An improved method for determining and characterizing alignments of pointlike features and its implications for the Pinacate volcanic field, Sonora, Mexico
An improved method for determining and characterizing alignments of pointlike features and its implications for the Pinacate volcanic field, Sonora, Mexico
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一种确定和表征点状特征排列的改进方法及其对墨西哥索诺拉皮纳卡特火山田的影响
DOI：
10.1029/95jb01058
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发表时间：
1995
影响因子：
--
通讯作者：
J. Gutmann
中科院分区：
文献类型：
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作者：
T. Lutz;J. Gutmann
我们提出了一种改进的方法来确定点状特征的统计显著对齐。目前使用的主要方法之一是两点方位角法，它依赖于感兴趣区域上点的均匀分布。通过使用相对较新的核密度估计统计技术对这种方法进行修改，可以处理异质点分布，而不会引入对明显首选方向显著性测试中所使用的网格选择的实质性依赖。改进后的方法可以选择性地显示不同空间尺度上的排列，并提示排列的位置和方向。我们使用这种方法分析了416个通风口的空间分布，这些通风口主要是更新世时代的，位于墨西哥索诺拉的Pinacate火山场，位于加利福尼亚湾北端以东。除了几组排列整齐的火山渣锥外，在航空和太空摄影中，Pinacate火山口的分布几乎是随机的。然而，经过统计处理，整个油田及其所有分区的老Pinacate喷口表现出约N10°E的构造控制趋势。相比之下，年龄小于0.4 Ma的喷口不仅受N10°E控制，而且N20°W和N55°W取向在95%的置信水平上也很显著。N10°走向可能反映了该地区当前的盆地和山脉水平应力状态，该地区位于Pinacate熔岩的地幔岩浆源之上。N55°W方向与该方向的一条主要区域裂缝有关，该裂缝穿过油田中部，并可能与相邻加利福尼亚湾开口相关的正常断层有关。相对于断裂迹线的通风口分布与岩浆沿西南倾断平面向上引导一致。N20°W排列的起源是未知的，但是前更新世的遗产。我们没有发现证据支持平行于裂谷的Pinacate喷口排列的控制或邻近海湾的转变方向。在大约0.4 m.y.以前或以后，沿N20°W和N55°W裂缝的侵入可能反映了地壳应力场的移动或Pinacate导管中岩浆压力的增加，使得岩浆沿着不平行于最大水平压应力的构造上升。
We present an improved method for determining statistically significant alignments of pointlike features. One of the principal such methods now in use, the two-point azimuth method, depends on a homogeneous distribution of points over the region of interest. Modification of this approach by use of the relatively new statistical technique of kernel density estimation permits treatment of heterogeneous point distributions without introducing substantial dependence on choice of the grid employed in the test for significance of apparent preferred orientations. The improved method can selectively reveal alignments on different spatial scales and can suggest the locations of alignments as well as their orientation. We use this method to analyze the spatial distribution of 416 vents, largely of Pleistocene age, in the Pinacate volcanic field, Sonora, Mexico, just east of the northern end of the Gulf of California. Apart from a few sets of aligned cinder cones, the distribution of Pinacate vents appears nearly random on aerial and space photography. However, when treated statistically, old Pinacate vents exhibit structural control trending approximately N10°E throughout the field and in all its subareas. In contrast, vents with ages estimated by comparison with dated cones to be younger than about 0.4 Ma show not only the N10°E control but also N20°W and N55°W alignments significant at the 95% confidence level. The N10° alignment probably reflects the current Basin and Range horizontal stress regime in this particular area, which is atop the mantle magma source of the Pinacate lavas. The N55°W direction is related to a major regional fracture of that orientation passing through the middle of the field and possibly related to normal faults associated with opening of the adjacent Gulf of California. The distribution of vents relative to the fracture trace is consistent with magma having been guided upward along a SW dipping fault plane. The origin of the N20° W alignment is unknown but of pre-Pleistocene heritage. We found no evidence to support control of the Pinacate vent alignments parallel to rifting or transform directions in the adjacent Gulf. Intrusion along N20°W and N55°W fractures at or since about 0.4 m.y. ago could reflect either a shift in the crustal stress field or an increase in magma pressure in Pinacate conduits that allowed magma to ascend along structures that were not parallel to the maximum horizontal compressive stress.