RUI: Paleomagnetic, Geochemical and Age Discrimination of ~18-19 Ma Tuffs of the Colorado River Extensional Corridor

区域广泛的灰流凝灰岩代表了重要的，近似等值线单元内的复杂变形区域的相关性。 在美国西部盆地山脉省的科罗拉多河延伸走廊的高度延伸范围内尤其如此，在这里，前第三纪沉积层段在中新世和更年轻的伸展期之前被侵蚀移除。灰流凝灰岩，如广泛分布的1850万年前的桃泉凝灰岩，通常是孤立山脉大部分火山岩段之间唯一可液化的单元。 火山灰流动单元的古地磁特征除了对区域对比和作为伸展生长断陷盆地的时间层位有价值外，对于评估伸展事件引起的构造旋转也是非常有用的标志。最近对科罗拉多河伸展走廊内1800 - 1900万年前火山灰流动的研究表明：（1）广泛用于对比的桃泉凝灰岩，可能在地层学上更加复杂，并且喷发的时间比以前认识到的要长得多，（2）桃泉凝灰岩的古地磁特征可能与广泛引用的桃泉凝灰岩参考方向有很大的偏差，这可能是由于在与磁漂移相关的快速长期变化期间的持久喷发，（3）其他凝灰岩与桃泉凝灰岩占据相同的地层位置，可能具有区域重要性，包括先前已知的库克峡谷和岩溪流纹英安岩凝灰岩，在西瑟巴特山脉发现的一种潜在的新凝灰岩，以及可能的其他凝灰岩。古地磁、地球化学和地质年代学技术正被用来研究科罗拉多河伸展走廊中1800 - 1900万年前的凝灰岩。研究目标是针对以下问题：（1）桃泉凝灰岩喷发确实发生在一个更长的时间间隔比以前认为的？(2)在科罗拉多河伸展走廊中存在着多少不同的、年龄约为18-19 Ma的凝灰岩，我们如何区分它们？ (3)科罗拉多河伸展走廊的18-19 Ma凝灰岩中，如果有的话，哪一个具有适合用作构造标志的古地磁方向？(4)这些凝灰岩的源区在哪里？ 这些研究将允许更好地解决地层的相关性和时间内的伸展生长断层盆地，提供了一个更好的基础，以评估在扩展过程中的结构旋转和测试模型的伸展变形，并可能突出主要的破火山口喷发中心和区域伸展结构之间的关系。

Regionally extensive ash flow tuffs represent important, approximately isochronous units for correlation within complexly deformed regions. This is particularly true within the highly extended ranges of the Colorado River extensional corridor of the Basin and Range Province of the western U.S., where the pre-Tertiary sedimentary section was erosionally removed prior to Miocene and younger extension. Ash flow tuffs, such as the widely distributed 18.5 million year old Peach Springs Tuff, often represent the only correlatable units between the largely volcanic sections of isolated mountain ranges. In addition to their value to regional correlation and as time horizons within extensional growth fault basins, the paleomagnetic signatures of ash flow units are also highly useful markers for assessing structural rotations due to extensional events.Recent research on 18-19 million year old ash flows within the Colorado River extensional corridor suggests that (1) the Peach Springs Tuff, widely used for correlation, may be more stratigraphically complex and have erupted over a significantly longer period than previously realized, (2) the paleomagnetic signature of the Peach Springs Tuff can deviate substantially from the widely cited Peach Springs Tuff reference direction, possibly due to protracted eruption during rapid secular variation related to a magnetic excursion, and (3) other tuffs occupy the same stratigraphic position as the Peach Springs Tuff and may be regionally important, including the previously known Cook Canyon and Rock Creek rhyodacite tuffs, a potentially new tuff discovered in the western Cerbat Mountains, and possibly others. Paleomagnetic, geochemical and geochronologic techniques are being used to study the 18-19 million year old tuffs of the Colorado River extensional corridor. Research goals are directed at the following questions: (1) Did the Peach Springs Tuff eruptions indeed occur over a much longer time interval than previously thought? (2) How many different and distinct tuffs of approximately 18-19 Ma age exist in the Colorado River extensional corridor and how do we discriminate them? (3) Which of the 18-19 Ma tuffs of the Colorado River extensional corridor, if any, have a paleomagnetic direction suitable for use as a structural marker? (4) Where are the source areas for these various tuffs? These studies will allow better resolution of stratigraphic correlation and timing within extensional growth fault basins, provide a better basis for assessing structural rotations during extension and for testing models of extensional deformation and, potentially highlight relationships between major caldera eruptive centers and regional extensional structures.