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

地磁反转有多复杂？

• 批准号: 0310316
• 负责人: Robert Coe
• 金额: $ 29.66万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-06-01 至 2007-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0310316&HistoricalAwards=false
• 关键词: How; Complex; Geomagnetic; Reversals; Tracking

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.

EAR-0310316ROBERT COOLY证据表明，地磁逆转可能比目前认为的要复杂得多。这项提议对广泛的黄石热点（YSHS）洪水泛滥的火山作品进行古磁和地球文学研究，发生在俄勒冈州及其四个边界状态之间的17至15 MA之间，将对逆转期间发生的事情进行批判性检查和重建。在YSHS熔岩流的各个部分中，有许多相反的（R-n）极性转变区，包括在俄勒冈州东南部的Steens Mountain记录的众所周知的，异常详细的详细信息，其他仅在侦察水平上闻名，还有其他尚未发现。由于未发现N-R区域，因此大多数这些部分似乎都记录了同样的Steens逆转。在侦察水平上研究的少数此类部分表明过渡记录总体相似，但它们也表现出与Steens Record明显不同的方向。从Steens Mountain进行详细的方向和AR/AR标准测定的详细的古磁性确定，将允许对记录相同逆转的部分进行积极识别，但包括一些带有新的过渡方向的不同熔岩流。这样，就可以将逆转过程中发生的事情拼凑在一起的更全面的记录。 此外，最近的研究表明，Steens玄武岩的喷发标志着YSHS火山的开始。因此，识别包含R-N Steens逆转的部分也将描绘出YSHS喷发几乎同时开始的空间范围，并表明火山爆发的速度迅速传播。这将提高人们对羽毛和热点与岩石圈的相互作用以散布岩浆的理解。尽管地磁逆转既不是在不久的将来发生的，但由于它们的大规模环境影响，它们都与社会相关。这些包括在前者期间的电磁干扰和地球表面的辐射增加以及在后者期间可能的物种灭绝。因此，它应该使我们尽可能多地学习它们。此外，最好就YSHS裂谷和岩浆主义的程度和时机来理解该地区经济上重要的表现矿石沉积物的起源。