How Complex are Geomagnetic Reversals? Tracking the Steens Reversal in Yellowstone Hotspot Lavas to Construct a Composite Record

EAR-0310316罗伯特·科一些证据表明，地磁逆转可能比目前认为的复杂得多。这项建议对广泛的黄石热点(YSHS)洪水-玄武岩火山作用进行古地磁和地质年代学研究，该火山作用发生在17至15 Ma之间的俄勒冈州及其邻近的四个州，将使人们能够对逆转期间发生的事情进行关键的检查和重建。在YSHS熔岩流的部分区域中有许多从R-N到正常(R-N)的反转(R-N)极性转换带，包括在俄勒冈州东南部的斯蒂恩斯山记录的著名的、异常详细的熔岩流，还有一些只在侦察层面上已知的，还有一些尚未被发现。由于没有发现N-R带，这些剖面中的大多数似乎都记录了同样的Steens反转。在侦察水平上研究的少数这样的剖面表明，过渡记录总体上是相似的，但它们也显示了一些与斯蒂恩记录明显不同的方向。从斯蒂恩斯山向外工作，通过详细的古地磁方向测定和Ar/Ar测年，将能够肯定地识别记录了相同逆转但包括一些携带新过渡方向的不同熔岩流的剖面。通过这种方式，可以将逆转期间发生的事情拼凑成更全面的记录。此外，最近的研究表明，斯蒂恩斯玄武岩的喷发标志着YSHS火山作用的开始。因此，确定包含R-N Steens反转的部分还将描绘YSHS喷发几乎同时开始的空间范围，并表明火山活动的开始传播有多快。这将提高对羽流和热点如何与岩石圈相互作用以安置其岩浆的理解。尽管地磁逆转或洪水玄武岩喷发不太可能在不久的将来发生，但由于它们的大规模环境影响，它们具有社会意义。这包括前者期间地球表面的电磁干扰和辐射增加，后者期间气候变化和可能的物种灭绝。因此，我们有必要尽可能多地了解它们。此外，根据YSHS裂谷作用和岩浆作用的程度和时间，可以最好地了解该地区重要的浅成低温热液矿床的成因。

EAR-0310316Robert CoeSome evidence suggests that geomagnetic reversals may be far more complex than currently believed. This proposal to conduct a paleomagnetic and geochronologic study of the widespread Yellowstone hotspot (YSHS) flood-basalt volcanism, which occurred between 17 and 15 Ma in Oregon and its four bordering states, will enable a critical examination and reconstruction of what happens during a reversal. There are numerous reversed-to-normal (R-N) polarity transition zones in sections of YSHS lava flows, including the well-known, unusually detailed one recorded at Steens Mountain in southeastern Oregon, others that are known only at the reconnaissance level, and still others yet to be discovered. Because no N-R zones have been found, it seems probable that most of these sections record this same Steens reversal. The few such sections that have been studied at the reconnaissance level indicate transition records that are similar overall, but they also exhibit some directions that are distinctly different from the Steens record. Working outward from Steens Mountain with detailed paleomagnetic determinations of direction and Ar/Ar dating will allow positive identification of the sections that record the same reversal yet include some different lava flows that carry new transitional directions. In this way a more comprehensive record of what happens during a reversal can be pieced together. Furthermore, recent studies show that eruption of the Steens Basalt marks the beginning of YSHS volcanism. Thus, identifying the sections that contain the R-N Steens reversal will also delineate the spatial extent over which YSHS eruptions began almost simultaneously and indicate how rapidly the onset of volcanism propagated. This will improve understanding of how plumes and hotspots interact with the lithosphere to emplace their magmas.Even though neither geomagnetic reversals nor flood basalt eruptions are likely to occur in the near future, they are societally relevant because of their large-scale environmental effects. These include increased electromagnetic disturbances and radiation at the earth's surface during the former and climate change and possible species extinctions during the latter. Therefore, it behooves us to learn as much as possible about them. Moreover, the genesis of the economically important epithermal ore deposits in this region is best understood in terms of the extent and timing of YSHS rifting and magmatism.