Temporal Constraints on Geomagnetic Filed Behavior From High-Precision 40Ar/39Ar Geochronology

该项目旨在通过获取精确的40Ar/39Ar年龄测定以及详细记录地球动力学行为的熔岩流磁测量来改善古地磁记录。(1)利用来自智利、塔希提岛、夏威夷和华盛顿的熔岩流序列的许多新的增量加热数据，探讨了Matuyama-Brunhes反转过程的持续时间和时间精细结构，这些熔岩流序列显然是在反转期间不同时间喷发的。(2)南半球的5个火山区将被开发为全球平衡阵列的新记录点，该阵列旨在测量过去500万年的古长期磁场变化。新的地质年代学将在确定岩浆记录的周期和极性状态方面发挥重要作用，这对模拟磁场的时间平均行为至关重要。(3)反转尝试的频率、时间、持续时间和地理范围是模拟地球动力学的重要观测约束。因此，我们将扩大努力，以验证至少三个极性事件或晚期松山亚时的时间和地理范围。其中包括最近提出的Punaruu （1.10 Ma）和Santa Rosa （0.92 Ma）事件，以及上胜事件（0.90 Ma）。对新墨西哥州和加利福尼亚州的硅熔岩流中的硅碱斑晶进行激光聚变和增量加热，将提供所需的年龄分辨率和空间覆盖范围。

This project seeks to improve the paleomagnetic record through acquisition of precise 40Ar/39Ar age determinations coupled with magnetic measurements of lava flows that record in detail the behavior of the geodynamo. Three problems will be addressed: (1) The duration and temporal fine-structure of the Matuyama-Brunhes reversal process will be probed using many new incremental-heating data from lava flow sequences in Chile, Tahiti, Hawaii, and Washington that apparently were erupted at different times during the reversal. (2) Five volcanic areas in the southern hemisphere will be developed as new recording sites in a globally balanced array designed to measure paleosecular variation of the magnetic field over the past 5 million years. The new geochronology will play an important role in determining the periods and polarity states recorded by the lavas essential to modeling time-averaged behavior of the magnetic field. (3) The frequency, timing, duration, and geographic extent of reversal attempts are important observational constraints on modeling the geodynamo. Accordingly, we will expand efforts to verify the timing and geographic extent of at least three polarity events or subchrons in the late Matuyama chron. These include the recently proposed Punaruu (1.10 Ma) and Santa Rosa (0.92 Ma) events, and the Kamikatsura event (0.90 Ma). Laser fusion and incremental-heating of sanidine phenocrysts from silicic lava flows in New Mexico and California will provide the needed age resolution and spatial coverage.