Geologic map of San Francisco Mountain, Elden Mountain, and Dry Lake Hills, Coconino County, Arizona
Geologic map of San Francisco Mountain, Elden Mountain, and Dry Lake Hills, Coconino County, Arizona
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亚利桑那州科科尼诺县旧金山山、埃尔登山和干湖山地质图
DOI：
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发表时间：
1988
期刊：
影响因子：
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通讯作者：
R. Holm
中科院分区：
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作者：
R. Holm
旧金山弗朗西斯科火山中心的火成岩在岩性上变化很大，在结构和地层上的关系也很复杂，因此，为了使地质图更有用，下面对它们进行详细描述。旧金山弗朗西斯科山是一座复合火山，主要是在第四纪期间由几个熔岩圆顶和至少两个层状火山锥组成，由层间熔岩流和火山碎屑沉积物组成，由安山岩到流纹岩组成。火山位于一个几乎水平的古生代，可能是三叠纪，地层加上第四纪或第三纪玄武岩熔岩流的平台上。对旧金山弗朗西斯科山的解剖提供了火山核心的独特视角，其中超过900米的火山岩暴露在内盆地和内谷。由于暴露，大量的岩石单元已被识别和绘图，它们的地层关系解释的置信度相对较高。尽管进行了深入的解剖，但仍有近900米的火成岩（可能包括一些最古老的熔岩）埋在内盆地之下。火山东北侧的裂口源于火山发育后期的崩塌。在埃尔登山和小埃尔登山及其附近的古生代沉积岩在埃尔登山的英安岩侵入体和更古老的英安岩的侵位过程中发生了倾斜和断裂。埃尔登山东侧的构造关系表明，地层最初被推高至陡倾，后来通过垂直于走向的旋转和沿沿着正断层的位移而沉降。两个或三个古生代地层的异常厚度意味着地层被断层重复，这些断层必须几乎平行于地层走向，但这种断层尚未被定位或记录。
The igneous rocks of the San Francisco Mountain volcanic center are so variable lithologically and so complexly related structurally and stratigraphically that they are described below in detail in order to make the geologic map more useful. San Francisco Mountain is a composite volcano that was constructed largely during the Quaternary from several silicic lava domes and at least two stratovolcano cones consisting of interlayered lava flows and pyroclastic deposits of andesitic to rhyolitic composition. The volcano rests on a platform of nearly horizontal Paleozoic, and possibly Triassic, strata plus Quaternary or Tertiary basalt lava flows. Dissection of San Francisco Mountain has provided an exceptional view of the core of the volcano, where over 900 m of volcanic rocks are exposed in the Inner Basin and Interior Valley. Because of the exposures, a large number of rock units have been recognized and mapped, and their stratigraphic relationships are interpreted with a relatively high degree of confidence. In spite of the deep dissection, nearly 900 m of igneous rocks, presumably including some of the oldest lavas, still remain buried beneath the Inner Basin. The breach in the northeast flank of the mountain originated from collapse late in the development of the volcano. Paleozoic sedimentary rocks that crop out on and near Elden Mountain and Little Elden Mountain were tilted and faulted during emplacement of the dacite intrusions and older dacite of Elden Mountain. Structural relationships on the east side of Elden Mountain indicate that the strata were initially pushed up to steep dips and later subsided by rotation normal to strike and displacement along normal faults. Anomalous thicknesses of two or three of the Paleozoic formations imply duplication of beds by faults that must strike nearly parallel to the beds, but such faults have not been located or documented.