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.

一些证据表明，地磁反转可能比目前认为的要复杂得多。这一建议进行广泛的黄石热点（YSHS）的洪水玄武岩火山活动，发生在17和15马之间的俄勒冈州及其四个接壤的国家，古地磁和地质年代学研究，将使一个关键的检查和重建过程中发生的逆转。在YSHS熔岩流的剖面中有许多反转到正常（R-N）的极性过渡带，包括在俄勒冈州东南部的Steens山记录的著名的、异常详细的极性过渡带，其他的只有在侦察水平上才知道，还有其他的尚未被发现。由于没有发现N-R带，这些剖面中的大部分似乎都记录了相同的Steens反转。在勘测水平上研究过的几个这样的部分表明，过渡记录总体上是相似的，但它们也表现出一些明显不同于Steens记录的方向。从Steens山向外，通过详细的古地磁方向测定和Ar/Ar测年，将能够对记录相同反转但包括一些携带新过渡方向的不同熔岩流的部分进行积极的识别。通过这种方式，可以拼凑出一个关于反转期间发生的事情的更全面的记录。 此外，最近的研究表明，Steens玄武岩的喷发标志着YSHS火山作用的开始。因此，识别包含R-N Steens反转的部分也将描绘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使其岩浆就位的理解。尽管在不久的将来不太可能发生地磁逆转或溢流玄武岩喷发，但由于其大规模的环境影响，它们与社会有关。其中包括前者地球表面电磁干扰和辐射的增加，后者气候变化和可能的物种灭绝。因此，我们应该尽可能多地了解它们。此外，该地区具有重要经济意义的浅成低温热液矿床的成因最好根据YSHS裂谷作用和岩浆作用的程度和时间来理解。