了大量的构造标志，主要是中生代逆冲断层。从地图上看，伸展是不均匀的，可分为两个主要的伸展域，拉斯维加斯和死亡谷正断层系统，分别位于相对未伸展的中间块的东部和西部。我们确定了全省参考点对之间的水平相对运动矢量，选择这些参考点是为了最好地允许地质标记在延伸过程中约束这对参考点的相对运动。我们识别出三个序列的对，两个在拉斯维加斯系统和一个在死亡谷系统，定义了一个完整的路径，整个省。沿这些路径的矢量沿着加起来为247 ± 56 km的净延伸，方向为N73° ± 12°W。时间上的考虑表明，扩展主要发生在过去的1500万年。内华达州山脉远离科罗拉多高原的向西运动发生在1000万~ 1500万年之间，速率为20-30毫米/年。但在过去的500万年里不超过10毫米/年。走滑断层是伸展系统的重要组成部分，在伸展过程中吸收了大约40-50 km的南北缩短，表明整个地壳存在收缩应变场。如果假定新生代伸展期间内华达州山脉没有大的旋转，在北方大盆地中部伸展之前，拉斯维加斯地区的地壳伸展了3-4倍，而更广泛的大盆地地区仅伸展了2倍。这种差异可以解释两个地区之间区域海拔的差异（北方大盆地平均高出约1，000米）以及拉斯维加斯地区的收缩应变。更广泛分布的向北延伸可能没有跟上更大的向南延伸的步伐，因此南部更快地失去了重力位。因此，相对浮力大的北方大盆地岩石圈被迫（并将继续）下降到拉斯维加斯地区的潜在梯度。平行于北方圣安德烈亚斯断层，我们的重建占214 ± 48公里的右侧剪切沿着太平洋-北美转换板块边界。
The Basin and Range province at the latitude of Las Vegas, Nevada (approximately 36°N), is ideally suited for reconstructing Neogene extension owing to an abundance of structural markers, primarily Mesozoic thrust faults, developed within the generally conformable Cordilleran miogeocline. In map view, extension is heterogeneous and is divisible into two major extensional domains, the Las Vegas and Death Valley normal fault systems, that lie east and west (respectively) of a relatively unextended median block. We determined horizontal relative-motion vectors between pairs of reference points across the province, chosen so as to best allow geologic markers to constrain the relative motion of the pair during extension. We recognize three sequences of pairs, two in the Las Vegas system and one in the Death Valley system, that define an unbroken path across the entire province. The vectors along these paths sum to give 247 ± 56 km of net extension oriented N73° ± 12°W. Timing considerations indicate that extension occurred principally during the past 15 m.y. Westward motion of the Sierra Nevada away from the Colorado Plateau occurred at a rate of 20-30 mm/yr in the interval 10-15 m.y. ago, but was no greater than 10 mm/yr over the past 5 m.y. Strike-slip faulting was an important component in the extending system and absorbed perhaps 40-50 km of north-south shortening of the region during extension, indicating a constrictional strain field for the crust as a whole. If one assumes no major rotations of the Sierra Nevada during Cenozoic extension, and about 100 km of pre-15-m.y.-ago extension in the central portion of the northern Great Basin, the crust in the Las Vegas region extended by a factor of 3-4, whereas the wider Great Basin region extended by only a factor of 2. This difference may explain the contrast in regional elevation between the two areas (the northern Great Basin is on average about 1,000 m higher) and the constrictional strain in the Las Vegas region. The more widely distributed extension to the north may not have kept pace with the larger extension to the south, such that the south lost gravitational potential more rapidly. Thus, comparatively buoyant northern Great Basin lithosphere was (and continues to be) forced down the potential gradient into the Las Vegas region. Resolved parallel to the northern San Andreas fault, our reconstruction accounts for 214 ± 48 km of right-lateral shear along the Pacific-North America transform plate boundary.