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 Coe一些证据表明地磁反转可能比目前认为的复杂得多。这项提议对黄石热点 (YSHS) 洪水玄武岩火山活动进行古地磁和地质年代学研究，该火山活动发生在 17 Ma 到 15 Ma 之间，发生在俄勒冈州及其四个毗邻州，这将使人们能够对逆转期间发生的情况进行严格的检查和重建。在 YSHS 熔岩流的部分区域中存在许多反转至正常 (R-N) 极性过渡区，包括在俄勒冈州东南部斯廷斯山记录的众所周知的、异常详细的过渡区，其他仅在侦察层面上已知的过渡区，还有其他尚未发现的过渡区。因为没有发现 N-R 区域，所以这些部分中的大多数似乎很可能记录了相同的斯廷斯反转。在侦察层面上研究的少数这样的部分表明过渡记录总体上相似，但它们也表现出一些与斯廷斯记录明显不同的方向。从斯廷斯山向外进行详细的古地磁方向测定和Ar/Ar测年，将能够准确识别记录相同反转但包括一些带有新过渡方向的不同熔岩流的部分。通过这种方式，可以拼凑出反转期间发生的情况的更全面的记录。 此外，最近的研究表明，斯廷斯玄武岩的喷发标志着 YSHS 火山活动的开始。因此，识别包含 R-N 斯蒂斯反转的部分也将描绘出 YSHS 喷发几乎同时开始的空间范围，并表明火山活动爆发传播的速度。这将增进对地磁柱和热点如何与岩石圈相互作用以安置岩浆的理解。尽管在不久的将来不太可能发生地磁反转或洪水玄武岩喷发，但由于其大规模的环境影响，它们具有社会相关性。其中包括前者期间地球表面电磁干扰和辐射的增加以及后者期间的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，该地区经济上重要的浅成热液矿床的成因最好通过 YSHS 裂谷和岩浆作用的程度和时间来理解。