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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Emplacement of pyroclastic dykes in Riedel shear fractures: An example from the Sierra de San Miguelito, central Mexico
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Emplacement of pyroclastic dykes in Riedel shear fractures: An example from the Sierra de San Miguelito, central Mexico

机译：里德尔剪切裂缝中火山碎屑岩堤的位置：墨西哥中部圣米格里托山脉的一个例子

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Although magmatic dykes are considered to be emplaced at depth, there are very few studies about the emplacement of pyroclastic dykes. There are two commonly accepted mechanisms for dike emplacements; namely, formation of a hydraulic (tension) fracture and filling of pre-existing fractures. In the Sierra de San Miguelito, central Mexico, there is a dike swarm with orientations that do not concur with any of the above two cases. Instead, the dikes have orientations resembling some type of secondary fractures within the fault-bounded blocks. Within a fault-bounded block, the reverse drag of the normal faults can be explained by simple shear. Based on the simple shear mechanism, we establish a series of equations to calculate the extension and the direction of the simple shear within a fault-bounded block. As an application of our methodology, the value of β, which is the angle measured from the vertical to the direction of the simple shear, is calculated from the domino faults in the Sierra de San Miguelito, Mesa Central, Mexico. The results demonstrate that the absolute values of β for the inclined shear are smaller than 34°. The inclined shear can be antithetic (β>0), synthetic (β<0) or vertical (β≈0). The pyroclastic dykes in the study area have most of the strikes between 300° and 330° and are sub-parallel to the major faults. The preferred dips of the pyroclastic dykes vary from 80° to 90°. The distribution of the pyroclastic dykes in the study area indicates that the dikes were primarily emplaced along the R fractures due to simple shear. These results are different from the traditional understanding, which assumes that the dykes were mainly emplaced within the tension fractures.
机译：尽管岩浆岩被认为是深埋的，但很少有关于火山碎屑岩沉积的研究。有两种公认的堤防安置机制：也就是说，形成水力（张力）裂缝并填充先前存在的裂缝。在墨西哥中部的塞拉利昂圣米格里托（Sierra de San Miguelito），有一个堤防群，其方位与上述两种情况都不相同。取而代之的是，堤坝的方向类似于断层边界块内某种类型的二次裂缝。在断层边界块内，正常断层的反向阻力可以通过简单的剪切来解释。基于简单剪切机制，我们建立了一系列方程来计算断层边界块内简单剪切的扩展和方向。作为我们方法学的一种应用，β值是从垂直方向到简单剪切方向的角度，是从墨西哥梅萨中部的塞拉利昂德圣米格利托山脉的多米诺断层计算得出的。结果表明，斜剪的β的绝对值小于34°。斜切可以是对数（β> 0），合成（β<0）或垂直（β≈0）。研究区的火山碎屑岩脉的大部分走向介于300°至330°之间，并且与主要断层次平行。火山碎屑堤的优选倾角在80°至90°之间。研究区的火山碎屑岩的分布表明，由于简单的剪切作用，这些堤坝主要沿R裂缝放置。这些结果与传统的认识不同，传统的认识认为堤坝主要位于张性裂缝内。

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